Adding upstream version 2.2.0.upstream/2.2.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

137 files changed, 49169 insertions, 0 deletions

diff --git a/doc/sphinx/Makefile.am b/doc/sphinx/Makefile.am
new file mode 100644
index 0000000..7fa957b
--- /dev/null
+++ b/doc/sphinx/Makefile.am
@@ -0,0 +1,226 @@
+EXTRA_DIST =
+sphinxbuilddir = $(builddir)/_build
+abs_sphinxbuilddir = $(abs_builddir)/_build
+
+if GENERATE_DOCS
+
+sphinxopts =
+sphinxopts += -v
+sphinxopts += -E
+sphinxopts += -a
+sphinxopts += -W
+sphinxopts += -j 2
+sphinxopts += -c "${abs_srcdir}"
+
+static_sources  =
+static_sources += static/kea-imageonly-100bw.png
+static_sources += static/kea-logo-100x70.png
+static_sources += static/kea-logo-200.png
+static_sources += static/kea.css
+
+# ARM
+rst_arm_sources =
+rst_arm_sources += index.rst
+rst_arm_sources += manpages.rst
+rst_arm_sources += umls.rst
+include arm/rst_arm_sources.mk
+
+EXTRA_DIST += arm/rst_arm_sources.mk
+
+main_sources = $(rst_arm_sources) conf.py $(static_sources)
+
+# mans
+rst_man_sources =
+include man/rst_man_sources.mk
+
+EXTRA_DIST += man/rst_man_sources.mk
+
+rst_arm_sources += grammar/grammar.rst
+rst_arm_sources += grammar/grammar-ca-parser.rst
+rst_arm_sources += grammar/grammar-d2-parser.rst
+rst_arm_sources += grammar/grammar-dhcp4-parser.rst
+rst_arm_sources += grammar/grammar-dhcp6-parser.rst
+rst_arm_sources += grammar/grammar-netconf-parser.rst
+
+man8s =
+include man/man8s.mk
+
+EXTRA_DIST += man/man8s.mk
+
+man_sources = $(rst_man_sources) conf.py
+
+EXTRA_DIST += $(main_sources) $(man_sources) mes2doc.py api2doc.py $(man8s)
+
+# list of messages files that are used to generate kea-messages.rst and then kea-messages.pdf
+mes_files =
+include $(srcdir)/mes_files.mk
+
+EXTRA_DIST += mes_files.mk
+
+# list of api files that are used to generate api.rst
+api_files =
+include $(top_srcdir)/src/share/api/api_files.mk
+
+if HAVE_PDFLATEX
+all: html mans pdf text
+else
+all: html mans text
+endif
+
+# build the list of message files
+mes-files.txt: mes_files.mk
+	@sed 's;mes_files .*)/;;' $< > $@
+
+# this rule is only used for development purposes and is not used in official
+# build process as kea-messages.rst is always generated via sphinx's conf.py
+$(srcdir)/kea-messages.rst: $(mes_files) mes2doc.py
+	$(PYTHON) $(srcdir)/mes2doc.py -o $@ $(mes_files)
+
+# build the list of api files
+api-files.txt: $(top_srcdir)/src/share/api/api_files.mk
+	@sed 's;api_files .*)/;;' $< > $@
+
+# some tools do not use this makefile but still need generate files.
+EXTRA_DIST += mes-files.txt api-files.txt
+
+# this rule is only used for development purposes and is not used in official
+# build process as api.rst is always generated via sphinx's conf.py
+$(srcdir)/api.rst: $(api_files) api-files.txt api2doc.py
+	$(PYTHON) $(srcdir)/api2doc.py -o $@ $(api_files)
+
+$(srcdir)/arm/platforms.rst:
+	rm -f $(srcdir)/arm/platforms.rst
+	cp $(srcdir)/../../platforms.rst $(srcdir)/arm/platforms.rst
+
+# UML files
+
+if HAVE_PLANTUML
+.uml.png:
+	@PLANTUML@ $<
+
+.uml.svg:
+	@PLANTUML@ -svg $<
+endif
+
+EXTRA_DIST += uml/appendRequestedOptions.png
+EXTRA_DIST += uml/appendRequestedOptions.svg
+EXTRA_DIST += uml/appendRequestedOptions.uml
+EXTRA_DIST += uml/appendRequestedVendorOptions.png
+EXTRA_DIST += uml/appendRequestedVendorOptions.svg
+EXTRA_DIST += uml/appendRequestedVendorOptions.uml
+EXTRA_DIST += uml/assign-lease4.png
+EXTRA_DIST += uml/assign-lease4.svg
+EXTRA_DIST += uml/assign-lease4.uml
+EXTRA_DIST += uml/buildCfgOptionList.png
+EXTRA_DIST += uml/buildCfgOptionList.svg
+EXTRA_DIST += uml/buildCfgOptionList.uml
+EXTRA_DIST += uml/currentHost4.png
+EXTRA_DIST += uml/currentHost4.svg
+EXTRA_DIST += uml/currentHost4.uml
+EXTRA_DIST += uml/lease-states.png
+EXTRA_DIST += uml/lease-states.svg
+EXTRA_DIST += uml/lease-states.uml
+EXTRA_DIST += uml/main-loop.png
+EXTRA_DIST += uml/main-loop.svg
+EXTRA_DIST += uml/main-loop.uml
+EXTRA_DIST += uml/packet4.png
+EXTRA_DIST += uml/packet4.svg
+EXTRA_DIST += uml/packet4.uml
+EXTRA_DIST += uml/request4-lease.png
+EXTRA_DIST += uml/request4-lease.svg
+EXTRA_DIST += uml/request4-lease.uml
+EXTRA_DIST += uml/request4.png
+EXTRA_DIST += uml/request4.svg
+EXTRA_DIST += uml/request4.uml
+EXTRA_DIST += uml/requestLease4.png
+EXTRA_DIST += uml/requestLease4.svg
+EXTRA_DIST += uml/requestLease4.uml
+EXTRA_DIST += uml/select4.png
+EXTRA_DIST += uml/select4.svg
+EXTRA_DIST += uml/select4.uml
+EXTRA_DIST += uml/tkey.png
+EXTRA_DIST += uml/tkey.svg
+EXTRA_DIST += uml/tkey.uml
+EXTRA_DIST += uml/update.png
+EXTRA_DIST += uml/update.svg
+EXTRA_DIST += uml/update.uml
+
+PDFLATEX_AND_OPTS=$(PDFLATEX) -interaction nonstopmode
+
+pdf: $(main_sources) api-files.txt mes-files.txt $(srcdir)/arm/platforms.rst
+	$(SPHINXBUILD) -M latex $(srcdir) $(sphinxbuilddir) $(sphinxopts)
+	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+	-cd $(abs_sphinxbuilddir)/latex && makeindex -s python.ist kea-arm.idx
+	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+	cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+	-cd $(abs_sphinxbuilddir)/latex && makeindex -s python.ist kea-messages.idx
+	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+	cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+
+html: $(main_sources) api-files.txt mes-files.txt $(srcdir)/arm/platforms.rst
+	$(SPHINXBUILD) -M html $(srcdir) $(sphinxbuilddir) $(sphinxopts)
+
+# This target is not used anywhere, but people who prefer single page docs
+# can do make -C doc/sphinx singlehtml and then enjoy their docs being
+# generated in doc/sphinx/_build/singlehtml
+singlehtml: $(main_sources) api-files.txt mes-files.txt $(srcdir)/arm/platforms.rst
+	$(SPHINXBUILD) -M singlehtml $(srcdir) $(sphinxbuilddir) $(sphinxopts)
+
+text: $(main_sources) api-files.txt mes-files.txt $(srcdir)/arm/platforms.rst
+	$(SPHINXBUILD) -M text $(srcdir) $(sphinxbuilddir) $(sphinxopts)
+
+$(man8s): mans
+
+mans: $(man_sources) api-files.txt mes-files.txt
+	$(SPHINXBUILD) -M man $(srcdir) $(sphinxbuilddir) $(sphinxopts)
+
+# Updates sphinx dependencies to the latest versions available on the current
+# host and freezes them in ./src/requirements.txt. Requires pip-compile:
+#   pip install pip-tools
+# Run this when dependencies are added, changed or removed.
+update-python-dependencies: ./src/requirements.in
+	pip-compile -r ./src/requirements.in
+
+clean-local:
+	rm -rf $(sphinxbuilddir)
+	rm -f $(srcdir)/mes-files.txt $(srcdir)/api-files.txt
+	rm -f $(srcdir)/kea-messages.rst $(srcdir)/api.rst
+	rm -f $(srcdir)/arm/platforms.rst
+
+.PHONY: all pdf html mans
+
+endif
+
+# install and uninstall can occur with GENERATE_DOCS and without it
+# so we want to install all when GENERATE_DOCS is and
+# just mans when GENERATE_DOCS is not used, and when man files exists (e.g release tarball)
+install-data-local:
+	mkdir -p $(DESTDIR)$(docdir)
+if GENERATE_DOCS
+	cp -r $(sphinxbuilddir)/html $(DESTDIR)$(docdir)
+if HAVE_PDFLATEX
+	${INSTALL_DATA} $(sphinxbuilddir)/latex/kea-arm.pdf $(DESTDIR)$(docdir)
+	${INSTALL_DATA} $(sphinxbuilddir)/latex/kea-messages.pdf $(DESTDIR)$(docdir)
+endif
+	${MKDIR_P} ${DESTDIR}${mandir}/man8
+	${INSTALL_DATA} $(man8s) ${DESTDIR}${mandir}/man8/
+else
+if INSTALL_MANS
+	${MKDIR_P} ${DESTDIR}${mandir}/man8
+	${INSTALL_DATA} $(sphinxbuilddir)/man/*.8 ${DESTDIR}${mandir}/man8/
+endif
+endif
+
+uninstall-local:
+	rm -rf $(DESTDIR)$(docdir)
+
+# There are sometimes conflicts when more then one sphinx-build is run at a time.
+# This target blocks running anything in parallel in this Makefile,
+# all is run serially.
+
+.NOTPARALLEL:
diff --git a/doc/sphinx/Makefile.in b/doc/sphinx/Makefile.in
new file mode 100644
index 0000000..dbc7de9
--- /dev/null
+++ b/doc/sphinx/Makefile.in
@@ -0,0 +1,962 @@
+# Makefile.in generated by automake 1.16.1 from Makefile.am.
+# @configure_input@
+
+# Copyright (C) 1994-2018 Free Software Foundation, Inc.
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+# This Makefile.in is free software; the Free Software Foundation
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+# with or without modifications, as long as this notice is preserved.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY, to the extent permitted by law; without
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+# some tools do not use this makefile but still need generate files.
+@GENERATE_DOCS_TRUE@am__append_1 = arm/rst_arm_sources.mk \
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+PERL = @PERL@
+PGSQL_CPPFLAGS = @PGSQL_CPPFLAGS@
+PGSQL_LIBS = @PGSQL_LIBS@
+PKGPYTHONDIR = @PKGPYTHONDIR@
+PKG_CONFIG = @PKG_CONFIG@
+PLANTUML = @PLANTUML@
+PREMIUM_DIR = @PREMIUM_DIR@
+PYTHON = @PYTHON@
+PYTHON_EXEC_PREFIX = @PYTHON_EXEC_PREFIX@
+PYTHON_PLATFORM = @PYTHON_PLATFORM@
+PYTHON_PREFIX = @PYTHON_PREFIX@
+PYTHON_VERSION = @PYTHON_VERSION@
+RANLIB = @RANLIB@
+SED = @SED@
+SEP = @SEP@
+SET_MAKE = @SET_MAKE@
+SHELL = @SHELL@
+SPHINXBUILD = @SPHINXBUILD@
+SRPD_PLUGINS_PATH = @SRPD_PLUGINS_PATH@
+SR_REPO_PATH = @SR_REPO_PATH@
+STRIP = @STRIP@
+SYSREPOCPP_VERSION = @SYSREPOCPP_VERSION@
+SYSREPO_CPPFLAGS = @SYSREPO_CPPFLAGS@
+SYSREPO_INCLUDEDIR = @SYSREPO_INCLUDEDIR@
+SYSREPO_LIBS = @SYSREPO_LIBS@
+SYSREPO_VERSION = @SYSREPO_VERSION@
+USE_LCOV = @USE_LCOV@
+VALGRIND = @VALGRIND@
+VERSION = @VERSION@
+WARNING_GCC_44_STRICT_ALIASING_CFLAG = @WARNING_GCC_44_STRICT_ALIASING_CFLAG@
+YACC = @YACC@
+abs_builddir = @abs_builddir@
+abs_srcdir = @abs_srcdir@
+abs_top_builddir = @abs_top_builddir@
+abs_top_srcdir = @abs_top_srcdir@
+ac_ct_AR = @ac_ct_AR@
+ac_ct_CC = @ac_ct_CC@
+ac_ct_CXX = @ac_ct_CXX@
+ac_ct_DUMPBIN = @ac_ct_DUMPBIN@
+am__include = @am__include@
+am__leading_dot = @am__leading_dot@
+am__quote = @am__quote@
+am__tar = @am__tar@
+am__untar = @am__untar@
+bindir = @bindir@
+build = @build@
+build_alias = @build_alias@
+build_cpu = @build_cpu@
+build_os = @build_os@
+build_vendor = @build_vendor@
+builddir = @builddir@
+datadir = @datadir@
+datarootdir = @datarootdir@
+docdir = @docdir@
+dvidir = @dvidir@
+exec_prefix = @exec_prefix@
+host = @host@
+host_alias = @host_alias@
+host_cpu = @host_cpu@
+host_os = @host_os@
+host_vendor = @host_vendor@
+htmldir = @htmldir@
+includedir = @includedir@
+infodir = @infodir@
+install_sh = @install_sh@
+libdir = @libdir@
+libexecdir = @libexecdir@
+localedir = @localedir@
+localstatedir = @localstatedir@
+mandir = @mandir@
+mkdir_p = @mkdir_p@
+oldincludedir = @oldincludedir@
+pdfdir = @pdfdir@
+pkgpyexecdir = @pkgpyexecdir@
+pkgpythondir = @pkgpythondir@
+prefix = @prefix@
+program_transform_name = @program_transform_name@
+psdir = @psdir@
+pyexecdir = @pyexecdir@
+pythondir = @pythondir@
+runstatedir = @runstatedir@
+sbindir = @sbindir@
+sharedstatedir = @sharedstatedir@
+srcdir = @srcdir@
+sysconfdir = @sysconfdir@
+target_alias = @target_alias@
+top_build_prefix = @top_build_prefix@
+top_builddir = @top_builddir@
+top_srcdir = @top_srcdir@
+EXTRA_DIST = $(am__append_1)
+sphinxbuilddir = $(builddir)/_build
+abs_sphinxbuilddir = $(abs_builddir)/_build
+@GENERATE_DOCS_TRUE@sphinxopts = -v -E -a -W -j 2 -c "${abs_srcdir}"
+@GENERATE_DOCS_TRUE@static_sources = static/kea-imageonly-100bw.png \
+@GENERATE_DOCS_TRUE@	static/kea-logo-100x70.png \
+@GENERATE_DOCS_TRUE@	static/kea-logo-200.png static/kea.css
+
+# ARM
+@GENERATE_DOCS_TRUE@rst_arm_sources = index.rst manpages.rst umls.rst \
+@GENERATE_DOCS_TRUE@	arm/acknowledgments.rst arm/admin.rst \
+@GENERATE_DOCS_TRUE@	arm/agent.rst arm/classify.rst \
+@GENERATE_DOCS_TRUE@	arm/config-backend.rst \
+@GENERATE_DOCS_TRUE@	arm/config-templates.rst arm/config.rst \
+@GENERATE_DOCS_TRUE@	arm/congestion-handling.rst \
+@GENERATE_DOCS_TRUE@	arm/ctrl-channel.rst \
+@GENERATE_DOCS_TRUE@	arm/database-connectivity.rst arm/ddns.rst \
+@GENERATE_DOCS_TRUE@	arm/dhcp4-srv.rst arm/dhcp6-srv.rst \
+@GENERATE_DOCS_TRUE@	arm/ext-gss-tsig.rst arm/ext-netconf.rst \
+@GENERATE_DOCS_TRUE@	arm/hammer.rst arm/hooks-bootp.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-cb-cmds.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-class-cmds.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-ddns-tuning.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-flex-id.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-flex-option.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-gss-tsig.rst arm/hooks-ha.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-host-cache.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-host-cmds.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-lease-cmds.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-lease-query.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-limits.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-cb-mysql.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-cb-pgsql.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-legal-log.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-radius.rst arm/hooks-rbac.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-run-script.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-stat-cmds.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-subnet-cmds.rst \
+@GENERATE_DOCS_TRUE@	arm/hooks-user-chk.rst arm/hooks.rst \
+@GENERATE_DOCS_TRUE@	arm/install.rst arm/integrations.rst \
+@GENERATE_DOCS_TRUE@	arm/intro.rst arm/keactrl.rst \
+@GENERATE_DOCS_TRUE@	arm/lease-expiration.rst arm/lfc.rst \
+@GENERATE_DOCS_TRUE@	arm/logging.rst arm/quickstart.rst \
+@GENERATE_DOCS_TRUE@	arm/security.rst arm/shell.rst \
+@GENERATE_DOCS_TRUE@	arm/stats.rst arm/stork.rst \
+@GENERATE_DOCS_TRUE@	grammar/grammar.rst \
+@GENERATE_DOCS_TRUE@	grammar/grammar-ca-parser.rst \
+@GENERATE_DOCS_TRUE@	grammar/grammar-d2-parser.rst \
+@GENERATE_DOCS_TRUE@	grammar/grammar-dhcp4-parser.rst \
+@GENERATE_DOCS_TRUE@	grammar/grammar-dhcp6-parser.rst \
+@GENERATE_DOCS_TRUE@	grammar/grammar-netconf-parser.rst
+@GENERATE_DOCS_TRUE@main_sources = $(rst_arm_sources) conf.py $(static_sources)
+
+# mans
+@GENERATE_DOCS_TRUE@rst_man_sources = man/kea-admin.8.rst \
+@GENERATE_DOCS_TRUE@	man/kea-ctrl-agent.8.rst \
+@GENERATE_DOCS_TRUE@	man/kea-dhcp4.8.rst man/kea-dhcp6.8.rst \
+@GENERATE_DOCS_TRUE@	man/kea-dhcp-ddns.8.rst man/kea-lfc.8.rst \
+@GENERATE_DOCS_TRUE@	man/kea-netconf.8.rst man/kea-shell.8.rst \
+@GENERATE_DOCS_TRUE@	man/keactrl.8.rst man/perfdhcp.8.rst
+@GENERATE_DOCS_TRUE@man8s = $(sphinxbuilddir)/man/kea-admin.8 \
+@GENERATE_DOCS_TRUE@	$(sphinxbuilddir)/man/kea-ctrl-agent.8 \
+@GENERATE_DOCS_TRUE@	$(sphinxbuilddir)/man/kea-dhcp4.8 \
+@GENERATE_DOCS_TRUE@	$(sphinxbuilddir)/man/kea-dhcp6.8 \
+@GENERATE_DOCS_TRUE@	$(sphinxbuilddir)/man/kea-dhcp-ddns.8 \
+@GENERATE_DOCS_TRUE@	$(sphinxbuilddir)/man/kea-lfc.8 \
+@GENERATE_DOCS_TRUE@	$(sphinxbuilddir)/man/kea-netconf.8 \
+@GENERATE_DOCS_TRUE@	$(sphinxbuilddir)/man/kea-shell.8 \
+@GENERATE_DOCS_TRUE@	$(sphinxbuilddir)/man/keactrl.8 \
+@GENERATE_DOCS_TRUE@	$(sphinxbuilddir)/man/perfdhcp.8
+@GENERATE_DOCS_TRUE@man_sources = $(rst_man_sources) conf.py
+
+# list of messages files that are used to generate kea-messages.rst and then kea-messages.pdf
+@GENERATE_DOCS_TRUE@mes_files = $(top_srcdir)/src/hooks/dhcp/flex_option/flex_option_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/hooks/dhcp/bootp/bootp_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/hooks/dhcp/mysql_cb/mysql_cb_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/hooks/dhcp/lease_cmds/lease_cmds_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/hooks/dhcp/high_availability/ha_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/hooks/dhcp/stat_cmds/stat_cmds_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/hooks/dhcp/user_chk/user_chk_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/config/config_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/hooks/hooks_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/dhcpsrv/dhcpsrv_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/dhcpsrv/alloc_engine_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/dhcpsrv/hosts_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/http/auth_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/http/http_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/dhcp_ddns/dhcp_ddns_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/database/db_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/log/log_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/log/logimpl_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/log/tests/log_test_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/process/process_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/asiodns/asiodns_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/eval/eval_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/lib/d2srv/d2_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/bin/dhcp4/dhcp4_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/bin/agent/ca_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/bin/dhcp6/dhcp6_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/bin/lfc/lfc_messages.mes \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/bin/netconf/netconf_messages.mes
+
+# list of api files that are used to generate api.rst
+@GENERATE_DOCS_TRUE@api_files = $(top_srcdir)/src/share/api/build-report.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/cache-clear.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/cache-flush.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/cache-get-by-id.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/cache-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/cache-insert.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/cache-load.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/cache-remove.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/cache-size.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/cache-write.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/class-add.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/class-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/class-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/class-list.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/class-update.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/config-backend-pull.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/config-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/config-reload.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/config-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/config-test.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/config-write.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/dhcp-disable.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/dhcp-enable.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-key-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-key-expire.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-key-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-list.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-purge-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-purge.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-rekey-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/gss-tsig-rekey.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/ha-continue.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/ha-heartbeat.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/ha-maintenance-cancel.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/ha-maintenance-notify.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/ha-maintenance-start.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/ha-reset.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/ha-scopes.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/ha-sync.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/ha-sync-complete-notify.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-add.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-get-by-client-id.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-get-by-hostname.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-get-by-hw-address.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-get-page.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-resend-ddns.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-update.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease4-wipe.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-add.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-bulk-apply.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-get-by-duid.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-get-by-hostname.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-get-page.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-resend-ddns.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-update.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/lease6-wipe.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/leases-reclaim.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/libreload.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/list-commands.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network4-add.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network4-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network4-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network4-list.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network4-subnet-add.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network4-subnet-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network6-add.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network6-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network6-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network6-list.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network6-subnet-add.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/network6-subnet-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-class4-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-class4-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-class4-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-class4-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-class6-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-class6-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-class6-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-class6-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-global-parameter4-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-global-parameter4-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-global-parameter4-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-global-parameter4-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-global-parameter6-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-global-parameter6-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-global-parameter6-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-global-parameter6-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-network4-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-network4-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-network4-list.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-network4-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-network6-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-network6-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-network6-list.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-network6-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option-def4-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option-def4-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option-def4-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option-def4-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option-def6-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option-def6-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option-def6-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option-def6-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option4-global-del.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option4-global-get-all.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option4-global-get.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option4-global-set.json \
+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/remote-option4-network-del.json \
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+@GENERATE_DOCS_TRUE@	$(top_srcdir)/src/share/api/version-get.json
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+	$(am__cd) $(top_srcdir) && \
+	  $(AUTOMAKE) --foreign doc/sphinx/Makefile
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+	@case '$?' in \
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+	    echo ' cd $(top_builddir) && $(SHELL) ./config.status $(subdir)/$@ $(am__maybe_remake_depfiles)'; \
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+$(top_srcdir)/configure:  $(am__configure_deps)
+	cd $(top_builddir) && $(MAKE) $(AM_MAKEFLAGS) am--refresh
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+	cd $(top_builddir) && $(MAKE) $(AM_MAKEFLAGS) am--refresh
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+distdir-am: $(DISTFILES)
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+	list='$(DISTFILES)'; \
+	  dist_files=`for file in $$list; do echo $$file; done | \
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+	      -e "s|^$$topsrcdirstrip/|$(top_builddir)/|;t"`; \
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+	    fi; \
+	    cp -fpR $$d/$$file "$(distdir)$$dir" || exit 1; \
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+	    test -f "$(distdir)/$$file" \
+	    || cp -p $$d/$$file "$(distdir)/$$file" \
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+install-am: all-am
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+	  $(MAKE) $(AM_MAKEFLAGS) INSTALL_PROGRAM="$(INSTALL_STRIP_PROGRAM)" \
+	    install_sh_PROGRAM="$(INSTALL_STRIP_PROGRAM)" INSTALL_STRIP_FLAG=-s \
+	      install; \
+	else \
+	  $(MAKE) $(AM_MAKEFLAGS) INSTALL_PROGRAM="$(INSTALL_STRIP_PROGRAM)" \
+	    install_sh_PROGRAM="$(INSTALL_STRIP_PROGRAM)" INSTALL_STRIP_FLAG=-s \
+	    "INSTALL_PROGRAM_ENV=STRIPPROG='$(STRIP)'" install; \
+	fi
+mostlyclean-generic:
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+clean-generic:
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+distclean-generic:
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+maintainer-clean-generic:
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+clean-am: clean-generic clean-libtool clean-local mostlyclean-am
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+distclean: distclean-am
+	-rm -f Makefile
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+dvi: dvi-am
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+dvi-am:
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+@GENERATE_DOCS_FALSE@html: html-am
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+html-am:
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+info: info-am
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+maintainer-clean: maintainer-clean-am
+	-rm -f Makefile
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+mostlyclean-am: mostlyclean-generic mostlyclean-libtool
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+@GENERATE_DOCS_FALSE@pdf: pdf-am
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+.PHONY: all all-am check check-am clean clean-generic clean-libtool \
+	clean-local cscopelist-am ctags-am distclean distclean-generic \
+	distclean-libtool distdir dvi dvi-am html html-am info info-am \
+	install install-am install-data install-data-am \
+	install-data-local install-dvi install-dvi-am install-exec \
+	install-exec-am install-html install-html-am install-info \
+	install-info-am install-man install-pdf install-pdf-am \
+	install-ps install-ps-am install-strip installcheck \
+	installcheck-am installdirs maintainer-clean \
+	maintainer-clean-generic mostlyclean mostlyclean-generic \
+	mostlyclean-libtool pdf pdf-am ps ps-am tags-am uninstall \
+	uninstall-am uninstall-local
+
+.PRECIOUS: Makefile
+
+
+@GENERATE_DOCS_TRUE@@HAVE_PDFLATEX_TRUE@all: html mans pdf text
+@GENERATE_DOCS_TRUE@@HAVE_PDFLATEX_FALSE@all: html mans text
+
+# build the list of message files
+@GENERATE_DOCS_TRUE@mes-files.txt: mes_files.mk
+@GENERATE_DOCS_TRUE@	@sed 's;mes_files .*)/;;' $< > $@
+
+# this rule is only used for development purposes and is not used in official
+# build process as kea-messages.rst is always generated via sphinx's conf.py
+@GENERATE_DOCS_TRUE@$(srcdir)/kea-messages.rst: $(mes_files) mes2doc.py
+@GENERATE_DOCS_TRUE@	$(PYTHON) $(srcdir)/mes2doc.py -o $@ $(mes_files)
+
+# build the list of api files
+@GENERATE_DOCS_TRUE@api-files.txt: $(top_srcdir)/src/share/api/api_files.mk
+@GENERATE_DOCS_TRUE@	@sed 's;api_files .*)/;;' $< > $@
+
+# this rule is only used for development purposes and is not used in official
+# build process as api.rst is always generated via sphinx's conf.py
+@GENERATE_DOCS_TRUE@$(srcdir)/api.rst: $(api_files) api-files.txt api2doc.py
+@GENERATE_DOCS_TRUE@	$(PYTHON) $(srcdir)/api2doc.py -o $@ $(api_files)
+
+@GENERATE_DOCS_TRUE@$(srcdir)/arm/platforms.rst:
+@GENERATE_DOCS_TRUE@	rm -f $(srcdir)/arm/platforms.rst
+@GENERATE_DOCS_TRUE@	cp $(srcdir)/../../platforms.rst $(srcdir)/arm/platforms.rst
+
+# UML files
+
+@GENERATE_DOCS_TRUE@@HAVE_PLANTUML_TRUE@.uml.png:
+@GENERATE_DOCS_TRUE@@HAVE_PLANTUML_TRUE@	@PLANTUML@ $<
+
+@GENERATE_DOCS_TRUE@@HAVE_PLANTUML_TRUE@.uml.svg:
+@GENERATE_DOCS_TRUE@@HAVE_PLANTUML_TRUE@	@PLANTUML@ -svg $<
+
+@GENERATE_DOCS_TRUE@pdf: $(main_sources) api-files.txt mes-files.txt $(srcdir)/arm/platforms.rst
+@GENERATE_DOCS_TRUE@	$(SPHINXBUILD) -M latex $(srcdir) $(sphinxbuilddir) $(sphinxopts)
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && makeindex -s python.ist kea-arm.idx
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+@GENERATE_DOCS_TRUE@	cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-arm.tex
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && makeindex -s python.ist kea-messages.idx
+@GENERATE_DOCS_TRUE@	-cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+@GENERATE_DOCS_TRUE@	cd $(abs_sphinxbuilddir)/latex && $(PDFLATEX_AND_OPTS) kea-messages.tex
+
+@GENERATE_DOCS_TRUE@html: $(main_sources) api-files.txt mes-files.txt $(srcdir)/arm/platforms.rst
+@GENERATE_DOCS_TRUE@	$(SPHINXBUILD) -M html $(srcdir) $(sphinxbuilddir) $(sphinxopts)
+
+# This target is not used anywhere, but people who prefer single page docs
+# can do make -C doc/sphinx singlehtml and then enjoy their docs being
+# generated in doc/sphinx/_build/singlehtml
+@GENERATE_DOCS_TRUE@singlehtml: $(main_sources) api-files.txt mes-files.txt $(srcdir)/arm/platforms.rst
+@GENERATE_DOCS_TRUE@	$(SPHINXBUILD) -M singlehtml $(srcdir) $(sphinxbuilddir) $(sphinxopts)
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+@GENERATE_DOCS_TRUE@text: $(main_sources) api-files.txt mes-files.txt $(srcdir)/arm/platforms.rst
+@GENERATE_DOCS_TRUE@	$(SPHINXBUILD) -M text $(srcdir) $(sphinxbuilddir) $(sphinxopts)
+
+@GENERATE_DOCS_TRUE@$(man8s): mans
+
+@GENERATE_DOCS_TRUE@mans: $(man_sources) api-files.txt mes-files.txt
+@GENERATE_DOCS_TRUE@	$(SPHINXBUILD) -M man $(srcdir) $(sphinxbuilddir) $(sphinxopts)
+
+# Updates sphinx dependencies to the latest versions available on the current
+# host and freezes them in ./src/requirements.txt. Requires pip-compile:
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+# Run this when dependencies are added, changed or removed.
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+@GENERATE_DOCS_TRUE@	pip-compile -r ./src/requirements.in
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+@GENERATE_DOCS_TRUE@	rm -f $(srcdir)/kea-messages.rst $(srcdir)/api.rst
+@GENERATE_DOCS_TRUE@	rm -f $(srcdir)/arm/platforms.rst
+
+@GENERATE_DOCS_TRUE@.PHONY: all pdf html mans
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+# install and uninstall can occur with GENERATE_DOCS and without it
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+uninstall-local:
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diff --git a/doc/sphinx/_build/man/kea-admin.8 b/doc/sphinx/_build/man/kea-admin.8
new file mode 100644
index 0000000..8f1816a
--- /dev/null
+++ b/doc/sphinx/_build/man/kea-admin.8
@@ -0,0 +1,176 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "KEA-ADMIN" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+kea-admin \- Shell script for managing Kea databases
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBkea\-admin\fP [command] [backend] [\fB\-h\fP database_host]
+[\fB\-P\fP database_port] [\fB\-u\fP database_username]
+[\fB\-p\fP [database_password]] [\fB\-n\fP database_name] [\fB\-d\fP script_directory]
+[\fB\-v\fP] [\fB\-x\fP extra_argument [\fB\-x\fP extra_argument ...]]
+[\fB\-4\fP | \fB\-6\fP] [\fB\-i\fP input_file] [\fB\-o\fP output_file] [\fB\-y\fP]
+.SH DESCRIPTION
+.sp
+\fBkea\-admin\fP is a shell script that offers database maintenance. In
+particular, it features database initialization, database version
+checking, and database schema upgrading.
+.SH ARGUMENTS
+.INDENT 0.0
+.TP
+.B \fBcommand\fP
+Specifies the command to be issued to the servers. It can be one of the
+following:
+.INDENT 7.0
+.TP
+.B \fBdb\-init\fP
+Initializes a new database schema. This is useful during a new Kea
+installation. The database is initialized to the latest version
+supported by the version of the software being installed.
+.TP
+.B \fBdb\-version\fP
+Reports the database backend version number. This is not necessarily
+equal to the Kea version number, as each backend has its own
+versioning scheme.
+.TP
+.B \fBdb\-upgrade\fP
+Conducts a database schema upgrade. This is useful when upgrading Kea.
+.TP
+.B \fBlease\-dump\fP
+Dumps the contents of the lease database (for MySQL or
+PostgreSQL backends) to a CSV (comma\-separated values) text file. (Support
+for the Cassandra backend has been deprecated.)
+The first line of the file contains the column names. This can be used
+as a way to switch from a database backend to a memfile backend.
+Alternatively, it can be used as a diagnostic tool, so it provides a
+portable form of the lease data.
+.TP
+.B \fBlease\-upload\fP
+Uploads leases from a CSV (comma\-separated values) text file to a MySQL or
+a PostgreSQL lease database. The CSV file needs to be in memfile format.
+.TP
+.B \fBstats\-recount\fP
+Recounts lease statistics for a MySQL or PostgreSQL database.
+.UNINDENT
+.TP
+.B \fBbackend\fP
+Specifies the backend type. Currently allowed backends are: memfile,
+mysql, and pgsql; cql has been deprecated.
+.TP
+.B \fB\-h|\-\-host hostname\fP
+Specifies the hostname when connecting to a database.
+The default value is \fBlocalhost\fP\&.
+.TP
+.B \fB\-P|\-\-port port\fP
+Specifies the port when connecting to a database. If not specified,
+the default value chosen by the database client is used.
+.TP
+.B \fB\-u|\-\-user username\fP
+Specifies the username when connecting to a database.
+The default value is \fBkeatest\fP\&.
+.TP
+.B \fB\-p|\-\-password password\fP
+Specifies the password when connecting to a database.
+If only \fB\-p\fP or \fB\-\-password\fP is given, the user is prompted for a password.
+If not specified at all, the \fBKEA_ADMIN_DB_PASSWORD\fP environment variable
+is checked for a value and used if it exists.
+Otherwise the default value of \fBkeatest\fP is used.
+.TP
+.B \fB\-n|\-\-name database\-name\fP
+Specifies the name of the database to connect to. The
+default value is \fBkeatest\fP\&.
+.TP
+.B \fB\-d|\-\-directory script\-directory\fP
+Specifies the override scripts directory. That script is used during
+upgrades, database initialization, and possibly other operations.
+The default value is \fB(prefix)/share/kea/scripts/\fP\&.
+.TP
+.B \fB\-o|\-\-output output_file\fP
+Specifies the file to which the lease data will be dumped. Required for
+\fBlease\-dump\fP\&.
+.TP
+.B \fB\-v|\-\-version\fP
+Prints the \fBkea\-admin\fP version and quits.
+.TP
+.B \fB\-4\fP
+Directs \fBkea\-admin\fP to lease\-dump the DHCPv4 leases. Incompatible with
+the \-6 option.
+.TP
+.B \fB\-6\fP
+Directs \fBkea\-admin\fP to lease\-dump the DHCPv6 leases. Incompatible with
+the \-4 option.
+.TP
+.B \fB\-x|\-\-extra\fP
+Specifies an extra argument to pass to the database command tool e.g.
+to invoke \fBmysql\fP with the \fB\-\-ssl\fP argument. This can be repeated
+to pass more than one argument. Quotes are not preserved. Avoid commands
+containing spaces.
+.TP
+.B \fB\-y|\-\-yes\fP
+Assume yes on overwriting temporary files.
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp4(8)\fP, \fBkea\-dhcp6(8)\fP,
+\fBkea\-dhcp\-ddns(8)\fP, \fBkea\-ctrl\-agent(8)\fP,
+\fBkeactrl(8)\fP, \fBperfdhcp(8)\fP, \fBkea\-netconf(8)\fP,
+Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/_build/man/kea-ctrl-agent.8 b/doc/sphinx/_build/man/kea-ctrl-agent.8
new file mode 100644
index 0000000..75c3fae
--- /dev/null
+++ b/doc/sphinx/_build/man/kea-ctrl-agent.8
@@ -0,0 +1,113 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "KEA-CTRL-AGENT" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+kea-ctrl-agent \- Control Agent process in Kea
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBkea\-ctrl\-agent\fP [\fB\-v\fP] [\fB\-V\fP] [\fB\-W\fP] [\fB\-d\fP] [\fB\-c\fP config\-file] [\fB\-t\fP config\-file]
+.SH DESCRIPTION
+.sp
+The \fBkea\-ctrl\-agent\fP provides a REST service for controlling Kea
+services. The received HTTP requests are decapsulated and forwarded to
+the respective Kea services in JSON format. Received JSON responses are
+encapsulated within HTTP responses and returned to the controlling
+entity. Some commands may be handled by the Control Agent directly, and
+not forwarded to any Kea service.
+.SH ARGUMENTS
+.sp
+The arguments are as follows:
+.INDENT 0.0
+.TP
+.B \fB\-v\fP
+Displays the version.
+.TP
+.B \fB\-V\fP
+Displays the extended version.
+.TP
+.B \fB\-W\fP
+Displays the configuration report.
+.TP
+.B \fB\-d\fP
+Sets the logging level to debug with extra verbosity. This is primarily for
+development purposes in stand\-alone mode.
+.TP
+.B \fB\-c config\-file\fP
+Specifies the file with the configuration for the Control Agent
+server. It may also contain configuration entries for other Kea
+services.
+.TP
+.B \fB\-t config\-file\fP
+Checks the syntax of the configuration file and reports the first error,
+if any. Note that not all parameters are completely checked; in
+particular, service and client sockets are not opened, and hook
+libraries are not loaded.
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH HISTORY
+.sp
+The \fBkea\-ctrl\-agent\fP was first coded in December 2016 by Marcin
+Siodelski.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp4(8)\fP, \fBkea\-dhcp6(8)\fP,
+\fBkea\-dhcp\-ddns(8)\fP, \fBkea\-admin(8)\fP, \fBkeactrl(8)\fP,
+\fBperfdhcp(8)\fP, \fBkea\-lfc(8)\fP, Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/_build/man/kea-dhcp-ddns.8 b/doc/sphinx/_build/man/kea-dhcp-ddns.8
new file mode 100644
index 0000000..62d9ddb
--- /dev/null
+++ b/doc/sphinx/_build/man/kea-dhcp-ddns.8
@@ -0,0 +1,113 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "KEA-DHCP-DDNS" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+kea-dhcp-ddns \- DHCP-DDNS process in Kea
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBkea\-dhcp\-ddns\fP [\fB\-v\fP] [\fB\-V\fP] [\fB\-W\fP] [\fB\-d\fP] [\fB\-c\fP config\-file] [\fB\-t\fP config\-file]
+.SH DESCRIPTION
+.sp
+The \fBkea\-dhcp\-ddns\fP service process requests an update of DNS mapping
+based on DHCP lease\-change events. It runs as a separate process that
+expects to receive Name Change Requests from Kea DHCP servers.
+.SH ARGUMENTS
+.sp
+The arguments are as follows:
+.INDENT 0.0
+.TP
+.B \fB\-v\fP
+Displays the version.
+.TP
+.B \fB\-V\fP
+Displays the extended version.
+.TP
+.B \fB\-W\fP
+Displays the configuration report.
+.TP
+.B \fB\-d\fP
+Sets the logging level to debug with extra verbosity. This is primarily for
+development purposes in stand\-alone mode.
+.TP
+.B \fB\-c config\-file\fP
+Specifies the configuration file with the configuration for the DHCP\-DDNS server. It
+may also contain configuration entries for other Kea services.
+.TP
+.B \fB\-t config\-file\fP
+Checks the syntax of the configuration file and reports the first error,
+if any. Note that not all parameters are completely checked; in
+particular, a service socket is not opened.
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH HISTORY
+.sp
+The \fBb10\-dhcp\-ddns\fP process was first coded in May 2013 by Thomas
+Markwalder.
+.sp
+Kea became a standalone server and the BIND 10 framework was removed. The
+DHCP\-DDNS server binary was renamed to kea\-dhcp\-ddns in July 2014. Kea
+1.0.0 was released in December 2015.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp4(8)\fP, \fBkea\-dhcp6(8)\fP,
+\fBkea\-ctrl\-agent(8)\fP, \fBkea\-admin(8)\fP, \fBkeactrl(8)\fP,
+\fBperfdhcp(8)\fP, \fBkea\-netconf(8)\fP, \fBkea\-lfc(8)\fP,
+Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/_build/man/kea-dhcp4.8 b/doc/sphinx/_build/man/kea-dhcp4.8
new file mode 100644
index 0000000..08f7158
--- /dev/null
+++ b/doc/sphinx/_build/man/kea-dhcp4.8
@@ -0,0 +1,119 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "KEA-DHCP4" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+kea-dhcp4 \- DHCPv4 server in Kea
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBkea\-dhcp4\fP [\fB\-v\fP] [\fB\-V\fP] [\fB\-W\fP] [\fB\-d\fP] [\fB\-c\fP config\-file] [\fB\-t\fP config\-file] [\fB\-p\fP server\-port\-number] [\fB\-P\fP client\-port\-number]
+.SH DESCRIPTION
+.sp
+The \fBkea\-dhcp4\fP daemon provides the DHCPv4 server implementation.
+.SH ARGUMENTS
+.sp
+The arguments are as follows:
+.INDENT 0.0
+.TP
+.B \fB\-v\fP
+Displays the version.
+.TP
+.B \fB\-V\fP
+Displays the extended version.
+.TP
+.B \fB\-W\fP
+Displays the configuration report.
+.TP
+.B \fB\-d\fP
+Enables the debug mode with extra verbosity.
+.TP
+.B \fB\-c config\-file\fP
+Specifies the configuration file with the configuration for the DHCPv4 server. It
+may also contain configuration entries for other Kea services.
+.TP
+.B \fB\-t config\-file\fP
+Checks the configuration file and reports the first error, if any. Note
+that not all parameters are completely checked; in particular,
+service and control channel sockets are not opened, and hook
+libraries are not loaded.
+.TP
+.B \fB\-p server\-port\-number\fP
+Specifies the server port number (1\-65535) on which the server listens. This is
+useful for testing purposes only.
+.TP
+.B \fB\-P client\-port\-number\fP
+Specifies the client port number (1\-65535) to which the server responds. This is
+useful for testing purposes only.
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH HISTORY
+.sp
+The \fBb10\-dhcp4\fP daemon was first coded in November 2011 by Tomek
+Mrugalski.
+.sp
+In mid\-2014, Kea was decoupled from the BIND 10 framework and became a
+standalone DHCP server. The DHCPv4 server binary was renamed to
+\fBkea\-dhcp4\fP\&. Kea 1.0.0 was released in December 2015.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp6(8)\fP, \fBkea\-dhcp\-ddns(8)\fP,
+\fBkea\-ctrl\-agent(8)\fP, \fBkea\-admin(8)\fP, \fBkeactrl(8)\fP,
+\fBperfdhcp(8)\fP, \fBkea\-netconf(8)\fP, \fBkea\-lfc(8)\fP,
+Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/_build/man/kea-dhcp6.8 b/doc/sphinx/_build/man/kea-dhcp6.8
new file mode 100644
index 0000000..a426cec
--- /dev/null
+++ b/doc/sphinx/_build/man/kea-dhcp6.8
@@ -0,0 +1,119 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "KEA-DHCP6" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+kea-dhcp6 \- DHCPv6 server in Kea
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBkea\-dhcp6\fP [\fB\-v\fP] [\fB\-V\fP] [\fB\-W\fP] [\fB\-d\fP] [\fB\-c\fP config\-file] [\fB\-t\fP config\-file] [\fB\-p\fP server\-port\-number] [\fB\-P\fP client\-port\-number]
+.SH DESCRIPTION
+.sp
+The \fBkea\-dhcp6\fP daemon provides the DHCPv6 server implementation.
+.SH ARGUMENTS
+.sp
+The arguments are as follows:
+.INDENT 0.0
+.TP
+.B \fB\-v\fP
+Displays the version.
+.TP
+.B \fB\-V\fP
+Displays the extended version.
+.TP
+.B \fB\-W\fP
+Displays the configuration report.
+.TP
+.B \fB\-d\fP
+Enables the debug mode with extra verbosity.
+.TP
+.B \fB\-c config\-file\fP
+Specifies the configuration file with the configuration for the DHCPv6 server. It
+may also contain configuration entries for other Kea services.
+.TP
+.B \fB\-t config\-file\fP
+Checks the configuration file and reports the first error, if any. Note
+that not all parameters are completely checked; in particular,
+service and control channel sockets are not opened, and hook
+libraries are not loaded.
+.TP
+.B \fB\-p server\-port\-number\fP
+Specifies the server port number (1\-65535) on which the server listens. This is
+useful for testing purposes only.
+.TP
+.B \fB\-P client\-port\-number\fP
+Specifies the client port number (1\-65535) to which the server responds. This is
+useful for testing purposes only.
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH HISTORY
+.sp
+The \fBb10\-dhcp6\fP daemon was first coded in June 2011 by Tomek
+Mrugalski.
+.sp
+In mid\-2014, Kea was decoupled from the BIND 10 framework and became a
+standalone DHCP server. The DHCPv6 server binary was renamed to
+\fBkea\-dhcp6\fP\&. Kea 1.0.0 was released in December 2015.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp4(8)\fP, \fBkea\-dhcp\-ddns(8)\fP,
+\fBkea\-ctrl\-agent(8)\fP, \fBkea\-admin(8)\fP, \fBkeactrl(8)\fP,
+\fBperfdhcp(8)\fP, \fBkea\-netconf(8)\fP, \fBkea\-lfc(8)\fP,
+Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/_build/man/kea-lfc.8 b/doc/sphinx/_build/man/kea-lfc.8
new file mode 100644
index 0000000..4f020b2
--- /dev/null
+++ b/doc/sphinx/_build/man/kea-lfc.8
@@ -0,0 +1,144 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "KEA-LFC" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+kea-lfc \- Lease File Cleanup process in Kea
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBkea\-lfc\fP [\fB\-4**|\fP\-6**] [\fB\-c\fP config\-file] [\fB\-p\fP pid\-file] [\fB\-x\fP previous\-file] [\fB\-i\fP copy\-file] [\fB\-o\fP output\-file] [\fB\-f\fP finish\-file] [\fB\-v\fP] [\fB\-V\fP] [\fB\-W\fP] [\fB\-d\fP] [\fB\-h\fP]
+.SH DESCRIPTION
+.sp
+The \fBkea\-lfc\fP service process removes redundant information from the
+files used to provide persistent storage for the memfile database
+backend. The service is written to run as a stand\-alone process. While
+it can be started externally, there is usually no need to do this. It
+is run periodically by the Kea DHCP servers.
+.SH ARGUMENTS
+.sp
+The arguments are as follows:
+.INDENT 0.0
+.TP
+.B \fB\-4 | \-6\fP
+Indicates the protocol version of the lease files; must be either 4 or 6.
+.TP
+.B \fB\-c config\-file\fP
+Specifies the file with the configuration for the \fBkea\-lfc\fP
+process. It may also contain configuration entries for other Kea
+services. Currently \fBkea\-lfc\fP gets all of its arguments from the
+command line.
+.TP
+.B \fB\-p pid\-file\fP
+Specifies the PID file. When the \fBkea\-lfc\fP process starts, it attempts to
+determine if another instance of the process is already running, by
+examining the PID file. If one is already running, the new process is
+terminated. If one is not running, Kea writes its PID into the PID file.
+.TP
+.B \fB\-x previous\-file\fP
+Specifies the previous or ex\-lease file. When \fBkea\-lfc\fP starts, this is the
+result of any previous run of \fBkea\-lfc\fP; when \fBkea\-lfc\fP finishes,
+it is the result of the current run. If \fBkea\-lfc\fP is interrupted before
+completing, this file may not exist.
+.TP
+.B \fB\-i copy\-file\fP
+Specifies the input or copy of lease file. Before the DHCP server invokes
+\fBkea\-lfc\fP, it moves the current lease file here and then calls
+\fBkea\-lfc\fP with this file.
+.TP
+.B \fB\-o output\-file\fP
+Specifies the output lease file, which is the temporary file \fBkea\-lfc\fP should use to
+write the leases. Once this file is finished writing, it is
+moved to the finish file (see below).
+.TP
+.B \fB\-f finish\-file\fP
+Specifies the finish or completion file, another temporary file \fBkea\-lfc\fP uses
+for bookkeeping. When \fBkea\-lfc\fP finishes writing the output file,
+it moves it to this file name. After \fBkea\-lfc\fP finishes deleting
+the other files (previous and input), it moves this file to the previous
+lease file. By moving the files in this fashion, the \fBkea\-lfc\fP and
+the DHCP server processes can determine the correct file to use even
+if one of the processes was interrupted before completing its task.
+.TP
+.B \fB\-v\fP
+Causes the version stamp to be printed.
+.TP
+.B \fB\-V\fP
+Causes a longer form of the version stamp to be printed.
+.TP
+.B \fB\-W\fP
+Displays the configuration report.
+.TP
+.B \fB\-d\fP
+Sets the logging level to debug with extra verbosity. This is primarily for
+development purposes in stand\-alone mode.
+.TP
+.B \fB\-h\fP
+Causes the usage string to be printed.
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH HISTORY
+.sp
+The \fBkea\-lfc\fP process was first coded in January 2015 by the ISC
+Kea/DHCP team.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp4(8)\fP, \fBkea\-dhcp6(8)\fP, \fBkea\-dhcp\-ddns(8)\fP,
+\fBkea\-ctrl\-agent(8)\fP, \fBkea\-admin(8)\fP, \fBkeactrl(8)\fP,
+\fBperfdhcp(8)\fP, \fBkea\-netconf(8)\fP, Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/_build/man/kea-netconf.8 b/doc/sphinx/_build/man/kea-netconf.8
new file mode 100644
index 0000000..d4c0831
--- /dev/null
+++ b/doc/sphinx/_build/man/kea-netconf.8
@@ -0,0 +1,108 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "KEA-NETCONF" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+kea-netconf \- NETCONF agent for configuring Kea
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBkea\-netconf\fP [\fB\-v\fP] [\fB\-V\fP] [\fB\-W\fP] [\fB\-d\fP] [\fB\-c\fP config\-file] [\fB\-t\fP config\-file]
+.SH DESCRIPTION
+.sp
+The \fBkea\-netconf\fP agent provides a YANG/NETCONF interface for the Kea
+environment.
+.SH ARGUMENTS
+.sp
+The arguments are as follows:
+.INDENT 0.0
+.TP
+.B \fB\-v\fP
+Displays the version.
+.TP
+.B \fB\-V\fP
+Displays the extended version.
+.TP
+.B \fB\-W\fP
+Displays the configuration report.
+.TP
+.B \fB\-d\fP
+Enables the debug mode with extra verbosity.
+.TP
+.B \fB\-c config\-file\fP
+Specifies the file with the configuration for the NETCONF agent.
+.TP
+.B \fB\-t config\-file\fP
+Checks the syntax of the configuration file and reports the first error,
+if any. Note that not all parameters are completely checked; in
+particular, service and client sockets are not opened, and hook
+libraries are not loaded.
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH HISTORY
+.sp
+Early prototypes of \fBkea\-netconf\fP implementation were written during IETF
+Hackathons in Berlin, London, and Montreal. An actual production\-ready
+implementation was started in August 2018 by Tomek Mrugalski and Francis
+Dupont.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp4(8)\fP, \fBkea\-dhcp6(8)\fP, \fBkea\-dhcp\-ddns(8)\fP,
+\fBkea\-ctrl\-agent(8)\fP, \fBkea\-admin(8)\fP, \fBkeactrl(8)\fP,
+\fBperfdhcp(8)\fP, \fBkea\-lfc(8)\fP, Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/_build/man/kea-shell.8 b/doc/sphinx/_build/man/kea-shell.8
new file mode 100644
index 0000000..466c1c6
--- /dev/null
+++ b/doc/sphinx/_build/man/kea-shell.8
@@ -0,0 +1,140 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "KEA-SHELL" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+kea-shell \- Text client for Control Agent process
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBkea\-shell\fP [\fB\-h\fP] [\fB\-v\fP] [\fB\-\-host\fP] [\fB\-\-port\fP] [\fB\-\-path\fP] [\fB\-\-ca\fP] [\fB\-\-cert\fP] [\fB\-\-key\fP] [\fB\-\-auth\-user\fP] [\fB\-\-auth\-password\fP] [\fB\-\-timeout\fP] [\fB\-\-service\fP] [command]
+.SH DESCRIPTION
+.sp
+The \fBkea\-shell\fP provides a REST client for the Kea Control Agent (CA).
+It takes commands as a command\-line parameter that is sent to the CA
+with proper JSON encapsulation. Optional arguments may be specified on
+the standard input. The request is sent via HTTP and a response is
+retrieved, displayed on the standard output. Basic HTTP authentication
+and HTTPS, i.e. TLS transport, are supported.
+.SH ARGUMENTS
+.sp
+The arguments are as follows:
+.INDENT 0.0
+.TP
+.B \fB\-h\fP
+Displays help regarding command\-line parameters.
+.TP
+.B \fB\-v\fP
+Displays the version.
+.TP
+.B \fB\-\-host\fP
+Specifies the host to connect to. The Control Agent must be running at the
+specified host. If not specified, 127.0.0.1 is used.
+.TP
+.B \fB\-\-port\fP
+Specifies the TCP port to connect to. Control Agent must be listening
+at the specified port. If not specified, 8000 is used.
+.TP
+.B \fB\-\-path\fP
+Specifies the path in the URL to connect to. If not specified, an empty
+path is used. As Control Agent listens at the empty path, this
+parameter is useful only with a reverse proxy.
+.TP
+.B \fB\-\-ca\fP
+Specifies the file or directory name of the Certification Authority.
+If not specified, HTTPS is not used.
+.TP
+.B \fB\-\-cert\fP
+Specifies the file name of the user end\-entity public key certificate.
+If specified, the file name of the user key must also be specified.
+.TP
+.B \fB\-\-key\fP
+Specifies the file name of the user key file. If specified, the file
+name of the user certificate must also be specified.
+Encrypted key files are not supported.
+.TP
+.B \fB\-\-auth\-user\fP
+Specifies the user ID for basic HTTP authentication. If not specified,
+or specified as the empty string, authentication is not used.
+.TP
+.B \fB\-\-auth\-password\fP
+Specifies the password for basic HTTP authentication. If not specified
+but the user ID is specified, an empty password is used.
+.TP
+.B \fB\-\-timeout\fP
+Specifies the connection timeout, in seconds. The default is 10.
+.TP
+.B \fB\-\-service\fP
+Specifies the service that is the target of a command. If not
+specified, the Control Agent itself is targeted. May be used more than once
+to specify multiple targets.
+.TP
+.B \fBcommand\fP
+Specifies the command to be sent to the CA. If not specified,
+\fBlist\-commands\fP is used.
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH HISTORY
+.sp
+The \fBkea\-shell\fP was first coded in March 2017 by Tomek Mrugalski.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp4(8)\fP, \fBkea\-dhcp6(8)\fP, \fBkea\-dhcp\-ddns(8)\fP,
+\fBkea\-ctrl\-agent(8)\fP, \fBkea\-admin(8)\fP, \fBkeactrl(8)\fP,
+\fBperfdhcp(8)\fP, \fBkea\-lfc(8)\fP, Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/_build/man/keactrl.8 b/doc/sphinx/_build/man/keactrl.8
new file mode 100644
index 0000000..4411353
--- /dev/null
+++ b/doc/sphinx/_build/man/keactrl.8
@@ -0,0 +1,143 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "KEACTRL" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+keactrl \- Shell script for managing Kea
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBkeactrl\fP [\fBcommand\fP] [\fB\-c\fP keactrl\-config\-file] [\fB\-s\fP server[,server,...]] [\fB\-v\fP]
+.SH DESCRIPTION
+.sp
+\fBkeactrl\fP is a shell script which controls the startup, shutdown, and
+reconfiguration of the Kea servers (\fBkea\-dhcp4\fP, \fBkea\-dhcp6\fP,
+\fBkea\-dhcp\-ddns\fP, \fBkea\-ctrl\-agent\fP, and \fBkea\-netconf\fP). It also
+provides a way to check the current status of the servers and
+determine the configuration files in use.
+.SH CONFIGURATION FILE
+.sp
+Depending on the user\(aqs requirements, not all of the available servers need be run.
+The \fBkeactrl\fP configuration file specifies which servers are enabled and which
+are disabled. By default the configuration file is
+\fB[kea\-install\-dir]/etc/kea/keactrl.conf\fP\&.
+.sp
+See the Kea Administrator Reference Manual for documentation of the
+parameters in the \fBkeactrl\fP configuration file.
+.SH OPTIONS
+.INDENT 0.0
+.TP
+.B \fBcommand\fP
+Specifies the command to be issued to the servers. It can be one of the following:
+.INDENT 7.0
+.TP
+.B \fBstart\fP
+Starts the servers.
+.TP
+.B \fBstop\fP
+Stops the servers.
+.TP
+.B \fBreload\fP
+Instructs the servers to re\-read the Kea configuration file. This
+command is not supported by the NETCONF agent.
+.TP
+.B \fBstatus\fP
+Prints the status of the servers.
+.UNINDENT
+.TP
+.B \fB\-c|\-\-ctrl\-config keactrl\-config\-file\fP
+Specifies the \fBkeactrl\fP configuration file. Without this switch,
+\fBkeactrl\fP uses the file
+\fB[kea\-install\-dir]/etc/kea/keactrl.conf\fP\&.
+.TP
+.B \fB\-s|\-\-server server[,server,...]\fP
+Specifies a subset of the enabled servers to which the command should
+be issued. The list of servers should be separated by commas, with no
+intervening spaces. Acceptable values are:
+.INDENT 7.0
+.TP
+.B \fBdhcp4\fP
+DHCPv4 server (\fBkea\-dhcp4\fP).
+.TP
+.B \fBdhcp6\fP
+DHCPv6 server (\fBkea\-dhcp6\fP).
+.TP
+.B \fBdhcp_ddns\fP
+DHCP DDNS server (\fBkea\-dhcp\-ddns\fP).
+.TP
+.B \fBctrl_agent\fP
+Control Agent (\fBkea\-ctrl\-agent\fP).
+.TP
+.B \fBnetconf\fP
+NETCONF agent (\fBkea\-netconf\fP).
+.TP
+.B \fBall\fP
+All servers, including NETCONF if it was configured to be
+built. This is the default.
+.UNINDENT
+.TP
+.B \fB\-v|\-\-version\fP
+Prints the \fBkeactrl\fP version and quits.
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp4(8)\fP, \fBkea\-dhcp6(8)\fP, \fBkea\-dhcp\-ddns(8)\fP,
+\fBkea\-ctrl\-agent(8)\fP, \fBkea\-admin(8)\fP, \fBkea\-netconf(8)\fP,
+\fBperfdhcp(8)\fP, \fBkea\-lfc(8)\fP, Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/_build/man/perfdhcp.8 b/doc/sphinx/_build/man/perfdhcp.8
new file mode 100644
index 0000000..1cb91d7
--- /dev/null
+++ b/doc/sphinx/_build/man/perfdhcp.8
@@ -0,0 +1,581 @@
+.\" Man page generated from reStructuredText.
+.
+.TH "PERFDHCP" "8" "Jul 26, 2022" "2.2.0" "Kea"
+.SH NAME
+perfdhcp \- DHCP benchmarking tool
+.
+.nr rst2man-indent-level 0
+.
+.de1 rstReportMargin
+\\$1 \\n[an-margin]
+level \\n[rst2man-indent-level]
+level margin: \\n[rst2man-indent\\n[rst2man-indent-level]]
+-
+\\n[rst2man-indent0]
+\\n[rst2man-indent1]
+\\n[rst2man-indent2]
+..
+.de1 INDENT
+.\" .rstReportMargin pre:
+. RS \\$1
+. nr rst2man-indent\\n[rst2man-indent-level] \\n[an-margin]
+. nr rst2man-indent-level +1
+.\" .rstReportMargin post:
+..
+.de UNINDENT
+. RE
+.\" indent \\n[an-margin]
+.\" old: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.nr rst2man-indent-level -1
+.\" new: \\n[rst2man-indent\\n[rst2man-indent-level]]
+.in \\n[rst2man-indent\\n[rst2man-indent-level]]u
+..
+.SH SYNOPSIS
+.sp
+\fBperfdhcp\fP [\fB\-1\fP] [\fB\-4\fP | \fB\-6\fP] [\fB\-A\fP encapsulation\-level] [\fB\-b\fP base] [\fB\-B\fP] [\fB\-c\fP] [\fB\-C\fP separator] [\fB\-d\fP drop\-time] [\fB\-D\fP max\-drop] [\-e lease\-type] [\fB\-E\fP time\-offset] [\fB\-f\fP renew\-rate] [\fB\-F\fP release\-rate] [\fB\-g\fP thread\-mode] [\fB\-h\fP] [\fB\-i\fP] [\fB\-I\fP ip\-offset] [\fB\-J\fP remote\-address\-list\-file] [\fB\-l\fP local\-address|interface] [\fB\-L\fP local\-port] [\fB\-M\fP mac\-list\-file] [\fB\-n\fP num\-request] [\fB\-N\fP remote\-port] [\fB\-O\fP random\-offset] [\fB\-o\fP code,hexstring] [\fB\-p\fP test\-period] [\fB\-P\fP preload] [\fB\-r\fP rate] [\fB\-R\fP num\-clients] [\fB\-s\fP seed] [\fB\-S\fP srvid\-offset] [\fB\-\-scenario\fP name] [\fB\-t\fP report] [\fB\-T\fP template\-file] [\fB\-u\fP] [\fB\-v\fP] [\fB\-W\fP exit\-wait\-time] [\fB\-w\fP script_name] [\fB\-x\fP diagnostic\-selector] [\fB\-X\fP xid\-offset] [server]
+.SH DESCRIPTION
+.sp
+\fBperfdhcp\fP is a DHCP benchmarking tool. It provides a way to measure
+the performance of DHCP servers by generating large amounts of traffic
+from multiple simulated clients. It is able to test both IPv4 and IPv6
+servers, and provides statistics concerning response times and the
+number of requests that are dropped.
+.sp
+The tool supports two different scenarios, which offer certain behaviors to be tested.
+By default (the basic scenario), tests are run using the full four\-packet exchange sequence
+(DORA for DHCPv4, SARR for DHCPv6). An option is provided to run tests
+using the initial two\-packet exchange (DO and SA) instead. It is also
+possible to configure \fBperfdhcp\fP to send DHCPv6 RENEW and RELEASE messages
+at a specified rate, in parallel with the DHCPv6 four\-way exchanges. By
+default, if there is no response received with one second, a response is
+considered lost and \fBperfdhcp\fP continues with other transactions.
+.sp
+A second scenario, called avalanche, is selected via \fB\-\-scenario avalanche\fP\&.
+It first sends the number of Discovery or Solicit messages specified by the \fB\-R\fP option; then
+a retransmission (with an exponential back\-off mechanism) is used for each simulated client, until all requests are
+answered. It generates a report when all clients receive their addresses, or when
+it is manually stopped. This scenario attempts to replicate a
+case where the server is not able to handle the traffic swiftly
+enough. Real clients will assume the packet or response was lost
+and will retransmit, further increasing DHCP traffic. This is
+sometimes called an avalanche effect, thus the scenario name.
+Option \fB\-p\fP is ignored in the avalanche scenario.
+.sp
+When running a performance test, \fBperfdhcp\fP exchanges packets with
+the server under test as quickly as possible, unless the \fB\-r\fP parameter is used to
+limit the request rate. The length of the test can be limited by setting
+a threshold on any or all of the number of requests made by
+\fBperfdhcp\fP, the elapsed time, or the number of requests dropped by the
+server.
+.SH TEMPLATES
+.sp
+To allow the contents of packets sent to the server to be customized,
+\fBperfdhcp\fP allows the specification of template files that determine
+the contents of the packets. For example, the customized packet may
+contain a DHCPv6 ORO to request a set of options to be returned by the
+server, or it may contain the Client FQDN option to request that the server
+perform DNS updates. This may be used to discover performance
+bottlenecks for different server configurations (e.g. DDNS enabled or
+disabled).
+.sp
+Up to two template files can be specified on the command line, with each file
+representing the contents of a particular type of packet, and the type being
+determined by the test being carried out. For example, if testing
+DHCPv6:
+.INDENT 0.0
+.IP \(bu 2
+With no template files specified on the command line, \fBperfdhcp\fP
+generates both Solicit and Request packets.
+.IP \(bu 2
+With one template file specified, that file is used as the
+pattern for Solicit packets: \fBperfdhcp\fP generates the Request
+packets.
+.IP \(bu 2
+With two template files given on the command line, the first is
+used as the pattern for Solicit packets, and the second as the pattern
+for Request packets.
+.UNINDENT
+.sp
+(A similar determination applies to DHCPv4\(aqs DHCPDISCOVER and DHCPREQUEST
+packets.)
+.sp
+The template file holds the DHCP packet, represented as a stream of ASCII
+hexadecimal digits; it excludes any IP/UDP stack headers. The
+template file must not contain any characters other than hexadecimal
+digits and spaces. Spaces are discarded when the template file is parsed;
+in the file, \fB12B4\fP is the same as \fB12 B4\fP, which is the same as
+\fB1 2 B 4\fP\&.
+.sp
+The template files should be used in conjunction with the command\-line
+parameters which specify offsets of the data fields being modified in
+outbound packets. For example, the \fB\-E time\-offset\fP switch specifies
+the offset of the DHCPv6 Elapsed Time option in the packet template.
+If the offset is specified, \fBperfdhcp\fP injects the current elapsed\-time
+value into this field before sending the packet to the server.
+.sp
+In many scenarios, \fBperfdhcp\fP needs to simulate multiple clients,
+each having a unique client identifier. Since packets for each client are
+generated from the same template file, it is necessary to randomize the
+client identifier (or HW address in DHCPv4) in the packet created from
+it. The \fB\-O random\-offset\fP option allows specification of the offset in
+the template where randomization should be performed. It is important to
+note that this offset points to the end (not the beginning) of the
+client identifier (or HW address field). The number of bytes being
+randomized depends on the number of simulated clients. If the number of
+simulated clients is between 1 and 255, only one byte (to which the
+randomization offset points) is randomized. If the number of
+simulated clients is between 256 and 65535, two bytes are
+randomized. Note that the last two bytes of the client identifier are
+randomized in this case: the byte which the randomization offset parameter
+points to, and the one which precedes it (random\-offset \- 1). If the
+number of simulated clients exceeds 65535, three bytes are
+randomized, and so on.
+.sp
+\fBperfdhcp\fP can simulate traffic from multiple subnets by enabling option
+\fB\-J\fP and passing a path to a file that contains v4 or v6 addresses to be
+used as relays in generated messages. That enables testing of vast numbers
+of Kea shared networks. While testing DHCPv4, Kea should be started with the
+\fBKEA_TEST_SEND_RESPONSES_TO_SOURCE\fP environment variable, to force Kea
+to send generated messages to the source address of the incoming packet.
+.sp
+Templates may currently be used to generate packets being sent to the
+server in 4\-way exchanges, i.e. Solicit, Request (DHCPv6) and DHCPDISCOVER,
+DHCPREQUEST (DHCPv4). They cannot be used when Renew or DHCPRELEASE packets are
+being sent.
+.SH OPTIONS
+.INDENT 0.0
+.TP
+.B \fB\-1\fP
+Takes the \fBserver\-id\fP option from the first received message.
+.TP
+.B \fB\-4\fP
+Establishes DHCPv4 operation; this is the default. It is incompatible with the
+\fB\-6\fP option.
+.TP
+.B \fB\-6\fP
+Establishes DHCPv6 operation. It is incompatible with the \fB\-4\fP option.
+.TP
+.B \fB\-b basetype=value\fP
+Indicates the base MAC or DUID used to simulate different clients. The basetype
+may be "mac" or "duid". (The keyword "ether" may alternatively used
+for MAC.) The \fB\-b\fP option can be specified multiple times. The MAC
+address must consist of six octets separated by single (:) or double
+(::) colons; for example: mac=00:0c:01:02:03:04. The DUID value is a
+hexadecimal string; it must be at least six octets long and not
+longer than 64 bytes, and the length must be less than 128
+hexadecimal digits. For example: duid=0101010101010101010110111F14.
+.TP
+.B \fB\-d drop\-time\fP
+Specifies the time after which a request is treated as having been
+lost. The value is given in seconds and may contain a fractional
+component. The default is 1.
+.TP
+.B \fB\-e lease\-type\fP
+Specifies the type of lease being requested from the server. It may
+be one of the following:
+.INDENT 7.0
+.TP
+.B \fBaddress\-only\fP
+Only regular addresses (v4 or v6) are requested.
+.TP
+.B \fBprefix\-only\fP
+Only IPv6 prefixes are requested.
+.TP
+.B \fBaddress\-and\-prefix\fP
+Both IPv6 addresses and prefixes are requested.
+.UNINDENT
+.sp
+The \fB\-e prefix\-only\fP and \fB\-e address\-and\-prefix\fP forms may not be used
+with the \fB\-4\fP option.
+.TP
+.B \fB\-F release\-rate\fP
+Specifies the rate at which DHCPv4 DHCPRELEASE or DHCPv6 Release requests are sent to a server. This value
+is only valid when used in conjunction with the exchange rate (given
+by \fB\-r rate\fP). Furthermore, the sum of this value and the renew\-rate
+(given by \fB\-f rate\fP) must be equal to or less than the exchange
+rate value.
+.TP
+.B \fB\-f renew\-rate\fP
+Specifies the rate at which DHCPv4 DHCPREQUEST or DHCPv6 Renew requests are sent to a server.
+This value is only valid when used in conjunction with the exchange
+rate (given by \fB\-r rate\fP). Furthermore, the sum of this value and
+the release\-rate (given by \fB\-F rate\fP) must be equal to or less than the
+exchange rate.
+.TP
+.B \fB\-g thread\-mode\fP
+Allows selection of thread\-mode, which can be either \fBsingle\fP or \fBmulti\fP\&. In multi\-thread mode,
+packets are received in a separate thread, which allows better
+utilisation of CPUs. In a single\-CPU system it is better to run in one
+thread, to avoid threads blocking each other. If more than one CPU is
+present in the system, multi\-thread mode is the default; otherwise
+single\-thread is the default.
+.TP
+.B \fB\-h\fP
+Prints help and exits.
+.TP
+.B \fB\-i\fP
+Performs only the initial part of the exchange: DISCOVER\-OFFER if \fB\-4\fP is
+selected, Solicit\-Advertise if \fB\-6\fP is chosen.
+.sp
+\fB\-i\fP is incompatible with the following options: \fB\-1\fP, \fB\-d\fP,
+\fB\-D\fP, \fB\-E\fP, \fB\-S\fP, \fB\-I\fP and \fB\-F\fP\&. In addition, it cannot be
+used with multiple instances of \fB\-O\fP, \fB\-T\fP, and \fB\-X\fP\&.
+.TP
+.B \fB\-J remote\-address\-list\-file\fP
+Specifies a text file that includes multiple addresses, and is
+designed to test shared networks. If provided, \fBperfdhcp\fP
+randomly chooses one of the addresses for each exchange, to generate traffic
+from multiple subnets. When testing DHCPv4, it
+should be started with the \fBKEA_TEST_SEND_RESPONSES_TO_SOURCE=ENABLE\fP
+environment variable; otherwise, \fBperfdhcp\fP will not be able to receive responses.
+.TP
+.B \fB\-l local\-addr|interface\fP
+For DHCPv4 operation, specifies the local hostname/address to use when
+communicating with the server. By default, the interface address
+through which traffic would normally be routed to the server is used.
+For DHCPv6 operation, specifies the name of the network interface
+through which exchanges are initiated.
+.TP
+.B \fB\-L local\-port\fP
+Specifies the local port to use. This must be zero or a positive
+integer up to 65535. A value of 0 (the default) allows \fBperfdhcp\fP
+to choose its own port.
+.TP
+.B \fB\-M mac\-list\-file\fP
+Specifies a text file containing a list of MAC addresses, one per line. If
+provided, a MAC address is chosen randomly from this list for
+every new exchange. In DHCPv6, MAC addresses are used to
+generate DUID\-LLs. This parameter must not be used in conjunction
+with the \fB\-b\fP parameter.
+.TP
+.B \fB\-N remote\-port\fP
+Specifies the remote port to use. This must be zero or a positive
+integer up to 65535. A value of 0 (the default) allows \fBperfdhcp\fP
+to choose the standard service port.
+.TP
+.B \fB\-o code,hexstring\fP
+Forces \fBperfdhcp\fP to insert the specified extra option (or options if
+used several times) into packets being transmitted. The code
+specifies the option code and the hexstring is a hexadecimal string that
+defines the content of the option. Care should be taken as \fBperfdhcp\fP
+does not offer any kind of logic behind those options; they are simply
+inserted into packets and sent as is. Be careful not to duplicate
+options that are already inserted. For example, to insert client
+class identifier (option code 60) with a string "docsis", use
+"\-o 60,646f63736973". The \fB\-o\fP may be used multiple times. It is
+necessary to specify the protocol family (either \fB\-4\fP or \fB\-6\fP) before
+using \fB\-o\fP\&.
+.TP
+.B \fB\-P preload\fP
+Initiates preload exchanges back\-to\-back at startup. Must be 0
+(the default) or a positive integer.
+.TP
+.B \fB\-r rate\fP
+Initiates the rate of DORA/SARR (or if \fB\-i\fP is given, DO/SA) exchanges per
+second. A periodic report is generated showing the number of
+exchanges which were not completed, as well as the average response
+latency. The program continues until interrupted, at which point a
+final report is generated.
+.TP
+.B \fB\-R num\-clients\fP
+Specifies how many different clients are used. With a value of 1 (the
+default), all requests appear to come from the same client.
+Must be a positive number.
+.TP
+.B \fB\-s seed\fP
+Specifies the seed for randomization, making runs of \fBperfdhcp\fP
+repeatable. This must be 0 or a positive integer. The value 0 means that a
+seed is not used; this is the default.
+.TP
+.B \fB\-\-scenario name\fP
+Specifies the type of scenario, and can be \fBbasic\fP (the default) or \fBavalanche\fP\&.
+.TP
+.B \fB\-T template\-file\fP
+Specifies a file containing the template to use as a stream of
+hexadecimal digits. This may be specified up to two times and
+controls the contents of the packets sent (see the "Templates"
+section above).
+.TP
+.B \fB\-u\fP
+Enables checks for address uniqueness. The lease valid\-lifetime should not be shorter
+than the test duration, and clients should not request an address more than once without
+releasing it.
+.TP
+.B \fB\-v\fP
+Prints the version of this program.
+.TP
+.B \fB\-W exit\-wait\-time\fP
+Specifies the exit\-wait\-time parameter, which causes \fBperfdhcp\fP to wait for
+a certain amount of time after an exit condition has been met, to receive all
+packets without sending any new packets. Expressed in microseconds.
+If not specified, 0 is used (i.e. exit immediately after exit
+conditions are met).
+.TP
+.B \fB\-w script_name\fP
+Specifies the name of the script to be run before/after \fBperfdhcp\fP\&.
+When called, the script is passed a single parameter, either "start" or
+"stop", indicating whether it is being called before or after \fBperfdhcp\fP\&.
+.TP
+.B \fB\-x diagnostic\-selector\fP
+Includes extended diagnostics in the output. This is a
+string of single keywords specifying the operations for which verbose
+output is desired. The selector key letters are:
+.INDENT 7.0
+.TP
+.B \fBa\fP
+Prints the decoded command\-line arguments.
+.TP
+.B \fBe\fP
+Prints the exit reason.
+.TP
+.B \fBi\fP
+Prints the rate\-processing details.
+.TP
+.B \fBl\fP
+Prints the received leases.
+.TP
+.B \fBs\fP
+Prints the first server ID.
+.TP
+.B \fBt\fP
+When finished, prints timers of all successful exchanges.
+.TP
+.B \fBT\fP
+When finished, prints templates.
+.UNINDENT
+.TP
+.B \fB\-y seconds\fP
+Time in seconds after which \fBperfdhcp\fP starts simulating the client waiting longer for server responses. This increases the
+\fBsecs\fP field in DHCPv4 and sends increased values in the \fBElapsed Time\fP option in DHCPv6. Must be used with \fB\-Y\fP\&.
+.TP
+.B \fB\-Y seconds\fP
+Time in seconds during which \fBperfdhcp\fP simulates the client waiting longer for server responses. This increases
+the \fBsecs\fP field in DHCPv4 and sends increased values in the \fBElapsed Time\fP option in DHCPv6. Must be used with \fB\-y\fP\&.
+.UNINDENT
+.SH DHCPV4-ONLY OPTIONS
+.sp
+The following options only apply for DHCPv4 (i.e. when \fB\-4\fP is given).
+.INDENT 0.0
+.TP
+.B \fB\-B\fP
+Forces broadcast handling.
+.UNINDENT
+.SH DHCPV6-ONLY OPTIONS
+.sp
+The following options only apply for DHCPv6 (i.e. when \fB\-6\fP is given).
+.INDENT 0.0
+.TP
+.B \fB\-c\fP
+Adds a rapid\-commit option (exchanges are Solicit\-Advertise).
+.TP
+.B \fB\-A encapsulation\-level\fP
+Specifies that relayed traffic must be generated. The argument
+specifies the level of encapsulation, i.e. how many relay agents are
+simulated. Currently the only supported encapsulation\-level value is
+1, which means that the generated traffic is equivalent to the amount of
+traffic passing through a single relay agent.
+.UNINDENT
+.SH TEMPLATE-RELATED OPTIONS
+.sp
+The following options may only be used in conjunction with \fB\-T\fP and
+control how \fBperfdhcp\fP modifies the template. The options may be
+specified multiple times on the command line; each occurrence affects
+the corresponding template file (see "Templates" above).
+.INDENT 0.0
+.TP
+.B \fB\-E time\-offset\fP
+Specifies the offset of the \fBsecs\fP field (DHCPv4) or \fBElapsed Time\fP option (DHCPv6) in the
+second (i.e. Request) template; must be 0 or a positive integer. A
+value of 0 disables this.
+.TP
+.B \fB\-I ip\-offset\fP
+Specifies the offset of the IP address (DHCPv4) in the \fBrequested\-ip\fP
+option or \fBIA_NA\fP option (DHCPv6) in the second (Request) template.
+.TP
+.B \fB\-O random\-offset\fP
+Specifies the offset of the last octet to randomize in the template. This
+must be an integer greater than 3. The \fB\-T\fP switch must be given to
+use this option.
+.TP
+.B \fB\-S srvid\-offset\fP
+Specifies the offset of the \fBserver\-id\fP option in the second (Request) template.
+This must be a positive integer, and the switch can only be used
+when the template option (\fB\-T\fP) is also given.
+.TP
+.B \fB\-X xid\-offset\fP
+Specifies the offset of the transaction ID (xid) in the template. This must be a
+positive integer, and the switch can only be used when the template
+option (\fB\-T\fP) is also given.
+.UNINDENT
+.SH OPTIONS CONTROLLING A TEST
+.INDENT 0.0
+.TP
+.B \fB\-D max\-drop\fP
+Aborts the test immediately if "max\-drop" requests have been dropped.
+Use \fB\-D 0\fP to abort if even a single request has
+been dropped. "max\-drop" must be a positive integer. If "max\-drop"
+includes the suffix \fB%\fP, it specifies the maximum percentage of
+requests that may be dropped before aborting. In this case, testing of
+the threshold begins after 10 requests are expected to have been
+received.
+.TP
+.B \fB\-n num\-requests\fP
+Initiates "num\-request" transactions. No report is generated until all
+transactions have been initiated/waited\-for, after which a report is
+generated and the program terminates.
+.TP
+.B \fB\-p test\-period\fP
+Sends requests for "test\-period", which is specified in the same manner
+as \fB\-d\fP\&. This can be used as an alternative to \fB\-n\fP, or both
+options can be given, in which case the testing is completed when
+either limit is reached.
+.TP
+.B \fB\-t interval\fP
+Sets the delay (in seconds) between two successive reports.
+.TP
+.B \fB\-C separator\fP
+Suppresses the preliminary output and causes the interim data to
+only contain the values delimited by \fBseparator\fP\&. Used in
+conjunction with \fB\-t\fP to produce easily parsable
+reports at \fB\-t\fP intervals.
+.UNINDENT
+.SH ARGUMENTS
+.INDENT 0.0
+.TP
+.B \fBserver\fP
+Indicates the server to test, specified as an IP address. In the DHCPv6 case, the
+special name \fBall\fP can be used to refer to
+\fBAll_DHCP_Relay_Agents_and_Servers\fP (the multicast address FF02::1:2),
+or the special name \fBservers\fP to refer to \fBAll_DHCP_Servers\fP (the
+multicast address FF05::1:3). The server is mandatory except where
+the \fB\-l\fP option is given to specify an interface, in which case it
+defaults to \fBall\fP\&.
+.UNINDENT
+.SH ERRORS
+.sp
+\fBperfdhcp\fP can report the following errors in the packet exchange:
+.INDENT 0.0
+.TP
+.B tooshort
+A message was received that was too short.
+.TP
+.B orphans
+A message was received which does not match one sent to the server (i.e.
+it is a duplicate message, a message that has arrived after an
+excessive delay, or one that is just not recognized).
+.TP
+.B locallimit
+Local system limits have been reached when sending a message.
+.UNINDENT
+.SH EXIT STATUS
+.sp
+\fBperfdhcp\fP exits with one of the following status codes:
+.INDENT 0.0
+.TP
+.B 0
+Success.
+.TP
+.B 1
+General error.
+.TP
+.B 2
+Error in command\-line arguments.
+.TP
+.B 3
+No general failures in operation, but one or more exchanges were
+unsuccessful.
+.UNINDENT
+.SH USAGE EXAMPLES
+.sp
+Here is an example that simulates regular DHCPv4 traffic of 100 DHCPv4 devices (\-R 100),
+10 packets per second (\-r 10), shows the query/response rate details (\-xi),
+shows a report every 2 seconds (\-t 2), and sends the packets to the IP 192.0.2.1:
+.INDENT 0.0
+.INDENT 3.5
+.sp
+.nf
+.ft C
+sudo perfdhcp \-xi \-t 2 \-r 10 \-R 100 192.0.2.1
+.ft P
+.fi
+.UNINDENT
+.UNINDENT
+.sp
+Here\(aqs a similar case, but for DHCPv6. Note that the DHCPv6 protocol uses link\-local
+addresses, so the interface (eth0 in this example) must be specified on which to send the
+traffic. \fBall\fP is a convenience alias for \fBAll_DHCP_Relay_Agents_and_Servers\fP
+(the multicast address FF02::1:2). It is also possible to use the \fBservers\fP alias
+to refer to \fBAll_DHCP_Servers\fP (the multicast address FF05::1:3). The default is \fBall\fP\&.
+.INDENT 0.0
+.INDENT 3.5
+.sp
+.nf
+.ft C
+sudo perfdhcp \-6 \-xi \-t 1 \-r 1 \-R 10 \-l eth0 all
+.ft P
+.fi
+.UNINDENT
+.UNINDENT
+.sp
+The following examples simulate normal DHCPv4 and DHCPv6 traffic that, after 3 seconds,
+starts pretending not to receive any responses from the server for 10 seconds. The
+DHCPv4 protocol signals this by an increased \fBsecs\fP field, while DHCPv6 uses the
+\fBElapsed Time\fP option. In real networks, this indicates that clients are not getting
+responses in a timely matter. This can be used to simulate some HA scenarios, as Kea
+uses the \fBsecs\fP field and \fBElapsed Time\fP option value as one of the indicators
+that the HA partner is not responding. When enabled with \fB\-y\fP and \fB\-Y\fP, the \fBsecs\fP
+and \fBElapsed Time\fP values increase steadily.
+.INDENT 0.0
+.INDENT 3.5
+.sp
+.nf
+.ft C
+sudo perfdhcp \-xi \-t 1 \-r 1 \-y 10 \-Y 3 192.0.2.1
+
+sudo perfdhcp \-6 \-xi \-t 1 \-r 1 \-y 10 \-Y 3 2001:db8::1
+.ft P
+.fi
+.UNINDENT
+.UNINDENT
+.SH DOCUMENTATION
+.sp
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software \- compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+\fI\%https://kea.readthedocs.io\fP\&.
+.sp
+Kea source code is documented in the Kea Developer\(aqs Guide,
+available at \fI\%https://reports.kea.isc.org/dev_guide/\fP\&.
+.sp
+The Kea project website is available at \fI\%https://kea.isc.org\fP\&.
+.SH MAILING LISTS AND SUPPORT
+.sp
+There are two public mailing lists available for the Kea project. \fBkea\-users\fP
+(kea\-users at lists.isc.org) is intended for Kea users, while \fBkea\-dev\fP
+(kea\-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+\fI\%https://lists.isc.org\fP\&. The community provides best\-effort support
+on both of those lists.
+.sp
+ISC provides professional support for Kea services. See
+\fI\%https://www.isc.org/kea/\fP for details.
+.SH HISTORY
+.sp
+The \fBperfdhcp\fP tool was initially coded in October 2011 by John
+DuBois, Francis Dupont, and Marcin Siodelski of ISC. Kea 1.0.0, which
+included \fBperfdhcp\fP, was released in December 2015.
+.SH SEE ALSO
+.sp
+\fBkea\-dhcp4(8)\fP, \fBkea\-dhcp6(8)\fP, \fBkea\-dhcp\-ddns(8)\fP,
+\fBkea\-ctrl\-agent(8)\fP, \fBkea\-admin(8)\fP, \fBkea\-netconf(8)\fP,
+\fBkeactrl(8)\fP, \fBkea\-lfc(8)\fP, Kea Administrator Reference Manual.
+.SH AUTHOR
+Internet Systems Consortium
+.SH COPYRIGHT
+2019-2022, Internet Systems Consortium
+.\" Generated by docutils manpage writer.
+.
diff --git a/doc/sphinx/api-files.txt b/doc/sphinx/api-files.txt
new file mode 100644
index 0000000..735d520
--- /dev/null
+++ b/doc/sphinx/api-files.txt
@@ -0,0 +1,190 @@
+src/share/api/build-report.json
+src/share/api/cache-clear.json
+src/share/api/cache-flush.json
+src/share/api/cache-get-by-id.json
+src/share/api/cache-get.json
+src/share/api/cache-insert.json
+src/share/api/cache-load.json
+src/share/api/cache-remove.json
+src/share/api/cache-size.json
+src/share/api/cache-write.json
+src/share/api/class-add.json
+src/share/api/class-del.json
+src/share/api/class-get.json
+src/share/api/class-list.json
+src/share/api/class-update.json
+src/share/api/config-backend-pull.json
+src/share/api/config-get.json
+src/share/api/config-reload.json
+src/share/api/config-set.json
+src/share/api/config-test.json
+src/share/api/config-write.json
+src/share/api/dhcp-disable.json
+src/share/api/dhcp-enable.json
+src/share/api/gss-tsig-get-all.json
+src/share/api/gss-tsig-get.json
+src/share/api/gss-tsig-key-del.json
+src/share/api/gss-tsig-key-expire.json
+src/share/api/gss-tsig-key-get.json
+src/share/api/gss-tsig-list.json
+src/share/api/gss-tsig-purge-all.json
+src/share/api/gss-tsig-purge.json
+src/share/api/gss-tsig-rekey-all.json
+src/share/api/gss-tsig-rekey.json
+src/share/api/ha-continue.json
+src/share/api/ha-heartbeat.json
+src/share/api/ha-maintenance-cancel.json
+src/share/api/ha-maintenance-notify.json
+src/share/api/ha-maintenance-start.json
+src/share/api/ha-reset.json
+src/share/api/ha-scopes.json
+src/share/api/ha-sync.json
+src/share/api/ha-sync-complete-notify.json
+src/share/api/lease4-add.json
+src/share/api/lease4-del.json
+src/share/api/lease4-get-all.json
+src/share/api/lease4-get-by-client-id.json
+src/share/api/lease4-get-by-hostname.json
+src/share/api/lease4-get-by-hw-address.json
+src/share/api/lease4-get-page.json
+src/share/api/lease4-get.json
+src/share/api/lease4-resend-ddns.json
+src/share/api/lease4-update.json
+src/share/api/lease4-wipe.json
+src/share/api/lease6-add.json
+src/share/api/lease6-bulk-apply.json
+src/share/api/lease6-del.json
+src/share/api/lease6-get-all.json
+src/share/api/lease6-get-by-duid.json
+src/share/api/lease6-get-by-hostname.json
+src/share/api/lease6-get-page.json
+src/share/api/lease6-get.json
+src/share/api/lease6-resend-ddns.json
+src/share/api/lease6-update.json
+src/share/api/lease6-wipe.json
+src/share/api/leases-reclaim.json
+src/share/api/libreload.json
+src/share/api/list-commands.json
+src/share/api/network4-add.json
+src/share/api/network4-del.json
+src/share/api/network4-get.json
+src/share/api/network4-list.json
+src/share/api/network4-subnet-add.json
+src/share/api/network4-subnet-del.json
+src/share/api/network6-add.json
+src/share/api/network6-del.json
+src/share/api/network6-get.json
+src/share/api/network6-list.json
+src/share/api/network6-subnet-add.json
+src/share/api/network6-subnet-del.json
+src/share/api/remote-class4-del.json
+src/share/api/remote-class4-get-all.json
+src/share/api/remote-class4-get.json
+src/share/api/remote-class4-set.json
+src/share/api/remote-class6-del.json
+src/share/api/remote-class6-get-all.json
+src/share/api/remote-class6-get.json
+src/share/api/remote-class6-set.json
+src/share/api/remote-global-parameter4-del.json
+src/share/api/remote-global-parameter4-get-all.json
+src/share/api/remote-global-parameter4-get.json
+src/share/api/remote-global-parameter4-set.json
+src/share/api/remote-global-parameter6-del.json
+src/share/api/remote-global-parameter6-get-all.json
+src/share/api/remote-global-parameter6-get.json
+src/share/api/remote-global-parameter6-set.json
+src/share/api/remote-network4-del.json
+src/share/api/remote-network4-get.json
+src/share/api/remote-network4-list.json
+src/share/api/remote-network4-set.json
+src/share/api/remote-network6-del.json
+src/share/api/remote-network6-get.json
+src/share/api/remote-network6-list.json
+src/share/api/remote-network6-set.json
+src/share/api/remote-option-def4-del.json
+src/share/api/remote-option-def4-get-all.json
+src/share/api/remote-option-def4-get.json
+src/share/api/remote-option-def4-set.json
+src/share/api/remote-option-def6-del.json
+src/share/api/remote-option-def6-get-all.json
+src/share/api/remote-option-def6-get.json
+src/share/api/remote-option-def6-set.json
+src/share/api/remote-option4-global-del.json
+src/share/api/remote-option4-global-get-all.json
+src/share/api/remote-option4-global-get.json
+src/share/api/remote-option4-global-set.json
+src/share/api/remote-option4-network-del.json
+src/share/api/remote-option4-network-set.json
+src/share/api/remote-option4-pool-del.json
+src/share/api/remote-option4-pool-set.json
+src/share/api/remote-option4-subnet-del.json
+src/share/api/remote-option4-subnet-set.json
+src/share/api/remote-option6-global-del.json
+src/share/api/remote-option6-global-get-all.json
+src/share/api/remote-option6-global-get.json
+src/share/api/remote-option6-global-set.json
+src/share/api/remote-option6-network-del.json
+src/share/api/remote-option6-network-set.json
+src/share/api/remote-option6-pd-pool-del.json
+src/share/api/remote-option6-pd-pool-set.json
+src/share/api/remote-option6-pool-del.json
+src/share/api/remote-option6-pool-set.json
+src/share/api/remote-option6-subnet-del.json
+src/share/api/remote-option6-subnet-set.json
+src/share/api/remote-server4-del.json
+src/share/api/remote-server4-get-all.json
+src/share/api/remote-server4-get.json
+src/share/api/remote-server4-set.json
+src/share/api/remote-server6-del.json
+src/share/api/remote-server6-get-all.json
+src/share/api/remote-server6-get.json
+src/share/api/remote-server6-set.json
+src/share/api/remote-subnet4-del-by-id.json
+src/share/api/remote-subnet4-del-by-prefix.json
+src/share/api/remote-subnet4-get-by-id.json
+src/share/api/remote-subnet4-get-by-prefix.json
+src/share/api/remote-subnet4-list.json
+src/share/api/remote-subnet4-set.json
+src/share/api/remote-subnet6-del-by-id.json
+src/share/api/remote-subnet6-del-by-prefix.json
+src/share/api/remote-subnet6-get-by-id.json
+src/share/api/remote-subnet6-get-by-prefix.json
+src/share/api/remote-subnet6-list.json
+src/share/api/remote-subnet6-set.json
+src/share/api/reservation-add.json
+src/share/api/reservation-del.json
+src/share/api/reservation-get-all.json
+src/share/api/reservation-get-by-hostname.json
+src/share/api/reservation-get-by-id.json
+src/share/api/reservation-get-page.json
+src/share/api/reservation-get.json
+src/share/api/server-tag-get.json
+src/share/api/shutdown.json
+src/share/api/stat-lease4-get.json
+src/share/api/stat-lease6-get.json
+src/share/api/statistic-get-all.json
+src/share/api/statistic-get.json
+src/share/api/statistic-remove-all.json
+src/share/api/statistic-remove.json
+src/share/api/statistic-reset-all.json
+src/share/api/statistic-reset.json
+src/share/api/statistic-sample-age-set-all.json
+src/share/api/statistic-sample-age-set.json
+src/share/api/statistic-sample-count-set-all.json
+src/share/api/statistic-sample-count-set.json
+src/share/api/status-get.json
+src/share/api/subnet4-add.json
+src/share/api/subnet4-del.json
+src/share/api/subnet4-delta-add.json
+src/share/api/subnet4-delta-del.json
+src/share/api/subnet4-get.json
+src/share/api/subnet4-list.json
+src/share/api/subnet4-update.json
+src/share/api/subnet6-add.json
+src/share/api/subnet6-del.json
+src/share/api/subnet6-delta-add.json
+src/share/api/subnet6-delta-del.json
+src/share/api/subnet6-get.json
+src/share/api/subnet6-list.json
+src/share/api/subnet6-update.json
+src/share/api/version-get.json
diff --git a/doc/sphinx/api2doc.py b/doc/sphinx/api2doc.py
new file mode 100755
index 0000000..4318fd2
--- /dev/null
+++ b/doc/sphinx/api2doc.py
@@ -0,0 +1,208 @@
+#!/usr/bin/env python3
+
+# Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http:#mozilla.org/MPL/2.0/.
+
+# Produce API Reference
+# - reads *.json files (each file describes a single command)
+# - produces .rst file suitable for Sphinx as output
+
+import os
+import json
+import argparse
+import collections
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description='Convert set of *.json files to .rst documentation format')
+    parser.add_argument('-o', '--output', help='Output file name (default to stdout).')
+    parser.add_argument('files', help='Input API .json files.', nargs='+')
+
+    args = parser.parse_args()
+    return args
+
+
+def read_input_files(files):
+    apis = {}
+    for f in files:
+        name = os.path.basename(f)[:-5]
+        # Skip special names starting with _ (such as _template.json)
+        if name.startswith('_'):
+            print("Skipping %s (starts with underscore)" % f)
+            continue
+        with open(f) as fp:
+            print("Processing %s" % f)
+            # use OrderedDict to preserve order of fields in cmd-syntax
+            try:
+                descr = json.load(fp, object_pairs_hook=collections.OrderedDict)
+            except:
+                print('\nError while processing %s\n\n' % f)
+                raise
+            assert name == descr['name']
+        apis[name] = descr
+
+    return apis
+
+
+def generate_rst(apis):
+    rst = '''.. _api:
+
+API Reference
+=============
+
+'''
+
+    daemons = {}
+    hooks = {}
+    for func in apis.values():
+        for dm in func['support']:
+            if dm not in daemons:
+                daemons[dm] = []
+            daemons[dm].append(func)
+
+        if 'hook' in func:
+            if func['hook'] not in hooks:
+                hooks[func['hook']] = []
+            hooks[func['hook']].append(func)
+
+    rst += 'Kea currently supports %d commands in %s daemons and %s hook libraries.\n\n' % (
+        len(apis),
+        ", ".join([':ref:`%s <commands-%s>`' % (m, m) for m in sorted(daemons.keys())]),
+        ", ".join([':ref:`%s <commands-%s>`' % (m, m) for m in sorted(hooks.keys())]))
+
+    for dm, funcs in sorted(daemons.items()):
+        rst += '.. _commands-%s:\n\n' % dm
+        rst += 'Commands supported by `%s` daemon: ' % dm
+        funcs = sorted([ ':ref:`%s <ref-%s>`' % (f['name'], f['name']) for f in funcs])
+        rst += ', '.join(funcs)
+        rst += '.\n\n'
+
+    for h, funcs in sorted(hooks.items()):
+        rst += '.. _commands-%s:\n\n' % h
+        rst += 'Commands supported by `%s` hook library: ' % h
+        funcs = sorted([ ':ref:`%s <ref-%s>`' % (f['name'], f['name']) for f in funcs])
+        rst += ', '.join(funcs)
+        rst += '.\n\n'
+
+    for func in sorted(apis.values(), key=lambda f: f['name']):
+        # "name" is visible in the ARM. "real_name" is used to provide links
+        # to commands. Keep both even if they're the same for when you want to
+        # make changes to "name" to change the way it's seen in the ARM.
+        name = func['name']
+        real_name = func['name']
+
+        rst += '.. _ref-%s:\n\n' % real_name
+        rst += name + '\n'
+        rst += '-' * len(name) + '\n\n'
+
+        # command overview
+        for brief_line in func['brief']:
+            rst += '%s\n' % brief_line
+        rst += '\n'
+
+        # command can be issued to the following daemons
+        rst += 'Supported by: '
+        rst += ', '.join(sorted([':ref:`%s <commands-%s>`' % (dm, dm) for dm in func['support']]))
+        rst += '\n\n'
+
+        # availability
+        rst += 'Availability: %s ' % func['avail']
+        rst += '(:ref:`%s <commands-%s>` hook library)' % (func['hook'], func['hook']) if 'hook' in func else '(built-in)'
+        rst += '\n\n'
+
+        # access
+        try:
+            access = func['access']
+        except:
+            print('\naccess missing in %s\n\n' % name)
+            raise
+        if not access in ['read', 'write']:
+            print('\nUnknown access %s in %s\n\n' % (access, name))
+            raise ValueError('access must be read or write')
+        rst += 'Access: %s *(parameter ignored in this Kea version)* \n\n' % access
+
+        # description and examples
+        rst += 'Description and examples: see :ref:`%s command <command-%s>`\n\n' % (name, real_name)
+
+        # command syntax
+        rst += 'Command syntax:\n\n'
+        rst += '::\n\n'
+        if 'cmd-syntax' in func:
+            cmd_syntaxes = [func['cmd-syntax']]
+            if isinstance(cmd_syntaxes, dict):
+                cmd_syntaxes = [cmd_syntax]
+            for cmd_syntax in cmd_syntaxes:
+                if 'comment' in cmd_syntax:
+                    rst += cmd_syntax['comment']
+                    rst += '\n\n'
+                    del cmd_syntax['comment']
+
+                for line in cmd_syntax:
+                    rst += '    %s\n' % line
+        else:
+            rst += '   {\n'
+            rst += '       "command": \"%s\"\n' % name
+            rst += '   }'
+        rst += '\n\n'
+
+        if 'cmd-comment' in func:
+            for l in func['cmd-comment']:
+                rst += "%s\n" % l
+            rst += '\n'
+
+        # response syntax
+        rst += 'Response syntax:\n\n'
+        rst += '::\n\n'
+        if 'resp-syntax' in func:
+            resp_syntaxes = [func['resp-syntax']]
+            if isinstance(resp_syntaxes, dict):
+                resp_syntaxes = [resp_syntax]
+            for resp_syntax in resp_syntaxes:
+
+                for line in resp_syntax:
+                    rst += '    %s\n' % line
+
+        else:
+            rst += '   {\n'
+            rst += '       "result": <integer>,\n'
+            rst += '       "text": "<string>"\n'
+            rst += '   }'
+        rst += '\n\n'
+
+        if 'resp-comment' in func:
+            for resp_comment_line in func['resp-comment']:
+                rst += "%s\n" % resp_comment_line
+            rst += '\n\n'
+        else:
+            rst += 'Result is an integer representation of the status. Currently supported statuses are:\n\n'
+            rst += '- 0 - success\n'
+            rst += '- 1 - error\n'
+            rst += '- 2 - unsupported\n'
+            rst += '- 3 - empty (command was completed successfully, but no data was affected or returned)\n\n'
+
+    return rst
+
+
+def generate(in_files, out_file):
+    apis = read_input_files(in_files)
+
+    rst = generate_rst(apis)
+
+    if out_file:
+        with open(out_file, 'w') as f:
+            f.write(rst)
+        print('Wrote generated RST content to: %s' % out_file)
+    else:
+        print(rst)
+
+
+def main():
+    args = parse_args()
+    generate(args.files, args.output)
+
+
+if __name__ == '__main__':
+    main()
diff --git a/doc/sphinx/arm/acknowledgments.rst b/doc/sphinx/arm/acknowledgments.rst
new file mode 100644
index 0000000..0df58dd
--- /dev/null
+++ b/doc/sphinx/arm/acknowledgments.rst
@@ -0,0 +1,29 @@
+Acknowledgments
+===============
+
+Kea is an open source project designed, developed, and maintained by
+Internet Systems Consortium, Inc, a 501(c)3 non-profit organization. ISC
+is primarily funded by revenues from support subscriptions for our open
+source, and we encourage all professional users to consider this option.
+To learn more, see \ https://www.isc.org/support/.
+
+We thank all the organizations and individuals who have helped to make
+Kea possible. `Comcast <https://www.comcast.com/>`__ and the Comcast
+Innovation Fund provided major support for the development of Kea's
+DHCPv4, DHCPv6, and DDNS modules. Mozilla funded initial work on the
+RESTful API via a MOSS award.
+
+Kea was initially implemented as a collection of applications within the
+BIND 10 framework. We thank the founding sponsors of the BIND 10
+project: `Afilias <https://www.afilias.info/>`__,
+`IIS.SE <https://www.iis.se/>`__,
+`Nominet <https://www.nominet.uk/>`__,
+`SIDN <https://www.sidn.nl/>`__, `JPRS <https://jprs.co.jp/>`__,
+and `CIRA <https://cira.ca/>`__; and additional sponsors
+`AFNIC <https://www.afnic.fr/>`__,
+`CNNIC <https://www.cnnic.net.cn/>`__, `CZ.NIC <https://www.nic.cz/>`__,
+`DENIC eG <https://www.denic.de/>`__,
+`Google <https://www.google.com/>`__, `RIPE
+NCC <https://www.ripe.net/>`__, `Registro.br <https://registro.br/>`__,
+`.nz Registry Services <https://nzrs.net.nz/>`__, and `Technical Center
+of Internet <https://www.tcinet.ru/>`__.
diff --git a/doc/sphinx/arm/admin.rst b/doc/sphinx/arm/admin.rst
new file mode 100644
index 0000000..e0d5f80
--- /dev/null
+++ b/doc/sphinx/arm/admin.rst
@@ -0,0 +1,629 @@
+.. _admin:
+
+***************************
+Kea Database Administration
+***************************
+
+.. _kea-database-version:
+
+Databases and Schema Versions
+=============================
+
+Kea may be configured to use a database as storage for leases or as a
+source of servers' configurations and host reservations (i.e. static
+assignments of addresses, prefixes, options, etc.). As Kea is
+updated, new database schemas are introduced to facilitate new
+features and correct discovered issues with the existing schemas.
+
+Each version of Kea expects a particular schema structure and checks for this by
+examining the version of the database it is using. Separate version numbers are
+maintained for the schemas, independent of the version of Kea itself. It is
+possible that the schema version will stay the same through several Kea
+revisions; similarly, it is possible that the version of the schema may go up
+several revisions during a single Kea version upgrade. Versions for each backend
+type are also independent, so an increment in the MySQL backend version does not
+imply an increment in that of PostgreSQL.
+
+Schema versions are specified in a major.minor format. For the most recent
+versions, the minor version is always zero and only the major version is
+incremented.
+
+Historically, the minor version used to be incremented when backward-compatible
+changes were introduced to the schema: for example - when a new index is added.
+This was opposed to incrementing the major version which implied an incompatible
+schema change: for example - changing the type of an existing column. If Kea
+attempts to run on a schema that is too old, as indicated by a mismatched schema
+version, it will fail; administrative action is required to upgrade the schema.
+
+.. _kea-admin:
+
+The ``kea-admin`` Tool
+======================
+
+To manage the databases, Kea provides the ``kea-admin`` tool. It can
+initialize a new backend, check its version number, perform a backend
+upgrade, and dump lease data to a text file.
+
+``kea-admin`` takes two mandatory parameters: ``command`` and
+``backend``. Additional, non-mandatory options may be specified. The
+currently supported commands are:
+
+-  ``db-init`` — initializes a new database schema. This is useful
+   during a new Kea installation. The database is initialized to the
+   latest version supported by the version of the software being
+   installed.
+
+-  ``db-version`` — reports the database backend version number. This
+   is not necessarily equal to the Kea version number, as each backend
+   has its own versioning scheme.
+
+-  ``db-upgrade`` — conducts a database schema upgrade. This is
+   useful when upgrading Kea.
+
+-  ``lease-dump`` — dumps the contents of the lease database (for MySQL or
+   PostgreSQL backends) to a CSV (comma-separated values) text file.
+
+   The first line of the file contains the column names. This can be used
+   as a way to switch from a database backend to a memfile backend.
+   Alternatively, it can be used as a diagnostic tool, so it provides a portable
+   form of the lease data.
+
+-  ``lease-upload`` — uploads leases from a CSV (comma-separated values) text
+   file to a MySQL or a PostgreSQL lease database. The CSV file needs to be in
+   memfile format.
+
+``backend`` specifies the type of backend database. The currently
+supported types are:
+
+-  ``memfile`` — lease information is stored on disk in a text file.
+
+-  ``mysql`` — information is stored in a MySQL relational database.
+
+-  ``pgsql`` — information is stored in a PostgreSQL relational
+   database.
+
+Additional parameters may be needed, depending on the setup and
+specific operation: username, password, and database name or the
+directory where specific files are located. See the appropriate manual
+page for details (``man 8 kea-admin``).
+
+.. _supported-databases:
+
+Supported Backends
+==================
+
+The following table presents the capabilities of available backends.
+Please refer to the specific sections dedicated to each backend to
+better understand their capabilities and limitations. Choosing the right
+backend is essential for the success of the deployment.
+
+.. table:: List of available backends
+
+   +---------------+----------------+----------------+---------------+
+   | Feature       | Memfile        | MySQL          | PostgreSQL    |
+   |               |                |                |               |
+   +===============+================+================+===============+
+   | Status        | Stable         | Stable         | Stable        |
+   |               |                |                |               |
+   +---------------+----------------+----------------+---------------+
+   | Data format   | CSV file       | SQL RMDB       | SQL RMDB      |
+   |               |                |                |               |
+   |               |                |                |               |
+   +---------------+----------------+----------------+---------------+
+   | Leases        | yes            | yes            | yes           |
+   +---------------+----------------+----------------+---------------+
+   | Host          | no             | yes            | yes           |
+   | reservations  |                |                |               |
+   |               |                |                |               |
+   +---------------+----------------+----------------+---------------+
+   | Options       | no             | yes            | yes           |
+   | defined on    |                |                |               |
+   | per host      |                |                |               |
+   | basis         |                |                |               |
+   +---------------+----------------+----------------+---------------+
+   | Configuration | no             | yes            | yes           |
+   | backend       |                |                |               |
+   |               |                |                |               |
+   +---------------+----------------+----------------+---------------+
+
+Memfile
+-------
+
+The memfile backend is able to store lease information, but cannot
+store host reservation details; these must be stored in the
+configuration file. (There are no plans to add a host reservations
+storage capability to this backend.)
+
+No special initialization steps are necessary for the memfile backend.
+During the first run, both ``kea-dhcp4`` and ``kea-dhcp6`` create
+an empty lease file if one is not present. Necessary disk-write
+permission is required.
+
+.. _memfile-upgrade:
+
+Upgrading Memfile Lease Files From an Earlier Version of Kea
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are no special steps required to upgrade memfile lease files
+between versions of Kea. During startup, the
+servers check the schema version of the lease files against their
+own. If there is a mismatch, the servers automatically launch the
+LFC process to convert the files to the server's schema version. While
+this mechanism is primarily meant to ease the process of upgrading to
+newer versions of Kea, it can also be used for downgrading should the
+need arise. When upgrading, any values not present in the original lease
+files are assigned appropriate default values. When downgrading, any
+data present in the files but not in the server's schema are
+dropped. To convert the files manually prior to starting the
+servers, run the lease file cleanup (LFC) process. See :ref:`kea-lfc` for more information.
+
+.. _mysql-database:
+
+MySQL
+-----
+
+MySQL is able to store leases, host reservations, options defined on a
+per-host basis, and a subset of the server configuration parameters
+(serving as a configuration backend).
+
+.. _mysql-database-create:
+
+First-Time Creation of the MySQL Database
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Before preparing any Kea-specific database and tables, the MySQL database
+must be configured to use the system timezone. It is recommended to use UTC
+as the timezone for both the system and the MySQL database.
+
+To check the system timezone:
+
+   .. code-block:: console
+
+      date +%Z
+
+To check the MySQL timezone:
+
+   .. code-block:: mysql
+
+      mysql> SELECT @@system_time_zone;
+      mysql> SELECT @@global.time_zone;
+      mysql> SELECT @@session.time_zone;
+
+To configure the MySQL timezone for a specific server, please refer to the
+installed version documentation.
+
+Usually the setting is configured in the [mysqld] section in ``/etc/mysql/my.cnf``,
+``/etc/mysql/mysql.cnf``, ``/etc/mysql/mysqld.cnf``, or
+``/etc/mysql/mysql.conf.d/mysqld.cnf``.
+
+   .. code-block:: ini
+
+      [mysqld]
+      # using default-time-zone
+      default-time-zone='+00:00'
+
+      # or using timezone
+      timezone='UTC'
+
+When setting up the MySQL database for the first time, the
+database area must be created within MySQL, and the MySQL user ID under
+which Kea will access the database must be set up. This needs to be done manually,
+rather than via ``kea-admin``.
+
+To create the database:
+
+1. Log into MySQL as "root":
+
+   .. code-block:: console
+
+      $ mysql -u root -p
+      Enter password:
+      mysql>
+
+2. Create the MySQL database:
+
+   .. code-block:: mysql
+
+      mysql> CREATE DATABASE database_name;
+
+   (``database_name`` is the name chosen for the database.)
+
+3. Create the user under which Kea will access the database (and give it
+   a password), then grant it access to the database tables:
+
+   .. code-block:: mysql
+
+      mysql> CREATE USER 'user-name'@'localhost' IDENTIFIED BY 'password';
+      mysql> GRANT ALL ON database-name.* TO 'user-name'@'localhost';
+
+   (``user-name`` and ``password`` are the user ID and password used to
+   allow Kea access to the MySQL instance. All apostrophes in the
+   command lines above are required.)
+
+4. Create the database.
+
+    Exit the MySQL client
+
+    .. code-block:: mysql
+
+      mysql> quit
+      Bye
+
+    Then use the  ``kea-admin`` tool to create the database.
+
+    .. code-block:: console
+
+        $ kea-admin db-init mysql -u database-user -p database-password -n database-name
+
+    While it is possible to create the database from within the MySQL client, we recommend
+    using the ``kea-admin`` tool as it performs some necessary validations to ensure Kea can
+    access the database at runtime. Among those checks is verification that the schema does not contain
+    any pre-existing tables; any pre-existing tables must be removed
+    manually. An additional check examines the user's ability to create functions and
+    triggers. The following error indicates that the user does not have the necessary
+    permissions to create functions or triggers:
+
+    .. code-block:: console
+
+        ERROR 1419 (HY000) at line 1: You do not have the SUPER privilege and binary logging is
+        enabled (you *might* want to use the less safe log_bin_trust_function_creators variable)
+        ERROR/kea-admin: mysql_can_create cannot trigger, check user permissions, mysql status = 1
+        mysql: [Warning] Using a password on the command line interface can be insecure.
+        ERROR/kea-admin: Create failed, the user, keatest, has insufficient privileges.
+
+    The simplest way around this is to set the global MySQL variable,
+    ``log_bin_trust_function_creators``, to 1 via the MySQL client.
+    Note this must be done as a user with SUPER privileges:
+
+    .. code-block:: mysql
+
+        mysql> set @@global.log_bin_trust_function_creators = 1;
+        Query OK, 0 rows affected (0.00 sec)
+
+    To create the database with MySQL directly, follow these steps:
+
+    .. code-block:: mysql
+
+      mysql> CONNECT database-name;
+      mysql> SOURCE path-to-kea/share/kea/scripts/mysql/dhcpdb_create.mysql
+
+   (where ``path-to-kea`` is the location where Kea is installed.)
+
+    The database may also be dropped manually as follows:
+
+    .. code-block:: mysql
+
+      mysql> CONNECT database-name;
+      mysql> SOURCE path-to-kea/share/kea/scripts/mysql/dhcpdb_drop.mysql
+
+   (where ``path-to-kea`` is the location where Kea is installed.)
+
+.. warning::
+
+    Dropping the database results in the unrecoverable loss of any data it contains.
+
+
+5. Exit MySQL:
+
+   .. code-block:: mysql
+
+      mysql> quit
+      Bye
+
+If the tables were not created in Step 4, run the ``kea-admin`` tool
+to create them now:
+
+.. code-block:: console
+
+   $ kea-admin db-init mysql -u database-user -p database-password -n database-name
+
+Do not do this if the tables were created in Step 4. ``kea-admin``
+implements rudimentary checks; it will refuse to initialize a database
+that contains any existing tables. To start from scratch,
+all data must be removed manually. (This process is a manual operation
+on purpose, to avoid accidentally irretrievable mistakes by ``kea-admin``.)
+
+.. _mysql-upgrade:
+
+Upgrading a MySQL Database From an Earlier Version of Kea
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Sometimes a new Kea version uses a newer database schema, so the
+existing database needs to be upgraded. This can be done using the
+``kea-admin db-upgrade`` command.
+
+To check the current version of the database, use the following command:
+
+.. code-block:: console
+
+   $ kea-admin db-version mysql -u database-user -p database-password -n database-name
+
+(See :ref:`kea-database-version`
+for a discussion about versioning.) If the version does not match the
+minimum required for the new version of Kea (as described in the release
+notes), the database needs to be upgraded.
+
+Before upgrading, please make sure that the database is backed up. The
+upgrade process does not discard any data, but depending on the nature
+of the changes, it may be impossible to subsequently downgrade to an
+earlier version.
+
+To perform an upgrade, issue the following command:
+
+.. code-block:: console
+
+   $ kea-admin db-upgrade mysql -u database-user -p database-password -n database-name
+
+.. note::
+
+    To search host reservations by hostname, it is critical that the collation of
+    the hostname column in the host table be case-insensitive. Fortunately, that
+    is the default in MySQL, but it can be verified via this command:
+
+    .. code-block:: mysql
+
+      mysql> SELECT COLLATION('');
+      +-----------------+
+      | COLLATION('')   |
+      +-----------------+
+      | utf8_general_ci |
+      +-----------------+
+
+    According to mysql's naming convention, when the name ends in ``_ci``,
+    the collation is case-insensitive.
+
+.. _mysql-performance:
+
+Improved Performance With MySQL
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Changing the MySQL internal value ``innodb_flush_log_at_trx_commit`` from the default value
+of 1 to 2 can result in a huge gain in Kea performance. In some deployments, the
+gain was over 1000% (10 times faster when set to 2, compared to the default value of 1).
+It can be set per-session for testing:
+
+.. code-block:: mysql
+
+    mysql> SET GLOBAL innodb_flush_log_at_trx_commit=2;
+    mysql> SHOW SESSION VARIABLES LIKE 'innodb_flush_log%';
+
+or permanently in ``/etc/mysql/my.cnf``:
+
+.. code-block:: ini
+
+    [mysqld]
+    innodb_flush_log_at_trx_commit=2
+
+Be aware that changing this value can cause problems during data recovery
+after a crash, so we recommend checking the `MySQL documentation
+<https://dev.mysql.com/doc/refman/8.0/en/innodb-parameters.html#sysvar_innodb_flush_log_at_trx_commit>`__.
+With the default value of 1, MySQL writes changes to disk after every INSERT or UPDATE query
+(in Kea terms, every time a client gets a new lease or renews an existing lease). When
+``innodb_flush_log_at_trx_commit`` is set to 2, MySQL writes the changes at intervals
+no longer than 1 second. Batching writes gives a substantial performance boost. The trade-off,
+however, is that in the worst-case scenario, all changes in the last second before crash
+could be lost. Given the fact that Kea is stable software and crashes very rarely,
+most deployments find it a beneficial trade-off.
+
+.. _pgsql-database:
+
+PostgreSQL
+----------
+
+PostgreSQL can store leases, host reservations, and options
+defined on a per-host basis.
+
+.. _pgsql-database-create:
+
+First-Time Creation of the PostgreSQL Database
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Before preparing any Kea-specific database and tables, the PostgreSQL database
+must be configured to use the system timezone. It is recommended to use UTC
+as the timezone for both the system and the PostgreSQL database.
+
+To check the system timezone:
+
+   .. code-block:: console
+
+      date +%Z
+
+To check the PostgreSQL timezone:
+
+   .. code-block:: psql
+
+      postgres=# show timezone;
+      postgres=# SELECT * FROM pg_timezone_names WHERE name = current_setting('TIMEZONE');
+
+To configure the PostgreSQL timezone for a specific server, please refer to the
+installed version documentation.
+
+Usually the setting is configured in the ``postgresql.conf`` with the varying
+version path ``/etc/postgresql/<version>/main/postgresql.conf``, but on some systems
+the files may be located in ``/var/lib/pgsql/data``.
+
+   .. code-block:: ini
+
+      timezone = 'UTC'
+
+The first task is to create both the database and the user under
+which the servers will access it. A number of steps are required:
+
+1. Log into PostgreSQL as "root":
+
+   .. code-block:: console
+
+      $ sudo -u postgres psql postgres
+      Enter password:
+      postgres=#
+
+2. Create the database:
+
+   .. code-block:: psql
+
+      postgres=# CREATE DATABASE database-name;
+      CREATE DATABASE
+      postgres=#
+
+   (``database-name`` is the name chosen for the database.)
+
+3. Create the user under which Kea will access the database (and give it
+   a password), then grant it access to the database:
+
+   .. code-block:: psql
+
+      postgres=# CREATE USER user-name WITH PASSWORD 'password';
+      CREATE ROLE
+      postgres=# GRANT ALL PRIVILEGES ON DATABASE database-name TO user-name;
+      GRANT
+      postgres=#
+
+4. Exit PostgreSQL:
+
+   .. code-block:: psql
+
+      postgres=# \q
+      Bye
+      $
+
+5. At this point, create the database tables either
+   using the ``kea-admin`` tool, as explained in the next section
+   (recommended), or manually. To create the tables manually, enter the
+   following command. PostgreSQL will prompt the administrator to enter the
+   new user's password that was specified in Step 3. When the command
+   completes, Kea will return to the shell prompt. The
+   output should be similar to the following:
+
+   .. code-block:: console
+
+      $ psql -d database-name -U user-name -f path-to-kea/share/kea/scripts/pgsql/dhcpdb_create.pgsql
+      Password for user user-name:
+      CREATE TABLE
+      CREATE INDEX
+      CREATE INDEX
+      CREATE TABLE
+      CREATE INDEX
+      CREATE TABLE
+      START TRANSACTION
+      INSERT 0 1
+      INSERT 0 1
+      INSERT 0 1
+      COMMIT
+      CREATE TABLE
+      START TRANSACTION
+      INSERT 0 1
+      COMMIT
+      $
+
+   (``path-to-kea`` is the location where Kea is installed.)
+
+   If instead an error is encountered, such as:
+
+   ::
+
+      psql: FATAL:  no pg_hba.conf entry for host "[local]", user "user-name", database "database-name", SSL off
+
+   ... the PostgreSQL configuration will need to be altered. Kea uses
+   password authentication when connecting to the database and must have
+   the appropriate entries added to PostgreSQL's pg_hba.conf file. This
+   file is normally located in the primary data directory for the
+   PostgreSQL server. The precise path may vary depending on the
+   operating system and version, but the default location for PostgreSQL is
+   ``/etc/postgresql/*/main/postgresql.conf``. However, on some systems
+   (notably CentOS 8), the file may reside in ``/var/lib/pgsql/data``.
+
+   Assuming Kea is running on the same host as PostgreSQL, adding lines
+   similar to the following should be sufficient to provide
+   password-authenticated access to Kea's database:
+
+   ::
+
+      local   database-name    user-name                                 password
+      host    database-name    user-name          127.0.0.1/32           password
+      host    database-name    user-name          ::1/128                password
+
+   These edits are primarily intended as a starting point, and are not a
+   definitive reference on PostgreSQL administration or database
+   security. Please consult the PostgreSQL user manual before making
+   these changes, as they may expose other databases that are running. It
+   may be necessary to restart PostgreSQL for the changes to
+   take effect.
+
+Initialize the PostgreSQL Database Using ``kea-admin``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If the tables were not created manually, do so now by
+running the ``kea-admin`` tool:
+
+.. code-block:: console
+
+   $ kea-admin db-init pgsql -u database-user -p database-password -n database-name
+
+Do not do this if the tables were already created manually. ``kea-admin``
+implements rudimentary checks; it will refuse to initialize a database
+that contains any existing tables. To start from scratch,
+all data must be removed manually. (This process is a manual operation
+on purpose, to avoid accidentally irretrievable mistakes by ``kea-admin``.)
+
+.. _pgsql-upgrade:
+
+Upgrading a PostgreSQL Database From an Earlier Version of Kea
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The PostgreSQL database schema can be upgraded using the same tool and
+commands as described in :ref:`mysql-upgrade`, with the exception that the "pgsql"
+database backend type must be used in the commands.
+
+Use the following command to check the current schema version:
+
+.. code-block:: console
+
+   $ kea-admin db-version pgsql -u database-user -p database-password -n database-name
+
+Use the following command to perform an upgrade:
+
+.. code-block:: console
+
+   $ kea-admin db-upgrade pgsql -u database-user -p database-password -n database-name
+
+.. _pgsl-ssl:
+
+PostgreSQL without OpenSSL support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Usually the PostgreSQL database client library is built with the OpenSSL
+support but Kea can be configured to handle the case where it is not
+supported:
+
+.. code-block:: console
+
+   $ ./configure [other-options] --disable-pgsql-ssl
+
+Using Read-Only Databases With Host Reservations
+------------------------------------------------
+
+If a read-only database is used for storing host reservations, Kea must
+be explicitly configured to operate on the database in read-only mode.
+Sections :ref:`read-only-database-configuration4` and
+:ref:`read-only-database-configuration6` describe when such
+a configuration may be required, and how to configure Kea to operate in
+this way for both DHCPv4 and DHCPv6.
+
+Limitations Related to the Use of SQL Databases
+-----------------------------------------------
+
+Year 2038 Issue
+~~~~~~~~~~~~~~~
+
+The lease expiration time in Kea is stored in the SQL database for each lease
+as a timestamp value. Kea developers have observed that the MySQL database
+does not accept timestamps beyond 2147483647 seconds (the maximum signed
+32-bit number) from the beginning of the UNIX epoch (00:00:00 on 1
+January 1970). Some versions of PostgreSQL do accept greater values, but
+the value is altered when it is read back. For this reason, the lease
+database backends put a restriction on the maximum timestamp to be
+stored in the database, which is equal to the maximum signed 32-bit
+number. This effectively means that the current Kea version cannot store
+leases whose expiration time is later than 2147483647 seconds since the
+beginning of the epoch (around the year 2038). This will be fixed when
+database support for longer timestamps is available.
diff --git a/doc/sphinx/arm/agent.rst b/doc/sphinx/arm/agent.rst
new file mode 100644
index 0000000..8e559b0
--- /dev/null
+++ b/doc/sphinx/arm/agent.rst
@@ -0,0 +1,378 @@
+.. _kea-ctrl-agent:
+
+*********************
+The Kea Control Agent
+*********************
+
+.. _agent-overview:
+
+Overview of the Kea Control Agent
+=================================
+
+The Kea Control Agent (CA) is a daemon which exposes a RESTful control
+interface for managing Kea servers. The daemon can receive control
+commands over HTTP and either forward these commands to the respective
+Kea servers or handle these commands on its own. The determination
+whether the command should be handled by the CA or forwarded is made by
+checking the value of the ``service`` parameter, which may be included in
+the command from the controlling client. The details of the supported
+commands, as well as their structures, are provided in
+:ref:`ctrl-channel`.
+
+The CA can use hook libraries to provide support for additional commands
+or to program custom behavior of existing commands. Such hook libraries must
+implement callouts for the ``control_command_receive`` hook point. Details
+about creating new hook libraries and supported hook points can be found
+in the `Kea Developer's
+Guide <https://reports.kea.isc.org/dev_guide/>`__.
+
+The CA processes received commands according to the following algorithm:
+
+-  Pass command into any installed hooks (regardless of service
+   value(s)). If the command is handled by a hook, return the response.
+
+-  If the service specifies one or more services, forward the command to
+   the specified services and return the accumulated responses.
+
+-  If the service is not specified or is an empty list, handle the
+   command if the CA supports it.
+
+.. _agent-configuration:
+
+Configuration
+=============
+
+The following example demonstrates the basic CA configuration.
+
+::
+
+   {
+       "Control-agent": {
+           "http-host": "10.20.30.40",
+           "http-port": 8000,
+           "trust-anchor": "/path/to/the/ca-cert.pem",
+           "cert-file": "/path/to/the/agent-cert.pem",
+           "key-file": "/path/to/the/agent-key.pem",
+           "cert-required": true,
+           "authentication": {
+               "type": "basic",
+               "realm": "kea-control-agent",
+               "clients": [
+               {
+                   "user": "admin",
+                   "password": "1234"
+               } ]
+           },
+
+           "control-sockets": {
+               "dhcp4": {
+                   "comment": "main server",
+                   "socket-type": "unix",
+                   "socket-name": "/path/to/the/unix/socket-v4"
+               },
+               "dhcp6": {
+                   "socket-type": "unix",
+                   "socket-name": "/path/to/the/unix/socket-v6",
+                   "user-context": { "version": 3 }
+               },
+               "d2": {
+                   "socket-type": "unix",
+                   "socket-name": "/path/to/the/unix/socket-d2"
+               },
+           },
+
+           "hooks-libraries": [
+           {
+               "library": "/opt/local/control-agent-commands.so",
+               "parameters": {
+                   "param1": "foo"
+               }
+           } ],
+
+           "loggers": [ {
+               "name": "kea-ctrl-agent",
+               "severity": "INFO"
+           } ]
+       }
+   }
+
+The ``http-host`` and ``http-port`` parameters specify an IP address and
+port to which HTTP service will be bound. In the example configuration
+provided above, the RESTful service will be available at the URL
+``https://10.20.30.40:8000/``. If these parameters are not specified, the
+default URL is ``http://127.0.0.1:8000/``.
+
+When using Kea's HA hook library with multi-threading, make sure
+that the address:port combination used for CA is
+different from the HA peer URLs, which are strictly
+for internal HA traffic between the peers. User commands should
+still be sent via CA.
+
+The ``trust-anchor``, ``cert-file``, ``key-file``, and ``cert-required``
+parameters specify the TLS setup for HTTP, i.e. HTTPS. If these parameters
+are not specified, HTTP is used. The TLS/HTTPS support in Kea is
+described in :ref:`tls`.
+
+As mentioned in :ref:`agent-overview`, the CA can forward
+received commands to the Kea servers for processing. For example,
+``config-get`` is sent to retrieve the configuration of one of the Kea
+services. When the CA receives this command, including a ``service``
+parameter indicating that the client wishes to retrieve the
+configuration of the DHCPv4 server, the CA forwards the command to that
+server and passes the received response back to the client. More about
+the ``service`` parameter and the general structure of commands can be
+found in :ref:`ctrl-channel`.
+
+The CA uses UNIX domain sockets to forward control commands and receive
+responses from other Kea services. The ``dhcp4``, ``dhcp6``, and ``d2``
+maps specify the files to which UNIX domain sockets are bound. In the
+configuration above, the CA connects to the DHCPv4 server via
+``/path/to/the/unix/socket-v4`` to forward the commands to it.
+Obviously, the DHCPv4 server must be configured to listen to connections
+via this same socket. In other words, the command-socket configuration
+for the DHCPv4 server and the CA (for that server) must match. Consult
+:ref:`dhcp4-ctrl-channel`, :ref:`dhcp6-ctrl-channel`, and
+:ref:`d2-ctrl-channel` to learn how the socket configuration is
+specified for the DHCPv4, DHCPv6, and D2 services.
+
+User contexts can store arbitrary data as long as they are in valid JSON
+syntax and their top-level element is a map (i.e. the data must be
+enclosed in curly brackets). Some hook libraries may expect specific
+formatting; please consult the relevant hook library documentation for
+details.
+
+User contexts can be specified on either global scope, control socket,
+basic authentication, or loggers. One other useful feature is the
+ability to store comments or descriptions; the parser translates a
+"comment" entry into a user context with the entry, which allows a
+comment to be attached within the configuration itself.
+
+Basic HTTP authentication was added in Kea 1.9.0; it protects
+against unauthorized uses of the control agent by local users. For
+protection against remote attackers, HTTPS and reverse proxy of
+:ref:`agent-secure-connection` provide stronger security.
+
+The authentication is described in the ``authentication`` block
+with the mandatory ``type`` parameter, which selects the authentication.
+Currently only the basic HTTP authentication (type basic) is supported.
+
+The ``realm`` authentication parameter is used for error messages when
+the basic HTTP authentication is required but the client is not
+authorized.
+
+When the ``clients`` authentication list is configured and not empty,
+basic HTTP authentication is required. Each element of the list
+specifies a user ID and a password. The user ID is mandatory, must
+be not empty, and must not contain the colon (:) character. The
+password is optional; when it is not specified an empty password
+is used.
+
+.. note::
+
+   The basic HTTP authentication user ID and password are encoded
+   in UTF-8, but the current Kea JSON syntax only supports the Latin-1
+   (i.e. 0x00..0xff) Unicode subset.
+
+To avoid to expose the password or both the user ID and the associated
+password these values can be read from files. The syntax was extended by:
+
+-  The ``directory`` authentication parameter which handles the common
+   part of file paths. By default the value is the empty string.
+
+-  The``password-file`` client parameter which with the ``directory``
+   parameter specifies the path of a file where the password or when no
+   user ID is given the whole basic HTTP authentication secret before
+   encoding can be read.
+
+-  The ``user-file`` client parameter which with the ``directory`` parameter
+   specifies the path of a file where the user ID can be read.
+
+When files are used they are read when the configuration is loaded in order
+to detect configuration errors as soon as possible.
+
+Hook libraries can be loaded by the Control Agent in the same way as
+they are loaded by the DHCPv4 and DHCPv6 servers. The CA currently
+supports one hook point - ``control_command_receive`` - which makes it
+possible to delegate processing of some commands to the hook library.
+The ``hooks-libraries`` list contains the list of hook libraries that
+should be loaded by the CA, along with their configuration information
+specified with ``parameters``.
+
+Please consult :ref:`logging` for the details on how to configure
+logging. The CA's root logger's name is ``kea-ctrl-agent``, as given in
+the example above.
+
+.. _agent-secure-connection:
+
+Secure Connections (in Versions Prior to Kea 1.9.6)
+===================================================
+
+The Control Agent does not natively support secure HTTP connections, like
+SSL or TLS, before Kea 1.9.6.
+
+To set up a secure connection, please use one of the
+available third-party HTTP servers and configure it to run as a reverse
+proxy to the Control Agent. Kea has been tested with two major HTTP
+server implementations working as a reverse proxy: Apache2 and nginx.
+Example configurations, including extensive comments, are provided in
+the ``doc/examples/https/`` directory.
+
+The reverse proxy forwards HTTP requests received over a secure
+connection to the Control Agent using unsecured HTTP. Typically, the
+reverse proxy and the Control Agent are running on the same machine, but
+it is possible to configure them to run on separate machines as well. In
+this case, security depends on the protection of the communications
+between the reverse proxy and the Control Agent.
+
+Apart from providing the encryption layer for the control channel, a
+reverse proxy server is also often used for authentication of the
+controlling clients. In this case, the client must present a valid
+certificate when it connects via reverse proxy. The proxy server
+authenticates the client by checking whether the presented certificate
+is signed by the certificate authority used by the server.
+
+To illustrate this, the following is a sample configuration for the
+nginx server running as a reverse proxy to the Kea Control Agent. The
+server enables authentication of the clients using certificates.
+
+::
+
+   #   The server certificate and key can be generated as follows:
+   #
+   #   openssl genrsa -des3 -out kea-proxy.key 4096
+   #   openssl req -new -x509 -days 365 -key kea-proxy.key -out kea-proxy.crt
+   #
+   #   The CA certificate and key can be generated as follows:
+   #
+   #   openssl genrsa -des3 -out ca.key 4096
+   #   openssl req -new -x509 -days 365 -key ca.key -out ca.crt
+   #
+   #
+   #   The client certificate needs to be generated and signed:
+   #
+   #   openssl genrsa -des3 -out kea-client.key 4096
+   #   openssl req -new -key kea-client.key -out kea-client.csr
+   #   openssl x509 -req -days 365 -in kea-client.csr -CA ca.crt \
+   #           -CAkey ca.key -set_serial 01 -out kea-client.crt
+   #
+   #   Note that the "common name" value used when generating the client
+   #   and the server certificates must differ from the value used
+   #   for the CA certificate.
+   #
+   #   The client certificate must be deployed on the client system.
+   #   In order to test the proxy configuration with "curl", run a
+   #   command similar to the following:
+   #
+   #   curl -k --key kea-client.key --cert kea-client.crt -X POST \
+   #        -H Content-Type:application/json -d '{ "command": "list-commands" }' \
+   #         https://kea.example.org/kea
+   #
+   #   curl syntax for basic authentication is -u user:password
+   #
+   #
+   #   nginx configuration starts here.
+
+   events {
+   }
+
+   http {
+           #   HTTPS server
+       server {
+           #     Use default HTTPS port.
+           listen 443 ssl;
+           #     Set server name.
+           server_name kea.example.org;
+
+           #   Server certificate and key.
+           ssl_certificate /path/to/kea-proxy.crt;
+           ssl_certificate_key /path/to/kea-proxy.key;
+
+           #   Certificate Authority. Client certificates must be signed by the CA.
+           ssl_client_certificate /path/to/ca.crt;
+
+           # Enable verification of the client certificate.
+           ssl_verify_client on;
+
+           # For URLs such as https://kea.example.org/kea, forward the
+           # requests to http://127.0.0.1:8000.
+           location /kea {
+               proxy_pass http://127.0.0.1:8000;
+           }
+       }
+   }
+
+.. note::
+
+   The configuration snippet provided above is for testing
+   purposes only. It should be modified according to the security
+   policies and best practices of the administrator's organization.
+
+When using an HTTP client without TLS support, such as ``kea-shell``, it
+is possible to use an HTTP/HTTPS translator such as ``stunnel`` in client mode. A
+sample configuration is provided in the ``doc/examples/https/shell/``
+directory.
+
+Secure Connections (in Kea 1.9.6 and Newer)
+===========================================
+
+Since Kea 1.9.6, the Control Agent natively supports secure
+HTTP connections using TLS. This allows protection against users from
+the node where the agent runs, something that a reverse proxy cannot
+provide. More about TLS/HTTPS support in Kea can be found in :ref:`tls`.
+
+TLS is configured using three string parameters, giving file names and
+a boolean parameter:
+
+-  The ``trust-anchor`` specifies the Certification Authority file name or
+   directory path.
+
+-  The ``cert-file`` specifies the server certificate file name.
+
+-  The ``key-file`` specifies the private key file name. The file must not
+   be encrypted.
+
+-  The ``cert-required`` specifies whether client certificates are required
+   or optional. The default is to require them and to perform mutual
+   authentication.
+
+The file format is PEM. Either all the string parameters are specified and
+HTTP over TLS (HTTPS) is used, or none is specified and plain HTTP is used.
+Configuring only one or two string parameters results in an error.
+
+.. note::
+
+   When client certificates are not required, only the server side is
+   authenticated, i.e. the communication is encrypted with an unknown
+   client. This protects only against passive attacks; active
+   attacks, such as "man-in-the-middle," are still possible.
+
+.. note::
+
+   No standard HTTP authentication scheme cryptographically binds its end
+   entity with TLS. This means that the TLS client and server can be
+   mutually authenticated, but there is no proof they are the same as
+   for the HTTP authentication.
+
+Since Kea 1.9.6, the ``kea-shell`` tool supports TLS.
+
+.. _agent-launch:
+
+Starting the Control Agent
+==========================
+
+The CA is started by running its binary and specifying the configuration
+file it should use. For example:
+
+.. code-block:: console
+
+   $ ./kea-ctrl-agent -c /usr/local/etc/kea/kea-ctrl-agent.conf
+
+It can be started by ``keactrl`` as well (see :ref:`keactrl`).
+
+.. _agent-clients:
+
+Connecting to the Control Agent
+===============================
+
+For an example of a tool that can take advantage of the RESTful API, see
+:ref:`kea-shell`.
diff --git a/doc/sphinx/arm/classify.rst b/doc/sphinx/arm/classify.rst
new file mode 100644
index 0000000..04cc95c
--- /dev/null
+++ b/doc/sphinx/arm/classify.rst
@@ -0,0 +1,1052 @@
+.. _classify:
+
+*********************
+Client Classification
+*********************
+
+Client Classification Overview
+==============================
+
+In certain cases it is useful to differentiate among different types
+of clients and treat them accordingly. Common reasons include:
+
+-  The clients represent different pieces of topology, e.g. a cable
+   modem is not the same as the clients behind that modem.
+
+-  The clients have different behavior, e.g. a smartphone behaves
+   differently from a laptop.
+
+-  The clients require different values for some options, e.g. a
+   docsis3.0 cable modem requires different settings from a docsis2.0
+   cable modem.
+
+To make management easier, different clients can be grouped into a
+client class to receive common options.
+
+An incoming packet can be associated with a client class in several
+ways:
+
+-  Implicitly, using a vendor class option or another built-in condition.
+
+-  Using an expression which evaluates to ``true``.
+
+-  Using static host reservations, a shared network, a subnet, etc.
+
+-  Using a hook.
+
+Client classification can be used to change the behavior of almost any
+part of the DHCP message processing. There are currently six
+mechanisms that take advantage of client classification: dropping
+queries, subnet selection, pool selection, definition of DHCPv4
+private (codes 224-254) and code 43 options, assignment of different
+options, and, for DHCPv4 cable modems, the setting of specific options
+for use with the TFTP server address and the boot file field.
+
+.. _classify-classification-steps:
+
+Classification Steps
+--------------------
+
+The classification process is conducted in several steps:
+
+1.  The ``ALL`` class is associated with the incoming packet.
+
+2.  Vendor class options are processed.
+
+3.  Classes with matching expressions and not marked for later evaluation ("on
+    request" or depending on the ``KNOWN``/``UNKNOWN`` built-in classes)
+    are processed in the order they are defined in the
+    configuration; the boolean expression is evaluated and, if it
+    returns ``true`` (a match), the incoming packet is associated with the
+    class.
+
+4.  If a private or code 43 DHCPv4 option is received, it is decoded
+    following its client-class or global (or, for option 43,
+    last-resort) definition.
+
+5.  When the incoming packet belongs to the special class ``DROP``, it is
+    dropped and an informational message is logged with the packet
+    information.
+
+.. note::
+
+    The ``pkt4_receive`` and ``pkt6_receive`` callouts are called here.
+
+6.  When the ``early-global-reservations-lookup`` global parameter is
+    configured to true global reservations are looked for and the 8, 9
+    and 10 steps are partially performed: the lookup is limited to
+    global reservations, if one is found the ``KNOWN`` class is set
+    but if none is found the ``UNKNOWN`` class is **not** set.
+
+7.  A subnet is chosen, possibly based on the class information when
+    some subnets are reserved. More precisely: when choosing a subnet,
+    the server iterates over all of the subnets that are feasible given
+    the information found in the packet (client address, relay address,
+    etc.). It uses the first subnet it finds that either has no
+    class associated with it, or has a class which matches one of the
+    packet's classes.
+
+.. note::
+
+    The ``subnet4_select`` and ``subnet6_select`` callouts are called here.
+
+8.  The server looks for host reservations. If an identifier from the
+    incoming packet matches a host reservation in the subnet or shared
+    network, the packet is associated with the ``KNOWN`` class and all
+    classes of the host reservation. If a reservation is not found, the
+    packet is assigned to the ``UNKNOWN`` class.
+
+9.  Classes with matching expressions - directly, or indirectly using the
+    ``KNOWN``/``UNKNOWN`` built-in classes and not marked for later evaluation ("on
+    request") - are processed in the order they are defined
+    in the configuration; the boolean expression is evaluated and, if it
+    returns ``true`` (a match), the incoming packet is associated with the
+    class. After a subnet is selected, the server determines whether
+    there is a reservation for a given client. Therefore, it is not
+    possible to use the ``UNKNOWN`` class to select a shared network or
+    a subnet. For the ``KNOWN`` class only global reservations only
+    global reservations are used and the ``early-global-reservations-lookup``
+    parameter must be configured to true
+
+10. When the incoming packet belongs to the special class ``DROP``, it is
+    dropped and an informational message is logged with the packet
+    information. Since Kea version 1.9.8, it is permissible to make the ``DROP``
+    class dependent on the ``KNOWN``/``UNKNOWN`` classes.
+
+11. If needed, addresses and prefixes from pools are assigned, possibly
+    based on the class information when some pools are reserved for
+    class members.
+
+.. note::
+
+    The ``lease4_select``, ``lease4_renew``, ``lease6_select``, ``lease6_renew``, and ``lease6_rebind``
+    callouts are called here.
+
+12. Classes marked as "required" are evaluated in the order in which
+    they are listed: first the shared network, then the subnet, and
+    finally the pools that assigned resources belong to.
+
+13. Options are assigned, again possibly based on the class information
+    in the order that classes were associated with the incoming packet.
+    For DHCPv4 private and code 43 options, this includes option
+    definitions specified within classes.
+
+.. note::
+
+   Client classes in Kea follow the order in which they are specified in
+   the configuration (vs. alphabetical order). Required classes follow
+   the order in which they are required.
+
+When determining which options to include in the response, the server
+examines the union of options from all of the assigned classes. If two
+or more classes include the same option, the value from the first class
+examined is used; classes are examined in the order they were
+associated, so ``ALL`` is always the first class and matching required
+classes are last.
+
+As an example, imagine that an incoming packet matches two classes.
+Class ``foo`` defines values for an NTP server (option 42 in DHCPv4) and
+an SMTP server (option 69 in DHCPv4), while class ``bar`` defines values
+for an NTP server and a POP3 server (option 70 in DHCPv4). The server
+examines the three options - NTP, SMTP, and POP3 - and returns any that
+the client requested. As the NTP server was defined twice, the server
+chooses only one of the values for the reply; the class from which the
+value is obtained is determined as explained in the previous paragraph.
+
+.. note::
+
+   Care should be taken with client classification, as it is easy for
+   clients that do not meet any class criteria to be denied service
+   altogether.
+
+.. _classification-using-vendor:
+
+Built-in Client Classes
+=======================
+
+Some classes are built-in, so they do not need to be defined.
+Vendor class information is the primary example: the server checks whether an
+incoming DHCPv4 packet includes the vendor class identifier option (60)
+or an incoming DHCPv6 packet includes the vendor class option (16). If
+it does, the content of that option is prepended with ``VENDOR_CLASS_``
+and the result is interpreted as a class. For example, modern cable
+modems send this option with value ``docsis3.0``, so the packet belongs to
+class ``VENDOR_CLASS_docsis3.0``.
+
+The ``HA_`` prefix is used by the High Availability hook library to
+designate certain servers to process DHCP packets as a result of load
+balancing. The class name is constructed by prepending the ``HA_`` prefix
+to the name of the server which should process the DHCP packet. This
+server uses an appropriate pool or subnet to allocate IP addresses
+(and/or prefixes), based on the assigned client classes. The details can
+be found in :ref:`hooks-high-availability`.
+
+The ``BOOTP`` class is used by the BOOTP hook library to classify and
+respond to inbound BOOTP queries.
+
+The ``SKIP_DDNS`` class is used by the DDNS-tuning hook library to suppress
+DDNS updates on a per client basis.
+
+Other examples are the ``ALL`` class, to which all incoming packets belong,
+and the ``KNOWN`` class, assigned when host reservations exist for a
+particular client. By convention, the names of built-in classes begin with all
+capital letters.
+
+Currently recognized built-in class names are ``ALL``, ``KNOWN`` and ``UNKNOWN``,
+and the prefixes ``VENDOR_CLASS_``, ``HA_``, ``AFTER_``, ``EXTERNAL_``,
+``SKIP_DDNS``. Although the ``AFTER_`` prefix is a provision for an
+as-yet-unwritten hook, the ``EXTERNAL_`` prefix can be freely used; built-in
+classes are implicitly defined so they never raise warnings if they do not
+appear in the configuration.
+
+.. _classification-using-expressions:
+
+Using Expressions in Classification
+===================================
+
+The expression portion of a classification definition contains operators
+and values. All values are currently strings; operators take a string or
+strings and return another string. When all the operations have
+completed, the result should be a value of ``true`` or ``false``. The packet
+belongs to the class (and the class name is added to the list of
+classes) if the result is ``true``. Expressions are written in standard
+format and can be nested.
+
+Expressions are pre-processed during the parsing of the configuration
+file and converted to an internal representation. This allows certain
+types of errors to be caught and logged during parsing. Examples of
+these errors include an incorrect number or type of argument to an
+operator. The evaluation code also checks for this class of error and
+generally throws an exception, though this should not occur in a
+normally functioning system.
+
+Other issues, such as the starting position of a substring being
+outside of the substring or an option not existing in the packet, result
+in the operator returning an empty string.
+
+Dependencies between classes are also checked. For instance, forward
+dependencies are rejected when the configuration is parsed; an
+expression can only depend on already-defined classes (including built-in
+classes) which are evaluated in a previous or the same evaluation phase.
+This does not apply to the ``KNOWN`` or ``UNKNOWN`` classes.
+
+.. table:: List of classification values
+
+   +-----------------------+-------------------------------+-----------------------+
+   | Name                  | Example expression            | Example value         |
+   +=======================+===============================+=======================+
+   | String literal        | 'example'                     | 'example'             |
+   +-----------------------+-------------------------------+-----------------------+
+   | Hexadecimal string    | 0x5a7d                        | 'Z}'                  |
+   | literal               |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | IP address literal    | 10.0.0.1                      | 0x0a000001            |
+   +-----------------------+-------------------------------+-----------------------+
+   | Integer literal       | 123                           | '123'                 |
+   +-----------------------+-------------------------------+-----------------------+
+   | Binary content of the | option[123].hex               | '(content of the      |
+   | option                |                               | option)'              |
+   +-----------------------+-------------------------------+-----------------------+
+   | Option existence      | option[123].exists            | 'true'                |
+   +-----------------------+-------------------------------+-----------------------+
+   | Binary content of the | option[12].option[34].hex     | '(content of the      |
+   | sub-option            |                               | sub-option)'          |
+   +-----------------------+-------------------------------+-----------------------+
+   | Sub-Option existence  | option[12].option[34].exists  | 'true'                |
+   +-----------------------+-------------------------------+-----------------------+
+   | Client class          | member('foobar')              | 'true'                |
+   | membership            |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Known client          | known                         | member('KNOWN')       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Unknown client        | unknown                       | not member('KNOWN')   |
+   +-----------------------+-------------------------------+-----------------------+
+   | DHCPv4 relay agent    | relay4[123].hex               | '(content of the RAI  |
+   | sub-option            |                               | sub-option)'          |
+   +-----------------------+-------------------------------+-----------------------+
+   | DHCPv6 Relay Options  | relay6[nest].option[code].hex | (value of the option) |
+   +-----------------------+-------------------------------+-----------------------+
+   | DHCPv6 Relay Peer     | relay6[nest].peeraddr         | 2001:DB8::1           |
+   | Address               |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | DHCPv6 Relay Link     | relay6[nest].linkaddr         | 2001:DB8::1           |
+   | Address               |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Interface name of     | pkt.iface                     | eth0                  |
+   | packet                |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Source address of     | pkt.src                       | 10.1.2.3              |
+   | packet                |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Destination address   | pkt.dst                       | 10.1.2.3              |
+   | of packet             |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Length of packet      | pkt.len                       | 513                   |
+   +-----------------------+-------------------------------+-----------------------+
+   | Hardware address in   | pkt4.mac                      | 0x010203040506        |
+   | DHCPv4 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Hardware length in    | pkt4.hlen                     | 6                     |
+   | DHCPv4 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Hardware type in      | pkt4.htype                    | 6                     |
+   | DHCPv4 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | ciaddr field in       | pkt4.ciaddr                   | 192.0.2.1             |
+   | DHCPv4 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | giaddr field in       | pkt4.giaddr                   | 192.0.2.1             |
+   | DHCPv4 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | yiaddr field in       | pkt4.yiaddr                   | 192.0.2.1             |
+   | DHCPv4 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | siaddr field in       | pkt4.siaddr                   | 192.0.2.1             |
+   | DHCPv4 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Message type in       | pkt4.msgtype                  | 1                     |
+   | DHCPv4 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Transaction ID (xid)  | pkt4.transid                  | 12345                 |
+   | in DHCPv4 packet      |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Message type in       | pkt6.msgtype                  | 1                     |
+   | DHCPv6 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Transaction ID in     | pkt6.transid                  | 12345                 |
+   | DHCPv6 packet         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Vendor option         | vendor[*].exists              | true                  |
+   | existence (any        |                               |                       |
+   | vendor)               |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Vendor option         | vendor[4491].exists           | true                  |
+   | existence (specific   |                               |                       |
+   | vendor)               |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Enterprise-id from    | vendor.enterprise             | 4491                  |
+   | vendor option         |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Vendor sub-option     | vendor[4491].option[1].exists | true                  |
+   | existence             |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Vendor sub-option     | vendor[4491].option[1].hex    | docsis3.0             |
+   | content               |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Vendor class option   | vendor-class[*].exist         | true                  |
+   | existence (any        | s                             |                       |
+   | vendor)               |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Vendor class option   | vendor-class[4491].exists     | true                  |
+   | existence (specific   |                               |                       |
+   | vendor)               |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Enterprise-id from    | vendor-class.enterprise       | 4491                  |
+   | vendor class option   |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | First data chunk from | vendor-class[4491].data       | docsis3.0             |
+   | vendor class option   |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+   | Specific data chunk   | vendor-class[4491].data[3]    | docsis3.0             |
+   | from vendor class     |                               |                       |
+   | option                |                               |                       |
+   +-----------------------+-------------------------------+-----------------------+
+
+Notes:
+
+-  Hexadecimal strings are converted into a string as expected. The
+   starting "0X" or "0x" is removed, and if the string is an odd number
+   of characters a "0" is prepended to it.
+
+-  IP addresses are converted into strings of length 4 or 16. IPv4,
+   IPv6, and IPv4-embedded IPv6 (e.g. IPv4-mapped IPv6) addresses are
+   supported.
+
+-  Integers in an expression are converted to 32-bit unsigned integers
+   and are represented as four-byte strings; for example, 123 is
+   represented as 0x0000007b. All expressions that return numeric values
+   use 32-bit unsigned integers, even if the field in the packet is
+   smaller. In general, it is easier to use decimal notation to
+   represent integers, but it is also possible to use hexadecimal
+   notation. When writing an integer in hexadecimal, care should be
+   taken to make sure the value is represented as 32 bits, e.g. use
+   0x00000001 instead of 0x1 or 0x01. Also, make sure the value is
+   specified in network order, e.g. 1 is represented as 0x00000001.
+
+-  ``option[code].hex`` extracts the value of the option with the code
+   ``code`` from the incoming packet. If the packet does not contain the
+   option, it returns an empty string. The string is presented as a byte
+   string of the option payload, without the type code or length fields.
+
+-  ``option[code].exists`` checks whether an option with the code ``code``
+   is present in the incoming packet. It can be used with empty options.
+
+-  ``member('foobar')`` checks whether the packet belongs to the client
+   class ``foobar``. To avoid dependency loops, the configuration file
+   parser verifies whether client classes were already defined or are
+   built-in, i.e., beginning with ``VENDOR_CLASS_``, ``AFTER_`` (for the
+   to-come "after" hook) and ``EXTERNAL_`` or equal to ``ALL``, ``KNOWN``,
+   ``UNKNOWN``, etc.
+
+   ``known`` and ``unknown`` are shorthand for ``member('KNOWN')`` and ``not
+   member('KNOWN')``. Note that the evaluation of any expression using
+   the ``KNOWN`` class (directly or indirectly) is deferred after the host
+   reservation lookup (i.e. when the ``KNOWN`` or ``UNKNOWN`` partition is
+   determined).
+
+-  ``relay4[code].hex`` attempts to extract the value of the sub-option
+   ``code`` from the option inserted as the DHCPv4 Relay Agent Information
+   (82) option. If the packet does not contain a RAI option, or the RAI
+   option does not contain the requested sub-option, the expression
+   returns an empty string. The string is presented as a byte string of
+   the option payload without the type code or length fields. This
+   expression is allowed in DHCPv4 only.
+
+-  ``relay4`` shares the same representation types as ``option``; for
+   instance, ``relay4[code].exists`` is supported.
+
+-  ``relay6[nest]`` allows access to the encapsulations used by any DHCPv6
+   relays that forwarded the packet. The ``nest`` level specifies the
+   relay from which to extract the information, with a value of 0
+   indicating the relay closest to the DHCPv6 server. Negative values
+   allow relays to be specified counting from the DHCPv6 client, with -1 indicating
+   the relay closest to the client. If the requested
+   encapsulation does not exist, an empty string ``""`` is returned. This
+   expression is allowed in DHCPv6 only.
+
+-  ``relay6[nest].option[code]`` shares the same representation types as
+   ``option``; for instance, ``relay6[nest].option[code].exists`` is
+   supported.
+
+-  Expressions starting with ``pkt4`` can be used only in DHCPv4. They
+   allow access to DHCPv4 message fields.
+
+-  ``pkt6`` refers to information from the client request. To access any
+   information from an intermediate relay, use ``relay6``. ``pkt6.msgtype``
+   and ``pkt6.transid`` output a 4-byte binary string for the message type
+   or transaction ID. For example, the message type ``SOLICIT`` is
+   ``0x00000001`` or simply 1, as in ``pkt6.msgtype == 1``.
+
+-  "Vendor option" means the Vendor-Identifying Vendor-Specific Information
+   option in DHCPv4 (code 125; see `Section 4 of RFC
+   3925 <https://tools.ietf.org/html/rfc3925#section-4>`__) and the
+   Vendor-Specific Information Option in DHCPv6 (code 17, defined in
+   `Section 21.17 of RFC
+   8415 <https://tools.ietf.org/html/rfc8415#section-21.17>`__). "Vendor
+   class option" means the Vendor-Identifying Vendor Class Option in DHCPv4
+   (code 124; see `Section 3 of RFC
+   3925 <https://tools.ietf.org/html/rfc3925#section-3>`__) in DHCPv4 and
+   the Class Option in DHCPv6 (code 16; see `Section 21.16 of RFC
+   8415 <https://tools.ietf.org/html/rfc8415#section-21.16>`__). Vendor
+   options may have sub-options that are referenced by their codes.
+   Vendor class options do not have sub-options, but rather data chunks,
+   which are referenced by index value. Index 0 means the first data
+   chunk, index 1 is for the second data chunk (if present), etc.
+
+-  In the vendor and vendor-class constructs an asterisk (*) or 0 can be
+   used to specify a wildcard ``enterprise-id`` value, i.e. it will match
+   any ``enterprise-id`` value.
+
+-  Vendor Class Identifier (option 60 in DHCPv4) can be accessed using the
+   option[60] expression.
+
+-  `RFC 3925 <https://tools.ietf.org/html/rfc3925>`__ and `RFC
+   8415 <https://tools.ietf.org/html/rfc8415>`__ allow for multiple
+   instances of vendor options to appear in a single message. The client
+   classification code currently examines the first instance if more
+   than one appear. For the ``vendor.enterprise`` and ``vendor-class.enterprise``
+   expressions, the value from the first instance is returned. Please
+   submit a feature request on the
+   `Kea GitLab site <https://gitlab.isc.org/isc-projects/kea>`__ to request
+   support for multiple instances.
+
+.. table:: List of classification expressions
+
+   +-----------------------+-------------------------+-----------------------+
+   | Name                  | Example                 | Description           |
+   +=======================+=========================+=======================+
+   | Equal                 | 'foo' == 'bar'          | Compare the two       |
+   |                       |                         | values and return     |
+   |                       |                         | `true` or `false`     |
+   +-----------------------+-------------------------+-----------------------+
+   | Not                   | not ('foo' == 'bar')    | Logical negation      |
+   +-----------------------+-------------------------+-----------------------+
+   | And                   | ('foo' == 'bar') and    | Logical and           |
+   |                       | ('bar' == 'foo')        |                       |
+   +-----------------------+-------------------------+-----------------------+
+   | Or                    | ('foo' == 'bar') or     | Logical or            |
+   |                       | ('bar' == 'foo')        |                       |
+   +-----------------------+-------------------------+-----------------------+
+   | Substring             | substring('foobar',0,3) | Return the requested  |
+   |                       |                         | substring             |
+   +-----------------------+-------------------------+-----------------------+
+   | Concat                | concat('foo','bar')     | Return the            |
+   |                       |                         | concatenation of the  |
+   |                       |                         | strings               |
+   +-----------------------+-------------------------+-----------------------+
+   | Concat (operator +)   | 'foo' + 'bar'           | Return the            |
+   |                       |                         | concatenation of the  |
+   |                       |                         | strings               |
+   +-----------------------+-------------------------+-----------------------+
+   | Ifelse                | ifelse('foo' ==         | Return the branch     |
+   |                       | 'bar','us','them')      | value according to    |
+   |                       |                         | the condition         |
+   +-----------------------+-------------------------+-----------------------+
+   | Hexstring             | hexstring('foo', '-')   | Converts the value to |
+   |                       |                         | a hexadecimal string, |
+   |                       |                         | e.g. 0a:1b:2c:3e      |
+   +-----------------------+-------------------------+-----------------------+
+   | Split                 | split('foo.bar', '.', 2)| Return the second     |
+   |                       |                         | field, splitting on   |
+   |                       |                         | dots.                 |
+   +-----------------------+-------------------------+-----------------------+
+
+.. table:: List of conversion-to-text expressions
+
+   +-----------------------+---------------------------+------------------------+
+   | Name                  | Example                   | Description            |
+   +=======================+===========================+========================+
+   | AddressToText         | addrtotext (192.10.0.1)   | Represent the 4 bytes  |
+   |                       | addrtotext (2003:db8::)   | of an IPv4 address or  |
+   |                       |                           | the 16 bytes of an     |
+   |                       |                           | IPv6 address in human  |
+   |                       |                           | readable format        |
+   +-----------------------+---------------------------+------------------------+
+   | Int8ToText            | int8totext (-1)           | Represents the 8-bit   |
+   |                       |                           | signed integer in text |
+   |                       |                           | format                 |
+   +-----------------------+---------------------------+------------------------+
+   | Int16ToText           | int16totext (-1)          | Represents the 16-bit  |
+   |                       |                           | signed integer in text |
+   |                       |                           | format                 |
+   +-----------------------+---------------------------+------------------------+
+   | Int32ToText           | int32totext (-1)          | Represents the 32-bit  |
+   |                       |                           | signed integer in text |
+   |                       |                           | format                 |
+   +-----------------------+---------------------------+------------------------+
+   | UInt8ToText           | uint8totext (255)         | Represents the 8-bit   |
+   |                       |                           | unsigned integer in    |
+   |                       |                           | text format            |
+   +-----------------------+---------------------------+------------------------+
+   | UInt16ToText          | uint16totext (65535)      | Represents the 16-bit  |
+   |                       |                           | unsigned integer in    |
+   |                       |                           | text format            |
+   +-----------------------+---------------------------+------------------------+
+   | UInt32ToText          | uint32totext (4294967295) | Represents the 32-bit  |
+   |                       |                           | unsigned integer in    |
+   |                       |                           | text format            |
+   +-----------------------+---------------------------+------------------------+
+
+Notes:
+
+The conversion operators can be used to transform data from binary to the text
+representation. The only requirement is that the input data type length matches
+an expected value.
+
+The ``AddressToText`` token expects 4 bytes for IPv4 addresses or 16 bytes for IPv6
+addresses. The ``Int8ToText`` and ``UInt8ToText`` tokens expect 1 byte, the ``Int16ToText`` and
+``UInt16ToText`` tokens expect 2 bytes, and ``Int32ToText`` and ``UInt32ToText`` expect 4 bytes.
+For all conversion tokens, if the data length is 0, the result string is empty.
+
+Logical Operators
+-----------------
+
+The Not, And, and Or logical operators are the common operators. Not has
+the highest precedence and Or the lowest. And and Or are (left)
+associative. Parentheses around a logical expression can be used to
+enforce a specific grouping; for instance, in "A and (B or C)". Without
+parentheses, "A and B or C" means "(A and B) or C".
+
+Substring
+---------
+
+The substring operator ``substring(value, start, length)`` accepts both
+positive and negative values for the starting position and the length.
+For ``start``, a value of 0 is the first byte in the string while -1 is
+the last byte. If the starting point is outside of the original string
+an empty string is returned. ``length`` is the number of bytes to extract.
+A negative number means to count towards the beginning of the string but
+does not include the byte pointed to by ``start``. The special value ``all``
+means to return all bytes from start to the end of the string. If the length
+is longer than the remaining portion of the string, then the entire
+remaining portion is returned. Some examples may be helpful:
+::
+
+           substring('foobar', 0, 6) == 'foobar'
+           substring('foobar', 3, 3) == 'bar'
+           substring('foobar', 3, all) == 'bar'
+           substring('foobar', 1, 4) == 'ooba'
+           substring('foobar', -5, 4) == 'ooba'
+           substring('foobar', -1, -3) == 'oba'
+           substring('foobar', 4, -2) == 'ob'
+           substring('foobar', 10, 2) == ''
+
+
+Concat
+------
+
+The concat function ``concat(string1, string2)`` returns the concatenation
+of its two arguments. For instance:
+::
+
+           concat('foo', 'bar') == 'foobar'
+
+For user convenience, Kea version 1.9.8 added an associative operator
+version of the concat function. For instance:
+::
+
+           'abc' + 'def' + 'ghi' + 'jkl' + '...'
+
+is the same as:
+::
+
+           concat(concat(concat(concat('abc', 'def'), 'ghi'), 'jkl'), '...')
+
+or:
+::
+
+           concat('abc', concat('def', concat('ghi', concat('jkl', '...'))))
+
+or:
+::
+
+           'abcdefghijkl...'
+
+Split
+---------
+
+The Split operator ``split(value, delimiters, field-number)`` accepts a list
+of characters to use as delimiters and a positive field number of the
+desired field when the value is split into fields separated by the delimiters.
+Adjacent delimiters are not compressed out, rather they result in an empty
+string for that field number. If value is an empty string, the result will be an
+empty string. If the delimiters list is empty, the result will be the original
+value. If the field-number is less than one or larger than the number of
+fields, the result will be an empty string. Some examples follow:
+::
+
+           split ('one.two..four', '.', 1) == 'one'
+           split ('one.two..four', '.', 2) == 'two'
+           split ('one.two..four', '.', 3) == ''
+           split ('one.two..four', '.', 4) == 'four'
+           split ('one.two..four', '.', 5) == ''
+
+Ifelse
+------
+
+The ifelse function ``ifelse(cond, iftrue, ifelse)`` returns the ``iftrue``
+or ``ifelse`` branch value following the boolean condition ``cond``. For
+instance:
+::
+
+            ifelse(option[230].exists, option[230].hex, 'none')
+
+
+Hexstring
+---------
+
+The hexstring function ``hexstring(binary, separator)`` returns the binary
+value as its hexadecimal string representation: pairs of hexadecimal
+digits separated by the separator, e.g ``':'``, ``'-'``, ``''`` (empty separator).
+::
+
+             hexstring(pkt4.mac, ':')
+
+
+.. note::
+
+   The expression for each class is executed on each packet received. If
+   the expressions are overly complex, the time taken to execute them
+   may impact the performance of the server. Administrators who need complex or
+   time-consuming expressions should consider writing a
+   :ref:`hook <hooks-libraries>` to perform the necessary work.
+
+.. _classification-configuring:
+
+Configuring Classes
+===================
+
+A class contains five items: a name, a test expression, option data,
+an option definition, and an ``only-if-required`` flag. The name must exist and
+must be unique among all classes. The test expression, option data and
+definition, and ``only-if-required`` flag are optional.
+
+The test expression is a string containing the logical expression used
+to determine membership in the class. The entire expression is in double
+quotes (").
+
+The option data is a list which defines any options that should be
+assigned to members of this class.
+
+The option definition is for DHCPv4 option 43
+(:ref:`dhcp4-vendor-opts`) and DHCPv4 private options
+(:ref:`dhcp4-private-opts`).
+
+Usually the test expression is evaluated before subnet selection, but in
+some cases it is useful to evaluate it later when the subnet,
+shared network, or pools are known but output-option processing has not yet
+been done. The ``only-if-required`` flag, which is ``false`` by default, allows the
+evaluation of the test expression only when it is required, i.e. in a
+``require-client-classes`` list of the selected subnet, shared network, or
+pool.
+
+The ``require-client-classes`` list, which is valid for shared-network,
+subnet, and pool scope, specifies the classes which are evaluated in the
+second pass before output-option processing. The list is built in the
+reversed precedence order of option data, i.e. an option data item in a
+subnet takes precedence over one in a shared network, but required class in
+a subnet is added after one in a shared network. The mechanism is
+related to the ``only-if-required`` flag but it is not mandatory that the
+flag be set to ``true``.
+
+In the following example, the class named "Client_foo" is defined. It is
+comprised of all clients whose client IDs (option 61) start with the
+string "foo". Members of this class will be given 192.0.2.1 and
+192.0.2.2 as their domain name servers.
+
+::
+
+   "Dhcp4": {
+       "client-classes": [
+           {
+               "name": "Client_foo",
+               "test": "substring(option[61].hex,0,3) == 'foo'",
+               "option-data": [
+                   {
+                       "name": "domain-name-servers",
+                       "code": 6,
+                       "space": "dhcp4",
+                       "csv-format": true,
+                       "data": "192.0.2.1, 192.0.2.2"
+                   }
+               ]
+           },
+           ...
+       ],
+       ...
+   }
+
+The next example shows a client class being defined for use by the DHCPv6
+server. In it the class named "Client_enterprise" is defined. It is
+comprised of all clients whose client identifiers start with the given
+hex string (which would indicate a DUID based on an enterprise ID of
+0xAABBCCDD). Members of this class will be given 2001:db8:0::1 and
+2001:db8:2::1 as their domain name servers.
+
+::
+
+   "Dhcp6": {
+       "client-classes": [
+           {
+               "name": "Client_enterprise",
+               "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD",
+               "option-data": [
+                   {
+                       "name": "dns-servers",
+                       "code": 23,
+                       "space": "dhcp6",
+                       "csv-format": true,
+                       "data": "2001:db8:0::1, 2001:db8:2::1"
+                   }
+               ]
+           },
+           ...
+       ],
+       ...
+   }
+
+.. _classification-using-host-reservations:
+
+Using Static Host Reservations in Classification
+================================================
+
+Classes can be statically assigned to the clients using techniques
+described in :ref:`reservation4-client-classes` and
+:ref:`reservation6-client-classes`.
+
+Subnet host reservations are searched after subnet selection.
+Global host reservations are searched at the same time by default but
+the ``early-global-reservations-lookup`` allows to change this behavior
+into searching them before the subnet selection.
+
+Pool selection is performed after all host reservations lookups.
+
+.. _classification-subnets:
+
+Configuring Subnets With Class Information
+==========================================
+
+In certain cases it is beneficial to restrict access to certain subnets
+only to clients that belong to a given class, using the ``client-class``
+keyword when defining the subnet.
+
+Let's assume that the server is connected to a network segment that uses
+the 192.0.2.0/24 prefix. The administrator of that network has decided
+that addresses from the range 192.0.2.10 to 192.0.2.20 will be
+managed by the DHCP4 server. Only clients belonging to client class
+"Client_foo" are allowed to use this subnet. Such a configuration can be
+achieved in the following way:
+
+::
+
+   "Dhcp4": {
+       "client-classes": [
+           {
+               "name": "Client_foo",
+               "test": "substring(option[61].hex,0,3) == 'foo'",
+               "option-data": [
+                   {
+                       "name": "domain-name-servers",
+                       "code": 6,
+                       "space": "dhcp4",
+                       "csv-format": true,
+                       "data": "192.0.2.1, 192.0.2.2"
+                   }
+               ]
+           },
+           ...
+       ],
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
+               "client-class": "Client_foo"
+           },
+           ...
+       ],,
+       ...
+   }
+
+The following example shows how to restrict access to a DHCPv6 subnet. This
+configuration restricts use of the addresses in the range 2001:db8:1::1 to
+2001:db8:1::FFFF to members of the "Client_enterprise" class.
+
+::
+
+   "Dhcp6": {
+       "client-classes": [
+           {
+               "name": "Client_enterprise",
+               "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD",
+               "option-data": [
+                   {
+                       "name": "dns-servers",
+                       "code": 23,
+                       "space": "dhcp6",
+                       "csv-format": true,
+                       "data": "2001:db8:0::1, 2001:db8:2::1"
+                   }
+               ]
+           },
+           ...
+       ],
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/64",
+               "pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
+               "client-class": "Client_enterprise"
+           }
+       ],
+       ...
+   }
+
+.. _classification-pools:
+
+Configuring Pools With Class Information
+========================================
+
+Similar to subnets, in certain cases access to certain address or prefix
+pools must be restricted to only clients that belong to a given class,
+using the ``client-class`` when defining the pool.
+
+Let's assume that the server is connected to a network segment that uses
+the 192.0.2.0/24 prefix. The administrator of that network has decided
+that addresses from the range 192.0.2.10 to 192.0.2.20 are going to be
+managed by the DHCP4 server. Only clients belonging to client class
+"Client_foo" are allowed to use this pool. Such a configuration can be
+achieved in the following way:
+
+::
+
+   "Dhcp4": {
+       "client-classes": [
+           {
+               "name": "Client_foo",
+               "test": "substring(option[61].hex,0,3) == 'foo'",
+               "option-data": [
+                   {
+                       "name": "domain-name-servers",
+                       "code": 6,
+                       "space": "dhcp4",
+                       "csv-format": true,
+                       "data": "192.0.2.1, 192.0.2.2"
+                   }
+               ]
+           },
+           ...
+       ],
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [
+                   {
+                       "pool": "192.0.2.10 - 192.0.2.20",
+                       "client-class": "Client_foo"
+                   }
+               ]
+           },
+           ...
+       ],,
+
+   }
+
+The following example shows how to restrict access to an address pool. This
+configuration restricts use of the addresses in the range 2001:db8:1::1 to
+2001:db8:1::FFFF to members of the "Client_enterprise" class.
+
+::
+
+   "Dhcp6": {
+       "client-classes": [
+           {
+               "name": "Client_enterprise_",
+               "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD",
+               "option-data": [
+                   {
+                       "name": "dns-servers",
+                       "code": 23,
+                       "space": "dhcp6",
+                       "csv-format": true,
+                       "data": "2001:db8:0::1, 2001:db8:2::1"
+                   }
+               ]
+           },
+           ...
+       ],
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/64",
+
+               "pools": [
+                   {
+                       "pool": "2001:db8:1::-2001:db8:1::ffff",
+                       "client-class": "Client_foo"
+                   }
+               ]
+           },
+           ...
+       ],
+       ...
+   }
+
+Using Classes
+=============
+
+Currently classes can be used for two functions: they can supply options
+to members of the class, and they can be used to choose a subnet from
+which an address will be assigned to a class member.
+
+When options are defined as part of the class definition
+they override any global options that may be defined, and
+in turn will be overridden by any options defined for an
+individual subnet.
+
+Classes and Hooks
+=================
+
+Hooks may be used to classify packets. This may be useful if the
+expression would be complex or time-consuming to write, and could be
+better or more easily written as code. Once the hook has added the proper class name
+to the packet, the rest of the classification system will work as expected
+in choosing a subnet and selecting options. For a description of hooks,
+see :ref:`hooks-libraries`; for information on configuring classes,
+see :ref:`classification-configuring` and :ref:`classification-subnets`.
+
+Debugging Expressions
+=====================
+
+While constructing classification expressions, administrators may find
+it useful to enable logging; see :ref:`logging` for a more complete
+description of the logging facility.
+
+To enable the debug statements in the classification system,
+the severity must be set to ``DEBUG`` and the debug level to at least 55.
+The specific loggers are ``kea-dhcp4.eval`` and ``kea-dhcp6.eval``.
+
+To understand the logging statements, it is essential to understand a bit about
+how expressions are evaluated; for a more complete description, refer to
+[the design document](https://gitlab.isc.org/isc-projects/kea/-/wikis/designs/client-classification-design).
+In brief, there are two structures used during the evaluation of an
+expression: a list of tokens which represent the expressions, and a value
+stack which represents the values being manipulated.
+
+The list of tokens is created when the configuration file is processed,
+with most expressions and values being converted to a token. The list is
+organized in reverse Polish notation. During execution, the list is
+traversed in order; as each token is executed, it is able to pop
+values from the top of the stack and eventually push its result on the
+top of the stack. Imagine the following expression:
+
+::
+
+          "test": "substring(option[61].hex,0,3) == 'foo'",
+
+
+This will result in the following tokens:
+
+::
+
+          option, number (0), number (3), substring, text ('foo'), equals
+
+
+In this example, the first three tokens will simply push values onto the
+stack. The substring token will then remove those three values and
+compute a result that it places on the stack. The text option also
+places a value on the stack, and finally the equals token removes the two
+tokens on the stack and places its result on the stack.
+
+When debug logging is enabled, each time a token is evaluated it
+emits a log message indicating the values of any objects that were popped
+off of the value stack, and any objects that were pushed onto the value
+stack.
+
+The values are displayed as either text, if the command is known to
+use text values, or hexadecimal, if the command either uses binary values
+or can manipulate either text or binary values. For expressions that pop
+multiple values off the stack, the values are displayed in the order
+they were popped. For most expressions this will not matter, but for the
+concat expression the values are displayed in reverse order from their
+written order in the expression.
+
+Let us assume that the following test has been entered into the
+configuration. This example skips most of the configuration to
+concentrate on the test.
+
+::
+
+          "test": "substring(option[61].hex,0,3) == 'foo'",
+
+
+The logging might then resemble this:
+
+::
+
+      2016-05-19 13:35:04.163 DEBUG [kea.eval/44478] EVAL_DEBUG_OPTION Pushing option 61 with value 0x666F6F626172
+      2016-05-19 13:35:04.164 DEBUG [kea.eval/44478] EVAL_DEBUG_STRING Pushing text string '0'
+      2016-05-19 13:35:04.165 DEBUG [kea.eval/44478] EVAL_DEBUG_STRING Pushing text string '3'
+      2016-05-19 13:35:04.166 DEBUG [kea.eval/44478] EVAL_DEBUG_SUBSTRING Popping length 3, start 0, string 0x666F6F626172 pushing result 0x666F6F
+      2016-05-19 13:35:04.167 DEBUG [kea.eval/44478] EVAL_DEBUG_STRING Pushing text string 'foo'
+      2016-05-19 13:35:04.168 DEBUG [kea.eval/44478] EVAL_DEBUG_EQUAL Popping 0x666F6F and 0x666F6F pushing result 'true'
+
+.. note::
+
+   The debug logging may be quite verbose if there are multiple
+   expressions to evaluate; it is intended as an aid in helping
+   create and debug expressions. Administrators should plan to disable debug
+   logging when expressions are working correctly. Users may also
+   wish to include only one set of expressions at a time in the
+   configuration file while debugging them, to limit the log
+   statements. For example, when adding a new set of expressions, an administrator
+   might find it more convenient to create a configuration file that
+   only includes the new expressions until they are working
+   correctly, and then add the new set to the main configuration file.
diff --git a/doc/sphinx/arm/config-backend.rst b/doc/sphinx/arm/config-backend.rst
new file mode 100644
index 0000000..58d6b1a
--- /dev/null
+++ b/doc/sphinx/arm/config-backend.rst
@@ -0,0 +1,330 @@
+.. _config-backend:
+
+Kea Configuration Backend
+=========================
+
+.. _cb-applicability:
+
+Applicability
+-------------
+
+Kea Configuration Backend (CB or config backend) gives Kea servers the ability
+to manage and fetch their configuration from one or more databases. In
+this documentation, the term "Configuration Backend" may also refer to
+the particular Kea module providing support to manage and fetch the
+configuration information from the particular database type.  For
+example, the MySQL Configuration Backend is the logic implemented within the
+``mysql_cb`` hook library, which provides a complete set of functions to
+manage and fetch the configuration information from the MySQL database.
+The PostgreSQL Configuration Backend is the logic implemented within the
+``pgsql_cb`` hook library, which provides a complete set of functions to
+manage and fetch the configuration information from the PostgreSQL database.
+From herein, the term "database" is used to refer to either a MySQL or
+PostgreSQL database.
+
+In small deployments, e.g. those comprising a single DHCP server
+instance with limited and infrequently changing number of subnets, it
+may be impractical to use the CB as a configuration repository because
+it requires additional third-party software to be installed and
+configured - in particular the database server, client and libraries.
+Once the number of DHCP servers and/or the number of managed subnets in the
+network grows, the usefulness of the CB becomes obvious.
+
+One use case for the CB is a pair of Kea DHCP servers that are configured
+to support High Availability as described in
+:ref:`hooks-high-availability`. The configurations of both servers
+(including the value of the ``server-tag`` parameter)
+are almost exactly the same: they may differ by the server identifier
+and designation of the server as a primary or standby (or secondary), and/or
+by their interfaces' configuration. Typically, the
+subnets, shared networks, option definitions, and global parameters are the
+same for both servers and can be sourced from a single database instance
+to both Kea servers.
+
+Using the database as a single source of configuration for subnets
+and/or other configuration information supported by the CB has the
+advantage that any modifications to the configuration in the database are
+automatically applied to both servers.
+
+Another case when the centralized configuration repository is useful is
+in deployments including a large number of DHCP servers, possibly
+using a common lease database to provide redundancy. New servers can
+be added to the pool frequently to fulfill growing scalability
+requirements. Adding a new server does not require replicating the
+entire configuration to the new server when a common database is used.
+
+Using the database as a configuration repository for Kea servers also
+brings other benefits, such as:
+
+-  the ability to use database specific tools to access the configuration
+   information;
+
+-  the ability to create customized statistics based on the information
+   stored in the database; and
+
+-  the ability to backup the configuration information using the database's
+   built-in replication mechanisms.
+
+.. _cb-limitations:
+
+CB Capabilities and Limitations
+-------------------------------
+
+Currently, the Kea CB has the following limitations:
+
+- It is only supported for MySQL and PostgreSQL databases.
+
+- It is only supported for the DHCPv4 and DHCPv6 daemons; the Control Agent,
+  D2 daemon, and the NETCONF daemon cannot be configured from the database,
+
+- Only certain DHCP configuration parameters can be set in the
+  database: global parameters, option definitions, global options, client
+  classes, shared networks, and subnets. Other configuration parameters
+  must be sourced from a JSON configuration file.
+
+Kea CB stores data in a schema that is public. It is possible to
+insert configuration data into the tables manually or automatically
+using SQL scripts, but this requires SQL and schema knowledge.
+The supported method for managing the data is through the ``cb-cmds`` hook library,
+which provides management commands for config backends. It simplifies many
+typical operations, such as listing, adding, retrieving, and deleting global
+parameters, shared networks, subnets, pools, options, option definitions, and
+client classes. In addition, it provides essential business logic that ensures
+the logical integrity of the data. See commands starting with ``remote-`` in
+Appendix A of this manual for a complete list.
+
+.. note::
+
+   The ``cb_cmds`` hook library is available only to ISC support subscribers.
+   For more information on subscription options, please complete the form
+   at https://www.isc.org/contact.
+
+
+The schema creation scripts can be found at `dhcpdb_create.mysql <https://gitlab.isc.org/isc-projects/kea/blob/master/src/share/database/scripts/mysql/dhcpdb_create.mysql>`__ and
+;
+`dhcpdb_create.pgsql <https://gitlab.isc.org/isc-projects/kea/blob/master/src/share/database/scripts/pgsql/dhcpdb_create.pgsql>`__ and
+;
+other related design documents are stored in our GitLab: `CB Design <https://gitlab.isc.org/isc-projects/kea/wikis/designs/configuration-in-db-design>`__ and
+`Client Classes in CB Design <https://gitlab.isc.org/isc-projects/kea/wikis/designs/client-classes-in-cb>`__.
+
+We strongly recommend against duplication of configuration information
+in both the file and the database. For example, when specifying subnets
+for the DHCP server, please store them in either the configuration backend
+or in the configuration file, not both. Storing some subnets in the database
+and others in the file may put users at risk of potential configuration
+conflicts. Note that the configuration instructions from the database take
+precedence over instructions from the file, so parts of the configuration
+specified in the file may be overridden if contradicted by information in
+the database.
+
+Although it is not recommended, it is possible to specify certain parameter
+types both in a configuration file and the database. For example, a subnet
+can be specified in the configuration file and another subnet in the database;
+in this case, the server will use both subnets. DHCP client classes, however,
+must not be specified in both the configuration file and the database, even if
+they do not overlap. If any client classes are specified in the database
+for a particular DHCP server, this server will use these classes and ignore
+all classes present in its configuration file. This behavior was introduced
+to ensure that the server receives a consistent set of client classes
+specified in an expected order with all inter-class dependencies fulfilled.
+It is impossible to guarantee consistency when client classes are specified
+in two independent configuration sources.
+
+.. note::
+
+   It is recommended that the ``subnet_cmds`` hook library not be used to
+   manage subnets when the configuration backend is used as a source
+   of information about the subnets. The ``subnet_cmds`` hook library
+   modifies the local subnets configuration in the server's memory,
+   not in the database. Use the ``cb_cmds`` hook library to manage the
+   subnets information in the database instead.
+
+.. note::
+
+   Using custom option formats requires creating definitions for these options.
+   Suppose a user wishes to set option data in the configuration backend. In
+   that case, we recommend specifying the definition for that option in the
+   configuration backend as well. It is essential when multiple servers are
+   managed via the configuration backend, and may differ in their
+   configurations. The option data parser can search for an option definition
+   appropriate for the server for which the option data is specified.
+
+   In a single-server deployment, or when all servers share the same
+   configuration file information, it is possible to specify option
+   definitions in the configuration files and option data in the configuration
+   backend. The server receiving a command to set option data must have a
+   valid definition in its configuration file, even when it sets option data
+   for another server.
+
+   It is not supported to specify option definitions in the configuration
+   backend and the corresponding option data in the server configuration files.
+
+CB Components
+-------------
+
+To use a MySQL configuration backend you must compile the ``mysql_cb`` open
+source hook library and configure the DHCP servers to load it.  It is compiled when
+the ``--with-mysql`` configuration switch is used during the Kea build. The MySQL
+C client libraries must be installed, as explained in :ref:`dhcp-install-configure`.
+
+To use a PostgreSQL configuration backend you must compile the ``pgsql_cb`` open
+source hook library and configure the DHCP servers to load it.  It is compiled when
+the ``--with-pgsql`` configuration switch is used during the Kea build. The PostgreSQL
+C client libraries must be installed, as explained in :ref:`dhcp-install-configure`.
+
+.. note::
+
+   An existing database schema must be upgraded to the latest schema
+   required by the particular Kea version using the ``kea-admin`` tool,
+   as described in :ref:`kea-admin`.
+
+The ``cb_cmds`` premium hook library, which is available to ISC's paid support
+customers, provides a complete set of commands to manage the
+servers' configuration information within the database. This library can
+be attached to both DHCPv4 and DHCPv6 server instances. While it is
+possible to manage the configuration information without the ``cb_cmds``
+hook library with commonly available tools, such as MySQL Workbench or
+the command-line MySQL client, or by directly working with the database;
+these avenues are neither recommended nor supported.
+
+Refer to :ref:`hooks-cb-cmds` for the details regarding the
+``cb_cmds`` hook library.
+
+The DHCPv4 and DHCPv6 server-specific configurations of the CB, as well as
+the list of supported configuration parameters, can be found in
+:ref:`dhcp4-cb` and :ref:`dhcp6-cb`, respectively.
+
+.. _cb-sharing:
+
+Configuration Sharing and Server Tags
+-------------------------------------
+
+The configuration database is designed to store configuration information
+for multiple Kea servers. Depending on the use case, the entire configuration
+may be shared by all servers; parts of the configuration may be shared by
+multiple servers and the rest of the configuration may be different for these
+servers; or each server may have its own non-shared configuration.
+
+The configuration elements in the database are associated with the servers
+by "server tags." The server tag is an arbitrary string holding the name
+of the Kea server instance. The tags of the DHCPv4 and DHCPv6 servers are
+independent in the database, i.e. the same server tag can be created for
+both the DHCPv4 and the DHCPv6 server. The value is configured
+using the ``server-tag`` parameter in the Dhcp4 or Dhcp6 scope. The current
+server tag can be checked with the ``server-tag-get`` command.
+
+The server definition, which consists of the server tag and the server
+description, must be stored in the configuration database prior to creating
+the dedicated configuration for that server. In cases when all servers use
+the same configuration, e.g. a pair of servers running as High Availability
+peers, there is no need to configure the server tags for these
+servers in the database.
+
+Commands which contain the logical server `all` are applied to all servers
+connecting to the database. The `all` server cannot be
+deleted or modified, and it is not returned among other servers
+as a result of the ``remote-server[46]-get-all`` command.
+
+In most cases, there are no server tags defined in the configuration
+database; all connecting servers get the same configuration
+regardless of the server tag they use. The server tag that a
+particular Kea instance presents to the database to fetch its configuration
+is specified in the Kea configuration file, using the
+`config-control` map (please refer to the :ref:`dhcp4-cb-json` and
+:ref:`dhcp6-cb-json` for details). All Kea instances presenting the same
+server tag to the configuration database
+are given the same configuration.
+
+It is the administrator's choice whether
+multiple Kea instances use the same server tag or each Kea instance uses
+a different server tag. There is no requirement that the instances
+running on the same physical or virtual machine use the same server tag. It is
+even possible to configure the Kea server without assigning it a server tag.
+In such a case the server will be given the configuration specified for `all`
+servers.
+
+To differentiate between different Kea server configurations, a
+list of the server tags used by the servers must be stored in the
+database. For the DHCPv4 and DHCPv6 servers, it can be done using the
+commands described in :ref:`command-remote-server4-set` and
+:ref:`command-remote-server6-set`. The
+server tags can then be used to associate the configuration information with
+the servers. However, it is important to note that some DHCP
+configuration elements may be associated with multiple server tags (known
+as "shareable" elements), while
+other configuration elements may be associated with only one
+server tag ("non-shareable" elements). The :ref:`dhcp4-cb`
+and :ref:`dhcp6-cb` sections list the DHCP-specific shareable and
+non-shareable configuration elements; however, in this section we
+briefly explain the differences between them.
+
+A shareable configuration element is one which has some unique
+property identifying it, and which may appear only once in
+the database. An example of a shareable DHCP element is a subnet
+instance: the subnet is a part of the network topology and we assume
+that any particular subnet may have only one definition within this
+network. Each subnet has two unique identifiers: the subnet identifier and the
+subnet prefix. The subnet identifier is used in Kea to uniquely
+identify the subnet within the network and to connect it with other configuration elements,
+e.g. in host reservations. Some commands provided by the
+``cb_cmds`` hook library allow the subnet
+information to be accessed by either subnet identifier or prefix, and explicitly prohibit
+using the server tag to access the subnet. This is because, in
+general, the subnet definition is associated with multiple servers
+rather than a single server. In fact, it may even be associated
+with no servers (unassigned). Still, the unassigned subnet has an
+identifier and prefix which can be used to access the subnet.
+
+A shareable configuration element may be associated with multiple
+servers, one server, or no servers. Deletion of the server which is
+associated with the shareable element does not cause the deletion of
+the shareable element. It merely deletes the association of the
+deleted server with the element.
+
+Unlike a shareable element, a non-shareable element must not be
+explicitly associated with more than one server and must not exist
+after the server is deleted (must not remain unassigned). A
+non-shareable element only exists within the context of the server.
+An example of a non-shareable element in DHCP is a global
+parameter, e.g. `renew-timer`. The renew timer
+is the value to be used by a particular server and only this
+server. Other servers may have their respective renew timers
+set to the same or different values. The renew timer
+parameter has no unique identifier by which it could be
+accessed, modified, or otherwise used. Global parameters like
+the renew timer can be accessed by the parameter name and the
+tag of the server for which they are configured. For example:
+the commands described in :ref:`command-remote-global-parameter4-get` allow
+the value of the global parameter to be fetched by the parameter name and
+the server name. Getting the global parameter only by its name (without
+specifying the server tag) is not possible, because there may be many
+global parameters with a given name in the database.
+
+When the server associated with a non-shareable configuration element
+is deleted, the configuration element is automatically deleted from
+the database along with the server because the non-shareable element
+must be always assigned to a server (or the logical server `all`).
+
+The terms "shareable" and "non-shareable" only apply to associations
+with user-defined servers; all configuration elements associated with
+the logical server `all` are by definition shareable. For example: the
+`renew-timer` associated with `all` servers is used
+by all servers connecting to the database which do not have their specific
+renew timers defined. In a special case, when none of the configuration
+elements are associated with user-defined servers, the entire
+configuration in the database is shareable because all its pieces
+belong to `all` servers.
+
+.. note::
+
+   Be very careful when associating configuration elements with
+   different server tags. The configuration backend does not protect
+   against some possible misconfigurations that may arise from the
+   wrong server tags' assignments. For example: if a shared
+   network is assigned to one server and the subnets belonging to this shared network
+   to another server, the servers will fail upon trying to fetch and
+   use this configuration. The server fetching the subnets will be
+   aware that the subnets are associated with the shared network, but
+   the shared network will not be found by this server since it doesn't
+   belong to it. In such a case, both the shared network and the subnets
+   should be assigned to the same set of servers.
diff --git a/doc/sphinx/arm/config-templates.rst b/doc/sphinx/arm/config-templates.rst
new file mode 100644
index 0000000..348c4e0
--- /dev/null
+++ b/doc/sphinx/arm/config-templates.rst
@@ -0,0 +1,41 @@
+.. _config-templates:
+
+Configuration Templates
+=======================
+
+The following sections include configuration templates for
+certain deployment types. The example configuration files are also available in the Kea sources,
+in the ``doc/examples`` directory.
+
+.. include:: template-power-user-home.md
+
+Some tweaking of these templates may be required to match specific system needs: at a
+minimum, the lines highlighted in yellow must be adjusted to match the actual deployment.
+
+Server1's Control Agent configuration file:
+
+.. literalinclude:: template-power-user-home-ca-1.conf
+   :language: javascript
+   :emphasize-lines: 9, 12
+   :linenos:
+
+Server1's DHCPv4 configuration file:
+
+.. literalinclude:: template-power-user-home-dhcp4-1.conf
+   :language: javascript
+   :emphasize-lines: 25,76,81,121,133,147,151,154-158,166-180,190-199
+   :linenos:
+
+Server2's Control Agent configuration file:
+
+.. literalinclude:: template-power-user-home-ca-2.conf
+   :language: javascript
+   :emphasize-lines: 9, 12
+   :linenos:
+
+Server2's DHCPv4 configuration file:
+
+.. literalinclude:: template-power-user-home-dhcp4-2.conf
+   :language: javascript
+   :emphasize-lines: 25,76,81,121,133,147,151,154-158,166-180,190-199
+   :linenos:
diff --git a/doc/sphinx/arm/config.rst b/doc/sphinx/arm/config.rst
new file mode 100644
index 0000000..cb29dcc
--- /dev/null
+++ b/doc/sphinx/arm/config.rst
@@ -0,0 +1,330 @@
+.. _kea-config:
+
+*****************
+Kea Configuration
+*****************
+
+Kea uses JSON structures to represent server configurations. The
+following sections describe how the configuration structures are
+organized.
+
+.. _json:
+
+JSON Configuration
+==================
+
+JSON is the notation used throughout the Kea project. The most obvious
+usage is for the configuration file, but JSON is also used for sending
+commands over the Management API (see :ref:`ctrl-channel`) and for
+communicating between DHCP servers and the DDNS update daemon.
+
+Typical usage assumes that the servers are started from the command
+line, either directly or using a script, e.g. ``keactrl``. The
+configuration file is specified upon startup using the ``-c`` parameter.
+
+.. _json-format:
+
+JSON Syntax
+-----------
+
+Configuration files for the DHCPv4, DHCPv6, DDNS, Control Agent, and
+NETCONF modules are defined in an extended JSON format. Basic JSON is
+defined in `RFC 7159 <https://tools.ietf.org/html/rfc7159>`__ and `ECMA
+404 <https://www.ecma-international.org/publications/standards/Ecma-404.htm>`__.
+In particular, the only boolean values allowed are true or false (all
+lowercase). The capitalized versions (True or False) are not accepted.
+
+Even though the JSON standard (ECMA 404) does not require JSON objects
+(i.e. name/value maps) to have unique entries, Kea implements them
+using a C++ STL map with unique entries. Therefore, if there are multiple
+values for the same name in an object/map, the last value overwrites previous values.
+Since Kea 1.9.0, configuration file parsers raise a syntax error in such cases.
+
+Kea components use extended JSON with additional features allowed:
+
+-  Shell comments: any text after the hash (#) character is ignored.
+
+-  C comments: any text after the double slashes (//) character is
+   ignored.
+
+-  Multiline comments: any text between /\* and \*/ is ignored. This
+   comment can span multiple lines.
+
+-  File inclusion: JSON files can include other JSON files by using a
+   statement of the form \<?include "file.json"?\>.
+
+-  Extra commas: to remove the inconvenience of errors caused by leftover commas
+   after making changes to configuration. While parsing, a warning is printed
+   with the location of the comma to give the user the ability to correct a
+   potential mistake.
+
+.. warning::
+
+   These features are meant to be used in a JSON configuration file.
+   Their usage in any other way may result in errors.
+
+The configuration file consists of a single object (often colloquially
+called a map) started with a curly bracket. It comprises only one of
+the "Dhcp4", "Dhcp6", "DhcpDdns", "Control-agent", or "Netconf" objects.
+It is possible to define additional elements but they will be ignored.
+
+A very simple configuration for DHCPv4 could look like this:
+
+::
+
+   # The whole configuration starts here.
+   {
+       # DHCPv4 specific configuration starts here.
+       "Dhcp4": {
+           "interfaces-config": {
+               "interfaces": [ "eth0" ],
+               "dhcp-socket-type": "raw"
+           },
+           "valid-lifetime": 4000,
+           "renew-timer": 1000,
+           "rebind-timer": 2000,
+           "subnet4": [{
+              "pools": [ { "pool": "192.0.2.1-192.0.2.200" } ],
+              "subnet": "192.0.2.0/24"
+           }],
+
+          # Now loggers are inside the DHCPv4 object.
+          "loggers": [{
+               "name": "*",
+               "severity": "DEBUG"
+           }]
+       }
+
+   # The whole configuration structure ends here.
+   }
+
+More examples are available in the installed ``share/doc/kea/examples``
+directory.
+
+To avoid repetition of mostly similar structures, examples in the rest
+of this guide will showcase only the subset of parameters appropriate
+for a given context. For example, when discussing the IPv6 subnets
+configuration in DHCPv6, only subnet6 parameters will be mentioned. It
+is implied that the remaining elements (the global map that holds Dhcp6)
+are present, but they are omitted for clarity. Usually,
+locations where extra parameters may appear are denoted by an ellipsis
+(...).
+
+.. _user-context:
+
+Comments and User Context
+-------------------------
+
+Shell, C, or C++ style comments are all permitted in the JSON configuration file if
+the file is used locally. This is convenient and works in simple cases where
+the configuration is kept statically using a local file. However, since comments
+are not part of JSON syntax, most JSON tools detect them as
+errors. Another problem with them is that once Kea loads its configuration, the
+shell, C, and C++ style comments are ignored. If commands such as
+``config-get`` or ``config-write`` are used, those comments are lost. An example of such
+comments was presented in the previous section.
+
+Historically, to address the problem, Kea code allowed the use of `comment` strings
+as valid JSON entities. This had the benefit of being retained through various
+operations (such as ``config-get``), or allowing processing by JSON tools. An
+example JSON comment looks like this:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [{
+           "subnet": "192.0.2.0/24",
+           "pools": [{ "pool": "192.0.2.10 - 192.0.2.20" }],
+           "comment": "second floor"
+       }]
+   }
+
+However, the facts that the comment could only be a single line, and that it was not
+possible to add any other information in a more structured form, were frustrating. One specific
+example was a request to add floor levels and building numbers to subnets. This
+was one of the reasons why the concept of user context was introduced. It
+allows adding an arbitrary JSON structure to most Kea configuration structures.
+
+This has a number of benefits compared to earlier approaches. First, it is fully
+compatible with JSON tools and Kea commands. Second, it allows storing simple
+comment strings, but it can also store much more complex data, such as
+multiple lines (as a string array), extra typed data (such as floor numbers being
+actual numbers), and more. Third, the data is exposed to hooks, so it is possible
+to develop third-party hooks that take advantage of that extra information. An
+example user context looks like this:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [{
+           "subnet": "192.0.2.0/24",
+           "pools": [{ "pool": "192.0.2.10 - 192.0.2.20" }],
+           "user-context": {
+               "comment": "second floor",
+               "floor": 2
+           }
+       }]
+   }
+
+User contexts can store an arbitrary data file as long as it has valid JSON
+syntax and its top-level element is a map (i.e. the data must be enclosed in
+curly brackets). However, some hook libraries may expect specific formatting;
+please consult the specific hook library documentation for details.
+
+In a sense the user-context mechanism has superseded the JSON comment
+capabilities; ISC encourages administrators to use user-context instead of
+the older mechanisms. To promote this way of storing comments, Kea compared
+converts JSON comments to user-context on the fly.
+
+However, if the configuration uses the old JSON
+comment, the ``config-get`` command returns a slightly modified
+configuration. It is not uncommon for a call for ``config-set`` followed by a
+``config-get`` to receive a slightly different structure.
+The best way to avoid this problem is simply to abandon JSON comments and
+use user-context.
+
+Kea supports user contexts at the following levels: global scope,
+interfaces configuration, shared networks,
+subnets, client classes, option data and definitions, host
+reservations, control socket, DHCP-DDNS, loggers, leases, and server ID. These
+are supported in both DHCPv4 and DHCPv6, with the exception of server ID,
+which is DHCPv6 only.
+
+User context can be added and edited in structures supported by commands.
+
+We encourage Kea users to utilize these functions to store information
+used by other systems and custom hooks.
+
+For example, the `subnet4-update` command can be used to add user context data
+to an existing subnet.
+
+::
+
+   "subnet4": [ {
+      "id": 1,
+      "subnet": "10.20.30.0/24",
+      "user-context": {
+         "building": "Main"
+         "floor": 1
+         }
+    } ]
+
+The same can be done with many other commands like lease6-add etc.
+
+Kea also uses user context to store non-standard data.
+Currently, only :ref:`dhcp4-store-extended-info` uses this feature.
+
+When enabled, it adds the ISC key in `user-context` to differentiate automatically
+added content.
+
+Example of relay information stored in a lease:
+
+::
+
+   {
+   "arguments": {
+      "client-id": "42:42:42:42:42:42:42:42",
+      "cltt": 12345678,
+      "fqdn-fwd": false,
+      "fqdn-rev": true,
+      "hostname": "myhost.example.com.",
+      "hw-address": "08:08:08:08:08:08",
+      "ip-address": "192.0.2.1",
+      "state": 0,
+      "subnet-id": 44,
+      "valid-lft": 3600
+      "user-context": {
+         "ISC": {
+         "relays": [
+         {
+               "hop": 2,
+               "link": "2001:db8::1",
+               "peer": "2001:db8::2"
+         },
+         {
+               "hop": 1,
+               "link": "2001:db8::3",
+               "options": "0x00C800080102030405060708",
+               "peer": "2001:db8::4"
+         }]
+         }
+      }
+   }
+
+
+User context can store configuration for multiple hooks and comments at once.
+
+For a discussion about user context used in hooks, see :ref:`user-context-hooks`.
+
+
+Simplified Notation
+-------------------
+
+It is sometimes convenient to refer to a specific element in the
+configuration hierarchy. Each hierarchy level is separated by a slash.
+If there is an array, a specific instance within that array is
+referenced by a number in square brackets (with numbering starting at
+zero). For example, in the above configuration the valid-lifetime in the
+Dhcp4 component can be referred to as Dhcp4/valid-lifetime, and the pool
+in the first subnet defined in the DHCPv4 configuration as
+Dhcp4/subnet4[0]/pool.
+
+
+.. include:: config-backend.rst
+
+
+Configuration Files Inclusion
+-----------------------------
+
+The parser provides the ability to include files. The syntax was chosen
+to look similar to how Apache includes PHP scripts in HTML code. This particular
+syntax was chosen to emphasize that the include directive is an additional
+feature and not a part of JSON syntax.
+
+The inclusion is implemented as a stack of files. You can use the include directive
+in nested includes. Up to ten nesting levels are supported. This arbitrarily chosen
+limit is protection against recursive inclusions.
+
+The include directive has the form:
+
+::
+
+   <?include "[PATH]"?>
+
+The *[PATH]* pattern should be replaced with an absolute path or a path relative to
+the current working directory at the time the Kea process was launched.
+
+To include one file from another, use the following syntax:
+
+.. code-block:: javascript
+
+   {
+      "Dhcp6": {
+         "interfaces-config": {
+            "interfaces": [ "*" ]},
+         "preferred-lifetime": 3000,
+         "rebind-timer": 2000,
+         "renew-timer": 1000,
+         <?include "subnets.json"?>
+         "valid-lifetime": 4000
+      }
+   }
+
+where the content of "subnets.json" may be:
+
+::
+
+   "subnet4": [
+      {
+         "id": 123,
+         "subnet": "192.0.2.0/24"
+      },
+      {
+         "id": 234,
+         "subnet": "192.0.3.0/24"
+      },
+      {
+         "id": 345,
+         "subnet": "10.0.0.0/8"
+      }
+   ],
diff --git a/doc/sphinx/arm/congestion-handling.rst b/doc/sphinx/arm/congestion-handling.rst
new file mode 100644
index 0000000..c8c9671
--- /dev/null
+++ b/doc/sphinx/arm/congestion-handling.rst
@@ -0,0 +1,131 @@
+.. _congestion-handling:
+
+*******************
+Congestion Handling
+*******************
+
+.. _congestion-handling-background:
+
+What is Congestion?
+===================
+
+Congestion occurs when servers are subjected to client queries faster
+than those queries can be processed. As a result, the servers begin accumulating
+a backlog of pending queries. The longer the high rate of traffic
+continues, the farther behind the servers fall. Depending on the client
+implementations, those that fail to get leases either give up or simply
+continue to retry forever. In the former case, the server may eventually
+recover, but the latter case is a vicious cycle from which the server is
+unable to escape.
+
+Congestion typically occurs when there is a network event that causes overly large
+numbers of clients to simultaneously need leases, such as recovery after
+a network outage. In a well-planned deployment, the number and capacity of servers is
+matched to the maximum expected client load. If the load is routinely too
+heavy, then the deployment needs to be re-evaluated. 
+
+The goal of congestion handling is to help servers mitigate the peak in
+traffic by fulfilling as many of the most relevant requests as possible
+until the congestion subsides.
+
+.. _congestion-handling-solution:
+
+Configuring Congestion Handling
+===============================
+
+Congestion handling
+offers the ability to configure the server to use a separate thread to
+read packets from the interface socket buffers. As the thread reads
+packets from the buffers, they are added to an internal packet queue,
+and the server's main application thread processes packets from this
+queue rather than from the socket buffers. By structuring it this way, a
+configurable layer has been introduced which can make decisions on which
+packets to process, how to store them, and the order in which they are
+processed by the server.
+
+The default packet queue implementation for both ``kea-dhcp4`` and ``kea-dhcp6``
+is a simple ring buffer. Once it reaches capacity, new packets get added
+to the back of the queue by discarding packets from the front of the
+queue. Rather than always discarding the newest packets, Kea now always
+discards the oldest packets. The capacity of the buffer, i.e. the maximum
+number of packets the buffer can contain, is configurable. A reasonable
+starting point is to match the capacity to the number of leases
+per second a specific installation of Kea can handle. This
+figure varies widely depending on the specifics of an individual deployment.
+
+As there is no one algorithm that can best handle the dynamics of all
+sites, and because over time new approaches will evolve, the packet
+queue is implemented as a plug-in, which can be replaced by a custom queue
+implementation via a hook library. This should make it straightforward
+for interested parties to experiment with their own solutions.
+(Developers can refer to ``isc::dhcp::PacketQueue`` and
+``isc::dhcp::PacketQueueMgr``, described in the
+`Kea Developer's Guide <https://reports.kea.isc.org/dev_guide/index.html>`__.)
+
+Packet queue behavior is configured in both ``kea-dhcp4`` and ``kea-dhcp6``
+servers through an optional, top-level, configuration element,
+``dhcp-queue-control``. Omitting this element disables packet queueing:
+
+::
+
+      "dhcp-queue-control": {
+          "enable-queue": true|false,
+          "queue-type": "queue type",
+          "capacity" : n
+      }
+
+where:
+
+-  ``enable-queue`` - enables or disables packet queueing.
+   When ``true``, the server processes packets from the packet queue, which
+   is filled by a separate thread. When ``false``, the server processes
+   packets directly from the socket buffers in the main thread. It is
+   disabled (``false``) by default.
+
+-  ``queue-type`` - the name of the queue implementation to use. This value
+   exists so that custom implementations can be registered (via a hook
+   library) and then selected. There is a default packet queue
+   implementation that is pre-registered during server start up:
+   "kea-ring4" for ``kea-dhcp4`` and "kea-ring6" for ``kea-dhcp6``.
+
+-  ``capacity`` - this is the maximum number of packets the
+   queue can hold before packets are discarded. The optimal value for
+   this is extremely site-dependent. The default value is 64 for both
+   "kea-ring4" and "kea-ring6".
+
+The following example enables the default packet queue for ``kea-dhcp4``,
+with a queue capacity of 250 packets:
+
+::
+
+   "Dhcp4":
+   {
+       ...
+      "dhcp-queue-control": {
+          "enable-queue": true,
+          "queue-type": "kea-ring4",
+          "capacity" : 250
+       },
+       ...
+   }
+
+The following example enables the default packet queue for ``kea-dhcp6``,
+with a queue capacity of 300 packets:
+
+::
+
+   "Dhcp6":
+   {
+       ...
+      "dhcp-queue-control": {
+          "enable-queue": true,
+          "queue-type": "kea-ring6",
+          "capacity" : 300
+       },
+       ...
+   }
+
+.. note:
+
+   Congestion handling is currently incompatible with multi-threading;
+   when both are enabled, congestion handling is silently disabled.
diff --git a/doc/sphinx/arm/ctrl-channel.rst b/doc/sphinx/arm/ctrl-channel.rst
new file mode 100644
index 0000000..c6ebbf2
--- /dev/null
+++ b/doc/sphinx/arm/ctrl-channel.rst
@@ -0,0 +1,823 @@
+.. _ctrl-channel:
+
+**************
+Management API
+**************
+
+A classic approach to daemon configuration assumes that the server's
+configuration is stored in configuration files and, when the
+configuration is changed, the daemon is restarted. This approach has the
+significant disadvantage of introducing periods of downtime when client
+traffic is not handled. Another risk is that if the new configuration is
+invalid for any reason, the server may refuse to start, which will
+further extend the downtime period until the issue is resolved.
+
+To avoid such problems, the DHCPv4, DHCPv6, and D2 servers in Kea include
+support for a mechanism that allows online reconfiguration without
+requiring server shutdown. Both servers can be instructed to open
+control sockets, which is a communications channel. The server is able
+to receive commands on that channel, act on them, and report back
+status.
+
+The DHCPv4, DHCPv6, and D2 servers receive commands over the UNIX domain
+sockets. For details on how to configure these sockets, see
+:ref:`dhcp4-ctrl-channel` and :ref:`dhcp6-ctrl-channel`. While
+it is possible to control the servers directly using UNIX domain sockets,
+that requires that the controlling client be running on the same machine
+as the server. SSH is usually used to connect remotely to the controlled
+machine.
+
+Network administrators usually prefer using some form of a RESTful API
+to control the servers, rather than using UNIX domain sockets directly.
+Therefore, Kea includes a component called the Control Agent (CA), which
+exposes a RESTful API to the controlling clients and can forward
+commands to the respective Kea services over the UNIX domain sockets.
+The CA configuration is described in
+:ref:`agent-configuration`.
+
+The HTTP requests received by the CA contain the control commands
+encapsulated within HTTP requests. Simply speaking, the CA is
+responsible for stripping the HTTP layer from the received commands and
+forwarding the commands in a JSON format over the UNIX domain sockets to
+the respective services. Because the CA receives commands for all
+services, it requires additional "forwarding" information to be included
+in the client's messages. This forwarding information is carried within
+the ``service`` parameter of the received command. If the ``service``
+parameter is not included, or if the parameter is a blank list, the CA
+assumes that the control command is targeted at the CA itself and
+attempts to respond.
+
+Control connections over both HTTP and UNIX domain sockets are guarded
+with timeouts. The timeout value is set to 10 seconds and is not
+configurable.
+
+This API can be used by external tools to manage and monitor Kea operation.
+An example of such a monitoring tool is ISC's Stork. For details, see
+:ref:`stork`.
+
+.. _ctrl-channel-syntax:
+
+Data Syntax
+===========
+
+Communication over the control channel is conducted using JSON
+structures. If configured, Kea opens a socket and listens for
+incoming connections. A process connecting to this socket is expected to
+send JSON commands structured as follows:
+
+::
+
+   {
+       "command": "foo",
+       "service": [ "dhcp4" ]
+       "arguments": {
+           "param1": "value1",
+           "param2": "value2",
+           ...
+       }
+   }
+
+The same command sent over the RESTful interface to the CA has the
+following structure:
+
+::
+
+       POST / HTTP/1.1\r\n
+       Content-Type: application/json\r\n
+       Content-Length: 147\r\n\r\n
+       {
+           "command": "foo",
+           "service": [ "dhcp4" ]
+           "arguments": {
+               "param1": "value1",
+               "param2": "value2",
+               ...
+           }
+       }
+
+``command`` is the name of the command to execute and is mandatory.
+``arguments`` is a map of the parameters required to carry out the given
+command. The exact content and format of the map are command-specific.
+
+``service`` is a list of the servers at which the control command is
+targeted. In the example above, the control command is targeted at the
+DHCPv4 server. In most cases, the CA simply forwards this command to
+the DHCPv4 server for processing via a UNIX domain socket. Sometimes,
+the command including a service value may also be processed by the CA,
+if the CA is running a hook library which handles such a command for
+the given server. As an example, the hook library loaded by the CA may
+perform some operations on the database, such as adding host
+reservations, modifying leases, etc. An advantage of performing
+DHCPv4-specific administrative operations in the CA, rather than
+forwarding it to the DHCPv4 server, is the ability to perform these
+operations without disrupting the DHCPv4 service, since the DHCPv4
+server does not have to stop processing DHCP messages to apply changes to
+the database. Nevertheless, these situations are rather rare; in
+most cases, when the ``service`` parameter contains a name of the
+service, the commands are simply forwarded by the CA. The forwarded
+command includes the ``service`` parameter, but this parameter is ignored
+by the receiving server. This parameter is only meaningful to the CA.
+
+If the command received by the CA does not include a ``service``
+parameter or this list is empty, the CA simply processes this message on
+its own. For example, a ``config-get`` command which includes no service
+parameter returns the Control Agent's own configuration. The
+``config-get`` command with a service value "dhcp4" is forwarded to the DHCPv4
+server and returns the DHCPv4 server's configuration.
+
+The following list shows the mapping of the values carried within the
+``service`` parameter to the servers to which the commands are
+forwarded:
+
+-  ``dhcp4`` - the command is forwarded to the ``kea-dhcp4`` server.
+
+-  ``dhcp6`` - the command is forwarded to the ``kea-dhcp6`` server.
+
+-  ``d2`` - the command is forwarded to the ``kea-dhcp-ddns`` server.
+
+The server processing the incoming command sends a response of the
+form:
+
+::
+
+   {
+       "result": 0|1|2|3,
+       "text": "textual description",
+       "arguments": {
+           "argument1": "value1",
+           "argument2": "value2",
+           ...
+       }
+   }
+
+``result`` indicates the outcome of the command. A value of 0 means
+success, while any non-zero value designates an error or a failure to
+complete the requested action. Currently 1 indicates a generic error, 2
+means that a command is not supported, and 3 means that the requested
+operation was completed, but the requested object was not found. For
+example, a well-formed command that requests a subnet that exists in a
+server's configuration returns the result 0. If the server encounters an
+error condition, it returns 1. If the command asks for the IPv6 subnet,
+but was sent to a DHCPv4 server, it returns 2. If the query asks for a
+``subnet-id`` and there is no subnet with such an ID, the result is 3.
+
+The ``text`` field typically appears when the result is non-zero and
+contains a description of the error encountered, but it often also
+appears for successful outcomes. The exact text is command-specific, but
+in general uses plain English to describe the outcome of the command.
+``arguments`` is a map of additional data values returned by the server
+which are specific to the command issued. The map may be present, but
+that depends on the specific command.
+
+.. note::
+
+   Since Kea 1.9.7, it is possible to put comments in commands as
+   in the configuration file. For instance:
+
+::
+
+   {
+       "command": "foo",
+       // service is a list
+       "service": [ "dhcp4" ]
+       # command arguments are here.
+       "arguments": {
+           "param1": "value1"/*,
+           "param2": "value2",
+           ...*/
+       }
+   }
+
+.. _ctrl-channel-control-agent-command-response-format:
+
+Control Agent Command Response Format
+=====================================
+
+When sending commands via the Control Agent, it is possible to specify
+multiple services at which the command is targeted. CA forwards this
+command to each service individually. Thus, the CA response to the
+controlling client is always wrapped in an array (JSON list) of
+individual responses.  For example, the response for a command sent
+to one service would be structured as follows:
+
+::
+
+    [
+        {
+            "result": 0|1|2|3,
+            "text": "textual description",
+            "arguments": {
+                "argument1": "value1",
+                "argument2": "value2",
+            ...
+        }
+    ]
+
+
+If the command is sent to more than one service, the array would
+contain responses from each service, in the order they were requested:
+
+::
+
+    [
+        {
+            "result": 0|1|2|3,
+            "text": "textual description",
+            "arguments": {
+                "argument1": "value1",
+                "argument2": "value2",
+            ...
+        },
+        {
+            "result": 0|1|2|3,
+            "text": "textual description",
+            "arguments": {
+                "argument1": "value1",
+                "argument2": "value2",
+            ...
+        },
+        ...
+    ]
+
+An exception to this are authentication or authorization errors which cause CA
+to reject the entirely.  The response to such an error will be formatted
+as a single entry (JSON map) as follows:
+
+::
+
+    {
+        "result": 403,
+        "text": "Forbidden"
+    }
+
+
+These types of errors are possible on systems configured for either basic
+authentication or agents that load the RBAC hook library.
+
+.. _ctrl-channel-client:
+
+Using the Control Channel
+=========================
+
+The easiest way to start interacting with the control API is to use
+common UNIX/Linux tools such as ``socat`` and ``curl``.
+
+In order to control the given Kea service via a UNIX domain socket, use
+``socat`` in interactive mode as follows:
+
+.. code-block:: console
+
+   $ socat UNIX:/path/to/the/kea/socket -
+
+or in batch mode, include the "ignoreeof" option as shown below to
+ensure ``socat`` waits long enough for the server to respond:
+
+.. code-block:: console
+
+   $ echo "{ some command...}" | socat UNIX:/path/to/the/kea/socket -,ignoreeof
+
+where ``/path/to/the/kea/socket`` is the path specified in the
+``Dhcp4/control-socket/socket-name`` parameter in the Kea configuration
+file. Text passed to ``socat`` is sent to Kea and the responses received
+from Kea are printed to standard output. This approach communicates with
+the specific server directly and bypasses the Control Agent.
+
+It is also easy to open a UNIX socket programmatically. An example of a
+simple client written in C is available in the Kea Developer's Guide, in
+the Control Channel Overview chapter, in the
+`Using Control Channel <https://reports.kea.isc.org/dev_guide/d2/d96/ctrlSocket.html#ctrlSocketClient>`__
+section.
+
+To use Kea's RESTful API with ``curl``, use the following:
+
+.. code-block:: console
+
+   $ curl -X POST -H "Content-Type: application/json" -d '{ "command": "config-get", "service": [ "dhcp4" ] }' http://ca.example.org:8000/
+
+This assumes that the Control Agent is running on host
+``ca.example.org`` and is running the RESTful service on port 8000.
+
+.. _commands-common:
+
+Commands Supported by Both the DHCPv4 and DHCPv6 Servers
+========================================================
+
+.. _command-build-report:
+
+The ``build-report`` Command
+----------------------------
+
+The ``build-report`` command returns on the control channel what the
+command line ``-W`` argument displays, i.e. the embedded content of the
+``config.report`` file. This command does not take any parameters.
+
+::
+
+   {
+       "command": "build-report"
+   }
+
+.. _command-config-get:
+
+The ``config-get`` Command
+--------------------------
+
+The ``config-get`` command retrieves the current configuration used by the
+server. This command does not take any parameters. The configuration
+returned is roughly equal to the configuration that was loaded using the
+``-c`` command-line option during server start-up, or was later set using the
+``config-set`` command. However, there may be certain differences, as
+comments are not retained. If the original configuration used file
+inclusion, the returned configuration will include all parameters from
+all included files.
+
+.. warning::
+
+   The returned configuration is not redacted, i.e. it
+   contains database passwords in plain text, if those were specified in the
+   original configuration. Care should be taken not to expose the command
+   channel to unprivileged users.
+
+An example command invocation looks like this:
+
+::
+
+   {
+       "command": "config-get"
+   }
+
+.. _command-config-reload:
+
+The ``config-reload`` Command
+-----------------------------
+
+The ``config-reload`` command instructs Kea to load again the
+configuration file that was used previously. This operation is useful if
+the configuration file has been changed by some external source; for
+example, a system administrator can tweak the configuration file and use this
+command to force Kea pick up the changes.
+
+Caution should be taken when mixing this with ``config-set`` commands. Kea
+remembers the location of the configuration file it was started with,
+and this configuration can be significantly changed using the ``config-set``
+command. When ``config-reload`` is issued after ``config-set``, Kea attempts
+to reload its original configuration from the file, possibly losing all
+changes introduced using ``config-set`` or other commands.
+
+``config-reload`` does not take any parameters. An example command
+invocation looks like this:
+
+::
+
+   {
+       "command": "config-reload"
+   }
+
+If the configuration file is incorrect, reloading it can raise an error
+which leaves the server in an unusable state. See :ref:`command-config-set`
+to learn how to recover from a non-working server.
+
+.. _command-config-test:
+
+The ``config-test`` Command
+---------------------------
+
+The ``config-test`` command instructs the server to check whether the new
+configuration supplied in the command's arguments can be loaded. The
+supplied configuration is expected to be the full configuration for the
+target server, along with an optional logger configuration. The configuration
+is sanity-checked to the extent possible without the server actually
+attempting to load it; it is possible for a configuration which successfully
+passes this command to still fail in the ``config-set`` command or at launch
+time. The structure of the command is as follows:
+
+::
+
+   {
+       "command": "config-test",
+       "arguments":  {
+           "<server>": {
+           }
+        }
+   }
+
+where <server> is the configuration element name for a given server, such
+as "Dhcp4" or "Dhcp6". For example:
+
+::
+
+   {
+       "command": "config-test",
+       "arguments":  {
+           "Dhcp6": {
+               :
+           }
+        }
+   }
+
+The server's response contains a numeric code, ``result`` (0 for
+success, non-zero on failure), and a string, ``text``, describing the
+outcome:
+
+::
+
+       {"result": 0, "text": "Configuration seems sane..." }
+
+       or
+
+       {"result": 1, "text": "unsupported parameter: BOGUS (<string>:16:26)" }
+
+.. _command-config-write:
+
+The ``config-write`` Command
+----------------------------
+
+The ``config-write`` command instructs the Kea server to write its current
+configuration to a file on disk. It takes one optional argument, called
+"filename", that specifies the name of the file to write the
+configuration to. If not specified, the name used when starting Kea
+(passed as a ``-c`` argument) is used. If a relative path is specified,
+Kea writes its files only in the directory where it is running.
+
+An example command invocation looks like this:
+
+::
+
+   {
+       "command": "config-write",
+       "arguments": {
+           "filename": "config-modified-2017-03-15.json"
+       }
+   }
+
+.. _command-leases-reclaim:
+
+The ``leases-reclaim`` Command
+------------------------------
+
+The ``leases-reclaim`` command instructs the server to reclaim all expired
+leases immediately. The command has the following JSON syntax:
+
+::
+
+   {
+       "command": "leases-reclaim",
+       "arguments": {
+           "remove": true
+       }
+   }
+
+The ``remove`` boolean parameter is mandatory and indicates whether the
+reclaimed leases should be removed from the lease database (if ``true``), or
+left in the ``expired-reclaimed`` state (if ``false``). The latter facilitates
+lease affinity, i.e. the ability to re-assign an expired lease to a
+returning client that previously used that lease. See :ref:`lease-affinity`
+for details. Also, see :ref:`lease-reclamation` for general
+information about the processing of expired leases (lease reclamation).
+
+.. _command-libreload:
+
+The ``libreload`` Command
+-------------------------
+
+The ``libreload`` command first unloads and then loads all currently
+loaded hook libraries. This is primarily intended to allow one or more
+hook libraries to be replaced with newer versions, without requiring Kea
+servers to be reconfigured or restarted. The hook libraries
+are passed the same parameter values (if any) that were passed when they
+originally loaded.
+
+::
+
+   {
+       "command": "libreload",
+       "arguments": { }
+   }
+
+The server responds with a result of either 0, indicating success,
+or 1, indicating failure.
+
+.. _command-list-commands:
+
+The ``list-commands`` Command
+-----------------------------
+
+The ``list-commands`` command retrieves a list of all commands supported
+by the server. It does not take any arguments. An example command may
+look like this:
+
+::
+
+   {
+       "command": "list-commands",
+       "arguments": { }
+   }
+
+The server responds with a list of all supported commands. The arguments
+element is a list of strings, each of which conveys one supported
+command.
+
+.. _command-config-set:
+
+The ``config-set`` Command
+--------------------------
+
+The ``config-set`` command instructs the server to replace its current
+configuration with the new configuration supplied in the command's
+arguments. The supplied configuration is expected to be the full
+configuration for the target server, along with an optional logger
+configuration. While optional, the logger configuration is highly
+recommended, as without it the server reverts to its default logging
+configuration. The structure of the command is as follows:
+
+::
+
+   {
+       "command": "config-set",
+       "arguments":  {
+           "<server>": {
+           }
+        }
+   }
+
+where <server> is the configuration element name for a given server, such
+as "Dhcp4" or "Dhcp6". For example:
+
+::
+
+   {
+       "command": "config-set",
+       "arguments":  {
+           "Dhcp6": {
+               :
+           }
+        }
+   }
+
+If the new configuration proves to be invalid, the server retains its
+current configuration; however, in some cases a fatal error message is logged
+indicating that the server no longer provides any service: a working
+configuration must be loaded as soon as possible. If the control channel
+is dead, the configuration file can still be reloaded using the ``SIGHUP``
+signal. If that is unsuccessful, restart the server.
+
+Please note that the new configuration is
+retained in memory only; if the server is restarted or a configuration
+reload is triggered via a signal, the server uses the configuration
+stored in its configuration file. The server's response contains a
+numeric code, ``result`` (0 for success, non-zero on failure), and a
+string, ``text``, describing the outcome:
+
+::
+
+       {"result": 0, "text": "Configuration successful." }
+
+       or
+
+       {"result": 1, "text": "unsupported parameter: BOGUS (<string>:16:26)" }
+
+.. _command-shutdown:
+
+The ``shutdown`` Command
+------------------------
+
+The ``shutdown`` command instructs the server to initiate its shutdown
+procedure. It is the equivalent of sending a ``SIGTERM`` signal to the
+process. This command does not take any arguments. An example command
+may look like this:
+
+::
+
+   {
+       "command": "shutdown"
+       "arguments": {
+           "exit-value": 3
+       }
+   }
+
+The server responds with a confirmation that the shutdown procedure has
+been initiated.  The optional parameter, ``exit-value``, specifies the
+numeric value with which the server process exits to the system.
+The default value is zero.
+
+The DDNS daemon supports an extra parameter, ``type``, which controls the way
+the process cleans up on exit. The supported shutdown types are:
+
+ -  "normal" - stops the queue manager and finishes all current transactions
+    before exiting. This is the default.
+
+ -  "drain_first" - stops the queue manager but continues processing requests
+    from the queue until it is empty.
+
+ -  "now" - exits immediately.
+
+An example command may look like this:
+
+::
+
+   {
+       "command": "shutdown"
+       "arguments": {
+           "exit-value": 3,
+           "type": "drain_first"
+       }
+   }
+
+.. _command-dhcp-disable:
+
+The ``dhcp-disable`` Command
+----------------------------
+
+The ``dhcp-disable`` command globally disables the DHCP service. The
+server continues to operate, but it drops all received DHCP messages.
+This command is useful when the server's maintenance requires that the
+server temporarily stop allocating new leases and renew existing leases.
+It is also useful in failover-like configurations during a
+synchronization of the lease databases at startup, or recovery after a
+failure. The optional parameter ``max-period`` specifies the time in
+seconds after which the DHCP service should be automatically re-enabled,
+if the ``dhcp-enable`` command is not sent before this time elapses.
+
+Since Kea 1.9.4, there is an additional ``origin`` parameter that specifies the
+command source. A server administrator should typically omit this parameter
+because the default value "user" indicates that the administrator sent the
+command. This command can also be sent by the partner server running HA hooks
+library. In that case, the partner server sets the parameter to "ha-partner".
+This value is reserved for the communication between HA partners and should not
+be specified in the administrator's commands, as it may interfere with
+HA operation. The administrator should either omit this parameter or set it to
+"user".
+
+::
+
+   {
+       "command": "dhcp-disable",
+       "arguments": {
+           "max-period": 20,
+           "origin": "user"
+       }
+   }
+
+.. _command-dhcp-enable:
+
+The ``dhcp-enable`` Command
+---------------------------
+
+The ``dhcp-enable`` command globally enables the DHCP service.
+
+Since Kea 1.9.4, there is an additional ``origin`` parameter that specifies the
+command source. A server administrator should typically omit this parameter
+because the default value "user" indicates that the administrator sent the
+command. This command can also be sent by the partner server running the HA hook
+library. In that case, the partner server sets the parameter to "ha-partner".
+This value is reserved for the communication between HA partners and should not
+be specified in the administrator's commands, as it may interfere with
+HA operation. The administrator should either omit this parameter or set it to
+"user".
+
+::
+
+   {
+       "command": "dhcp-enable",
+       "arguments": {
+           "origin": "user"
+       }
+   }
+
+.. _command-status-get:
+
+The ``status-get`` Command
+--------------------------
+
+The ``status-get`` command returns the server's runtime information:
+
+ - ``pid``: the process ID.
+
+ - ``uptime``: the number of seconds since the start of the server.
+
+ - ``reload``: the number of seconds since the last configuration (re)load.
+
+ - ``high-availability``: HA-specific status information about the DHCP servers
+   configured to use the HA hook library:
+
+     * ``local``: the state, the role (primary,
+       secondary, ...), and the scopes (i.e. what the server is actually
+       processing) of the local server.
+
+     * ``remote``: the remote server's last known state, its served
+       HA scopes, and the role of the remote server in the HA relationship.
+
+ - ``multi-threading-enabled``: a flag indicating whether multi-threading is enabled.
+
+ - ``thread-pool-size``: the number of DHCP service threads.
+
+ - ``packet-queue-size``: the maximum size of the packet queue. There is one queue,
+   regardless of the number of running threads.
+
+ - ``packet-queue-statistics``: the average queue size for the last 10, 100, and 1000
+   packets, using an approach similar to the UNIX ``top`` command.
+   The average queue size for the last 10 packets can be considered an
+   instantaneous value, while the average for the last 1000 packets shows
+   a longer-term trend.
+
+The ``high-availability`` information is returned only when the command is
+sent to the DHCP servers in an HA setup. This parameter is
+never returned when the ``status-get`` command is sent to the
+Control Agent or DDNS daemon.
+
+The ``thread-pool-size``, ``packet-queue-size`` and
+``packet-queue-statistics`` parameters are returned only when the
+command is sent to DHCP servers with multi-threading enabled. These
+three parameters and ``multi-threading-enabled`` are never returned when
+the ``status-get`` command is sent to the Control Agent or DDNS daemon.
+
+To learn more about the HA status information returned by the
+``status-get`` command, please refer to the :ref:`command-ha-status-get`
+section.
+
+
+.. _command-server-tag-get:
+
+The ``server-tag-get`` Command:
+-------------------------------
+
+The ``server-tag-get`` command returns the configured server tag of
+the DHCPv4 or DHCPv6 server (:ref:`cb-sharing` explains the server tag concept).
+
+.. _command-config-backend-pull:
+
+The ``config-backend-pull`` Command:
+------------------------------------
+
+The ``config-backend-pull`` command triggers the polling of configuration backends
+(which must be configured for this command to have an effect),
+explained in :ref:`dhcp4-cb-json`.
+
+.. _command-version-get:
+
+The ``version-get`` Command
+---------------------------
+
+The ``version-get`` command returns extended information about the Kea
+version. It is the same information available via the ``-V``
+command-line argument. This command does not take any parameters.
+
+::
+
+   {
+       "command": "version-get"
+   }
+
+Commands Supported by the D2 Server
+===================================
+
+The D2 server supports only a subset of the DHCPv4/DHCPv6 server commands:
+
+-  ``build-report``
+
+-  ``config-get``
+
+-  ``config-reload``
+
+-  ``config-set``
+
+-  ``config-test``
+
+-  ``config-write``
+
+-  ``list-commands``
+
+-  ``shutdown``
+
+-  ``status-get``
+
+- ``version-get``
+
+.. _agent-commands:
+
+Commands Supported by the Control Agent
+=======================================
+
+The following commands, listed in :ref:`commands-common`, are also supported by the
+Control Agent; when the ``service`` parameter is blank, the
+commands are handled by the CA and they relate to the CA process itself:
+
+-  ``build-report``
+
+-  ``config-get``
+
+-  ``config-reload``
+
+-  ``config-set``
+
+-  ``config-test``
+
+-  ``config-write``
+
+-  ``list-commands``
+
+-  ``shutdown``
+
+-  ``status-get``
+
+-  ``version-get``
diff --git a/doc/sphinx/arm/database-connectivity.rst b/doc/sphinx/arm/database-connectivity.rst
new file mode 100644
index 0000000..6ece268
--- /dev/null
+++ b/doc/sphinx/arm/database-connectivity.rst
@@ -0,0 +1,84 @@
+.. _database-connectivity:
+
+*********************
+Database Connectivity
+*********************
+The Kea servers (``kea-dhcp4`` and ``kea-dhcp6``) can be configured to use a variety of
+database backends for leases, hosts, and configuration. They can be
+configured to support automatic recovery when connectivity is lost, via
+the ``on-fail`` parameter. (The ``reconnect-wait-time`` and
+``max-reconnect-tries`` parameters are described
+in :ref:`database-configuration4` and :ref:`database-configuration6`.)
+
+It is important to understand how and when automatic recovery comes into play.
+Automatic recovery, when configured, only operates after a successful startup
+or reconfiguration during which connectivity to all backends has been
+successfully established.
+
+During server startup, the inability to connect to any of the configured
+backends is always considered fatal. A fatal error is logged and the server
+exits, based on the idea that the configuration should be valid
+at startup. Exiting to the operating system allows nanny scripts to detect
+the problem.
+
+During dynamic reconfiguration, all backends are disconnected and then
+reconnected using the new configuration. If connectivity to any of the
+backends cannot be established, the server logs a fatal error but remains
+up. It is able to process commands but does not serve clients. This
+allows the configuration to be corrected via the ``config-set`` or
+``remote-*`` commands, if required.
+
+During normal operations, if connectivity to any of the backends is lost and
+automatic recovery for that backend is enabled, the server disconnects from the
+respective backend and then attempts to reconnect. During the recovery process,
+the server ceases to serve clients according to the ``on-fail`` configured
+option but continues to respond to commands.
+
+The ``on-fail`` parameter configures the actions the server should take when a
+connection is lost. It can have one of the following values:
+
+-  ``stop-retry-exit`` - indicates that the server should stop the service
+   while it tries to recover the connection, and exit if recovery is not
+   successful after ``max-reconnect-tries``.
+
+-  ``serve-retry-exit`` - indicates that the server should not stop the
+   service while it tries to recover the connection, and exit if recovery is not
+   successful after ``max-reconnect-tries``.
+
+-  ``serve-retry-continue`` - indicates that the server should not stop the
+   service while it tries to recover the connection, and not exit if recovery is
+   not successful after ``max-reconnect-tries``.
+
+If connectivity to all backends is restored, the server returns to normal
+operations. If the connection cannot be restored and the server is configured
+to exit, it issues a fatal error before shutdown.
+
+The connection to the database server can optionally be protected by TLS.
+Corresponding database configuration parameters for Kea servers are:
+
+-  The ``trust-anchor`` specifies the Certification Authority file name or
+   directory path.
+
+-  The ``cert-file`` specifies the client certificate file name.
+
+-  The ``key-file`` specifies the private key file name.
+
+-  The ``cipher-list`` specifies the list of TLS ciphers (the syntax of
+   the content of this parameter is described in the OpenSSL ciphers
+   manual).
+
+These parameters are similar to the parameters of the secure connections
+with the agent but are interpreted by different backends using database
+configurations too.
+
+Currently the support for each database is:
+
+-  MySQL supports the whole set, additional configuration must be done
+   in the MySQL local setup, for instance certificate revocation list,
+   choice of a specific TLS version, mutual authentication, etc.
+   When a TLS connection was required but the actual connection is in
+   clear text an error log is emitted.
+
+-  PostgreSQL only uses the configuration to enable the SSL/TLS support
+   in the client library (libpq). Anything else must be done in the
+   PostgreSQL local configuration.
diff --git a/doc/sphinx/arm/ddns.rst b/doc/sphinx/arm/ddns.rst
new file mode 100644
index 0000000..52d1996
--- /dev/null
+++ b/doc/sphinx/arm/ddns.rst
@@ -0,0 +1,1011 @@
+.. _dhcp-ddns-server:
+
+********************
+The DHCP-DDNS Server
+********************
+
+.. _dhcp-ddns-overview:
+
+Overview
+========
+
+The DHCP-DDNS Server (``kea-dhcp-ddns``, known informally as D2) conducts
+the client side of the Dynamic DNS protocol (DDNS, defined in `RFC
+2136 <https://tools.ietf.org/html/rfc2136>`__) on behalf of the DHCPv4
+and DHCPv6 servers (``kea-dhcp4`` and ``kea-dhcp6`` respectively). The DHCP
+servers construct DDNS update requests, known as NameChangeRequests
+(NCRs), based on DHCP lease change events and then post them to D2. D2
+attempts to match each request to the appropriate DNS server(s) and
+carries out the necessary conversation with those servers to update the
+DNS data.
+
+.. _dhcp-ddns-dns-server-selection:
+
+DNS Server Selection
+--------------------
+
+To match a request to the appropriate DNS servers, D2 must have
+a catalog of servers from which to select. In fact, D2 has two such
+catalogs, one for forward DNS and one for reverse DNS; these catalogs
+are referred to as "DDNS domain lists." Each list consists of one or more
+named DDNS domains. Further, each DDNS domain has a list of one or more
+DNS servers that publish the DNS data for that domain.
+
+When conducting forward-domain matching, D2 compares the fully qualified
+domain name (FQDN) in the request against the name of each forward DDNS
+domain in its catalog. The domain whose name matches the longest portion
+of the FQDN is considered the best match. For example, if the FQDN is
+"myhost.sample.example.com.", and there are two forward domains in the
+catalog, "sample.example.com." and "example.com.", the former is
+regarded as the best match. In some cases, it may not be possible to
+find a suitable match. Given the same two forward domains there would be
+no match for the FQDN "bogus.net", so the request would be rejected.
+Finally, if there are no forward DDNS domains defined, D2 simply
+disregards the forward-update portion of requests.
+
+When conducting reverse-domain matching, D2 constructs a reverse FQDN
+from the lease address in the request and compares that against the name
+of each reverse DDNS domain. Again, the domain whose name matches the
+longest portion of the FQDN is considered the best match. For instance,
+if the lease address is "172.16.1.40" and there are two reverse domains
+in the catalog, "1.16.172.in-addr.arpa." and "16.172.in-addr.arpa", the
+former is the best match. As with forward matching, D2 may not find a
+suitable match. Given the same two domains, there would be no match for
+the lease address, "192.168.1.50", and the request would be rejected.
+As with forward-domain matching, if there are no reverse DDNS domains defined, D2 simply
+disregards the reverse-update portion of requests.
+
+.. _dhcp-ddns-conflict-resolution:
+
+Conflict Resolution
+-------------------
+
+D2 implements the conflict resolution strategy prescribed by `RFC
+4703 <https://tools.ietf.org/html/rfc4703>`__. Conflict resolution is
+intended to prevent different clients from mapping to the same FQDN at
+the same time. To make this possible, the RFC requires that forward DNS
+entries for a given FQDN must be accompanied by a DHCID resource record
+(RR). This record contains a client identifier that uniquely identifies
+the client to whom the name belongs. Furthermore, any DNS updater that
+wishes to update or remove existing forward entries for an FQDN may only
+do so if their client matches that of the DHCID RR.
+
+In other words, the DHCID RR maps an FQDN to the client to whom it
+belongs, and thereafter changes to that mapping can only be done by
+or at the behest of that client.
+
+Conflict resolution can be indirectly enabled or disabled via
+the configuration parameter ``ddns-use-conflict-resolution``, supported
+by both ``kea-dhcp4`` and ``kea-dhcp6``. These servers use this parameter to
+set a flag within each NameChangeRequest they send that tells D2
+whether conflict resolution should be employed for that request.
+By default, conflict resolution is enabled. For more details, please refer
+to discussions of ``ddns-use-conflict-resolution`` in :ref:`dhcp4-ddns-config` and :ref:`dhcp6-ddns-config`.
+
+When conflict resolution is disabled, D2 still adds DHCID RRs but does
+not use them to enforce client ownership of DNS entries. Disabling it should
+only be used after careful consideration.
+
+.. _dhcp-ddns-dual-stack:
+
+Dual-Stack Environments
+-----------------------
+
+`RFC 4703, section
+5.2, <https://tools.ietf.org/html/rfc4703#section-5.2>`__ describes
+issues that may arise with dual-stack clients. These are clients that
+wish to have both IPv4 and IPv6 mappings for the same FQDN.
+To work properly, clients must embed their IPv6 DUID
+within their IPv4 client identifier option, as described in `RFC
+4361 <https://tools.ietf.org/html/rfc4361>`__. In this way, DNS updates
+for both IPv4 and IPv6 can be managed under the same DHCID RR. This feature
+is supported by Kea beginning with release 2.1.2.
+
+.. _dhcp-ddns-server-start-stop:
+
+Starting and Stopping the DHCP-DDNS Server
+==========================================
+
+``kea-dhcp-ddns`` is the Kea DHCP-DDNS server and, due to the nature of
+DDNS, it runs alongside either the DHCPv4 or DHCPv6 component (or both).
+Like other parts of Kea, it is a separate binary that can be run on its
+own or through ``keactrl`` (see :ref:`keactrl`). In normal
+operation, controlling ``kea-dhcp-ddns`` with ``keactrl`` is
+recommended; however, it is also possible to run the DHCP-DDNS server
+directly. It accepts the following command-line switches:
+
+-  ``-c file`` - specifies the configuration file. This is the only
+   mandatory switch.
+
+-  ``-d`` - specifies whether server logging should be switched to
+   debug/verbose mode. In verbose mode, the logging severity and
+   debuglevel specified in the configuration file are ignored and
+   "debug" severity and the maximum debuglevel (99) are assumed. The
+   flag is convenient for temporarily switching the server into maximum
+   verbosity, e.g. when debugging.
+
+-  ``-v`` - displays the Kea version and exits.
+
+-  ``-W`` - displays the Kea configuration report and exits. The report
+   is a copy of the ``config.report`` file produced by ``./configure``;
+   it is embedded in the executable binary.
+
+-  ``-t file`` - specifies the configuration file to be tested.
+   ``kea-dhcp-ddns`` attempts to load it and conducts sanity checks.
+   Certain checks are possible only while running the actual
+   server. The actual status is reported with an exit code (0 =
+   configuration looks okay, 1 = error encountered). Kea prints out log
+   messages to standard output and errors to standard error when testing
+   the configuration.
+
+The ``config.report`` file may also be accessed directly, via the
+following command. The binary ``path`` may be found in the install
+directory or in the ``.libs`` subdirectory in the source tree. For
+example: ``kea/src/bin/d2/.libs/kea-dhcp-ddns``.
+
+::
+
+   strings path/kea-dhcp-ddns | sed -n 's/;;;; //p'
+
+Upon startup, the module loads its configuration and begins listening
+for NCRs based on that configuration.
+
+During startup, the server attempts to create a PID file of the form:
+``[runstatedir]/[conf name].kea-dhcp-ddns.pid`` where:
+
+-  ``runstatedir`` - is the value as passed into the build configure
+   script; it defaults to "/usr/local/var/run". Note that this value may be
+   overridden at runtime by setting the environment variable
+   ``KEA_PIDFILE_DIR``. This is intended primarily for testing purposes.
+
+-  ``conf name`` - is the configuration file name used to start the server,
+   minus all preceding paths and the file extension. For example, given
+   a pathname of "/usr/local/etc/kea/myconf.txt", the portion used would
+   be "myconf".
+
+If the file already exists and contains the PID of a live process, the
+server issues a ``DHCP_DDNS_ALREADY_RUNNING`` log message and exits. It
+is possible, though unlikely, that the file is a remnant of a system
+crash and the process to which the PID belongs is unrelated to Kea. In
+such a case it is necessary to manually delete the PID file.
+
+.. _d2-configuration:
+
+Configuring the DHCP-DDNS Server
+================================
+
+Before starting the ``kea-dhcp-ddns`` module for the first time, a
+configuration file must be created. The following default configuration
+is a template that can be customized to individual requirements.
+
+::
+
+   "DhcpDdns": {
+       "ip-address": "127.0.0.1",
+       "port": 53001,
+       "dns-server-timeout": 100,
+       "ncr-protocol": "UDP",
+       "ncr-format": "JSON",
+       "tsig-keys": [ ],
+       "forward-ddns": {
+           "ddns-domains": [ ]
+       },
+       "reverse-ddns": {
+           "ddns-domains": [ ]
+       }
+   }
+
+The configuration can be divided into the following sections, each of
+which is described below:
+
+-  *Global Server Parameters* - define values which control connectivity and
+   global server behavior.
+
+-  *Control Socket* - defines the Control Socket type and name.
+
+-  *TSIG Key Info* - defines the TSIG keys used for secure traffic with
+   DNS servers.
+
+-  *Forward DDNS* - defines the catalog of forward DDNS domains.
+
+-  *Reverse DDNS* - defines the catalog of reverse DDNS domains.
+
+.. _d2-server-parameter-config:
+
+Global Server Parameters
+------------------------
+
+-  ``ip-address`` - the IP address on which D2 listens for requests. The
+   default is the local loopback interface at address 127.0.0.1.
+   Either an IPv4 or IPv6 address may be specified.
+
+-  ``port`` - the port on which D2 listens for requests. The default value
+   is 53001.
+
+-  ``dns-server-timeout`` - the maximum amount of time, in milliseconds,
+   that D2 will wait for a response from a DNS server to a single DNS
+   update message.
+
+-  ``ncr-protocol`` - the socket protocol to use when sending requests to
+   D2. Currently only UDP is supported.
+
+-  ``ncr-format`` - the packet format to use when sending requests to D2.
+   Currently only JSON format is supported.
+
+D2 must listen for change requests on a known address and port. By
+default it listens at 127.0.0.1 on port 53001. The following example
+illustrates how to change D2's global parameters so it will listen at
+192.168.1.10 port 900:
+
+::
+
+   "DhcpDdns": {
+       "ip-address": "192.168.1.10",
+       "port": 900,
+       ...
+       }
+   }
+
+.. warning::
+
+   It is possible for a malicious attacker to send bogus
+   NameChangeRequests to the DHCP-DDNS server. Addresses other than the
+   IPv4 or IPv6 loopback addresses (127.0.0.1 or ::1) should only be
+   used for testing purposes; note that local users may still
+   communicate with the DHCP-DDNS server.
+
+.. note::
+
+   If the ``ip-address`` and ``port`` are changed, the corresponding values in
+   the DHCP servers' ``dhcp-ddns`` configuration section must be changed.
+
+.. _d2-ctrl-channel:
+
+Management API for the D2 Server
+--------------------------------
+
+The management API allows the issuing of specific management commands,
+such as configuration retrieval or shutdown. For more details, see
+:ref:`ctrl-channel`. Currently, the only supported communication
+channel type is the UNIX stream socket. By default there are no sockets
+open; to instruct Kea to open a socket, the following entry in the
+configuration file can be used:
+
+::
+
+   "DhcpDdns": {
+       "control-socket": {
+           "socket-type": "unix",
+           "socket-name": "/path/to/the/unix/socket"
+       },
+       ...
+   }
+
+The length of the path specified by the ``socket-name`` parameter is
+restricted by the maximum length for the UNIX socket name on the
+operating system, i.e. the size of the ``sun_path`` field in the
+``sockaddr_un`` structure, decreased by 1. This value varies on
+different operating systems, between 91 and 107 characters. Typical
+values are 107 on Linux and 103 on FreeBSD.
+
+Communication over the control channel is conducted using JSON structures.
+See the `Control Channel section in the Kea Developer's
+Guide <https://reports.kea.isc.org/dev_guide/d2/d96/ctrlSocket.html>`__
+for more details.
+
+The D2 server supports the following operational commands:
+
+-  build-report
+-  config-get
+-  config-reload
+-  config-set
+-  config-test
+-  config-write
+-  list-commands
+-  shutdown
+-  status-get
+-  version-get
+
+Since Kea version 2.0.0, the D2 server also supports the following
+operational commands for statistics:
+
+-  statistic-get
+-  statistic-get-all
+-  statistic-reset
+-  statistic-reset-all
+
+The ``shutdown`` command supports the extra ``type`` argument, which controls the
+way the D2 server cleans up on exit.
+The supported shutdown types are:
+
+-  ``normal`` - stops the queue manager and finishes all current transactions
+   before exiting. This is the default.
+
+-  ``drain_first`` - stops the queue manager but continues processing requests
+   from the queue until it is empty.
+
+-  ``now`` - exits immediately.
+
+An example command may look like this:
+
+::
+
+   {
+       "command": "shutdown"
+       "arguments": {
+           "exit-value": 3,
+           "type": "drain_first"
+       }
+   }
+
+.. _d2-tsig-key-list-config:
+
+TSIG Key List
+-------------
+
+A DDNS protocol exchange can be conducted with or without a transaction
+signature, or TSIG (defined
+in `RFC 2845 <https://tools.ietf.org/html/rfc2845>`__). This
+configuration section allows the administrator to define the set of TSIG
+keys that may be used in such exchanges.
+
+To use TSIG when updating entries in a DNS domain, a key must be defined
+in the TSIG key list and referenced by name in that domain's
+configuration entry. When D2 matches a change request to a domain, it
+checks whether the domain has a TSIG key associated with it. If so, D2
+uses that key to sign DNS update messages sent to and verify
+responses received from the domain's DNS server(s). For each TSIG key
+required by the DNS servers that D2 is working with, there must be
+a corresponding TSIG key in the TSIG key list.
+
+As one might gather from the name, the ``tsig-key`` section of the D2
+configuration lists the TSIG keys. Each entry describes a TSIG key used
+by one or more DNS servers to authenticate requests and sign responses.
+Every entry in the list has three parameters:
+
+-  ``name`` - is a unique text label used to identify this key within the
+   list. This value is used to specify which key (if any) should be used
+   when updating a specific domain. As long as the name is unique its
+   content is arbitrary, although for clarity and ease of maintenance it
+   is recommended that it match the name used on the DNS server(s). This
+   field cannot be blank.
+
+-  ``algorithm`` - specifies which hashing algorithm should be used with
+   this key. This value must specify the same algorithm used for the key
+   on the DNS server(s). The supported algorithms are listed below:
+
+   -  HMAC-MD5
+   -  HMAC-SHA1
+   -  HMAC-SHA224
+   -  HMAC-SHA256
+   -  HMAC-SHA384
+   -  HMAC-SHA512
+
+   This value is not case-sensitive.
+
+-  ``digest-bits`` - is used to specify the minimum truncated length in
+   bits. The default value 0 means truncation is forbidden; non-zero
+   values must be an integral number of octets, and be greater than both
+   80 and half of the full length. (Note that in BIND 9 this parameter
+   is appended to the algorithm name, after a dash.)
+
+-  ``secret`` - is used to specify the shared secret key code for this
+   key. This value is case-sensitive and must exactly match the value
+   specified on the DNS server(s). It is a base64-encoded text value.
+
+As an example, suppose that a domain D2 will be updating is maintained
+by a BIND 9 DNS server, which requires dynamic updates to be secured
+with TSIG. Suppose further that the entry for the TSIG key in BIND 9's
+named.conf file looks like this:
+
+::
+
+      :
+      key "key.four.example.com." {
+          algorithm hmac-sha224;
+          secret "bZEG7Ow8OgAUPfLWV3aAUQ==";
+      };
+      :
+
+By default, the TSIG key list is empty:
+
+::
+
+   "DhcpDdns": {
+      "tsig-keys": [ ],
+      ...
+   }
+
+A new key must be added to the list:
+
+::
+
+   "DhcpDdns": {
+       "tsig-keys": [
+           {
+               "name": "key.four.example.com.",
+               "algorithm": "HMAC-SHA224",
+               "secret": "bZEG7Ow8OgAUPfLWV3aAUQ=="
+           }
+       ],
+       ...
+   }
+
+These steps must be repeated for each TSIG key needed, although the
+same TSIG key can be used with more than one domain.
+
+.. _d2-forward-ddns-config:
+
+Forward DDNS
+------------
+
+The forward DDNS section is used to configure D2's forward-update
+behavior. Currently it contains a single parameter, the catalog of
+forward DDNS domains, which is a list of structures.
+
+::
+
+   "DhcpDdns": {
+       "forward-ddns": {
+           "ddns-domains": [ ]
+       },
+       ...
+   }
+
+By default, this list is empty, which causes the server to ignore
+the forward-update portions of requests.
+
+.. _add-forward-ddns-domain:
+
+Adding Forward DDNS Domains
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+A forward DDNS domain maps a forward DNS zone to a set of DNS servers
+which maintain the forward DNS data (i.e. name-to-address mapping) for
+that zone. Each zone served needs one forward DDNS domain.
+Some or all of the zones may be maintained by the same
+servers, but one DDNS domain is still needed for each zone. Remember that
+matching a request to the appropriate server(s) is done by zone and a
+DDNS domain only defines a single zone.
+
+This section describes how to add forward DDNS domains; repeat these
+steps for each forward DDNS domain desired. Each forward DDNS domain has
+the following parameters:
+
+-  ``name`` - this is the fully qualified domain name (or zone) that this DDNS
+   domain can update. This value is compared against the request FQDN
+   during forward matching. It must be unique within the catalog.
+
+-  ``key-name`` - if TSIG is used with this domain's servers, this value
+   should be the name of the key from the TSIG key list. If the
+   value is blank (the default), TSIG will not be used in DDNS
+   conversations with this domain's servers.
+
+-  ``dns-servers`` - this is a list of one or more DNS servers which can conduct
+   the server side of the DDNS protocol for this domain. The servers are
+   used in a first-to-last preference; in other words, when D2 begins to
+   process a request for this domain, it will pick the first server in
+   this list and attempt to communicate with it. If that attempt fails,
+   D2 will move to the next one in the list and so on, until either it
+   is successful or the list is exhausted.
+
+To create a new forward DDNS domain, add a new domain element and set
+its parameters:
+
+::
+
+   "DhcpDdns": {
+       "forward-ddns": {
+           "ddns-domains": [
+               {
+                   "name": "other.example.com.",
+                   "key-name": "",
+                   "dns-servers": [
+                   ]
+               }
+           ]
+       }
+   }
+
+It is possible to add a domain without any servers; however, if that
+domain matches a request, the request will fail. To make the domain
+useful, at least one DNS server must be added to it.
+
+.. _add-forward-dns-servers:
+
+Adding Forward DNS Servers
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This section describes how to add DNS servers to a forward DDNS domain.
+Repeat these instructions as needed for all the servers in each domain.
+
+Forward DNS server entries represent actual DNS servers which support
+the server side of the DDNS protocol. Each forward DNS server has the
+following parameters:
+
+-  ``hostname`` - the resolvable host name of the DNS server; this
+   parameter is not yet implemented.
+
+-  ``ip-address`` - the IP address at which the server listens for DDNS
+   requests. This may be either an IPv4 or an IPv6 address.
+
+-  ``port`` - the port on which the server listens for DDNS requests. It
+   defaults to the standard DNS service port of 53.
+
+To create a new forward DNS server, a new server element must be added to
+the domain and its parameters filled in. If, for example, the service is
+running at "172.88.99.10", set the forward DNS server as follows:
+
+::
+
+   "DhcpDdns": {
+       "forward-ddns": {
+           "ddns-domains": [
+               {
+                   "name": "other.example.com.",
+                   "key-name": "",
+                   "dns-servers": [
+                       {
+                           "ip-address": "172.88.99.10",
+                           "port": 53
+                       }
+                   ]
+               }
+           ]
+       }
+   }
+
+.. note::
+
+   Since ``hostname`` is not yet supported, the parameter ``ip-address``
+   must be set to the address of the DNS server.
+
+.. _d2-reverse-ddns-config:
+
+Reverse DDNS
+------------
+
+The reverse DDNS section is used to configure D2's reverse update
+behavior, and the concepts are the same as for the forward DDNS section.
+Currently it contains a single parameter, the catalog of reverse DDNS
+domains, which is a list of structures.
+
+::
+
+   "DhcpDdns": {
+       "reverse-ddns": {
+           "ddns-domains": [ ]
+       }
+       ...
+   }
+
+By default, this list is empty, which causes the server to ignore
+the reverse-update portions of requests.
+
+.. _add-reverse-ddns-domain:
+
+Adding Reverse DDNS Domains
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+A reverse DDNS domain maps a reverse DNS zone to a set of DNS servers
+which maintain the reverse DNS data (address-to-name mapping) for that
+zone. Each zone served needs one reverse DDNS domain.
+Some or all of the zones may be maintained by the same servers, but
+one DDNS domain entry is needed for each zone. Remember that
+matching a request to the appropriate server(s) is done by zone and a
+DDNS domain only defines a single zone.
+
+This section describes how to add reverse DDNS domains; repeat these
+steps for each reverse DDNS domain desired. Each reverse DDNS domain has
+the following parameters:
+
+-  ``name`` - this is the fully qualified reverse zone that this DDNS domain can
+   update. This is the value used during reverse matching, which
+   compares it with a reversed version of the request's lease address.
+   The zone name should follow the appropriate standards; for example,
+   to support the IPv4 subnet 172.16.1, the name should be
+   "1.16.172.in-addr.arpa.". Similarly, to support an IPv6 subnet of
+   2001:db8:1, the name should be "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa."
+   The name must be unique within the catalog.
+
+-  ``key-name`` - if TSIG is used with this domain's servers,
+   this value should be the name of the key from the TSIG key list. If
+   the value is blank (the default), TSIG will not be used in DDNS
+   conversations with this domain's servers.
+
+-  ``dns-servers`` - this is a list of one or more DNS servers which can conduct
+   the server side of the DDNS protocol for this domain. Currently, the
+   servers are used in a first-to-last preference; in other words, when
+   D2 begins to process a request for this domain, it will pick the
+   first server in this list and attempt to communicate with it. If that
+   attempt fails, D2 will move to the next one in the list and so on,
+   until either it is successful or the list is exhausted.
+
+To create a new reverse DDNS domain, a new domain element must be added
+and its parameters set. For example, to support subnet 2001:db8:1::, the
+following configuration could be used:
+
+::
+
+   "DhcpDdns": {
+       "reverse-ddns": {
+           "ddns-domains": [
+               {
+                   "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
+                   "key-name": "",
+                   "dns-servers": [
+                   ]
+               }
+           ]
+       }
+   }
+
+It is possible to add a domain without any servers; however, if that
+domain matches a request, the request will fail. To make the domain
+useful, at least one DNS server must be added to it.
+
+.. _add-reverse-dns-servers:
+
+Adding Reverse DNS Servers
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This section describes how to add DNS servers to a reverse DDNS domain.
+Repeat these instructions as needed for all the servers in each domain.
+
+Reverse DNS server entries represent actual DNS servers which support
+the server side of the DDNS protocol. Each reverse DNS server has the
+following parameters:
+
+-  ``hostname`` - the resolvable host name of the DNS server; this value
+   is currently ignored.
+
+-  ``ip-address`` - the IP address at which the server listens for DDNS
+   requests.
+
+-  ``port`` - the port on which the server listens for DDNS requests. It
+   defaults to the standard DNS service port of 53.
+
+To create a new reverse DNS server, a new server
+element must be added to the domain and its parameters specified. If, for example, the
+service is running at "172.88.99.10", then set it as follows:
+
+::
+
+   "DhcpDdns": {
+       "reverse-ddns": {
+           "ddns-domains": [
+               {
+                   "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
+                   "key-name": "",
+                   "dns-servers": [
+                       {
+                           "ip-address": "172.88.99.10",
+                           "port": 53
+                       }
+                   ]
+               }
+           ]
+       }
+   }
+
+.. note::
+
+   Since ``hostname`` is not yet supported, the parameter ``ip-address``
+   must be set to the address of the DNS server.
+
+.. _per-server-keys:
+
+Per-DNS-Server TSIG Keys
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Since Kea version 2.0.0, a TSIG key can be specified in a DNS server
+configuration. The priority rule is:
+
+-  if a not-empty key name is specified in a DNS server entry, this TSIG
+   key protects DNS updates sent to this server.
+
+-  if the DNS server entry is empty, but a
+   not-empty key name is specified in the parent's domain entry, the parent domain's
+   TSIG key protects DNS updates sent to this server.
+
+-  if the DNS server entry is empty, and no key name is specified in its parent
+   domain entry, no TSIG protects DNS updates sent to this server.
+
+For instance, in this configuration:
+
+::
+
+   "DhcpDdns": {
+       "forward-ddns": {
+           "ddns-domains": [
+               {
+                   "name": "other.example.com.",
+                   "key-name": "foo",
+                   "dns-servers": [
+                       {
+                           "ip-address": "172.88.99.10",
+                           "port": 53
+                       },
+                       {
+                           "ip-address": "172.88.99.11",
+                           "port": 53,
+                           "key-name": "bar"
+                       }
+                   ]
+               }
+           ]
+       },
+       "reverse-ddns": {
+           "ddns-domains": [
+               {
+                   "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
+                   "dns-servers": [
+                       {
+                           "ip-address": "172.88.99.12",
+                           "port": 53
+                       },
+                       {
+                           "ip-address": "172.88.99.13",
+                           "port": 53,
+                           "key-name": "bar"
+                       }
+                   ]
+               }
+           ]
+       },
+       "tsig-keys": [
+           {
+               "name": "foo",
+               "algorithm": "HMAC-MD5",
+               "secret": "LSWXnfkKZjdPJI5QxlpnfQ=="
+           },
+           {
+               "name": "bar",
+               "algorithm": "HMAC-SHA224",
+               "secret": "bZEG7Ow8OgAUPfLWV3aAUQ=="
+           }
+       ]
+   }
+
+
+The 172.88.99.10 server will use the "foo" TSIG key, the 172.88.99.11 and
+172.88.99.13 servers will use the "bar" key. and 172.88.99.12 will not use TSIG.
+
+.. _d2-user-contexts:
+
+User Contexts in DDNS
+---------------------
+
+See :ref:`user-context` for additional background regarding the user
+context idea.
+
+User contexts can be specified on a global scope, a DDNS domain, a DNS server,
+a TSIG key, and loggers. One other useful usage is the ability to store
+comments or descriptions; the parser translates a "comment" entry into a
+user context with the entry, which allows a comment to be attached
+inside the configuration itself.
+
+.. _d2-example-config:
+
+Example DHCP-DDNS Server Configuration
+--------------------------------------
+
+This section provides a sample DHCP-DDNS server configuration, based on
+a small example network. Let's suppose our example network has three
+domains, each with their own subnet.
+
+.. table:: Our example network
+
+   +------------------+-----------------+-----------------+-----------------+
+   | Domain           | Subnet          | Forward DNS     | Reverse DNS     |
+   |                  |                 | Servers         | Servers         |
+   +==================+=================+=================+=================+
+   | four.example.com | 192.0.2.0/24    | 172.16.1.5,     | 172.16.1.5,     |
+   |                  |                 | 172.16.2.5      | 172.16.2.5      |
+   +------------------+-----------------+-----------------+-----------------+
+   | six.example.com  | 2001:db8:1::/64 | 3001:1::50      | 3001:1::51      |
+   +------------------+-----------------+-----------------+-----------------+
+   | example.com      | 192.0.0.0/16    | 172.16.2.5      | 172.16.2.5      |
+   +------------------+-----------------+-----------------+-----------------+
+
+We need to construct three forward DDNS domains:
+
+.. table:: Forward DDNS domains needed
+
+   +----+-------------------+------------------------+
+   | #  | DDNS Domain Name  | DNS Servers            |
+   +====+===================+========================+
+   | 1. | four.example.com. | 172.16.1.5, 172.16.2.5 |
+   +----+-------------------+------------------------+
+   | 2. | six.example.com.  | 3001:1::50             |
+   +----+-------------------+------------------------+
+   | 3. | example.com.      | 172.16.2.5             |
+   +----+-------------------+------------------------+
+
+As discussed earlier, FQDN-to-domain matching is based on the longest
+match. The FQDN "myhost.four.example.com." matches the first domain
+("four.example.com"), while "admin.example.com." matches the third
+domain ("example.com"). The FQDN "other.example.net." fails to
+match any domain and is rejected.
+
+The following example configuration specifies the forward DDNS domains.
+
+::
+
+   "DhcpDdns": {
+       "comment": "example configuration: forward part",
+       "forward-ddns": {
+           "ddns-domains": [
+               {
+                   "name": "four.example.com.",
+                   "key-name": "",
+                   "dns-servers": [
+                       { "ip-address": "172.16.1.5" },
+                       { "ip-address": "172.16.2.5" }
+                   ]
+               },
+               {
+                   "name": "six.example.com.",
+                   "key-name": "",
+                   "dns-servers": [
+                       { "ip-address": "2001:db8::1" }
+                   ]
+               },
+               {
+                   "name": "example.com.",
+                   "key-name": "",
+                   "dns-servers": [
+                       { "ip-address": "172.16.2.5" }
+                   ],
+                   "user-context": { "backup": false }
+               },
+
+           ]
+       }
+   }
+
+Similarly, we need to construct the three reverse DDNS domains:
+
+.. table:: Reverse DDNS domains needed
+
+   +----+-----------------------------------+------------------------+
+   | #  | DDNS Domain Name                  | DNS Servers            |
+   +====+===================================+========================+
+   | 1. | 2.0.192.in-addr.arpa.             | 172.16.1.5, 172.16.2.5 |
+   +----+-----------------------------------+------------------------+
+   | 2. | 1.0.0.0.8.d.b.0.1.0.0.2.ip6.arpa. | 3001:1::50             |
+   +----+-----------------------------------+------------------------+
+   | 3. | 0.182.in-addr.arpa.               | 172.16.2.5             |
+   +----+-----------------------------------+------------------------+
+
+An address of "192.0.2.150" matches the first domain,
+"2001:db8:1::10" matches the second domain, and "192.0.50.77" matches the
+third domain.
+
+These reverse DDNS domains are specified as follows:
+
+::
+
+   "DhcpDdns": {
+       "comment": "example configuration: reverse part",
+       "reverse-ddns": {
+           "ddns-domains": [
+               {
+                   "name": "2.0.192.in-addr.arpa.",
+                   "key-name": "",
+                   "dns-servers": [
+                       { "ip-address": "172.16.1.5" },
+                       { "ip-address": "172.16.2.5" }
+                   ]
+               }
+               {
+                   "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
+                   "key-name": "",
+                   "dns-servers": [
+                       { "ip-address": "2001:db8::1" }
+                   ]
+               }
+               {
+                   "name": "0.192.in-addr.arpa.",
+                   "key-name": "",
+                   "dns-servers": [
+                       { "ip-address": "172.16.2.5" }
+                   ]
+               }
+           ]
+       }
+   }
+
+DHCP-DDNS Server Statistics
+===========================
+
+Kea version 2.0.0 introduced statistics support for DHCP-DDNS.
+
+Statistics are divided into three groups: NameChangeRequests, DNS updates,
+and per-TSIG-key DNS updates. While the statistics of the first two groups
+are cumulative, i.e. not affected by configuration change or reload,
+per-key statistics are reset to 0 when the underlying object is
+(re)created.
+
+Currently Kea's statistics management has the following limitations:
+
+-  only integer samples (i.e. a counter and a timestamp) are used;
+-  the maximum sample count is 1;
+-  there is no API to remove one or all statistics;
+-  there is no API to set the maximum sample count or age.
+
+.. note::
+
+    Hook libraries, such as the the ISC subscriber-only GSS-TSIG library,
+    make new statistics available in Kea.
+
+More information about Kea statistics can be found at :ref:`stats`.
+
+NCR Statistics
+--------------
+
+The NameChangeRequest statistics are:
+
+-  ``ncr-received`` - the number of received valid NCRs
+-  ``ncr-invalid`` - the number of received invalid NCRs
+-  ``ncr-error`` - the number of errors in NCR receptions other than an I/O cancel on shutdown
+
+DNS Update Statistics
+---------------------
+
+The global DNS update statistics are:
+
+-  ``update-sent`` - the number of DNS updates sent
+-  ``update-signed`` - the number of DNS updates sent and protected by TSIG
+-  ``update-unsigned`` - the number of DNS updates sent and not protected by TSIG
+-  ``update-success`` - the number of DNS updates which successfully completed
+-  ``update-timeout`` - the number of DNS updates which completed on timeout
+-  ``update-error`` - the number of DNS updates which completed with an error other than
+   timeout
+
+Per-TSIG-Key DNS Update Statistics
+----------------------------------
+
+The per TSIG key DNS update statistics are:
+
+-  ``update-sent`` - the number of DNS updates sent
+-  ``update-success`` - the number of DNS updates which successfully completed
+-  ``update-timeout`` - the number of DNS updates which completed on timeout
+-  ``update-error`` - the number of DNS updates which completed with an error other than
+   timeout
+
+The name format for per-key statistics is ``key[<key-DNS-name>].<stat-name>``:
+for instance, the name of the ``update-sent`` statistics for the
+``key.example.com.`` TSIG key is ``key[key.example.com.].update-sent``.
+
+DHCP-DDNS Server Limitations
+============================
+
+The following are the current limitations of the DHCP-DDNS server.
+
+-  Requests received from the DHCP servers are placed in a queue until
+   they are processed. Currently, all queued requests are lost if the
+   server shuts down.
+
+Supported Standards
+===================
+
+The following RFCs are supported by the DHCP-DDNS server:
+
+- *Secret Key Transaction Authentication for DNS (TSIG)*, `RFC 2845
+  <https://tools.ietf.org/html/rfc2845>`__: All DNS update packets sent and
+  received by the DHCP-DDNS server can be protected by TSIG signatures.
+
+- *Dynamic Updates in the Domain Name System (DNS UPDATE)*, `RFC 2136
+  <https://tools.ietf.org/html/rfc2136>`__: The complete DNS update mechanism is
+  supported.
+
+- *Resolution of Fully Qualified Domain Name (FQDN) Conflicts among Dynamic Host
+  Configuration Protocol (DHCP) Clients*, `RFC 4703
+  <https://tools.ietf.org/html/rfc4703>`__: DHCP-DDNS takes care of
+  conflict resolution, for both DHCPv4 and DHCPv6 servers.
+
+- *A DNS Resource Record (RR) for Encoding Dynamic Host Configuration Protocol
+  (DHCP) Information (DHCID RR)*, `RFC 4701
+  <https://tools.ietf.org/html/rfc4701>`__: The DHCP-DDNS server uses DHCID
+  records.
diff --git a/doc/sphinx/arm/dhcp4-srv.rst b/doc/sphinx/arm/dhcp4-srv.rst
new file mode 100644
index 0000000..534c18e
--- /dev/null
+++ b/doc/sphinx/arm/dhcp4-srv.rst
@@ -0,0 +1,7184 @@
+.. _dhcp4:
+
+*****************
+The DHCPv4 Server
+*****************
+
+.. _dhcp4-start-stop:
+
+Starting and Stopping the DHCPv4 Server
+=======================================
+
+It is recommended that the Kea DHCPv4 server be started and stopped
+using ``keactrl`` (described in :ref:`keactrl`); however, it is also
+possible to run the server directly via the ``kea-dhcp4`` command, which accepts
+the following command-line switches:
+
+-  ``-c file`` - specifies the configuration file. This is the only
+   mandatory switch.
+
+-  ``-d`` - specifies whether the server logging should be switched to
+   debug/verbose mode. In verbose mode, the logging severity and debuglevel
+   specified in the configuration file are ignored; "debug" severity
+   and the maximum debuglevel (99) are assumed. The flag is convenient
+   for temporarily switching the server into maximum verbosity, e.g.
+   when debugging.
+
+-  ``-p server-port`` - specifies the local UDP port on which the server
+   listens. This is only useful during testing, as a DHCPv4 server
+   listening on ports other than the standard ones is not able to
+   handle regular DHCPv4 queries.
+
+-  ``-P client-port`` - specifies the remote UDP port to which the
+   server sends all responses. This is only useful during testing,
+   as a DHCPv4 server sending responses to ports other than the standard
+   ones is not able to handle regular DHCPv4 queries.
+
+-  ``-t file`` - specifies a configuration file to be tested. ``kea-dhcp4``
+   loads it, checks it, and exits. During the test, log messages are
+   printed to standard output and error messages to standard error. The
+   result of the test is reported through the exit code (0 =
+   configuration looks OK, 1 = error encountered). The check is not
+   comprehensive; certain checks are possible only when running the
+   server.
+
+-  ``-v`` - displays the Kea version and exits.
+
+-  ``-V`` - displays the Kea extended version with additional parameters
+   and exits. The listing includes the versions of the libraries
+   dynamically linked to Kea.
+
+-  ``-W`` - displays the Kea configuration report and exits. The report
+   is a copy of the ``config.report`` file produced by ``./configure``;
+   it is embedded in the executable binary.
+
+On startup, the server detects available network interfaces and
+attempts to open UDP sockets on all interfaces listed in the
+configuration file. Since the DHCPv4 server opens privileged ports, it
+requires root access; this daemon must be run as root.
+
+During startup, the server attempts to create a PID file of the
+form: ``[runstatedir]/kea/[conf name].kea-dhcp4.pid``, where:
+
+-  ``runstatedir``: The value as passed into the build configure
+   script; it defaults to ``/usr/local/var/run``. Note that this value may be
+   overridden at runtime by setting the environment variable
+   ``KEA_PIDFILE_DIR``, although this is intended primarily for testing
+   purposes.
+
+-  ``conf name``: The configuration file name used to start the server,
+   minus all preceding paths and the file extension. For example, given
+   a pathname of ``/usr/local/etc/kea/myconf.txt``, the portion used would
+   be ``myconf``.
+
+If the file already exists and contains the PID of a live process, the
+server issues a ``DHCP4_ALREADY_RUNNING`` log message and exits. It is
+possible, though unlikely, that the file is a remnant of a system crash
+and the process to which the PID belongs is unrelated to Kea. In such a
+case, it would be necessary to manually delete the PID file.
+
+The server can be stopped using the ``kill`` command. When running in a
+console, the server can also be shut down by pressing Ctrl-c. Kea detects
+the key combination and shuts down gracefully.
+
+.. _dhcp4-configuration:
+
+DHCPv4 Server Configuration
+===========================
+
+Introduction
+------------
+
+This section explains how to configure the Kea DHCPv4 server using a
+configuration file.
+
+Before DHCPv4 is started, its configuration file must
+be created. The basic configuration is as follows:
+
+::
+
+   {
+   # DHCPv4 configuration starts on the next line
+   "Dhcp4": {
+
+   # First we set up global values
+       "valid-lifetime": 4000,
+       "renew-timer": 1000,
+       "rebind-timer": 2000,
+
+   # Next we set up the interfaces to be used by the server.
+       "interfaces-config": {
+           "interfaces": [ "eth0" ]
+       },
+
+   # And we specify the type of lease database
+       "lease-database": {
+           "type": "memfile",
+           "persist": true,
+           "name": "/var/lib/kea/dhcp4.leases"
+       },
+
+   # Finally, we list the subnets from which we will be leasing addresses.
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [
+                   {
+                       "pool": "192.0.2.1 - 192.0.2.200"
+                   }
+               ]
+           }
+       ]
+   # DHCPv4 configuration ends with the next line
+   }
+
+   }
+
+The following paragraphs provide a brief overview of the parameters in
+the above example, along with their format. Subsequent sections of this
+chapter go into much greater detail for these and other parameters.
+
+The lines starting with a hash (#) are comments and are ignored by the
+server; they do not impact its operation in any way.
+
+The configuration starts in the first line with the initial opening
+curly bracket (or brace). Each configuration must contain an object
+specifying the configuration of the Kea module using it. In the example
+above, this object is called ``Dhcp4``.
+
+The ``Dhcp4`` configuration starts with the ``"Dhcp4": {`` line and ends
+with the corresponding closing brace (in the above example, the brace
+after the last comment). Everything defined between those lines is
+considered to be the ``Dhcp4`` configuration.
+
+In general, the order in which those parameters appear does not
+matter, but there are two caveats. The first one is that the
+configuration file must be well-formed JSON, meaning that the
+parameters for any given scope must be separated by a comma, and there
+must not be a comma after the last parameter. When reordering a
+configuration file, moving a parameter to or from the
+last position in a given scope may also require moving the comma. The
+second caveat is that it is uncommon — although legal JSON — to repeat
+the same parameter multiple times. If that happens, the last occurrence
+of a given parameter in a given scope is used, while all previous
+instances are ignored. This is unlikely to cause any confusion as there
+are no real-life reasons to keep multiple copies of the same parameter
+in the configuration file.
+
+The first few DHCPv4 configuration elements
+define some global parameters. ``valid-lifetime`` defines how long the
+addresses (leases) given out by the server are valid; the default
+is for a client to be allowed to use a given address for 4000
+seconds. (Note that integer numbers are specified as is, without any
+quotes around them.) ``renew-timer`` and ``rebind-timer`` are values
+(also in seconds) that define the T1 and T2 timers that govern when the
+client begins the renewal and rebind processes.
+
+.. note::
+
+   The lease valid lifetime is expressed as a triplet with minimum, default, and
+   maximum values using configuration entries
+   ``min-valid-lifetime``, ``valid-lifetime``, and ``max-valid-lifetime``.
+   Since Kea 1.9.5, these values may be specified in client classes. The procedure
+   the server uses to select which lifetime value to use is as follows:
+
+   If the client query is a BOOTP query, the server always uses the
+   infinite lease time (e.g. 0xffffffff). Otherwise, the server must
+   determine which configured triplet to use by first searching all
+   classes assigned to the query, and then the subnet selected for
+   the query.
+
+   Classes are searched in the order they were assigned to the query; the
+   server uses the triplet from the first class that specifies it.
+   If no classes specify the triplet, the server uses the triplet
+   specified by the subnet selected for the client. If the subnet does not
+   explicitly specify it, the server next looks at the subnet's
+   shared-network (if one exists), then for a global specification, and
+   finally the global default.
+
+   If the client requested a lifetime value via DHCP option 51, then the
+   lifetime value used is the requested value bounded by the configured
+   triplet. In other words, if the requested lifetime is less than the
+   configured minimum, the configured minimum is used; if it is more
+   than the configured maximum, the configured maximum is used. If
+   the client did not provide a requested value, the lifetime value used
+   is the triplet default value.
+
+.. note::
+
+   Both ``renew-timer`` and ``rebind-timer``
+   are optional. The server only sends ``rebind-timer`` to the client,
+   via DHCPv4 option code 59, if it is less than ``valid-lifetime``; and it
+   only sends ``renew-timer``, via DHCPv4 option code 58, if it is less
+   than ``rebind-timer`` (or ``valid-lifetime`` if ``rebind-timer`` was not
+   specified). In their absence, the client should select values for T1
+   and T2 timers according to `RFC 2131 <https://tools.ietf.org/html/rfc2131>`_.
+   See section :ref:`dhcp4-t1-t2-times`
+   for more details on generating T1 and T2.
+
+The ``interfaces-config`` map specifies the
+network interfaces on which the server should listen to
+DHCP messages. The ``interfaces`` parameter specifies a list of
+network interfaces on which the server should listen. Lists are opened
+and closed with square brackets, with elements separated by commas. To
+listen on two interfaces, the ``interfaces-config`` element should look like
+this:
+
+::
+
+   "interfaces-config": {
+       "interfaces": [ "eth0", "eth1" ]
+   },
+
+The next lines define the lease database, the place where the
+server stores its lease information. This particular example tells the
+server to use memfile, which is the simplest and fastest database
+backend. It uses an in-memory database and stores leases on disk in a
+CSV (comma-separated values) file. This is a very simple configuration example;
+usually the lease database configuration is more extensive and contains
+additional parameters. Note that ``lease-database`` is an object and opens up a
+new scope, using an opening brace. Its parameters (just one in this example:
+``type``) follow. If there were more than one, they would be separated
+by commas. This scope is closed with a closing brace. As more parameters
+for the ``Dhcp4`` definition follow, a trailing comma is present.
+
+Finally, we need to define a list of IPv4 subnets. This is the most
+important DHCPv4 configuration structure, as the server uses that
+information to process clients' requests. It defines all subnets from
+which the server is expected to receive DHCP requests. The subnets are
+specified with the ``subnet4`` parameter. It is a list, so it starts and
+ends with square brackets. Each subnet definition in the list has
+several attributes associated with it, so it is a structure and is
+opened and closed with braces. At a minimum, a subnet definition must
+have at least two parameters: ``subnet``, which defines the whole
+subnet; and ``pools``, which is a list of dynamically allocated pools
+that are governed by the DHCP server.
+
+The example contains a single subnet. If more than one were defined,
+additional elements in the ``subnet4`` parameter would be specified and
+separated by commas. For example, to define three subnets, the following
+syntax would be used:
+
+::
+
+   "subnet4": [
+       {
+           "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
+           "subnet": "192.0.2.0/24"
+       },
+       {
+           "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
+           "subnet": "192.0.3.0/24"
+       },
+       {
+           "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
+           "subnet": "192.0.4.0/24"
+       }
+   ]
+
+Note that indentation is optional and is used for aesthetic purposes
+only. In some cases it may be preferable to use more compact notation.
+
+After all the parameters have been specified, there are two contexts open:
+``global`` and ``Dhcp4``; thus, two closing curly brackets must be used to close
+them.
+
+Lease Storage
+-------------
+
+All leases issued by the server are stored in the lease database.
+There are three database backends available: memfile
+(the default), MySQL, PostgreSQL.
+
+Memfile - Basic Storage for Leases
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The server is able to store lease data in different repositories. Larger
+deployments may elect to store leases in a database;
+:ref:`database-configuration4` describes this option. In
+typical smaller deployments, though, the server stores lease
+information in a CSV file rather than a database. As well as requiring
+less administration, an advantage of using a file for storage is that it
+eliminates a dependency on third-party database software.
+
+The configuration of the memfile backend is controlled through
+the ``Dhcp4``/``lease-database`` parameters. The ``type`` parameter is mandatory
+and specifies which storage for leases the server should use, through
+the ``"memfile"`` value. The following list gives additional optional parameters
+that can be used to configure the memfile backend.
+
+-  ``persist``: controls whether the new leases and updates to existing
+   leases are written to the file. It is strongly recommended that the
+   value of this parameter be set to ``true`` at all times during the
+   server's normal operation. Not writing leases to disk means that if a
+   server is restarted (e.g. after a power failure), it will not know
+   which addresses have been assigned. As a result, it may assign new clients
+   addresses that are already in use. The value of
+   ``false`` is mostly useful for performance-testing purposes. The
+   default value of the ``persist`` parameter is ``true``, which enables
+   writing lease updates to the lease file.
+
+-  ``name``: specifies an absolute location of the lease file in which
+   new leases and lease updates are recorded. The default value for
+   this parameter is ``"[kea-install-dir]/var/lib/kea/kea-leases4.csv"``.
+
+-  ``lfc-interval``: specifies the interval, in seconds, at which the
+   server will perform a lease file cleanup (LFC). This removes
+   redundant (historical) information from the lease file and
+   effectively reduces the lease file size. The cleanup process is
+   described in more detail later in this section. The default
+   value of the ``lfc-interval`` is ``3600``. A value of ``0`` disables the LFC.
+
+-  ``max-row-errors``: specifies the number of row errors before the server
+   stops attempting to load a lease file. When the server loads a lease file, it is processed
+   row by row, each row containing a single lease. If a row is flawed and
+   cannot be processed correctly the server logs it, discards the row,
+   and goes on to the next row. This parameter can be used to set a limit on
+   the number of such discards that can occur, after which the server
+   abandons the effort and exits. The default value of ``0`` disables the limit
+   and allows the server to process the entire file, regardless of how many
+   rows are discarded.
+
+An example configuration of the memfile backend is presented below:
+
+::
+
+   "Dhcp4": {
+       "lease-database": {
+           "type": "memfile",
+           "persist": true,
+           "name": "/tmp/kea-leases4.csv",
+           "lfc-interval": 1800,
+           "max-row-errors": 100
+       }
+   }
+
+This configuration selects ``/tmp/kea-leases4.csv`` as the storage
+for lease information and enables persistence (writing lease updates to
+this file). It also configures the backend to perform a periodic cleanup
+of the lease file every 1800 seconds (30 minutes) and sets the maximum number of
+row errors to 100.
+
+Why Is Lease File Cleanup Necessary?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+It is important to know how the lease file contents are organized to
+understand why the periodic lease file cleanup is needed. Every time the
+server updates a lease or creates a new lease for a client, the new
+lease information must be recorded in the lease file. For performance
+reasons, the server does not update the existing client's lease in the
+file, as this would potentially require rewriting the entire file.
+Instead, it simply appends the new lease information to the end of the
+file; the previous lease entries for the client are not removed. When
+the server loads leases from the lease file, e.g. at server startup,
+it assumes that the latest lease entry for the client is the valid one.
+Previous entries are discarded, meaning that the server can
+reconstruct accurate information about the leases even though there
+may be many lease entries for each client. However, storing many entries
+for each client results in a bloated lease file and impairs the
+performance of the server's startup and reconfiguration, as it needs to
+process a larger number of lease entries.
+
+Lease file cleanup (LFC) removes all previous entries for each client
+and leaves only the latest ones. The interval at which the cleanup is
+performed is configurable, and it should be selected according to the
+frequency of lease renewals initiated by the clients. The more frequent
+the renewals, the smaller the value of ``lfc-interval`` should be. Note,
+however, that the LFC takes time and thus it is possible (although
+unlikely) that, if the ``lfc-interval`` is too short, a new cleanup may
+be started while the previous one is still running. The server would
+recover from this by skipping the new cleanup when it detected that the
+previous cleanup was still in progress, but it implies that the actual
+cleanups will be triggered more rarely than the configured interval. Moreover,
+triggering a new cleanup adds overhead to the server, which is not
+able to respond to new requests for a short period of time when the new
+cleanup process is spawned. Therefore, it is recommended that the
+``lfc-interval`` value be selected in a way that allows the LFC
+to complete the cleanup before a new cleanup is triggered.
+
+Lease file cleanup is performed by a separate process (in the
+background) to avoid a performance impact on the server process. To
+avoid conflicts between two processes using the same lease
+files, the LFC process starts with Kea opening a new lease file; the
+actual LFC process operates on the lease file that is no longer used by
+the server. There are also other files created as a side effect of the
+lease file cleanup. The detailed description of the LFC process is located later
+in this Kea Administrator's Reference Manual: :ref:`kea-lfc`.
+
+.. _database-configuration4:
+
+Lease Database Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. note::
+
+   Lease database access information must be configured for the DHCPv4
+   server, even if it has already been configured for the DHCPv6 server.
+   The servers store their information independently, so each server can
+   use a separate database or both servers can use the same database.
+
+.. note::
+
+   Kea requires the database timezone to match the system timezone.
+   For more details, see :ref:`mysql-database-create` and
+   :ref:`pgsql-database-create`.
+
+Lease database configuration is controlled through the
+``Dhcp4``/``lease-database`` parameters. The database type must be set to
+``memfile``, ``mysql`` or ``postgresql``, e.g.:
+
+::
+
+   "Dhcp4": { "lease-database": { "type": "mysql", ... }, ... }
+
+Next, the name of the database to hold the leases must be set; this is
+the name used when the database was created (see
+:ref:`mysql-database-create` or :ref:`pgsql-database-create`).
+
+For MySQL or PostgreSQL:
+
+::
+
+   "Dhcp4": { "lease-database": { "name": "database-name" , ... }, ... }
+
+If the database is located on a different system from the DHCPv4 server,
+the database host name must also be specified:
+
+::
+
+   "Dhcp4": { "lease-database": { "host": "remote-host-name", ... }, ... }
+
+Normally, the database is on the same machine as the DHCPv4 server.
+In this case, set the value to the empty string:
+
+::
+
+   "Dhcp4": { "lease-database": { "host" : "", ... }, ... }
+
+Should the database use a port other than the default, it may be
+specified as well:
+
+::
+
+   "Dhcp4": { "lease-database": { "port" : 12345, ... }, ... }
+
+Should the database be located on a different system, the administrator may need to
+specify a longer interval for the connection timeout:
+
+::
+
+   "Dhcp4": { "lease-database": { "connect-timeout" : timeout-in-seconds, ... }, ... }
+
+The default value of five seconds should be more than adequate for local
+connections. If a timeout is given, though, it should be an integer
+greater than zero.
+
+The maximum number of times the server automatically attempts to
+reconnect to the lease database after connectivity has been lost may be
+specified:
+
+::
+
+   "Dhcp4": { "lease-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }
+
+If the server is unable to reconnect to the database after making the
+maximum number of attempts, the server will exit. A value of 0 (the
+default) disables automatic recovery and the server will exit
+immediately upon detecting a loss of connectivity (MySQL and PostgreSQL
+only).
+
+The number of milliseconds the server waits between attempts to
+reconnect to the lease database after connectivity has been lost may
+also be specified:
+
+::
+
+   "Dhcp4": { "lease-database": { "reconnect-wait-time" : number-of-milliseconds, ... }, ... }
+
+The default value for MySQL and PostgreSQL is 0, which disables automatic
+recovery and causes the server to exit immediately upon detecting the
+loss of connectivity.
+
+::
+
+   "Dhcp4": { "lease-database": { "on-fail" : "stop-retry-exit", ... }, ... }
+
+The possible values are:
+
+-  ``stop-retry-exit`` - disables the DHCP service while trying to automatically
+   recover lost connections. Shuts down the server on failure after exhausting
+   ``max-reconnect-tries``. This is the default value for MySQL and PostgreSQL.
+
+-  ``serve-retry-exit`` - continues the DHCP service while trying to automatically
+   recover lost connections. Shuts down the server on failure after exhausting
+   ``max-reconnect-tries``.
+
+-  ``serve-retry-continue`` - continues the DHCP service and does not shut down the
+   server even if the recovery fails.
+
+.. note::
+
+   Automatic reconnection to database backends is configured individually per
+   backend; this allows users to tailor the recovery parameters to each backend
+   they use. We suggest that users enable it either for all backends or none,
+   so behavior is consistent.
+
+   Losing connectivity to a backend for which reconnection is disabled results
+   (if configured) in the server shutting itself down. This includes cases when
+   the lease database backend and the hosts database backend are connected to
+   the same database instance.
+
+   It is highly recommended not to change the ``stop-retry-exit`` default
+   setting for the lease manager, as it is critical for the connection to be
+   active while processing DHCP traffic. Change this only if the server is used
+   exclusively as a configuration tool.
+
+The host parameter is used by the MySQL and PostgreSQL backends.
+
+Finally, the credentials of the account under which the server will
+access the database should be set:
+
+::
+
+   "Dhcp4": { "lease-database": { "user": "user-name",
+                                  "password": "password",
+                                 ... },
+              ... }
+
+If there is no password to the account, set the password to the empty
+string ``""``. (This is the default.)
+
+.. _hosts4-storage:
+
+Hosts Storage
+-------------
+
+Kea is also able to store information about host reservations in the
+database. The hosts database configuration uses the same syntax as the
+lease database. In fact, the Kea server opens independent connections for
+each purpose, be it lease or hosts information, which gives
+the most flexibility. Kea can keep leases and host reservations
+separately, but can also point to the same database. Currently the
+supported hosts database types are MySQL and PostgreSQL.
+
+The following configuration can be used to configure a
+connection to MySQL:
+
+::
+
+   "Dhcp4": {
+       "hosts-database": {
+           "type": "mysql",
+           "name": "kea",
+           "user": "kea",
+           "password": "secret123",
+           "host": "localhost",
+           "port": 3306
+       }
+   }
+
+Depending on the database configuration, many of the
+parameters may be optional.
+
+Please note that usage of hosts storage is optional. A user can define
+all host reservations in the configuration file, and that is the
+recommended way if the number of reservations is small. However, when
+the number of reservations grows, it is more convenient to use host
+storage. Please note that both storage methods (the configuration file and
+one of the supported databases) can be used together. If hosts are
+defined in both places, the definitions from the configuration file are
+checked first and external storage is checked later, if necessary.
+
+Host information can be placed in multiple stores. Operations
+are performed on the stores in the order they are defined in the
+configuration file, although this leads to a restriction in ordering
+in the case of a host reservation addition; read-only stores must be
+configured after a (required) read-write store, or the addition will
+fail.
+
+.. note::
+
+   Kea requires the database timezone to match the system timezone.
+   For more details, see :ref:`mysql-database-create` and
+   :ref:`pgsql-database-create`.
+
+.. _hosts-databases-configuration4:
+
+DHCPv4 Hosts Database Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Hosts database configuration is controlled through the
+``Dhcp4``/``hosts-database`` parameters. If enabled, the type of database must
+be set to ``mysql`` or ``postgresql``.
+
+::
+
+   "Dhcp4": { "hosts-database": { "type": "mysql", ... }, ... }
+
+Next, the name of the database to hold the reservations must be set;
+this is the name used when the lease database was created (see
+:ref:`supported-databases` for instructions on how to set up the
+desired database type):
+
+::
+
+   "Dhcp4": { "hosts-database": { "name": "database-name" , ... }, ... }
+
+If the database is located on a different system than the DHCPv4 server,
+the database host name must also be specified:
+
+::
+
+   "Dhcp4": { "hosts-database": { "host": remote-host-name, ... }, ... }
+
+Normally, the database is on the same machine as the DHCPv4 server.
+In this case, set the value to the empty string:
+
+::
+
+   "Dhcp4": { "hosts-database": { "host" : "", ... }, ... }
+
+Should the database use a port different than the default, it may be
+specified as well:
+
+::
+
+   "Dhcp4": { "hosts-database": { "port" : 12345, ... }, ... }
+
+The maximum number of times the server automatically attempts to
+reconnect to the host database after connectivity has been lost may be
+specified:
+
+::
+
+   "Dhcp4": { "hosts-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }
+
+If the server is unable to reconnect to the database after making the
+maximum number of attempts, the server will exit. A value of 0 (the
+default) disables automatic recovery and the server will exit
+immediately upon detecting a loss of connectivity (MySQL and PostgreSQL
+only).
+
+The number of milliseconds the server waits between attempts to
+reconnect to the host database after connectivity has been lost may also
+be specified:
+
+::
+
+   "Dhcp4": { "hosts-database": { "reconnect-wait-time" : number-of-milliseconds, ... }, ... }
+
+The default value for MySQL and PostgreSQL is 0, which disables automatic
+recovery and causes the server to exit immediately upon detecting the
+loss of connectivity.
+
+::
+
+   "Dhcp4": { "hosts-database": { "on-fail" : "stop-retry-exit", ... }, ... }
+
+The possible values are:
+
+-  ``stop-retry-exit`` - disables the DHCP service while trying to automatically
+   recover lost connections. Shuts down the server on failure after exhausting
+   ``max-reconnect-tries``. This is the default value for MySQL and PostgreSQL.
+
+-  ``serve-retry-exit`` - continues the DHCP service while trying to automatically
+   recover lost connections. Shuts down the server on failure after exhausting
+   ``max-reconnect-tries``.
+
+-  ``serve-retry-continue`` - continues the DHCP service and does not shut down the
+   server even if the recovery fails.
+
+.. note::
+
+   Automatic reconnection to database backends is configured individually per
+   backend. This allows users to tailor the recovery parameters to each backend
+   they use. We suggest that users enable it either for all backends or none,
+   so behavior is consistent.
+
+   Losing connectivity to a backend for which reconnection is disabled results
+   (if configured) in the server shutting itself down. This includes cases when
+   the lease database backend and the hosts database backend are connected to
+   the same database instance.
+
+Finally, the credentials of the account under which the server will
+access the database should be set:
+
+::
+
+   "Dhcp4": { "hosts-database": { "user": "user-name",
+                                  "password": "password",
+                                 ... },
+              ... }
+
+If there is no password to the account, set the password to the empty
+string ``""``. (This is the default.)
+
+The multiple-storage extension uses a similar syntax; a configuration is
+placed into a ``hosts-databases`` list instead of into a ``hosts-database``
+entry, as in:
+
+::
+
+   "Dhcp4": { "hosts-databases": [ { "type": "mysql", ... }, ... ], ... }
+
+If the same host is configured both in-file and in-database, Kea does not issue a warning,
+as it would if both were specified in the same data source.
+Instead, the host configured in-file has priority over the one configured
+in-database.
+
+.. _read-only-database-configuration4:
+
+Using Read-Only Databases for Host Reservations With DHCPv4
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In some deployments, the user whose name is specified in the
+database backend configuration may not have write privileges to the
+database. This is often required by the policy within a given network to
+secure the data from being unintentionally modified. In many cases
+administrators have deployed inventory databases, which contain
+substantially more information about the hosts than just the static
+reservations assigned to them. The inventory database can be used to
+create a view of a Kea hosts database and such a view is often
+read-only.
+
+Kea host-database backends operate with an implicit configuration to
+both read from and write to the database. If the user does not
+have write access to the host database, the backend will fail to start
+and the server will refuse to start (or reconfigure). However, if access
+to a read-only host database is required for retrieving reservations
+for clients and/or assigning specific addresses and options, it is
+possible to explicitly configure Kea to start in "read-only" mode. This
+is controlled by the ``readonly`` boolean parameter as follows:
+
+::
+
+   "Dhcp4": { "hosts-database": { "readonly": true, ... }, ... }
+
+Setting this parameter to ``false`` configures the database backend to
+operate in "read-write" mode, which is also the default configuration if
+the parameter is not specified.
+
+.. note::
+
+   The ``readonly`` parameter is only supported for MySQL and
+   PostgreSQL databases.
+
+.. _dhcp4-interface-configuration:
+
+Interface Configuration
+-----------------------
+
+The DHCPv4 server must be configured to listen on specific network
+interfaces. The simplest network interface configuration tells the
+server to listen on all available interfaces:
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "*" ]
+       }
+       ...
+   },
+
+The asterisk plays the role of a wildcard and means "listen on all
+interfaces." However, it is usually a good idea to explicitly specify
+interface names:
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ]
+       },
+       ...
+   }
+
+
+It is possible to use an interface wildcard (*) concurrently
+with explicit interface names:
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3", "*" ]
+       },
+       ...
+   }
+
+This format should only be used when it is
+desired to temporarily override a list of interface names and listen on
+all interfaces.
+
+Some deployments of DHCP servers require that the servers listen on
+interfaces with multiple IPv4 addresses configured. In these situations,
+the address to use can be selected by appending an IPv4 address to the
+interface name in the following manner:
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "eth1/10.0.0.1", "eth3/192.0.2.3" ]
+       },
+       ...
+   }
+
+
+Should the server be required to listen on multiple IPv4 addresses
+assigned to the same interface, multiple addresses can be specified for
+an interface as in the example below:
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "eth1/10.0.0.1", "eth1/10.0.0.2" ]
+       },
+       ...
+   }
+
+
+Alternatively, if the server should listen on all addresses for the
+particular interface, an interface name without any address should be
+specified.
+
+Kea supports responding to directly connected clients which do not have
+an address configured. This requires the server to inject the hardware
+address of the destination into the data-link layer of the packet
+being sent to the client. The DHCPv4 server uses raw sockets to
+achieve this, and builds the entire IP/UDP stack for the outgoing
+packets. The downside of raw socket use, however, is that incoming and
+outgoing packets bypass the firewalls (e.g. iptables).
+
+Handling traffic on multiple IPv4 addresses assigned to the same
+interface can be a challenge, as raw sockets are bound to the
+interface. When the DHCP server is configured to use the raw socket on
+an interface to receive DHCP traffic, advanced packet filtering
+techniques (e.g. the BPF) must be used to receive unicast traffic on
+the desired addresses assigned to the interface. Whether clients use
+the raw socket or the UDP socket depends on whether they are directly
+connected (raw socket) or relayed (either raw or UDP socket).
+
+Therefore, in deployments where the server does not need to provision
+the directly connected clients and only receives the unicast packets
+from the relay agents, the Kea server should be configured to use UDP
+sockets instead of raw sockets. The following configuration
+demonstrates how this can be achieved:
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ],
+           "dhcp-socket-type": "udp"
+       },
+       ...
+   }
+
+
+The ``dhcp-socket-type`` parameter specifies that the IP/UDP sockets will be
+opened on all interfaces on which the server listens, i.e. "eth1" and
+"eth3" in this example. If ``dhcp-socket-type`` is set to ``raw``, it
+configures the server to use raw sockets instead. If the
+``dhcp-socket-type`` value is not specified, the default value ``raw``
+is used.
+
+Using UDP sockets automatically disables the reception of broadcast
+packets from directly connected clients. This effectively means that UDP
+sockets can be used for relayed traffic only. When using raw sockets,
+both the traffic from the directly connected clients and the relayed
+traffic are handled.
+
+Caution should be taken when configuring the server
+to open multiple raw sockets on the interface with several IPv4
+addresses assigned. If the directly connected client sends the message
+to the broadcast address, all sockets on this link will receive this
+message and multiple responses will be sent to the client. Therefore,
+the configuration with multiple IPv4 addresses assigned to the interface
+should not be used when the directly connected clients are operating on
+that link. To use a single address on such an interface, the
+"interface-name/address" notation should be used.
+
+.. note::
+
+   Specifying the value ``raw`` as the socket type does not guarantee
+   that raw sockets will be used! The use of raw sockets to handle
+   traffic from the directly connected clients is currently
+   supported on Linux and BSD systems only. If raw sockets are not
+   supported on the particular OS in use, the server issues a warning and
+   fall back to using IP/UDP sockets.
+
+In a typical environment, the DHCP server is expected to send back a
+response on the same network interface on which the query was received.
+This is the default behavior. However, in some deployments it is desired
+that the outbound (response) packets be sent as regular traffic and
+the outbound interface be determined by the routing tables. This
+kind of asymmetric traffic is uncommon, but valid. Kea supports a
+parameter called ``outbound-interface`` that controls this behavior. It
+supports two values: the first one, ``same-as-inbound``, tells Kea to
+send back the response on the same interface where the query packet was
+received. This is the default behavior. The second parameter, ``use-routing``,
+tells Kea to send regular UDP packets and let the kernel's routing table
+determine the most appropriate interface. This only works when
+``dhcp-socket-type`` is set to ``udp``. An example configuration looks
+as follows:
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ],
+           "dhcp-socket-type": "udp",
+           "outbound-interface": "use-routing"
+       },
+       ...
+   }
+
+Interfaces are re-detected at each reconfiguration. This behavior can be
+disabled by setting the ``re-detect`` value to ``false``, for instance:
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ],
+           "re-detect": false
+       },
+       ...
+   }
+
+
+Note that interfaces are not re-detected during ``config-test``.
+
+Usually loopback interfaces (e.g. the ``lo`` or ``lo0`` interface) are not
+configured, but if a loopback interface is explicitly configured and
+IP/UDP sockets are specified, the loopback interface is accepted.
+
+For example, this setup can be used to run Kea in a FreeBSD jail having only a
+loopback interface, to service a relayed DHCP request:
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "lo0" ],
+           "dhcp-socket-type": "udp"
+       },
+       ...
+   }
+
+Kea binds the service sockets for each interface on startup. If another
+process is already using a port, then Kea logs the message and suppresses an
+error. DHCP service runs, but it is unavailable on some interfaces.
+
+The "service-sockets-require-all" option makes Kea require all sockets to
+be successfully bound. If any opening fails, Kea interrupts the
+initialization and exits with a non-zero status. (Default is false).
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ],
+           "service-sockets-require-all": true
+       },
+       ...
+   }
+
+Sometimes, immediate interruption isn't a good choice. The port can be
+unavailable only temporary. In this case, retrying the opening may resolve
+the problem. Kea provides two options to specify the retrying:
+``service-sockets-max-retries`` and ``service-sockets-retry-wait-time``.
+
+The first defines a maximal number of retries that Kea makes to open a socket.
+The zero value (default) means that the Kea doesn't retry the process.
+
+The second defines a wait time (in milliseconds) between attempts. The default
+value is 5000 (5 seconds).
+
+::
+
+   "Dhcp4": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ],
+           "service-sockets-max-retries": 5,
+           "service-sockets-retry-wait-time": 5000
+       },
+       ...
+   }
+
+If "service-sockets-max-retries" is non-zero and "service-sockets-require-all"
+is false, then Kea retries the opening (if needed) but does not fail if any
+socket is still not opened.
+
+.. _dhcpinform-unicast-issues:
+
+Issues With Unicast Responses to DHCPINFORM
+-------------------------------------------
+
+The use of UDP sockets has certain benefits in deployments where the
+server receives only relayed traffic; these benefits are mentioned in
+:ref:`dhcp4-interface-configuration`. From the
+administrator's perspective it is often desirable to configure the
+system's firewall to filter out unwanted traffic, and the use of UDP
+sockets facilitates this. However, the administrator must also be aware
+of the implications related to filtering certain types of traffic, as it
+may impair the DHCP server's operation.
+
+In this section we focus on the case when the server receives the
+DHCPINFORM message from the client via a relay. According to `RFC
+2131 <https://tools.ietf.org/html/rfc2131>`__, the server should unicast
+the DHCPACK response to the address carried in the ``ciaddr`` field. When
+the UDP socket is in use, the DHCP server relies on the low-level
+functions of an operating system to build the data link, IP, and UDP
+layers of the outgoing message. Typically, the OS first uses ARP to
+obtain the client's link-layer address to be inserted into the frame's
+header, if the address is not cached from a previous transaction that
+the client had with the server. When the ARP exchange is successful, the
+DHCP message can be unicast to the client, using the obtained address.
+
+Some system administrators block ARP messages in their network, which
+causes issues for the server when it responds to the DHCPINFORM
+messages because the server is unable to send the DHCPACK if the
+preceding ARP communication fails. Since the OS is entirely responsible
+for the ARP communication and then sending the DHCP packet over the
+wire, the DHCP server has no means to determine that the ARP exchange
+failed and the DHCP response message was dropped. Thus, the server does
+not log any error messages when the outgoing DHCP response is dropped.
+At the same time, all hooks pertaining to the packet-sending operation
+will be called, even though the message never reaches its destination.
+
+Note that the issue described in this section is not observed when
+raw sockets are in use, because, in this case, the DHCP server builds
+all the layers of the outgoing message on its own and does not use ARP.
+Instead, it inserts the value carried in the ``chaddr`` field of the
+DHCPINFORM message into the link layer.
+
+Server administrators willing to support DHCPINFORM messages via relays
+should not block ARP traffic in their networks, or should use raw sockets
+instead of UDP sockets.
+
+.. _ipv4-subnet-id:
+
+IPv4 Subnet Identifier
+----------------------
+
+The subnet identifier (subnet ID) is a unique number associated with a particular
+subnet. In principle, it is used to associate clients' leases with their
+respective subnets. When a subnet identifier is not specified for a
+subnet being configured, it is automatically assigned by the
+configuration mechanism. The identifiers are assigned starting at 1 and are
+monotonically increased for each subsequent subnet: 1, 2, 3, ....
+
+If there are multiple subnets configured with auto-generated identifiers
+and one of them is removed, the subnet identifiers may be renumbered.
+For example: if there are four subnets and the third is removed, the
+last subnet will be assigned the identifier that the third subnet had
+before removal. As a result, the leases stored in the lease database for
+subnet 3 are now associated with subnet 4, something that may have
+unexpected consequences. The only remedy for this issue at present is to
+manually specify a unique identifier for each subnet.
+
+.. note::
+
+   Subnet IDs must be greater than zero and less than 4294967295.
+
+The following configuration assigns the specified subnet identifier
+to a newly configured subnet:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "id": 1024,
+               ...
+           }
+       ]
+   }
+
+This identifier will not change for this subnet unless the ``id``
+parameter is removed or set to 0. The value of 0 forces auto-generation
+of the subnet identifier.
+
+.. _ipv4-subnet-prefix:
+
+IPv4 Subnet Prefix
+------------------
+
+The subnet prefix is the second way to identify a subnet. Kea can
+accept non-canonical subnet addresses; for instance,
+this configuration is accepted:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+              "subnet": "192.0.2.1/24",
+               ...
+           }
+       ]
+   }
+
+This works even if there is another subnet with the "192.0.2.0/24" prefix;
+only the textual form of subnets are compared to avoid duplicates.
+
+.. note::
+
+    Abuse of this feature can lead to incorrect subnet selection
+    (see :ref:`dhcp4-subnet-selection`).
+
+.. _dhcp4-address-config:
+
+Configuration of IPv4 Address Pools
+-----------------------------------
+
+The main role of a DHCPv4 server is address assignment. For this, the
+server must be configured with at least one subnet and one pool of
+dynamic addresses to be managed. For example, assume that the server is
+connected to a network segment that uses the 192.0.2.0/24 prefix. The
+administrator of that network decides that addresses from the range
+192.0.2.10 to 192.0.2.20 are going to be managed by the DHCPv4 server.
+Such a configuration can be achieved in the following way:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [
+                   { "pool": "192.0.2.10 - 192.0.2.20" }
+               ],
+               ...
+           }
+       ]
+   }
+
+Note that ``subnet`` is defined as a simple string, but the ``pools``
+parameter is actually a list of pools; for this reason, the pool
+definition is enclosed in square brackets, even though only one range of
+addresses is specified.
+
+Each ``pool`` is a structure that contains the parameters that describe
+a single pool. Currently there is only one parameter, ``pool``, which
+gives the range of addresses in the pool.
+
+It is possible to define more than one pool in a subnet; continuing the
+previous example, further assume that 192.0.2.64/26 should also be
+managed by the server. It could be written as 192.0.2.64 to 192.0.2.127,
+or it can be expressed more simply as 192.0.2.64/26. Both
+formats are supported by ``Dhcp4`` and can be mixed in the pool list. For
+example, the following pools could be defined:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [
+                   { "pool": "192.0.2.10-192.0.2.20" },
+                   { "pool": "192.0.2.64/26" }
+               ],
+               ...
+           }
+       ],
+       ...
+   }
+
+White space in pool definitions is ignored, so spaces before and after
+the hyphen are optional. They can be used to improve readability.
+
+The number of pools is not limited, but for performance reasons it is
+recommended to use as few as possible.
+
+The server may be configured to serve more than one subnet. To add a
+second subnet, use a command similar to the following:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
+               ...
+           },
+           {
+               "subnet": "192.0.3.0/24",
+               "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
+               ...
+           },
+           {
+               "subnet": "192.0.4.0/24",
+               "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
+               ...
+           }
+       ]
+   }
+
+When configuring a DHCPv4 server using prefix/length notation, please
+pay attention to the boundary values. When specifying that the server
+can use a given pool, it is also able to allocate the first
+(typically a network address) and the last (typically a broadcast
+address) address from that pool. In the aforementioned example of pool
+192.0.3.0/24, both the 192.0.3.0 and 192.0.3.255 addresses may be
+assigned as well. This may be invalid in some network configurations. To
+avoid this, use the ``min-max`` notation.
+
+.. note::
+
+    Here are some liberties and limits to the values that subnets and pools can
+    take in Kea configurations that are out of the ordinary:
+
+    +-------------------------------------------------------------+---------+--------------------------------------------------------------------------------------+
+    | Kea configuration case                                      | Allowed | Comment                                                                              |
+    +=============================================================+=========+======================================================================================+
+    | Overlapping subnets                                         | Yes     | Administrator should consider how clients are matched to these subnets.              |
+    +-------------------------------------------------------------+---------+--------------------------------------------------------------------------------------+
+    | Overlapping pools in one subnet                             | No      | Startup error: DHCP4_PARSER_FAIL                                                     |
+    +-------------------------------------------------------------+---------+--------------------------------------------------------------------------------------+
+    | Overlapping address pools in different subnets              | Yes     | Specifying the same address pool in different subnets can be used as an equivalent   |
+    |                                                             |         | of the global address pool. In that case, the server can assign addresses from the   |
+    |                                                             |         | same range regardless of the client's subnet. If an address from such a pool is      |
+    |                                                             |         | assigned to a client in one subnet, the same address will be renewed for this        |
+    |                                                             |         | client if it moves to another subnet. Another client in a different subnet will      |
+    |                                                             |         | not be assigned an address already assigned to the client in any of the subnets.     |
+    +-------------------------------------------------------------+---------+--------------------------------------------------------------------------------------+
+    | Pools not matching the subnet prefix                        | No      | Startup error: DHCP4_PARSER_FAIL                                                     |
+    +-------------------------------------------------------------+---------+--------------------------------------------------------------------------------------+
+
+.. _dhcp4-t1-t2-times:
+
+Sending T1 (Option 58) and T2 (Option 59)
+-----------------------------------------
+
+According to `RFC 2131 <https://tools.ietf.org/html/rfc2131>`__,
+servers should send values for T1 and T2 that are 50% and 87.5% of the
+lease lifetime, respectively. By default, ``kea-dhcp4`` does not send
+either value; it can be configured to send values that are either specified
+explicitly or that are calculated as percentages of the lease time. The
+server's behavior is governed by a combination of configuration
+parameters, two of which have already been mentioned.
+To send specific, fixed values use the following two parameters:
+
+-  ``renew-timer`` - specifies the value of T1 in seconds.
+
+-  ``rebind-timer`` - specifies the value of T2 in seconds.
+
+The server only sends T2 if it is less than the valid lease time. T1
+is only sent if T2 is being sent and T1 is less than T2; or T2
+is not being sent and T1 is less than the valid lease time.
+
+Calculating the values is controlled by the following three parameters.
+
+-  ``calculate-tee-times`` - when true, T1 and T2 are calculated as
+   percentages of the valid lease time. It defaults to false.
+
+-  ``t1-percent`` - the percentage of the valid lease time to use for
+   T1. It is expressed as a real number between 0.0 and 1.0 and must be
+   less than ``t2-percent``. The default value is 0.50, per RFC 2131.
+
+-  ``t2-percent`` - the percentage of the valid lease time to use for
+   T2. It is expressed as a real number between 0.0 and 1.0 and must be
+   greater than ``t1-percent``. The default value is .875, per RFC 2131.
+
+.. note::
+
+   In the event that both explicit values are specified and
+   ``calculate-tee-times`` is true, the server will use the explicit values.
+   Administrators with a setup where some subnets or shared-networks
+   use explicit values and some use calculated values must
+   not define the explicit values at any level higher than where they
+   will be used. Inheriting them from too high a scope, such as
+   global, will cause them to have explicit values at every level underneath
+   (shared-networks and subnets), effectively disabling calculated
+   values.
+
+.. _dhcp4-std-options:
+
+Standard DHCPv4 Options
+-----------------------
+
+One of the major features of the DHCPv4 server is the ability to provide
+configuration options to clients. Most of the options are sent by the
+server only if the client explicitly requests them using the Parameter
+Request List option. Those that do not require inclusion in the
+Parameter Request List option are commonly used options, e.g. "Domain
+Server", and options which require special behavior, e.g. "Client FQDN",
+which is returned to the client if the client has included this option
+in its message to the server.
+
+:ref:`dhcp4-std-options-list` comprises the list of the
+standard DHCPv4 options whose values can be configured using the
+configuration structures described in this section. This table excludes
+the options which require special processing and thus cannot be
+configured with fixed values. The last column of the table
+indicates which options can be sent by the server even when they are not
+requested in the Parameter Request List option, and those which are sent
+only when explicitly requested.
+
+The following example shows how to configure the addresses of DNS
+servers, which is one of the most frequently used options. Options
+specified in this way are considered global and apply to all configured
+subnets.
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+              "name": "domain-name-servers",
+              "code": 6,
+              "space": "dhcp4",
+              "csv-format": true,
+              "data": "192.0.2.1, 192.0.2.2"
+           },
+           ...
+       ]
+   }
+
+
+Note that either ``name`` or ``code`` is required; there is no need to
+specify both. ``space`` has a default value of ``dhcp4``, so this can be skipped
+as well if a regular (not encapsulated) DHCPv4 option is defined.
+Finally, ``csv-format`` defaults to ``true``, so it too can be skipped, unless
+the option value is specified as a hexadecimal string. Therefore,
+the above example can be simplified to:
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+              "name": "domain-name-servers",
+              "data": "192.0.2.1, 192.0.2.2"
+           },
+           ...
+       ]
+   }
+
+
+Defined options are added to the response when the client requests them,
+with a few exceptions which are always added. To enforce the addition of
+a particular option, set the ``always-send`` flag to ``true`` as in:
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+              "name": "domain-name-servers",
+              "data": "192.0.2.1, 192.0.2.2",
+              "always-send": true
+           },
+           ...
+       ]
+   }
+
+
+The effect is the same as if the client added the option code in the
+Parameter Request List option (or its equivalent for vendor options):
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+              "name": "domain-name-servers",
+              "data": "192.0.2.1, 192.0.2.2",
+              "always-send": true
+           },
+           ...
+       ],
+       "subnet4": [
+           {
+              "subnet": "192.0.3.0/24",
+              "option-data": [
+                  {
+                      "name": "domain-name-servers",
+                      "data": "192.0.3.1, 192.0.3.2"
+                  },
+                  ...
+              ],
+              ...
+           },
+           ...
+       ],
+       ...
+   }
+
+
+The ``domain-name-servers`` option is always added to responses (the
+always-send is "sticky"), but the value is the subnet one when the client
+is localized in the subnet.
+
+The ``name`` parameter specifies the option name. For a list of
+currently supported names, see :ref:`dhcp4-std-options-list`
+below. The ``code`` parameter specifies the option code, which must
+match one of the values from that list. The next line specifies the
+option space, which must always be set to ``dhcp4`` as these are standard
+DHCPv4 options. For other option spaces, including custom option spaces,
+see :ref:`dhcp4-option-spaces`. The next line specifies the format in
+which the data will be entered; use of CSV (comma-separated values) is
+recommended. The sixth line gives the actual value to be sent to
+clients. The data parameter is specified as normal text, with values separated by
+commas if more than one value is allowed.
+
+Options can also be configured as hexadecimal values. If ``csv-format``
+is set to ``false``, option data must be specified as a hexadecimal string.
+The following commands configure the ``domain-name-servers`` option for all
+subnets with the following addresses: 192.0.3.1 and 192.0.3.2. Note that
+``csv-format`` is set to ``false``.
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+               "name": "domain-name-servers",
+               "code": 6,
+               "space": "dhcp4",
+               "csv-format": false,
+               "data": "C0 00 03 01 C0 00 03 02"
+           },
+           ...
+       ],
+       ...
+   }
+
+Kea supports the following formats when specifying hexadecimal data:
+
+-  ``Delimited octets`` - one or more octets separated by either colons or
+   spaces (":" or " "). While each octet may contain one or two digits,
+   we strongly recommend always using two digits. Valid examples are
+   "ab:cd:ef" and "ab cd ef".
+
+-  ``String of digits`` - a continuous string of hexadecimal digits with
+   or without a "0x" prefix. Valid examples are "0xabcdef" and "abcdef".
+
+Care should be taken to use proper encoding when using hexadecimal
+format; Kea's ability to validate data correctness in hexadecimal is
+limited.
+
+It is also possible to specify data for binary options as
+a single-quoted text string within double quotes as shown (note that
+``csv-format`` must be set to ``false``):
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+               "name": "user-class",
+               "code": 77,
+               "space": "dhcp4",
+               "csv-format": false,
+               "data": "'convert this text to binary'"
+           },
+           ...
+       ],
+       ...
+   }
+
+Most of the parameters in the ``option-data`` structure are optional and
+can be omitted in some circumstances, as discussed in :ref:`dhcp4-option-data-defaults`.
+
+It is possible to specify or override options on a per-subnet basis. If
+clients connected to most subnets are expected to get the same
+values of a given option, administrators should use global options. On the other
+hand, if different values are used in each subnet, it does not make sense
+to specify global option values; rather, only
+subnet-specific ones should be set.
+
+The following commands override the global DNS servers option for a
+particular subnet, setting a single DNS server with address 192.0.2.3:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "option-data": [
+                   {
+                       "name": "domain-name-servers",
+                       "code": 6,
+                       "space": "dhcp4",
+                       "csv-format": true,
+                       "data": "192.0.2.3"
+                   },
+                   ...
+               ],
+               ...
+           },
+           ...
+       ],
+       ...
+   }
+
+In some cases it is useful to associate some options with an address
+pool from which a client is assigned a lease. Pool-specific option
+values override subnet-specific and global option values; it
+is not possible to prioritize assignment of pool-specific
+options via the order of pool declarations in the server
+configuration.
+
+The following configuration snippet demonstrates how to specify the DNS
+servers option, which is assigned to a client only if the client
+obtains an address from the given pool:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "pools": [
+                   {
+                       "pool": "192.0.2.1 - 192.0.2.200",
+                       "option-data": [
+                           {
+                               "name": "domain-name-servers",
+                               "data": "192.0.2.3"
+                            },
+                            ...
+                       ],
+                       ...
+                   },
+                   ...
+               ],
+               ...
+           },
+           ...
+       ],
+       ...
+   }
+
+Options can also be specified in class or host-reservation scope. The
+current Kea options precedence order is (from most important to least): host
+reservation, pool, subnet, shared network, class, global.
+
+When a data field is a string and that string contains the comma (``,``;
+U+002C) character, the comma must be escaped with two backslashes (``\\,``;
+U+005C). This double escape is required because both the routine
+splitting of CSV data into fields and JSON use the same escape character; a
+single escape (``\,``) would make the JSON invalid. For example, the string
+"foo,bar" must be represented as:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "pools": [
+                   {
+                       "option-data": [
+                           {
+                               "name": "boot-file-name",
+                               "data": "foo\\,bar"
+                           }
+                       ]
+                   },
+                   ...
+               ],
+               ...
+           },
+           ...
+       ],
+       ...
+   }
+
+Some options are designated as arrays, which means that more than one
+value is allowed. For example, the option ``time-servers``
+allows the specification of more than one IPv4 address, enabling clients
+to obtain the addresses of multiple NTP servers.
+
+:ref:`dhcp4-custom-options` describes the
+configuration syntax to create custom option definitions (formats).
+Creation of custom definitions for standard options is generally not
+permitted, even if the definition being created matches the actual
+option format defined in the RFCs. There is an exception to this rule
+for standard options for which Kea currently does not provide a
+definition. To use such options, a server administrator must
+create a definition as described in
+:ref:`dhcp4-custom-options` in the ``dhcp4`` option space. This
+definition should match the option format described in the relevant RFC,
+but the configuration mechanism will allow any option format as it
+currently has no means to validate it.
+
+The currently supported standard DHCPv4 options are listed in
+the table below. "Name" and "Code" are the
+values that should be used as a name/code in the option-data structures.
+"Type" designates the format of the data; the meanings of the various
+types are given in :ref:`dhcp-types`.
+
+.. _dhcp4-std-options-list:
+
+.. table:: List of standard DHCPv4 options configurable by an administrator
+
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | Name                                   | Code | Type                      | Array?      | Returned if |
+   |                                        |      |                           |             | not         |
+   |                                        |      |                           |             | requested?  |
+   +========================================+======+===========================+=============+=============+
+   | time-offset                            | 2    | int32                     | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | routers                                | 3    | ipv4-address              | true        | true        |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | time-servers                           | 4    | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | name-servers                           | 5    | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | domain-name-servers                    | 6    | ipv4-address              | true        | true        |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | log-servers                            | 7    | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | cookie-servers                         | 8    | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | lpr-servers                            | 9    | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | impress-servers                        | 10   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | resource-location-servers              | 11   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | boot-size                              | 13   | uint16                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | merit-dump                             | 14   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | domain-name                            | 15   | fqdn                      | false       | true        |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | swap-server                            | 16   | ipv4-address              | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | root-path                              | 17   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | extensions-path                        | 18   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | ip-forwarding                          | 19   | boolean                   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | non-local-source-routing               | 20   | boolean                   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | policy-filter                          | 21   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | max-dgram-reassembly                   | 22   | uint16                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | default-ip-ttl                         | 23   | uint8                     | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | path-mtu-aging-timeout                 | 24   | uint32                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | path-mtu-plateau-table                 | 25   | uint16                    | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | interface-mtu                          | 26   | uint16                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | all-subnets-local                      | 27   | boolean                   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | broadcast-address                      | 28   | ipv4-address              | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | perform-mask-discovery                 | 29   | boolean                   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | mask-supplier                          | 30   | boolean                   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | router-discovery                       | 31   | boolean                   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | router-solicitation-address            | 32   | ipv4-address              | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | static-routes                          | 33   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | trailer-encapsulation                  | 34   | boolean                   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | arp-cache-timeout                      | 35   | uint32                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | ieee802-3-encapsulation                | 36   | boolean                   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | default-tcp-ttl                        | 37   | uint8                     | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | tcp-keepalive-interval                 | 38   | uint32                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | tcp-keepalive-garbage                  | 39   | boolean                   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nis-domain                             | 40   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nis-servers                            | 41   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | ntp-servers                            | 42   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | vendor-encapsulated-options            | 43   | empty                     | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | netbios-name-servers                   | 44   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | netbios-dd-server                      | 45   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | netbios-node-type                      | 46   | uint8                     | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | netbios-scope                          | 47   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | font-servers                           | 48   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | x-display-manager                      | 49   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | dhcp-option-overload                   | 52   | uint8                     | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | dhcp-server-identifier                 | 54   | ipv4-address              | false       | true        |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | dhcp-message                           | 56   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | dhcp-max-message-size                  | 57   | uint16                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | vendor-class-identifier                | 60   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nwip-domain-name                       | 62   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nwip-suboptions                        | 63   | binary                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nisplus-domain-name                    | 64   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nisplus-servers                        | 65   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | tftp-server-name                       | 66   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | boot-file-name                         | 67   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | mobile-ip-home-agent                   | 68   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | smtp-server                            | 69   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | pop-server                             | 70   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nntp-server                            | 71   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | www-server                             | 72   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | finger-server                          | 73   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | irc-server                             | 74   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | streettalk-server                      | 75   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | streettalk-directory-assistance-server | 76   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | user-class                             | 77   | binary                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | slp-directory-agent                    | 78   | record (boolean,          | true        | false       |
+   |                                        |      | ipv4-address)             |             |             |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | slp-service-scope                      | 79   | record (boolean, string)  | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nds-server                             | 85   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nds-tree-name                          | 86   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | nds-context                            | 87   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | bcms-controller-names                  | 88   | fqdn                      | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | bcms-controller-address                | 89   | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | client-system                          | 93   | uint16                    | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | client-ndi                             | 94   | record (uint8, uint8,     | false       | false       |
+   |                                        |      | uint8)                    |             |             |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | uuid-guid                              | 97   | record (uint8, binary)    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | uap-servers                            | 98   | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | geoconf-civic                          | 99   | binary                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | pcode                                  | 100  | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | tcode                                  | 101  | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | v6-only-preferred                      | 108  | uint32                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | netinfo-server-address                 | 112  | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | netinfo-server-tag                     | 113  | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | v4-captive-portal                      | 114  | string                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | auto-config                            | 116  | uint8                     | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | name-service-search                    | 117  | uint16                    | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | domain-search                          | 119  | fqdn                      | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | vivco-suboptions                       | 124  | record (uint32, binary)   | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | vivso-suboptions                       | 125  | uint32                    | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | pana-agent                             | 136  | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | v4-lost                                | 137  | fqdn                      | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | capwap-ac-v4                           | 138  | ipv4-address              | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | sip-ua-cs-domains                      | 141  | fqdn                      | true        | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | rdnss-selection                        | 146  | record (uint8,            | true        | false       |
+   |                                        |      | ipv4-address,             |             |             |
+   |                                        |      | ipv4-address, fqdn)       |             |             |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | v4-portparams                          | 159  | record (uint8, psid)      | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | option-6rd                             | 212  | record (uint8, uint8,     | true        | false       |
+   |                                        |      | ipv6-address,             |             |             |
+   |                                        |      | ipv4-address)             |             |             |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+   | v4-access-domain                       | 213  | fqdn                      | false       | false       |
+   +----------------------------------------+------+---------------------------+-------------+-------------+
+
+.. note::
+
+  The ``default-url`` option was replaced with ``v4-captive-portal`` in Kea 2.1.2, as introduced by
+  `RFC 8910 <https://tools.ietf.org/html/rfc8910>`_. The new option has exactly the same format as the
+  old one. The general perception is that ``default-url`` was seldom used. If you used it and migrating,
+  please replace ``default-url`` with ``v4-captive-portal`` and your configuration will continue to work
+  as before.
+
+Kea also supports other options than those listed above; the following options
+are returned by the Kea engine itself and in general should not be configured
+manually.
+
+.. table:: List of standard DHCPv4 options managed by Kea on its own and not directly configurable by an administrator
+
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | Name                           | Code  | Type                                  | Description                                                       |
+   +================================+=======+=======================================+===================================================================+
+   | subnet-mask                    | 1     | ipv4-address                          | calculated automatically, based on subnet definition.             |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | host-name                      | 12    | string                                | sent by client, generally governed by the DNS configuration.      |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | dhcp-requested-address         | 50    | ipv6-address                          | may be sent by the client and the server should not set it.       |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | dhcp-lease-time                | 51    | uint32                                | set automatically based on the ``valid-lifetime`` parameter.      |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | dhcp-message-type              | 53    | string                                | sent by clients and servers. Set by the Kea engine depending on   |
+   |                                |       |                                       | the situation and should never be configured explicitly.          |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | dhcp-parameter-request-list    | 55    | uint8 array                           | sent by clients and should never be sent by the server.           |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | dhcp-renewal-time              | 58    | uint32                                | governed by ``renew-timer`` parameter.                            |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | dhcp-rebinding-time            | 59    | uint32                                | governed by ``rebind-timer`` parameter.                           |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | dhcp-client-identifier         | 61    | binary                                | sent by client, echoed back with the value sent by the client.    |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | fqdn                           | 81    | record (uint8, uint8, uint8, fqdn)    | part of the DDNS and D2 configuration.                            |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | dhcp-agent-options             | 82    | empty                                 | sent by the relay agent. This is an empty container option; see   |
+   |                                |       |                                       | RAI option detail later in this section.                          |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | authenticate                   | 90    | binary                                | sent by client, Kea does not yet validate it.                     |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | client-last-transaction-time   | 91    | uint32                                | sent by client, server does not set it.                           |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | associated-ip                  | 92    | ipv4-address array                    | sent by client, server responds with list of addresses.           |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+   | subnet-selection               | 118   | ipv4-address                          | if present in client's messages, will be used in the subnet       |
+   |                                |       |                                       | selection process.                                                |
+   +--------------------------------+-------+---------------------------------------+-------------------------------------------------------------------+
+
+The following table lists all option types used in the previous two tables with a description of
+what values are accepted for them.
+
+.. _dhcp-types:
+
+.. table:: List of standard DHCP option types
+
+   +-----------------+-------------------------------------------------------+
+   | Name            | Meaning                                               |
+   +=================+=======================================================+
+   | binary          | An arbitrary string of bytes, specified as a set      |
+   |                 | of hexadecimal digits.                                |
+   +-----------------+-------------------------------------------------------+
+   | boolean         | A boolean value with allowed                          |
+   |                 | values true or false.                                 |
+   +-----------------+-------------------------------------------------------+
+   | empty           | No value; data is carried in                          |
+   |                 | sub-options.                                          |
+   +-----------------+-------------------------------------------------------+
+   | fqdn            | Fully qualified domain name (e.g.                     |
+   |                 | www.example.com).                                     |
+   +-----------------+-------------------------------------------------------+
+   | ipv4-address    | IPv4 address in the usual                             |
+   |                 | dotted-decimal notation (e.g.                         |
+   |                 | 192.0.2.1).                                           |
+   +-----------------+-------------------------------------------------------+
+   | ipv6-address    | IPv6 address in the usual colon                       |
+   |                 | notation (e.g. 2001:db8::1).                          |
+   +-----------------+-------------------------------------------------------+
+   | ipv6-prefix     | IPv6 prefix and prefix length                         |
+   |                 | specified using CIDR notation,                        |
+   |                 | e.g. 2001:db8:1::/64. This data                       |
+   |                 | type is used to represent an                          |
+   |                 | 8-bit field conveying a prefix                        |
+   |                 | length and the variable length                        |
+   |                 | prefix value.                                         |
+   +-----------------+-------------------------------------------------------+
+   | psid            | PSID and PSID length separated by                     |
+   |                 | a slash, e.g. 3/4 specifies                           |
+   |                 | PSID=3 and PSID length=4. In the                      |
+   |                 | wire format it is represented by                      |
+   |                 | an 8-bit field carrying PSID                          |
+   |                 | length (in this case equal to 4)                      |
+   |                 | and the 16-bits-long PSID value                       |
+   |                 | field (in this case equal to                          |
+   |                 | "0011000000000000b" using binary                      |
+   |                 | notation). Allowed values for a                       |
+   |                 | PSID length are 0 to 16. See `RFC                     |
+   |                 | 7597 <https://tools.ietf.org/html/rfc7597>`__         |
+   |                 | for details about the PSID wire                       |
+   |                 | representation.                                       |
+   +-----------------+-------------------------------------------------------+
+   | record          | Structured data that may be                           |
+   |                 | comprised of any types (except                        |
+   |                 | "record" and "empty"). The array                      |
+   |                 | flag applies to the last field                        |
+   |                 | only.                                                 |
+   +-----------------+-------------------------------------------------------+
+   | string          | Any text. Please note that Kea                        |
+   |                 | silently discards any                                 |
+   |                 | terminating/trailing nulls from                       |
+   |                 | the end of "string" options when                      |
+   |                 | unpacking received packets. This                      |
+   |                 | is in keeping with `RFC 2132,                         |
+   |                 | Section                                               |
+   |                 | 2 <https://tools.ietf.org/html/rfc2132#section-2>`__. |
+   +-----------------+-------------------------------------------------------+
+   | tuple           | A length encoded as an 8-bit (16-bit                  |
+   |                 | for DHCPv6) unsigned integer                          |
+   |                 | followed by a string of this                          |
+   |                 | length.                                               |
+   +-----------------+-------------------------------------------------------+
+   | uint8           | An 8-bit unsigned integer with                        |
+   |                 | allowed values 0 to 255.                              |
+   +-----------------+-------------------------------------------------------+
+   | uint16          | A 16-bit unsigned integer with                        |
+   |                 | allowed values 0 to 65535.                            |
+   +-----------------+-------------------------------------------------------+
+   | uint32          | A 32-bit unsigned integer with                        |
+   |                 | allowed values 0 to 4294967295.                       |
+   +-----------------+-------------------------------------------------------+
+   | int8            | An 8-bit signed integer with allowed                  |
+   |                 | values -128 to 127.                                   |
+   +-----------------+-------------------------------------------------------+
+   | int16           | A 16-bit signed integer with                          |
+   |                 | allowed values -32768 to 32767.                       |
+   +-----------------+-------------------------------------------------------+
+   | int32           | A 32-bit signed integer with                          |
+   |                 | allowed values -2147483648 to                         |
+   |                 | 2147483647.                                           |
+   +-----------------+-------------------------------------------------------+
+
+Kea also supports the Relay Agent Information (RAI) option, sometimes referred to as the relay option, agent
+option, or simply option 82. The option itself is just a container and does not convey any information
+on its own. The following table contains a list of RAI sub-options that Kea can understand. The RAI
+and its sub-options are inserted by the relay agent and received by Kea; there is no need for Kea
+to be configured with those options.
+
+.. table:: List of RAI sub-options that Kea can understand
+
+   +--------------------+------+----------------------------------------------------------------------+
+   | Name               | Code | Comment                                                              |
+   +====================+======+======================================================================+
+   | circuit-id         | 1    | Used when host-reservation-identifiers is set to `circuit-id`.       |
+   +--------------------+------+----------------------------------------------------------------------+
+   | remote-id          | 2    | Can be used with flex-id to identify hosts.                          |
+   +--------------------+------+----------------------------------------------------------------------+
+   | link selection     | 5    | If present, is used to select the appropriate subnet.                |
+   +--------------------+------+----------------------------------------------------------------------+
+   | subscriber-id      | 6    | Can be used with flex-id to identify hosts.                          |
+   +--------------------+------+----------------------------------------------------------------------+
+   | server-id-override | 11   | If sent by the relay, Kea accepts it as the `server-id`.             |
+   +--------------------+------+----------------------------------------------------------------------+
+   | relay-source-port  | 19   | If sent by the relay, Kea sends back its responses to this port.     |
+   +--------------------+------+----------------------------------------------------------------------+
+
+All other RAI sub-options can be used in client classification to classify incoming packets to specific classes
+and/or by ``flex-id`` to construct a unique device identifier.
+
+.. _dhcp4-custom-options:
+
+Custom DHCPv4 Options
+---------------------
+
+Kea supports custom (non-standard) DHCPv4 options. Let's say that we want
+to define a new DHCPv4 option called ``foo``, which will have code 222
+and will convey a single, unsigned, 32-bit integer value.
+Such an option can be defined by putting the following entry in the configuration file:
+
+::
+
+   "Dhcp4": {
+       "option-def": [
+           {
+               "name": "foo",
+               "code": 222,
+               "type": "uint32",
+               "array": false,
+               "record-types": "",
+               "space": "dhcp4",
+               "encapsulate": ""
+           }, ...
+       ],
+       ...
+   }
+
+The ``false`` value of the ``array`` parameter determines that the
+option does NOT comprise an array of ``uint32`` values but is, instead, a
+single value. Two other parameters have been left blank:
+``record-types`` and ``encapsulate``. The former specifies the
+comma-separated list of option data fields, if the option comprises a
+record of data fields. The ``record-types`` value should be non-empty if
+``type`` is set to "record"; otherwise it must be left blank. The latter
+parameter specifies the name of the option space being encapsulated by
+the particular option. If the particular option does not encapsulate any
+option space, the parameter should be left blank. Note that the ``option-def``
+configuration statement only defines the format of an option and does
+not set its value(s).
+
+The ``name``, ``code``, and ``type`` parameters are required; all others
+are optional. The ``array`` default value is ``false``. The
+``record-types`` and ``encapsulate`` default values are blank (``""``).
+The default ``space`` is ``dhcp4``.
+
+Once the new option format is defined, its value is set in the same way
+as for a standard option. For example, the following commands set a
+global value that applies to all subnets.
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+               "name": "foo",
+               "code": 222,
+               "space": "dhcp4",
+               "csv-format": true,
+               "data": "12345"
+           }, ...
+       ],
+       ...
+   }
+
+New options can take more complex forms than the simple use of primitives
+(uint8, string, ipv4-address, etc.); it is possible to define an option
+comprising a number of existing primitives.
+
+For example, say we want to define a new option that will consist of
+an IPv4 address, followed by an unsigned 16-bit integer, followed by a
+boolean value, followed by a text string. Such an option could be
+defined in the following way:
+
+::
+
+   "Dhcp4": {
+       "option-def": [
+           {
+               "name": "bar",
+               "code": 223,
+               "space": "dhcp4",
+               "type": "record",
+               "array": false,
+               "record-types": "ipv4-address, uint16, boolean, string",
+               "encapsulate": ""
+           }, ...
+       ],
+       ...
+   }
+
+The ``type`` is set to ``"record"`` to indicate that the option contains
+multiple values of different types. These types are given as a
+comma-separated list in the ``record-types`` field and should be ones
+from those listed in :ref:`dhcp-types`.
+
+The option's values are set in an ``option-data`` statement as follows:
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+               "name": "bar",
+               "space": "dhcp4",
+               "code": 223,
+               "csv-format": true,
+               "data": "192.0.2.100, 123, true, Hello World"
+           }
+       ],
+       ...
+   }
+
+``csv-format`` is set to ``"true"`` to indicate that the ``data`` field
+comprises a comma-separated list of values. The values in ``data``
+must correspond to the types set in the ``record-types`` field of the
+option definition.
+
+When ``array`` is set to ``"true"`` and ``type`` is set to ``"record"``, the
+last field is an array, i.e. it can contain more than one value, as in:
+
+::
+
+   "Dhcp4": {
+       "option-def": [
+           {
+               "name": "bar",
+               "code": 223,
+               "space": "dhcp4",
+               "type": "record",
+               "array": true,
+               "record-types": "ipv4-address, uint16",
+               "encapsulate": ""
+           }, ...
+       ],
+       ...
+   }
+
+The new option content is one IPv4 address followed by one or more 16-bit
+unsigned integers.
+
+.. note::
+
+   In general, boolean values are specified as ``true`` or ``false``,
+   without quotes. Some specific boolean parameters may also accept
+   ``"true"``, ``"false"``, ``0``, ``1``, ``"0"``, and ``"1"``.
+
+.. note::
+
+   Numbers can be specified in decimal or hexadecimal format. The
+   hexadecimal format can be either plain (e.g. abcd) or prefixed with
+   0x (e.g. 0xabcd).
+
+.. _dhcp4-private-opts:
+
+DHCPv4 Private Options
+----------------------
+
+Options with a code between 224 and 254 are reserved for private use.
+They can be defined at the global scope or at the client-class local
+scope; this allows option definitions to be used depending on context,
+and option data to be set accordingly. For instance, to configure an old
+PXEClient vendor:
+
+::
+
+   "Dhcp4": {
+       "client-classes": [
+           {
+               "name": "pxeclient",
+               "test": "option[vendor-class-identifier].text == 'PXEClient'",
+               "option-def": [
+                   {
+                       "name": "configfile",
+                       "code": 209,
+                       "type": "string"
+                   }
+               ],
+               ...
+           }, ...
+       ],
+       ...
+   }
+
+As the Vendor-Specific Information (VSI) option (code 43) has a vendor-specific
+format, i.e. can carry either raw binary value or sub-options, this
+mechanism is also available for this option.
+
+In the following example taken from a real configuration, two vendor
+classes use option 43 for different and incompatible purposes:
+
+::
+
+   "Dhcp4": {
+       "option-def": [
+           {
+               "name": "cookie",
+               "code": 1,
+               "type": "string",
+               "space": "APC"
+           },
+           {
+               "name": "mtftp-ip",
+               "code": 1,
+               "type": "ipv4-address",
+               "space": "PXE"
+           },
+           ...
+       ],
+       "client-classes": [
+           {
+               "name": "APC",
+               "test": "option[vendor-class-identifier].text == 'APC'",
+               "option-def": [
+                   {
+                       "name": "vendor-encapsulated-options",
+                       "type": "empty",
+                       "encapsulate": "APC"
+                   }
+               ],
+               "option-data": [
+                   {
+                       "name": "cookie",
+                       "space": "APC",
+                       "data": "1APC"
+                   },
+                   {
+                       "name": "vendor-encapsulated-options"
+                   },
+                   ...
+               ],
+               ...
+           },
+           {
+               "name": "PXE",
+               "test": "option[vendor-class-identifier].text == 'PXE'",
+               "option-def": [
+                   {
+                       "name": "vendor-encapsulated-options",
+                       "type": "empty",
+                       "encapsulate": "PXE"
+                   }
+               ],
+               "option-data": [
+                   {
+                       "name": "mtftp-ip",
+                       "space": "PXE",
+                       "data": "0.0.0.0"
+                   },
+                   {
+                       "name": "vendor-encapsulated-options"
+                   },
+                   ...
+               ],
+               ...
+           },
+           ...
+       ],
+       ...
+   }
+
+The definition used to decode a VSI option is:
+
+1. The local definition of a client class the incoming packet belongs
+   to;
+
+2. If none, the global definition;
+
+3. If none, the last-resort definition described in the next section,
+   :ref:`dhcp4-vendor-opts` (backward-compatible with previous Kea versions).
+
+.. note::
+
+   This last-resort definition for the Vendor-Specific Information
+   option (code 43) is not compatible with a raw binary value. When
+   there are known cases where a raw binary value will be used, a
+   client class must be defined with both a classification expression
+   matching these cases and an option definition for the VSI option with
+   a binary type and no encapsulation.
+
+.. note::
+
+   By default, in the Vendor-Specific Information option (code 43),
+   sub-option code 0 and 255 mean PAD and END respectively, according to
+   `RFC 2132 <https://tools.ietf.org/html/rfc2132>`_. In other words, the
+   sub-option code values of 0 and 255 are reserved. Kea does, however,
+   allow users to define sub-option codes from 0 to 255. If
+   sub-options with codes 0 and/or 255 are defined, bytes with that value are
+   no longer treated as a PAD or an END, but as the sub-option code
+   when parsing a VSI option in an incoming query.
+
+   Option 43 input processing (also called unpacking) is deferred so that it
+   happens after classification. This means clients cannot be classified
+   using option 43 sub-options. The definition used to unpack option 43
+   is determined as follows:
+
+   - If defined at the global scope, this definition is used.
+   - If defined at client class scope and the packet belongs to this
+     class, the client class definition is used.
+   - If not defined at global scope nor in a client class to which the
+     packet belongs, the built-in last resort definition is used. This
+     definition only says the sub-option space is
+     ``"vendor-encapsulated-options-space"``.
+
+   The output definition selection is a bit simpler:
+
+   - If the packet belongs to a client class which defines the option
+     43, use this definition.
+   - If defined at the global scope, use this definition.
+   - Otherwise, use the built-in last-resort definition.
+
+   Since they use a specific/per vendor option space, sub-options
+   are defined at the global scope.
+
+.. note::
+
+   Option definitions in client classes are allowed only for this
+   limited option set (codes 43 and from 224 to 254), and only for
+   DHCPv4.
+
+.. _dhcp4-vendor-opts:
+
+DHCPv4 Vendor-Specific Options
+------------------------------
+
+Currently there are two option spaces defined for the DHCPv4 daemon:
+``dhcp4`` (for the top-level DHCPv4 options) and
+``"vendor-encapsulated-options-space"``, which is empty by default but in
+which options can be defined. Those options are carried in the
+Vendor-Specific Information option (code 43). The following examples
+show how to define an option ``foo`` with code 1 that
+comprises an IPv4 address, an unsigned 16-bit integer, and a string. The
+``foo`` option is conveyed in a Vendor-Specific Information option.
+
+The first step is to define the format of the option:
+
+::
+
+   "Dhcp4": {
+       "option-def": [
+           {
+               "name": "foo",
+               "code": 1,
+               "space": "vendor-encapsulated-options-space",
+               "type": "record",
+               "array": false,
+               "record-types": "ipv4-address, uint16, string",
+               "encapsulate": ""
+           }
+       ],
+       ...
+   }
+
+(Note that the option space is set to
+``"vendor-encapsulated-options-space"``.) Once the option format is defined,
+the next step is to define actual values for that option:
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+               "name": "foo",
+               "space": "vendor-encapsulated-options-space",
+               "code": 1,
+               "csv-format": true,
+               "data": "192.0.2.3, 123, Hello World"
+           }
+       ],
+       ...
+   }
+
+In this example, we also include the Vendor-Specific Information option, which
+conveys our sub-option ``foo``. This is required; otherwise, the option
+will not be included in messages sent to the client.
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+               "name": "vendor-encapsulated-options"
+           }
+       ],
+       ...
+   }
+
+Alternatively, the option can be specified using its code.
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+               "code": 43
+           }
+       ],
+       ...
+   }
+
+Another popular option that is often somewhat imprecisely called the "vendor
+option" is option 125. Its proper name is the "vendor-independent
+vendor-specific information option" or "vivso". The idea behind vivso options
+is that each vendor has its own unique set of options with their own custom
+formats. The vendor is identified by a 32-bit unsigned integer called
+``enterprise-number`` or ``vendor-id``.
+
+
+The standard spaces defined in Kea and their options are:
+
+- ``vendor-4491``: Cable Television Laboratories, Inc. for DOCSIS3 options:
+
++-------------+--------------+------------------------------------------------------------------------+
+| option code | option name  | option description                                                     |
++=============+==============+========================================================================+
+| 1           | oro          | ORO (or Option Request Option) is used by clients to request a list of |
+|             |              | options they are interested in.                                        |
++-------------+--------------+------------------------------------------------------------------------+
+| 2           | tftp-servers | a list of IPv4 addresses of TFTP servers to be used by the cable modem |
++-------------+--------------+------------------------------------------------------------------------+
+
+In Kea each vendor is represented by its own vendor space. Since there
+are hundreds of vendors and sometimes they use different option
+definitions for different hardware, it is impossible for Kea to support
+them all natively. Fortunately, it's easy to define support for
+new vendor options. Let's take an example of the Genexis home gateway. This
+device requires sending the vivso 125 option with a sub-option 2 that
+contains a string with the TFTP server URL. To support such a device, three
+steps are needed: first, we need to define option definitions that will
+explain how the option is supposed to be formed. Second, we need to
+define option values. Third, we need to tell Kea when to send those
+specific options, which we can do via client classification.
+
+An example snippet of a configuration could look similar to the
+following:
+
+::
+
+   {
+       // First, we need to define that the suboption 2 in vivso option for
+       // vendor-id 25167 has a specific format (it's a plain string in this example).
+       // After this definition, we can specify values for option tftp.
+       "option-def": [
+       {
+           // We define a short name, so the option can be referenced by name.
+           // The option has code 2 and resides within vendor space 25167.
+           // Its data is a plain string.
+           "name": "tftp",
+           "code": 2,
+           "space": "vendor-25167",
+           "type": "string"
+       } ],
+
+       "client-classes": [
+       {
+           // We now need to tell Kea how to recognize when to use vendor space 25167.
+           // Usually we can use a simple expression, such as checking if the device
+           // sent a vivso option with specific vendor-id, e.g. "vendor[4491].exists".
+           // Unfortunately, Genexis is a bit unusual in this aspect, because it
+           // doesn't send vivso. In this case we need to look into the vendor class
+           // (option code 60) and see if there's a specific string that identifies
+           // the device.
+           "name": "cpe_genexis",
+           "test": "substring(option[60].hex,0,7) == 'HMC1000'",
+
+           // Once the device is recognized, we want to send two options:
+           // the vivso option with vendor-id set to 25167, and a suboption 2.
+           "option-data": [
+               {
+                   "name": "vivso-suboptions",
+                   "data": "25167"
+               },
+
+               // The suboption 2 value is defined as any other option. However,
+               // we want to send this suboption 2, even when the client didn't
+               // explicitly request it (often there is no way to do that for
+               // vendor options). Therefore we use always-send to force Kea
+               // to always send this option when 25167 vendor space is involved.
+               {
+                   "name": "tftp",
+                   "space": "vendor-25167",
+                   "data": "tftp://192.0.2.1/genexis/HMC1000.v1.3.0-R.img",
+                   "always-send": true
+               }
+           ]
+       } ]
+   }
+
+By default, Kea sends back
+only those options that are requested by a client, unless there are
+protocol rules that tell the DHCP server to always send an option. This
+approach works nicely in most cases and avoids problems with clients
+refusing responses with options they do not understand. However,
+the situation with vendor options is more complex, as they
+are not requested the same way as other options, are
+not well-documented in official RFCs, or vary by vendor.
+
+Some vendors (such
+as DOCSIS, identified by vendor option 4491) have a mechanism to
+request specific vendor options and Kea is able to honor those.
+Unfortunately, for many other vendors, such as Genexis (25167, discussed
+above), Kea does not have such a mechanism, so it cannot send any
+sub-options on its own. To solve this issue, we devised the concept of
+persistent options. Kea can be told to always send options, even if the
+client did not request them. This can be achieved by adding
+``"always-send": true`` to the option definition. Note that in this
+particular case an option is defined in vendor space 25167. With
+``always-send`` enabled, the option is sent every time there is a
+need to deal with vendor space 25167.
+
+Another possibility is to redefine the option; see :ref:`dhcp4-private-opts`.
+
+Kea comes with several example configuration files. Some of them showcase
+how to configure options 60 and 43. See ``doc/examples/kea4/vendor-specific.json``
+and ``doc/examples/kea6/vivso.json`` in the Kea sources.
+
+.. note::
+
+   Currently only one vendor is supported for the ``vivco-suboptions`` (code 124)
+   and ``vivso-suboptions`` (code 125) options. Specifying
+   multiple enterprise numbers within a single option instance or multiple
+   options with different enterprise numbers is not supported.
+
+.. _dhcp4-option-spaces:
+
+Nested DHCPv4 Options (Custom Option Spaces)
+--------------------------------------------
+
+It is sometimes useful to define a completely new option space, such as
+when a user creates a new option in the standard option space
+(``dhcp4``) and wants this option to convey sub-options. Since they are in
+a separate space, sub-option codes have a separate numbering scheme
+and may overlap with the codes of standard options.
+
+Note that the creation of a new option space is not required when
+defining sub-options for a standard option, because one is created by
+default if the standard option is meant to convey any sub-options (see
+:ref:`dhcp4-vendor-opts`).
+
+If we want a DHCPv4 option called ``container`` with code
+222, that conveys two sub-options with codes 1 and 2, we first need to
+define the new sub-options:
+
+::
+
+   "Dhcp4": {
+       "option-def": [
+           {
+               "name": "subopt1",
+               "code": 1,
+               "space": "isc",
+               "type": "ipv4-address",
+               "record-types": "",
+               "array": false,
+               "encapsulate": ""
+           },
+           {
+               "name": "subopt2",
+               "code": 2,
+               "space": "isc",
+               "type": "string",
+               "record-types": "",
+               "array": false,
+               "encapsulate": ""
+           }
+       ],
+       ...
+   }
+
+Note that we have defined the options to belong to a new option space
+(in this case, ``"isc"``).
+
+The next step is to define a regular DHCPv4 option with the desired code
+and specify that it should include options from the new option space:
+
+::
+
+   "Dhcp4": {
+       "option-def": [
+           ...,
+           {
+               "name": "container",
+               "code": 222,
+               "space": "dhcp4",
+               "type": "empty",
+               "array": false,
+               "record-types": "",
+               "encapsulate": "isc"
+           }
+       ],
+       ...
+   }
+
+The name of the option space in which the sub-options are defined is set
+in the ``encapsulate`` field. The ``type`` field is set to ``"empty"``, to
+indicate that this option does not carry any data other than
+sub-options.
+
+Finally, we can set values for the new options:
+
+::
+
+   "Dhcp4": {
+       "option-data": [
+           {
+               "name": "subopt1",
+               "code": 1,
+               "space": "isc",
+               "data": "192.0.2.3"
+           },
+           }
+               "name": "subopt2",
+               "code": 2,
+               "space": "isc",
+               "data": "Hello world"
+           },
+           {
+               "name": "container",
+               "code": 222,
+               "space": "dhcp4"
+           }
+       ],
+       ...
+   }
+
+It is possible to create an option which carries some data in
+addition to the sub-options defined in the encapsulated option space.
+For example, if the ``container`` option from the previous example were
+required to carry a uint16 value as well as the sub-options, the
+``type`` value would have to be set to ``"uint16"`` in the option
+definition. (Such an option would then have the following data
+structure: DHCP header, uint16 value, sub-options.) The value specified
+with the ``data`` parameter — which should be a valid integer enclosed
+in quotes, e.g. ``"123"`` — would then be assigned to the ``uint16`` field in
+the ``container`` option.
+
+.. _dhcp4-option-data-defaults:
+
+Unspecified Parameters for DHCPv4 Option Configuration
+------------------------------------------------------
+
+In many cases it is not required to specify all parameters for an option
+configuration, and the default values can be used. However, it is
+important to understand the implications of not specifying some of them,
+as it may result in configuration errors. The list below explains the
+behavior of the server when a particular parameter is not explicitly
+specified:
+
+-  ``name`` - the server requires either an option name or an option code to
+   identify an option. If this parameter is unspecified, the option code
+   must be specified.
+
+-  ``code`` - the server requires either an option name or an option code to
+   identify an option; this parameter may be left unspecified if the
+   ``name`` parameter is specified. However, this also requires that the
+   particular option have a definition (either as a standard option or
+   an administrator-created definition for the option using an
+   ``option-def`` structure), as the option definition associates an
+   option with a particular name. It is possible to configure an option
+   for which there is no definition (unspecified option format).
+   Configuration of such options requires the use of the option code.
+
+-  ``space`` - if the option space is unspecified it defaults to
+   ``dhcp4``, which is an option space holding standard DHCPv4 options.
+
+-  ``data`` - if the option data is unspecified it defaults to an empty
+   value. The empty value is mostly used for the options which have no
+   payload (boolean options), but it is legal to specify empty values
+   for some options which carry variable-length data and for which the
+   specification allows a length of 0. For such options, the data
+   parameter may be omitted in the configuration.
+
+-  ``csv-format`` - if this value is not specified, the server
+   assumes that the option data is specified as a list of comma-separated
+   values to be assigned to individual fields of the DHCP option.
+
+.. _dhcp4-support-for-long-options:
+
+Support for Long Options
+------------------------
+
+The kea-dhcp4 server partially supports long options (RFC3396).
+Since Kea 2.1.6, the server accepts configuring long options and suboptions
+(longer than 255 bytes). The options and suboptions are stored internally
+in their unwrapped form and they can be processed as usual using the parser
+language. On send, the server splits long options and suboptions into multiple
+options and suboptions, using the respective option code.
+
+::
+
+   "option-def": [
+       {
+           "array": false,
+           "code\": 240,
+           "encapsulate": "",
+           "name": "my-option",
+           "space": "dhcp4",
+           "type": "string"
+       }
+   ],
+   "subnet4": [
+       {
+           "subnet": "192.0.2.0/24",
+           "reservations": [
+               {
+                   "hw-address": "aa:bb:cc:dd:ee:ff",
+                   "option-data": [
+                       {
+                           "always-send": false,
+                           "code": 240,
+                           "name": "my-option",
+                           "csv-format": true,
+                           "data": "data
+                                    -00010203040506070809-00010203040506070809-00010203040506070809-00010203040506070809
+                                    -00010203040506070809-00010203040506070809-00010203040506070809-00010203040506070809
+                                    -00010203040506070809-00010203040506070809-00010203040506070809-00010203040506070809
+                                    -data",
+                           "space": "dhcp4"
+                       }
+                   ]
+               }
+           ]
+       }
+   ]
+
+.. note::
+
+   For this example, the data has been split on several lines, but Kea does not
+   support this in the configuration file.
+
+This example illustrates configuring a custom long option in a reservation.
+The server, when sending a response, will split this option into several options
+with the same code (11 options with option code 240).
+
+.. note::
+
+   Currently the server does not support storing long options in the databases,
+   either host reservations or configuration backend.
+
+The server is also able to receive packets with split options (options using
+the same option code) and to fuse the data chunks into one option. This is
+also supported for suboptions if each suboption data chunk also contains the
+suboption code and suboption length.
+
+.. _dhcp4-stateless-configuration:
+
+Stateless Configuration of DHCPv4 Clients
+-----------------------------------------
+
+The DHCPv4 server supports stateless client configuration, whereby
+the client has an IP address configured (e.g. using manual
+configuration) and only contacts the server to obtain other
+configuration parameters, such as addresses of DNS servers. To
+obtain the stateless configuration parameters, the client sends the
+DHCPINFORM message to the server with the ``ciaddr`` set to the address
+that the client is currently using. The server unicasts the DHCPACK
+message to the client that includes the stateless configuration
+("yiaddr" not set).
+
+The server responds to the DHCPINFORM when the client is associated
+with a subnet defined in the server's configuration. An example subnet
+configuration looks like this:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24"
+               "option-data": [ {
+                   "name": "domain-name-servers",
+                   "code": 6,
+                   "data": "192.0.2.200,192.0.2.201",
+                   "csv-format": true,
+                   "space": "dhcp4"
+               } ]
+           }
+       ]
+   }
+
+This subnet specifies the single option which will be included in the
+DHCPACK message to the client in response to DHCPINFORM. The
+subnet definition does not require the address pool configuration if it
+will be used solely for stateless configuration.
+
+This server will associate the subnet with the client if one of the
+following conditions is met:
+
+-  The DHCPINFORM is relayed and the ``giaddr`` matches the configured
+   subnet.
+
+-  The DHCPINFORM is unicast from the client and the ``ciaddr`` matches the
+   configured subnet.
+
+-  The DHCPINFORM is unicast from the client and the ``ciaddr`` is not set,
+   but the source address of the IP packet matches the configured
+   subnet.
+
+-  The DHCPINFORM is not relayed and the IP address on the interface on
+   which the message is received matches the configured subnet.
+
+.. _dhcp4-client-classifier:
+
+Client Classification in DHCPv4
+-------------------------------
+
+The DHCPv4 server includes support for client classification. For a
+deeper discussion of the classification process, see :ref:`classify`.
+
+In certain cases it is useful to configure the server to differentiate
+between DHCP client types and treat them accordingly. Client
+classification can be used to modify the behavior of almost any part of
+DHCP message processing. Kea currently offers client classification
+via private options and option 43 deferred unpacking; subnet selection;
+pool selection; assignment of different options; and, for cable modems,
+specific options for use with the TFTP server address and the boot file
+field.
+
+Kea can be instructed to limit access to given subnets based on class
+information. This is particularly useful for cases where two types of
+devices share the same link and are expected to be served from two
+different subnets. The primary use case for such a scenario is cable
+networks, where there are two classes of devices: the cable modem
+itself, which should be handed a lease from subnet A; and all other
+devices behind the modem, which should get leases from subnet B. That
+segregation is essential to prevent overly curious end-users from playing
+with their cable modems. For details on how to set up class restrictions
+on subnets, see :ref:`classification-subnets`.
+
+When subnets belong to a shared network, the classification applies to
+subnet selection but not to pools; that is, a pool in a subnet limited to a
+particular class can still be used by clients which do not belong to the
+class, if the pool they are expected to use is exhausted. The limit
+on access based on class information is also available at the pool
+level within a subnet: see :ref:`classification-pools`. This is
+useful when segregating clients belonging to the same subnet into
+different address ranges.
+
+In a similar way, a pool can be constrained to serve only known clients,
+i.e. clients which have a reservation, using the built-in ``KNOWN`` or
+``UNKNOWN`` classes. Addresses can be assigned to registered clients
+without giving a different address per reservation: for instance, when
+there are not enough available addresses. The determination whether
+there is a reservation for a given client is made after a subnet is
+selected, so it is not possible to use ``KNOWN``/``UNKNOWN`` classes to select a
+shared network or a subnet.
+
+The process of classification is conducted in five steps. The first step
+is to assess an incoming packet and assign it to zero or more classes.
+The second step is to choose a subnet, possibly based on the class
+information. When the incoming packet is in the special class ``DROP``,
+it is dropped and a debug message logged.
+The next step is to evaluate class expressions depending on
+the built-in ``KNOWN``/``UNKNOWN`` classes after host reservation lookup,
+using them for pool selection and assigning classes from host
+reservations. The list of required classes is then built and each class
+of the list has its expression evaluated; when it returns ``true``, the
+packet is added as a member of the class. The last step is to assign
+options, again possibly based on the class information. More complete
+and detailed information is available in :ref:`classify`.
+
+There are two main methods of classification. The first is automatic and
+relies on examining the values in the vendor class options or the
+existence of a host reservation. Information from these options is
+extracted, and a class name is constructed from it and added to the
+class list for the packet. The second method specifies an expression that is
+evaluated for each packet. If the result is ``true``, the packet is a
+member of the class.
+
+.. note::
+
+   The new ``early-global-reservations-lookup`` global parameter flag
+   enables a lookup for global reservations before the subnet selection
+   phase. This lookup is similar to the general lookup described above
+   with two differences:
+
+   - the lookup is limited to global host reservations
+
+   - the ``UNKNOWN`` class is never set
+
+.. note::
+
+   Care should be taken with client classification, as it is easy for
+   clients that do not meet class criteria to be denied all service.
+
+Setting Fixed Fields in Classification
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+It is possible to specify that clients belonging to a particular class
+should receive packets with specific values in certain fixed fields. In
+particular, three fixed fields are supported: ``next-server`` (conveys
+an IPv4 address, which is set in the ``siaddr`` field), ``server-hostname``
+(conveys a server hostname, can be up to 64 bytes long, and is sent in
+the ``sname`` field) and ``boot-file-name`` (conveys the configuration file,
+can be up to 128 bytes long, and is sent using the ``file`` field).
+
+Obviously, there are many ways to assign clients to specific classes,
+but for PXE clients the client architecture type option (code 93)
+seems to be particularly suited to make the distinction. The following
+example checks whether the client identifies itself as a PXE device with
+architecture EFI x86-64, and sets several fields if it does. See
+`Section 2.1 of RFC
+4578 <https://tools.ietf.org/html/rfc4578#section-2.1>`__) or the
+client documentation for specific values.
+
+::
+
+   "Dhcp4": {
+       "client-classes": [
+           {
+               "name": "ipxe_efi_x64",
+               "test": "option[93].hex == 0x0009",
+               "next-server": "192.0.2.254",
+               "server-hostname": "hal9000",
+               "boot-file-name": "/dev/null"
+           },
+           ...
+       ],
+       ...
+             }
+
+If an incoming packet is matched to multiple classes, then the
+value used for each field will come from the first class that
+specifies the field, in the order the classes are assigned to the
+packet.
+
+.. note::
+
+   The classes are ordered as specified in the configuration.
+
+Using Vendor Class Information in Classification
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The server checks whether an incoming packet includes the vendor class
+identifier option (60). If it does, the content of that option is
+prepended with ``VENDOR_CLASS_``, and it is interpreted as a class. For
+example, modern cable modems send this option with value
+``docsis3.0``, so the packet belongs to the class
+``VENDOR_CLASS_docsis3.0``.
+
+.. note::
+
+   Certain special actions for clients in ``VENDOR_CLASS_docsis3.0`` can be
+   achieved by defining ``VENDOR_CLASS_docsis3.0`` and setting its
+   ``next-server`` and ``boot-file-name`` values appropriately.
+
+This example shows a configuration using an automatically generated
+``VENDOR_CLASS_`` class. The administrator of the network has decided that
+addresses from the range 192.0.2.10 to 192.0.2.20 are going to be managed by
+the Dhcp4 server and only clients belonging to the DOCSIS 3.0 client
+class are allowed to use that pool.
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
+               "client-class": "VENDOR_CLASS_docsis3.0"
+           }
+       ],
+       ...
+   }
+
+Defining and Using Custom Classes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following example shows how to configure a class using an expression
+and a subnet using that class. This configuration defines the class
+named ``Client_foo``. It is comprised of all clients whose client IDs
+(option 61) start with the string ``foo``. Members of this class will be
+given addresses from 192.0.2.10 to 192.0.2.20 and the addresses of their
+DNS servers set to 192.0.2.1 and 192.0.2.2.
+
+::
+
+   "Dhcp4": {
+       "client-classes": [
+           {
+               "name": "Client_foo",
+               "test": "substring(option[61].hex,0,3) == 'foo'",
+               "option-data": [
+                   {
+                       "name": "domain-name-servers",
+                       "code": 6,
+                       "space": "dhcp4",
+                       "csv-format": true,
+                       "data": "192.0.2.1, 192.0.2.2"
+                   }
+               ]
+           },
+           ...
+       ],
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
+               "client-class": "Client_foo"
+           },
+           ...
+       ],
+       ...
+   }
+
+.. _dhcp4-required-class:
+
+Required Classification
+~~~~~~~~~~~~~~~~~~~~~~~
+
+In some cases it is useful to limit the scope of a class to a
+shared network, subnet, or pool. There are two parameters which are used
+to limit the scope of the class by instructing the server to evaluate test
+expressions when required.
+
+The first one is the per-class ``only-if-required`` flag, which is ``false``
+by default. When it is set to ``true``, the test expression of the class
+is not evaluated at the reception of the incoming packet but later, and
+only if the class evaluation is required.
+
+The second is ``require-client-classes``, which takes a list of class
+names and is valid in shared-network, subnet, and pool scope. Classes in
+these lists are marked as required and evaluated after selection of this
+specific shared network/subnet/pool and before output-option processing.
+
+In this example, a class is assigned to the incoming packet when the
+specified subnet is used:
+
+::
+
+   "Dhcp4": {
+       "client-classes": [
+          {
+              "name": "Client_foo",
+              "test": "member('ALL')",
+              "only-if-required": true
+          },
+          ...
+       ],
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
+               "require-client-classes": [ "Client_foo" ],
+               ...
+           },
+           ...
+       ],
+       ...
+   }
+
+Required evaluation can be used to express complex dependencies like
+subnet membership. It can also be used to reverse the
+precedence; if ``option-data`` is set in a subnet, it takes precedence
+over ``option-data`` in a class. If ``option-data`` is moved to a
+required class and required in the subnet, a class evaluated earlier
+may take precedence.
+
+Required evaluation is also available at the shared-network and pool levels.
+The order in which required classes are considered is: shared-network,
+subnet, and pool, i.e. in the reverse order from the way in which ``option-data`` is
+processed.
+
+.. _dhcp4-ddns-config:
+
+DDNS for DHCPv4
+---------------
+
+As mentioned earlier, ``kea-dhcp4`` can be configured to generate requests
+to the DHCP-DDNS server, ``kea-dhcp-ddns``, (referred to herein as "D2") to
+update DNS entries. These requests are known as NameChangeRequests or
+NCRs. Each NCR contains the following information:
+
+1. Whether it is a request to add (update) or remove DNS entries.
+
+2. Whether the change requests forward DNS updates (A records), reverse
+   DNS updates (PTR records), or both.
+
+3. The Fully Qualified Domain Name (FQDN), lease address, and DHCID
+   (information identifying the client associated with the FQDN).
+
+DDNS-related parameters are split into two groups:
+
+1. Connectivity Parameters
+
+    These are parameters which specify where and how ``kea-dhcp4`` connects to
+    and communicates with D2. These parameters can only be specified
+    within the top-level ``dhcp-ddns`` section in the ``kea-dhcp4``
+    configuration. The connectivity parameters are listed below:
+
+    -  ``enable-updates``
+    -  ``server-ip``
+    -  ``server-port``
+    -  ``sender-ip``
+    -  ``sender-port``
+    -  ``max-queue-size``
+    -  ``ncr-protocol``
+    -  ``ncr-format"``
+
+2. Behavioral Parameters
+
+    These parameters influence behavior such as how client host names and
+    FQDN options are handled. They have been moved out of the ``dhcp-ddns``
+    section so that they may be specified at the global, shared-network,
+    and/or subnet levels. Furthermore, they are inherited downward from global to
+    shared-network to subnet. In other words, if a parameter is not specified at
+    a given level, the value for that level comes from the level above it.
+    The behavioral parameters are as follows:
+
+    -  ``ddns-send-updates``
+    -  ``ddns-override-no-update``
+    -  ``ddns-override-client-update``
+    -  ``ddns-replace-client-name"``
+    -  ``ddns-generated-prefix``
+    -  ``ddns-qualifying-suffix``
+    -  ``ddns-update-on-renew``
+    -  ``ddns-use-conflict-resolution``
+    -  ``hostname-char-set``
+    -  ``hostname-char-replacement``
+
+.. note::
+
+    For backward compatibility, configuration parsing still recognizes
+    the original behavioral parameters specified in ``dhcp-ddns``,
+    by translating the parameter into its global equivalent. If a
+    parameter is specified both globally and in ``dhcp-ddns``, the latter
+    value is ignored. In either case, a log is emitted explaining
+    what has occurred. Specifying these values within ``dhcp-ddns`` is
+    deprecated and support for it will be removed.
+
+The default configuration and values would appear as follows:
+
+::
+
+   "Dhcp4": {
+        "dhcp-ddns": {
+           // Connectivity parameters
+           "enable-updates": false,
+            "server-ip": "127.0.0.1",
+            "server-port":53001,
+            "sender-ip":"",
+            "sender-port":0,
+            "max-queue-size":1024,
+            "ncr-protocol":"UDP",
+            "ncr-format":"JSON"
+        },
+
+        // Behavioral parameters (global)
+        "ddns-send-updates": true,
+        "ddns-override-no-update": false,
+        "ddns-override-client-update": false,
+        "ddns-replace-client-name": "never",
+        "ddns-generated-prefix": "myhost",
+        "ddns-qualifying-suffix": "",
+        "ddns-update-on-renew": false,
+        "ddns-use-conflict-resolution": true,
+        "hostname-char-set": "",
+        "hostname-char-replacement": ""
+        ...
+   }
+
+There are two parameters which determine if ``kea-dhcp4``
+can generate DDNS requests to D2: the existing ``dhcp-ddns:enable-updates``
+parameter, which now only controls whether ``kea-dhcp4`` connects to D2;
+and the new behavioral parameter, ``ddns-send-updates``, which determines
+whether DDNS updates are enabled at a given level (i.e. global, shared-network,
+or subnet). The following table shows how the two parameters function
+together:
+
+.. table:: Enabling and disabling DDNS updates
+
+   +-----------------+--------------------+-------------------------------------+
+   | dhcp-ddns:      | Global             | Outcome                             |
+   | enable-updates  | ddns-send-updates  |                                     |
+   +=================+====================+=====================================+
+   | false (default) | false              | no updates at any scope             |
+   +-----------------+--------------------+-------------------------------------+
+   | false           | true (default)     | no updates at any scope             |
+   +-----------------+--------------------+-------------------------------------+
+   | true            | false              | updates only at scopes with         |
+   |                 |                    | a local value of ``true`` for       |
+   |                 |                    | ``ddns-enable-updates``             |
+   +-----------------+--------------------+-------------------------------------+
+   | true            | true               | updates at all scopes except those  |
+   |                 |                    | with a local value of ``false``     |
+   |                 |                    | for ``ddns-enable-updates``         |
+   +-----------------+--------------------+-------------------------------------+
+
+Kea 1.9.1 added two new parameters; the first is ``ddns-update-on-renew``.
+Normally, when leases are renewed, the server only updates DNS if the DNS
+information for the lease (e.g. FQDN, DNS update direction flags) has changed.
+Setting ``ddns-update-on-renew`` to ``true`` instructs the server to always update
+the DNS information when a lease is renewed, even if its DNS information has not
+changed. This allows Kea to "self-heal" if it was previously unable
+to add DNS entries or they were somehow lost by the DNS server.
+
+.. note::
+
+    Setting ``ddns-update-on-renew`` to ``true`` may impact performance, especially
+    for servers with numerous clients that renew often.
+
+The second parameter added in Kea 1.9.1 is ``ddns-use-conflict-resolution``.
+The value of this parameter is passed by ``kea-dhcp4`` to D2 with each DNS update
+request. When ``true`` (the default value), D2 employs conflict resolution,
+as described in `RFC 4703 <https://tools.ietf.org/html/rfc4703>`__, when
+attempting to fulfill the update request. When ``false``, D2 simply attempts
+to update the DNS entries per the request, regardless of whether they
+conflict with existing entries owned by other DHCPv4 clients.
+
+.. note::
+
+    Setting ``ddns-use-conflict-resolution`` to ``false`` disables the overwrite
+    safeguards that the rules of conflict resolution (from
+    `RFC 4703 <https://tools.ietf.org/html/rfc4703>`__) are intended to
+    prevent. This means that existing entries for an FQDN or an
+    IP address made for Client-A can be deleted or replaced by entries
+    for Client-B. Furthermore, there are two scenarios by which entries
+    for multiple clients for the same key (e.g. FQDN or IP) can be created.
+
+    1. Client-B uses the same FQDN as Client-A but a different IP address.
+    In this case, the forward DNS entries (A and DHCID RRs) for
+    Client-A will be deleted as they match the FQDN and new entries for
+    Client-B will be added. The reverse DNS entries (PTR and DHCID RRs)
+    for Client-A, however, will not be deleted as they belong to a different
+    IP address, while new entries for Client-B will still be added.
+
+    2. Client-B uses the same IP address as Client-A but a different FQDN.
+    In this case the reverse DNS entries (PTR and DHCID RRs) for Client-A
+    will be deleted as they match the IP address, and new entries for
+    Client-B will be added. The forward DNS entries (A and DHCID RRs)
+    for Client-A, however, will not be deleted, as they belong to a different
+    FQDN, while new entries for Client-B will still be added.
+
+    Disabling conflict resolution should be done only after careful review of
+    specific use cases. The best way to avoid unwanted DNS entries is to
+    always ensure lease changes are processed through Kea, whether they are
+    released, expire, or are deleted via the ``lease-del4`` command, prior to
+    reassigning either FQDNs or IP addresses. Doing so causes ``kea-dhcp4``
+    to generate DNS removal requests to D2.
+
+.. note::
+
+    The DNS entries Kea creates contain a value for TTL (time to live). Since
+    Kea 1.9.3, ``kea-dhcp4`` calculates that value based on
+    `RFC 4702, Section 5 <https://tools.ietf.org/html/rfc4702#section-5>`__,
+    which suggests that the TTL value be 1/3 of the lease's lifetime, with
+    a minimum value of 10 minutes. In earlier versions, the server set the TTL value
+    equal to the lease's valid lifetime.
+
+.. _dhcpv4-d2-io-config:
+
+DHCP-DDNS Server Connectivity
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+For NCRs to reach the D2 server, ``kea-dhcp4`` must be able to communicate
+with it. ``kea-dhcp4`` uses the following configuration parameters to
+control this communication:
+
+-  ``enable-updates`` - Enables connectivity to ``kea-dhcp-ddns`` such that DDNS
+   updates can be constructed and sent.
+   It must be ``true`` for NCRs to be generated and sent to D2.
+   It defaults to ``false``.
+
+-  ``server-ip`` - This is the IP address on which D2 listens for requests. The
+   default is the local loopback interface at address 127.0.0.1.
+   Either an IPv4 or IPv6 address may be specified.
+
+-  ``server-port`` - This is the port on which D2 listens for requests. The default
+   value is 53001.
+
+-  ``sender-ip`` - This is the IP address which ``kea-dhcp4`` uses to send requests to
+   D2. The default value is blank, which instructs ``kea-dhcp4`` to select a
+   suitable address.
+
+-  ``sender-port`` - This is the port which ``kea-dhcp4`` uses to send requests to D2.
+   The default value of 0 instructs ``kea-dhcp4`` to select a suitable port.
+
+-  ``max-queue-size`` - This is the maximum number of requests allowed to queue
+   while waiting to be sent to D2. This value guards against requests
+   accumulating uncontrollably if they are being generated faster than
+   they can be delivered. If the number of requests queued for
+   transmission reaches this value, DDNS updating is turned off
+   until the queue backlog has been sufficiently reduced. The intent is
+   to allow the ``kea-dhcp4`` server to continue lease operations without
+   running the risk that its memory usage grows without limit. The
+   default value is 1024.
+
+-  ``ncr-protocol`` - This specifies the socket protocol to use when sending requests to
+   D2. Currently only UDP is supported.
+
+-  ``ncr-format`` - This specifies the packet format to use when sending requests to D2.
+   Currently only JSON format is supported.
+
+By default, ``kea-dhcp-ddns`` is assumed to be running on the same machine
+as ``kea-dhcp4``, and all of the default values mentioned above should be
+sufficient. If, however, D2 has been configured to listen on a different
+address or port, these values must be altered accordingly. For example,
+if D2 has been configured to listen on 192.168.1.10 port 900, the
+following configuration is required:
+
+::
+
+   "Dhcp4": {
+       "dhcp-ddns": {
+           "server-ip": "192.168.1.10",
+           "server-port": 900,
+           ...
+       },
+       ...
+   }
+
+.. _dhcpv4-d2-rules-config:
+
+When Does the ``kea-dhcp4`` Server Generate a DDNS Request?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``kea-dhcp4`` follows the behavior prescribed for DHCP servers in `RFC
+4702 <https://tools.ietf.org/html/rfc4702>`__. It is important to keep in
+mind that ``kea-dhcp4`` makes the initial decision of when and what to
+update and forwards that information to D2 in the form of NCRs. Carrying
+out the actual DNS updates and dealing with such things as conflict
+resolution are within the purview of D2 itself
+(see :ref:`dhcp-ddns-server`). This section describes when ``kea-dhcp4``
+generates NCRs and the configuration parameters that can be used to
+influence this decision. It assumes that both the connectivity parameter
+``enable-updates`` and the behavioral parameter ``ddns-send-updates``,
+are ``true``.
+
+In general, ``kea-dhcp4`` generates DDNS update requests when:
+
+1. A new lease is granted in response to a DHCPREQUEST;
+
+2. An existing lease is renewed but the FQDN associated with it has
+   changed; or
+
+3. An existing lease is released in response to a DHCPRELEASE.
+
+In the second case, lease renewal, two DDNS requests are issued: one
+request to remove entries for the previous FQDN, and a second request to
+add entries for the new FQDN. In the third case, a lease release - a
+single DDNS request - to remove its entries will be made.
+
+As for the first case, the decisions involved when granting a new lease are
+more complex. When a new lease is granted, ``kea-dhcp4`` generates a
+DDNS update request if the DHCPREQUEST contains either the FQDN option
+(code 81) or the Host Name option (code 12). If both are present, the
+server uses the FQDN option. By default, ``kea-dhcp4`` respects the
+FQDN N and S flags specified by the client as shown in the following
+table:
+
+.. table:: Default FQDN flag behavior
+
+   +------------+---------------------+-----------------+-------------+
+   | Client     | Client Intent       | Server Response | Server      |
+   | Flags:N-S  |                     |                 | Flags:N-S-O |
+   +============+=====================+=================+=============+
+   | 0-0        | Client wants to     | Server          | 1-0-0       |
+   |            | do forward          | generates       |             |
+   |            | updates, server     | reverse-only    |             |
+   |            | should do           | request         |             |
+   |            | reverse updates     |                 |             |
+   +------------+---------------------+-----------------+-------------+
+   | 0-1        | Server should       | Server          | 0-1-0       |
+   |            | do both forward     | generates       |             |
+   |            | and reverse         | request to      |             |
+   |            | updates             | update both     |             |
+   |            |                     | directions      |             |
+   +------------+---------------------+-----------------+-------------+
+   | 1-0        | Client wants no     | Server does not | 1-0-0       |
+   |            | updates done        | generate a      |             |
+   |            |                     | request         |             |
+   +------------+---------------------+-----------------+-------------+
+
+The first row in the table above represents "client delegation." Here
+the DHCP client states that it intends to do the forward DNS updates and
+the server should do the reverse updates. By default, ``kea-dhcp4``
+honors the client's wishes and generates a DDNS request to the D2 server
+to update only reverse DNS data. The parameter
+``ddns-override-client-update`` can be used to instruct the server to
+override client delegation requests. When this parameter is ``true``,
+``kea-dhcp4`` disregards requests for client delegation and generates a
+DDNS request to update both forward and reverse DNS data. In this case,
+the N-S-O flags in the server's response to the client will be 0-1-1
+respectively.
+
+(Note that the flag combination N=1, S=1 is prohibited according to `RFC
+4702 <https://tools.ietf.org/html/rfc4702>`__. If such a combination is
+received from the client, the packet will be dropped by ``kea-dhcp4``.)
+
+To override client delegation, set the following values in the
+configuration file:
+
+::
+
+    "Dhcp4": {
+        ...
+        "ddns-override-client-update": true,
+        ...
+    }
+
+The third row in the table above describes the case in which the client
+requests that no DNS updates be done. The parameter
+``ddns-override-no-update`` can be used to instruct the server to disregard
+the client's wishes. When this parameter is ``true``, ``kea-dhcp4``
+generates DDNS update requests to ``kea-dhcp-ddns`` even if the client
+requests that no updates be done. The N-S-O flags in the server's
+response to the client will be 0-1-1.
+
+To override client delegation, issue the following commands:
+
+::
+
+    "Dhcp4": {
+        ...
+        "ddns-override-no-update": true,
+        ...
+    }
+
+``kea-dhcp4`` always generates DDNS update requests if the client
+request only contains the Host Name option. In addition, it includes
+an FQDN option in the response to the client with the FQDN N-S-O flags
+set to 0-1-0, respectively. The domain name portion of the FQDN option
+is the name submitted to D2 in the DDNS update request.
+
+.. _dhcpv4-fqdn-name-generation:
+
+``kea-dhcp4`` Name Generation for DDNS Update Requests
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Each NameChangeRequest must of course include the fully qualified domain
+name whose DNS entries are to be affected. ``kea-dhcp4`` can be configured
+to supply a portion or all of that name, based on what it receives
+from the client in the DHCPREQUEST.
+
+The default rules for constructing the FQDN that will be used for DNS
+entries are:
+
+1. If the DHCPREQUEST contains the client FQDN option, take the
+   candidate name from there; otherwise, take it from the Host Name
+   option.
+
+2. If the candidate name is a partial (i.e. unqualified) name, then add
+   a configurable suffix to the name and use the result as the FQDN.
+
+3. If the candidate name provided is empty, generate an FQDN using a
+   configurable prefix and suffix.
+
+4. If the client provides neither option, then take no DNS action.
+
+These rules can be amended by setting the ``ddns-replace-client-name``
+parameter, which provides the following modes of behavior:
+
+-  ``never`` - use the name the client sent. If the client sent no name,
+   do not generate one. This is the default mode.
+
+-  ``always`` - replace the name the client sent. If the client sent no
+   name, generate one for the client.
+
+-  ``when-present`` - replace the name the client sent. If the client
+   sent no name, do not generate one.
+
+-  ``when-not-present`` - use the name the client sent. If the client
+   sent no name, generate one for the client.
+
+.. note::
+
+   In early versions of Kea, this parameter was a boolean and permitted only
+   values of ``true`` and ``false``. Boolean values have been deprecated
+   and are no longer accepted. Administrators currently using booleans
+   must replace them with the desired mode name. A value of ``true``
+   maps to ``when-present``, while ``false`` maps to ``never``.
+
+For example, to instruct ``kea-dhcp4`` to always generate the FQDN for a
+client, set the parameter ``ddns-replace-client-name`` to ``always`` as
+follows:
+
+::
+
+    "Dhcp4": {
+        ...
+        "ddns-replace-client-name": "always",
+        ...
+    }
+
+The prefix used in the generation of an FQDN is specified by the
+``ddns-generated-prefix`` parameter. The default value is "myhost". To alter
+its value, simply set it to the desired string:
+
+::
+
+    "Dhcp4": {
+        ...
+        "ddns-generated-prefix": "another.host",
+        ...
+    }
+
+The suffix used when generating an FQDN, or when qualifying a partial
+name, is specified by the ``ddns-qualifying-suffix`` parameter. It is
+strongly recommended that the user supply a value for the qualifying prefix when
+DDNS updates are enabled. For obvious reasons, we cannot supply a
+meaningful default.
+
+::
+
+    "Dhcp4": {
+        ...
+        "ddns-qualifying-suffix": "foo.example.org",
+        ...
+    }
+
+When generating a name, ``kea-dhcp4`` constructs the name in the format:
+
+``[ddns-generated-prefix]-[address-text].[ddns-qualifying-suffix].``
+
+where ``address-text`` is simply the lease IP address converted to a
+hyphenated string. For example, if the lease address is 172.16.1.10, the
+qualifying suffix is "example.com", and the default value is used for
+``ddns-generated-prefix``, the generated FQDN is:
+
+``myhost-172-16-1-10.example.com.``
+
+.. _dhcp4-host-name-sanitization:
+
+Sanitizing Client Host Name and FQDN Names
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Some DHCP clients may provide values in the Host Name
+option (option code 12) or FQDN option (option code 81) that contain
+undesirable characters. It is possible to configure ``kea-dhcp4`` to
+sanitize these values. The most typical use case is ensuring that only
+characters that are permitted by RFC 1035 be included: A-Z, a-z, 0-9,
+and "-". This may be accomplished with the following two parameters:
+
+-  ``hostname-char-set`` - a regular expression describing the invalid
+   character set. This can be any valid, regular expression using POSIX
+   extended expression syntax. Embedded nulls (0x00) are always
+   considered an invalid character to be replaced (or omitted).
+   The default is ``"[^A-Za-z0-9.-]"``. This matches any character that is not
+   a letter, digit, dot, hyphen, or null.
+
+-  ``hostname-char-replacement`` - a string of zero or more characters
+   with which to replace each invalid character in the host name. An empty
+   string causes invalid characters to be OMITTED rather than replaced.
+   The default is ``""``.
+
+The following configuration replaces anything other than a letter,
+digit, dot, or hyphen with the letter "x":
+::
+
+    "Dhcp4": {
+        ...
+        "hostname-char-set": "[^A-Za-z0-9.-]",
+        "hostname-char-replacement": "x",
+        ...
+    }
+
+Thus, a client-supplied value of "myhost-$[123.org" would become
+"myhost-xx123.org". Sanitizing is performed only on the portion of the
+name supplied by the client, and it is performed before applying a
+qualifying suffix (if one is defined and needed).
+
+.. note::
+
+   Name sanitizing is meant to catch the more common cases of invalid
+   characters through a relatively simple character-replacement scheme.
+   It is difficult to devise a scheme that works well in all cases, for
+   both Host Name and FQDN options. Administrators who find they have clients
+   with odd corner cases of character combinations that cannot be
+   readily handled with this mechanism should consider writing a
+   hook that can carry out sufficiently complex logic to address their
+   needs.
+
+   If clients include domain names in the Host Name option and the administrator
+   wants these preserved, they need to make sure that the dot, ".",
+   is considered a valid character by the ``hostname-char-set`` expression,
+   such as this: ``"[^A-Za-z0-9.-]"``. This does not affect dots in FQDN
+   Option values. When scrubbing FQDNs, dots are treated as delimiters
+   and used to separate the option value into individual domain labels
+   that are scrubbed and then re-assembled.
+
+   If clients are sending values that differ only by characters
+   considered as invalid by the ``hostname-char-set``, be aware that
+   scrubbing them will yield identical values. In such cases, DDNS
+   conflict rules will permit only one of them to register the name.
+
+   Finally, given the latitude clients have in the values they send, it
+   is virtually impossible to guarantee that a combination of these two
+   parameters will always yield a name that is valid for use in DNS. For
+   example, using an empty value for ``hostname-char-replacement`` could
+   yield an empty domain label within a name, if that label consists
+   only of invalid characters.
+
+.. note::
+
+   It is possible to specify ``hostname-char-set``
+   and/or ``hostname-char-replacement`` at the global scope. This allows
+   host names to be sanitized without requiring a ``dhcp-ddns`` entry. When
+   a ``hostname-char`` parameter is defined at both the global scope and
+   in a ``dhcp-ddns`` entry, the second (local) value is used.
+
+.. _dhcp4-next-server:
+
+Next Server (``siaddr``)
+------------------------
+
+In some cases, clients want to obtain configuration from a TFTP server.
+Although there is a dedicated option for it, some devices may use the
+``siaddr`` field in the DHCPv4 packet for that purpose. That specific field
+can be configured using the ``next-server`` directive. It is possible to
+define it in the global scope or for a given subnet only. If both are
+defined, the subnet value takes precedence. The value in the subnet can be
+set to "0.0.0.0", which means that ``next-server`` should not be sent. It
+can also be set to an empty string, which is equivalent to it
+not being defined at all; that is, it uses the global value.
+
+The ``server-hostname`` (which conveys a server hostname, can be up to
+64 bytes long, and is in the ``sname`` field) and
+``boot-file-name`` (which conveys the configuration file, can be up to
+128 bytes long, and is sent using the ``file`` field) directives are
+handled the same way as ``next-server``.
+
+::
+
+   "Dhcp4": {
+       "next-server": "192.0.2.123",
+       "boot-file-name": "/dev/null",
+       ...,
+       "subnet4": [
+           {
+               "next-server": "192.0.2.234",
+               "server-hostname": "some-name.example.org",
+               "boot-file-name": "bootfile.efi",
+               ...
+           }
+       ]
+   }
+
+.. _dhcp4-echo-client-id:
+
+Echoing Client-ID (RFC 6842)
+----------------------------
+
+The original DHCPv4 specification (`RFC
+2131 <https://tools.ietf.org/html/rfc2131>`__) states that the DHCPv4
+server must not send back client-id options when responding to clients.
+However, in some cases that results in confused clients that do not have a MAC
+address or client-id; see `RFC
+6842 <https://tools.ietf.org/html/rfc6842>`__ for details. That behavior
+changed with the publication of `RFC
+6842 <https://tools.ietf.org/html/rfc6842>`__, which updated `RFC
+2131 <https://tools.ietf.org/html/rfc2131>`__. That update states that
+the server must send the client-id if the client sent it, and that is Kea's
+default behavior. However, in some cases older devices that do not
+support `RFC 6842 <https://tools.ietf.org/html/rfc6842>`__ may refuse to
+accept responses that include the client-id option. To enable backward
+compatibility, an optional configuration parameter has been introduced.
+To configure it, use the following configuration statement:
+
+::
+
+   "Dhcp4": {
+       "echo-client-id": false,
+       ...
+   }
+
+.. _dhcp4-match-client-id:
+
+Using Client Identifier and Hardware Address
+--------------------------------------------
+
+The DHCP server must be able to identify the client from which it
+receives the message and distinguish it from other clients. There are
+many reasons why this identification is required; the most important
+ones are:
+
+-  When the client contacts the server to allocate a new lease, the
+   server must store the client identification information in the lease
+   database as a search key.
+
+-  When the client tries to renew or release the existing lease, the
+   server must be able to find the existing lease entry in the database
+   for this client, using the client identification information as a
+   search key.
+
+-  Some configurations use static reservations for the IP addresses and
+   other configuration information. The server's administrator uses
+   client identification information to create these static assignments.
+
+-  In dual-stack networks there is often a need to correlate the lease
+   information stored in DHCPv4 and DHCPv6 servers for a particular
+   host. Using common identification information by the DHCPv4 and
+   DHCPv6 clients allows the network administrator to achieve this
+   correlation and better administer the network.  Beginning with
+   release 2.1.2, Kea supports DHCPv6 DUIDs embedded within DHCPv4
+   Client Identifier options as described in
+   `RFC 4361 <https://tools.ietf.org/html/rfc4361>`__.
+
+DHCPv4 uses two distinct identifiers which are placed by the client in
+the queries sent to the server and copied by the server to its responses
+to the client: ``chaddr`` and ``client-identifier``. The former was
+introduced as a part of the BOOTP specification and it is also used by
+DHCP to carry the hardware address of the interface used to send the
+query to the server (MAC address for the Ethernet). The latter is
+carried in the client-identifier option, introduced in `RFC
+2132 <https://tools.ietf.org/html/rfc2132>`__.
+
+`RFC 2131 <https://tools.ietf.org/html/rfc2131>`__ indicates that the
+server may use both of these identifiers to identify the client but the
+client identifier, if present, takes precedence over ``chaddr``. One of
+the reasons for this is that the client identifier is independent from the
+hardware used by the client to communicate with the server. For example,
+if the client obtained the lease using one network card and then the
+network card is moved to another host, the server will wrongly identify
+this host as the one which obtained the lease. Moreover, `RFC
+4361 <https://tools.ietf.org/html/rfc4361>`__ gives the recommendation
+to use a DUID (see `RFC 8415 <https://tools.ietf.org/html/rfc8415>`__,
+the DHCPv6 specification) carried as a client identifier when dual-stack
+networks are in use to provide consistent identification information for
+the client, regardless of the type of protocol it is using. Kea adheres to
+these specifications, and the client identifier by default takes
+precedence over the value carried in the ``chaddr`` field when the server
+searches, creates, updates, or removes the client's lease.
+
+When the server receives a DHCPDISCOVER or DHCPREQUEST message from the
+client, it tries to find out if the client already has a lease in the
+database; if it does, the server hands out that lease rather than allocates a new one.
+Each lease in the lease database is associated with the client
+identifier and/or ``chaddr``. The server first uses the client
+identifier (if present) to search for the lease; if one is found, the
+server treats this lease as belonging to the client, even if the
+current ``chaddr`` and the ``chaddr`` associated with the lease do not
+match. This facilitates the scenario when the network card on the client
+system has been replaced and thus the new MAC address appears in the
+messages sent by the DHCP client. If the server fails to find the lease
+using the client identifier, it performs another lookup using the
+``chaddr``. If this lookup returns no result, the client is considered to
+not have a lease and a new lease is created.
+
+A common problem reported by network operators is that poor client
+implementations do not use stable client identifiers, instead generating
+a new client identifier each time the client connects to the network.
+Another well-known case is when the client changes its client
+identifier during the multi-stage boot process (PXE). In such cases,
+the MAC address of the client's interface remains stable, and using the
+``chaddr`` field to identify the client guarantees that the particular
+system is considered to be the same client, even though its client
+identifier changes.
+
+To address this problem, Kea includes a configuration option which
+enables client identification using ``chaddr`` only. This instructs the
+server to ignore the client identifier during lease lookups and allocations
+for a particular subnet. Consider the following simplified server configuration:
+
+::
+
+   "Dhcp4": {
+       ...
+       "match-client-id": true,
+       ...
+       "subnet4": [
+       {
+           "subnet": "192.0.10.0/24",
+           "pools": [ { "pool": "192.0.2.23-192.0.2.87" } ],
+           "match-client-id": false
+       },
+       {
+           "subnet": "10.0.0.0/8",
+           "pools": [ { "pool": "10.0.0.23-10.0.2.99" } ],
+       }
+       ]
+   }
+
+The ``match-client-id`` is a boolean value which controls this behavior.
+The default value of ``true`` indicates that the server will use the
+client identifier for lease lookups and ``chaddr`` if the first lookup
+returns no results. ``false`` means that the server will only use
+the ``chaddr`` to search for the client's lease. Whether the DHCID for DNS
+updates is generated from the client identifier or ``chaddr`` is
+controlled through the same parameter.
+
+The ``match-client-id`` parameter may appear both in the global
+configuration scope and/or under any subnet declaration. In the example
+shown above, the effective value of the ``match-client-id`` will be
+``false`` for the subnet 192.0.10.0/24, because the subnet-specific
+setting of the parameter overrides the global value of the parameter.
+The effective value of the ``match-client-id`` for the subnet 10.0.0.0/8
+will be set to ``true``, because the subnet declaration lacks this
+parameter and the global setting is by default used for this subnet. In
+fact, the global entry for this parameter could be omitted in this case,
+because ``true`` is the default value.
+
+It is important to understand what happens when the client obtains its
+lease for one setting of the ``match-client-id`` and then renews it when
+the setting has been changed. First, consider the case when the client
+obtains the lease and the ``match-client-id`` is set to ``true``. The
+server stores the lease information, including the client identifier
+(if supplied) and ``chaddr``, in the lease database. When the setting is
+changed and the client renews the lease, the server will determine that
+it should use the ``chaddr`` to search for the existing lease. If the
+client has not changed its MAC address, the server should successfully
+find the existing lease. The client identifier associated with the
+returned lease will be ignored and the client will be allowed to use this lease.
+When the lease is renewed only the ``chaddr`` will be recorded for this lease,
+according to the new server setting.
+
+In the second case, the client has the lease with only a ``chaddr`` value
+recorded. When the ``match-client-id`` setting is changed to ``true``,
+the server will first try to use the client identifier to find the
+existing client's lease. This will return no results because the client
+identifier was not recorded for this lease. The server will then use
+the ``chaddr`` and the lease will be found. If the lease appears to have
+no client identifier recorded, the server will assume that this lease
+belongs to the client and that it was created with the previous setting
+of the ``match-client-id``. However, if the lease contains a client
+identifier which is different from the client identifier used by the
+client, the lease will be assumed to belong to another client and a
+new lease will be allocated.
+
+.. _dhcp4-authoritative:
+
+Authoritative DHCPv4 Server Behavior
+------------------------------------
+
+The original DHCPv4 specification (`RFC
+2131 <https://tools.ietf.org/html/rfc2131>`__) states that if a client
+requests an address in the INIT-REBOOT state of which the server has no
+knowledge, the server must remain silent, except if the server knows
+that the client has requested an IP address from the wrong network. By
+default, Kea follows the behavior of the ISC ``dhcpd`` daemon instead of the
+specification and also remains silent if the client requests an IP
+address from the wrong network, because configuration information about
+a given network segment is not known to be correct. Kea only rejects a
+client's DHCPREQUEST with a DHCPNAK message if it already has a lease
+for the client with a different IP address. Administrators can
+override this behavior through the boolean ``authoritative`` (``false``
+by default) setting.
+
+In authoritative mode, ``authoritative`` set to ``true``, Kea always
+rejects INIT-REBOOT requests from unknown clients with DHCPNAK messages.
+The ``authoritative`` setting can be specified in global,
+shared-network, and subnet configuration scope and is automatically
+inherited from the parent scope, if not specified. All subnets in a
+shared-network must have the same ``authoritative`` setting.
+
+.. _dhcp4-dhcp4o6-config:
+
+DHCPv4-over-DHCPv6: DHCPv4 Side
+-------------------------------
+
+The support of DHCPv4-over-DHCPv6 transport is described in `RFC
+7341 <https://tools.ietf.org/html/rfc7341>`__ and is implemented using
+cooperating DHCPv4 and DHCPv6 servers. This section is about the
+configuration of the DHCPv4 side (the DHCPv6 side is described in
+:ref:`dhcp6-dhcp4o6-config`).
+
+.. note::
+
+   DHCPv4-over-DHCPv6 support is experimental and the details of the
+   inter-process communication may change; for instance, the
+   support of port relay (RFC 8357) introduced an incompatible change.
+   Both the DHCPv4 and DHCPv6 sides should be running the same version of Kea.
+
+The ``dhcp4o6-port`` global parameter specifies the first of the two
+consecutive ports of the UDP sockets used for the communication between
+the DHCPv6 and DHCPv4 servers. The DHCPv4 server is bound to ::1 on
+``port`` + 1 and connected to ::1 on ``port``.
+
+With DHCPv4-over-DHCPv6, the DHCPv4 server does not have access to
+several of the identifiers it would normally use to select a subnet. To
+address this issue, three new configuration entries are available; the
+presence of any of these allows the subnet to be used with
+DHCPv4-over-DHCPv6. These entries are:
+
+-  ``4o6-subnet``: takes a prefix (i.e., an IPv6 address followed by a
+   slash and a prefix length) which is matched against the source
+   address.
+
+-  ``4o6-interface-id``: takes a relay interface ID option value.
+
+-  ``4o6-interface``: takes an interface name which is matched against
+   the incoming interface name.
+
+ISC tested the following configuration:
+
+::
+
+   {
+
+   # DHCPv4 conf
+   "Dhcp4": {
+
+       "interfaces-config": {
+           "interfaces": [ "eno33554984" ]
+       },
+
+       "lease-database": {
+           "type": "memfile",
+           "name": "leases4"
+       },
+
+       "valid-lifetime": 4000,
+
+       "subnet4": [ {
+           "subnet": "10.10.10.0/24",
+           "4o6-interface": "eno33554984",
+           "4o6-subnet": "2001:db8:1:1::/64",
+           "pools": [ { "pool": "10.10.10.100 - 10.10.10.199" } ]
+       } ],
+
+       "dhcp4o6-port": 6767,
+
+       "loggers": [ {
+           "name": "kea-dhcp4",
+           "output_options": [ {
+               "output": "/tmp/kea-dhcp4.log"
+           } ],
+           "severity": "DEBUG",
+           "debuglevel": 0
+       } ]
+   }
+
+   }
+
+.. _sanity-checks4:
+
+Sanity Checks in DHCPv4
+-----------------------
+
+An important aspect of a well-running DHCP system is an assurance that
+the data remains consistent; however, in some cases it may be convenient
+to tolerate certain inconsistent data. For example, a network
+administrator who temporarily removes a subnet from a configuration
+would not want all the leases associated with it to disappear from the
+lease database. Kea has a mechanism to implement sanity checks for situations
+like this.
+
+Kea supports a configuration scope called ``sanity-checks``. It
+currently allows only a single parameter, called ``lease-checks``, which
+governs the verification carried out when a new lease is loaded from a
+lease file. This mechanism permits Kea to attempt to correct inconsistent data.
+
+Every subnet has a ``subnet-id`` value; this is how Kea internally
+identifies subnets. Each lease has a ``subnet-id`` parameter as well, which
+identifies the subnet it belongs to. However, if the configuration has
+changed, it is possible that a lease could exist with a ``subnet-id`` but
+without any subnet that matches it. Also, it is possible that the
+subnet's configuration has changed and the ``subnet-id`` now belongs to a
+subnet that does not match the lease.
+
+Kea's corrective algorithm first
+checks to see if there is a subnet with the ``subnet-id`` specified by the
+lease. If there is, it verifies whether the lease belongs to that
+subnet. If not, depending on the ``lease-checks`` setting, the lease is
+discarded, a warning is displayed, or a new subnet is selected for the
+lease that matches it topologically.
+
+There are five levels which are supported:
+
+-  ``none`` - do no special checks; accept the lease as is.
+
+-  ``warn`` - if problems are detected display a warning, but
+   accept the lease data anyway. This is the default value.
+
+-  ``fix`` - if a data inconsistency is discovered, try to
+   correct it. If the correction is not successful, insert the incorrect data
+   anyway.
+
+-  ``fix-del`` - if a data inconsistency is discovered, try to
+   correct it. If the correction is not successful, reject the lease.
+   This setting ensures the data's correctness, but some
+   incorrect data may be lost. Use with care.
+
+-  ``del`` - if any inconsistency is
+   detected, reject the lease. This is the strictest mode; use with care.
+
+This feature is currently implemented for the memfile backend. The
+sanity check applies to the lease database in memory, not to the lease file,
+i.e. inconsistent leases will stay in the lease file.
+
+An example configuration that sets this parameter looks as follows:
+
+::
+
+   "Dhcp4": {
+       "sanity-checks": {
+           "lease-checks": "fix-del"
+       },
+       ...
+   }
+
+.. _dhcp4-store-extended-info:
+
+Storing Extended Lease Information
+----------------------------------
+
+To support such features as DHCP Leasequery
+(`RFC 4388 <https://tools.ietf.org/html/rfc4388>`__),
+additional information must be stored with each lease. Because the amount
+of information for each lease has ramifications in terms of
+performance and system resource consumption, storage of this additional
+information is configurable through the ``store-extended-info`` parameter.
+It defaults to ``false`` and may be set at the global, shared-network, and
+subnet levels.
+
+::
+
+   "Dhcp4": {
+       "store-extended-info": true,
+       ...
+   }
+
+When set to ``true``, information relevant to the DHCPREQUEST asking for the lease is
+added into the lease's user-context as a map element labeled "ISC". Currently,
+the map contains a single value, the ``relay-agent-info`` option (DHCP Option 82),
+when the DHCPREQUEST received contains it. Since DHCPREQUESTs sent as renewals will likely not contain this
+information, the values taken from the last DHCPREQUEST that did contain it are
+retained on the lease. The lease's user-context looks something like this:
+
+::
+
+  { "ISC": { "relay-agent-info": "0x52050104AABBCCDD" } }
+
+.. note::
+
+    It is possible that other hook libraries are already using ``user-context``.
+    Enabling ``store-extended-info`` should not interfere with any other ``user-context``
+    content, as long as it does not also use an element labeled "ISC". In other
+    words, ``user-context`` is intended to be a flexible container serving multiple
+    purposes. As long as no other purpose also writes an "ISC" element to
+    ``user-context`` there should not be a conflict.
+
+.. _dhcp4-multi-threading-settings:
+
+Multi-Threading Settings
+------------------------
+
+The Kea server can be configured to process packets in parallel using multiple
+threads. These settings can be found under the ``multi-threading`` structure and are
+represented by:
+
+-  ``enable-multi-threading`` - use multiple threads to process packets in
+   parallel. The default is ``false``.
+
+-  ``thread-pool-size`` - specify the number of threads to process packets in
+   parallel. It may be set to 0 (auto-detect), or any positive number explicitly sets
+   the thread count. The default is 0.
+
+-  ``packet-queue-size`` - specify the size of the queue used by the thread
+   pool to process packets. It may be set to 0 (unlimited), or any positive
+   number explicitly sets the queue size. The default is 64.
+
+An example configuration that sets these parameters looks as follows:
+
+::
+
+   "Dhcp4": {
+       "multi-threading": {
+          "enable-multi-threading": true,
+          "thread-pool-size": 4,
+          "packet-queue-size": 16
+       }
+       ...
+   }
+
+Multi-Threading Settings With Different Database Backends
+---------------------------------------------------------
+
+Both ``kea-dhcp4`` and ``kea-dhcp6`` are tested by ISC to determine which settings
+give the best performance. Although this section describes our results, they are merely
+recommendations and are very dependent on the particular hardware used
+for testing. We strongly advise that administrators run their own performance tests.
+
+A full report of performance results for the latest stable Kea version can be found
+`here <https://reports.kea.isc.org/>`_.
+This includes hardware and test scenario descriptions, as well as
+current results.
+
+After enabling multi-threading, the number of threads is set by the ``thread-pool-size``
+parameter. Results from our tests show that the best settings for
+``kea-dhcp4`` are:
+
+-  ``thread-pool-size``: 4 when using ``memfile`` for storing leases.
+
+-  ``thread-pool-size``: 12 or more when using ``mysql`` for storing leases.
+
+-  ``thread-pool-size``: 8 when using ``postgresql``.
+
+Another very important parameter is ``packet-queue-size``; in our tests we
+used it as a multiplier of ``thread-pool-size``. The actual setting strongly depends
+on ``thread-pool-size``.
+
+We saw the best results in our tests with the following settings:
+
+-  ``packet-queue-size``: 7 * ``thread-pool-size`` when using ``memfile`` for
+   storing leases; in our case it was 7 * 4 = 28. This means that at any given
+   time, up to 28 packets could be queued.
+
+-  ``packet-queue-size``: 66 * ``thread-pool-size`` when using ``mysql`` for
+   storing leases; in our case it was 66 * 12 = 792. This means that up to
+   792 packets could be queued.
+
+-  ``packet-queue-size``: 11 * ``thread-pool-size`` when using ``postgresql`` for
+   storing leases; in our case it was 11 * 8 = 88.
+
+IPv6-Only Preferred Networks
+----------------------------
+
+`RFC8925 <https://tools.ietf.org/html/rfc8925>`_, recently published by the IETF,
+specifies a DHCPv4 option to indicate that a host supports an IPv6-only mode and is willing to
+forgo obtaining an IPv4 address if the network provides IPv6 connectivity. The general idea is that
+a network administrator can enable this option to signal to compatible dual-stack devices that
+IPv6 connectivity is available and they can shut down their IPv4 stack. The new option
+``v6-only-preferred`` content is a 32-bit unsigned integer and specifies for how long the device
+should disable its stack. The value is expressed in seconds.
+
+The RFC mentions the ``V6ONLY_WAIT`` timer. This is implemented in Kea by setting the value of
+the ``v6-only-preferred`` option. This follows the usual practice of setting options; the
+option value can be specified on the pool, subnet, shared network, or global levels, or even
+via host reservations.
+
+There is no special processing involved; it follows the standard Kea option processing
+regime. The option is not sent back unless the client explicitly requests it. For example, to
+enable the option for the whole subnet, the following configuration can be used:
+
+::
+
+    "subnet4": [
+        {
+            "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
+            "subnet": "192.0.2.0/24",
+            "option-data": [
+                {
+                    // This will make the v6-only capable devices to disable their
+                    // v4 stack for half an hour and then try again
+                    "name": "v6-only-preferred",
+                    "data": "1800"
+                }
+            ]
+        }
+    ],
+
+Lease Caching
+-------------
+
+Clients that attempt multiple renewals in a short period can cause the server to update
+and write to the database frequently, resulting in a performance impact
+on the server. The cache parameters instruct the DHCP server to avoid
+updating leases too frequently, thus avoiding this behavior. Instead,
+the server assigns the same lease (i.e. reuses it) with no
+modifications except for CLTT (Client Last Transmission Time), which
+does not require disk operations.
+
+The two parameters are the ``cache-threshold`` double and the
+``cache-max-age`` integer; they have no default setting, i.e. the lease caching
+feature must be explicitly enabled. These parameters can be configured
+at the global, shared-network, and subnet levels. The subnet level has
+precedence over the shared-network level, while the global level is used
+as a last resort. For example:
+
+::
+
+    "subnet4": [
+        {
+            "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
+            "subnet": "192.0.2.0/24",
+            "cache-threshold": .25,
+            "cache-max-age": 600,
+            "valid-lifetime": 2000,
+            ...
+        }
+    ],
+
+When an already-assigned lease can fulfill a client query:
+
+  - any important change, e.g. for DDNS parameter, hostname, or
+    valid lifetime reduction, makes the lease not reusable.
+
+  - lease age, i.e. the difference between the creation or last modification
+    time and the current time, is computed (elapsed duration).
+
+  - if ``cache-max-age`` is explicitly configured, it is compared with the lease age;
+    leases that are too old are not reusable. This means that the value 0
+    for ``cache-max-age`` disables the lease cache feature.
+
+  - if ``cache-threshold`` is explicitly configured and is between 0.0 and 1.0,
+    it expresses the percentage of the lease valid lifetime which is
+    allowed for the lease age. Values below and including 0.0 and
+    values greater than 1.0 disable the lease cache feature.
+
+In our example, a lease with a valid lifetime of 2000 seconds can be
+reused if it was committed less than 500 seconds ago. With a lifetime
+of 3000 seconds, a maximum age of 600 seconds applies.
+
+In outbound client responses (e.g. DHCPACK messages), the
+``dhcp-lease-time`` option is set to the reusable valid lifetime,
+i.e. the expiration date does not change. Other options based on the
+valid lifetime e.g. ``dhcp-renewal-time`` and ``dhcp-rebinding-time``,
+also depend on the reusable lifetime.
+
+.. _host-reservation-v4:
+
+Host Reservations in DHCPv4
+===========================
+
+There are many cases where it is useful to provide a configuration on a
+per-host basis. The most obvious one is to reserve a specific, static
+address for exclusive use by a given client (host); the returning client
+receives the same address from the server every time, and other
+clients generally do not receive that address. Host
+reservations are also convenient when a host has
+specific requirements, e.g. a printer that needs additional DHCP
+options. Yet another possible use case is to define unique names for
+hosts.
+
+There may be cases when a new reservation has been made for a
+client for an address currently in use by another client. We call this
+situation a "conflict."
+These conflicts get resolved automatically over time, as described in
+subsequent sections. Once a conflict is resolved, the correct client will
+receive the reserved configuration when it renews.
+
+Host reservations are defined as parameters for each subnet. Each host
+must have its own unique identifier, such as the hardware/MAC
+address. There is an optional ``reservations`` array in the ``subnet4``
+structure; each element in that array is a structure that holds
+information about reservations for a single host. In particular, the
+structure has an identifier that uniquely identifies a host. In
+the DHCPv4 context, the identifier is usually a hardware or MAC address.
+In most cases an IP address will be specified. It is also possible to
+specify a hostname, host-specific options, or fields carried within the
+DHCPv4 message such as ``siaddr``, ``sname``, or ``file``.
+
+.. note::
+
+   The reserved address must be within the subnet.
+
+The following example shows how to reserve addresses for specific hosts
+in a subnet:
+
+::
+
+   "subnet4": [
+       {
+           "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
+           "subnet": "192.0.2.0/24",
+           "interface": "eth0",
+           "reservations": [
+               {
+                   "hw-address": "1a:1b:1c:1d:1e:1f",
+                   "ip-address": "192.0.2.202"
+               },
+               {
+                   "duid": "0a:0b:0c:0d:0e:0f",
+                   "ip-address": "192.0.2.100",
+                   "hostname": "alice-laptop"
+               },
+               {
+                   "circuit-id": "'charter950'",
+                   "ip-address": "192.0.2.203"
+               },
+               {
+                   "client-id": "01:11:22:33:44:55:66",
+                   "ip-address": "192.0.2.204"
+               }
+           ]
+       }
+   ]
+
+The first entry reserves the 192.0.2.202 address for the client that
+uses a MAC address of 1a:1b:1c:1d:1e:1f. The second entry reserves the
+address 192.0.2.100 and the hostname of "alice-laptop" for the client
+using a DUID 0a:0b:0c:0d:0e:0f. (If DNS updates are planned,
+it is strongly recommended that the hostnames be unique.) The
+third example reserves address 192.0.3.203 for a client whose request
+would be relayed by a relay agent that inserts a ``circuit-id`` option with
+the value "charter950". The fourth entry reserves address 192.0.2.204
+for a client that uses a client identifier with value
+01:11:22:33:44:55:66.
+
+The above example is used for illustrational purposes only; in actual
+deployments it is recommended to use as few types as possible
+(preferably just one). See :ref:`reservations4-tuning` for a detailed discussion of this
+point.
+
+Making a reservation for a mobile host that may visit multiple subnets
+requires a separate host definition in each subnet that host is expected to
+visit. It is not possible to define multiple host definitions with the
+same hardware address in a single subnet. Multiple host definitions with
+the same hardware address are valid if each is in a different subnet.
+
+Adding host reservations incurs a performance penalty. In principle, when
+a server that does not support host reservation responds to a query, it
+needs to check whether there is a lease for a given address being
+considered for allocation or renewal. The server that does support host
+reservation has to perform additional checks: not only whether the
+address is currently used (i.e., if there is a lease for it), but also
+whether the address could be used by someone else (i.e., if there is a
+reservation for it). That additional check incurs extra overhead.
+
+.. _reservation4-types:
+
+Address Reservation Types
+-------------------------
+
+In a typical Kea scenario there is an IPv4 subnet defined, e.g.
+192.0.2.0/24, with a certain part of it dedicated for dynamic allocation
+by the DHCPv4 server. That dynamic part is referred to as a dynamic pool
+or simply a pool. In principle, a host reservation can reserve any
+address that belongs to the subnet. The reservations that specify
+addresses that belong to configured pools are called "in-pool
+reservations." In contrast, those that do not belong to dynamic pools
+are called "out-of-pool reservations." There is no formal difference in
+the reservation syntax and both reservation types are handled uniformly.
+
+Kea supports global host reservations. These are reservations that are
+specified at the global level within the configuration and that do not
+belong to any specific subnet. Kea still matches inbound client
+packets to a subnet as before, but when the subnet's reservation mode is
+set to "global", Kea looks for host reservations only among the
+global reservations defined. Typically, such reservations would be used
+to reserve hostnames for clients which may move from one subnet to
+another.
+
+.. note::
+
+   Global reservations, while useful in certain circumstances, have aspects
+   that must be given due consideration when using them. Please see
+   :ref:`reservation4-conflict` for more details.
+
+.. note::
+
+   Since Kea 1.9.1, reservation mode has been replaced by three
+   boolean flags, ``reservations-global``, ``reservations-in-subnet``,
+   and ``reservations-out-of-pool``, which allow the configuration of
+   host reservations both globally and in a subnet. In such cases a subnet
+   host reservation has preference over a global reservation
+   when both exist for the same client.
+
+.. _reservation4-conflict:
+
+Conflicts in DHCPv4 Reservations
+--------------------------------
+
+As reservations and lease information are stored separately, conflicts
+may arise. Consider the following series of events: the server has
+configured the dynamic pool of addresses from the range of 192.0.2.10 to
+192.0.2.20. Host A requests an address and gets 192.0.2.10. Now the
+system administrator decides to reserve address 192.0.2.10 for Host B.
+In general, reserving an address that is currently assigned to someone
+else is not recommended, but there are valid use cases where such an
+operation is warranted.
+
+The server now has a conflict to resolve. If Host B boots up and
+requests an address, the server cannot immediately assign the reserved
+address 192.0.2.10. A naive approach would to be immediately remove the
+existing lease for Host A and create a new one for Host B. That would
+not solve the problem, though, because as soon as Host B gets the
+address, it will detect that the address is already in use (by Host A) and
+will send a DHCPDECLINE message. Therefore, in this situation, the
+server has to temporarily assign a different address from the dynamic
+pool (not matching what has been reserved) to Host B.
+
+When Host A renews its address, the server will discover that the
+address being renewed is now reserved for another host - Host B.
+The server will inform Host A that it is no longer allowed to
+use it by sending a DHCPNAK message. The server will not remove the
+lease, though, as there's a small chance that the DHCPNAK will not be delivered if
+the network is lossy. If that happens, the client will not receive any
+responses, so it will retransmit its DHCPREQUEST packet. Once the
+DHCPNAK is received by Host A, it will revert to server discovery and
+will eventually get a different address. Besides allocating a new lease,
+the server will also remove the old one. As a result, address 192.0.2.10
+will become free.
+
+When Host B tries to renew its temporarily assigned
+address, the server will detect that it has a valid lease, but will note
+that there is a reservation for a different address. The server will
+send DHCPNAK to inform Host B that its address is no longer usable, but
+will keep its lease (again, the DHCPNAK may be lost, so the server will
+keep it until the client returns for a new address). Host B will revert
+to the server discovery phase and will eventually send a DHCPREQUEST
+message. This time the server will find that there is a reservation for
+that host and that the reserved address 192.0.2.10 is not used, so it
+will be granted. It will also remove the lease for the temporarily
+assigned address that Host B previously obtained.
+
+This recovery will succeed, even if other hosts attempt to get the
+reserved address. If Host C requests the address 192.0.2.10 after the
+reservation is made, the server will either offer a different address
+(when responding to DHCPDISCOVER) or send DHCPNAK (when responding to
+DHCPREQUEST).
+
+This mechanism allows the server to fully recover from a case
+where reservations conflict with existing leases; however, this procedure
+takes roughly as long as the value set for ``renew-timer``. The
+best way to avoid such a recovery is not to define new reservations that
+conflict with existing leases. Another recommendation is to use
+out-of-pool reservations; if the reserved address does not belong to a
+pool, there is no way that other clients can get it.
+
+.. note::
+
+   The conflict-resolution mechanism does not work for global
+   reservations. Although the global address reservations feature may be useful
+   in certain settings, it is generally recommended not to use
+   global reservations for addresses. Administrators who do choose
+   to use global reservations must manually ensure that the reserved
+   addresses are not in dynamic pools.
+
+.. _reservation4-hostname:
+
+Reserving a Hostname
+--------------------
+
+When the reservation for a client includes the ``hostname``, the server
+returns this hostname to the client in the Client FQDN or Hostname
+option. The server responds with the Client FQDN option only if the
+client has included the Client FQDN option in its message to the server. The
+server responds with the Hostname option if the client included
+the Hostname option in its message to the server, or if the client
+requested the Hostname option using the Parameter Request List option.
+The server returns the Hostname option even if it is not configured
+to perform DNS updates. The reserved hostname always takes precedence
+over the hostname supplied by the client or the autogenerated (from the
+IPv4 address) hostname.
+
+The server qualifies the reserved hostname with the value of the
+``ddns-qualifying-suffix`` parameter. For example, the following subnet
+configuration:
+
+::
+
+       {
+           "subnet4": [ {
+               "subnet": "10.0.0.0/24",
+               "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
+               "ddns-qualifying-suffix": "example.isc.org.",
+               "reservations": [
+                  {
+                    "hw-address": "aa:bb:cc:dd:ee:ff",
+                    "hostname": "alice-laptop"
+                  }
+               ]
+            }],
+           "dhcp-ddns": {
+               "enable-updates": true,
+           }
+       }
+
+will result in the "alice-laptop.example.isc.org." hostname being assigned to
+the client using the MAC address "aa:bb:cc:dd:ee:ff". If the
+``ddns-qualifying-suffix`` is not specified, the default (empty) value will
+be used, and in this case the value specified as a ``hostname`` will be
+treated as a fully qualified name. Thus, by leaving the
+``ddns-qualifying-suffix`` empty it is possible to qualify hostnames for
+different clients with different domain names:
+
+::
+
+       {
+           "subnet4": [ {
+               "subnet": "10.0.0.0/24",
+               "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
+               "reservations": [
+                  {
+                    "hw-address": "aa:bb:cc:dd:ee:ff",
+                    "hostname": "alice-laptop.isc.org."
+                  },
+                  {
+                    "hw-address": "12:34:56:78:99:AA",
+                    "hostname": "mark-desktop.example.org."
+                  }
+
+               ]
+            }],
+           "dhcp-ddns": {
+               "enable-updates": true,
+           }
+       }
+
+The above example results in the assignment of the
+"alice-laptop.isc.org." hostname to the client using the MAC
+address "aa:bb:cc:dd:ee:ff", and the hostname  "mark-desktop.example.org."
+to the client using the MAC address "12:34:56:78:99:AA".
+
+.. _reservation4-options:
+
+Including Specific DHCPv4 Options in Reservations
+-------------------------------------------------
+
+Kea offers the ability to specify options on a per-host basis. These
+options follow the same rules as any other options. These can be
+standard options (see :ref:`dhcp4-std-options`),
+custom options (see :ref:`dhcp4-custom-options`),
+or vendor-specific options (see :ref:`dhcp4-vendor-opts`). The following
+example demonstrates how standard options can be defined:
+
+::
+
+   {
+       "subnet4": [ {
+           "reservations": [
+           {
+               "hw-address": "aa:bb:cc:dd:ee:ff",
+               "ip-address": "192.0.2.1",
+               "option-data": [
+               {
+                   "name": "cookie-servers",
+                   "data": "10.1.1.202,10.1.1.203"
+               },
+               {
+                   "name": "log-servers",
+                   "data": "10.1.1.200,10.1.1.201"
+               } ]
+           } ]
+       } ]
+   }
+
+Vendor-specific options can be reserved in a similar manner:
+
+::
+
+   {
+       "subnet4": [ {
+           "reservations": [
+           {
+               "hw-address": "aa:bb:cc:dd:ee:ff",
+               "ip-address": "10.0.0.7",
+               "option-data": [
+               {
+                   "name": "vivso-suboptions",
+                   "data": "4491"
+               },
+               {
+                   "name": "tftp-servers",
+                   "space": "vendor-4491",
+                   "data": "10.1.1.202,10.1.1.203"
+               } ]
+           } ]
+       } ]
+   }
+
+Options defined at the host level have the highest priority. In other words,
+if there are options defined with the same type on the global, subnet,
+class, and host levels, the host-specific values are used.
+
+.. _reservation4-message-fields:
+
+Reserving Next Server, Server Hostname, and Boot File Name
+----------------------------------------------------------
+
+BOOTP/DHCPv4 messages include "siaddr", "sname", and "file" fields. Even
+though DHCPv4 includes corresponding options, such as option 66 and
+option 67, some clients may not support these options. For this reason,
+server administrators often use the "siaddr", "sname", and "file" fields
+instead.
+
+With Kea, it is possible to make static reservations for these DHCPv4
+message fields:
+
+::
+
+   {
+       "subnet4": [ {
+           "reservations": [
+           {
+               "hw-address": "aa:bb:cc:dd:ee:ff",
+               "next-server": "10.1.1.2",
+               "server-hostname": "server-hostname.example.org",
+               "boot-file-name": "/tmp/bootfile.efi"
+           } ]
+       } ]
+   }
+
+Note that those parameters can be specified in combination with other
+parameters for a reservation, such as a reserved IPv4 address. These
+parameters are optional; a subset of them can be specified, or all
+of them can be omitted.
+
+.. _reservation4-client-classes:
+
+Reserving Client Classes in DHCPv4
+----------------------------------
+
+:ref:`classification-using-expressions` explains how to configure
+the server to assign classes to a client, based on the content of the
+options that this client sends to the server. Host reservation
+mechanisms also allow for the static assignment of classes to clients.
+The definitions of these classes are placed in the Kea configuration file or
+a database. The following configuration snippet shows how to specify that
+a client belongs to the classes ``reserved-class1`` and ``reserved-class2``. Those
+classes are associated with specific options sent to the clients which belong
+to them.
+
+::
+
+   {
+       "client-classes": [
+       {
+          "name": "reserved-class1",
+          "option-data": [
+          {
+              "name": "routers",
+              "data": "10.0.0.200"
+          }
+          ]
+       },
+       {
+          "name": "reserved-class2",
+          "option-data": [
+          {
+              "name": "domain-name-servers",
+              "data": "10.0.0.201"
+          }
+          ]
+       }
+       ],
+       "subnet4": [ {
+           "subnet": "10.0.0.0/24",
+           "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
+           "reservations": [
+           {
+               "hw-address": "aa:bb:cc:dd:ee:ff",
+
+               "client-classes": [ "reserved-class1", "reserved-class2" ]
+
+           }
+           ]
+       } ]
+    }
+
+In some cases the host reservations can be used in conjunction with client
+classes specified within the Kea configuration. In particular, when a
+host reservation exists for a client within a given subnet, the "KNOWN"
+built-in class is assigned to the client. Conversely, when there is no
+static assignment for the client, the "UNKNOWN" class is assigned to the
+client. Class expressions within the Kea configuration file can
+refer to "KNOWN" or "UNKNOWN" classes using the "member" operator.
+For example:
+
+::
+
+    {
+        "client-classes": [
+            {
+                "name": "dependent-class",
+                "test": "member('KNOWN')",
+                "only-if-required": true
+            }
+        ]
+    }
+
+The ``only-if-required`` parameter is needed here to force
+evaluation of the class after the lease has been allocated and thus the
+reserved class has been also assigned.
+
+.. note::
+
+   The classes specified in non-global host reservations
+   are assigned to the processed packet after all classes with the
+   ``only-if-required`` parameter set to ``false`` have been evaluated.
+   This means that these classes must not depend on the
+   statically assigned classes from the host reservations. If
+   such a dependency is needed, the ``only-if-required`` parameter must
+   be set to ``true`` for the dependent classes. Such classes are
+   evaluated after the static classes have been assigned to the packet.
+   This, however, imposes additional configuration overhead, because
+   all classes marked as ``only-if-required`` must be listed in the
+   ``require-client-classes`` list for every subnet where they are used.
+
+.. note::
+
+   Client classes specified within the Kea configuration file may
+   depend on the classes specified within the global host reservations.
+   In such a case the ``only-if-required`` parameter is not needed.
+   Refer to :ref:`pool-selection-with-class-reservations4` and
+   :ref:`subnet-selection-with-class-reservations4`
+   for specific use cases.
+
+.. _reservations4-mysql-pgsql:
+
+Storing Host Reservations in MySQL or PostgreSQL
+------------------------------------------------
+
+Kea can store host reservations in MySQL or PostgreSQL.
+See :ref:`hosts4-storage` for information on how to
+configure Kea to use reservations stored in MySQL or PostgreSQL.
+Kea provides a dedicated hook for managing reservations in a
+database; section :ref:`hooks-host-cmds` provides detailed information.
+The `Kea wiki
+<https://gitlab.isc.org/isc-projects/kea/wikis/designs/commands#23-host-reservations-hr-management>`__
+provides some examples of how to conduct common host reservation
+operations.
+
+.. note::
+
+   In Kea, the maximum length of an option specified per-host-reservation is
+   arbitrarily set to 4096 bytes.
+
+.. _reservations4-tuning:
+
+Fine-Tuning DHCPv4 Host Reservation
+-----------------------------------
+
+The host reservation capability introduces additional restrictions for
+the allocation engine (the component of Kea that selects an address for
+a client) during lease selection and renewal. In particular, three major
+checks are necessary. First, when selecting a new lease, it is not
+sufficient for a candidate lease to simply not be in use by another DHCP
+client; it also must not be reserved for another client. Similarly, when
+renewing a lease, an additional check must be performed to see whether
+the address being renewed is reserved for another client. Finally, when
+a host renews an address, the server must check whether there is a
+reservation for this host, which would mean the existing (dynamically allocated)
+address should be revoked and the reserved one be used instead.
+
+Some of those checks may be unnecessary in certain deployments, and not
+performing them may improve performance. The Kea server provides the
+``reservation-mode`` configuration parameter to select the types of
+reservations allowed for a particular subnet. Each reservation type has
+different constraints for the checks to be performed by the server when
+allocating or renewing a lease for the client. Although ``reservation-mode``
+was deprecated in Kea 1.9.1, it is still available; the allowed values are:
+
+-  ``all`` - enables both in-pool and out-of-pool host reservation
+   types. This setting is the default value, and is the safest and most
+   flexible. However, as all checks are conducted, it is also the slowest.
+   It does not check against global reservations.
+
+-  ``out-of-pool`` - allows only out-of-pool host reservations. With
+   this setting in place, the server assumes that all host
+   reservations are for addresses that do not belong to the dynamic
+   pool. Therefore, it can skip the reservation checks when dealing with
+   in-pool addresses, thus improving performance. Do not use this mode
+   if any reservations use in-pool addresses. Caution is advised
+   when using this setting; Kea does not sanity-check the reservations
+   against ``reservation-mode`` and misconfiguration may cause problems.
+
+-  ``global`` - allows only global host reservations. With this setting
+   in place, the server searches for reservations for a client only
+   among the defined global reservations. If an address is specified,
+   the server skips the reservation checks carried out in
+   other modes, thus improving performance. Caution is advised when
+   using this setting; Kea does not sanity-check reservations when
+   ``global`` is set, and misconfiguration may cause problems.
+
+-  ``disabled`` - host reservation support is disabled. As there are no
+   reservations, the server skips all checks. Any reservations
+   defined are completely ignored. As checks are skipped, the
+   server may operate faster in this mode.
+
+Since Kea 1.9.1, the ``reservation-mode`` parameter is replaced by the
+``reservations-global``, ``reservations-in-subnet``, and
+``reservations-out-of-pool`` flags.
+The flags can be activated independently and can produce various combinations,
+some of which were not supported by the deprecated ``reservation-mode``.
+
+The ``reservation-mode`` parameter can be specified at:
+
+- global level: ``.Dhcp4["reservation-mode"]`` (lowest priority: gets overridden
+  by all others)
+
+- subnet level: ``.Dhcp4.subnet4[]["reservation-mode"]`` (low priority)
+
+- shared-network level: ``.Dhcp4["shared-networks"][]["reservation-mode"]``
+  (high priority)
+
+- shared-network subnet-level:
+  ``.Dhcp4["shared-networks"][].subnet4[]["reservation-mode"]`` (highest
+  priority: overrides all others)
+
+To decide which ``reservation-mode`` to choose, the
+following decision diagram may be useful:
+
+::
+
+                                  O
+                                  |
+                                  v
+    +-----------------------------+------------------------------+
+    |         Is per-host configuration needed, such as          |
+    |                reserving specific addresses,               |
+    |               assigning specific options or                |
+    | assigning packets to specific classes on per-device basis? |
+    +-+-----------------+----------------------------------------+
+      |                 |
+    no|              yes|
+      |                 |   +--------------------------------------+
+      |                 |   |         For all given hosts,         |
+      +--> "disabled"   +-->+      can the reserved resources      |
+                            |  be used in all configured subnets?  |
+                            +--------+---------------------------+-+
+                                     |                           |
+    +----------------------------+   |no                         |yes
+    |             Is             |   |                           |
+    |  at least one reservation  +<--+               "global" <--+
+    | used to reserve addresses? |
+    +-+------------------------+-+
+      |                        |
+    no|                     yes|   +---------------------------+
+      |                        |   | Is high leases-per-second |
+      +--> "out-of-pool"       +-->+ performance or efficient  |
+            ^                      |      resource usage       |
+            |                      |  (CPU ticks, RAM usage,   |
+            |                      |   database roundtrips)    |
+            |                      | important to your setup?  |
+            |                      +-+----------------+--------+
+            |                        |                |
+            |                     yes|              no|
+            |                        |                |
+            |          +-------------+                |
+            |          |                              |
+            |          |   +----------------------+   |
+            |          |   | Can it be guaranteed |   |
+            |          +-->+  that the reserved   |   |
+            |              |      addresses       |   |
+            |              |  aren't part of the  |   |
+            |              |   pools configured   |   |
+            |              |  in the respective   |   |
+            |              |       subnet?        |   |
+            |              +-+------------------+-+   |
+            |                |                  |     |
+            |             yes|                no|     |
+            |                |                  |     V
+            +----------------+                  +--> "all"
+
+An example configuration that disables reservations looks as follows:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "subnet4": [
+          {
+            "pools": [
+              {
+                "pool": "192.0.2.10-192.0.2.100"
+              }
+            ],
+            "reservation-mode": "disabled",
+            "subnet": "192.0.2.0/24"
+          }
+        ]
+      }
+    }
+
+An example configuration using global reservations is shown below:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "reservation-mode": "global",
+        "reservations": [
+          {
+            "hostname": "host-one",
+            "hw-address": "01:bb:cc:dd:ee:ff"
+          },
+          {
+            "hostname": "host-two",
+            "hw-address": "02:bb:cc:dd:ee:ff"
+          }
+        ],
+        "subnet4": [
+          {
+            "pools": [
+              {
+                "pool": "192.0.2.10-192.0.2.100"
+              }
+            ],
+            "subnet": "192.0.2.0/24"
+          }
+        ]
+      }
+    }
+
+The meaning of the reservation flags are:
+
+- ``reservations-global``: fetch global reservations.
+
+- ``reservations-in-subnet``: fetch subnet reservations. For a shared network
+  this includes all subnet members of the shared network.
+
+- ``reservations-out-of-pool``: this makes sense only when the
+  ``reservations-in-subnet`` flag is ``true``. When ``reservations-out-of-pool``
+  is ``true``, the server assumes that all host reservations are for addresses
+  that do not belong to the dynamic pool. Therefore, it can skip the reservation
+  checks when dealing with in-pool addresses, thus improving performance.
+  The server will not assign reserved addresses that are inside the dynamic
+  pools to the respective clients. This also means that the addresses matching
+  the respective reservations from inside the dynamic pools (if any) can be
+  dynamically assigned to any client.
+
+The ``disabled`` value from the deprecated ``reservation-mode`` corresponds to:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "reservations-global": false,
+        "reservations-in-subnet": false
+      }
+    }
+
+The ``global`` value from the deprecated ``reservation-mode`` corresponds to:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "reservations-global": true,
+        "reservations-in-subnet": false
+      }
+    }
+
+The ``out-of-pool`` value from the deprecated ``reservation-mode`` corresponds to:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "reservations-global": false,
+        "reservations-in-subnet": true,
+        "reservations-out-of-pool": true
+      }
+    }
+
+And the ``all`` value from the deprecated ``reservation-mode`` corresponds to:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "reservations-global": false,
+        "reservations-in-subnet": true,
+        "reservations-out-of-pool": false
+      }
+    }
+
+To activate both ``global`` and ``all``, the following combination can be used:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "reservations-global": true,
+        "reservations-in-subnet": true,
+        "reservations-out-of-pool": false
+      }
+    }
+
+To activate both ``global`` and ``out-of-pool``, the following combination can
+be used:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "reservations-global": true,
+        "reservations-in-subnet": true,
+        "reservations-out-of-pool": true
+      }
+    }
+
+Enabling ``out-of-pool`` and disabling ``in-subnet`` at the same time
+is not recommended because ``out-of-pool`` applies to host reservations in a
+subnet, which are fetched only when the ``in-subnet`` flag is ``true``.
+
+The parameter can be specified at the global, subnet, and shared-network
+levels.
+
+An example configuration that disables reservations looks as follows:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "subnet4": [
+          {
+            "reservations-global": false,
+            "reservations-in-subnet": false,
+            "subnet": "192.0.2.0/24"
+          }
+        ]
+      }
+    }
+
+An example configuration using global reservations is shown below:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "reservations": [
+          {
+            "hostname": "host-one",
+            "hw-address": "01:bb:cc:dd:ee:ff"
+          },
+          {
+            "hostname": "host-two",
+            "hw-address": "02:bb:cc:dd:ee:ff"
+          }
+        ],
+        "reservations-global": true,
+        "reservations-in-subnet": false,
+        "subnet4": [
+          {
+            "pools": [
+              {
+                "pool": "192.0.2.10-192.0.2.100"
+              }
+            ],
+            "subnet": "192.0.2.0/24"
+          }
+        ]
+      }
+    }
+
+For more details regarding global reservations, see :ref:`global-reservations4`.
+
+Another aspect of host reservations is the different types of
+identifiers. Kea currently supports four types of identifiers:
+``hw-address``, ``duid``, ``client-id``, and ``circuit-id``. This is beneficial from a
+usability perspective; however, there is one drawback. For each incoming
+packet, Kea has to extract each identifier type and then query the
+database to see if there is a reservation by this particular identifier.
+If nothing is found, the next identifier is extracted and the next query
+is issued. This process continues until either a reservation is found or
+all identifier types have been checked. Over time, with an increasing
+number of supported identifier types, Kea would become slower and
+slower.
+
+To address this problem, a parameter called
+``host-reservation-identifiers`` is available. It takes a list of
+identifier types as a parameter. Kea checks only those identifier
+types enumerated in ``host-reservation-identifiers``. From a performance
+perspective, the number of identifier types should be kept to a minimum,
+ideally one. If the deployment uses several reservation types, please
+enumerate them from most- to least-frequently used, as this increases
+the chances of Kea finding the reservation using the fewest queries. An
+example of a ``host-reservation-identifiers`` configuration looks as follows:
+
+::
+
+   "host-reservation-identifiers": [ "circuit-id", "hw-address", "duid", "client-id" ],
+   "subnet4": [
+       {
+           "subnet": "192.0.2.0/24",
+           ...
+       }
+   ]
+
+If not specified, the default value is:
+
+::
+
+   "host-reservation-identifiers": [ "hw-address", "duid", "circuit-id", "client-id" ]
+
+.. _global-reservations4:
+
+Global Reservations in DHCPv4
+-----------------------------
+
+In some deployments, such as mobile, clients can roam within the network
+and certain parameters must be specified regardless of the client's
+current location. To meet such a need, Kea offers a global reservation
+mechanism. The idea behind it is that regular host
+reservations are tied to specific subnets, by using a specific
+subnet ID. Kea can specify a global reservation that can be used in
+every subnet that has global reservations enabled.
+
+This feature can be used to assign certain parameters, such as hostname
+or other dedicated, host-specific options. It can also be used to assign
+addresses. However, global reservations that assign addresses bypass the
+whole topology determination provided by the DHCP logic implemented in Kea.
+It is very easy to misuse this feature and get a configuration that is
+inconsistent. To give a specific example, imagine a global reservation
+for the address 192.0.2.100 and two subnets 192.0.2.0/24 and 192.0.5.0/24.
+If global reservations are used in both subnets and a device matching
+global host reservations visits part of the network that is serviced by
+192.0.5.0/24, it will get an IP address 192.0.2.100, a subnet 192.0.5.0,
+and a default router 192.0.5.1. Obviously, such a configuration is
+unusable, as the client will not be able to reach its default gateway.
+
+To use global host reservations, a configuration similar to the
+following can be used:
+
+::
+
+   "Dhcp4:" {
+       # This specifies global reservations.
+       # They will apply to all subnets that
+       # have global reservations enabled.
+
+       "reservations": [
+       {
+          "hw-address": "aa:bb:cc:dd:ee:ff",
+          "hostname": "hw-host-dynamic"
+       },
+       {
+          "hw-address": "01:02:03:04:05:06",
+          "hostname": "hw-host-fixed",
+
+          # Use of IP addresses in global reservations is risky.
+          # If used outside of a matching subnet, such as 192.0.1.0/24,
+          # it will result in a broken configuration being handed
+          # to the client.
+          "ip-address": "192.0.1.77"
+       },
+       {
+          "duid": "01:02:03:04:05",
+          "hostname": "duid-host"
+       },
+       {
+          "circuit-id": "'charter950'",
+          "hostname": "circuit-id-host"
+       },
+       {
+          "client-id": "01:11:22:33:44:55:66",
+          "hostname": "client-id-host"
+       }
+       ],
+       "valid-lifetime": 600,
+       "subnet4": [ {
+           "subnet": "10.0.0.0/24",
+           # It is replaced by the "reservations-global"
+           # "reservations-in-subnet" and "reservations-out-of-pool"
+           # parameters.
+           # "reservation-mode": "global",
+           # Specify if the server should lookup global reservations.
+           "reservations-global": true,
+           # Specify if the server should lookup in-subnet reservations.
+           "reservations-in-subnet": false,
+           # Specify if the server can assume that all reserved addresses
+           # are out-of-pool. It can be ignored because "reservations-in-subnet"
+           # is false.
+           # "reservations-out-of-pool": false,
+           "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ]
+       } ]
+   }
+
+When using database backends, the global host reservations are
+distinguished from regular reservations by using a ``subnet-id`` value of
+0.
+
+.. _pool-selection-with-class-reservations4:
+
+Pool Selection with Client Class Reservations
+---------------------------------------------
+
+Client classes can be specified in the Kea configuration file and/or via
+host reservations. The classes specified in the Kea configuration file are
+evaluated immediately after receiving the DHCP packet and therefore can be
+used to influence subnet selection using the ``client-class`` parameter
+specified in the subnet scope. The classes specified within the host
+reservations are fetched and assigned to the packet after the server has
+already selected a subnet for the client. This means that the client
+class specified within a host reservation cannot be used to influence
+subnet assignment for this client, unless the subnet belongs to a
+shared network. If the subnet belongs to a shared network, the server may
+dynamically change the subnet assignment while trying to allocate a lease.
+If the subnet does not belong to a shared network, the subnet
+is not changed once selected.
+
+If the subnet does not belong to a shared network, it is possible to
+use host reservation-based client classification to select an address pool
+within the subnet as follows:
+
+::
+
+    "Dhcp4": {
+        "client-classes": [
+            {
+                "name": "reserved_class"
+            },
+            {
+                "name": "unreserved_class",
+                "test": "not member('reserved_class')"
+            }
+        ],
+        "subnet4": [
+            {
+                "subnet": "192.0.2.0/24",
+                "reservations": [{"
+                    "hw-address": "aa:bb:cc:dd:ee:fe",
+                    "client-classes": [ "reserved_class" ]
+                 }],
+                "pools": [
+                    {
+                        "pool": "192.0.2.10-192.0.2.20",
+                        "client-class": "reserved_class"
+                    },
+                    {
+                        "pool": "192.0.2.30-192.0.2.40",
+                        "client-class": "unreserved_class"
+                    }
+                ]
+            }
+        ]
+    }
+
+The ``reserved_class`` is declared without the ``test`` parameter because
+it may only be assigned to the client via the host reservation mechanism. The
+second class, ``unreserved_class``, is assigned to clients which do not
+belong to the ``reserved_class``. The first pool within the subnet is only
+used for clients having a reservation for the ``reserved_class``. The
+second pool is used for clients not having such a reservation. The
+configuration snippet includes one host reservation which causes the client
+with the MAC address aa:bb:cc:dd:ee:fe to be assigned to the
+``reserved_class``. Thus, this client will be given an IP address from the
+first address pool.
+
+.. _subnet-selection-with-class-reservations4:
+
+Subnet Selection with Client Class Reservations
+-----------------------------------------------
+
+There is one specific use case when subnet selection may be influenced by
+client classes specified within host reservations: when the
+client belongs to a shared network. In such a case it is possible to use
+classification to select a subnet within this shared network. Consider the
+following example:
+
+::
+
+    "Dhcp4": {
+        "client-classes": [
+            {
+                "name": "reserved_class"
+            },
+            {
+                "name: "unreserved_class",
+                "test": "not member('reserved_class')"
+            }
+        ],
+        "reservations": [{"
+            "hw-address": "aa:bb:cc:dd:ee:fe",
+            "client-classes": [ "reserved_class" ]
+        }],
+        # It is replaced by the "reservations-global"
+        # "reservations-in-subnet" and "reservations-out-of-pool" parameters.
+        # Specify if the server should lookup global reservations.
+        "reservations-global": true,
+        # Specify if the server should lookup in-subnet reservations.
+        "reservations-in-subnet": false,
+        # Specify if the server can assume that all reserved addresses
+        # are out-of-pool. It can be ignored because "reservations-in-subnet"
+        # is false, but if specified, it is inherited by "shared-networks"
+        # and "subnet4" levels.
+        # "reservations-out-of-pool": false,
+        "shared-networks": [{
+            "subnet4": [
+                {
+                    "subnet": "192.0.2.0/24",
+                    "pools": [
+                        {
+                            "pool": "192.0.2.10-192.0.2.20",
+                            "client-class": "reserved_class"
+                        }
+                    ]
+                },
+                {
+                    "subnet": "192.0.3.0/24",
+                    "pools": [
+                        {
+                            "pool": "192.0.3.10-192.0.3.20",
+                            "client-class": "unreserved_class"
+                        }
+                    ]
+                }
+            ]
+        }]
+    }
+
+This is similar to the example described in
+:ref:`pool-selection-with-class-reservations4`. This time, however, there
+are two subnets, each of which has a pool associated with a different
+class. The clients that do not have a reservation for the ``reserved_class``
+are assigned an address from the subnet 192.0.3.0/24. Clients with
+a reservation for the ``reserved_class`` are assigned an address from
+the subnet 192.0.2.0/24. The subnets must belong to the same shared network.
+In addition, the reservation for the client class must be specified at the
+global scope (global reservation) and ``reservations-global`` must be
+set to ``true``.
+
+In the example above, the ``client-class`` could also be specified at the
+subnet level rather than the pool level, and would yield the same effect.
+
+.. _multiple-reservations-same-ip4:
+
+Multiple Reservations for the Same IP
+-------------------------------------
+
+Host reservations were designed to preclude the creation of multiple
+reservations for the same IP address within a particular subnet, to avoid
+having two different clients compete for the same address.
+When using the default settings, the server returns a configuration error
+when it finds two or more reservations for the same IP address within
+a subnet in the Kea configuration file. The :ref:`hooks-host-cmds` hook
+library returns an error in response to the ``reservation-add`` command
+when it detects that the reservation exists in the database for the IP
+address for which the new reservation is being added.
+
+In some deployments a single host can select one of several network
+interfaces to communicate with the DHCP server, and the server must assign
+the same IP address to the host regardless of the interface used. Since
+each interface is assigned a different MAC address, it implies that
+several host reservations must be created to associate all of the MAC
+addresses present on this host with IP addresses. Using different
+IP addresses for each interface is impractical and is considered a waste
+of the IPv4 address space, especially since the host typically uses only one
+interface for communication with the server, hence only one IP address
+is in use.
+
+This causes a need to create multiple host reservations for a single
+IP address within a subnet; this is supported since the Kea 1.9.1
+release as an optional mode of operation, enabled with the
+``ip-reservations-unique`` global parameter.
+
+The ``ip-reservations-unique`` is a boolean parameter that defaults to
+``true``, which forbids the specification of more than one reservation
+for the same IP address within a given subnet. Setting this parameter to
+``false`` allows such reservations to be created both in the Kea configuration
+file and in the host database backend, via the ``host-cmds`` hook library.
+
+This setting is currently supported by the most popular host database
+backends, i.e. MySQL and PostgreSQL.
+Host Cache (see :ref:`hooks-host-cache`), or the RADIUS backend
+(see :ref:`hooks-radius`). An attempt to set ``ip-reservations-unique``
+to ``false`` when any of these three backends is in use yields a
+configuration error.
+
+.. note::
+
+   When ``ip-reservations-unique`` is set to ``true`` (the default value),
+   the server ensures that IP reservations are unique for a subnet within
+   a single host backend and/or Kea configuration file. It does not
+   guarantee that the reservations are unique across multiple backends.
+
+The following is an example configuration with two reservations for
+the same IP address but different MAC addresses:
+
+::
+
+   "Dhcp4": {
+       "ip-reservations-unique": false,
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "reservations": [
+                   {
+                       "hw-address": "1a:1b:1c:1d:1e:1f",
+                       "ip-address": "192.0.2.11"
+                   },
+                   {
+                       "hw-address": "2a:2b:2c:2d:2e:2f",
+                       "ip-address": "192.0.2.11"
+                   }
+               ]
+           }
+       ]
+   }
+
+It is possible to control the ``ip-reservations-unique`` parameter via the
+:ref:`dhcp4-cb`. If the new setting of this parameter conflicts with
+the currently used backends (i.e. backends do not support the new setting),
+the new setting is ignored and a warning log message is generated.
+The backends continue to use the default setting, expecting that
+IP reservations are unique within each subnet. To allow the
+creation of non-unique IP reservations, the administrator must remove
+the backends which lack support for them from the configuration file.
+
+Administrators must be careful when they have been using multiple
+reservations for the same IP address and later decide to return to
+the default mode in which this is no longer allowed. They
+must make sure that at most one reservation for a given IP address
+exists within a subnet, prior to switching back to the default mode.
+If such duplicates are left in the configuration file, the server
+reports a configuration error. Leaving such reservations in the host
+databases does not cause configuration errors but may lead to lease
+allocation errors during the server's operation, when it unexpectedly
+finds multiple reservations for the same IP address.
+
+.. note::
+
+   Currently the Kea server does not verify whether multiple reservations for
+   the same IP address exist in MySQL and/or PostgreSQL host databases when
+   ``ip-reservations-unique`` is updated from ``true`` to ``false``. This may
+   cause issues with lease allocations. The administrator must ensure that there
+   is at most one reservation for each IP address within each subnet, prior to
+   the configuration update.
+
+The ``reservations-lookup-first`` is a boolean parameter which controls whether
+host reservations lookup should be performed before lease lookup. This parameter
+has effect only when multi-threading is disabled. When multi-threading is
+enabled, host reservations lookup is always performed first to avoid lease
+lookup resource locking. The ``reservations-lookup-first`` defaults to ``false``
+when multi-threading is disabled.
+
+.. _shared-network4:
+
+Shared Networks in DHCPv4
+=========================
+
+DHCP servers use subnet information in two ways. It is used to
+both determine the point of attachment, i.e. where the client is
+connected to the network, and to
+group information pertaining to a specific location in the network.
+Sometimes it is useful to have more than one
+logical IP subnet deployed on the same physical link.
+Understanding that two or more subnets are used on the same link requires
+additional logic in the DHCP server. This capability is called "shared
+networks" in Kea, and sometimes also
+"shared subnets"; in Microsoft's nomenclature it is called "multinet."
+
+There are many cases where the shared networks feature is useful; here we
+explain just a handful of the most common ones. The first and by far
+most common use case is an existing IPv4 network that has grown and is
+running out of available address space. Rather than migrating all
+devices to a new, larger subnet, it is easier to simply configure
+additional subnets on top of the existing one. Sometimes, due to address
+space fragmentation (e.g. only many disjointed /24s are available), this
+is the only choice. Also, configuring additional subnets has the
+advantage of not disrupting the operation of existing devices.
+
+Another very frequent use case comes from cable networks. There are two
+types of devices in cable networks: cable modems and the end-user
+devices behind them. It is a common practice to use different subnets
+for cable modems to prevent users from tinkering with them. In this
+case, the distinction is based on the type of device, rather than
+on address-space exhaustion.
+
+A client connected to a shared network may be assigned an address from
+any of the pools defined within the subnets belonging to the shared
+network. Internally, the server selects one of the subnets belonging to
+a shared network and tries to allocate an address from this subnet. If
+the server is unable to allocate an address from the selected subnet
+(e.g., due to address-pool exhaustion), it uses another subnet from
+the same shared network and tries to allocate an address from this subnet.
+The server typically allocates all
+addresses available in a given subnet before it starts allocating
+addresses from other subnets belonging to the same shared network.
+However, in certain situations the client can be allocated an address
+from another subnet before the address pools in the first subnet get
+exhausted; this sometimes occurs when the client provides a hint that belongs to another
+subnet, or the client has reservations in a subnet other than the
+default.
+
+.. note::
+
+   Deployments should not assume that Kea waits until it has allocated
+   all the addresses from the first subnet in a shared network before
+   allocating addresses from other subnets.
+
+To define a shared network, an additional configuration scope is
+introduced:
+
+::
+
+   {
+   "Dhcp4": {
+       "shared-networks": [
+           {
+               # Name of the shared network. It may be an arbitrary string
+               # and it must be unique among all shared networks.
+               "name": "my-secret-lair-level-1",
+
+               # The subnet selector can be specified at the shared network level.
+               # Subnets from this shared network will be selected for directly
+               # connected clients sending requests to the server's "eth0" interface.
+               "interface": "eth0",
+
+               # This starts a list of subnets in this shared network.
+               # There are two subnets in this example.
+               "subnet4": [
+                   {
+                       "subnet": "10.0.0.0/8",
+                       "pools": [ { "pool":  "10.0.0.1 - 10.0.0.99" } ],
+                   },
+                   {
+                       "subnet": "192.0.2.0/24",
+                       "pools": [ { "pool":  "192.0.2.100 - 192.0.2.199" } ]
+                   }
+               ],
+           } ], # end of shared-networks
+
+       # It is likely that in the network there will be a mix of regular,
+       # "plain" subnets and shared networks. It is perfectly valid to mix
+       # them in the same configuration file.
+       #
+       # This is a regular subnet. It is not part of any shared network.
+       "subnet4": [
+           {
+               "subnet": "192.0.3.0/24",
+               "pools": [ { "pool":  "192.0.3.1 - 192.0.3.200" } ],
+               "interface": "eth1"
+           }
+       ]
+
+   } # end of Dhcp4
+   }
+
+As demonstrated in the example, it is possible to mix shared and regular
+("plain") subnets. Each shared network must have a unique name. This is
+similar to the ID for subnets, but gives administrators more
+flexibility. It is used for logging, but also internally for identifying
+shared networks.
+
+In principle it makes sense to define only shared networks that consist
+of two or more subnets. However, for testing purposes, an empty subnet
+or a network with just a single subnet is allowed. This is not a
+recommended practice in production networks, as the shared network logic
+requires additional processing and thus lowers the server's performance.
+To avoid unnecessary performance degradation, shared subnets should
+only be defined when required by the deployment.
+
+Shared networks provide the ability to specify many parameters in the
+shared network scope that apply to all subnets within it. If
+necessary, it is possible to specify a parameter in the shared-network scope and
+then override its value in the subnet scope. For example:
+
+::
+
+   "shared-networks": [
+       {
+           "name": "lab-network3",
+
+           "interface": "eth0",
+
+           # This applies to all subnets in this shared network, unless
+           # values are overridden on subnet scope.
+           "valid-lifetime": 600,
+
+           # This option is made available to all subnets in this shared
+           # network.
+           "option-data": [ {
+               "name": "log-servers",
+               "data": "1.2.3.4"
+           } ],
+
+           "subnet4": [
+               {
+                   "subnet": "10.0.0.0/8",
+                   "pools": [ { "pool":  "10.0.0.1 - 10.0.0.99" } ],
+
+                   # This particular subnet uses different values.
+                   "valid-lifetime": 1200,
+                   "option-data": [
+                   {
+                       "name": "log-servers",
+                       "data": "10.0.0.254"
+                   },
+                   {
+                       "name": "routers",
+                       "data": "10.0.0.254"
+                   } ]
+               },
+               {
+                    "subnet": "192.0.2.0/24",
+                    "pools": [ { "pool":  "192.0.2.100 - 192.0.2.199" } ],
+
+                    # This subnet does not specify its own valid-lifetime value,
+                    # so it is inherited from shared network scope.
+                    "option-data": [
+                    {
+                        "name": "routers",
+                        "data": "192.0.2.1"
+                    } ]
+               }
+           ]
+       } ]
+
+In this example, there is a ``log-servers`` option defined that is available
+to clients in both subnets in this shared network. Also, the valid
+lifetime is set to 10 minutes (600s). However, the first subnet
+overrides some of the values (the valid lifetime is 20 minutes, there is a different IP
+address for ``log-servers``), but also adds its own option (the router address).
+Assuming a client asking for router and ``log-servers`` options is assigned
+a lease from this subnet, it will get a lease for 20 minutes and a
+``log-servers`` and routers value of 10.0.0.254. If the same client is
+assigned to the second subnet, it will get a 10-minute lease, a
+``log-servers`` value of 1.2.3.4, and routers set to 192.0.2.1.
+
+Local and Relayed Traffic in Shared Networks
+--------------------------------------------
+
+It is possible to specify an interface name at the shared network level,
+to tell the server that this specific shared network is reachable
+directly (not via relays) using the local network interface. As all
+subnets in a shared network are expected to be used on the same physical
+link, it is a configuration error to attempt to define a shared network
+using subnets that are reachable over different interfaces. In other
+words, all subnets within the shared network must have the same value
+for the ``interface`` parameter. The following configuration is an
+example of what **NOT** to do:
+
+::
+
+   "shared-networks": [
+       {
+           "name": "office-floor-2",
+           "subnet4": [
+               {
+                   "subnet": "10.0.0.0/8",
+                   "pools": [ { "pool":  "10.0.0.1 - 10.0.0.99" } ],
+                   "interface": "eth0"
+               },
+               {
+                    "subnet": "192.0.2.0/24",
+                    "pools": [ { "pool":  "192.0.2.100 - 192.0.2.199" } ],
+
+                    # Specifying the different interface name is a configuration
+                    # error. This value should rather be "eth0" or the interface
+                    # name in the other subnet should be "eth1".
+                    "interface": "eth1"
+               }
+           ]
+       } ]
+
+To minimize the chance of configuration errors, it is often more convenient
+to simply specify the interface name once, at the shared-network level, as
+shown in the example below.
+
+::
+
+   "shared-networks": [
+       {
+           "name": "office-floor-2",
+
+           # This tells Kea that the whole shared network is reachable over a
+           # local interface. This applies to all subnets in this network.
+           "interface": "eth0",
+
+           "subnet4": [
+               {
+                   "subnet": "10.0.0.0/8",
+                   "pools": [ { "pool":  "10.0.0.1 - 10.0.0.99" } ],
+               },
+               {
+                    "subnet": "192.0.2.0/24",
+                    "pools": [ { "pool":  "192.0.2.100 - 192.0.2.199" } ]
+               }
+           ]
+       } ]
+
+
+With relayed traffic, subnets are typically selected using
+the relay agents' addresses. If the subnets are used independently (not
+grouped within a shared network), a different relay
+address can be specified for each of these subnets. When multiple subnets belong to a
+shared network they must be selected via the same relay address and,
+similarly to the case of the local traffic described above, it is a
+configuration error to specify different relay addresses for the respective
+subnets in the shared network. The following configuration is another example
+of what **NOT** to do:
+
+::
+
+   "shared-networks": [
+       {
+           "name": "kakapo",
+           "subnet4": [
+               {
+                   "subnet": "192.0.2.0/26",
+                   "relay": {
+                       "ip-addresses": [ "192.1.1.1" ]
+                   },
+                   "pools": [ { "pool": "192.0.2.63 - 192.0.2.63" } ]
+               },
+               {
+                   "subnet": "10.0.0.0/24",
+                   "relay": {
+                       # Specifying a different relay address for this
+                       # subnet is a configuration error. In this case
+                       # it should be 192.1.1.1 or the relay address
+                       # in the previous subnet should be 192.2.2.2.
+                       "ip-addresses": [ "192.2.2.2" ]
+                   },
+                   "pools": [ { "pool": "10.0.0.16 - 10.0.0.16" } ]
+               }
+           ]
+       }
+   ]
+
+Again, it is better to specify the relay address at the shared-network
+level; this value will be inherited by all subnets belonging to the
+shared network.
+
+::
+
+   "shared-networks": [
+       {
+           "name": "kakapo",
+           "relay": {
+               # This relay address is inherited by both subnets.
+               "ip-addresses": [ "192.1.1.1" ]
+           },
+           "subnet4": [
+               {
+                   "subnet": "192.0.2.0/26",
+                   "pools": [ { "pool": "192.0.2.63 - 192.0.2.63" } ]
+               },
+               {
+                   "subnet": "10.0.0.0/24",
+                   "pools": [ { "pool": "10.0.0.16 - 10.0.0.16" } ]
+               }
+           ]
+       }
+   ]
+
+Even though it is technically possible to configure two (or more) subnets
+within the shared network to use different relay addresses, this will almost
+always lead to a different behavior than what the user expects. In this
+case, the Kea server will initially select one of the subnets by matching
+the relay address in the client's packet with the subnet's configuration.
+However, it MAY end up using the other subnet (even though it does not match
+the relay address) if the client already has a lease in this subnet or has a
+host reservation in this subnet, or simply if the initially selected subnet has no
+more addresses available. Therefore, it is strongly recommended to always
+specify subnet selectors (interface or relay address) at the shared-network
+level if the subnets belong to a shared network, as it is rarely useful to
+specify them at the subnet level and may lead to the configuration errors
+described above.
+
+Client Classification in Shared Networks
+----------------------------------------
+
+Sometimes it is desirable to segregate clients into specific subnets
+based on certain properties. This mechanism is called client
+classification and is described in :ref:`classify`. Client
+classification can be applied to subnets belonging to shared networks in
+the same way as it is used for subnets specified outside of shared
+networks. It is important to understand how the server selects subnets
+for clients when client classification is in use, to ensure that the
+appropriate subnet is selected for a given client type.
+
+If a subnet is associated with a class, only the clients belonging to
+this class can use this subnet. If there are no classes specified for a
+subnet, any client connected to a given shared network can use this
+subnet. A common mistake is to assume that a subnet that includes a client
+class is preferred over subnets without client classes. Consider the
+following example:
+
+::
+
+   {
+       "client-classes": [
+           {
+               "name": "b-devices",
+               "test": "option[93].hex == 0x0002"
+           }
+       ],
+       "shared-networks": [
+           {
+               "name": "galah",
+               "interface": "eth0",
+               "subnet4": [
+                   {
+                       "subnet": "192.0.2.0/26",
+                       "pools": [ { "pool": "192.0.2.1 - 192.0.2.63" } ],
+                   },
+                   {
+                       "subnet": "10.0.0.0/24",
+                       "pools": [ { "pool": "10.0.0.2 - 10.0.0.250" } ],
+                       "client-class": "b-devices"
+                   }
+               ]
+           }
+       ]
+   }
+
+If the client belongs to the "b-devices" class (because it includes
+option 93 with a value of 0x0002), that does not guarantee that the
+subnet 10.0.0.0/24 will be used (or preferred) for this client. The
+server can use either of the two subnets, because the subnet 192.0.2.0/26
+is also allowed for this client. The client classification used in this
+case should be perceived as a way to restrict access to certain subnets,
+rather than as a way to express subnet preference. For example, if the
+client does not belong to the "b-devices" class, it may only use the
+subnet 192.0.2.0/26 and will never use the subnet 10.0.0.0/24.
+
+A typical use case for client classification is in a cable network,
+where cable modems should use one subnet and other devices should use
+another subnet within the same shared network. In this case it is
+necessary to apply classification on all subnets. The following example
+defines two classes of devices, and the subnet selection is made based
+on option 93 values.
+
+::
+
+   {
+       "client-classes": [
+           {
+
+               "name": "a-devices",
+               "test": "option[93].hex == 0x0001"
+           },
+           {
+               "name": "b-devices",
+               "test": "option[93].hex == 0x0002"
+           }
+       ],
+       "shared-networks": [
+           {
+               "name": "galah",
+               "interface": "eth0",
+               "subnet4": [
+                   {
+                       "subnet": "192.0.2.0/26",
+                       "pools": [ { "pool": "192.0.2.1 - 192.0.2.63" } ],
+                       "client-class": "a-devices"
+                   },
+                   {
+                       "subnet": "10.0.0.0/24",
+                       "pools": [ { "pool": "10.0.0.2 - 10.0.0.250" } ],
+                       "client-class": "b-devices"
+                   }
+               ]
+           }
+       ]
+   }
+
+In this example each class has its own restriction. Only clients that
+belong to class "a-devices" are able to use subnet 192.0.2.0/26 and
+only clients belonging to "b-devices" are able to use subnet
+10.0.0.0/24. Care should be taken not to define too-restrictive
+classification rules, as clients that are unable to use any subnets will
+be refused service. However, this may be a desired outcome if one wishes
+to provide service only to clients with known properties (e.g. only VoIP
+phones allowed on a given link).
+
+It is possible to achieve an effect similar to the one
+presented in this section without the use of shared networks. If the
+subnets are placed in the global subnets scope, rather than in the
+shared network, the server will still use classification rules to pick
+the right subnet for a given class of devices. The major benefit of
+placing subnets within the shared network is that common parameters for
+the logically grouped subnets can be specified once in the
+shared-network scope, e.g. the ``interface`` or ``relay`` parameter. All subnets
+belonging to this shared network will inherit those parameters.
+
+Host Reservations in Shared Networks
+------------------------------------
+
+Subnets that are part of a shared network allow host reservations,
+similar to regular subnets:
+
+::
+
+   {
+       "shared-networks": [
+       {
+           "name": "frog",
+           "interface": "eth0",
+           "subnet4": [
+               {
+                   "subnet": "192.0.2.0/26",
+                   "id": 100,
+                   "pools": [ { "pool": "192.0.2.1 - 192.0.2.63" } ],
+                   "reservations": [
+                       {
+                           "hw-address": "aa:bb:cc:dd:ee:ff",
+                           "ip-address": "192.0.2.28"
+                       }
+                   ]
+               },
+               {
+                   "subnet": "10.0.0.0/24",
+                   "id": 101,
+                   "pools": [ { "pool": "10.0.0.1 - 10.0.0.254" } ],
+                   "reservations": [
+                       {
+                           "hw-address": "11:22:33:44:55:66",
+                           "ip-address": "10.0.0.29"
+                       }
+                   ]
+               }
+           ]
+       }
+       ]
+   }
+
+
+It is worth noting that Kea conducts additional checks when processing a
+packet if shared networks are defined. First, instead of simply checking
+whether there is a reservation for a given client in its initially
+selected subnet, Kea looks through all subnets in a shared network for a
+reservation. This is one of the reasons why defining a shared network
+may impact performance. If there is a reservation for a client in any
+subnet, that particular subnet is selected for the client. Although
+it is technically not an error, it is considered bad practice to define
+reservations for the same host in multiple subnets belonging to the same
+shared network.
+
+While not strictly mandatory, it is strongly recommended to use explicit
+"id" values for subnets if database storage will be used for host
+reservations. If an ID is not specified, the values for it are
+auto-generated, i.e. Kea assigns increasing integer values starting from
+1. Thus, the auto-generated IDs are not stable across configuration
+changes.
+
+.. _dhcp4-serverid:
+
+Server Identifier in DHCPv4
+===========================
+
+The DHCPv4 protocol uses a "server identifier" to allow clients to
+discriminate between several servers present on the same link; this
+value is an IPv4 address of the server. The server chooses the IPv4
+address of the interface on which the message from the client (or relay)
+has been received. A single server instance uses multiple server
+identifiers if it is receiving queries on multiple interfaces.
+
+It is possible to override the default server identifier values by specifying
+the ``dhcp-server-identifier`` option. This option configuration is only
+supported at the subnet, shared network, client class, and global levels. It
+must not be specified at the host-reservation level.
+When configuring the ``dhcp-server-identifier`` option at client-class level, the
+class must not set the ``only-if-required`` flag, because this class would not
+be evaluated before the server determines if the received DHCP message should
+be accepted for processing. Such classes are evaluated after subnet selection.
+See :ref:`dhcp4-required-class` for details.
+
+The following example demonstrates how to override the server identifier
+for a subnet:
+
+::
+
+   "subnet4": [
+       {
+           "subnet": "192.0.2.0/24",
+           "option-data": [
+               {
+                   "name": "dhcp-server-identifier",
+                   "data": "10.2.5.76"
+               }
+           ],
+           ...
+       }
+   ]
+
+.. _dhcp4-subnet-selection:
+
+How the DHCPv4 Server Selects a Subnet for the Client
+=====================================================
+
+The DHCPv4 server differentiates among directly connected clients,
+clients trying to renew leases, and clients sending their messages
+through relays. For directly connected clients, the server checks
+the configuration for the interface on which the message has been
+received and, if the server configuration does not match any configured
+subnet, the message is discarded.
+
+Assuming that the server's interface is configured with the IPv4 address
+192.0.2.3, the server only processes messages received through this
+interface from a directly connected client if there is a subnet
+configured to which this IPv4 address belongs, such as 192.0.2.0/24. The
+server uses this subnet to assign an IPv4 address for the client.
+
+The rule above does not apply when the client unicasts its message, i.e.
+is trying to renew its lease; such a message is accepted through any
+interface. The renewing client sets ``ciaddr`` to the currently used IPv4
+address, and the server uses this address to select the subnet for the
+client (in particular, to extend the lease using this address).
+
+If the message is relayed it is accepted through any interface. The
+``giaddr`` set by the relay agent is used to select the subnet for the
+client.
+
+It is also possible to specify a relay IPv4 address for a given subnet.
+It can be used to match incoming packets into a subnet in uncommon
+configurations, e.g. shared networks. See :ref:`dhcp4-relay-override` for details.
+
+.. note::
+
+   The subnet selection mechanism described in this section is based on
+   the assumption that client classification is not used. The
+   classification mechanism alters the way in which a subnet is selected
+   for the client, depending on the classes to which the client belongs.
+
+.. note::
+
+   When the selected subnet is a member of a shared network, the
+   whole shared network is selected.
+
+.. _dhcp4-relay-override:
+
+Using a Specific Relay Agent for a Subnet
+-----------------------------------------
+
+A relay must have an interface connected to the link on which the
+clients are being configured. Typically the relay has an IPv4 address
+configured on that interface, which belongs to the subnet from which the
+server assigns addresses. Normally, the server is able to use the
+IPv4 address inserted by the relay (in the ``giaddr`` field of the DHCPv4
+packet) to select the appropriate subnet.
+
+However, that is not always the case. In certain uncommon — but valid —
+deployments, the relay address may not match the subnet. This usually
+means that there is more than one subnet allocated for a given link. The
+two most common examples of this are long-lasting network
+renumbering (where both old and new address spaces are still being used)
+and a cable network. In a cable network, both cable modems and the
+devices behind them are physically connected to the same link, yet they
+use distinct addressing. In such a case, the DHCPv4 server needs
+additional information (the IPv4 address of the relay) to properly
+select an appropriate subnet.
+
+The following example assumes that there is a subnet 192.0.2.0/24 that
+is accessible via a relay that uses 10.0.0.1 as its IPv4 address. The
+server is able to select this subnet for any incoming packets that come
+from a relay that has an address in the 192.0.2.0/24 subnet. It also
+selects that subnet for a relay with address 10.0.0.1.
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
+               "relay": {
+                   "ip-addresses": [ "10.0.0.1" ]
+               },
+           }
+       ],
+   }
+
+If ``relay`` is specified, the ``ip-addresses`` parameter within it is
+mandatory. The ``ip-addresses`` parameter supports specifying a list of addresses.
+
+.. _dhcp4-srv-example-client-class-relay:
+
+Segregating IPv4 Clients in a Cable Network
+-------------------------------------------
+
+In certain cases, it is useful to mix relay address information
+(introduced in :ref:`dhcp4-relay-override`) with client classification (explained
+in :ref:`classify`). One specific example is in a cable network,
+where modems typically get addresses from a different subnet than all
+the devices connected behind them.
+
+Let us assume that there is one Cable Modem Termination System (CMTS)
+with one CM MAC (a physical link that modems are connected to). We want
+the modems to get addresses from the 10.1.1.0/24 subnet, while
+everything connected behind the modems should get addresses from the
+192.0.2.0/24 subnet. The CMTS that acts as a relay uses address
+10.1.1.1. The following configuration can serve that situation:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [
+           {
+               "subnet": "10.1.1.0/24",
+               "pools":  [ { "pool": "10.1.1.2 - 10.1.1.20" } ],
+               "client-class" "docsis3.0",
+               "relay": {
+                   "ip-addresses": [ "10.1.1.1 ]"
+               }
+           },
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
+               "relay": {
+                   "ip-addresses": [ "10.1.1.1" ]
+               }
+           }
+       ],
+       ...
+   }
+
+.. _dhcp4-decline:
+
+Duplicate Addresses (DHCPDECLINE Support)
+=========================================
+
+The DHCPv4 server is configured with a certain pool of addresses that it
+is expected to hand out to DHCPv4 clients. It is assumed that the server
+is authoritative and has complete jurisdiction over those addresses.
+However, for various reasons such as misconfiguration or a faulty
+client implementation that retains its address beyond the valid
+lifetime, there may be devices connected that use those addresses
+without the server's approval or knowledge.
+
+Such an unwelcome event can be detected by legitimate clients (using ARP
+or ICMP Echo Request mechanisms) and reported to the DHCPv4 server using
+a DHCPDECLINE message. The server does a sanity check (to see whether
+the client declining an address really was supposed to use it) and then
+conducts a clean-up operation. Any DNS entries related to that
+address are removed, the event is logged, and hooks are
+triggered. After that is complete, the address is marked as
+declined (which indicates that it is used by an unknown entity and thus
+not available for assignment) and a probation time is set on it.
+Unless otherwise configured, the probation period lasts 24 hours; after
+that time, the server will recover the lease (i.e. put it back into
+the available state) and the address will be available for assignment
+again. It should be noted that if the underlying issue of a
+misconfigured device is not resolved, the duplicate-address scenario
+will repeat. If reconfigured correctly, this mechanism provides an
+opportunity to recover from such an event automatically, without any
+system administrator intervention.
+
+To configure the decline probation period to a value other than the
+default, the following syntax can be used:
+
+::
+
+     "Dhcp4": {
+       "decline-probation-period": 3600,
+       "subnet4": [ ... ],
+       ...
+   }
+
+The parameter is expressed in seconds, so the example above
+instructs the server to recycle declined leases after one hour.
+
+There are several statistics and hook points associated with the decline
+handling procedure. The ``lease4_decline`` hook is triggered after the
+incoming DHCPDECLINE message has been sanitized and the server is about
+to decline the lease. The ``declined-addresses`` statistic is increased
+after the hook returns (both the global and subnet-specific variants). (See
+:ref:`dhcp4-stats` and :ref:`hooks-libraries`
+for more details on DHCPv4 statistics and Kea hook points.)
+
+Once the probation time elapses, the declined lease is recovered using
+the standard expired-lease reclamation procedure, with several
+additional steps. In particular, both ``declined-addresses`` statistics
+(global and subnet-specific) are decreased. At the same time,
+``reclaimed-declined-addresses`` statistics (again in two variants, global
+and subnet-specific) are increased.
+
+A note about statistics: The Kea server does not decrease the
+``assigned-addresses`` statistics when a DHCPDECLINE is received and
+processed successfully. While technically a declined address is no
+longer assigned, the primary usage of the ``assigned-addresses`` statistic
+is to monitor pool utilization. Most people would forget to include
+``declined-addresses`` in the calculation, and would simply use
+``assigned-addresses``/``total-addresses``. This would cause a bias towards
+under-representing pool utilization. As this has a potential to cause serious
+confusion, ISC decided not to decrease ``assigned-addresses`` immediately after
+receiving DHCPDECLINE, but to do it later when Kea recovers the address
+back to the available pool.
+
+.. _dhcp4-stats:
+
+Statistics in the DHCPv4 Server
+===============================
+
+The DHCPv4 server supports the following statistics:
+
+.. tabularcolumns:: |p{0.2\linewidth}|p{0.1\linewidth}|p{0.7\linewidth}|
+
+.. table:: DHCPv4 statistics
+   :class: longtable
+   :widths: 20 10 70
+
+
+   +----------------------------------------------+----------------+------------------------------------+
+   | Statistic                                    | Data Type      | Description                        |
+   +==============================================+================+====================================+
+   | pkt4-received                                | integer        | Number of DHCPv4 packets received. |
+   |                                              |                | This includes all packets: valid,  |
+   |                                              |                | bogus, corrupted, rejected, etc.   |
+   |                                              |                | This statistic is expected to grow |
+   |                                              |                | rapidly.                           |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-discover-received                       | integer        | Number of DHCPDISCOVER packets     |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to grow; its increase     |
+   |                                              |                | means that clients that just       |
+   |                                              |                | booted started their configuration |
+   |                                              |                | process and their initial packets  |
+   |                                              |                | reached the Kea server.            |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-offer-received                          | integer        | Number of DHCPOFFER packets        |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to remain zero at all     |
+   |                                              |                | times, as DHCPOFFER packets are    |
+   |                                              |                | sent by the server and the server  |
+   |                                              |                | is never expected to receive them. |
+   |                                              |                | A non-zero value indicates an      |
+   |                                              |                | error. One likely cause would be a |
+   |                                              |                | misbehaving relay agent that       |
+   |                                              |                | incorrectly forwards DHCPOFFER     |
+   |                                              |                | messages towards the server,       |
+   |                                              |                | rather than back to the clients.   |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-request-received                        | integer        | Number of DHCPREQUEST packets      |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to grow. Its increase     |
+   |                                              |                | means that clients that just       |
+   |                                              |                | booted received the server's       |
+   |                                              |                | response (DHCPOFFER) and accepted  |
+   |                                              |                | it, and are now requesting an      |
+   |                                              |                | address (DHCPREQUEST).             |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-ack-received                            | integer        | Number of DHCPACK packets          |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to remain zero at all     |
+   |                                              |                | times, as DHCPACK packets are sent |
+   |                                              |                | by the server and the server is    |
+   |                                              |                | never expected to receive them. A  |
+   |                                              |                | non-zero value indicates an error. |
+   |                                              |                | One likely cause would be a        |
+   |                                              |                | misbehaving relay agent that       |
+   |                                              |                | incorrectly forwards DHCPACK       |
+   |                                              |                | messages towards the server,       |
+   |                                              |                | rather than back to the clients.   |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-nak-received                            | integer        | Number of DHCPNAK packets          |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to remain zero at all     |
+   |                                              |                | times, as DHCPNAK packets are sent |
+   |                                              |                | by the server and the server is    |
+   |                                              |                | never expected to receive them. A  |
+   |                                              |                | non-zero value indicates an error. |
+   |                                              |                | One likely cause would be a        |
+   |                                              |                | misbehaving relay agent that       |
+   |                                              |                | incorrectly forwards DHCPNAK       |
+   |                                              |                | messages towards the server,       |
+   |                                              |                | rather than back to the clients.   |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-release-received                        | integer        | Number of DHCPRELEASE packets      |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to grow. Its increase     |
+   |                                              |                | means that clients that had an     |
+   |                                              |                | address are shutting down or       |
+   |                                              |                | ceasing to use their addresses.    |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-decline-received                        | integer        | Number of DHCPDECLINE packets      |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to remain close to zero.  |
+   |                                              |                | Its increase means that a client   |
+   |                                              |                | leased an address, but discovered  |
+   |                                              |                | that the address is currently      |
+   |                                              |                | used by an unknown device          |
+   |                                              |                | elsewhere in the network.          |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-inform-received                         | integer        | Number of DHCPINFORM packets       |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to grow. Its increase     |
+   |                                              |                | means that there are clients       |
+   |                                              |                | that either do not need an address |
+   |                                              |                | or already have an address and are |
+   |                                              |                | interested only in getting         |
+   |                                              |                | additional configuration           |
+   |                                              |                | parameters.                        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-unknown-received                        | integer        | Number of packets received of an   |
+   |                                              |                | unknown type. A non-zero value of  |
+   |                                              |                | this statistic indicates that the  |
+   |                                              |                | server received a packet that it   |
+   |                                              |                | was not able to recognize, either  |
+   |                                              |                | with an unsupported type or        |
+   |                                              |                | possibly malformed (without a      |
+   |                                              |                | message-type option).              |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-sent                                    | integer        | Number of DHCPv4 packets sent.     |
+   |                                              |                | This statistic is expected to grow |
+   |                                              |                | every time the server transmits a  |
+   |                                              |                | packet. In general, it should      |
+   |                                              |                | roughly match pkt4-received, as    |
+   |                                              |                | most incoming packets cause the    |
+   |                                              |                | server to respond. There are       |
+   |                                              |                | exceptions (e.g. DHCPRELEASE), so  |
+   |                                              |                | do not worry if it is less than    |
+   |                                              |                | pkt4-received.                     |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-offer-sent                              | integer        | Number of DHCPOFFER packets sent.  |
+   |                                              |                | This statistic is expected to grow |
+   |                                              |                | in most cases after a DHCPDISCOVER |
+   |                                              |                | is processed. There are certain    |
+   |                                              |                | uncommon, but valid, cases where   |
+   |                                              |                | incoming DHCPDISCOVER packets are  |
+   |                                              |                | dropped, but in general this       |
+   |                                              |                | statistic is expected to be close  |
+   |                                              |                | to pkt4-discover-received.         |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-ack-sent                                | integer        | Number of DHCPACK packets sent.    |
+   |                                              |                | This statistic is expected to grow |
+   |                                              |                | in most cases after a DHCPREQUEST  |
+   |                                              |                | is processed. There are certain    |
+   |                                              |                | cases where DHCPNAK is sent        |
+   |                                              |                | instead. In general, the sum of    |
+   |                                              |                | pkt4-ack-sent and pkt4-nak-sent    |
+   |                                              |                | should be close to                 |
+   |                                              |                | pkt4-request-received.             |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-nak-sent                                | integer        | Number of DHCPNAK packets sent.    |
+   |                                              |                | This statistic is expected to grow |
+   |                                              |                | when the server chooses not to     |
+   |                                              |                | honor the address requested by a   |
+   |                                              |                | client. In general, the sum of     |
+   |                                              |                | pkt4-ack-sent and pkt4-nak-sent    |
+   |                                              |                | should be close to                 |
+   |                                              |                | pkt4-request-received.             |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-parse-failed                            | integer        | Number of incoming packets that    |
+   |                                              |                | could not be parsed. A non-zero    |
+   |                                              |                | value of this statistic indicates  |
+   |                                              |                | that the server received a         |
+   |                                              |                | malformed or truncated packet.     |
+   |                                              |                | This may indicate problems in the  |
+   |                                              |                | network, faulty clients, or a bug  |
+   |                                              |                | in the server.                     |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-receive-drop                            | integer        | Number of incoming packets that    |
+   |                                              |                | were dropped. The exact reason for |
+   |                                              |                | dropping packets is logged, but    |
+   |                                              |                | the most common reasons may be: an |
+   |                                              |                | unacceptable packet type was       |
+   |                                              |                | received, direct responses are     |
+   |                                              |                | forbidden, or the server-id sent   |
+   |                                              |                | by the client does not match the   |
+   |                                              |                | server's server-id.                |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].total-addresses                   | integer        | Total number of addresses          |
+   |                                              |                | available for DHCPv4 management;   |
+   |                                              |                | in other words, this is the sum of |
+   |                                              |                | all addresses in all configured    |
+   |                                              |                | pools. This statistic changes only |
+   |                                              |                | during configuration updates. It   |
+   |                                              |                | does not take into account any     |
+   |                                              |                | addresses that may be reserved due |
+   |                                              |                | to host reservation. The *id* is   |
+   |                                              |                | the subnet-id of a given subnet.   |
+   |                                              |                | This statistic is exposed for each |
+   |                                              |                | subnet separately, and is reset    |
+   |                                              |                | during a reconfiguration event.    |
+   +----------------------------------------------+----------------+------------------------------------+
+   | cumulative-assigned-addresses                | integer        | Cumulative number of addresses     |
+   |                                              |                | that have been assigned since      |
+   |                                              |                | server startup. It is incremented  |
+   |                                              |                | each time an address is assigned   |
+   |                                              |                | and is not reset when the server   |
+   |                                              |                | is reconfigured.                   |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].cumulative-assigned-addresses     | integer        | Cumulative number of assigned      |
+   |                                              |                | addresses in a given subnet. It    |
+   |                                              |                | increases every time a new lease   |
+   |                                              |                | is allocated (as a result of       |
+   |                                              |                | receiving a DHCPREQUEST message)   |
+   |                                              |                | and never decreases. The *id* is   |
+   |                                              |                | the subnet-id of the subnet. This  |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately, and is reset    |
+   |                                              |                | during a reconfiguration event.    |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].assigned-addresses                | integer        | Number of assigned addresses in a  |
+   |                                              |                | given subnet. It increases every   |
+   |                                              |                | time a new lease is allocated (as  |
+   |                                              |                | a result of receiving a            |
+   |                                              |                | DHCPREQUEST message) and decreases |
+   |                                              |                | every time a lease is released (a  |
+   |                                              |                | DHCPRELEASE message is received)   |
+   |                                              |                | or expires. The *id* is the        |
+   |                                              |                | subnet-id of the subnet. This      |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately, and is reset    |
+   |                                              |                | during a reconfiguration event.    |
+   +----------------------------------------------+----------------+------------------------------------+
+   | reclaimed-leases                             | integer        | Number of expired leases that have |
+   |                                              |                | been reclaimed since server        |
+   |                                              |                | startup. It is incremented each    |
+   |                                              |                | time an expired lease is reclaimed |
+   |                                              |                | and never decreases. It can be     |
+   |                                              |                | used as a long-term indicator of   |
+   |                                              |                | how many actual leases have been   |
+   |                                              |                | reclaimed. This is a global        |
+   |                                              |                | statistic that covers all subnets. |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].reclaimed-leases                  | integer        | Number of expired leases           |
+   |                                              |                | associated with a given subnet     |
+   |                                              |                | (*id* is the subnet-id) that have  |
+   |                                              |                | been reclaimed since server        |
+   |                                              |                | startup. It is incremented each    |
+   |                                              |                | time an expired lease is           |
+   |                                              |                | reclaimed. The *id* is the         |
+   |                                              |                | subnet-id of a given subnet. This  |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+   | declined-addresses                           | integer        | Number of IPv4 addresses that are  |
+   |                                              |                | currently declined; a count of the |
+   |                                              |                | number of leases currently         |
+   |                                              |                | unavailable. Once a lease is       |
+   |                                              |                | recovered, this statistic is       |
+   |                                              |                | decreased; ideally, this statistic |
+   |                                              |                | should be zero. If this statistic  |
+   |                                              |                | is non-zero or increasing, a       |
+   |                                              |                | network administrator should       |
+   |                                              |                | investigate whether there is a     |
+   |                                              |                | misbehaving device in the network. |
+   |                                              |                | This is a global statistic that    |
+   |                                              |                | covers all subnets.                |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].declined-addresses                | integer        | Number of IPv4 addresses that are  |
+   |                                              |                | currently declined in a given      |
+   |                                              |                | subnet; a count of the number of   |
+   |                                              |                | leases currently unavailable. Once |
+   |                                              |                | a lease is recovered, this         |
+   |                                              |                | statistic is decreased; ideally,   |
+   |                                              |                | this statistic should be zero. If  |
+   |                                              |                | this statistic is non-zero or      |
+   |                                              |                | increasing, a network              |
+   |                                              |                | administrator should investigate   |
+   |                                              |                | whether there is a misbehaving     |
+   |                                              |                | device in the network. The *id* is |
+   |                                              |                | the subnet-id of a given subnet.   |
+   |                                              |                | This statistic is exposed for each |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+   | reclaimed-declined-addresses                 | integer        | Number of IPv4 addresses that were |
+   |                                              |                | declined, but have now been        |
+   |                                              |                | recovered. Unlike                  |
+   |                                              |                | declined-addresses, this statistic |
+   |                                              |                | never decreases. It can be used as |
+   |                                              |                | a long-term indicator of how many  |
+   |                                              |                | actual valid declines were         |
+   |                                              |                | processed and recovered from. This |
+   |                                              |                | is a global statistic that covers  |
+   |                                              |                | all subnets.                       |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].reclaimed-declined-addresses      | integer        | Number of IPv4 addresses that were |
+   |                                              |                | declined, but have now been        |
+   |                                              |                | recovered. Unlike                  |
+   |                                              |                | declined-addresses, this statistic |
+   |                                              |                | never decreases. It can be used as |
+   |                                              |                | a long-term indicator of how many  |
+   |                                              |                | actual valid declines were         |
+   |                                              |                | processed and recovered from. The  |
+   |                                              |                | *id* is the subnet-id of a given   |
+   |                                              |                | subnet. This statistic is exposed  |
+   |                                              |                | for each subnet separately.        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-lease-query-received                    | integer        | Number of IPv4 DHCPLEASEQUERY      |
+   |                                              |                | packets received. (Only exists if  |
+   |                                              |                | Leasequery hook library is         |
+   |                                              |                | loaded.)                           |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-lease-query-response-unknown-sent       | integer        | Number of IPv4 DHCPLEASEUNKNOWN    |
+   |                                              |                | responses sent. (Only exists if    |
+   |                                              |                | Leasequery hook library is         |
+   |                                              |                | loaded.)                           |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-lease-query-response-unassigned-sent    | integer        | Number of IPv4 DHCPLEASEUNASSIGNED |
+   |                                              |                | responses sent. (Only exists if    |
+   |                                              |                | Leasequery hook library is         |
+   |                                              |                | loaded.)                           |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt4-lease-query-response-active-sent        | integer        | Number of IPv4 DHCPLEASEACTIVE     |
+   |                                              |                | responses sent. (Only exists if    |
+   |                                              |                | Leasequery hook library is         |
+   |                                              |                | loaded.)                           |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v4-allocation-fail                           | integer        | Number of total address allocation |
+   |                                              |                | failures for a particular client.  |
+   |                                              |                | This consists in the number of     |
+   |                                              |                | lease allocation attempts that the |
+   |                                              |                | server made before giving up and   |
+   |                                              |                | was unable to use any of the       |
+   |                                              |                | address pools. This is a global    |
+   |                                              |                | statistic that covers all subnets. |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v4-allocation-fail                | integer        | Number of total address allocation |
+   |                                              |                | failures for a particular client.  |
+   |                                              |                | This consists in the number of     |
+   |                                              |                | lease allocation attempts that the |
+   |                                              |                | server made before giving up and   |
+   |                                              |                | was unable to use any of the       |
+   |                                              |                | address pools. The *id* is the     |
+   |                                              |                | subnet-id of a given subnet. This  |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v4-allocation-fail-shared-network            | integer        | Number of address allocation       |
+   |                                              |                | failures for a particular client   |
+   |                                              |                | connected to a shared network.     |
+   |                                              |                | This is a global statistic that    |
+   |                                              |                | covers all subnets.                |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v4-allocation-fail-shared-network | integer        | Number of address allocation       |
+   |                                              |                | failures for a particular client   |
+   |                                              |                | connected to a shared network.     |
+   |                                              |                | The *id* is the subnet-id of a     |
+   |                                              |                | given subnet. This statistic is    |
+   |                                              |                | exposed for each subnet            |
+   |                                              |                | separately.                        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v4-allocation-fail-subnet                    | integer        | Number of address allocation       |
+   |                                              |                | failures for a particular client   |
+   |                                              |                | connected to a subnet that does    |
+   |                                              |                | not belong to a shared network.    |
+   |                                              |                | This is a global statistic that    |
+   |                                              |                | covers all subnets.                |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v4-allocation-fail-subnet         | integer        | Number of address allocation       |
+   |                                              |                | failures for a particular client   |
+   |                                              |                | connected to a subnet that does    |
+   |                                              |                | not belong to a shared network.    |
+   |                                              |                | The *id* is the subnet-id of a     |
+   |                                              |                | given subnet. This statistic is    |
+   |                                              |                | exposed for each subnet            |
+   |                                              |                | separately.                        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v4-allocation-fail-no-pools                  | integer        | Number of address allocation       |
+   |                                              |                | failures because the server could  |
+   |                                              |                | not use any configured pools for   |
+   |                                              |                | a particular client. It is also    |
+   |                                              |                | possible that all of the subnets   |
+   |                                              |                | from which the server attempted to |
+   |                                              |                | assign an address lack address     |
+   |                                              |                | pools. In this case, it should be  |
+   |                                              |                | considered misconfiguration if an  |
+   |                                              |                | operator expects that some clients |
+   |                                              |                | should be assigned dynamic         |
+   |                                              |                | addresses. This is a global        |
+   |                                              |                | statistic that covers all subnets. |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v4-allocation-fail-no-pools       | integer        | Number of address allocation       |
+   |                                              |                | failures because the server could  |
+   |                                              |                | not use any configured pools for   |
+   |                                              |                | a particular client. It is also    |
+   |                                              |                | possible that all of the subnets   |
+   |                                              |                | from which the server attempted to |
+   |                                              |                | assign an address lack address     |
+   |                                              |                | pools. In this case, it should be  |
+   |                                              |                | considered misconfiguration if an  |
+   |                                              |                | operator expects that some clients |
+   |                                              |                | should be assigned dynamic         |
+   |                                              |                | addresses. The *id* is the         |
+   |                                              |                | subnet-id of a given subnet. This  |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v4-allocation-fail-classes                   | integer        | Number of address allocation       |
+   |                                              |                | failures when the client's packet  |
+   |                                              |                | belongs to one or more classes.    |
+   |                                              |                | There may be several reasons why a |
+   |                                              |                | lease was not assigned. One of     |
+   |                                              |                | them may be a case when all pools  |
+   |                                              |                | require packet to belong to        |
+   |                                              |                | certain classes and the incoming   |
+   |                                              |                | packet didn't belong to any of     |
+   |                                              |                | them. Another case where this      |
+   |                                              |                | information may be useful is to    |
+   |                                              |                | point out that the pool reserved   |
+   |                                              |                | to a given class has ran out of    |
+   |                                              |                | addresses. This is a global        |
+   |                                              |                | statistic that covers all subnets. |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v4-allocation-fail-classes        | integer        | Number of address allocation       |
+   |                                              |                | failures when the client's packet  |
+   |                                              |                | belongs to one or more classes.    |
+   |                                              |                | There may be several reasons why a |
+   |                                              |                | lease was not assigned. One of     |
+   |                                              |                | them may be a case when all pools  |
+   |                                              |                | require packet to belong to        |
+   |                                              |                | certain classes and the incoming   |
+   |                                              |                | packet didn't belong to any of     |
+   |                                              |                | them. Another case where this      |
+   |                                              |                | information may be useful is to    |
+   |                                              |                | point out that the pool reserved   |
+   |                                              |                | to a given class has ran out of    |
+   |                                              |                | addresses. The *id* is the         |
+   |                                              |                | subnet-id of a given subnet. This  |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v4-reservation-conflicts                     | integer        | Number of host reservation         |
+   |                                              |                | allocation conflicts which have    |
+   |                                              |                | occurred across every subnet. When |
+   |                                              |                | a client sends a DHCP Discover and |
+   |                                              |                | is matched to a host reservation   |
+   |                                              |                | which is already leased to another |
+   |                                              |                | client, this counter is increased  |
+   |                                              |                | by 1.                              |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v4-reservation-conflicts          | integer        | Number of host reservation         |
+   |                                              |                | allocation conflicts which have    |
+   |                                              |                | occurred in a specific subnet.     |
+   |                                              |                | When a client sends a DHCP         |
+   |                                              |                | Discover and is matched to a host  |
+   |                                              |                | reservation which is already       |
+   |                                              |                | leased to another client, this     |
+   |                                              |                | counter is increased by 1.         |
+   +----------------------------------------------+----------------+------------------------------------+
+
+.. note::
+
+   This section describes DHCPv4-specific statistics. For a general
+   overview and usage of statistics, see :ref:`stats`.
+
+The DHCPv4 server provides two global parameters to control the default sample
+limits of statistics:
+
+- ``statistic-default-sample-count`` - determines the default maximum
+  number of samples which are kept. The special value of 0
+  indicates that a default maximum age should be used.
+
+- ``statistic-default-sample-age`` - determines the default maximum
+  age in seconds of samples which are kept.
+
+For instance, to reduce the statistic-keeping overhead, set
+the default maximum sample count to 1 so only one sample is kept:
+
+::
+
+     "Dhcp4": {
+       "statistic-default-sample-count": 1,
+       "subnet4": [ ... ],
+       ...
+   }
+
+Statistics can be retrieved periodically to gain more insight into Kea operations. One tool that
+leverages that capability is ISC Stork. See :ref:`stork` for details.
+
+
+.. _dhcp4-ctrl-channel:
+
+Management API for the DHCPv4 Server
+====================================
+
+The management API allows the issuing of specific management commands,
+such as statistics retrieval, reconfiguration, or shutdown. For more
+details, see :ref:`ctrl-channel`. Currently, the only supported
+communication channel type is the UNIX stream socket. By default there are
+no sockets open; to instruct Kea to open a socket, the following entry
+in the configuration file can be used:
+
+::
+
+   "Dhcp4": {
+       "control-socket": {
+           "socket-type": "unix",
+           "socket-name": "/path/to/the/unix/socket"
+       },
+
+       "subnet4": [
+           ...
+       ],
+       ...
+   }
+
+The length of the path specified by the ``socket-name`` parameter is
+restricted by the maximum length for the UNIX socket name on the administrator's
+operating system, i.e. the size of the ``sun_path`` field in the
+``sockaddr_un`` structure, decreased by 1. This value varies on
+different operating systems, between 91 and 107 characters. Typical
+values are 107 on Linux and 103 on FreeBSD.
+
+Communication over the control channel is conducted using JSON
+structures. See the
+`Control Channel section in the Kea Developer's Guide
+<https://reports.kea.isc.org/dev_guide/d2/d96/ctrlSocket.html>`__
+for more details.
+
+The DHCPv4 server supports the following operational commands:
+
+-  build-report
+-  config-get
+-  config-reload
+-  config-set
+-  config-test
+-  config-write
+-  dhcp-disable
+-  dhcp-enable
+-  leases-reclaim
+-  list-commands
+-  shutdown
+-  status-get
+-  version-get
+
+as described in :ref:`commands-common`. In addition, it supports the
+following statistics-related commands:
+
+-  statistic-get
+-  statistic-reset
+-  statistic-remove
+-  statistic-get-all
+-  statistic-reset-all
+-  statistic-remove-all
+-  statistic-sample-age-set
+-  statistic-sample-age-set-all
+-  statistic-sample-count-set
+-  statistic-sample-count-set-all
+
+as described in :ref:`command-stats`.
+
+.. _dhcp4-user-contexts:
+
+User Contexts in IPv4
+=====================
+
+Kea allows the loading of hook libraries that can sometimes benefit from
+additional parameters. If such a parameter is specific to the whole
+library, it is typically defined as a parameter for the hook library.
+However, sometimes there is a need to specify parameters that are
+different for each pool.
+
+See :ref:`user-context` for additional background regarding the
+user-context idea. See :ref:`user-context-hooks` for a discussion from the
+hooks perspective.
+
+User contexts can be specified at global scope; at the shared-network, subnet,
+pool, client-class, option-data, or definition level; and via host
+reservation. One other useful feature is the ability to store comments or
+descriptions.
+
+Let's consider an imaginary case of devices that have colored LED lights.
+Depending on their location, they should glow red, blue, or green. It
+would be easy to write a hook library that would send specific values,
+maybe as a vendor option. However, the server has to have some way to
+specify that value for each pool. This need is addressed by user
+contexts. In essence, any user data can be specified in the user context
+as long as it is a valid JSON map. For example, the aforementioned case
+of LED devices could be configured in the following way:
+
+::
+
+   "Dhcp4": {
+       "subnet4": [{
+           "subnet": "192.0.2.0/24",
+           "pools": [{
+               "pool": "192.0.2.10 - 192.0.2.20",
+               # This is pool specific user context
+               "user-context": { "color": "red" }
+           } ],
+
+           # This is a subnet-specific user context. Any type
+           # of information can be entered here as long as it is valid JSON.
+           "user-context": {
+               "comment": "network on the second floor",
+               "last-modified": "2017-09-04 13:32",
+               "description": "you can put anything you like here",
+               "phones": [ "x1234", "x2345" ],
+               "devices-registered": 42,
+               "billing": false
+           }
+       } ]
+   }
+
+Kea does not interpret or use the user-context information; it simply stores it and makes it
+available to the hook libraries. It is up to each hook library to
+extract that information and use it. The parser translates a ``comment``
+entry into a user context with the entry, which allows a comment to be
+attached inside the configuration itself.
+
+.. _dhcp4-std:
+
+Supported DHCP Standards
+========================
+
+The following standards are currently supported in Kea:
+
+-  *BOOTP Vendor Information Extensions*, `RFC 1497
+   <https://tools.ietf.org/html/rfc1497>`__: This requires the open source
+   BOOTP hook to be loaded. See :ref:`hooks-bootp` for details.
+
+-  *Dynamic Host Configuration Protocol*, `RFC 2131
+   <https://tools.ietf.org/html/rfc2131>`__: Supported messages are
+   DHCPDISCOVER (1), DHCPOFFER (2), DHCPREQUEST (3), DHCPRELEASE (7),
+   DHCPINFORM (8), DHCPACK (5), and DHCPNAK(6).
+
+-  *DHCP Options and BOOTP Vendor Extensions*, `RFC 2132
+   <https://tools.ietf.org/html/rfc2132>`__: Supported options are PAD (0),
+   END(255), Message Type(53), DHCP Server Identifier (54), Domain Name (15),
+   DNS Servers (6), IP Address Lease Time (51), Subnet Mask (1), and Routers (3).
+
+-  *The IPv4 Subnet Selection Option for DHCP*, `RFC 3011
+   <https://tools.ietf.org/html/rfc3011>`__: The subnet-selection option is
+   supported; if received in a packet, it is used in the subnet-selection
+   process.
+
+-  *DHCP Relay Agent Information Option*, `RFC 3046
+   <https://tools.ietf.org/html/rfc3046>`__: Relay Agent Information,
+   Circuit ID, and Remote ID options are supported.
+
+-  *Link Selection sub-option for the Relay Agent Option*, `RFC 3527
+   <https://tools.ietf.org/html/rfc3527>`__: The link selection sub-option
+   is supported.
+
+-  *Vendor-Identifying Vendor Options for Dynamic Host Configuration
+   Protocol version 4*, `RFC 3925
+   <https://tools.ietf.org/html/rfc3925>`__: The Vendor-Identifying Vendor Class
+   and Vendor-Identifying Vendor-Specific Information options are supported.
+
+-  *Subscriber-ID Suboption for the DHCP Relay Agent Option*, `RFC 3993
+   <https://tools.ietf.org/html/rfc3993>`__: The Subscriber-ID option is
+   supported.
+
+-  *The Dynamic Host Configuration Protocol (DHCP) Client Fully
+   Qualified Domain Name (FQDN) Option*, `RFC 4702
+   <https://tools.ietf.org/html/rfc4702>`__: The Kea server is able to handle
+   the Client FQDN option. Also, it is able to use the ``kea-dhcp-ddns``
+   component to initiate appropriate DNS Update operations.
+
+-  *Resolution of Fully Qualified Domain Name (FQDN) Conflicts among Dynamic
+   Host Configuration Protocol (DHCP) Clients*, `RFC 4703
+   <https://tools.ietf.org/html/rfc4703>`__: The DHCPv6 server uses a DHCP-DDNS
+   server to resolve conflicts.
+
+-  *Client Identifier Option in DHCP Server Replies*, `RFC 6842
+   <https://tools.ietf.org/html/rfc6842>`__: The server by default sends back
+   the ``client-id`` option. That capability can be disabled. See
+   :ref:`dhcp4-echo-client-id` for details.
+
+-  *Generalized UDP Source Port for the DHCP Relay Agent Option*, `RFC 8357
+   <https://tools.ietf.org/html/rfc8357>`__: The Kea server handles the Relay
+   Agent Information Source Port sub-option in a received message, remembers the
+   UDP port, and sends back a reply to the same relay agent using this UDP port.
+
+-  *Captive-Portal Identification in DHCP and Router Advertisements (RAs)*, `RFC
+   8910 <https://tools.ietf.org/html/rfc8910>`__: The Kea server can configure
+   both v4 and v6 versions of the captive portal options.
+
+-  *IPv6-Only Preferred Option for DHCPv4*, `RFC 8925
+   <https://tools.ietf.org/html/rfc8925>`__: The Kea server is able to designate
+   its pools and subnets as IPv6-Only Preferred and send back the
+   ``v6-only-preferred`` option to clients that requested it.
+
+-  *Server Identifier Override sub-option for the Relay Agent Option*, `RFC 5107
+   <https://tools.ietf.org/html/rfc5107>`__: The server identifier override
+   sub-option is supported. The implementation is not complete according to the
+   RFC, because the server does not store the RAI, but the functionality handles
+   expected use cases.
+
+Known RFC Violations
+--------------------
+
+In principle, Kea aspires to be a reference implementation and aims to implement 100% of the RFC standards.
+However, in some cases there are practical aspects that prevent Kea from completely adhering to the text of the RFC documents.
+
+- `RFC 2131 <https://tools.ietf.org/html/rfc2131>`__, page 30, says that if the incoming DHCPREQUEST packet has no
+  "requested IP address" option and ``ciaddr`` is not set, the server is supposed to respond with NAK. However,
+  broken clients exist that will always send a DHCPREQUEST without those options indicated. In that event, Kea accepts the DHCPREQUEST,
+  assigns an address, and responds with an ACK.
+
+- `RFC 2131 <https://tools.ietf.org/html/rfc2131>`__, table 5, says that messages
+  of type DHCPDECLINE or DHCPRELEASE must have the server identifier set and
+  should be dropped if that option is missing. However, ISC DHCP does not enforce this, presumably as a compatibility
+  effort for broken clients, and the Kea team decided to follow suit.
+
+.. _dhcp4-limit:
+
+DHCPv4 Server Limitations
+=========================
+
+These are the current known limitations of the Kea DHCPv4 server software. Most of
+them are reflections of the current stage of development and should be
+treated as “not implemented yet,” rather than as actual limitations.
+However, some of them are implications of the design choices made. Those
+are clearly marked as such.
+
+-  On the Linux and BSD system families, DHCP messages are sent and
+   received over raw sockets (using LPF and BPF) and all packet
+   headers (including data link layer, IP, and UDP headers) are created
+   and parsed by Kea, rather than by the system kernel. Currently, Kea
+   can only parse the data-link layer headers with a format adhering to
+   the IEEE 802.3 standard, and assumes this data-link-layer header
+   format for all interfaces. Thus, Kea does not work on interfaces
+   which use different data-link-layer header formats (e.g. Infiniband).
+
+-  The DHCPv4 server does not verify that an assigned address is unused.
+   According to `RFC 2131 <https://tools.ietf.org/html/rfc2131>`__, the
+   allocating server should verify that an address is not used by
+   sending an ICMP echo request.
+
+.. _dhcp4-srv-examples:
+
+Kea DHCPv4 Server Examples
+==========================
+
+A collection of simple-to-use examples for the DHCPv4 component of Kea
+is available with the source files, located in the ``doc/examples/kea4``
+directory.
+
+.. _dhcp4-cb:
+
+Configuration Backend in DHCPv4
+===============================
+
+In the :ref:`config-backend` section we have described the Configuration
+Backend (CB) feature, its applicability, and its limitations. This section focuses
+on the usage of the CB with the Kea DHCPv4 server. It lists the supported
+parameters, describes limitations, and gives examples of DHCPv4
+server configurations to take advantage of the CB. Please also refer to
+the corresponding section :ref:`dhcp6-cb` for DHCPv6-specific usage of
+the CB.
+
+.. _dhcp4-cb-parameters:
+
+Supported Parameters
+--------------------
+
+The ultimate goal for the CB is to serve as a central configuration
+repository for one or multiple Kea servers connected to a database.
+In currently supported Kea versions, only a subset of
+the DHCPv4 server parameters can be configured in the database. All other
+parameters must be specified in the JSON configuration file, if
+required.
+
+All supported parameters can be configured via the ``cb_cmds`` hook library
+described in the :ref:`hooks-cb-cmds` section. The general rule is that
+scalar global parameters are set using
+``remote-global-parameter4-set``; shared-network-specific parameters
+are set using ``remote-network4-set``; and subnet- and pool-level
+parameters are set using ``remote-subnet4-set``. Whenever
+there is an exception to this general rule, it is highlighted in the
+table. Non-scalar global parameters have dedicated commands; for example,
+the global DHCPv4 options (``option-data``) are modified using
+``remote-option4-global-set``. Client classes, together with class-specific
+option definitions and DHCPv4 options, are configured using the
+``remote-class4-set`` command.
+
+The :ref:`cb-sharing` section explains the concept of shareable
+and non-shareable configuration elements and the limitations for
+sharing them between multiple servers. In the DHCP configuration (both DHCPv4
+and DHCPv6), the shareable configuration elements are subnets and shared
+networks. Thus, they can be explicitly associated with multiple server tags.
+The global parameters, option definitions, and global options are non-shareable
+and can be associated with only one server tag. This rule does not apply
+to the configuration elements associated with ``all`` servers. Any configuration
+element associated with ``all`` servers (using the ``all`` keyword as a server tag) is
+used by all servers connecting to the configuration database.
+
+The following table lists DHCPv4-specific parameters supported by the
+Configuration Backend, with an indication of the level of the hierarchy
+at which it is currently supported.
+
+.. table:: List of DHCPv4 parameters supported by the Configuration Backend
+
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | Parameter                   | Global                     | Client       | Shared      | Subnet      | Pool        |
+   |                             |                            | Class        | Network     |             |             |
+   +=============================+============================+==============+=============+=============+=============+
+   | 4o6-interface               | n/a                        | n/a          | n/a         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | 4o6-interface-id            | n/a                        | n/a          | n/a         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | 4o6-subnet                  | n/a                        | n/a          | n/a         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | boot-file-name              | yes                        | yes          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | cache-max-age               | yes                        | n/a          | no          | no          | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | cache-threshold             | yes                        | n/a          | no          | no          | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | calculate-tee-times         | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | client-class                | n/a                        | n/a          | yes         | yes         | yes         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | ddns-send-update            | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | ddns-override-no-update     | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | ddns-override-client-update | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | ddns-replace-client-name    | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | ddns-generated-prefix       | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | ddns-qualifying-suffix      | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | decline-probation-period    | yes                        | n/a          | n/a         | n/a         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | dhcp4o6-port                | yes                        | n/a          | n/a         | n/a         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | echo-client-id              | yes                        | n/a          | n/a         | n/a         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | hostname-char-set           | no                         | n/a          | no          | no          | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | hostname-char-replacement   | no                         | n/a          | no          | no          | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | interface                   | n/a                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | match-client-id             | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | min-valid-lifetime          | yes                        | yes          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | max-valid-lifetime          | yes                        | yes          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | next-server                 | yes                        | yes          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | option-data                 | yes (via                   | yes          | yes         | yes         | yes         |
+   |                             | remote-option4-global-set) |              |             |             |             |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | option-def                  | yes (via                   | yes          | n/a         | n/a         | n/a         |
+   |                             | remote-option-def4-set)    |              |             |             |             |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | rebind-timer                | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | renew-timer                 | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | server-hostname             | yes                        | yes          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | valid-lifetime              | yes                        | yes          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | relay                       | n/a                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | require-client-classes      | no                         | n/a          | yes         | yes         | yes         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | reservation-mode            | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | reservations-global         | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | reservations-in-subnet      | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | reservations-out-of-pool    | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | t1-percent                  | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+   | t2-percent                  | yes                        | n/a          | yes         | yes         | n/a         |
+   +-----------------------------+----------------------------+--------------+-------------+-------------+-------------+
+
+-  ``yes`` - indicates that the parameter is supported at the given
+   level of the hierarchy and can be configured via the Configuration Backend.
+
+-  ``no`` - indicates that a parameter is supported at the given level
+   of the hierarchy but cannot be configured via the Configuration Backend.
+
+-  ``n/a`` -  indicates that a given parameter is not applicable
+   at the particular level of the hierarchy or that the
+   server does not support the parameter at that level.
+
+.. _dhcp4-cb-json:
+
+Enabling the Configuration Backend
+----------------------------------
+
+Consider the following configuration snippet, which uses a MySQL configuration
+database:
+
+::
+
+   "Dhcp4": {
+       "server-tag": "my DHCPv4 server",
+       "config-control": {
+           "config-databases": [{
+               "type": "mysql",
+               "name": "kea",
+               "user": "kea",
+               "password": "kea",
+               "host": "192.0.2.1",
+               "port": 3302
+           }],
+           "config-fetch-wait-time": 20
+       },
+       "hooks-libraries": [{
+           "library": "/usr/local/lib/kea/hooks/libdhcp_mysql_cb.so"
+       }, {
+           "library": "/usr/local/lib/kea/hooks/libdhcp_cb_cmds.so"
+       }],
+   }
+
+The ``config-control`` command contains two parameters. ``config-databases``
+is a list that contains one element, which includes the database type, its location,
+and the credentials to be used to connect to this database. (Note that
+the parameters specified here correspond to the database specification
+for the lease database backend and hosts database backend.) Currently
+only one database connection can be specified on the
+``config-databases`` list. The server connects to this database
+during startup or reconfiguration, and fetches the configuration
+available for this server from the database. This configuration is
+merged into the configuration read from the configuration file.
+
+The following snippet illustrates the use of a PostgreSQL database:
+
+::
+
+   "Dhcp4": {
+       "server-tag": "my DHCPv4 server",
+       "config-control": {
+           "config-databases": [{
+               "type": "postgresql",
+               "name": "kea",
+               "user": "kea",
+               "password": "kea",
+               "host": "192.0.2.1",
+               "port": 5432
+           }],
+           "config-fetch-wait-time": 20
+       },
+       "hooks-libraries": [{
+           "library": "/usr/local/lib/kea/hooks/libdhcp_pgsql_cb.so"
+       }, {
+           "library": "/usr/local/lib/kea/hooks/libdhcp_cb_cmds.so"
+       }],
+   }
+
+.. note::
+
+   Whenever there is a conflict between the parameters specified in the
+   configuration file and the database, the parameters from the database
+   take precedence. We strongly recommend avoiding the duplication of
+   parameters in the file and the database, but this recommendation is
+   not enforced by the Kea servers. In particular, if the subnets'
+   configuration is sourced from the database, we recommend that all
+   subnets be specified in the database and that no subnets be specified in
+   the configuration file. It is possible to specify the subnets in both
+   places, but the subnets in the
+   configuration file with overlapping IDs and/or prefixes with the
+   subnets from the database will be superseded by those from the
+   database.
+
+Once the Kea server is configured, it starts periodically polling
+the database for configuration changes. The polling frequency is
+controlled by the ``config-fetch-wait-time`` parameter, expressed
+in seconds; it is the period between the time when the server
+completed its last poll (and possibly the local configuration update) and
+the time when it will begin polling again. In the example above, this period
+is set to 20 seconds. This means that after adding a new configuration
+into the database (e.g. adding a new subnet), it will take up to 20 seconds
+(plus the time needed to fetch and apply the new configuration) before
+the server starts using this subnet. The lower the
+``config-fetch-wait-time`` value, the shorter the time for the server to
+react to incremental configuration updates in the database. On the
+other hand, polling the database too frequently may impact the DHCP
+server's performance, because the server needs to make at least one query
+to the database to discover any pending configuration updates. The
+default value of ``config-fetch-wait-time`` is 30 seconds.
+
+The ``config-backend-pull`` command can be used to force the server to
+immediately poll any configuration changes from the database and avoid
+waiting for the next fetch cycle.
+
+In the configuration examples above, two hook libraries are loaded. The first
+is a library which implements the Configuration Backend for a specific database
+type: ``libdhcp_mysql_cb.so`` provides support for MySQL and ``libdhcp_pgsql_cb.so``
+provides support for PostgreSQL.  The library loaded must match the database
+``type`` specified within the ``config-control`` parameter or an will error be
+logged when the server attempts to load its configuration and the load will
+fail.
+
+The second hook library, ``libdhcp_cb_cmds.so``, is optional. It should
+be loaded when the Kea server instance is to be used to manage the
+configuration in the database. See the :ref:`hooks-cb-cmds` section for
+details. This hook library is only available to ISC
+customers with a paid support contract.
+
+.. _dhcp4-compatibility:
+
+Kea DHCPv4 Compatibility Configuration Parameters
+=================================================
+
+ISC's intention is for Kea to follow the RFC documents to promote better standards
+compliance. However, many buggy DHCP implementations already exist that cannot be
+easily fixed or upgraded. Therefore, Kea provides an easy-to-use compatibility
+mode for broken or non-compliant clients. For that purpose, the compatibility option must be
+enabled to permit uncommon practices:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "compatibility": {
+        }
+      }
+    }
+
+
+Lenient Option Parsing
+----------------------
+
+By default, tuple fields defined in custom options are parsed as a set of
+length-value pairs.
+
+With ``"lenient-option-parsing": true``, if a length ever exceeds the rest of
+the option's buffer, previous versions of Kea returned a log message ``unable to
+parse the opaque data tuple, the buffer length is x, but the tuple length is y``
+with ``x < y``; this no longer occurs. Instead, the value is considered to be the rest of the buffer,
+or in terms of the log message above, the tuple length ``y`` becomes ``x``.
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "compatibility": {
+          "lenient-option-parsing": true
+        }
+      }
+    }
diff --git a/doc/sphinx/arm/dhcp6-srv.rst b/doc/sphinx/arm/dhcp6-srv.rst
new file mode 100644
index 0000000..1009a6e
--- /dev/null
+++ b/doc/sphinx/arm/dhcp6-srv.rst
@@ -0,0 +1,6975 @@
+.. _dhcp6:
+
+*****************
+The DHCPv6 Server
+*****************
+
+.. _dhcp6-start-stop:
+
+Starting and Stopping the DHCPv6 Server
+=======================================
+
+It is recommended that the Kea DHCPv6 server be started and stopped
+using ``keactrl`` (described in :ref:`keactrl`); however, it is also
+possible to run the server directly via the ``kea-dhcp6`` command, which accepts
+the following command-line switches:
+
+-  ``-c file`` - specifies the configuration file. This is the only
+   mandatory switch.
+
+-  ``-d`` - specifies whether the server logging should be switched to
+   debug/verbose mode. In verbose mode, the logging severity and debuglevel
+   specified in the configuration file are ignored; "debug" severity
+   and the maximum debuglevel (99) are assumed. The flag is convenient
+   for temporarily switching the server into maximum verbosity, e.g.
+   when debugging.
+
+-  ``-p server-port`` - specifies the local UDP port on which the server
+   listens. This is only useful during testing, as a DHCPv6 server
+   listening on ports other than the standard ones is not able to
+   handle regular DHCPv6 queries.
+
+-  ``-P client-port`` - specifies the remote UDP port to which the
+   server sends all responses. This is only useful during testing,
+   as a DHCPv6 server sending responses to ports other than the standard
+   ones is not able to handle regular DHCPv6 queries.
+
+-  ``-t file`` - specifies a configuration file to be tested. ``kea-dhcp6``
+   loads it, checks it, and exits. During the test, log messages are
+   printed to standard output and error messages to standard error. The
+   result of the test is reported through the exit code (0 =
+   configuration looks OK, 1 = error encountered). The check is not
+   comprehensive; certain checks are possible only when running the
+   server.
+
+-  ``-v`` - displays the Kea version and exits.
+
+-  ``-V`` - displays the Kea extended version with additional parameters
+   and exits. The listing includes the versions of the libraries
+   dynamically linked to Kea.
+
+-  ``-W`` - displays the Kea configuration report and exits. The report
+   is a copy of the ``config.report`` file produced by ``./configure``;
+   it is embedded in the executable binary.
+
+On startup, the server detects available network interfaces and
+attempts to open UDP sockets on all interfaces listed in the
+configuration file. Since the DHCPv6 server opens privileged ports, it
+requires root access; this daemon must be run as root.
+
+During startup, the server attempts to create a PID file of the
+form: ``[runstatedir]/kea/[conf name].kea-dhcp6.pid``, where:
+
+-  ``runstatedir``: The value as passed into the build configure
+   script; it defaults to ``/usr/local/var/run``. Note that this value may be
+   overridden at runtime by setting the environment variable
+   ``KEA_PIDFILE_DIR``, although this is intended primarily for testing
+   purposes.
+
+-  ``conf name``: The configuration file name used to start the server,
+   minus all preceding paths and the file extension. For example, given
+   a pathname of ``/usr/local/etc/kea/myconf.txt``, the portion used would
+   be ``myconf``.
+
+If the file already exists and contains the PID of a live process, the
+server issues a ``DHCP6_ALREADY_RUNNING`` log message and exits. It is
+possible, though unlikely, that the file is a remnant of a system crash
+and the process to which the PID belongs is unrelated to Kea. In such a
+case, it would be necessary to manually delete the PID file.
+
+The server can be stopped using the ``kill`` command. When running in a
+console, the server can also be shut down by pressing Ctrl-c. Kea detects
+the key combination and shuts down gracefully.
+
+.. _dhcp6-configuration:
+
+DHCPv6 Server Configuration
+===========================
+
+Introduction
+------------
+
+This section explains how to configure the Kea DHCPv6 server using a
+configuration file.
+
+Before DHCPv6 is started, its configuration file must
+be created. The basic configuration is as follows:
+
+::
+
+   {
+   # DHCPv6 configuration starts on the next line
+   "Dhcp6": {
+
+   # First we set up global values
+       "valid-lifetime": 4000,
+       "renew-timer": 1000,
+       "rebind-timer": 2000,
+       "preferred-lifetime": 3000,
+
+   # Next we set up the interfaces to be used by the server.
+       "interfaces-config": {
+           "interfaces": [ "eth0" ]
+       },
+
+   # And we specify the type of lease database
+       "lease-database": {
+           "type": "memfile",
+           "persist": true,
+           "name": "/var/lib/kea/dhcp6.leases"
+       },
+
+   # Finally, we list the subnets from which we will be leasing addresses.
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/64",
+               "pools": [
+                   {
+                       "pool": "2001:db8:1::1-2001:db8:1::ffff"
+                   }
+                ]
+           }
+       ]
+   # DHCPv6 configuration ends with the next line
+   }
+
+   }
+
+The following paragraphs provide a brief overview of the parameters in
+the above example, along with their format. Subsequent sections of this
+chapter go into much greater detail for these and other parameters.
+
+The lines starting with a hash (#) are comments and are ignored by the
+server; they do not impact its operation in any way.
+
+The configuration starts in the first line with the initial opening
+curly bracket (or brace). Each configuration must contain an object
+specifying the configuration of the Kea module using it. In the example
+above, this object is called ``Dhcp6``.
+
+The ``Dhcp6`` configuration starts with the ``"Dhcp6": {`` line and ends
+with the corresponding closing brace (in the above example, the brace
+after the last comment). Everything defined between those lines is
+considered to be the ``Dhcp6`` configuration.
+
+In general, the order in which those parameters appear does not
+matter, but there are two caveats. The first one is that the
+configuration file must be well-formed JSON, meaning that the
+parameters for any given scope must be separated by a comma, and there
+must not be a comma after the last parameter. When reordering a
+configuration file, moving a parameter to or from the
+last position in a given scope may also require moving the comma. The
+second caveat is that it is uncommon — although legal JSON — to repeat
+the same parameter multiple times. If that happens, the last occurrence
+of a given parameter in a given scope is used, while all previous
+instances are ignored. This is unlikely to cause any confusion as there
+are no real-life reasons to keep multiple copies of the same parameter
+in the configuration file.
+
+The first few DHCPv6 configuration elements
+define some global parameters. ``valid-lifetime`` defines how long the
+addresses (leases) given out by the server are valid; the default
+is for a client to be allowed to use a given address for 4000
+seconds. (Note that integer numbers are specified as is, without any
+quotes around them.) The address will become deprecated in 3000 seconds,
+i.e. clients are allowed to keep old connections, but cannot use this
+address to create new connections. ``renew-timer`` and
+``rebind-timer`` are values (also in seconds) that define T1 and T2 timers, which govern
+when the client begins the renewal and rebind procedures.
+
+The ``interfaces-config`` map specifies the
+network interfaces on which the server should listen to
+DHCP messages. The ``interfaces`` parameter specifies a list of
+network interfaces on which the server should listen. Lists are opened
+and closed with square brackets, with elements separated by commas. To
+listen on two interfaces, the ``interfaces-config`` element should look like
+this:
+
+::
+
+   "interfaces-config": {
+       "interfaces": [ "eth0", "eth1" ]
+   },
+
+The next lines define the lease database, the place where the
+server stores its lease information. This particular example tells the
+server to use memfile, which is the simplest and fastest database
+backend. It uses an in-memory database and stores leases on disk in a
+CSV (comma-separated values) file. This is a very simple configuration example;
+usually the lease database configuration is more extensive and contains
+additional parameters. Note that ``lease-database`` is an object and opens up a
+new scope, using an opening brace. Its parameters (just one in this example:
+``type``) follow. If there were more than one, they would be separated
+by commas. This scope is closed with a closing brace. As more parameters
+for the ``Dhcp6`` definition follow, a trailing comma is present.
+
+Finally, we need to define a list of IPv6 subnets. This is the most
+important DHCPv6 configuration structure, as the server uses that
+information to process clients' requests. It defines all subnets from
+which the server is expected to receive DHCP requests. The subnets are
+specified with the ``subnet6`` parameter. It is a list, so it starts and
+ends with square brackets. Each subnet definition in the list has
+several attributes associated with it, so it is a structure and is
+opened and closed with braces. At a minimum, a subnet definition must
+have at least two parameters: ``subnet``, which defines the whole
+subnet; and ``pools``, which is a list of dynamically allocated pools
+that are governed by the DHCP server.
+
+The example contains a single subnet. If more than one were defined,
+additional elements in the ``subnet6`` parameter would be specified and
+separated by commas. For example, to define two subnets, the following
+syntax would be used:
+
+::
+
+   "subnet6": [
+       {
+           "pools": [ { "pool": "2001:db8:1::/112" } ],
+           "subnet": "2001:db8:1::/64"
+       },
+       {
+           "pools": [ { "pool": "2001:db8:2::1-2001:db8:2::ffff" } ],
+           "subnet": "2001:db8:2::/64"
+       }
+   ]
+
+Note that indentation is optional and is used for aesthetic purposes
+only. In some cases it may be preferable to use more compact notation.
+
+After all the parameters have been specified, there are two contexts open:
+``global`` and ``Dhcp6``; thus, two closing curly brackets must be used to close
+them.
+
+Lease Storage
+-------------
+
+All leases issued by the server are stored in the lease database.
+There are three database backends available: memfile
+(the default), MySQL, PostgreSQL.
+
+Memfile - Basic Storage for Leases
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The server is able to store lease data in different repositories. Larger
+deployments may elect to store leases in a database;
+:ref:`database-configuration6` describes this option. In
+typical smaller deployments, though, the server stores lease
+information in a CSV file rather than a database. As well as requiring
+less administration, an advantage of using a file for storage is that it
+eliminates a dependency on third-party database software.
+
+The configuration of the memfile backend is controlled through
+the ``Dhcp6``/``lease-database`` parameters. The ``type`` parameter is mandatory
+and specifies which storage for leases the server should use, through
+the ``"memfile"`` value. The following list gives additional optional parameters
+that can be used to configure the memfile backend.
+
+-  ``persist``: controls whether the new leases and updates to existing
+   leases are written to the file. It is strongly recommended that the
+   value of this parameter be set to ``true`` at all times during the
+   server's normal operation. Not writing leases to disk means that if a
+   server is restarted (e.g. after a power failure), it will not know
+   which addresses have been assigned. As a result, it may assign new clients
+   addresses that are already in use. The value of
+   ``false`` is mostly useful for performance-testing purposes. The
+   default value of the ``persist`` parameter is ``true``, which enables
+   writing lease updates to the lease file.
+
+-  ``name``: specifies an absolute location of the lease file in which
+   new leases and lease updates are recorded. The default value for
+   this parameter is ``"[kea-install-dir]/var/lib/kea/kea-leases6.csv"``.
+
+-  ``lfc-interval``: specifies the interval, in seconds, at which the
+   server will perform a lease file cleanup (LFC). This removes
+   redundant (historical) information from the lease file and
+   effectively reduces the lease file size. The cleanup process is
+   described in more detail later in this section. The default
+   value of the ``lfc-interval`` is ``3600``. A value of ``0`` disables the LFC.
+
+-  ``max-row-errors``: specifies the number of row errors before the server
+   stops attempting to load a lease file. When the server loads a lease file, it is processed
+   row by row, each row containing a single lease. If a row is flawed and
+   cannot be processed correctly the server logs it, discards the row,
+   and goes on to the next row. This parameter can be used to set a limit on
+   the number of such discards that can occur, after which the server
+   abandons the effort and exits. The default value of ``0`` disables the limit
+   and allows the server to process the entire file, regardless of how many
+   rows are discarded.
+
+An example configuration of the memfile backend is presented below:
+
+::
+
+   "Dhcp6": {
+       "lease-database": {
+           "type": "memfile",
+           "persist": true,
+           "name": "/tmp/kea-leases6.csv",
+           "lfc-interval": 1800,
+           "max-row-errors": 100
+       }
+   }
+
+This configuration selects ``/tmp/kea-leases6.csv`` as the storage file
+for lease information and enables persistence (writing lease updates to
+this file). It also configures the backend to perform a periodic cleanup
+of the lease file every 1800 seconds (30 minutes) and sets the maximum number of
+row errors to 100.
+
+Why Is Lease File Cleanup Necessary?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+It is important to know how the lease file contents are organized to
+understand why the periodic lease file cleanup is needed. Every time the
+server updates a lease or creates a new lease for a client, the new
+lease information must be recorded in the lease file. For performance
+reasons, the server does not update the existing client's lease in the
+file, as this would potentially require rewriting the entire file.
+Instead, it simply appends the new lease information to the end of the
+file; the previous lease entries for the client are not removed. When
+the server loads leases from the lease file, e.g. at server startup,
+it assumes that the latest lease entry for the client is the valid one.
+Previous entries are discarded, meaning that the server can
+reconstruct accurate information about the leases even though there
+may be many lease entries for each client. However, storing many entries
+for each client results in a bloated lease file and impairs the
+performance of the server's startup and reconfiguration, as it needs to
+process a larger number of lease entries.
+
+Lease file cleanup (LFC) removes all previous entries for each client
+and leaves only the latest ones. The interval at which the cleanup is
+performed is configurable, and it should be selected according to the
+frequency of lease renewals initiated by the clients. The more frequent
+the renewals, the smaller the value of ``lfc-interval`` should be. Note,
+however, that the LFC takes time and thus it is possible (although
+unlikely) that, if the ``lfc-interval`` is too short, a new cleanup may
+be started while the previous one is still running. The server would
+recover from this by skipping the new cleanup when it detected that the
+previous cleanup was still in progress, but it implies that the actual
+cleanups will be triggered more rarely than the configured interval. Moreover,
+triggering a new cleanup adds overhead to the server, which is not
+able to respond to new requests for a short period of time when the new
+cleanup process is spawned. Therefore, it is recommended that the
+``lfc-interval`` value be selected in a way that allows the LFC
+to complete the cleanup before a new cleanup is triggered.
+
+Lease file cleanup is performed by a separate process (in the
+background) to avoid a performance impact on the server process. To
+avoid conflicts between two processes using the same lease
+files, the LFC process starts with Kea opening a new lease file; the
+actual LFC process operates on the lease file that is no longer used by
+the server. There are also other files created as a side effect of the
+lease file cleanup. The detailed description of the LFC process is located later
+in this Kea Administrator's Reference Manual: :ref:`kea-lfc`.
+
+.. _database-configuration6:
+
+Lease Database Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. note::
+
+   Lease database access information must be configured for the DHCPv6
+   server, even if it has already been configured for the DHCPv4 server.
+   The servers store their information independently, so each server can
+   use a separate database or both servers can use the same database.
+
+.. note::
+
+   Kea requires the database timezone to match the system timezone.
+   For more details, see :ref:`mysql-database-create` and
+   :ref:`pgsql-database-create`.
+
+Lease database configuration is controlled through the
+``Dhcp6``/``lease-database`` parameters. The database type must be set to
+``memfile``, ``mysql`` or ``postgresql``, e.g.:
+
+::
+
+   "Dhcp6": { "lease-database": { "type": "mysql", ... }, ... }
+
+Next, the name of the database to hold the leases must be set; this is
+the name used when the database was created (see
+:ref:`mysql-database-create` or :ref:`pgsql-database-create`).
+
+For MySQL or PostgreSQL:
+
+::
+
+   "Dhcp6": { "lease-database": { "name": "database-name" , ... }, ... }
+
+If the database is located on a different system from the DHCPv6 server,
+the database host name must also be specified:
+
+::
+
+   "Dhcp6": { "lease-database": { "host": "remote-host-name", ... }, ... }
+
+Normally, the database is on the same machine as the DHCPv6 server.
+In this case, set the value to the empty string:
+
+::
+
+   "Dhcp6": { "lease-database": { "host" : "", ... }, ... }
+
+Should the database use a port other than the default, it may be
+specified as well:
+
+::
+
+   "Dhcp6": { "lease-database": { "port" : 12345, ... }, ... }
+
+Should the database be located on a different system, the administrator may need to
+specify a longer interval for the connection timeout:
+
+::
+
+   "Dhcp6": { "lease-database": { "connect-timeout" : timeout-in-seconds, ... }, ... }
+
+The default value of five seconds should be more than adequate for local
+connections. If a timeout is given, though, it should be an integer
+greater than zero.
+
+The maximum number of times the server automatically attempts to
+reconnect to the lease database after connectivity has been lost may be
+specified:
+
+::
+
+   "Dhcp6": { "lease-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }
+
+If the server is unable to reconnect to the database after making the
+maximum number of attempts, the server will exit. A value of 0 (the
+default) disables automatic recovery and the server will exit
+immediately upon detecting a loss of connectivity (MySQL and PostgreSQL
+only).
+
+The number of milliseconds the server waits between attempts to
+reconnect to the lease database after connectivity has been lost may
+also be specified:
+
+::
+
+   "Dhcp6": { "lease-database": { "reconnect-wait-time" : number-of-milliseconds, ... }, ... }
+
+The default value for MySQL and PostgreSQL is 0, which disables automatic
+recovery and causes the server to exit immediately upon detecting the
+loss of connectivity.
+
+::
+
+   "Dhcp6": { "lease-database": { "on-fail" : "stop-retry-exit", ... }, ... }
+
+The possible values are:
+
+-  ``stop-retry-exit`` - disables the DHCP service while trying to automatically
+   recover lost connections. Shuts down the server on failure after exhausting
+   ``max-reconnect-tries``. This is the default value for MySQL and PostgreSQL.
+
+-  ``serve-retry-exit`` - continues the DHCP service while trying to automatically
+   recover lost connections. Shuts down the server on failure after exhausting
+   ``max-reconnect-tries``.
+
+-  ``serve-retry-continue`` - continues the DHCP service and does not shut down the
+   server even if the recovery fails.
+
+.. note::
+
+   Automatic reconnection to database backends is configured individually per
+   backend; this allows users to tailor the recovery parameters to each backend
+   they use. We suggest that users enable it either for all backends or none,
+   so behavior is consistent.
+
+   Losing connectivity to a backend for which reconnection is disabled results
+   (if configured) in the server shutting itself down. This includes cases when
+   the lease database backend and the hosts database backend are connected to
+   the same database instance.
+
+   It is highly recommended not to change the ``stop-retry-exit`` default
+   setting for the lease manager, as it is critical for the connection to be
+   active while processing DHCP traffic. Change this only if the server is used
+   exclusively as a configuration tool.
+
+The host parameter is used by the MySQL and PostgreSQL backends.
+
+Finally, the credentials of the account under which the server will
+access the database should be set:
+
+::
+
+   "Dhcp6": { "lease-database": { "user": "user-name",
+                                  "password": "password",
+                                 ... },
+              ... }
+
+If there is no password to the account, set the password to the empty
+string ``""``. (This is the default.)
+
+.. _hosts6-storage:
+
+Hosts Storage
+-------------
+
+Kea is also able to store information about host reservations in the
+database. The hosts database configuration uses the same syntax as the
+lease database. In fact, the Kea server opens independent connections for
+each purpose, be it lease or hosts information, which gives
+the most flexibility. Kea can keep leases and host reservations
+separately, but can also point to the same database. Currently the
+supported hosts database types are MySQL and PostgreSQL.
+
+The following configuration can be used to configure a
+connection to MySQL:
+
+::
+
+   "Dhcp6": {
+       "hosts-database": {
+           "type": "mysql",
+           "name": "kea",
+           "user": "kea",
+           "password": "secret123",
+           "host": "localhost",
+           "port": 3306
+       }
+   }
+
+Depending on the database configuration, many of the
+parameters may be optional.
+
+Please note that usage of hosts storage is optional. A user can define
+all host reservations in the configuration file, and that is the
+recommended way if the number of reservations is small. However, when
+the number of reservations grows, it is more convenient to use host
+storage. Please note that both storage methods (the configuration file and
+one of the supported databases) can be used together. If hosts are
+defined in both places, the definitions from the configuration file are
+checked first and external storage is checked later, if necessary.
+
+Host information can be placed in multiple stores. Operations
+are performed on the stores in the order they are defined in the
+configuration file, although this leads to a restriction in ordering
+in the case of a host reservation addition; read-only stores must be
+configured after a (required) read-write store, or the addition will
+fail.
+
+.. note::
+
+   Kea requires the database timezone to match the system timezone.
+   For more details, see :ref:`mysql-database-create` and
+   :ref:`pgsql-database-create`.
+
+.. _hosts-databases-configuration6:
+
+DHCPv6 Hosts Database Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Hosts database configuration is controlled through the
+``Dhcp6``/``hosts-database`` parameters. If enabled, the type of database must
+be set to ``mysql`` or ``postgresql``.
+
+::
+
+   "Dhcp6": { "hosts-database": { "type": "mysql", ... }, ... }
+
+Next, the name of the database to hold the reservations must be set;
+this is the name used when the lease database was created (see
+:ref:`supported-databases` for instructions on how to set up the
+desired database type):
+
+::
+
+   "Dhcp6": { "hosts-database": { "name": "database-name" , ... }, ... }
+
+If the database is located on a different system than the DHCPv6 server,
+the database host name must also be specified:
+
+::
+
+   "Dhcp6": { "hosts-database": { "host": remote-host-name, ... }, ... }
+
+Normally, the database is on the same machine as the DHCPv6 server.
+In this case, set the value to the empty string:
+
+::
+
+   "Dhcp6": { "hosts-database": { "host" : "", ... }, ... }
+
+Should the database use a port different than the default, it may be
+specified as well:
+
+::
+
+   "Dhcp6": { "hosts-database": { "port" : 12345, ... }, ... }
+
+The maximum number of times the server automatically attempts to
+reconnect to the host database after connectivity has been lost may be
+specified:
+
+::
+
+   "Dhcp6": { "hosts-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }
+
+If the server is unable to reconnect to the database after making the
+maximum number of attempts, the server will exit. A value of 0 (the
+default) disables automatic recovery and the server will exit
+immediately upon detecting a loss of connectivity (MySQL and PostgreSQL
+only).
+
+The number of milliseconds the server waits between attempts to
+reconnect to the host database after connectivity has been lost may also
+be specified:
+
+::
+
+   "Dhcp6": { "hosts-database": { "reconnect-wait-time" : number-of-milliseconds, ... }, ... }
+
+The default value for MySQL and PostgreSQL is 0, which disables automatic
+recovery and causes the server to exit immediately upon detecting the
+loss of connectivity.
+
+::
+
+   "Dhcp6": { "hosts-database": { "on-fail" : "stop-retry-exit", ... }, ... }
+
+The possible values are:
+
+-  ``stop-retry-exit`` - disables the DHCP service while trying to automatically
+   recover lost connections. Shuts down the server on failure after exhausting
+   ``max-reconnect-tries``. This is the default value for MySQL and PostgreSQL.
+
+-  ``serve-retry-exit`` - continues the DHCP service while trying to automatically
+   recover lost connections. Shuts down the server on failure after exhausting
+   ``max-reconnect-tries``.
+
+-  ``serve-retry-continue`` - continues the DHCP service and does not shut down the
+   server even if the recovery fails.
+
+.. note::
+
+   Automatic reconnection to database backends is configured individually per
+   backend. This allows users to tailor the recovery parameters to each backend
+   they use. We suggest that users enable it either for all backends or none,
+   so behavior is consistent.
+
+   Losing connectivity to a backend for which reconnection is disabled results
+   (if configured) in the server shutting itself down. This includes cases when
+   the lease database backend and the hosts database backend are connected to
+   the same database instance.
+
+Finally, the credentials of the account under which the server will
+access the database should be set:
+
+::
+
+   "Dhcp6": { "hosts-database": { "user": "user-name",
+                                  "password": "password",
+                                 ... },
+              ... }
+
+If there is no password to the account, set the password to the empty
+string ``""``. (This is the default.)
+
+The multiple-storage extension uses a similar syntax; a configuration is
+placed into a ``hosts-databases`` list instead of into a ``hosts-database``
+entry, as in:
+
+::
+
+   "Dhcp6": { "hosts-databases": [ { "type": "mysql", ... }, ... ], ... }
+
+If the same host is configured both in-file and in-database, Kea does not issue a warning,
+as it would if both were specified in the same data source.
+Instead, the host configured in-file has priority over the one configured
+in-database.
+
+.. _read-only-database-configuration6:
+
+Using Read-Only Databases for Host Reservations with DHCPv6
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In some deployments, the user whose name is specified in the
+database backend configuration may not have write privileges to the
+database. This is often required by the policy within a given network to
+secure the data from being unintentionally modified. In many cases
+administrators have deployed inventory databases, which contain
+substantially more information about the hosts than just the static
+reservations assigned to them. The inventory database can be used to
+create a view of a Kea hosts database and such a view is often
+read-only.
+
+Kea host-database backends operate with an implicit configuration to
+both read from and write to the database. If the user does not
+have write access to the host database, the backend will fail to start
+and the server will refuse to start (or reconfigure). However, if access
+to a read-only host database is required for retrieving reservations
+for clients and/or assigning specific addresses and options, it is
+possible to explicitly configure Kea to start in "read-only" mode. This
+is controlled by the ``readonly`` boolean parameter as follows:
+
+::
+
+   "Dhcp6": { "hosts-database": { "readonly": true, ... }, ... }
+
+Setting this parameter to ``false`` configures the database backend to
+operate in "read-write" mode, which is also the default configuration if
+the parameter is not specified.
+
+.. note::
+
+   The ``readonly`` parameter is only supported for MySQL and
+   PostgreSQL databases.
+
+.. _dhcp6-interface-configuration:
+
+Interface Configuration
+-----------------------
+
+The DHCPv6 server must be configured to listen on specific network
+interfaces. The simplest network interface configuration tells the
+server to listen on all available interfaces:
+
+::
+
+   "Dhcp6": {
+       "interfaces-config": {
+           "interfaces": [ "*" ]
+       }
+       ...
+   }
+
+The asterisk plays the role of a wildcard and means "listen on all
+interfaces." However, it is usually a good idea to explicitly specify
+interface names:
+
+::
+
+   "Dhcp6": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ]
+       },
+       ...
+   }
+
+
+It is possible to use an interface wildcard (*) concurrently
+with explicit interface names:
+
+::
+
+   "Dhcp6": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3", "*" ]
+       },
+       ...
+   }
+
+This format should only be used when it is
+desired to temporarily override a list of interface names and listen on
+all interfaces.
+
+As with the DHCPv4 server, binding to specific addresses and disabling
+re-detection of interfaces are supported. But ``dhcp-socket-type`` is
+not supported, because DHCPv6 uses only UDP/IPv6 sockets. The following example
+shows how to disable interface detection:
+
+::
+
+   "Dhcp6": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ],
+           "re-detect": false
+       },
+       ...
+   }
+
+
+The loopback interfaces (i.e. the ``lo`` or ``lo0`` interface) are not
+configured by default, unless explicitly mentioned in the
+configuration. Note that Kea requires a link-local address (which does
+not exist on all systems) or a specified unicast address, as in:
+
+::
+
+   "Dhcp6": {
+       "interfaces-config": {
+           "interfaces": [ "enp0s2/2001:db8::1234:abcd" ]
+       },
+       ...
+   }
+
+Kea binds the service sockets for each interface on startup. If another
+process is already using a port, then Kea logs the message and suppresses an
+error. DHCP service runs, but it is unavailable on some interfaces.
+
+The "service-sockets-require-all" option makes Kea require all sockets to
+be successfully bound. If any opening fails, Kea interrupts the
+initialization and exits with a non-zero status. (Default is false).
+
+::
+
+   "Dhcp6": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ],
+           "service-sockets-require-all": true
+       },
+       ...
+   }
+
+Sometimes, immediate interruption isn't a good choice. The port can be
+unavailable only temporary. In this case, retrying the opening may resolve
+the problem. Kea provides two options to specify the retrying:
+``service-sockets-max-retries`` and ``service-sockets-retry-wait-time``.
+
+The first defines a maximal number of retries that Kea makes to open a socket.
+The zero value (default) means that the Kea doesn't retry the process.
+
+The second defines a wait time (in milliseconds) between attempts. The default
+value is 5000 (5 seconds).
+
+::
+
+   "Dhcp6": {
+       "interfaces-config": {
+           "interfaces": [ "eth1", "eth3" ],
+           "service-sockets-max-retries": 5,
+           "service-sockets-retry-wait-time": 5000
+       },
+       ...
+   }
+
+If "service-sockets-max-retries" is non-zero and "service-sockets-require-all"
+is false, then Kea retries the opening (if needed) but does not fail if any
+socket is still not opened.
+
+.. _ipv6-subnet-id:
+
+IPv6 Subnet Identifier
+----------------------
+
+The subnet identifier (subnet ID) is a unique number associated with a particular
+subnet. In principle, it is used to associate clients' leases with their
+respective subnets. When a subnet identifier is not specified for a
+subnet being configured, it is automatically assigned by the
+configuration mechanism. The identifiers are assigned starting at 1 and are
+monotonically increased for each subsequent subnet: 1, 2, 3, ....
+
+If there are multiple subnets configured with auto-generated identifiers
+and one of them is removed, the subnet identifiers may be renumbered.
+For example: if there are four subnets and the third is removed, the
+last subnet will be assigned the identifier that the third subnet had
+before removal. As a result, the leases stored in the lease database for
+subnet 3 are now associated with subnet 4, something that may have
+unexpected consequences. The only remedy for this issue at present is to
+manually specify a unique identifier for each subnet.
+
+.. note::
+
+   Subnet IDs must be greater than zero and less than 4294967295.
+
+The following configuration assigns the specified subnet identifier
+to a newly configured subnet:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/64",
+               "id": 1024,
+               ...
+           }
+       ]
+   }
+
+This identifier will not change for this subnet unless the ``id``
+parameter is removed or set to 0. The value of 0 forces auto-generation
+of the subnet identifier.
+
+.. _ipv6-subnet-prefix:
+
+IPv6 Subnet Prefix
+------------------
+
+The subnet prefix is the second way to identify a subnet. Kea can
+accept non-canonical subnet addresses; for instance,
+this configuration is accepted:
+
+::
+
+   "Dhcp6": {
+      "subnet6": [
+          {
+               "subnet": "2001:db8:1::1/64",
+               ...
+          }
+       ]
+   }
+
+This works even if there is another subnet with the "2001:db8:1::/64" prefix;
+only the textual form of subnets are compared to avoid duplicates.
+
+.. note::
+
+   Abuse of this feature can lead to incorrect subnet selection
+   (see :ref:`dhcp6-config-subnets`).
+
+.. _dhcp6-unicast:
+
+Unicast Traffic Support
+-----------------------
+
+When the DHCPv6 server starts, by default it listens to the DHCP traffic
+sent to multicast address ff02::1:2 on each interface that it is
+configured to listen on (see :ref:`dhcp6-interface-configuration`). In some cases it is
+useful to configure a server to handle incoming traffic sent to global
+unicast addresses as well; the most common reason for this is to have
+relays send their traffic to the server directly. To configure the
+server to listen on a specific unicast address, add a slash (/) after the interface name,
+followed by the global unicast
+address on which the server should listen. The server will listen to this
+address in addition to normal link-local binding and listening on the
+ff02::1:2 address. The sample configuration below shows how to listen on
+2001:db8::1 (a global address) configured on the ``eth1`` interface.
+
+::
+
+   "Dhcp6": {
+       "interfaces-config": {
+           "interfaces": [ "eth1/2001:db8::1" ]
+       },
+       ...
+       "option-data": [
+           {
+               "name": "unicast",
+               "data": "2001:db8::1"
+           } ],
+       ...
+   }
+
+
+This configuration will cause the server to listen on ``eth1`` on the
+link-local address, the multicast group (ff02::1:2), and 2001:db8::1.
+
+Usually, unicast support is associated with a server unicast option which
+allows clients to send unicast messages to the server. The example above
+includes a server unicast option specification which causes the
+client to send messages to the specified unicast address.
+
+It is possible to mix interface names, wildcards, and interface
+names/addresses in the list of interfaces. It is not possible, however,
+to specify more than one unicast address on a given interface.
+
+Care should be taken to specify proper unicast addresses, as the server
+will attempt to bind to the addresses specified without any additional
+checks. This approach was selected intentionally, to allow the software to
+communicate over uncommon addresses if so desired.
+
+.. _dhcp6-address-config:
+
+Configuration of IPv6 Address Pools
+-----------------------------------
+
+The main role of a DHCPv6 server is address assignment. For this, the
+server must be configured with at least one subnet and one pool of
+dynamic addresses to be managed. For example, assume that the server is
+connected to a network segment that uses the 2001:db8:1::/64 prefix. The
+administrator of that network decides that addresses from the range
+2001:db8:1::1 to 2001:db8:1::ffff are going to be managed by the DHCPv6
+server. Such a configuration can be achieved in the following way:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+          {
+              "subnet": "2001:db8:1::/64",
+              "pools": [
+                  {
+                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
+                  }
+              ],
+              ...
+          }
+       ]
+   }
+
+Note that ``subnet`` is defined as a simple string, but the ``pools``
+parameter is actually a list of pools; for this reason, the pool
+definition is enclosed in square brackets, even though only one range of
+addresses is specified.
+
+Each ``pool`` is a structure that contains the parameters that describe
+a single pool. Currently there is only one parameter, ``pool``, which
+gives the range of addresses in the pool.
+
+It is possible to define more than one pool in a subnet; continuing the
+previous example, further assume that 2001:db8:1:0:5::/80 should also be
+managed by the server. It could be written as 2001:db8:1:0:5:: to
+2001:db8:1::5:ffff:ffff:ffff, but typing so many ``f``s is cumbersome. It
+can be expressed more simply as 2001:db8:1:0:5::/80. Both formats are
+supported by ``Dhcp6`` and can be mixed in the pool list. For example,
+the following pools could be defined:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+       {
+           "subnet": "2001:db8:1::/64",
+           "pools": [
+               { "pool": "2001:db8:1::1-2001:db8:1::ffff" },
+               { "pool": "2001:db8:1:05::/80" }
+           ],
+           ...
+       }
+       ]
+   }
+
+White space in pool definitions is ignored, so spaces before and after
+the hyphen are optional. They can be used to improve readability.
+
+The number of pools is not limited, but for performance reasons it is
+recommended to use as few as possible.
+
+The server may be configured to serve more than one subnet. To add a
+second subnet, use a command similar to the following:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+       {
+           "subnet": "2001:db8:1::/64",
+           "pools": [
+               { "pool": "2001:db8:1::1-2001:db8:1::ffff" }
+           ]
+       },
+       {
+           "subnet": "2001:db8:2::/64",
+           "pools": [
+               { "pool": "2001:db8:2::/64" }
+           ]
+       },
+
+           ...
+       ]
+   }
+
+In this example, we allow the server to dynamically assign all addresses
+available in the whole subnet. Although rather wasteful, it is certainly
+a valid configuration to dedicate the whole /64 subnet for that purpose.
+Note that the Kea server does not preallocate the leases, so there is no
+danger in using gigantic address pools.
+
+When configuring a DHCPv6 server using prefix/length notation, please
+pay attention to the boundary values. When specifying that the server
+can use a given pool, it is also able to allocate the first
+(typically a network address) address from that pool. For example, for
+pool 2001:db8:2::/64, the 2001:db8:2:: address may be assigned as well.
+To avoid this, use the ``min-max`` notation.
+
+.. _dhcp6-prefix-config:
+
+Subnet and Prefix Delegation Pools
+----------------------------------
+
+Subnets may also be configured to delegate prefixes, as defined in `RFC
+8415 <https://tools.ietf.org/html/rfc8415>`__, section 6.3. A subnet may
+have one or more prefix delegation pools. Each pool has a prefixed
+address, which is specified as a prefix (``prefix``) and a prefix length
+(``prefix-len``), as well as a delegated prefix length
+(``delegated-len``). The delegated length must not be shorter than
+(i.e. it must be numerically greater than or equal to) the prefix length.
+If both the delegated and prefix lengths are equal, the server will be
+able to delegate only one prefix. The delegated prefix does not have to
+match the subnet prefix.
+
+Below is a sample subnet configuration which enables prefix delegation
+for the subnet:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "subnet": "2001:d8b:1::/64",
+               "pd-pools": [
+                   {
+                       "prefix": "3000:1::",
+                       "prefix-len": 64,
+                       "delegated-len": 96
+                   }
+               ]
+           }
+       ],
+       ...
+   }
+
+.. _pd-exclude-option:
+
+Prefix Exclude Option
+---------------------
+
+For each delegated prefix, the delegating router may choose to exclude a
+single prefix out of the delegated prefix as specified in `RFC
+6603 <https://tools.ietf.org/html/rfc6603>`__. The requesting router must
+not assign the excluded prefix to any of its downstream interfaces.
+The excluded prefix is intended to be used on a link through which the delegating router
+exchanges DHCPv6 messages with the requesting router. The configuration
+example below demonstrates how to specify an excluded prefix within a
+prefix pool definition. The excluded prefix
+``2001:db8:1:8000:cafe:80::/72`` will be sent to a requesting router which
+includes the Prefix Exclude option in the Option Request option (ORO),
+and which is delegated a prefix from this pool.
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/48",
+               "pd-pools": [
+                   {
+                       "prefix": "2001:db8:1:8000::",
+                       "prefix-len": 48,
+                       "delegated-len": 64,
+                       "excluded-prefix": "2001:db8:1:8000:cafe:80::",
+                       "excluded-prefix-len": 72
+                   }
+               ]
+           }
+       ]
+   }
+
+.. note::
+
+    Here are some liberties and limits to the values that subnets and pools can
+    take in Kea configurations that are out of the ordinary:
+
+    +-------------------------------------------------------------------------------+---------+------------------------------------------------------------------------------------+
+    | Kea configuration case                                                        | Allowed | Comment                                                                            |
+    +===============================================================================+=========+====================================================================================+
+    | Overlapping subnets                                                           | Yes     | Administrator consideration needs to be given to how clients are matched to        |
+    |                                                                               |         | these subnets.                                                                     |
+    +-------------------------------------------------------------------------------+---------+------------------------------------------------------------------------------------+
+    | Overlapping address pools in one subnet                                       | No      | Startup error: DHCP6_PARSER_FAIL                                                   |
+    +-------------------------------------------------------------------------------+---------+------------------------------------------------------------------------------------+
+    | Overlapping address pools in different subnets                                | Yes     | Specifying the same address pool in different subnets can be used as an equivalent |
+    |                                                                               |         | of the global address pool. In that case, the server can assign addresses from the |
+    |                                                                               |         | same range regardless of the client's subnet. If an address from such a pool is    |
+    |                                                                               |         | assigned to a client in one subnet, the same address will be renewed for this      |
+    |                                                                               |         | client if it moves to another subnet. Another client in a different subnet will    |
+    |                                                                               |         | not be assigned an address already assigned to the client in any of the subnets.   |
+    +-------------------------------------------------------------------------------+---------+------------------------------------------------------------------------------------+
+    | Address pools that are outside the subnet they are configured under           | No      | Startup error: DHCP6_PARSER_FAIL                                                   |
+    +-------------------------------------------------------------------------------+---------+------------------------------------------------------------------------------------+
+    | Overlapping prefix delegation pools in one subnet                             | No      | Startup error: DHCP6_PARSER_FAIL                                                   |
+    +-------------------------------------------------------------------------------+---------+------------------------------------------------------------------------------------+
+    | Overlapping prefix delegation pools in different subnets                      | Yes     | Specifying the same prefix delegation pool in different subnets can be used as an  |
+    |                                                                               |         | equivalent of the global pool. In that case, the server can delegate the same      |
+    |                                                                               |         | prefixes regardless of the client's subnet. If a prefix from such a pool is        |
+    |                                                                               |         | delegated to a client in one subnet, the same prefix will be renewed for this      |
+    |                                                                               |         | client if it moves to another subnet. Another client in a different subnet will    |
+    |                                                                               |         | not be delegated a prefix already delegated to the client in any of the subnets.   |
+    +-------------------------------------------------------------------------------+---------+------------------------------------------------------------------------------------+
+    | Prefix delegation pools not matching the subnet prefix                        | Yes     | It is common in many deployments to configure the prefix delegation pools not      |
+    |                                                                               |         | matching the subnet prefix, e.g. a prefix pool of 3000::/96 within the             |
+    |                                                                               |         | 2001:db8:1::/64 subnet. Such use cases are supported by Kea DHCPv6 server.         |
+    +-------------------------------------------------------------------------------+---------+------------------------------------------------------------------------------------+
+
+.. _dhcp6-std-options:
+
+Standard DHCPv6 Options
+-----------------------
+
+One of the major features of the DHCPv6 server is the ability to provide
+configuration options to clients. Although there are several options
+that require special behavior, most options are sent by the server only
+if the client explicitly requests them. The following example shows how
+to configure the addresses of DNS servers, one of the most frequently used options.
+Options specified in this way are considered global and apply to all configured subnets.
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+              "name": "dns-servers",
+              "code": 23,
+              "space": "dhcp6",
+              "csv-format": true,
+              "data": "2001:db8::cafe, 2001:db8::babe"
+           },
+           ...
+       ]
+   }
+
+The ``option-data`` line creates a new entry in the option-data table.
+This table contains information on all global options that the server is
+supposed to configure in all subnets. The ``name`` line specifies the
+option name. (For a complete list of currently supported names, see
+:ref:`dhcp6-std-options-list`.) The next line specifies the
+option code, which must match one of the values from that list. The line
+beginning with ``space`` specifies the option space, which must always
+be set to ``dhcp6`` as these are standard DHCPv6 options. For other name
+spaces, including custom option spaces, see :ref:`dhcp6-option-spaces`. The following line
+specifies the format in which the data will be entered; use of CSV
+(comma-separated values) is recommended. Finally, the ``data`` line
+gives the actual value to be sent to clients. The data parameter is specified as
+normal text, with values separated by commas if more than one value is
+allowed.
+
+Options can also be configured as hexadecimal values. If ``csv-format`` is
+set to ``false``, the option data must be specified as a hexadecimal string.
+The following commands configure the ``dns-servers`` option for all subnets
+with the addresses 2001:db8:1::cafe and 2001:db8:1::babe.
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+              "name": "dns-servers",
+              "code": 23,
+              "space": "dhcp6",
+              "csv-format": false,
+              "data": "20 01 0D B8 00 01 00 00 00 00 00 00 00 00 CA FE
+                       20 01 0D B8 00 01 00 00 00 00 00 00 00 00 BA BE"
+           },
+           ...
+       ]
+   }
+
+.. note::
+
+   The value for the setting of the ``data`` element is split across two
+   lines in this example for clarity; when entering the command, the
+   whole string should be entered on the same line.
+
+Kea supports the following formats when specifying hexadecimal data:
+
+-  ``Delimited octets`` - one or more octets separated by either colons or
+   spaces (":" or " "). While each octet may contain one or two digits,
+   we strongly recommend always using two digits. Valid examples are
+   "ab:cd:ef" and "ab cd ef".
+
+-  ``String of digits`` - a continuous string of hexadecimal digits with
+   or without a "0x" prefix. Valid examples are "0xabcdef" and "abcdef".
+
+Care should be taken to use proper encoding when using hexadecimal
+format; Kea's ability to validate data correctness in hexadecimal is
+limited.
+
+It is also possible to specify data for binary options as
+a single-quoted text string within double quotes, as shown (note that
+``csv-format`` must be set to ``false``):
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+               "name": "subscriber-id",
+               "code": 38,
+               "space": "dhcp6",
+               "csv-format": false,
+               "data": "'convert this text to binary'"
+           },
+           ...
+       ],
+       ...
+   }
+
+Most of the parameters in the ``option-data`` structure are optional and
+can be omitted in some circumstances, as discussed in :ref:`dhcp6-option-data-defaults`.
+Only one of ``name`` or ``code``
+is required; it is not necessary to specify both. Space has a default value
+of ``dhcp6``, so this can be skipped as well if a regular (not
+encapsulated) DHCPv6 option is defined. Finally, ``csv-format`` defaults to ``true``, so it
+too can be skipped, unless the option value is specified as
+hexstring. Therefore, the above example can be simplified to:
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+              "name": "dns-servers",
+              "data": "2001:db8::cafe, 2001:db8::babe"
+           },
+           ...
+       ]
+   }
+
+
+Defined options are added to the response when the client requests them,
+as well as any options required by a protocol. An administrator can also
+specify that an option is always sent, even if a client did not
+specifically request it. To enforce the addition of a particular option,
+set the ``always-send`` flag to ``true``, as in:
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+              "name": "dns-servers",
+              "data": "2001:db8::cafe, 2001:db8::babe",
+              "always-send": true
+           },
+           ...
+       ]
+   }
+
+
+The effect is the same as if the client added the option code in the
+Option Request Option (or its equivalent for vendor options), as in:
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+              "name": "dns-servers",
+              "data": "2001:db8::cafe, 2001:db8::babe",
+              "always-send": true
+           },
+           ...
+       ],
+       "subnet6": [
+           {
+              "subnet": "2001:db8:1::/64",
+              "option-data": [
+                  {
+                      "name": "dns-servers",
+                      "data": "2001:db8:1::cafe, 2001:db8:1::babe"
+                  },
+                  ...
+              ],
+              ...
+           },
+           ...
+       ],
+       ...
+   }
+
+
+The ``dns-servers`` option is always added to responses (the always-send is
+"sticky"), but the value is the subnet one when the client is localized
+in the subnet.
+
+It is possible to override options on a per-subnet basis. If clients
+connected to most subnets are expected to get the same values of
+a given option, administrators should use global options; it is possible to override
+specific values for a small number of subnets. On the other hand, if
+different values are used in each subnet, it does not make sense to specify
+global option values; rather, only subnet-specific ones should be set.
+
+The following commands override the global ``dns-servers`` option for a
+particular subnet, setting a single DNS server with address
+2001:db8:1::3.
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "option-data": [
+                   {
+                       "name": "dns-servers",
+                       "code": 23,
+                       "space": "dhcp6",
+                       "csv-format": true,
+                       "data": "2001:db8:1::3"
+                   },
+                   ...
+               ],
+               ...
+           },
+           ...
+       ],
+       ...
+   }
+
+In some cases it is useful to associate some options with an address or
+prefix pool from which a client is assigned a lease. Pool-specific
+option values override subnet-specific and global option values. If the
+client is assigned multiple leases from different pools, the server
+assigns options from all pools from which the leases have been obtained.
+However, if the particular option is specified in multiple pools from
+which the client obtains the leases, only one instance of this option
+is handed out to the client. The server's administrator must not
+try to prioritize assignment of pool-specific options by trying to order
+pool declarations in the server configuration.
+
+The following configuration snippet demonstrates how to specify the
+``dns-servers`` option, which will be assigned to a client only if the client
+obtains an address from the given pool:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "pools": [
+                   {
+                       "pool": "2001:db8:1::100-2001:db8:1::300",
+                       "option-data": [
+                           {
+                               "name": "dns-servers",
+                               "data": "2001:db8:1::10"
+                           }
+                       ]
+                   }
+               ]
+           },
+           ...
+       ],
+       ...
+   }
+
+Options can also be specified in class or host-reservation scope. The
+current Kea options precedence order is (from most important): host
+reservation, pool, subnet, shared network, class, global.
+
+When a data field is a string and that string contains the comma (``,``;
+U+002C) character, the comma must be escaped with two backslashes (``\\,``;
+U+005C). This double escape is required because both the routine
+splitting CSV data into fields and JSON use the same escape character; a
+single escape (``\,``) would make the JSON invalid. For example, the string
+"EST5EDT4,M3.2.0/02:00,M11.1.0/02:00" must be represented as:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "pools": [
+                   {
+                       "option-data": [
+                           {
+                               "name": "new-posix-timezone",
+                               "data": "EST5EDT4\\,M3.2.0/02:00\\,M11.1.0/02:00"
+                           }
+                       ]
+                   },
+                   ...
+               ],
+               ...
+           },
+           ...
+       ],
+       ...
+   }
+
+Some options are designated as arrays, which means that more than one
+value is allowed. For example, the option ``dns-servers``
+allows the specification of more than one IPv6 address, enabling clients
+to obtain the addresses of multiple DNS servers.
+
+:ref:`dhcp6-custom-options` describes the
+configuration syntax to create custom option definitions (formats).
+Creation of custom definitions for standard options is generally not
+permitted, even if the definition being created matches the actual
+option format defined in the RFCs. However, there is an exception to this rule
+for standard options for which Kea currently does not provide a
+definition. To use such options, a server administrator must
+create a definition as described in :ref:`dhcp6-custom-options` in the ``dhcp6`` option space. This
+definition should match the option format described in the relevant RFC,
+but the configuration mechanism allows any option format as there is
+currently no way to validate it.
+
+The currently supported standard DHCPv6 options are listed in
+the table below. "Name" and "Code" are the
+values that should be used as a name/code in the option-data structures.
+"Type" designates the format of the data; the meanings of the various
+types are given in :ref:`dhcp-types`.
+
+.. _dhcp6-std-options-list:
+
+.. table:: List of standard DHCPv6 options configurable by an administrator
+
+   +--------------------------+-----------------+-----------------+-----------------+
+   | Name                     | Code            | Type            | Array?          |
+   +==========================+=================+=================+=================+
+   | preference               | 7               | uint8           | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | unicast                  | 12              | ipv6-address    | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | sip-server-dns           | 21              | fqdn            | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | sip-server-addr          | 22              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | dns-servers              | 23              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | domain-search            | 24              | fqdn            | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | nis-servers              | 27              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | nisp-servers             | 28              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | nis-domain-name          | 29              | fqdn            | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | nisp-domain-name         | 30              | fqdn            | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | sntp-servers             | 31              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | information-refresh-time | 32              | uint32          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | bcmcs-server-dns         | 33              | fqdn            | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | bcmcs-server-addr        | 34              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | geoconf-civic            | 36              | record (uint8,  | false           |
+   |                          |                 | uint16, binary) |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | remote-id                | 37              | record (uint32, | false           |
+   |                          |                 | binary)         |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | subscriber-id            | 38              | binary          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | client-fqdn              | 39              | record (uint8,  | false           |
+   |                          |                 | fqdn)           |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | pana-agent               | 40              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | new-posix-timezone       | 41              | string          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | new-tzdb-timezone        | 42              | string          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | ero                      | 43              | uint16          | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | lq-query (1)             | 44              | record (uint8,  | false           |
+   |                          |                 | ipv6-address)   |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | client-data (1)          | 45              | empty           | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | clt-time (1)             | 46              | uint32          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | lq-relay-data (1)        | 47              | record          | false           |
+   |                          |                 | (ipv6-address,  |                 |
+   |                          |                 | binary)         |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | lq-client-link (1)       | 48              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | v6-lost                  | 51              | fqdn            | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | capwap-ac-v6             | 52              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | relay-id                 | 53              | binary          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | v6-access-domain         | 57              | fqdn            | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | sip-ua-cs-list           | 58              | fqdn            | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | bootfile-url             | 59              | string          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | bootfile-param           | 60              | tuple           | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | client-arch-type         | 61              | uint16          | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | nii                      | 62              | record (uint8,  | false           |
+   |                          |                 | uint8, uint8)   |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | aftr-name                | 64              | fqdn            | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | erp-local-domain-name    | 65              | fqdn            | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | rsoo                     | 66              | empty           | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | pd-exclude               | 67              | binary          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | rdnss-selection          | 74              | record          | true            |
+   |                          |                 | (ipv6-address,  |                 |
+   |                          |                 | uint8, fqdn)    |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | client-linklayer-addr    | 79              | binary          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | link-address             | 80              | ipv6-address    | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | solmax-rt                | 82              | uint32          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | inf-max-rt               | 83              | uint32          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | dhcp4o6-server-addr      | 88              | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | s46-rule                 | 89              | record (uint8,  | false           |
+   |                          |                 | uint8, uint8,   |                 |
+   |                          |                 | ipv4-address,   |                 |
+   |                          |                 | ipv6-prefix)    |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | s46-br                   | 90              | ipv6-address    | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | s46-dmr                  | 91              | ipv6-prefix     | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | s46-v4v6bind             | 92              | record          | false           |
+   |                          |                 | (ipv4-address,  |                 |
+   |                          |                 | ipv6-prefix)    |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | s46-portparams           | 93              | record(uint8,   | false           |
+   |                          |                 | psid)           |                 |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | s46-cont-mape            | 94              | empty           | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | s46-cont-mapt            | 95              | empty           | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | s46-cont-lw              | 96              | empty           | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | v6-captive-portal        | 103             | string          | false           |
+   +--------------------------+-----------------+-----------------+-----------------+
+   | ipv6-address-andsf       | 143             | ipv6-address    | true            |
+   +--------------------------+-----------------+-----------------+-----------------+
+
+Options marked with (1) have option definitions, but the logic behind
+them is not implemented. That means that, technically, Kea knows how to
+parse them in incoming messages or how to send them if configured to do
+so, but not what to do with them. Since the related RFCs require certain
+processing, the support for those options is non-functional. However, it
+may be useful in some limited lab testing; hence the definition formats
+are listed here.
+
+Kea supports more options than those listed above. The following list is mostly useful for readers who
+want to understand whether Kea is able to support certain options. The following options are
+returned by the Kea engine itself and in general should not be configured manually.
+
+.. table:: List of standard DHCPv6 options managed by Kea on its own and not directly configurable by an administrator
+
+   +--------------+------+------------------------------------------------------------------------+
+   | Name         | Code | Description                                                            |
+   +==============+======+========================================================================+
+   | client-id    | 1    | Sent by the client; Kea uses it to distinguish between clients.        |
+   +--------------+------+------------------------------------------------------------------------+
+   | server-id    | 2    | Sent by clients to request action from a specific server and by the    |
+   |              |      | server to identify itself. See :ref:`dhcp6-serverid` for details.      |
+   +--------------+------+------------------------------------------------------------------------+
+   | ia-na        | 3    | A container option that conveys IPv6 addresses (``iaddr`` options). Kea|
+   |              |      | receives and sends those options using its allocation engine.          |
+   +--------------+------+------------------------------------------------------------------------+
+   | ia-ta        | 4    | Conveys temporary addresses. Deprecated feature, not supported.        |
+   +--------------+------+------------------------------------------------------------------------+
+   | iaaddr       | 5    | Conveys addresses with lifetimes in ``ia-na`` and ``ia-ta`` options.   |
+   +--------------+------+------------------------------------------------------------------------+
+   | oro          | 6    | ORO (or Option Request Option) is used by clients to request a list    |
+   |              |      | of options they are interested in. Kea supports it and sends the       |
+   |              |      | requested options back if configured with required options.            |
+   +--------------+------+------------------------------------------------------------------------+
+   | elapsed-time | 8    | Sent by clients to identify how long they have been trying to obtain a |
+   |              |      | configuration. Kea uses high values sent by clients as an indicator    |
+   |              |      | that something is wrong; this is one of the aspects used in HA to      |
+   |              |      | determine if the partner is healthy or not.                            |
+   +--------------+------+------------------------------------------------------------------------+
+   | relay-msg    | 9    | Used by relays to encapsulate the original client message. Kea uses it |
+   |              |      | when sending back relayed responses to the relay agent.                |
+   +--------------+------+------------------------------------------------------------------------+
+   | auth         | 11   | Used to pass authentication information between clients and server. The|
+   |              |      | support for this option is very limited.                               |
+   +--------------+------+------------------------------------------------------------------------+
+   | status-code  | 13   | An option that the server can attach in case of various failures, such |
+   |              |      | as running out of addresses or not being configured to assign prefixes.|
+   +--------------+------+------------------------------------------------------------------------+
+   | rapid-commit | 14   | Used to signal the client's willingness to support ``rapid-commit`` and|
+   |              |      | the server's acceptance for this configuration. See                    |
+   |              |      | :ref:`dhcp6-rapid-commit` for details.                                 |
+   +--------------+------+------------------------------------------------------------------------+
+   | user-class   | 15   | Sent by the client to self-identify the device type. Kea               |
+   |              |      | can use this for client classification.                                |
+   +--------------+------+------------------------------------------------------------------------+
+   | vendor-class | 16   | Similar to ``user-class``, but vendor-specific.                        |
+   +--------------+------+------------------------------------------------------------------------+
+   | vendor-opts  | 17   | A vendor-specific container that is used by both the client and the    |
+   |              |      | server to exchange vendor-specific options. The logic behind those     |
+   |              |      | options varies between vendors. Vendor options are explained in        |
+   |              |      | :ref:`dhcp6-vendor-opts`.                                              |
+   +--------------+------+------------------------------------------------------------------------+
+   | interface-id | 18   | May be inserted by the relay agent to identify the interface that the  |
+   |              |      | original client message was received on. Kea may be told to use this   |
+   |              |      | information to select specific subnets. Also, if specified, Kea        |
+   |              |      | echoes this option back, so the relay will know which interface to use |
+   |              |      | to reach the client.                                                   |
+   +--------------+------+------------------------------------------------------------------------+
+   | ia-pd        | 25   | A container for conveying Prefix Delegations (PDs)) that are being     |
+   |              |      | delegated to clients. See :ref:`dhcp6-prefix-config` for details.      |
+   +--------------+------+------------------------------------------------------------------------+
+   | iaprefix     | 26   | Conveys the IPv6 prefix in the ``ia-pd`` option. See                   |
+   |              |      | :ref:`dhcp6-prefix-config` for details.                                |
+   +--------------+------+------------------------------------------------------------------------+
+
+.. _s46-options:
+
+Common Softwire46 Options
+-------------------------
+
+Softwire46 options are involved in IPv4-over-IPv6 provisioning by means
+of tunneling or translation, as specified in `RFC
+7598 <https://tools.ietf.org/html/rfc7598>`__. The following sections
+provide configuration examples of these options.
+
+.. _s46-containers:
+
+Softwire46 Container Options
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Softwire46 (S46) container options group rules and optional port parameters for a
+specified domain. There are three container options specified in the
+"dhcp6" (top-level) option space: the MAP-E Container option, the MAP-T
+Container option, and the S46 Lightweight 4over6 Container option. These
+options only contain the encapsulated options specified below; they do not
+include any data fields.
+
+To configure the server to send a specific container option along with
+all encapsulated options, the container option must be included in the
+server configuration as shown below:
+
+::
+
+   "Dhcp6": {
+       ...
+       "option-data": [
+           {
+               "name": "s46-cont-mape"
+           } ],
+       ...
+   }
+
+This configuration will cause the server to include the MAP-E Container
+option to the client. Use ``s46-cont-mapt`` or ``s46-cont-lw`` for the MAP-T
+Container and S46 Lightweight 4over6 Container options, respectively.
+
+All remaining Softwire46 options described below are included in one of
+the container options. Thus, they must be included in appropriate
+option spaces by selecting a ``space`` name, which specifies the
+option where they are supposed to be included.
+
+S46 Rule Option
+~~~~~~~~~~~~~~~
+
+The S46 Rule option is used to convey the Basic Mapping Rule (BMR)
+and Forwarding Mapping Rule (FMR).
+
+::
+
+   {
+       "space": "s46-cont-mape-options",
+       "name": "s46-rule",
+       "data": "128, 0, 24, 192.0.2.0, 2001:db8:1::/64"
+   }
+
+Another possible ``space`` value is ``s46-cont-mapt-options``.
+
+The S46 Rule option conveys a number of parameters:
+
+-  ``flags`` - an unsigned 8-bit integer, with currently only the
+   most-significant bit specified. It denotes whether the rule can be
+   used for forwarding (128) or not (0).
+
+-  ``ea-len`` - an 8-bit-long Embedded Address length. Allowed values
+   range from 0 to 48.
+
+-  ``IPv4 prefix length`` - an 8-bit-long expression of the prefix length of
+   the Rule IPv4 prefix specified in the ``ipv4-prefix`` field. Allowed
+   values range from 0 to 32.
+
+-  ``IPv4 prefix`` - a fixed-length 32-bit field that specifies the IPv4
+   prefix for the S46 rule. The bits in the prefix after
+   a specific number of bits (defined in ``prefix4-len``) are reserved, and MUST
+   be initialized to zero by the sender and ignored by the receiver.
+
+-  ``IPv6 prefix`` - a field in prefix/length notation that specifies the IPv6
+   domain prefix for the S46 rule. The field is padded on the right with
+   zero bits up to the nearest octet boundary, when ``prefix6-len`` is not
+   evenly divisible by 8.
+
+S46 BR Option
+~~~~~~~~~~~~~
+
+The S46 BR option is used to convey the IPv6 address of the Border
+Relay. This option is mandatory in the MAP-E Container option and is not
+permitted in the MAP-T and S46 Lightweight 4over6 Container options.
+
+::
+
+   {
+       "space": "s46-cont-mape-options",
+       "name": "s46-br",
+       "data": "2001:db8:cafe::1",
+   }
+
+Another possible ``space`` value is ``s46-cont-lw-options``.
+
+S46 DMR Option
+~~~~~~~~~~~~~~
+
+The S46 DMR option is used to convey values for the Default Mapping Rule
+(DMR). This option is mandatory in the MAP-T container option and is not
+permitted in the MAP-E and S46 Lightweight 4over6 Container options.
+
+::
+
+   {
+       "space": "s46-cont-mapt-options",
+       "name": "s46-dmr",
+       "data": "2001:db8:cafe::/64",
+   }
+
+This option must not be included in other containers.
+
+S46 IPv4/IPv6 Address Binding Option
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The S46 IPv4/IPv6 Address Binding option may be used to specify the full
+or shared IPv4 address of the Customer Edge (CE). The IPv6 prefix field
+is used by the CE to identify the correct prefix to use for the tunnel
+source.
+
+::
+
+   {
+       "space": "s46-cont-lw",
+       "name": "s46-v4v6bind",
+       "data": "192.0.2.3, 2001:db8:1:cafe::/64"
+   }
+
+This option must not be included in other containers.
+
+S46 Port Parameters
+~~~~~~~~~~~~~~~~~~~
+
+The S46 Port Parameters option specifies optional port-set information
+that may be provided to CEs.
+
+::
+
+   {
+       "space": "s46-rule-options",
+       "name": "s46-portparams",
+       "data": "2, 3/4",
+   }
+
+Another possible ``space`` value is ``s46-v4v6bind``, to include this option
+in the S46 IPv4/IPv6 Address Binding option.
+
+Note that the second value in the example above specifies the PSID and
+PSID-length fields in the format of PSID/PSID length. This is equivalent
+to the values of ``PSID-len=4`` and ``PSID=12288`` conveyed in the S46 Port
+Parameters option.
+
+.. _dhcp6-custom-options:
+
+Custom DHCPv6 Options
+---------------------
+
+Kea supports custom (non-standard) DHCPv6 options.
+Let's say that we want to define a new DHCPv6 option called ``foo``, which
+will have code 100 and will convey a single, unsigned, 32-bit
+integer value. Such an option can be defined by putting the following entry
+in the configuration file:
+
+::
+
+   "Dhcp6": {
+       "option-def": [
+           {
+               "name": "foo",
+               "code": 100,
+               "type": "uint32",
+               "array": false,
+               "record-types": "",
+               "space": "dhcp6",
+               "encapsulate": ""
+           }, ...
+       ],
+       ...
+   }
+
+The ``false`` value of the ``array`` parameter determines that the option
+does NOT comprise an array of ``uint32`` values but is, instead, a single
+value. Two other parameters have been left blank: ``record-types`` and
+``encapsulate``. The former specifies the comma-separated list of option
+data fields, if the option comprises a record of data fields. The
+``record-types`` value should be non-empty if ``type`` is set to
+``record``; otherwise it must be left blank. The latter parameter
+specifies the name of the option space being encapsulated by the
+particular option. If the particular option does not encapsulate any
+option space, the parameter should be left blank. Note that the ``option-def``
+configuration statement only defines the format of an option and does
+not set its value(s).
+
+The ``name``, ``code``, and ``type`` parameters are required; all
+others are optional. The ``array`` default value is ``false``. The
+``record-types`` and ``encapsulate`` default values are blank (``""``).
+The default ``space`` is ``dhcp6``.
+
+Once the new option format is defined, its value is set in the same way
+as for a standard option. For example, the following commands set a
+global value that applies to all subnets.
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+               "name": "foo",
+               "code": 100,
+               "space": "dhcp6",
+               "csv-format": true,
+               "data": "12345"
+           }, ...
+       ],
+       ...
+   }
+
+New options can take more complex forms than the simple use of primitives
+(uint8, string, ipv6-address, etc.); it is possible to define an option
+comprising a number of existing primitives.
+
+For example, say we want to define a new option that will consist of
+an IPv6 address, followed by an unsigned 16-bit integer, followed by a
+boolean value, followed by a text string. Such an option could be
+defined in the following way:
+
+::
+
+   "Dhcp6": {
+       "option-def": [
+           {
+               "name": "bar",
+               "code": 101,
+               "space": "dhcp6",
+               "type": "record",
+               "array": false,
+               "record-types": "ipv6-address, uint16, boolean, string",
+               "encapsulate": ""
+           }, ...
+       ],
+       ...
+   }
+
+The ``type`` is set to ``record`` to indicate that the option contains
+multiple values of different types. These types are given as a
+comma-separated list in the ``record-types`` field and should be ones
+from those listed in :ref:`dhcp-types`.
+
+The values of the options are set in an ``option-data`` statement as
+follows:
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+               "name": "bar",
+               "space": "dhcp6",
+               "code": 101,
+               "csv-format": true,
+               "data": "2001:db8:1::10, 123, false, Hello World"
+           }
+       ],
+       ...
+   }
+
+``csv-format`` is set to ``true`` to indicate that the ``data`` field
+comprises a comma-separated list of values. The values in ``data``
+must correspond to the types set in the ``record-types`` field of the
+option definition.
+
+When ``array`` is set to ``"true"`` and ``type`` is set to ``"record"``, the
+last field is an array, i.e. it can contain more than one value, as in:
+
+::
+
+   "Dhcp6": {
+       "option-def": [
+           {
+               "name": "bar",
+               "code": 101,
+               "space": "dhcp6",
+               "type": "record",
+               "array": true,
+               "record-types": "ipv6-address, uint16",
+               "encapsulate": ""
+           }, ...
+       ],
+       ...
+   }
+
+The new option content is one IPv6 address followed by one or more 16-bit
+unsigned integers.
+
+.. note::
+
+   In general, boolean values are specified as ``true`` or ``false``,
+   without quotes. Some specific boolean parameters may also accept
+   ``"true"``, ``"false"``, ``0``, ``1``, ``"0"``, and ``"1"``.
+
+.. _dhcp6-vendor-opts:
+
+DHCPv6 Vendor-Specific Options
+------------------------------
+
+Vendor options in DHCPv6 are carried in the Vendor-Specific
+Information option (code 17). The idea behind option 17
+is that each vendor has its own unique set of options with their own custom
+formats. The vendor is identified by a 32-bit unsigned integer called
+``enterprise-number`` or ``vendor-id``.
+
+The standard spaces defined in Kea and their options are:
+
+- ``vendor-2495``: Internet Systems Consortium, Inc. for 4o6 options:
+
++-------------+--------------------+------------------------------------------------------------------------+
+| option code | option name        | option description                                                     |
++=============+====================+========================================================================+
+| 60000       | 4o6-interface      | the name of the 4o6 server's client-facing interface                   |
++-------------+--------------------+------------------------------------------------------------------------+
+| 60001       | 4o6-source-address | the address that the 4o6 server uses to send packets to the client     |
++-------------+--------------------+------------------------------------------------------------------------+
+| 60002       | 4o6-source-port    | the port that the 4o6 server opens to send packets to the client       |
++-------------+--------------------+------------------------------------------------------------------------+
+
+- ``vendor-4491``: Cable Television Laboratories, Inc. for DOCSIS3 options:
+
++-------------+--------------------+------------------------------------------------------------------------+
+| option code | option name        | option description                                                     |
++=============+====================+========================================================================+
+| 1           | oro                | ORO (or Option Request Option) is used by clients to request a list of |
+|             |                    | options they are interested in.                                        |
++-------------+--------------------+------------------------------------------------------------------------+
+| 2           | tftp-servers       | a list of IPv4 addresses of TFTP servers to be used by the cable modem |
++-------------+--------------------+------------------------------------------------------------------------+
+
+The following examples show how to
+define an option ``"foo"`` with code 1 that consists of an IPv6 address,
+an unsigned 16-bit integer, and a string.  The ``"foo"`` option is
+conveyed in a Vendor-Specific Information option, which comprises a
+single uint32 value that is set to ``12345``. The sub-option ``"foo"``
+follows the data field holding this value.
+
+The first step is to define the format of the option:
+
+::
+
+   "Dhcp6": {
+       "option-def": [
+           {
+               "name": "foo",
+               "code": 1,
+               "space": "vendor-12345",
+               "type": "record",
+               "array": false,
+               "record-types": "ipv6-address, uint16, string",
+               "encapsulate": ""
+           }
+       ],
+       ...
+   }
+
+(Note that the option space is set to ``"vendor-12345"``.) Once the
+option format is defined, the next step is to define actual values for
+that option:
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+               "name": "foo",
+               "space": "vendor-12345",
+               "data": "2001:db8:1::10, 123, Hello World"
+           },
+           ...
+       ],
+       ...
+   }
+
+We should also define a value (``"enterprise-number"``) for the
+Vendor-Specific Information option, to convey the option ``foo``.
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           ...,
+           {
+               "name": "vendor-opts",
+               "data": "12345"
+           }
+       ],
+       ...
+   }
+
+Alternatively, the option can be specified using its code.
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           ...,
+           {
+               "code": 17,
+               "data": "12345"
+           }
+       ],
+       ...
+   }
+
+A common configuration is to set the ``always-send`` flag to ``true``, so the
+vendor option is sent even when the client did not specify it in the query.
+
+.. note::
+
+   Only a single instance of the ``vendor-class`` (code 16) and
+   a single instance of the ``vendor-opts`` (code 17) options can be
+   specified. Specifying multiple options with different enterprise
+   numbers is currently not supported by Kea.
+
+.. _dhcp6-option-spaces:
+
+Nested DHCPv6 Options (Custom Option Spaces)
+--------------------------------------------
+
+It is sometimes useful to define a completely new option space, such as
+when a user creates a new option to convey sub-options that
+use a separate numbering scheme, such as sub-options with codes 1
+and 2. Those option codes conflict with standard DHCPv6 options, so a
+separate option space must be defined.
+
+Note that the creation of a new option space is not required when
+defining sub-options for a standard option, because one is created by
+default if the standard option is meant to convey any sub-options (see
+:ref:`dhcp6-vendor-opts`).
+
+If we want a DHCPv6 option called ``container`` with code
+102, that conveys two sub-options with codes 1 and 2, we first need to
+define the new sub-options:
+
+::
+
+   "Dhcp6": {
+       "option-def": [
+           {
+               "name": "subopt1",
+               "code": 1,
+               "space": "isc",
+               "type": "ipv6-address",
+               "record-types": "",
+               "array": false,
+               "encapsulate": ""
+           },
+           {
+               "name": "subopt2",
+               "code": 2,
+               "space": "isc",
+               "type": "string",
+               "record-types": "",
+               "array": false
+               "encapsulate": ""
+           }
+       ],
+       ...
+   }
+
+Note that we have defined the options to belong to a new option space
+(in this case, ``"isc"``).
+
+The next step is to define a regular DHCPv6 option with the desired code
+and specify that it should include options from the new option space:
+
+::
+
+   "Dhcp6": {
+       "option-def": [
+           ...,
+           {
+               "name": "container",
+               "code": 102,
+               "space": "dhcp6",
+               "type": "empty",
+               "array": false,
+               "record-types": "",
+               "encapsulate": "isc"
+           }
+       ],
+       ...
+   }
+
+The name of the option space in which the sub-options are defined is set
+in the ``encapsulate`` field. The ``type`` field is set to ``"empty"``,
+to indicate that this option does not carry any data other than
+sub-options.
+
+Finally, we can set values for the new options:
+
+::
+
+   "Dhcp6": {
+       "option-data": [
+           {
+               "name": "subopt1",
+               "code": 1,
+               "space": "isc",
+               "data": "2001:db8::abcd"
+           },
+           }
+               "name": "subopt2",
+               "code": 2,
+               "space": "isc",
+               "data": "Hello world"
+           },
+           {
+               "name": "container",
+               "code": 102,
+               "space": "dhcp6"
+           }
+       ],
+       ...
+   }
+
+It is possible to create an option which carries some data in
+addition to the sub-options defined in the encapsulated option space.
+For example, if the ``container`` option from the previous example were
+required to carry a uint16 value as well as the sub-options, the
+``type`` value would have to be set to ``"uint16"`` in the option
+definition. (Such an option would then have the following data
+structure: DHCP header, uint16 value, sub-options.) The value specified
+with the ``data`` parameter — which should be a valid integer enclosed
+in quotes, e.g. ``"123"`` — would then be assigned to the ``uint16`` field in
+the ``container`` option.
+
+.. _dhcp6-option-data-defaults:
+
+Unspecified Parameters for DHCPv6 Option Configuration
+------------------------------------------------------
+
+In many cases it is not required to specify all parameters for an option
+configuration, and the default values can be used. However, it is
+important to understand the implications of not specifying some of them,
+as it may result in configuration errors. The list below explains the
+behavior of the server when a particular parameter is not explicitly
+specified:
+
+-  ``name`` - the server requires either an option name or an option code to
+   identify an option. If this parameter is unspecified, the option code
+   must be specified.
+
+-  ``code`` - the server requires either an option name or an option code to
+   identify an option; this parameter may be left unspecified if the
+   ``name`` parameter is specified. However, this also requires that the
+   particular option have a definition (either as a standard option or
+   an administrator-created definition for the option using an
+   ``option-def`` structure), as the option definition associates an
+   option with a particular name. It is possible to configure an option
+   for which there is no definition (unspecified option format).
+   Configuration of such options requires the use of the option code.
+
+-  ``space`` - if the option space is unspecified it defaults to
+   ``dhcp6``, which is an option space holding standard DHCPv6 options.
+
+-  ``data`` - if the option data is unspecified it defaults to an empty
+   value. The empty value is mostly used for the options which have no
+   payload (boolean options), but it is legal to specify empty values
+   for some options which carry variable-length data and for which the
+   specification allows a length of 0. For such options, the data
+   parameter may be omitted in the configuration.
+
+-  ``csv-format`` - if this value is not specified, the server
+   assumes that the option data is specified as a list of comma-separated
+   values to be assigned to individual fields of the DHCP option.
+
+.. _dhcp6-t1-t2-times:
+
+Controlling the Values Sent for T1 and T2 Times
+-----------------------------------------------
+
+According to RFC 8415, section 21.4, the recommended T1 and T2 values
+are 50% and 80% of the preferred
+lease time, respectively. Kea can be configured to send values that are
+specified explicitly or that are calculated as percentages of the
+preferred lease time. The server's behavior is determined by a combination
+of configuration parameters, of which T1 and T2 are only two.
+
+The lease's preferred and valid lifetimes are expressed as triplets with
+minimum, default, and maximum values using configuration entries:
+
+- ``min-preferred-lifetime`` - specifies the minimum preferred lifetime (optional).
+
+- ``preferred-lifetime`` - specifies the default preferred lifetime.
+
+- ``max-preferred-lifetime`` - specifies the maximum preferred lifetime (optional).
+
+- ``min-valid-lifetime`` - specifies the minimum valid lifetime (optional).
+
+- ``valid-lifetime`` - specifies the default valid lifetime.
+
+- ``max-valid-lifetime`` - specifies the maximum valid lifetime (optional).
+
+Since Kea 1.9.11, these values may be specified within client classes.
+
+When the client does not specify lifetimes, the default is used.
+A specified lifetime - using the IAADDR or IAPREFIX sub-option with
+non-zero values - uses these values when they are between the configured
+minimum and maximum bounds. Values outside the bounds are rounded up or down as
+needed.
+
+To send specific fixed values, use the following two parameters:
+
+-  ``renew-timer`` - specifies the value of T1 in seconds.
+
+-  ``rebind-timer`` - specifies the value of T2 in seconds.
+
+Any value greater than or equal to zero may be specified for T2.
+T1, if specified, must be less than T2. This flexibility allows
+a use case where administrators want to suppress client renewals and
+rebinds by deferring them beyond the lifespan of the lease. This should
+cause the lease to expire, rather than get renewed by clients. If T1 is
+specified as larger than T2, T1 is silently set to zero in the outbound IA.
+
+In the great majority of cases, the values should follow this rule: T1 < T2 <
+preferred lifetime < valid lifetime. Alternatively, both T1 and T2
+values can be configured to 0, which is a signal to DHCPv6 clients that
+they may renew at their own discretion. However, there are known broken
+client implementations in use that will start renewing immediately.
+Administrators who plan to use T1=T2=0 values should test first and make sure
+their clients behave rationally.
+
+In some rare cases there may be a need to disable a client's ability to
+renew addresses. This is undesired from a protocol perspective and should
+be avoided if possible. However, if necessary, administrators can
+configure the T1 and T2 values to be equal or greater to the valid
+lifetime. Be advised that this will cause clients to occasionally
+lose their addresses, which is generally perceived as poor service.
+However, there may be some rare business cases when this is desired
+(e.g. when it is desirable to intentionally break long-lasting connections).
+
+Calculation of the values is controlled by the following three parameters:
+
+-  ``calculate-tee-times`` - when ``true``, T1 and T2 are calculated as
+   percentages of the valid lease time. It defaults to ``true``.
+
+-  ``t1-percent`` - the percentage of the valid lease time to use for
+   T1. It is expressed as a real number between 0.0 and 1.0 and must be
+   less than ``t2-percent``. The default value is 0.5, per RFC 8415.
+
+-  ``t2-percent`` - the percentage of the valid lease time to use for
+   T2. It is expressed as a real number between 0.0 and 1.0 and must be
+   greater than ``t1-percent``. The default value is 0.8 per RFC 8415.
+
+.. note::
+
+   If both explicit values are specified and
+   ``calculate-tee-times`` is ``true``, the server will use the explicit values.
+   Administrators with a setup where some subnets or shared-networks
+   use explicit values and some use calculated values must
+   not define the explicit values at any level higher than where they
+   will be used. Inheriting them from too high a scope, such as
+   global, will cause them to have values at every level underneath
+   (both shared-networks and subnets), effectively disabling calculated
+   values.
+
+.. _dhcp6-config-subnets:
+
+IPv6 Subnet Selection
+---------------------
+
+The DHCPv6 server may receive requests from local (connected to the same
+subnet as the server) and remote (connected via relays) clients. As the
+server may have many subnet configurations defined, it must select an
+appropriate subnet for a given request.
+
+In IPv4, the server can determine which of the configured subnets are
+local, as there is a reasonable expectation that the server will have a
+(global) IPv4 address configured on the interface. That assumption is not
+true in IPv6; the DHCPv6 server must be able to operate while only using
+link-local addresses. Therefore, an optional ``interface`` parameter is
+available within a subnet definition to designate that a given subnet is
+local, i.e. reachable directly over the specified interface. For
+example, a server that is intended to serve a local subnet over eth0
+may be configured as follows:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "subnet": "2001:db8:beef::/48",
+               "pools": [
+                    {
+                        "pool": "2001:db8:beef::/48"
+                    }
+                ],
+               "interface": "eth0"
+           }
+       ],
+       ...
+   }
+
+.. _dhcp6-rapid-commit:
+
+Rapid Commit
+------------
+
+The Rapid Commit option, described in `RFC
+8415 <https://tools.ietf.org/html/rfc8415>`__, is supported by the Kea
+DHCPv6 server. However, support is disabled by default. It can be
+enabled on a per-subnet basis using the ``rapid-commit`` parameter as
+shown below:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "subnet": "2001:db8:beef::/48",
+               "rapid-commit": true,
+               "pools": [
+                    {
+                        "pool": "2001:db8:beef::1-2001:db8:beef::10"
+                    }
+                ],
+           }
+       ],
+       ...
+   }
+
+This setting only affects the subnet for which ``rapid-commit`` is
+set to ``true``. For clients connected to other subnets, the server
+ignores the Rapid Commit option sent by the client and follows the
+4-way exchange procedure, i.e. responds with an Advertise for a Solicit
+containing a Rapid Commit option.
+
+.. _dhcp6-relays:
+
+DHCPv6 Relays
+-------------
+
+A DHCPv6 server with multiple subnets defined must select the
+appropriate subnet when it receives a request from a client. For clients
+connected via relays, two mechanisms are used:
+
+The first uses the ``linkaddr`` field in the ``RELAY_FORW`` message. The name of
+this field is somewhat misleading in that it does not contain a
+link-layer address; instead, it holds an address (typically a global
+address) that is used to identify a link. The DHCPv6 server checks to
+see whether the address belongs to a defined subnet and, if it does,
+that subnet is selected for the client's request.
+
+The second mechanism is based on ``interface-id`` options. While forwarding
+a client's message, relays may insert an ``interface-id`` option into the
+message that identifies the interface on the relay that received the
+message. (Some relays allow configuration of that parameter, but it is
+sometimes hard-coded and may range from the very simple [e.g. "vlan100"]
+to the very cryptic; one example seen on real hardware was
+"ISAM144|299|ipv6|nt:vp:1:110".) The server can use this information to
+select the appropriate subnet. The information is also returned to the
+relay, which then knows the interface to use to transmit the response to
+the client. For this to work successfully, the relay interface IDs must
+be unique within the network and the server configuration must match
+those values.
+
+When configuring the DHCPv6 server, two
+similarly named parameters can be configured for a subnet:
+
+-  ``interface`` - defines which local network interface can be used to
+   access a given subnet.
+
+-  ``interface-id`` - specifies the content of the ``interface-id`` option
+   used by relays to identify the interface on the relay to which the
+   response packet is sent.
+
+The two are mutually exclusive; a subnet cannot be reachable both
+locally (direct traffic) and via relays (remote traffic). Specifying
+both is a configuration error and the DHCPv6 server will refuse such a
+configuration.
+
+The following example configuration shows how to specify an ``interface-id``
+with a value of "vlan123":
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "subnet": "2001:db8:beef::/48",
+               "pools": [
+                    {
+                        "pool": "2001:db8:beef::/48"
+                    }
+                ],
+               "interface-id": "vlan123"
+           }
+       ],
+       ...
+   }
+
+.. _dhcp6-rsoo:
+
+Relay-Supplied Options
+----------------------
+
+`RFC 6422 <https://tools.ietf.org/html/rfc6422>`__ defines a mechanism
+called Relay-Supplied DHCP Options. In certain cases relay agents are
+the only entities that may have specific information, and they can
+insert options when relaying messages from the client to the server. The
+server then does certain checks and copies those options to the
+response sent to the client.
+
+There are certain conditions that must be met for the option to be
+included. First, the server must not provide the option itself; in other
+words, if both relay and server provide an option, the server always
+takes precedence. Second, the option must be RSOO-enabled. (RSOO is the
+"Relay Supplied Options option.") IANA maintains a list of RSOO-enabled
+options
+`here <https://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-parameters.xhtml#options-relay-supplied>`__.
+However, there may be cases when system administrators want to echo
+other options. Kea can be instructed to treat other options as
+RSOO-enabled; for example, to mark options 110, 120, and 130 as
+RSOO-enabled, the following syntax should be used:
+
+::
+
+   "Dhcp6": {
+       "relay-supplied-options": [ "110", "120", "130" ],
+       ...
+   }
+
+At this time, only option 65 is RSOO-enabled by IANA. This option
+will always be treated as RSOO-enabled, so there is no need to explicitly mark
+it. When enabling standard options, it is also possible to use their
+names rather than their option code, e.g. use ``dns-servers`` instead of
+``23``. See ref:`dhcp6-std-options-list` for the names. In
+certain cases this may also work for custom options, but due to the
+nature of the parser code this may be unreliable and should be avoided.
+
+.. _dhcp6-client-classifier:
+
+Client Classification in DHCPv6
+-------------------------------
+
+The DHCPv6 server includes support for client classification. For a
+deeper discussion of the classification process, see :ref:`classify`.
+
+In certain cases it is useful to configure the server to differentiate
+between DHCP client types and treat them accordingly. Client
+classification can be used to modify the behavior of almost any part of
+DHCP message processing. Kea currently offers
+three mechanisms that take advantage of client classification in DHCPv6:
+subnet selection, address pool selection, and DHCP options assignment.
+
+Kea can be instructed to limit access to given subnets based on class
+information. This is particularly useful for cases where two types of
+devices share the same link and are expected to be served from two
+different subnets. The primary use case for such a scenario is cable
+networks, where there are two classes of devices: the cable modem
+itself, which should be handed a lease from subnet A; and all other
+devices behind the modem, which should get leases from subnet B. That
+segregation is essential to prevent overly curious end-users from playing
+with their cable modems. For details on how to set up class restrictions
+on subnets, see :ref:`classification-subnets`.
+
+When subnets belong to a shared network, the classification applies to
+subnet selection but not to pools; that is, a pool in a subnet limited to a
+particular class can still be used by clients which do not belong to the
+class, if the pool they are expected to use is exhausted. The limit
+on access based on class information is also available at the
+address/prefix pool level within a subnet: see :ref:`classification-pools`.
+This is useful when segregating clients belonging to the same
+subnet into different address ranges.
+
+In a similar way, a pool can be constrained to serve only known clients,
+i.e. clients which have a reservation, using the built-in ``KNOWN`` or
+``UNKNOWN`` classes. Addresses can be assigned to registered clients
+without giving a different address per reservation: for instance, when
+there are not enough available addresses. The determination whether
+there is a reservation for a given client is made after a subnet is
+selected, so it is not possible to use ``KNOWN``/``UNKNOWN`` classes to select a
+shared network or a subnet.
+
+The process of classification is conducted in five steps. The first step
+is to assess an incoming packet and assign it to zero or more classes.
+The second step is to choose a subnet, possibly based on the class
+information. When the incoming packet is in the special class ``DROP``,
+it is dropped and a debug message logged.
+The next step is to evaluate class expressions depending on the built-in
+``KNOWN``/``UNKNOWN`` classes after host reservation lookup, using them for
+pool/pd-pool selection and assigning classes from host reservations. The
+list of required classes is then built and each class of the list has
+its expression evaluated; when it returns ``true``, the packet is added as
+a member of the class. The last step is to assign options, again possibly
+based on the class information. More complete and detailed information
+is available in :ref:`classify`.
+
+There are two main methods of classification. The first is automatic and
+relies on examining the values in the vendor class options or the
+existence of a host reservation. Information from these options is
+extracted, and a class name is constructed from it and added to the
+class list for the packet. The second method specifies an expression that is
+evaluated for each packet. If the result is ``true``, the packet is a
+member of the class.
+
+.. note::
+
+   The new ``early-global-reservations-lookup`` global parameter flag
+   enables a lookup for global reservations before the subnet selection
+   phase. This lookup is similar to the general lookup described above
+   with two differences:
+
+   - the lookup is limited to global host reservations
+
+   - the ``UNKNOWN`` class is never set
+
+.. note::
+
+   Care should be taken with client classification, as it is easy for
+   clients that do not meet class criteria to be denied all service.
+
+Defining and Using Custom Classes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following example shows how to configure a class using an expression
+and a subnet using that class. This configuration defines the class
+named ``Client_enterprise``. It is comprised of all clients whose client
+identifiers start with the given hex string (which would indicate a DUID
+based on an enterprise id of 0xAABBCCDD). Members of this class will be given an address
+from 2001:db8:1::0 to 2001:db8:1::FFFF and the addresses of their DNS
+servers set to 2001:db8:0::1 and 2001:db8:2::1.
+
+::
+
+   "Dhcp6": {
+       "client-classes": [
+           {
+               "name": "Client_enterprise",
+               "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD",
+               "option-data": [
+                   {
+                       "name": "dns-servers",
+                       "code": 23,
+                       "space": "dhcp6",
+                       "csv-format": true,
+                       "data": "2001:db8:0::1, 2001:db8:2::1"
+                   }
+               ]
+           },
+           ...
+       ],
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/64",
+               "pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
+               "client-class": "Client_enterprise"
+           }
+       ],
+       ...
+   }
+
+This example shows a configuration using an automatically generated
+``VENDOR_CLASS_`` class. The administrator of the network has decided that
+addresses in the range 2001:db8:1::1 to 2001:db8:1::ffff are to be
+managed by the DHCP6 server and that only clients belonging to the
+eRouter1.0 client class are allowed to use that pool.
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/64",
+               "pools": [
+                    {
+                        "pool": "2001:db8:1::-2001:db8:1::ffff"
+                    }
+                ],
+               "client-class": "VENDOR_CLASS_eRouter1.0"
+           }
+       ],
+       ...
+   }
+
+.. _dhcp6-required-class:
+
+Required Classification
+~~~~~~~~~~~~~~~~~~~~~~~
+
+In some cases it is useful to limit the scope of a class to a
+shared network, subnet, or pool. There are two parameters which are used
+to limit the scope of the class by instructing the server to evaluate
+test expressions when required.
+
+The first one is the per-class ``only-if-required`` flag, which is ``false``
+by default. When it is set to ``true``, the test expression of the class
+is not evaluated at the reception of the incoming packet but later, and
+only if the class evaluation is required.
+
+The second is ``require-client-classes``, which takes a list of class
+names and is valid in shared-network, subnet, and pool scope. Classes in
+these lists are marked as required and evaluated after selection of this
+specific shared network/subnet/pool and before output-option processing.
+
+In this example, a class is assigned to the incoming packet when the
+specified subnet is used:
+
+::
+
+   "Dhcp6": {
+       "client-classes": [
+          {
+              "name": "Client_foo",
+              "test": "member('ALL')",
+              "only-if-required": true
+          },
+          ...
+       ],
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/64"
+               "pools": [
+                    {
+                        "pool": "2001:db8:1::-2001:db8:1::ffff"
+                    }
+                ],
+               "require-client-classes": [ "Client_foo" ],
+               ...
+           },
+           ...
+       ],
+       ...
+   }
+
+Required evaluation can be used to express complex dependencies like
+subnet membership. It can also be used to reverse the
+precedence; if ``option-data`` is set in a subnet, it takes precedence
+over ``option-data`` in a class. If ``option-data`` is moved to a
+required class and required in the subnet, a class evaluated earlier
+may take precedence.
+
+Required evaluation is also available at shared-network and pool/pd-pool
+levels. The order in which required classes are considered is:
+shared-network, subnet, and (pd-)pool, i.e. in the reverse order from the
+way in which ``option-data`` is processed.
+
+.. _dhcp6-ddns-config:
+
+DDNS for DHCPv6
+---------------
+
+As mentioned earlier, kea-dhcp6 can be configured to generate requests
+to the DHCP-DDNS server (referred to here as "D2") to update DNS
+entries. These requests are known as NameChangeRequests or NCRs. Each
+NCR contains the following information:
+
+1. Whether it is a request to add (update) or remove DNS entries.
+
+2. Whether the change requests forward DNS updates (AAAA records),
+   reverse DNS updates (PTR records), or both.
+
+3. The Fully Qualified Domain Name (FQDN), lease address, and DHCID
+   (information identifying the client associated with the FQDN).
+
+DDNS-related parameters are split into two groups:
+
+1. Connectivity Parameters
+
+    These are parameters which specify where and how ``kea-dhcp6`` connects to
+    and communicates with D2. These parameters can only be specified
+    within the top-level ``dhcp-ddns`` section in the ``kea-dhcp6``
+    configuration. The connectivity parameters are listed below:
+
+    -  ``enable-updates``
+    -  ``server-ip``
+    -  ``server-port``
+    -  ``sender-ip``
+    -  ``sender-port``
+    -  ``max-queue-size``
+    -  ``ncr-protocol``
+    -  ``ncr-format"``
+
+2. Behavioral Parameters
+
+    These parameters influence behavior such as how client host names and
+    FQDN options are handled. They have been moved out of the ``dhcp-ddns``
+    section so that they may be specified at the global, shared-network,
+    and/or subnet levels. Furthermore, they are inherited downward from global to
+    shared-network to subnet. In other words, if a parameter is not specified at
+    a given level, the value for that level comes from the level above it.
+    The behavioral parameters are as follows:
+
+    -  ``ddns-send-updates``
+    -  ``ddns-override-no-update``
+    -  ``ddns-override-client-update``
+    -  ``ddns-replace-client-name"``
+    -  ``ddns-generated-prefix``
+    -  ``ddns-qualifying-suffix``
+    -  ``ddns-update-on-renew``
+    -  ``ddns-use-conflict-resolution``
+    -  ``hostname-char-set``
+    -  ``hostname-char-replacement``
+
+.. note::
+
+    For backward compatibility, configuration parsing still recognizes
+    the original behavioral parameters specified in ``dhcp-ddns``,
+    by translating the parameter into its global equivalent. If a
+    parameter is specified both globally and in ``dhcp-ddns``, the latter
+    value is ignored. In either case, a log is emitted explaining
+    what has occurred. Specifying these values within ``dhcp-ddns`` is
+    deprecated and support for it will be removed.
+
+The default configuration and values would appear as follows:
+
+::
+
+   "Dhcp6": {
+        "dhcp-ddns": {
+           // Connectivity parameters
+           "enable-updates": false,
+            "server-ip": "127.0.0.1",
+            "server-port":53001,
+            "sender-ip":"",
+            "sender-port":0,
+            "max-queue-size":1024,
+            "ncr-protocol":"UDP",
+            "ncr-format":"JSON"
+        },
+
+        // Behavioral parameters (global)
+        "ddns-send-updates": true,
+        "ddns-override-no-update": false,
+        "ddns-override-client-update": false,
+        "ddns-replace-client-name": "never",
+        "ddns-generated-prefix": "myhost",
+        "ddns-qualifying-suffix": "",
+        "ddns-update-on-renew": false,
+        "ddns-use-conflict-resolution": true,
+        "hostname-char-set": "",
+        "hostname-char-replacement": ""
+        ...
+   }
+
+There are two parameters which determine if ``kea-dhcp6``
+can generate DDNS requests to D2: the existing ``dhcp-ddns:enable-updates``
+parameter, which now only controls whether ``kea-dhcp6`` connects to D2;
+and the new behavioral parameter, ``ddns-send-updates``, which determines
+whether DDNS updates are enabled at a given level (i.e. global, shared-network,
+or subnet). The following table shows how the two parameters function
+together:
+
+.. table:: Enabling and disabling DDNS updates
+
+   +-----------------+--------------------+-------------------------------------+
+   | dhcp-ddns:      | Global             | Outcome                             |
+   | enable-updates  | ddns-send-updates  |                                     |
+   +=================+====================+=====================================+
+   | false (default) | false              | no updates at any scope             |
+   +-----------------+--------------------+-------------------------------------+
+   | false           | true (default)     | no updates at any scope             |
+   +-----------------+--------------------+-------------------------------------+
+   | true            | false              | updates only at scopes with         |
+   |                 |                    | a local value of ``true`` for       |
+   |                 |                    | ``ddns-enable-updates``             |
+   +-----------------+--------------------+-------------------------------------+
+   | true            | true               | updates at all scopes except those  |
+   |                 |                    | with a local value of ``false``     |
+   |                 |                    | for ``ddns-enable-updates``         |
+   +-----------------+--------------------+-------------------------------------+
+
+Kea 1.9.1 added two new parameters; the first is ``ddns-update-on-renew``.
+Normally, when leases are renewed, the server only updates DNS if the DNS
+information for the lease (e.g. FQDN, DNS update direction flags) has changed.
+Setting ``ddns-update-on-renew`` to ``true`` instructs the server to always update
+the DNS information when a lease is renewed, even if its DNS information has not
+changed. This allows Kea to "self-heal" if it was previously unable
+to add DNS entries or they were somehow lost by the DNS server.
+
+.. note::
+
+    Setting ``ddns-update-on-renew`` to ``true`` may impact performance, especially
+    for servers with numerous clients that renew often.
+
+The second parameter added in Kea 1.9.1 is ``ddns-use-conflict-resolution``.
+The value of this parameter is passed by ``kea-dhcp6`` to D2 with each DNS update
+request.  When ``true`` (the default value), D2 employs conflict resolution,
+as described in `RFC 4703 <https://tools.ietf.org/html/rfc4703>`__, when
+attempting to fulfill the update request. When ``false``, D2 simply attempts
+to update the DNS entries per the request, regardless of whether they
+conflict with existing entries owned by other DHCPv6 clients.
+
+.. note::
+
+    Setting ``ddns-use-conflict-resolution`` to ``false`` disables the overwrite
+    safeguards that the rules of conflict resolution (from
+    `RFC 4703 <https://tools.ietf.org/html/rfc4703>`__) are intended to
+    prevent. This means that existing entries for an FQDN or an
+    IP address made for Client-A can be deleted or replaced by entries
+    for Client-B. Furthermore, there are two scenarios by which entries
+    for multiple clients for the same key (e.g. FQDN or IP) can be created.
+
+    1. Client-B uses the same FQDN as Client-A but a different IP address.
+    In this case, the forward DNS entries (AAAA and DHCID RRs) for
+    Client-A will be deleted as they match the FQDN and new entries for
+    Client-B will be added. The reverse DNS entries (PTR and DHCID RRs)
+    for Client-A, however, will not be deleted as they belong to a different
+    IP address, while new entries for Client-B will still be added.
+
+    2. Client-B uses the same IP address as Client-A but a different FQDN.
+    In this case the reverse DNS entries (PTR and DHCID RRs) for Client-A
+    will be deleted as they match the IP address, and new entries for
+    Client-B will be added. The forward DNS entries (AAAA and DHCID RRs)
+    for Client-A, however, will not be deleted, as they belong to a different
+    FQDN, while new entries for Client-B will still be added.
+
+    Disabling conflict resolution should be done only after careful review of
+    specific use cases. The best way to avoid unwanted DNS entries is to
+    always ensure lease changes are processed through Kea, whether they are
+    released, expire, or are deleted via the ``lease-del6`` command, prior to
+    reassigning either FQDNs or IP addresses. Doing so causes ``kea-dhcp6``
+    to generate DNS removal requests to D2.
+
+.. note::
+
+    The DNS entries Kea creates contain a value for TTL (time to live). Since
+    Kea 1.9.3, ``kea-dhcp6`` calculates that value based on
+    `RFC 4702, Section 5 <https://tools.ietf.org/html/rfc4702#section-5>`__,
+    which suggests that the TTL value be 1/3 of the lease's lifetime, with
+    a minimum value of 10 minutes. In earlier versions, the server set the TTL value
+    equal to the lease's valid lifetime.
+
+.. _dhcpv6-d2-io-config:
+
+DHCP-DDNS Server Connectivity
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+For NCRs to reach the D2 server, ``kea-dhcp6`` must be able to communicate
+with it. ``kea-dhcp6`` uses the following configuration parameters to
+control this communication:
+
+-  ``enable-updates`` - Enables connectivity to ``kea-dhcp-ddns`` such that DDNS
+   updates can be constructed and sent. It must be ``true`` for NCRs to be generated and sent to D2.
+   It defaults to ``false``.
+
+-  ``server-ip`` - This is the IP address on which D2 listens for requests. The
+   default is the local loopback interface at address 127.0.0.1.
+   Either an IPv4 or IPv6 address may be specified.
+
+-  ``server-port`` - This is the port on which D2 listens for requests. The default
+   value is 53001.
+
+-  ``sender-ip`` - This is the IP address which ``kea-dhcp6`` uses to send requests to
+   D2. The default value is blank, which instructs ``kea-dhcp6`` to select a
+   suitable address.
+
+-  ``sender-port`` - This is the port which ``kea-dhcp6`` uses to send requests to D2.
+   The default value of 0 instructs kea-dhcp6 to select a suitable port.
+
+-  ``max-queue-size`` - This is the maximum number of requests allowed to queue
+   while waiting to be sent to D2. This value guards against requests
+   accumulating uncontrollably if they are being generated faster than
+   they can be delivered. If the number of requests queued for
+   transmission reaches this value, DDNS updating is turned off
+   until the queue backlog has been sufficiently reduced. The intent is
+   to allow the ``kea-dhcp6`` server to continue lease operations without running the
+   risk that its memory usage grows without limit. The default value is
+   1024.
+
+-  ``ncr-protocol`` - This specifies the socket protocol to use when sending requests to
+   D2. Currently only UDP is supported.
+
+-  ``ncr-format`` - This specifies the packet format to use when sending requests to D2.
+   Currently only JSON format is supported.
+
+By default, ``kea-dhcp-ddns`` is assumed to be running on the same machine
+as ``kea-dhcp6``, and all of the default values mentioned above should be
+sufficient. If, however, D2 has been configured to listen on a different
+address or port, these values must be altered accordingly. For example, if
+D2 has been configured to listen on 2001:db8::5 port 900, the following
+configuration is required:
+
+::
+
+   "Dhcp6": {
+       "dhcp-ddns": {
+           "server-ip": "2001:db8::5",
+           "server-port": 900,
+           ...
+       },
+       ...
+   }
+
+.. _dhcpv6-d2-rules-config:
+
+When Does the ``kea-dhcp6`` Server Generate a DDNS Request?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``kea-dhcp6`` follows the behavior prescribed for DHCP servers in `RFC
+4704 <https://tools.ietf.org/html/rfc4704>`__. It is important to keep in
+mind that ``kea-dhcp6`` makes the initial decision of when and what to
+update and forwards that information to D2 in the form of NCRs. Carrying
+out the actual DNS updates and dealing with such things as conflict
+resolution are within the purview of D2 itself
+(see :ref:`dhcp-ddns-server`). This section describes when ``kea-dhcp6``
+generates NCRs and the configuration parameters that can be used to
+influence this decision. It assumes that the ``enable-updates``
+parameter is ``true``.
+
+.. note::
+
+   Currently the interface between ``kea-dhcp6`` and D2 only supports
+   requests which update DNS entries for a single IP address. If a lease
+   grants more than one address, ``kea-dhcp6`` creates the DDNS update
+   request for only the first of these addresses.
+
+In general, ``kea-dhcp6`` generates DDNS update requests when:
+
+1. A new lease is granted in response to a DHCPREQUEST;
+
+2. An existing lease is renewed but the FQDN associated with it has
+   changed; or
+
+3. An existing lease is released in response to a DHCPRELEASE.
+
+In the second case, lease renewal, two DDNS requests are issued: one
+request to remove entries for the previous FQDN, and a second request to
+add entries for the new FQDN. In the third case, a lease release - a
+single DDNS request - to remove its entries will be made.
+
+As for the first case, the decisions involved when granting a new lease are
+more complex. When a new lease is granted, ``kea-dhcp6`` generates a
+DDNS update request only if the DHCPREQUEST contains the FQDN option
+(code 39). By default, ``kea-dhcp6`` respects the FQDN N and S flags
+specified by the client as shown in the following table:
+
+.. table:: Default FQDN flag behavior
+
+   +-----------------+-----------------+-----------------+-----------------+
+   | Client          | Client Intent   | Server Response | Server          |
+   | Flags:N-S       |                 |                 | Flags:N-S-O     |
+   +=================+=================+=================+=================+
+   | 0-0             | Client wants to | Server          | 1-0-0           |
+   |                 | do forward      | generates       |                 |
+   |                 | updates, server | reverse-only    |                 |
+   |                 | should do       | request         |                 |
+   |                 | reverse updates |                 |                 |
+   +-----------------+-----------------+-----------------+-----------------+
+   | 0-1             | Server should   | Server          | 0-1-0           |
+   |                 | do both forward | generates       |                 |
+   |                 | and reverse     | request to      |                 |
+   |                 | updates         | update both     |                 |
+   |                 |                 | directions      |                 |
+   +-----------------+-----------------+-----------------+-----------------+
+   | 1-0             | Client wants no | Server does not | 1-0-0           |
+   |                 | updates done    | generate a      |                 |
+   |                 |                 | request         |                 |
+   +-----------------+-----------------+-----------------+-----------------+
+
+The first row in the table above represents "client delegation." Here
+the DHCP client states that it intends to do the forward DNS updates and
+the server should do the reverse updates. By default, ``kea-dhcp6``
+honors the client's wishes and generates a DDNS request to D2 to update
+only reverse DNS data. The parameter ``ddns-override-client-update`` can be
+used to instruct the server to override client delegation requests. When
+this parameter is ``true``, ``kea-dhcp6`` disregards requests for client
+delegation and generates a DDNS request to update both forward and
+reverse DNS data. In this case, the N-S-O flags in the server's response
+to the client will be 0-1-1 respectively.
+
+(Note that the flag combination N=1, S=1 is prohibited according to `RFC
+4702 <https://tools.ietf.org/html/rfc4702>`__. If such a combination is
+received from the client, the packet will be dropped by ``kea-dhcp6``.)
+
+To override client delegation, set the following values in the
+configuration file:
+
+::
+
+    "Dhcp6": {
+        ...
+        "ddns-override-client-update": true,
+        ...
+    }
+
+The third row in the table above describes the case in which the client
+requests that no DNS updates be done. The parameter
+``ddns-override-no-update`` can be used to instruct the server to disregard
+the client's wishes. When this parameter is ``true``, ``kea-dhcp6``
+generates DDNS update requests to ``kea-dhcp-ddns`` even if the client
+requests that no updates be done. The N-S-O flags in the server's response to
+the client will be 0-1-1.
+
+To override client delegation, issue the following commands:
+
+::
+
+    "Dhcp6": {
+        ...
+        "ddns-override-no-update": true,
+        ...
+    }
+
+.. _dhcpv6-fqdn-name-generation:
+
+``kea-dhcp6`` Name Generation for DDNS Update Requests
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Each NameChangeRequest must of course include the fully qualified
+domain name whose DNS entries are to be affected. kea-dhcp6 can be
+configured to supply a portion or all of that name, based upon what it
+receives from the client in the DHCPREQUEST.
+
+The default rules for constructing the FQDN that will be used for DNS
+entries are:
+
+1. If the DHCPREQUEST contains the client FQDN option, take the
+   candidate name from there.
+
+2. If the candidate name is a partial (i.e. unqualified) name, then add
+   a configurable suffix to the name and use the result as the FQDN.
+
+3. If the candidate name provided is empty, generate an FQDN using a
+   configurable prefix and suffix.
+
+4. If the client provides neither option, then take no DNS action.
+
+These rules can be amended by setting the ``ddns-replace-client-name``
+parameter, which provides the following modes of behavior:
+
+-  ``never`` - use the name the client sent. If the client sent no name,
+   do not generate one. This is the default mode.
+
+-  ``always`` - replace the name the client sent. If the client sent no
+   name, generate one for the client.
+
+-  ``when-present`` - replace the name the client sent. If the client
+   sent no name, do not generate one.
+
+-  ``when-not-present`` - use the name the client sent. If the client
+   sent no name, generate one for the client.
+
+.. note::
+
+   In early versions of Kea, this parameter was a boolean and
+   permitted only values of ``true`` and ``false``.
+   Boolean values have been deprecated and are no longer accepted.
+   Administrators currently using booleans must replace them with the
+   desired mode name. A value of ``true`` maps to ``when-present``, while
+   ``false`` maps to ``never``.
+
+For example, to instruct ``kea-dhcp6`` to always generate the FQDN for a
+client, set the parameter ``ddns-replace-client-name`` to ``always`` as
+follows:
+
+::
+
+    "Dhcp6": {
+        ...
+        "ddns-replace-client-name": "always",
+        ...
+    }
+
+The prefix used in the generation of an FQDN is specified by the
+``ddns-generated-prefix`` parameter. The default value is "myhost". To alter
+its value, simply set it to the desired string:
+
+::
+
+    "Dhcp6": {
+        ...
+        "ddns-generated-prefix": "another.host",
+        ...
+    }
+
+The suffix used when generating an FQDN, or when qualifying a partial
+name, is specified by the ``ddns-qualifying-suffix`` parameter. This
+parameter has no default value; thus, it is mandatory when DDNS updates
+are enabled. To set its value simply set it to the desired string:
+
+::
+
+    "Dhcp6": {
+        ...
+        "ddns-qualifying-suffix": "foo.example.org",
+        ...
+    }
+
+When qualifying a partial name, ``kea-dhcp6`` constructs the name in the
+format:
+
+``[candidate-name].[ddns-qualifying-suffix].``
+
+where ``candidate-name`` is the partial name supplied in the DHCPREQUEST.
+For example, if the FQDN domain name value is "some-computer" and the
+``ddns-qualifying-suffix`` is "example.com", the generated FQDN is:
+
+``some-computer.example.com.``
+
+When generating the entire name, ``kea-dhcp6`` constructs the name in
+the format:
+
+``[ddns-generated-prefix]-[address-text].[ddns-qualifying-suffix].``
+
+where ``address-text`` is simply the lease IP address converted to a
+hyphenated string. For example, if the lease address is 3001:1::70E, the
+qualifying suffix is "example.com", and the default value is used for
+``ddns-generated-prefix``, the generated FQDN is:
+
+``myhost-3001-1--70E.example.com.``
+
+.. _dhcp6-host-name-sanitization:
+
+Sanitizing Client FQDN Names
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Some DHCP clients may provide values in the name
+component of the FQDN option (option code 39) that contain undesirable
+characters. It is possible to configure ``kea-dhcp6`` to sanitize these
+values. The most typical use case is ensuring that only characters that
+are permitted by RFC 1035 be included: A-Z, a-z, 0-9, and "-". This may be
+accomplished with the following two parameters:
+
+-  ``hostname-char-set`` - a regular expression describing the invalid
+   character set. This can be any valid, regular expression using POSIX
+   extended expression syntax. Embedded nulls (0x00) are always
+   considered an invalid character to be replaced (or omitted).
+   The default is ``"[^A-Za-z0-9.-]"``. This matches any character that is not
+   a letter, digit, dot, hyphen, or null.
+
+-  ``hostname-char-replacement`` - a string of zero or more characters
+   with which to replace each invalid character in the host name. An empty
+   string causes invalid characters to be OMITTED rather than replaced.
+   The default is ``""``.
+
+The following configuration replaces anything other than a letter,
+digit, dot, or hyphen with the letter "x":
+::
+
+    "Dhcp6": {
+        ...
+        "hostname-char-set": "[^A-Za-z0-9.-]",
+        "hostname-char-replacement": "x",
+        ...
+    }
+
+Thus, a client-supplied value of "myhost-$[123.org" would become
+"myhost-xx123.org". Sanitizing is performed only on the portion of the
+name supplied by the client, and it is performed before applying a
+qualifying suffix (if one is defined and needed).
+
+.. note::
+
+   Name sanitizing is meant to catch the more common cases of invalid
+   characters through a relatively simple character-replacement scheme.
+   It is difficult to devise a scheme that works well in all cases.
+   Administrators who find they have clients with odd corner cases of
+   character combinations that cannot be readily handled with this
+   mechanism should consider writing a hook that can carry out
+   sufficiently complex logic to address their needs.
+
+   Do not include dots in the ``hostname-char-set`` expression. When
+   scrubbing FQDNs, dots are treated as delimiters and used to separate
+   the option value into individual domain labels that are scrubbed and
+   then re-assembled.
+
+   If clients are sending values that differ only by characters
+   considered as invalid by the hostname-char-set, be aware that
+   scrubbing them will yield identical values. In such cases, DDNS
+   conflict rules will permit only one of them to register the name.
+
+   Finally, given the latitude clients have in the values they send, it
+   is virtually impossible to guarantee that a combination of these two
+   parameters will always yield a name that is valid for use in DNS. For
+   example, using an empty value for ``hostname-char-replacement`` could
+   yield an empty domain label within a name, if that label consists
+   only of invalid characters.
+
+.. note::
+
+   It is possible to specify ``hostname-char-set``
+   and/or ``hostname-char-replacement`` at the global scope. This allows
+   host names to be sanitized without requiring a ``dhcp-ddns`` entry. When
+   a ``hostname-char`` parameter is defined at both the global scope and
+   in a ``dhcp-ddns`` entry, the second (local) value is used.
+
+.. _dhcp6-dhcp4o6-config:
+
+DHCPv4-over-DHCPv6: DHCPv6 Side
+-------------------------------
+
+The support of DHCPv4-over-DHCPv6 transport is described in `RFC
+7341 <https://tools.ietf.org/html/rfc7341>`__ and is implemented using
+cooperating DHCPv4 and DHCPv6 servers. This section is about the
+configuration of the DHCPv6 side (the DHCPv4 side is described in
+:ref:`dhcp4-dhcp4o6-config`).
+
+.. note::
+
+   DHCPv4-over-DHCPv6 support is experimental and the details of the
+   inter-process communication may change; for instance, the
+   support of port relay (RFC 8357) introduced an incompatible change.
+   Both the DHCPv4 and DHCPv6 sides should be running the same version of Kea.
+
+There is only one specific parameter for the DHCPv6 side:
+``dhcp4o6-port``, which specifies the first of the two consecutive ports
+of the UDP sockets used for the communication between the DHCPv6 and
+DHCPv4 servers. The DHCPv6 server is bound to ::1 on ``port`` and
+connected to ::1 on ``port`` + 1.
+
+Two other configuration entries are generally required: unicast traffic
+support (see :ref:`dhcp6-unicast`) and the DHCP 4o6
+server address option (name "dhcp4o6-server-addr", code 88).
+
+ISC tested the following configuration:
+
+::
+
+   {
+
+   # DHCPv6 conf
+   "Dhcp6": {
+
+       "interfaces-config": {
+           "interfaces": [ "eno33554984/2001:db8:1:1::1" ]
+       },
+
+       "lease-database": {
+           "type": "memfile",
+           "name": "leases6"
+       },
+
+       "preferred-lifetime": 3000,
+       "valid-lifetime": 4000,
+       "renew-timer": 1000,
+       "rebind-timer": 2000,
+
+       "subnet6": [ {
+           "subnet": "2001:db8:1:1::/64",
+           "interface": "eno33554984",
+           "pools": [ { "pool": "2001:db8:1:1::1:0/112" } ]
+       } ],
+
+       "dhcp4o6-port": 6767,
+
+       "option-data": [ {
+           "name": "dhcp4o6-server-addr",
+           "code": 88,
+           "space": "dhcp6",
+           "csv-format": true,
+           "data": "2001:db8:1:1::1"
+       } ],
+
+
+       "loggers": [ {
+           "name": "kea-dhcp6",
+           "output_options": [ {
+               "output": "/tmp/kea-dhcp6.log"
+           } ],
+           "severity": "DEBUG",
+           "debuglevel": 0
+       } ]
+   }
+
+   }
+
+.. note::
+
+   Relayed DHCPv4-QUERY DHCPv6 messages are not supported.
+
+.. _sanity-checks6:
+
+Sanity Checks in DHCPv6
+-----------------------
+
+An important aspect of a well-running DHCP system is an assurance that
+the data remains consistent; however, in some cases it may be convenient
+to tolerate certain inconsistent data. For example, a network
+administrator who temporarily removes a subnet from a configuration
+would not want all the leases associated with it to disappear from the
+lease database. Kea has a mechanism to implement sanity checks for situations
+like this.
+
+Kea supports a configuration scope called ``sanity-checks``. It
+currently allows only a single parameter, called ``lease-checks``, which
+governs the verification carried out when a new lease is loaded from a
+lease file. This mechanism permits Kea to attempt to correct inconsistent data.
+
+Every subnet has a ``subnet-id`` value; this is how Kea internally
+identifies subnets. Each lease has a ``subnet-id`` parameter as well, which
+identifies the subnet it belongs to. However, if the configuration has
+changed, it is possible that a lease could exist with a ``subnet-id`` but
+without any subnet that matches it. Also, it is possible that the
+subnet's configuration has changed and the ``subnet-id`` now belongs to a
+subnet that does not match the lease.
+
+Kea's corrective algorithm first
+checks to see if there is a subnet with the ``subnet-id`` specified by the
+lease. If there is, it verifies whether the lease belongs to that
+subnet. If not, depending on the ``lease-checks`` setting, the lease is
+discarded, a warning is displayed, or a new subnet is selected for the
+lease that matches it topologically.
+
+Since delegated prefixes do not have to belong to a subnet in which
+they are offered, there is no way to implement such a mechanism for IPv6
+prefixes. As such, the mechanism works for IPv6 addresses only.
+
+There are five levels which are supported:
+
+-  ``none`` - do no special checks; accept the lease as is.
+
+-  ``warn`` - if problems are detected display a warning, but
+   accept the lease data anyway. This is the default value.
+
+-  ``fix`` - if a data inconsistency is discovered, try to
+   correct it. If the correction is not successful, insert the incorrect data
+   anyway.
+
+-  ``fix-del`` - if a data inconsistency is discovered, try to
+   correct it. If the correction is not successful, reject the lease.
+   This setting ensures the data's correctness, but some
+   incorrect data may be lost. Use with care.
+
+-  ``del`` - if any inconsistency is
+   detected, reject the lease. This is the strictest mode; use with care.
+
+This feature is currently implemented for the memfile backend. The
+sanity check applies to the lease database in memory, not to the lease file,
+i.e. inconsistent leases will stay in the lease file.
+
+An example configuration that sets this parameter looks as follows:
+
+::
+
+   "Dhcp6": {
+       "sanity-checks": {
+           "lease-checks": "fix-del"
+       },
+       ...
+   }
+
+.. _store-extended-info-v6:
+
+Storing Extended Lease Information
+----------------------------------
+To support such features as DHCPv6 Reconfigure
+(`RFC 3315 <https://tools.ietf.org/html/rfc3315>`__) and Leasequery
+(`RFC 5007 <https://tools.ietf.org/html/rfc5007>`__),
+additional information must be stored with each lease. Because the amount
+of information stored for each lease has ramifications in terms of
+performance and system resource consumption, storage of this additional
+information is configurable through the ``store-extended-info`` parameter.
+It defaults to ``false`` and may be set at the global, shared-network, and
+subnet levels.
+
+::
+
+   "Dhcp6": {
+       "store-extended-info": true,
+       ...
+   }
+
+When set to ``true``, information relevant to the DHCPv6 query (e.g. REQUEST, RENEW,
+or REBIND) asking for the lease is added into the lease's ``user-context`` as a
+map element labeled "ISC". Currently, the information contained in the map
+is a list of relays, one for each relay message layer that encloses the
+client query. The lease's
+``user-context`` for a two-hop query might look something like this (shown
+pretty-printed for clarity):
+
+::
+
+    {
+        "ISC": {
+            "relays": [
+            {
+                "hop": 2,
+                "link": "2001:db8::1",
+                "peer": "2001:db8::2"
+            },
+            {
+                "hop": 1,
+                "link": "2001:db8::3",
+                "options": "0x00C800080102030405060708",
+                "peer": "2001:db8::4"
+            }]
+        }
+    }
+
+.. note::
+
+    It is possible that other hook libraries are already using
+    ``user-context``. Enabling ``store-extended-info`` should not interfere with
+    any other ``user-context`` content, as long as it does not also use an element
+    labeled "ISC". In other words, ``user-context`` is intended to be a flexible
+    container serving multiple purposes. As long as no other purpose also
+    writes an "ISC" element to ``user-context`` there should not be a conflict.
+
+.. _dhcp6-multi-threading-settings:
+
+Multi-Threading Settings
+------------------------
+
+The Kea server can be configured to process packets in parallel using multiple
+threads. These settings can be found under the ``multi-threading`` structure and are
+represented by:
+
+-  ``enable-multi-threading`` - use multiple threads to process packets in
+   parallel. The default is ``false``.
+
+-  ``thread-pool-size`` - specify the number of threads to process packets in
+   parallel. It may be set to 0 (auto-detect), or any positive number explicitly sets
+   the thread count. The default is 0.
+
+-  ``packet-queue-size`` - specify the size of the queue used by the thread
+   pool to process packets. It may be set to 0 (unlimited), or any positive
+   number explicitly sets the queue size. The default is 64.
+
+An example configuration that sets these parameters looks as follows:
+
+::
+
+   "Dhcp6": {
+       "multi-threading": {
+          "enable-multi-threading": true,
+          "thread-pool-size": 4,
+          "packet-queue-size": 16
+       }
+       ...
+   }
+
+Multi-Threading Settings With Different Database Backends
+---------------------------------------------------------
+
+Both ``kea-dhcp4`` and ``kea-dhcp6`` are tested by ISC to determine which settings
+give the best performance. Although this section describes our results, they are merely
+recommendations and are very dependent on the particular hardware used
+for testing. We strongly advise that administrators run their own performance tests.
+
+A full report of performance results for the latest stable Kea version can be found
+`here <https://reports.kea.isc.org/>`_.
+This includes hardware and test scenario descriptions, as well as
+current results.
+
+After enabling multi-threading, the number of threads is set by the ``thread-pool-size``
+parameter. Results from our tests show that best configurations for
+``kea-dhcp6`` are:
+
+-  ``thread-pool-size``: 4 when using ``memfile`` for storing leases.
+
+-  ``thread-pool-size``: 12 or more when using ``mysql`` for storing leases.
+
+-  ``thread-pool-size``: 6 when using ``postgresql``.
+
+Another very important parameter is ``packet-queue-size``; in our tests we
+used it as a multiplier of ``thread-pool-size``. The actual setting strongly depends
+on ``thread-pool-size``.
+
+We saw the best results in our tests with the following settings:
+
+-  ``packet-queue-size``: 150 * ``thread-pool-size`` when using ``memfile`` for
+   storing leases; in our case it was 150 * 4 = 600. This means that at any given
+   time, up to 600 packets could be queued.
+
+-  ``packet-queue-size``: 200 * ``thread-pool-size`` when using ``mysql`` for
+   storing leases; in our case it was 200 * 12 = 2400. This means that up to
+   2400 packets could be queued.
+
+-  ``packet-queue-size``: 11 * ``thread-pool-size`` when using ``postgresql`` for
+   storing leases; in our case it was 11 * 6 = 66.
+
+Lease Caching
+-------------
+
+Clients that attempt multiple renewals in a short period can cause the server to update
+and write to the database frequently, resulting in a performance impact
+on the server. The cache parameters instruct the DHCP server to avoid
+updating leases too frequently, thus avoiding this behavior. Instead,
+the server assigns the same lease (i.e. reuses it) with no
+modifications except for CLTT (Client Last Transmission Time), which
+does not require disk operations.
+
+The two parameters are the ``cache-threshold`` double and the
+``cache-max-age`` integer; they have no default setting, i.e. the lease caching
+feature must be explicitly enabled. These parameters can be configured
+at the global, shared-network and subnet levels. The subnet level has
+the precedence over the shared-network level, while the global level is used
+as a last resort. For example:
+
+::
+
+    "subnet6": [
+        {
+            "subnet": "2001:db8:1:1::/64",
+            "pools": [ { "pool": "2001:db8:1:1::1:0/112" } ],
+            "cache-threshold": .25,
+            "cache-max-age": 600,
+            "valid-lifetime": 2000,
+            ...
+        }
+    ],
+
+When an already-assigned lease can fulfill a client query:
+
+  - any important change, e.g. for DDNS parameter, hostname, or
+    preferred or valid lifetime reduction, makes the lease not reusable.
+
+  - lease age, i.e. the difference between the creation or last modification
+    time and the current time, is computed (elapsed duration).
+
+  - if ``cache-max-age`` is explicitly configured, it is compared with the lease age;
+    leases that are too old are not reusable. This means that the value 0
+    for ``cache-max-age`` disables the lease cache feature.
+
+  - if ``cache-threshold`` is explicitly configured and is between 0.0 and 1.0,
+    it expresses the percentage of the lease valid lifetime which is
+    allowed for the lease age. Values below and including 0.0 and
+    values greater than 1.0 disable the lease cache feature.
+
+In our example, a lease with a valid lifetime of 2000 seconds can be
+reused if it was committed less than 500 seconds ago. With a lifetime
+of 3000 seconds, a maximum age of 600 seconds applies.
+
+In outbound client responses (e.g. DHCPV6_REPLY messages), the used
+preferred and valid lifetimes are the reusable values, i.e. the
+expiration dates do not change.
+
+.. _host-reservation-v6:
+
+Host Reservations in DHCPv6
+===========================
+
+There are many cases where it is useful to provide a configuration on a
+per-host basis. The most obvious one is to reserve a specific, static
+IPv6 address or/and prefix for exclusive use by a given client (host);
+the returning client receives the same address and/or prefix every time,
+and other clients will never get that address. Host
+reservations are also convenient when a host has specific requirements,
+e.g. a printer that needs additional DHCP options or a cable modem that
+needs specific parameters. Yet another possible use case is to define
+unique names for hosts.
+
+There may be cases when a new reservation has been made for a
+client for an address or prefix currently in use by another client. We
+call this situation a "conflict." These conflicts get resolved
+automatically over time, as described in subsequent sections. Once a
+conflict is resolved, the correct client will receive the reserved
+configuration when it renews.
+
+Host reservations are defined as parameters for each subnet. Each host
+must be identified by either DUID or its hardware/MAC address; see
+:ref:`mac-in-dhcpv6` for details. There
+is an optional ``reservations`` array in the ``subnet6`` structure; each
+element in that array is a structure that holds information about reservations for a
+single host. In particular, the structure has an identifier that
+uniquely identifies a host. In the DHCPv6 context, the identifier is
+usually a DUID, but it can also be a hardware or MAC address. One or more
+addresses or prefixes may also be specified, and it is possible to
+specify a hostname and DHCPv6 options for a given host.
+
+.. note::
+
+   The reserved address must be within the subnet.
+   This does not apply to reserved prefixes.
+
+The following example shows how to reserve addresses and prefixes for
+specific hosts:
+
+::
+
+   "subnet6": [
+       {
+           "subnet": "2001:db8:1::/48",
+           "pools": [ { "pool": "2001:db8:1::/80" } ],
+           "pd-pools": [
+               {
+                   "prefix": "2001:db8:1:8000::",
+                   "prefix-len": 48,
+                   "delegated-len": 64
+               }
+           ],
+           "reservations": [
+               {
+                   "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
+                   "ip-addresses": [ "2001:db8:1::100" ]
+               },
+               {
+                   "hw-address": "00:01:02:03:04:05",
+                   "ip-addresses": [ "2001:db8:1::101", "2001:db8:1::102" ]
+               },
+               {
+                   "duid": "01:02:03:04:05:06:07:08:09:0A",
+                   "ip-addresses": [ "2001:db8:1::103" ],
+                   "prefixes": [ "2001:db8:2:abcd::/64" ],
+                   "hostname": "foo.example.com"
+               }
+           ]
+       }
+   ]
+
+This example includes reservations for three different clients. The
+first reservation is for the address 2001:db8:1::100, for a client using
+DUID 01:02:03:04:05:0A:0B:0C:0D:0E. The second reservation is for two
+addresses, 2001:db8:1::101 and 2001:db8:1::102, for a client using MAC
+address 00:01:02:03:04:05. Lastly, address 2001:db8:1::103 and prefix
+2001:db8:2:abcd::/64 are reserved for a client using DUID
+01:02:03:04:05:06:07:08:09:0A. The last reservation also assigns a
+hostname to this client.
+
+DHCPv6 allows a single client to lease multiple addresses and
+multiple prefixes at the same time. Therefore ``ip-addresses`` and
+``prefixes`` are plural and are actually arrays. When the client sends
+multiple IA options (IA_NA or IA_PD), each reserved address or prefix is
+assigned to an individual IA of the appropriate type. If the number of
+IAs of a specific type is lower than the number of reservations of that
+type, the number of reserved addresses or prefixes assigned to the
+client is equal to the number of IA_NAs or IA_PDs sent by the client;
+that is, some reserved addresses or prefixes are not assigned. However,
+they still remain reserved for this client and the server will not
+assign them to any other client. If the number of IAs of a specific type
+sent by the client is greater than the number of reserved addresses or
+prefixes, the server will try to assign all reserved addresses or
+prefixes to the individual IAs and dynamically allocate addresses or
+prefixes to the remaining IAs. If the server cannot assign a reserved
+address or prefix because it is in use, the server will select the next
+reserved address or prefix and try to assign it to the client. If the
+server subsequently finds that there are no more reservations that can
+be assigned to the client at that moment, the server will try to assign
+leases dynamically.
+
+Making a reservation for a mobile host that may visit multiple subnets
+requires a separate host definition in each subnet that host is expected to
+visit. It is not possible to define multiple host definitions with the
+same hardware address in a single subnet. Multiple host definitions with
+the same hardware address are valid if each is in a different subnet.
+The reservation for a given host should include only one identifier,
+either DUID or hardware address; defining both for the same host is
+considered a configuration error.
+
+Adding host reservations incurs a performance penalty. In principle,
+when a server that does not support host reservation responds to a
+query, it needs to check whether there is a lease for a given address
+being considered for allocation or renewal. The server that does
+support host reservation has to perform additional checks: not only
+whether the address is currently used (i.e., if there is a lease for
+it), but also whether the address could be used by someone else (i.e.,
+if there is a reservation for it). That additional check incurs extra
+overhead.
+
+.. _reservation6-types:
+
+Address/Prefix Reservation Types
+--------------------------------
+
+In a typical Kea scenario there is an IPv6 subnet defined, with a certain
+part of it dedicated for dynamic address allocation by the DHCPv6
+server. There may be an additional address space defined for prefix
+delegation. Those dynamic parts are referred to as dynamic pools,
+address and prefix pools, or simply pools. In principle, a host
+reservation can reserve any address or prefix that belongs to the
+subnet. The reservations that specify addresses that belong to
+configured pools are called "in-pool reservations." In contrast, those
+that do not belong to dynamic pools are called "out-of-pool
+reservations." There is no formal difference in the reservation syntax
+and both reservation types are handled uniformly.
+
+Kea supports global host reservations. These are reservations that are
+specified at the global level within the configuration and that do not
+belong to any specific subnet. Kea still matches inbound client
+packets to a subnet as before, but when the subnet's reservation mode is
+set to "global", Kea looks for host reservations only among the
+global reservations defined. Typically, such reservations would be used
+to reserve hostnames for clients which may move from one subnet to
+another.
+
+.. note::
+
+   Global reservations, while useful in certain circumstances, have aspects
+   that must be given due consideration when using them. Please see
+   :ref:`reservation6-conflict` for more details.
+
+.. note::
+
+   Since Kea 1.9.1, reservation mode has been replaced by three
+   boolean flags, ``reservations-global``, ``reservations-in-subnet``
+   and ``reservations-out-of-pool``, which allow the configuration of
+   host reservations both globally and in a subnet. In such cases a subnet
+   host reservation has preference over a global reservation
+   when both exist for the same client.
+
+.. _reservation6-conflict:
+
+Conflicts in DHCPv6 Reservations
+--------------------------------
+
+As reservations and lease information are stored separately, conflicts
+may arise. Consider the following series of events: the server has
+configured the dynamic pool of addresses from the range of 2001:db8::10
+to 2001:db8::20. Host A requests an address and gets 2001:db8::10. Now
+the system administrator decides to reserve address 2001:db8::10 for
+Host B. In general, reserving an address that is currently assigned to
+someone else is not recommended, but there are valid use cases where
+such an operation is warranted.
+
+The server now has a conflict to resolve. If Host B boots up and
+requests an address, the server cannot immediately assign the reserved
+address 2001:db8::10. A naive approach would to be immediately remove
+the lease for Host A and create a new one for Host B. That would not
+solve the problem, though, because as soon as Host B gets the address,
+it will detect that the address is already in use (by Host
+A) and will send a DHCPDECLINE message. Therefore, in this situation,
+the server has to temporarily assign a different address from the
+dynamic pool (not matching what has been reserved) to Host B.
+
+When Host A renews its address, the server will discover that the
+address being renewed is now reserved for someone else - Host B.
+The server will remove the lease for 2001:db8::10, select a
+new address, and create a new lease for it. It will send two addresses
+in its response: the old address, with the lifetime set to 0 to explicitly
+indicate that it is no longer valid; and the new address, with a
+non-zero lifetime. When Host B tries to renew its temporarily assigned address,
+the server will detect that the existing lease does not match the
+reservation, so it will release the current address Host B has and will
+create a new lease matching the reservation. As before, the server will
+send two addresses: the temporarily assigned one with a zero lifetime,
+and the new one that matches the reservation with the proper lifetime set.
+
+This recovery will succeed, even if other hosts attempt to get the
+reserved address. If Host C requests the address 2001:db8::10 after the
+reservation is made, the server will propose a different address.
+
+This recovery mechanism allows the server to fully recover from a case
+where reservations conflict with existing leases; however, this procedure
+takes roughly as long as the value set for ``renew-timer``. The
+best way to avoid such a recovery is not to define new reservations that
+conflict with existing leases. Another recommendation is to use
+out-of-pool reservations; if the reserved address does not belong to a
+pool, there is no way that other clients can get it.
+
+.. note::
+
+   The conflict-resolution mechanism does not work for global
+   reservations. Although the global address reservations feature may be useful
+   in certain settings, it is generally recommended not to use
+   global reservations for addresses. Administrators who do choose
+   to use global reservations must manually ensure that the reserved
+   addresses are not in dynamic pools.
+
+.. _reservation6-hostname:
+
+Reserving a Hostname
+--------------------
+
+When the reservation for a client includes the ``hostname``, the server
+assigns this hostname to the client and sends it back in the Client
+FQDN option, if the client included the Client FQDN option in its message
+to the server. The reserved hostname always takes precedence over the
+hostname supplied by the client (via the FQDN option) or the autogenerated
+(from the IPv6 address) hostname.
+
+The server qualifies the reserved hostname with the value of the
+``ddns-qualifying-suffix`` parameter. For example, the following subnet
+configuration:
+
+::
+
+   "subnet6": [
+       {
+           "subnet": "2001:db8:1::/48",
+           "pools": [ { "pool": "2001:db8:1::/80" } ],
+           "ddns-qualifying-suffix": "example.isc.org.",
+           "reservations": [
+               {
+                   "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
+                   "ip-addresses": [ "2001:db8:1::100" ]
+                   "hostname": "alice-laptop"
+               }
+           ]
+       }
+   ],
+   "dhcp-ddns": {
+       "enable-updates": true
+   }
+
+will result the "alice-laptop.example.isc.org." hostname being assigned to
+the client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E". If the
+``ddns-qualifying-suffix`` is not specified, the default (empty) value will
+be used, and in this case the value specified as a ``hostname`` will be
+treated as a fully qualified name. Thus, by leaving the
+``ddns-qualifying-suffix`` empty it is possible to qualify hostnames for
+different clients with different domain names:
+
+::
+
+   "subnet6": [
+       {
+           "subnet": "2001:db8:1::/48",
+           "pools": [ { "pool": "2001:db8:1::/80" } ],
+           "reservations": [
+               {
+                   "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
+                   "ip-addresses": [ "2001:db8:1::100" ]
+                   "hostname": "mark-desktop.example.org."
+               }
+           ]
+       }
+   ],
+   "dhcp-ddns": {
+       "enable-updates": true,
+   }
+
+The above example results in the assignment of the
+"mark-desktop.example.org." hostname to the client using the DUID
+"01:02:03:04:05:0A:0B:0C:0D:0E".
+
+.. _reservation6-options:
+
+Including Specific DHCPv6 Options in Reservations
+-------------------------------------------------
+
+Kea offers the ability to specify options on a per-host basis. These
+options follow the same rules as any other options. These can be
+standard options (see :ref:`dhcp6-std-options`),
+custom options (see :ref:`dhcp6-custom-options`),
+or vendor-specific options (see :ref:`dhcp6-vendor-opts`). The following
+example demonstrates how standard options can be defined.
+
+::
+
+   "reservations": [
+   {
+      "duid": "01:02:03:05:06:07:08",
+      "ip-addresses": [ "2001:db8:1::2" ],
+       "option-data": [
+       {
+           "option-data": [ {
+               "name": "dns-servers",
+               "data": "3000:1::234"
+           },
+           {
+               "name": "nis-servers",
+               "data": "3000:1::234"
+           }
+       } ]
+   } ]
+
+Vendor-specific options can be reserved in a similar manner:
+
+::
+
+   "reservations": [
+   {
+       "duid": "aa:bb:cc:dd:ee:ff",
+       "ip-addresses": [ "2001:db8::1" ],
+       "option-data": [
+       {
+           "name": "vendor-opts",
+           "data": 4491
+       },
+       {
+           "name": "tftp-servers",
+           "space": "vendor-4491",
+           "data": "3000:1::234"
+       } ]
+   } ]
+
+Options defined at the host level have the highest priority. In other words,
+if there are options defined with the same type on global, subnet,
+class, and host levels, the host-specific values are used.
+
+.. _reservation6-client-classes:
+
+Reserving Client Classes in DHCPv6
+----------------------------------
+
+:ref:`classification-using-expressions` explains how to configure
+the server to assign classes to a client, based on the content of the
+options that this client sends to the server. Host reservation
+mechanisms also allow for the static assignment of classes to clients.
+The definitions of these classes are placed in the Kea configuration file or
+a database. The following configuration snippet shows how to specify that
+a client belongs to the classes ``reserved-class1`` and ``reserved-class2``. Those
+classes are associated with specific options sent to the clients which belong
+to them.
+
+::
+
+   {
+       "client-classes": [
+       {
+          "name": "reserved-class1",
+          "option-data": [
+          {
+              "name": "dns-servers",
+              "data": "2001:db8:1::50"
+          }
+          ]
+       },
+       {
+          "name": "reserved-class2",
+          "option-data": [
+          {
+              "name": "nis-servers",
+              "data": "2001:db8:1::100"
+          }
+          ]
+       }
+       ],
+       "subnet6": [
+       {   "pools": [ { "pool": "2001:db8:1::/64" } ],
+           "subnet": "2001:db8:1::/48",
+           "reservations": [
+           {
+               "duid": "01:02:03:04:05:06:07:08",
+
+               "client-classes": [ "reserved-class1", "reserved-class2" ]
+
+           }
+           ]
+       } ]
+    }
+
+In some cases the host reservations can be used in conjunction with client
+classes specified within the Kea configuration. In particular, when a
+host reservation exists for a client within a given subnet, the "KNOWN"
+built-in class is assigned to the client. Conversely, when there is no
+static assignment for the client, the "UNKNOWN" class is assigned to the
+client. Class expressions within the Kea configuration file can
+refer to "KNOWN" or "UNKNOWN" classes using the "member" operator.
+For example:
+
+::
+
+    {
+        "client-classes": [
+            {
+                "name": "dependent-class",
+                "test": "member('KNOWN')",
+                "only-if-required": true
+            }
+        ]
+    }
+
+The ``only-if-required`` parameter is needed here to force
+evaluation of the class after the lease has been allocated and thus the
+reserved class has been also assigned.
+
+.. note::
+
+   The classes specified in non-global host reservations
+   are assigned to the processed packet after all classes with the
+   ``only-if-required`` parameter set to ``false`` have been evaluated.
+   This means that these classes must not depend on the
+   statically assigned classes from the host reservations. If
+   such a dependency is needed, the ``only-if-required`` must
+   be set to ``true`` for the dependent classes. Such classes are
+   evaluated after the static classes have been assigned to the packet.
+   This, however, imposes additional configuration overhead, because
+   all classes marked as ``only-if-required`` must be listed in the
+   ``require-client-classes`` list for every subnet where they are used.
+
+.. note::
+
+   Client classes specified within the Kea configuration file may
+   depend on the classes specified within the global host reservations.
+   In such a case the ``only-if-required`` parameter is not needed.
+   Refer to the :ref:`pool-selection-with-class-reservations6` and
+   :ref:`subnet-selection-with-class-reservations6`
+   for specific use cases.
+
+.. _reservations6-mysql-pgsql:
+
+Storing Host Reservations in MySQL or PostgreSQL
+------------------------------------------------
+
+Kea can store host reservations in MySQL or PostgreSQL.
+See :ref:`hosts6-storage` for information on how to
+configure Kea to use reservations stored in MySQL or PostgreSQL.
+Kea provides a dedicated hook for managing reservations in a
+database; section :ref:`hooks-host-cmds` provides detailed information.
+The `Kea wiki
+<https://gitlab.isc.org/isc-projects/kea/wikis/designs/commands#23-host-reservations-hr-management>`__
+provides some examples of how to conduct common host reservation
+operations.
+
+.. note::
+
+   In Kea, the maximum length of an option specified per-host is
+   arbitrarily set to 4096 bytes.
+
+.. _reservations6-tuning:
+
+Fine-Tuning DHCPv6 Host Reservation
+-----------------------------------
+
+The host reservation capability introduces additional restrictions for
+the allocation engine (the component of Kea that selects an address for
+a client) during lease selection and renewal. In particular, three major
+checks are necessary. First, when selecting a new lease, it is not
+sufficient for a candidate lease to simply not be in use by another DHCP
+client; it also must not be reserved for another client. Similarly, when
+renewing a lease, an additional check must be performed to see whether
+the address being renewed is reserved for another client. Finally, when
+a host renews an address or a prefix, the server must check whether
+there is a reservation for this host, which would mean the existing (dynamically
+allocated) address should be revoked and the reserved one be used
+instead.
+
+Some of those checks may be unnecessary in certain deployments, and not
+performing them may improve performance. The Kea server provides the
+``reservation-mode`` configuration parameter to select the types of
+reservations allowed for a particular subnet. Each reservation type has
+different constraints for the checks to be performed by the server when
+allocating or renewing a lease for the client. Allowed values are:
+
+-  ``all`` - enables both in-pool and out-of-pool host reservation
+   types. This setting is the default value, and is the safest and most
+   flexible. However, as all checks are conducted, it is also the slowest.
+   It does not check against global reservations.
+
+-  ``out-of-pool`` - allows only out-of-pool host reservations. With
+   this setting in place, the server assumes that all host
+   reservations are for addresses that do not belong to the dynamic
+   pool. Therefore, it can skip the reservation checks when dealing with
+   in-pool addresses, thus improving performance. Do not use this mode
+   if any reservations use in-pool addresses. Caution is advised
+   when using this setting; Kea does not sanity-check the reservations
+   against ``reservation-mode`` and misconfiguration may cause problems.
+
+-  ``global`` - allows only global host reservations. With this setting
+   in place, the server searches for reservations for a client only
+   among the defined global reservations. If an address is specified,
+   the server skips the reservation checks carried out in
+   other modes, thus improving performance. Caution is advised when
+   using this setting; Kea does not sanity-check the reservations when
+   ``global`` is set, and misconfiguration may cause problems.
+
+-  ``disabled`` - host reservation support is disabled. As there are no
+   reservations, the server skips all checks. Any reservations
+   defined are completely ignored. As checks are skipped, the
+   server may operate faster in this mode.
+
+Since Kea 1.9.1, the ``reservation-mode`` parameter is replaced by the
+``reservations-global``, ``reservations-in-subnet`` and
+``reservations-out-of-pool`` flags.
+The flags can be activated independently and can produce various combinations,
+some of them being unsupported by the deprecated ``reservation-mode``.
+
+The ``reservation-mode`` parameter can be specified at:
+
+- global level: ``.Dhcp6["reservation-mode"]`` (lowest priority: gets overridden
+  by all others)
+
+- subnet level: ``.Dhcp6.subnet6[]["reservation-mode"]`` (low priority)
+
+- shared-network level: ``.Dhcp6["shared-networks"][]["reservation-mode"]``
+  (high priority)
+
+- shared-network subnet-level:
+  ``.Dhcp6["shared-networks"][].subnet6[]["reservation-mode"]`` (highest
+  priority: overrides all others)
+
+To decide which ``"reservation-mode"`` to choose, the
+following decision diagram may be useful:
+
+::
+
+                                  O
+                                  |
+                                  v
+    +-----------------------------+------------------------------+
+    |         Is per-host configuration needed, such as          |
+    |                reserving specific addresses,               |
+    |               assigning specific options or                |
+    | assigning packets to specific classes on per-device basis? |
+    +-+-----------------+----------------------------------------+
+      |                 |
+    no|              yes|
+      |                 |   +--------------------------------------+
+      |                 |   |         For all given hosts,         |
+      +--> "disabled"   +-->+      can the reserved resources      |
+                            |  be used in all configured subnets?  |
+                            +--------+---------------------------+-+
+                                     |                           |
+    +----------------------------+   |no                         |yes
+    |             Is             |   |                           |
+    |  at least one reservation  +<--+               "global" <--+
+    | used to reserve addresses  |
+    |        or prefixes?        |
+    +-+------------------------+-+
+      |                        |
+    no|                     yes|   +---------------------------+
+      |                        |   | Is high leases-per-second |
+      +--> "out-of-pool"       +-->+ performance or efficient  |
+            ^                      |      resource usage       |
+            |                      |  (CPU ticks, RAM usage,   |
+            |                      |   database roundtrips)    |
+            |                      | important to your setup?  |
+            |                      +-+----------------+--------+
+            |                        |                |
+            |                     yes|              no|
+            |                        |                |
+            |          +-------------+                |
+            |          |                              |
+            |          |   +----------------------+   |
+            |          |   | Can it be guaranteed |   |
+            |          +-->+  that the reserved   |   |
+            |              |  addresses/prefixes  |   |
+            |              |  aren't part of the  |   |
+            |              |   pools configured   |   |
+            |              |  in the respective   |   |
+            |              |       subnet?        |   |
+            |              +-+------------------+-+   |
+            |                |                  |     |
+            |             yes|                no|     |
+            |                |                  |     V
+            +----------------+                  +--> "all"
+
+An example configuration that disables reservations looks as follows:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "subnet6": [
+          {
+            "pools": [
+              {
+                "pool": "2001:db8:1::-2001:db8:1::100"
+              }
+            ],
+            "reservation-mode": "disabled",
+            "subnet": "2001:db8:1::/64"
+          }
+        ]
+      }
+    }
+
+An example configuration using global reservations is shown below:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "reservation-mode": "global",
+        "reservations": [
+          {
+            "duid": "00:03:00:01:11:22:33:44:55:66",
+            "hostname": "host-one"
+          },
+          {
+            "duid": "00:03:00:01:99:88:77:66:55:44",
+            "hostname": "host-two"
+          }
+        ],
+        "subnet6": [
+          {
+            "pools": [
+              {
+                "pool": "2001:db8:1::-2001:db8:1::100"
+              }
+            ],
+            "subnet": "2001:db8:1::/64"
+          }
+        ]
+      }
+    }
+
+The meaning of the reservation flags are:
+
+- ``reservations-global``: fetch global reservations.
+
+- ``reservations-in-subnet``: fetch subnet reservations. For a shared network
+  this includes all subnet members of the shared network.
+
+- ``reservations-out-of-pool``: this makes sense only when the
+  ``reservations-in-subnet`` flag is ``true``. When ``reservations-out-of-pool``
+  is ``true``, the server assumes that all host reservations are for addresses
+  that do not belong to the dynamic pool. Therefore, it can skip the reservation
+  checks when dealing with in-pool addresses, thus improving performance.
+  The server will not assign reserved addresses that are inside the dynamic
+  pools to the respective clients. This also means that the addresses matching
+  the respective reservations from inside the dynamic pools (if any) can be
+  dynamically assigned to any client.
+
+The ``disabled`` value from the deprecated ``reservation-mode`` corresponds to:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "reservations-global": false,
+        "reservations-in-subnet": false
+      }
+    }
+
+The ``global`` value from the deprecated ``reservation-mode`` corresponds to:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "reservations-global": true,
+        "reservations-in-subnet": false
+      }
+    }
+
+The ``out-of-pool`` value from the deprecated ``reservation-mode`` corresponds to:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "reservations-global": false,
+        "reservations-in-subnet": true,
+        "reservations-out-of-pool": true
+      }
+    }
+
+And the ``all`` value from the deprecated ``reservation-mode`` corresponds to:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "reservations-global": false,
+        "reservations-in-subnet": true,
+        "reservations-out-of-pool": false
+      }
+    }
+
+To activate both ``global`` and ``all``, the following combination can be used:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "reservations-global": true,
+        "reservations-in-subnet": true,
+        "reservations-out-of-pool": false
+      }
+    }
+
+To activate both ``global`` and ``out-of-pool``, the following combination can
+be used:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "reservations-global": true,
+        "reservations-in-subnet": true,
+        "reservations-out-of-pool": true
+      }
+    }
+
+Enabling ``out-of-pool`` and disabling ``in-subnet`` at the same time
+is not recommended because ``out-of-pool`` applies to host reservations in a
+subnet, which are fetched only when the ``in-subnet`` flag is ``true``.
+
+The parameter can be specified at the global, subnet, and shared-network
+levels.
+
+An example configuration that disables reservations looks as follows:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "subnet6": [
+          {
+            "reservations-global": false,
+            "reservations-in-subnet": false,
+            "subnet": "2001:db8:1::/64"
+          }
+        ]
+      }
+    }
+
+An example configuration using global reservations is shown below:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "reservations": [
+          {
+            "duid": "00:03:00:01:11:22:33:44:55:66",
+            "hostname": "host-one"
+          },
+          {
+            "duid": "00:03:00:01:99:88:77:66:55:44",
+            "hostname": "host-two"
+          }
+        ],
+        "reservations-global": true,
+        "reservations-in-subnet": false,
+        "subnet6": [
+          {
+            "pools": [
+              {
+                "pool": "2001:db8:1::-2001:db8:1::100"
+              }
+            ],
+            "subnet": "2001:db8:1::/64"
+          }
+        ]
+      }
+    }
+
+For more details regarding global reservations, see :ref:`global-reservations6`.
+
+Another aspect of host reservations is the different types of
+identifiers. Kea currently supports two types of identifiers in DHCPv6:
+hardware address and DUID. This is beneficial from a usability
+perspective; however, there is one drawback. For each incoming packet
+Kea has to extract each identifier type and then query the database
+to see if there is a reservation by this particular identifier. If
+nothing is found, the next identifier is extracted and the next query is
+issued. This process continues until either a reservation is found or
+all identifier types have been checked. Over time, with an increasing
+number of supported identifier types, Kea would become slower and
+slower.
+
+To address this problem, a parameter called
+``host-reservation-identifiers`` is available. It takes a list of
+identifier types as a parameter. Kea checks only those identifier
+types enumerated in ``host-reservation-identifiers``. From a performance
+perspective, the number of identifier types should be kept to a minimum,
+ideally one. If the deployment uses several reservation types, please
+enumerate them from most- to least-frequently used, as this increases
+the chances of Kea finding the reservation using the fewest queries. An
+example of a ``host-reservation-identifiers`` configuration looks as follows:
+
+::
+
+   "host-reservation-identifiers": [ "duid", "hw-address" ],
+   "subnet6": [
+       {
+           "subnet": "2001:db8:1::/64",
+           ...
+       }
+   ]
+
+If not specified, the default value is:
+
+::
+
+   "host-reservation-identifiers": [ "hw-address", "duid" ]
+
+.. _global-reservations6:
+
+Global Reservations in DHCPv6
+-----------------------------
+
+In some deployments, such as mobile, clients can roam within the network
+and certain parameters must be specified regardless of the client's
+current location. To meet such a need, Kea offers a global reservation
+mechanism. The idea behind it is that regular host
+reservations are tied to specific subnets, by using a specific
+subnet ID. Kea can specify a global reservation that can be used in
+every subnet that has global reservations enabled.
+
+This feature can be used to assign certain parameters, such as hostname
+or other dedicated, host-specific options. It can also be used to assign
+addresses or prefixes. However, global reservations that assign either
+of these bypass the whole topology determination provided by the DHCP logic
+implemented in Kea. It is very easy to misuse this feature and get a
+configuration that is inconsistent. To give a specific example, imagine
+a global reservation for the address 2001:db8:1111::1 and two subnets
+2001:db8:1111::/48 and 2001:db8:ffff::/48. If global reservations are
+used in both subnets and a device matching global host reservations
+visits part of the network that is covered by 2001:db8:ffff::/48, it
+will get the IP address 2001:db8:ffff::1, which is outside of the
+prefix announced by its local router using router advertisements. Such a
+configuration is unusable or, at the very least, riddled with
+issues, such as downlink traffic not reaching the device.
+
+To use global host reservations, a configuration similar to the
+following can be used:
+
+::
+
+   "Dhcp6:" {
+       # This specifies global reservations.
+       # They will apply to all subnets that
+       # have global reservations enabled.
+
+       "reservations": [
+       {
+          "hw-address": "aa:bb:cc:dd:ee:ff",
+          "hostname": "hw-host-dynamic"
+       },
+       {
+          "hw-address": "01:02:03:04:05:06",
+          "hostname": "hw-host-fixed",
+
+          # Use of IP addresses in global reservations is risky.
+          # If used outside of matching subnet, such as 3001::/64,
+          # it will result in a broken configuration being handed
+          # to the client.
+          "ip-address": "2001:db8:ff::77"
+       },
+       {
+          "duid": "01:02:03:04:05",
+          "hostname": "duid-host"
+       }
+       ],
+       "valid-lifetime": 600,
+       "subnet4": [ {
+           "subnet": "2001:db8:1::/64",
+           # It is replaced by the "reservations-global"
+           # "reservations-in-subnet" and "reservations-out-of-pool"
+           # parameters.
+           # "reservation-mode": "global",
+           # Specify if the server should lookup global reservations.
+           "reservations-global": true,
+           # Specify if the server should lookup in-subnet reservations.
+           "reservations-in-subnet": false,
+           # Specify if the server can assume that all reserved addresses
+           # are out-of-pool. It can be ignored because "reservations-in-subnet"
+           # is false.
+           # "reservations-out-of-pool": false,
+           "pools": [ { "pool": "2001:db8:1::-2001:db8:1::100" } ]
+       } ]
+   }
+
+When using database backends, the global host reservations are
+distinguished from regular reservations by using a ``subnet-id`` value of
+0.
+
+.. _pool-selection-with-class-reservations6:
+
+Pool Selection with Client Class Reservations
+---------------------------------------------
+
+Client classes can be specified both in the Kea configuration file and/or
+via host reservations. The classes specified in the Kea configuration file are
+evaluated immediately after receiving the DHCP packet and therefore can be
+used to influence subnet selection using the ``client-class`` parameter
+specified in the subnet scope. The classes specified within the host
+reservations are fetched and assigned to the packet after the server has
+already selected a subnet for the client. This means that the client
+class specified within a host reservation cannot be used to influence
+subnet assignment for this client, unless the subnet belongs to a
+shared network. If the subnet belongs to a shared network, the server may
+dynamically change the subnet assignment while trying to allocate a lease.
+If the subnet does not belong to a shared network, once selected, the subnet
+is not changed once selected.
+
+If the subnet does not belong to a shared network, it is possible to
+use host reservation-based client classification to select an address pool
+within the subnet as follows:
+
+::
+
+    "Dhcp6": {
+        "client-classes": [
+            {
+                "name": "reserved_class"
+            },
+            {
+                "name": "unreserved_class",
+                "test": "not member('reserved_class')"
+            }
+        ],
+        "subnet6": [
+            {
+                "subnet": "2001:db8:1::/64",
+                "reservations": [{"
+                    "hw-address": "aa:bb:cc:dd:ee:fe",
+                    "client-classes": [ "reserved_class" ]
+                 }],
+                "pools": [
+                    {
+                        "pool": "2001:db8:1::10-2001:db8:1::20",
+                        "client-class": "reserved_class"
+                    },
+                    {
+                        "pool": "2001:db8:1::30-2001:db8:1::40",
+                        "client-class": "unreserved_class"
+                    }
+                ]
+            }
+        ]
+    }
+
+The ``reserved_class`` is declared without the ``test`` parameter because
+it may be only assigned to the client via host reservation mechanism. The
+second class, ``unreserved_class``, is assigned to clients which do not
+belong to the ``reserved_class``. The first pool within the subnet is only
+used for clients having a reservation for the ``reserved_class``. The
+second pool is used for clients not having such a reservation. The
+configuration snippet includes one host reservation which causes the client
+with the MAC address aa:bb:cc:dd:ee:fe to be assigned to the
+``reserved_class``. Thus, this client will be given an IP address from the
+first address pool.
+
+.. _subnet-selection-with-class-reservations6:
+
+Subnet Selection with Client Class Reservations
+-----------------------------------------------
+
+There is one specific use case when subnet selection may be influenced by
+client classes specified within host reservations: when the
+client belongs to a shared network. In such a case it is possible to use
+classification to select a subnet within this shared network. Consider the
+following example:
+
+::
+
+    "Dhcp6": {
+        "client-classes": [
+            {
+                "name": "reserved_class"
+            },
+            {
+                "name: "unreserved_class",
+                "test": "not member('reserved_class')"
+            }
+        ],
+        "reservations": [{"
+            "hw-address": "aa:bb:cc:dd:ee:fe",
+            "client-classes": [ "reserved_class" ]
+        }],
+        # It is replaced by the "reservations-global"
+        # "reservations-in-subnet" and "reservations-out-of-pool" parameters.
+        # Specify if the server should lookup global reservations.
+        "reservations-global": true,
+        # Specify if the server should lookup in-subnet reservations.
+        "reservations-in-subnet": false,
+        # Specify if the server can assume that all reserved addresses
+        # are out-of-pool. It can be ignored because "reservations-in-subnet"
+        # is false, but if specified, it is inherited by "shared-networks"
+        # and "subnet6" levels.
+        # "reservations-out-of-pool": false,
+        "shared-networks": [{
+            "subnet6": [
+                {
+                    "subnet": "2001:db8:1::/64",
+                    "pools": [
+                        {
+                            "pool": "2001:db8:1::10-2001:db8:1::20",
+                            "client-class": "reserved_class"
+                        }
+                    ]
+                },
+                {
+                    "subnet": "2001:db8:2::/64",
+                    "pools": [
+                        {
+                            "pool": "2001:db8:2::10-2001:db8:2::20",
+                            "client-class": "unreserved_class"
+                        }
+                    ]
+                }
+            ]
+        }]
+    }
+
+This is similar to the example described in the
+:ref:`pool-selection-with-class-reservations6`. This time, however, there
+are two subnets, each of which has a pool associated with a different
+class. The clients that do not have a reservation for the ``reserved_class``
+are assigned an address from the subnet 2001:db8:2::/64. Clients with
+a reservation for the ``reserved_class`` are assigned an address from
+the subnet 2001:db8:1::/64. The subnets must belong to the same shared network.
+In addition, the reservation for the client class must be specified at the
+global scope (global reservation) and ``reservations-global`` must be
+set to ``true``.
+
+In the example above, the ``client-class`` could also be specified at the
+subnet level rather than the pool level, and would yield the same effect.
+
+.. _multiple-reservations-same-ip6:
+
+Multiple Reservations for the Same IP
+-------------------------------------
+
+Host reservations were designed to preclude the creation of multiple
+reservations for the same IP address or delegated prefix within a
+particular subnet, to avoid having two different clients
+compete for the same lease. When using the default settings, the server
+returns a configuration error when it finds two or more reservations for
+the same lease within a subnet in the Kea configuration file. The
+:ref:`hooks-host-cmds` hook library returns an error in response to the
+``reservation-add`` command when it detects that the reservation exists
+in the database for the lease for which the new reservation is being added.
+
+Similar to DHCPv4 (see :ref:`multiple-reservations-same-ip4`), the DHCPv6
+server can also be configured to allow the creation of multiple reservations
+for the same IPv6 address and/or delegated prefix in a given subnet. This
+is supported since Kea release 1.9.1 as an optional mode of operation
+enabled with the ``ip-reservations-unique`` global parameter.
+
+The ``ip-reservations-unique`` is a boolean parameter that defaults to
+``true``, which forbids the specification of more than one reservation
+for the same lease in a given subnet. Setting this parameter to ``false``
+allows such reservations to be created both in the Kea configuration
+file and in the host database backend, via the ``host-cmds`` hook library.
+
+This setting is currently supported by the most popular host database
+backends, i.e. MySQL and PostgreSQL.
+Host Cache (see :ref:`hooks-host-cache`), or the RADIUS backend
+(see :ref:`hooks-radius`). An attempt to set ``ip-reservations-unique``
+to ``false`` when any of these three backends is in use yields a
+configuration error.
+
+.. note::
+
+   When ``ip-reservations-unique`` is set to ``true`` (the default value),
+   the server ensures that IP reservations are unique for a subnet within
+   a single host backend and/or Kea configuration file. It does not
+   guarantee that the reservations are unique across multiple backends.
+
+
+The following is an example configuration with two reservations for
+the same IPv6 address but different MAC addresses:
+
+::
+
+   "Dhcp6": {
+       "ip-reservations-unique": false,
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/64",
+               "reservations": [
+                   {
+                       "hw-address": "1a:1b:1c:1d:1e:1f",
+                       "ip-address": "2001:db8:1::11"
+                   },
+                   {
+                       "hw-address": "2a:2b:2c:2d:2e:2f",
+                       "ip-address": "2001:db8:1::11"
+                   }
+               ]
+           }
+       ]
+   }
+
+It is possible to control the ``ip-reservations-unique`` parameter via the
+:ref:`dhcp6-cb`. If the new setting of this parameter conflicts with
+the currently used backends (i.e. backends do not support the new setting),
+the new setting is ignored and a warning log message is generated.
+The backends continue to use the default setting, expecting that
+IP reservations are unique within each subnet. To allow the
+creation of non-unique IP reservations, the administrator must remove
+the backends which lack support for them from the configuration file.
+
+Administrators must be careful when they have been using multiple
+reservations for the same IP address and/or delegated prefix and later
+decide to return to the default mode in which this is no longer allowed.
+They must make sure that at most one reservation for
+a given IP address or delegated prefix exists within a subnet, prior
+to switching back to the default mode. If such duplicates are left in
+the configuration file, the server reports a configuration error.
+Leaving such reservations in the host databases does not cause
+configuration errors but may lead to lease allocation errors during
+the server's operation, when it unexpectedly finds multiple reservations
+for the same IP address or delegated prefix.
+
+.. note::
+
+   Currently the Kea server does not verify whether multiple reservations for
+   the same IP address and/or delegated prefix exist in
+   MySQL and/or PostgreSQL) host databases when ``ip-reservations-unique``
+   is updated from ``true`` to ``false``. This may cause issues with
+   lease allocations. The administrator must ensure that there is at
+   most one reservation for each IP address and/or delegated prefix
+   within each subnet, prior to the configuration update.
+
+The ``reservations-lookup-first`` is a boolean parameter which controls whether
+host reservations lookup should be performed before lease lookup. This parameter
+has effect only when multi-threading is disabled. When multi-threading is
+enabled, host reservations lookup is always performed first to avoid lease
+lookup resource locking. The ``reservations-lookup-first`` defaults to ``false``
+when multi-threading is disabled.
+
+.. _shared-network6:
+
+Shared Networks in DHCPv6
+=========================
+
+DHCP servers use subnet information in two ways. It is used to
+both determine the point of attachment, i.e. where the client is
+connected to the network, and to
+group information pertaining to a specific location in the network.
+Sometimes it is useful to have more than one
+logical IP subnet being deployed on the same physical link.
+Understanding that two or more subnets are used on the same link requires
+additional logic in the DHCP server. This capability is called "shared
+networks" in Kea, and sometimes also
+"shared subnets"; in Microsoft's nomenclature it is called
+"multinet."
+
+There are many cases where the shared networks feature is useful; here we explain
+just a handful of the most common ones. The first and by far most common
+use case is an existing IPv4 network that has grown and
+is running out of available
+address space. This is less common in IPv6, but shared networks
+are still useful: for example, with the exhaustion of IPv6-
+delegated prefixes within a subnet, or the desire to
+experiment with an addressing scheme. With the advent of IPv6 deployment
+and a vast address space, many organizations split the address space
+into subnets, deploy it, and then after a while discover that they want
+to split it differently. In the transition period, they want both the old
+and new addressing to be available: thus the need for more than one
+subnet on the same physical link.
+
+Finally, the case of cable networks is directly applicable in IPv6.
+There are two types of devices in cable networks: cable modems and the
+end-user devices behind them. It is a common practice to use different
+subnets for cable modems to prevent users from tinkering with them. In
+this case, the distinction is based on the type of device, rather than
+on address-space exhaustion.
+
+A client connected to a shared network may be assigned a lease (address
+or prefix) from any of the pools defined within the subnets belonging to
+the shared network. Internally, the server selects one of the subnets
+belonging to a shared network and tries to allocate a lease from this
+subnet. If the server is unable to allocate a lease from the selected
+subnet (e.g., due to pool exhaustion), it uses another subnet from
+the same shared network and tries to allocate a lease from this subnet.
+The server typically allocates all leases
+available in a given subnet before it starts allocating leases from
+other subnets belonging to the same shared network. However, in certain
+situations the client can be allocated a lease from another subnet
+before the pools in the first subnet get exhausted; this sometimes occurs
+when the client provides a hint that belongs to another subnet, or the client has
+reservations in a subnet other than the default.
+
+.. note::
+
+   Deployments should not assume that Kea waits until it has allocated
+   all the addresses from the first subnet in a shared network before
+   allocating addresses from other subnets.
+
+To define a shared network, an additional configuration scope is
+introduced:
+
+::
+
+   "Dhcp6": {
+       "shared-networks": [{
+           # Name of the shared network. It may be an arbitrary string
+           # and it must be unique among all shared networks.
+           "name": "ipv6-lab-1",
+
+           # The subnet selector can be specified on the shared network
+           # level. Subnets from this shared network will be selected
+           # for clients communicating via relay agent having
+           # the specified IP address.
+           "relay": {
+               "ip-addresses": [ "2001:db8:2:34::1" ]
+           },
+
+           # This starts a list of subnets in this shared network.
+           # There are two subnets in this example.
+           "subnet6": [{
+               "subnet": "2001:db8::/48",
+               "pools": [{ "pool":  "2001:db8::1 - 2001:db8::ffff" }]
+           }, {
+               "subnet": "3ffe:ffe::/64",
+               "pools": [{ "pool":  "3ffe:ffe::/64" }]
+           }]
+       }], # end of shared-networks
+
+       # It is likely that in the network there will be a mix of regular,
+       # "plain" subnets and shared networks. It is perfectly valid
+       # to mix them in the same configuration file.
+       #
+       # This is a regular subnet. It is not part of any shared-network.
+       "subnet6": [{
+           "subnet": "2001:db9::/48",
+           "pools": [{ "pool":  "2001:db9::/64" }],
+           "relay": {
+               "ip-addresses": [ "2001:db8:1:2::1" ]
+           }
+       }]
+   } # end of Dhcp6
+
+As demonstrated in the example, it is possible to mix shared and regular
+("plain") subnets. Each shared network must have a unique name. This is
+similar to the ID for subnets, but gives administrators more
+flexibility. It is used for logging, but also internally for
+identifying shared networks.
+
+In principle it makes sense to define only shared networks that consist
+of two or more subnets. However, for testing purposes, an empty subnet
+or a network with just a single subnet is allowed. This
+is not a recommended practice in production networks, as the shared
+network logic requires additional processing and thus lowers the
+server's performance. To avoid unnecessary performance degradation,
+shared subnets should only be defined when required by the deployment.
+
+Shared networks provide an ability to specify many parameters in the
+shared network scope that apply to all subnets within it. If
+necessary, it is possible to specify a parameter in the shared-network scope and
+then override its value in the subnet scope. For example:
+
+::
+
+   "shared-networks": [
+       {
+           "name": "lab-network3",
+           "relay": {
+                "ip-addresses": [ "2001:db8:2:34::1" ]
+           },
+
+           # This applies to all subnets in this shared network, unless
+           # values are overridden on subnet scope.
+           "valid-lifetime": 600,
+
+           # This option is made available to all subnets in this shared
+           # network.
+           "option-data": [ {
+               "name": "dns-servers",
+               "data": "2001:db8::8888"
+           } ],
+
+           "subnet6": [
+               {
+                   "subnet": "2001:db8:1::/48",
+                   "pools": [ { "pool":  "2001:db8:1::1 - 2001:db8:1::ffff" } ],
+
+                   # This particular subnet uses different values.
+                   "valid-lifetime": 1200,
+                   "option-data": [
+                   {
+                       "name": "dns-servers",
+                       "data": "2001:db8::1:2"
+                   },
+                   {
+                       "name": "unicast",
+                       "data": "2001:abcd::1"
+                   } ]
+               },
+               {
+                    "subnet": "2001:db8:2::/48",
+                    "pools": [ { "pool":  "2001:db8:2::1 - 2001:db8:2::ffff" } ],
+
+                    # This subnet does not specify its own valid-lifetime value,
+                    # so it is inherited from shared network scope.
+                    "option-data": [
+                    {
+                        "name": "dns-servers",
+                        "data": "2001:db8:cafe::1"
+                    } ]
+               }
+           ],
+       } ]
+
+In this example, there is a ``dns-servers`` option defined that is available
+to clients in both subnets in this shared network. Also, the valid
+lifetime is set to 10 minutes (600s). However, the first subnet
+overrides some of the values (the valid lifetime is 20 minutes, there is a different IP
+address for ``dns-servers``), but also adds its own option (the unicast
+address). Assuming a client asking for server unicast and ``dns-servers``
+options is assigned a lease from this subnet, it will get a lease for 20
+minutes and ``dns-servers``, and be allowed to use server unicast at address
+2001:abcd::1. If the same client is assigned to the second subnet, it
+will get a 10-minute lease, a ``dns-servers`` value of 2001:db8:cafe::1, and
+no server unicast.
+
+Some parameters must be the same in all subnets in the same shared
+network. This restriction applies to the ``interface`` and
+``rapid-commit`` settings. The most convenient way is to define them on
+the shared-network scope, but they can be specified for each subnet.
+However, each subnet must have the same value.
+
+.. note::
+
+    There is an inherent ambiguity when using clients that send multiple IA
+    options in a single request, and shared-networks whose subnets have
+    different values for options and configuration parameters. The server
+    sequentially processes IA options in the order that they occur in the
+    client's query; if the leases requested in the IA options end up being
+    fulfilled from different subnets, which parameters and options should
+    apply? Currently, the code uses the values from the last subnet of
+    the last IA option fulfilled.
+
+    We view this largely as a site configuration issue. A shared network
+    generally means the same physical link, so services configured by options
+    from subnet A should be as easily reachable from subnet B and vice versa.
+    There are a number of ways to avoid this situation:
+
+    - Use the same values for options and parameters for subnets within the shared network.
+    - Use subnet selectors or client class guards that ensure that for a single client's query, the same subnet is used for all IA options in that query.
+    - Avoid using shared networks with clients that send multiple IA options per query.
+
+Local and Relayed Traffic in Shared Networks
+--------------------------------------------
+
+It is possible to specify an interface name at the shared network level,
+to tell the server that this specific shared network is reachable
+directly (not via relays) using the local network interface. As all
+subnets in a shared network are expected to be used on the same physical
+link, it is a configuration error to attempt to define a shared network
+using subnets that are reachable over different interfaces. In other
+words, all subnets within the shared network must have the same value
+for the ``interface`` parameter. The following configuration is an example
+of what **NOT** to do:
+
+::
+
+   "shared-networks": [
+       {
+           "name": "office-floor-2",
+           "subnet6": [
+               {
+                   "subnet": "2001:db8::/64",
+                   "pools": [ { "pool":  "2001:db8::1 - 2001:db8::ffff" } ],
+                   "interface": "eth0"
+               },
+               {
+                    "subnet": "3ffe:abcd::/64",
+                    "pools": [ { "pool":  "3ffe:abcd::1 - 3ffe:abcd::ffff" } ],
+
+                    # Specifying the different interface name is a configuration
+                    # error. This value should rather be "eth0" or the interface
+                    # name in the other subnet should be "eth1".
+                    # "interface": "eth1"
+               }
+           ],
+       } ]
+
+To minimize the chance of configuration errors, it is often more convenient
+to simply specify the interface name once, at the shared-network level, as
+shown in the example below.
+
+::
+
+   "shared-networks": [
+       {
+           "name": "office-floor-2",
+
+           # This tells Kea that the whole shared network is reachable over a
+           # local interface. This applies to all subnets in this network.
+           "interface": "eth0",
+
+           "subnet6": [
+               {
+                   "subnet": "2001:db8::/64",
+                   "pools": [ { "pool":  "2001:db8::1 - 2001:db8::ffff" } ],
+               },
+               {
+                    "subnet": "3ffe:abcd::/64",
+                    "pools": [ { "pool":  "3ffe:abcd::1 - 3ffe:abcd::ffff" } ]
+               }
+           ],
+       } ]
+
+
+With relayed traffic, subnets are typically selected using
+the relay agents' addresses. If the subnets are used independently (not
+grouped within a shared network), a different relay
+address can be specified for each of these subnets. When multiple subnets belong to a
+shared network they must be selected via the same relay address and,
+similarly to the case of the local traffic described above, it is a
+configuration error to specify different relay addresses for the respective
+subnets in the shared network. The following configuration is another example
+of what **NOT** to do:
+
+::
+
+   "shared-networks": [
+       {
+           "name": "kakapo",
+           "subnet6": [
+               {
+                   "subnet": "2001:db8::/64",
+                   "relay": {
+                       "ip-addresses": [ "2001:db8::1234" ]
+                   },
+                   "pools": [ { "pool":  "2001:db8::1 - 2001:db8::ffff" } ]
+               },
+               {
+                   "subnet": "3ffe:abcd::/64",
+                   "pools": [ { "pool":  "3ffe:abcd::1 - 3ffe:abcd::ffff" } ],
+                   "relay": {
+                       # Specifying a different relay address for this
+                       # subnet is a configuration error. In this case
+                       # it should be 2001:db8::1234 or the relay address
+                       # in the previous subnet should be 3ffe:abcd::cafe.
+                       "ip-addresses": [ "3ffe:abcd::cafe" ]
+                   }
+               }
+           ]
+       }
+   ]
+
+Again, it is better to specify the relay address at the shared-network
+level; this value will be inherited by all subnets belonging to the
+shared network.
+
+::
+
+   "shared-networks": [
+       {
+           "name": "kakapo",
+           "relay": {
+               # This relay address is inherited by both subnets.
+               "ip-addresses": [ "2001:db8::1234" ]
+           },
+           "subnet6": [
+               {
+                   "subnet": "2001:db8::/64",
+                   "pools": [ { "pool":  "2001:db8::1 - 2001:db8::ffff" } ]
+               },
+               {
+                    "subnet": "3ffe:abcd::/64",
+                    "pools": [ { "pool":  "3ffe:abcd::1 - 3ffe:abcd::ffff" } ]
+               }
+           ]
+       }
+   ]
+
+Even though it is technically possible to configure two (or more) subnets
+within the shared network to use different relay addresses, this will almost
+always lead to a different behavior than what the user would expect. In this
+case, the Kea server will initially select one of the subnets by matching
+the relay address in the client's packet with the subnet's configuration.
+However, it MAY end up using the other subnet (even though it does not match
+the relay address) if the client already has a lease in this subnet or has a
+host reservation in this subnet, or simply if the initially selected subnet has no
+more addresses available. Therefore, it is strongly recommended to always
+specify subnet selectors (interface or relay address) at the shared-network
+level if the subnets belong to a shared network, as it is rarely useful to
+specify them at the subnet level and may lead to the configuration errors
+described above.
+
+Client Classification in Shared Networks
+----------------------------------------
+
+Sometimes it is desirable to segregate clients into specific subnets
+based on certain properties. This mechanism is called client
+classification and is described in :ref:`classify`. Client
+classification can be applied to subnets belonging to shared networks in
+the same way as it is used for subnets specified outside of shared
+networks. It is important to understand how the server selects subnets
+for clients when client classification is in use, to ensure that the
+appropriate subnet is selected for a given client type.
+
+If a subnet is associated with a class, only the clients belonging to
+this class can use this subnet. If there are no classes specified for a
+subnet, any client connected to a given shared network can use this
+subnet. A common mistake is to assume that the subnet that includes a client
+class is preferred over subnets without client classes. Consider the
+following example:
+
+::
+
+   {
+       "client-classes": [
+           {
+               "name": "b-devices",
+               "test": "option[1234].hex == 0x0002"
+           }
+       ],
+       "shared-networks": [
+           {
+               "name": "galah",
+               "relay": {
+                   "ip-address": [ "2001:db8:2:34::1" ]
+               },
+               "subnet6": [
+                   {
+                       "subnet": "2001:db8:1::/64",
+                       "pools": [ { "pool": "2001:db8:1::20 - 2001:db8:1::ff" } ],
+                   },
+                   {
+                       "subnet": "2001:db8:3::/64",
+                       "pools": [ { "pool": "2001:db8:3::20 - 2001:db8:3::ff" } ],
+                       "client-class": "b-devices"
+                   }
+               ]
+           }
+       ]
+   }
+
+If the client belongs to the "b-devices" class (because it includes
+option 1234 with a value of 0x0002), that does not guarantee that the
+subnet 2001:db8:3::/64 will be used (or preferred) for this client. The
+server can use either of the two subnets, because the subnet
+2001:db8:1::/64 is also allowed for this client. The client
+classification used in this case should be perceived as a way to
+restrict access to certain subnets, rather than as a way to express subnet
+preference. For example, if the client does not belong to the "b-devices"
+class, it may only use the subnet 2001:db8:1::/64 and will never use the
+subnet 2001:db8:3::/64.
+
+A typical use case for client classification is in a cable network,
+where cable modems should use one subnet and other devices should use
+another subnet within the same shared network. In this case it is
+necessary to apply classification on all subnets. The following example
+defines two classes of devices, and the subnet selection is made based
+on option 1234 values.
+
+::
+
+   {
+       "client-classes": [
+           {
+
+               "name": "a-devices",
+               "test": "option[1234].hex == 0x0001"
+           },
+           {
+               "name": "b-devices",
+               "test": "option[1234].hex == 0x0002"
+           }
+       ],
+       "shared-networks": [
+           {
+               "name": "galah",
+               "relay": {
+                   "ip-addresses":  [ "2001:db8:2:34::1" ]
+               },
+               "subnet6": [
+                   {
+                       "subnet": "2001:db8:1::/64",
+                       "pools": [ { "pool": "2001:db8:1::20 - 2001:db8:1::ff" } ],
+                       "client-class": "a-devices"
+                   },
+                   {
+                       "subnet": "2001:db8:3::/64",
+                       "pools": [ { "pool": "2001:db8:3::20 - 2001:db8:3::ff" } ],
+                       "client-class": "b-devices"
+                   }
+               ]
+           }
+       ]
+   }
+
+In this example each class has its own restriction. Only clients that
+belong to class "a-devices" are able to use subnet 2001:db8:1::/64
+and only clients belonging to "b-devices" are able to use subnet
+2001:db8:3::/64. Care should be taken not to define too-restrictive
+classification rules, as clients that are unable to use any subnets will
+be refused service. However, this may be a desired outcome if one wishes
+to provide service only to clients with known properties (e.g. only VoIP
+phones allowed on a given link).
+
+It is possible to achieve an effect similar to the one
+presented in this section without the use of shared networks. If the
+subnets are placed in the global subnets scope, rather than in the
+shared network, the server will still use classification rules to pick
+the right subnet for a given class of devices. The major benefit of
+placing subnets within the shared network is that common parameters for
+the logically grouped subnets can be specified once, in the shared
+network scope, e.g. the ``interface`` or ``relay`` parameter. All subnets
+belonging to this shared network will inherit those parameters.
+
+Host Reservations in Shared Networks
+------------------------------------
+
+Subnets that are part of a shared network allow host reservations,
+similar to regular subnets:
+
+::
+
+   {
+       "shared-networks": [
+       {
+           "name": "frog",
+           "relay": {
+               "ip-addresses": [ "2001:db8:2:34::1" ]
+           },
+           "subnet6": [
+               {
+                   "subnet": "2001:db8:1::/64",
+                   "id": 100,
+                   "pools": [ { "2001:db8:1::1 - 2001:db8:1::64" } ],
+                   "reservations": [
+                   {
+                       "duid": "00:03:00:01:11:22:33:44:55:66",
+                       "ip-addresses": [ "2001:db8:1::28" ]
+                   }
+                   ]
+               },
+               {
+                   "subnet": "2001:db8:3::/64",
+                   "id": 101,
+                   "pools": [ { "pool": "2001:db8:3::1 - 2001:db8:3::64" } ],
+                   "reservations": [
+                       {
+                           "duid": "00:03:00:01:aa:bb:cc:dd:ee:ff",
+                           "ip-addresses": [ "2001:db8:2::28" ]
+                       }
+                   ]
+               }
+           ]
+       }
+       ]
+   }
+
+
+It is worth noting that Kea conducts additional checks when processing a
+packet if shared networks are defined. First, instead of simply checking
+whether there is a reservation for a given client in its initially
+selected subnet, Kea looks through all subnets in a shared network for a
+reservation. This is one of the reasons why defining a shared network
+may impact performance. If there is a reservation for a client in any
+subnet, that particular subnet is picked for the client. Although
+it is technically not an error, it is considered bad practice to define
+reservations for the same host in multiple subnets belonging to the same
+shared network.
+
+While not strictly mandatory, it is strongly recommended to use explicit
+"id" values for subnets if database storage will be used for host
+reservations. If an ID is not specified, the values for it are
+auto generated, i.e. Kea assigns increasing integer values starting from
+1. Thus, the auto-generated IDs are not stable across configuration
+changes.
+
+.. _dhcp6-serverid:
+
+Server Identifier in DHCPv6
+===========================
+
+The DHCPv6 protocol uses a "server identifier" (also known as a DUID) to
+allow clients to discriminate between several servers present on the
+same link. `RFC 8415 <https://tools.ietf.org/html/rfc8415>`__ currently
+defines four DUID types: DUID-LLT, DUID-EN, DUID-LL, and DUID-UUID.
+
+The Kea DHCPv6 server generates a server identifier once, upon the first
+startup, and stores it in a file. This identifier is not modified across
+restarts of the server and so is a stable identifier.
+
+Kea follows the recommendation from `RFC
+8415 <https://tools.ietf.org/html/rfc8415>`__ to use DUID-LLT as the
+default server identifier. However, ISC has received reports that some
+deployments require different DUID types, and that there is a need to
+administratively select both the DUID type and/or its contents.
+
+The server identifier can be configured using parameters within the
+``server-id`` map element in the global scope of the Kea configuration
+file. The following example demonstrates how to select DUID-EN as a
+server identifier:
+
+::
+
+   "Dhcp6": {
+       "server-id": {
+           "type": "EN"
+       },
+       ...
+   }
+
+Currently supported values for the ``type`` parameter are: "LLT", "EN", and
+"LL", for DUID-LLT, DUID-EN, and DUID-LL respectively.
+
+When a new DUID type is selected, the server generates its value and
+replaces any existing DUID in the file. The server then uses the new
+server identifier in all future interactions with clients.
+
+.. note::
+
+   If the new server identifier is created after some clients have
+   obtained their leases, the clients using the old identifier are not
+   able to renew their leases; the server will ignore messages containing
+   the old server identifier. Clients will continue sending RENEW until
+   they transition to the rebinding state. In this state, they will
+   start sending REBIND messages to the multicast address without a
+   server identifier. The server will respond to the REBIND messages
+   with a new server identifier, and the clients will associate the new
+   server identifier with their leases. Although the clients will be
+   able to keep their leases and will eventually learn the new server
+   identifier, this will be at the cost of an increased number of
+   renewals and multicast traffic due to a need to rebind. Therefore, it
+   is recommended that modification of the server-identifier type and
+   value be avoided if the server has already assigned leases and these
+   leases are still valid.
+
+There are cases when an administrator needs to explicitly specify a DUID
+value rather than allow the server to generate it. The following example
+demonstrates how to explicitly set all components of a DUID-LLT.
+
+::
+
+   "Dhcp6": {
+       "server-id": {
+           "type": "LLT",
+           "htype": 8,
+           "identifier": "A65DC7410F05",
+           "time": 2518920166
+       },
+       ...
+   }
+
+where:
+
+-  ``htype`` is a 16-bit unsigned value specifying hardware type,
+
+-  ``identifier`` is a link-layer address, specified as a string of
+   hexadecimal digits, and
+
+-  ``time`` is a 32-bit unsigned time value.
+
+The hexadecimal representation of the DUID generated as a result of the
+configuration specified above is:
+
+::
+
+    00:01:00:08:96:23:AB:E6:A6:5D:C7:41:0F:05
+   |type |htype|   time    |   identifier    |
+
+A special value of "0" for ``htype`` and ``time`` is allowed, which indicates
+that the server should use ANY value for these components. If the server
+already uses a DUID-LLT, it will use the values from this DUID; if the
+server uses a DUID of a different type or does not yet use any DUID, it
+will generate these values. Similarly, if the ``identifier`` is assigned
+an empty string, the value of the ``identifier`` will be generated. Omitting
+any of these parameters is equivalent to setting them to those special
+values.
+
+For example, the following configuration:
+
+::
+
+   "Dhcp6": {
+       "server-id": {
+           "type": "LLT",
+           "htype": 0,
+           "identifier": "",
+           "time": 2518920166
+       },
+       ...
+   }
+
+indicates that the server should use ANY link-layer address and hardware
+type. If the server is already using DUID-LLT, it will use the
+link-layer address and hardware type from the existing DUID. If the
+server is not yet using any DUID, it will use the link-layer address and
+hardware type from one of the available network interfaces. The server
+will use an explicit value of time; if it is different than a time value
+present in the currently used DUID, that value will be replaced,
+effectively modifying the current server identifier.
+
+The following example demonstrates an explicit configuration of a
+DUID-EN:
+
+::
+
+   "Dhcp6": {
+       "server-id": {
+           "type": "EN",
+           "enterprise-id": 2495,
+           "identifier": "87ABEF7A5BB545"
+       },
+       ...
+   }
+
+where:
+
+-  ``enterprise-id`` is a 32-bit unsigned value holding an enterprise
+   number, and
+
+-  ``identifier`` is a variable- length identifier within DUID-EN.
+
+The hexadecimal representation of the DUID-EN created according to the
+configuration above is:
+
+::
+
+    00:02:00:00:09:BF:87:AB:EF:7A:5B:B5:45
+   |type |  ent-id   |     identifier     |
+
+As in the case of the DUID-LLT, special values can be used for the
+configuration of the DUID-EN. If the ``enterprise-id`` is "0", the server
+will use a value from the existing DUID-EN. If the server is not using
+any DUID or the existing DUID has a different type, the ISC enterprise
+ID will be used. When an empty string is entered for ``identifier``, the
+identifier from the existing DUID-EN will be used. If the server is not
+using any DUID-EN, a new 6-byte-long ``identifier`` will be generated.
+
+DUID-LL is configured in the same way as DUID-LLT except that the
+``time`` parameter has no effect for DUID-LL, because this DUID type
+only comprises a hardware type and link-layer address. The following
+example demonstrates how to configure DUID-LL:
+
+::
+
+   "Dhcp6": {
+       "server-id": {
+           "type": "LL",
+           "htype": 8,
+           "identifier": "A65DC7410F05"
+       },
+       ...
+   }
+
+which will result in the following server identifier:
+
+::
+
+    00:03:00:08:A6:5D:C7:41:0F:05
+   |type |htype|   identifier    |
+
+The server stores the generated server identifier in the following
+location: ``[kea-install-dir]/var/lib/kea/kea-dhcp6-serverid``.
+
+In some uncommon deployments where no stable storage is available, the
+server should be configured not to try to store the server identifier.
+This choice is controlled by the value of the ``persist`` boolean
+parameter:
+
+::
+
+   "Dhcp6": {
+       "server-id": {
+           "type": "EN",
+           "enterprise-id": 2495,
+           "identifier": "87ABEF7A5BB545",
+           "persist": false
+       },
+       ...
+   }
+
+The default value of the ``persist`` parameter is ``true``, which
+configures the server to store the server identifier on a disk.
+
+In the example above, the server is configured not to store the
+generated server identifier on a disk. But if the server identifier is
+not modified in the configuration, the same value is used after
+server restart, because the entire server identifier is explicitly
+specified in the configuration.
+
+.. _data-directory:
+
+DHCPv6 Data Directory
+=====================
+
+The Kea DHCPv6 server puts the server identifier file and the default
+memory lease file into its data directory. By default this directory is
+``prefix/var/lib/kea`` but this location can be changed using the
+``data-directory`` global parameter, as in:
+
+::
+
+   "Dhcp6": {
+       "data-directory": "/var/tmp/kea-server6",
+       ...
+   }
+
+.. _stateless-dhcp6:
+
+Stateless DHCPv6 (INFORMATION-REQUEST Message)
+==============================================
+
+Typically DHCPv6 is used to assign both addresses and options. These
+assignments (leases) have a state that changes over time, hence their
+description as "stateful." DHCPv6 also supports a "stateless" mode, where clients
+request only configuration options. This mode is considered lightweight
+from the server perspective, as it does not require any state tracking.
+
+The Kea server supports stateless mode. When clients send
+INFORMATION-REQUEST messages, the server sends back answers with the
+requested options, if they are available in the server
+configuration. The server attempts to use per-subnet options first; if
+that fails, it then tries to provide options
+defined in the global scope.
+
+Stateless and stateful mode can be used together. No special
+configuration directives are required to handle this; simply use the
+configuration for stateful clients and the stateless clients will get
+only the options they requested.
+
+It is possible to run a server that provides only options and no addresses or
+prefixes. If the options have the same value in each subnet, the
+configuration can define the required options in the global scope and skip
+subnet definitions altogether. Here's a simple example of such a
+configuration:
+
+::
+
+   "Dhcp6": {
+       "interfaces-config": {
+           "interfaces": [ "ethX" ]
+       },
+       "option-data": [ {
+           "name": "dns-servers",
+           "data": "2001:db8::1, 2001:db8::2"
+       } ],
+       "lease-database": {
+           "type": "memfile"
+       }
+    }
+
+This very simple configuration provides DNS server information to
+all clients in the network, regardless of their location. The
+memfile lease database must be specified, as Kea
+requires a lease database to be specified even if it is not used.
+
+.. _dhcp6-rfc7550:
+
+Support for RFC 7550 (now part of RFC 8415)
+===========================================
+
+`RFC 7550 <https://tools.ietf.org/html/rfc7550>`__ introduced some
+changes to the previous DHCPv6 specifications, `RFC
+3315 <https://tools.ietf.org/html/rfc3315>`__ and `RFC
+3633 <https://tools.ietf.org/html/rfc3633>`__, to resolve issues
+with the coexistence of multiple stateful options in the messages sent
+between clients and servers. Those changes were later included in
+the most recent DHCPv6 protocol specification, `RFC
+8415 <https://tools.ietf.org/html/rfc8415>`__, which obsoleted `RFC
+7550 <https://tools.ietf.org/html/rfc7550>`__. Kea supports `RFC
+8415 <https://tools.ietf.org/html/rfc8415>`__ along with these protocol
+changes, which are briefly described below.
+
+When a client, such as a requesting router, requests an allocation of
+both addresses and prefixes during the 4-way (SARR) exchange with the
+server, and the server is not configured to allocate any prefixes but
+can allocate some addresses, it will respond with the IA_NA(s)
+containing allocated addresses and the IA_PD(s) containing the
+NoPrefixAvail status code. According to the updated specifications, if
+the client can operate without prefixes it should accept allocated
+addresses and transition to the "bound" state. When the client
+subsequently sends RENEW/REBIND messages to the server to extend the
+lifetimes of the allocated addresses, according to the T1 and T2 times, and
+if the client is still interested in obtaining prefixes from the server,
+it may also include an IA_PD in the RENEW/REBIND to request allocation
+of the prefixes. If the server still cannot allocate the prefixes, it
+will respond with the IA_PD(s) containing the NoPrefixAvail status code.
+However, if the server can allocate the prefixes, it allocates and
+sends them in the IA_PD(s) to the client. A similar situation occurs when
+the server is unable to allocate addresses for the client but can
+delegate prefixes: the client may request allocation of the addresses
+while renewing the delegated prefixes. Allocating leases for other IA
+types while renewing existing leases is by default supported by the Kea
+DHCPv6 server, and the server provides no configuration mechanisms to
+disable this behavior.
+
+The following are the other behaviors first introduced in `RFC
+7550 <https://tools.ietf.org/html/rfc7550>`__ (now part of `RFC
+8415 <https://tools.ietf.org/html/rfc8415>`__) and supported by the Kea
+DHCPv6 server:
+
+-  Set T1/T2 timers to the same value for all stateful (IA_NA and IA_PD)
+   options to facilitate renewal of all of a client's leases at the same
+   time (in a single message exchange).
+
+-  Place NoAddrsAvail and NoPrefixAvail status codes in the IA_NA and
+   IA_PD options in the ADVERTISE message, rather than as the top-level
+   options.
+
+.. _dhcp6-relay-override:
+
+Using a Specific Relay Agent for a Subnet
+=========================================
+
+The DHCPv6 server follows the same principles as the DHCPv4 server to
+select a subnet for the client, with noticeable differences mainly for
+relays.
+
+.. note::
+
+   When the selected subnet is a member of a shared network, the
+   whole shared network is selected.
+
+A relay must have an interface connected to the link on which the
+clients are being configured. Typically the relay has a global IPv6
+address configured on that interface, which belongs to the subnet from
+which the server assigns addresses. Normally, the server is able to
+use the IPv6 address inserted by the relay (in the ``link-addr`` field in
+the RELAY-FORW message) to select the appropriate subnet.
+
+However, that is not always the case; the relay address may not match
+the subnet in certain deployments. This usually means that there is more
+than one subnet allocated for a given link. The two most common examples
+of this are long-lasting network renumbering (where both the
+old and new address spaces are still being used) and a cable network. In a
+cable network, both cable modems and the devices behind them are
+physically connected to the same link, yet they use distinct addressing.
+In such a case, the DHCPv6 server needs additional information (the
+value of the ``interface-id`` option or the IPv6 address inserted in the
+``link-addr`` field in the RELAY-FORW message) to properly select an
+appropriate subnet.
+
+The following example assumes that there is a subnet 2001:db8:1::/64
+that is accessible via a relay that uses 3000::1 as its IPv6 address.
+The server is able to select this subnet for any incoming packets that
+come from a relay that has an address in the 2001:db8:1::/64 subnet. It also
+selects that subnet for a relay with address 3000::1.
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "subnet": "2001:db8:1::/64",
+               "pools": [
+                    {
+                        "pool": "2001:db8:1::1-2001:db8:1::ffff"
+                    }
+               ],
+               "relay": {
+                   "ip-addresses": [ "3000::1" ]
+               }
+           }
+       ]
+   }
+
+If ``relay`` is specified, the ``ip-addresses`` parameter within it is
+mandatory. The ``ip-addresses`` parameter supports specifying a list of addresses.
+
+.. _dhcp6-client-class-relay:
+
+Segregating IPv6 Clients in a Cable Network
+===========================================
+
+In certain cases, it is useful to mix relay address information
+(introduced in :ref:`dhcp6-relay-override`) with client classification (explained
+in :ref:`classify`). One specific example is in a cable network,
+where modems typically get addresses from a different subnet than all
+the devices connected behind them.
+
+Let us assume that there is one Cable Modem Termination System (CMTS)
+with one CM MAC (a physical link that modems are connected to). We want
+the modems to get addresses from the 3000::/64 subnet, while everything
+connected behind the modems should get addresses from the 2001:db8:1::/64
+subnet. The CMTS that acts as a relay uses address 3000::1.
+The following configuration can serve that situation:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [
+           {
+               "subnet": "3000::/64",
+               "pools": [
+                   { "pool": "3000::2 - 3000::ffff" }
+               ],
+               "client-class": "VENDOR_CLASS_docsis3.0",
+               "relay": {
+                   "ip-addresses": [ "3000::1" ]
+               }
+           },
+           {
+               "subnet": "2001:db8:1::/64",
+               "pools": [
+                    {
+                        "pool": "2001:db8:1::1-2001:db8:1::ffff"
+                    }
+               ],
+               "relay": {
+                   "ip-addresses": [ "3000::1" ]
+               }
+           }
+       ]
+   }
+
+.. _mac-in-dhcpv6:
+
+MAC/Hardware Addresses in DHCPv6
+================================
+
+MAC/hardware addresses are available in DHCPv4 messages from
+clients, and administrators frequently use that information to perform
+certain tasks like per-host configuration and address reservation for
+specific MAC addresses. Unfortunately, the DHCPv6 protocol does not
+provide any completely reliable way to retrieve that information. To
+mitigate that issue, a number of mechanisms have been implemented in
+Kea. Each of these mechanisms works in certain cases, but may not in
+others. Whether the mechanism works in a particular deployment is
+somewhat dependent on the network topology and the technologies used.
+
+Kea allows specification of which of the supported methods should be
+used and in what order, via the ``mac-sources`` parameter. This configuration
+may be considered a fine
+tuning of the DHCP deployment.
+
+Here is an example:
+
+::
+
+   "Dhcp6": {
+       "mac-sources": [ "method1", "method2", "method3", ... ],
+
+       "subnet6": [ ... ],
+
+       ...
+   }
+
+When not specified, a value of "any" is used, which instructs
+the server to attempt to try all the methods in sequence and use the
+value returned by the first one that succeeds. In a typical deployment the default value
+of "any" is sufficient and there is no need to select specific
+methods. Changing the value of this parameter is most useful in
+cases when an administrator wants to disable certain methods; for
+example, if the administrator trusts the network infrastructure more
+than the information provided by the clients themselves, they may prefer
+information provided by the relays over that provided by clients.
+
+If specified, ``mac-sources`` must have at least one value.
+
+Supported methods are:
+
+-  ``any`` - this is not an actual method, just a keyword that instructs Kea to
+   try all other methods and use the first one that succeeds. This is
+   the default operation if no ``mac-sources`` are defined.
+
+-  ``raw`` - in principle, a DHCPv6 server could use raw sockets to
+   receive incoming traffic and extract MAC/hardware address
+   information. This is currently not implemented for DHCPv6 and this
+   value has no effect.
+
+-  ``duid`` - DHCPv6 uses DUID identifiers instead of MAC addresses.
+   There are currently four DUID types defined, and two of them
+   (DUID-LLT, which is the default, and DUID-LL) convey MAC address
+   information. Although `RFC 8415 <https://tools.ietf.org/html/rfc8415>`__
+   forbids it, it is possible to
+   parse those DUIDs and extract necessary information from them. This
+   method is not completely reliable, as clients may use other DUID
+   types, namely DUID-EN or DUID-UUID.
+
+-  ``ipv6-link-local`` - another possible acquisition method comes from
+   the source IPv6 address. In typical usage, clients are sending their
+   packets from IPv6 link-local addresses. There is a good chance that
+   those addresses are based on EUI-64, which contains a MAC address.
+   This method is not completely reliable, as clients may use other
+   link-local address types. In particular, privacy extensions, defined
+   in `RFC 4941 <https://tools.ietf.org/html/rfc4941>`__, do not use MAC
+   addresses. Also note that successful extraction requires that the
+   address's u-bit must be set to "1" and its g-bit set to "0", indicating
+   that it is an interface identifier as per `RFC 2373, section
+   2.5.1 <https://tools.ietf.org/html/rfc2373#section-2.5.1>`__.
+
+-  ``client-link-addr-option`` - one extension defined to alleviate
+   missing MAC issues is the client link-layer address option, defined
+   in `RFC 6939 <https://tools.ietf.org/html/rfc6939>`__. This is an
+   option that is inserted by a relay and contains information about a
+   client's MAC address. This method requires a relay agent that
+   supports the option and is configured to insert it. This method is
+   useless for directly connected clients. The value ``rfc6939`` is an alias for
+   ``client-link-addr-option``.
+
+-  ``remote-id`` - `RFC 4649 <https://tools.ietf.org/html/rfc4649>`__
+   defines a ``remote-id`` option that is inserted by a relay agent.
+   Depending on the relay agent configuration, the inserted option may
+   convey the client's MAC address information. The value ``rfc4649``
+   is an alias for ``remote-id``.
+
+-  ``subscriber-id`` - Defined in `RFC 4580 <https://tools.ietf.org/html/rfc4580>`__,
+   ``subscriber-id`` is somewhat similar to ``remote-id``; it is also inserted
+   by a relay agent. The value ``rfc4580`` is an alias for
+   ``subscriber-id``. This method is currently not implemented.
+
+-  ``docsis-cmts`` - Yet another possible source of MAC address
+   information are the DOCSIS options inserted by a CMTS that acts as a
+   DHCPv6 relay agent in cable networks. This method attempts to extract
+   MAC address information from sub-option 1026 (cm mac) of the
+   vendor-specific option with ``vendor-id=4491``. This vendor option is
+   extracted from the Relay-forward message, not the original client's
+   message.
+
+-  ``docsis-modem`` - The final possible source of MAC address
+   information are the DOCSIS options inserted by the cable modem
+   itself. This method attempts to extract MAC address information from
+   sub-option 36 (``device-id``) of the vendor-specific option with
+   ``vendor-id=4491``. This vendor option is extracted from the original
+   client's message, not from any relay options.
+
+An empty ``mac-sources`` parameter is not allowed. Administrators who do not want to specify it
+should either simply omit the ``mac-sources`` definition or specify it with the
+"any" value, which is the default.
+
+.. _dhcp6-decline:
+
+Duplicate Addresses (DHCPDECLINE Support)
+=========================================
+
+The DHCPv6 server is configured with a certain pool of addresses that it
+is expected to hand out to DHCPv6 clients. It is assumed that the server
+is authoritative and has complete jurisdiction over those addresses.
+However, for various reasons such as misconfiguration or a faulty
+client implementation that retains its address beyond the valid
+lifetime, there may be devices connected that use those addresses
+without the server's approval or knowledge.
+
+Such an unwelcome event can be detected by legitimate clients (using
+Duplicate Address Detection) and reported to the DHCPv6 server using a
+DHCPDECLINE message. The server does a sanity check (to see whether
+the client declining an address really was supposed to use it), then
+conducts a clean-up operation, and confirms the DHCPDECLINE by sending back a REPLY
+message. Any DNS entries related to that address are removed, the
+event is logged, and hooks are triggered. After that is
+complete, the address is marked as declined (which indicates that
+it is used by an unknown entity and thus not available for assignment)
+and a probation time is set on it. Unless otherwise configured, the
+probation period lasts 24 hours; after that time, the server will
+recover the lease (i.e. put it back into the available state) and the
+address will be available for assignment again. It should be noted that
+if the underlying issue of a misconfigured device is not resolved, the
+duplicate-address scenario will repeat. If reconfigured correctly, this
+mechanism provides an opportunity to recover from such an event
+automatically, without any system administrator intervention.
+
+To configure the decline probation period to a value other than the
+default, the following syntax can be used:
+
+::
+
+     "Dhcp6": {
+       "decline-probation-period": 3600,
+       "subnet6": [ ... ],
+       ...
+   }
+
+The parameter is expressed in seconds, so the example above
+instructs the server to recycle declined leases after one hour.
+
+There are several statistics and hook points associated with the decline
+handling procedure. The ``lease6_decline`` hook is triggered after the
+incoming DHCPDECLINE message has been sanitized and the server is about
+to decline the lease. The ``declined-addresses`` statistic is increased
+after the hook returns (both the global and subnet-specific variants). (See
+:ref:`dhcp6-stats` and :ref:`hooks-libraries`
+for more details on DHCPv6 statistics and Kea hook points.)
+
+Once the probation time elapses, the declined lease is recovered using
+the standard expired-lease reclamation procedure, with several
+additional steps. In particular, both ``declined-addresses`` statistics
+(global and subnet-specific) are decreased. At the same time,
+``reclaimed-declined-addresses`` statistics (again in two variants, global
+and subnet-specific) are increased.
+
+A note about statistics: The Kea server does not decrease the
+``assigned-nas`` statistics when a DHCPDECLINE message is received and
+processed successfully. While technically a declined address is no
+longer assigned, the primary usage of the ``assigned-nas`` statistic
+is to monitor pool utilization. Most people would forget to include
+``declined-addresses`` in the calculation, and would simply use
+``assigned-nas``/``total-nas``. This would cause a bias towards
+under-representing pool utilization. As this has a potential to cause serious
+confusion, ISC decided not to decrease ``assigned-nas`` immediately after
+receiving DHCPDECLINE, but to do it later when Kea recovers the address
+back to the available pool.
+
+.. _dhcp6-stats:
+
+Statistics in the DHCPv6 Server
+===============================
+
+The DHCPv6 server supports the following statistics:
+
+.. tabularcolumns:: |p{0.2\linewidth}|p{0.1\linewidth}|p{0.7\linewidth}|
+
+.. table:: DHCPv6 statistics
+   :class: longtable
+   :widths: 20 10 70
+
+
+   +----------------------------------------------+----------------+------------------------------------+
+   | Statistic                                    | Data Type      | Description                        |
+   +==============================================+================+====================================+
+   | pkt6-received                                | integer        | Number of DHCPv6 packets received. |
+   |                                              |                | This includes all packets: valid,  |
+   |                                              |                | bogus, corrupted, rejected, etc.   |
+   |                                              |                | This statistic is expected to grow |
+   |                                              |                | rapidly.                           |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-receive-drop                            | integer        | Number of incoming packets that    |
+   |                                              |                | were dropped. The exact reason for |
+   |                                              |                | dropping packets is logged, but    |
+   |                                              |                | the most common reasons may be: an |
+   |                                              |                | unacceptable or not supported      |
+   |                                              |                | packet type is received, direct    |
+   |                                              |                | responses are forbidden, the       |
+   |                                              |                | server-id sent by the client does  |
+   |                                              |                | not match the server's server-id,  |
+   |                                              |                | or the packet is malformed.        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-parse-failed                            | integer        | Number of incoming packets that    |
+   |                                              |                | could not be parsed. A non-zero    |
+   |                                              |                | value of this statistic indicates  |
+   |                                              |                | that the server received a         |
+   |                                              |                | malformed or truncated packet.     |
+   |                                              |                | This may indicate problems in the  |
+   |                                              |                | network, faulty clients, faulty    |
+   |                                              |                | relay agents, or a bug in the      |
+   |                                              |                | server.                            |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-solicit-received                        | integer        | Number of SOLICIT packets          |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to grow; its increase     |
+   |                                              |                | means that clients that just       |
+   |                                              |                | booted started their configuration |
+   |                                              |                | process and their initial packets  |
+   |                                              |                | reached the Kea server.            |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-advertise-received                      | integer        | Number of ADVERTISE packets        |
+   |                                              |                | received. ADVERTISE packets are    |
+   |                                              |                | sent by the server and the server  |
+   |                                              |                | is never expected to receive them. |
+   |                                              |                | A non-zero value of this statistic |
+   |                                              |                | indicates an error occurring in    |
+   |                                              |                | the network. One likely cause      |
+   |                                              |                | would be a misbehaving relay       |
+   |                                              |                | agent that incorrectly forwards    |
+   |                                              |                | ADVERTISE messages towards the     |
+   |                                              |                | server, rather than back to the    |
+   |                                              |                | clients.                           |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-request-received                        | integer        | Number of DHCPREQUEST packets      |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to grow. Its increase     |
+   |                                              |                | means that clients that just       |
+   |                                              |                | booted received the server's       |
+   |                                              |                | response (DHCPADVERTISE) and       |
+   |                                              |                | accepted it, and are now           |
+   |                                              |                | requesting an address              |
+   |                                              |                | (DHCPREQUEST).                     |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-reply-received                          | integer        | Number of REPLY packets received.  |
+   |                                              |                | This statistic is expected to      |
+   |                                              |                | remain zero at all times, as REPLY |
+   |                                              |                | packets are sent by the server and |
+   |                                              |                | the server is never expected to    |
+   |                                              |                | receive them. A non-zero value     |
+   |                                              |                | indicates an error. One likely     |
+   |                                              |                | cause would be a misbehaving relay |
+   |                                              |                | agent that incorrectly forwards    |
+   |                                              |                | REPLY messages towards the server, |
+   |                                              |                | rather than back to the clients.   |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-renew-received                          | integer        | Number of RENEW packets received.  |
+   |                                              |                | This statistic is expected to      |
+   |                                              |                | grow; its increase means that      |
+   |                                              |                | clients received their addresses   |
+   |                                              |                | and prefixes and are trying to     |
+   |                                              |                | renew them.                        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-rebind-received                         | integer        | Number of REBIND packets received. |
+   |                                              |                | A non-zero value indicates that    |
+   |                                              |                | clients did not receive responses  |
+   |                                              |                | to their RENEW messages (through   |
+   |                                              |                | the regular lease-renewal          |
+   |                                              |                | mechanism) and are attempting to   |
+   |                                              |                | find any server that is able to    |
+   |                                              |                | take over their leases. It may     |
+   |                                              |                | mean that some servers' REPLY      |
+   |                                              |                | messages never reached the         |
+   |                                              |                | clients.                           |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-release-received                        | integer        | Number of RELEASE packets          |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to grow when a device is  |
+   |                                              |                | being shut down in the network; it |
+   |                                              |                | indicates that the address or      |
+   |                                              |                | prefix assigned is reported as no  |
+   |                                              |                | longer needed. Note that many      |
+   |                                              |                | devices, especially wireless, do   |
+   |                                              |                | not send RELEASE packets either    |
+   |                                              |                | because of design choice or due to |
+   |                                              |                | the client moving out of range.    |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-decline-received                        | integer        | Number of DECLINE packets          |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to remain close to zero.  |
+   |                                              |                | Its increase means that a client   |
+   |                                              |                | leased an address, but discovered  |
+   |                                              |                | that the address is currently used |
+   |                                              |                | by an unknown device in the        |
+   |                                              |                | network. If this statistic is      |
+   |                                              |                | growing, it may indicate a         |
+   |                                              |                | misconfigured server or devices    |
+   |                                              |                | that have statically assigned      |
+   |                                              |                | conflicting addresses.             |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-infrequest-received                     | integer        | Number of INFORMATION-REQUEST      |
+   |                                              |                | packets received. This statistic   |
+   |                                              |                | is expected to grow if there are   |
+   |                                              |                | devices that are using stateless   |
+   |                                              |                | DHCPv6. INFORMATION-REQUEST        |
+   |                                              |                | messages are used by clients that  |
+   |                                              |                | request stateless configuration,   |
+   |                                              |                | i.e. options and parameters other  |
+   |                                              |                | than addresses or prefixes.        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-dhcpv4-query-received                   | integer        | Number of DHCPv4-QUERY packets     |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to grow if there are      |
+   |                                              |                | devices that are using             |
+   |                                              |                | DHCPv4-over-DHCPv6. DHCPv4-QUERY   |
+   |                                              |                | messages are used by DHCPv4        |
+   |                                              |                | clients on an IPv6-only line which |
+   |                                              |                | encapsulates the requests over     |
+   |                                              |                | DHCPv6.                            |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-dhcpv4-response-received                | integer        | Number of DHCPv4-RESPONSE packets  |
+   |                                              |                | received. This statistic is        |
+   |                                              |                | expected to remain zero at all     |
+   |                                              |                | times, as DHCPv4-RESPONSE packets  |
+   |                                              |                | are sent by the server and the     |
+   |                                              |                | server is never expected to        |
+   |                                              |                | receive them. A non-zero value     |
+   |                                              |                | indicates an error. One likely     |
+   |                                              |                | cause would be a misbehaving relay |
+   |                                              |                | agent that incorrectly forwards    |
+   |                                              |                | DHCPv4-RESPONSE message towards    |
+   |                                              |                | the server rather than back to the |
+   |                                              |                | clients.                           |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-unknown-received                        | integer        | Number of packets received of an   |
+   |                                              |                | unknown type. A non-zero value of  |
+   |                                              |                | this statistic indicates that the  |
+   |                                              |                | server received a packet that it   |
+   |                                              |                | was unable to recognize; either it |
+   |                                              |                | had an unsupported type or was     |
+   |                                              |                | possibly malformed.                |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-sent                                    | integer        | Number of DHCPv6 packets sent.     |
+   |                                              |                | This statistic is expected to grow |
+   |                                              |                | every time the server transmits a  |
+   |                                              |                | packet. In general, it should      |
+   |                                              |                | roughly match pkt6-received, as    |
+   |                                              |                | most incoming packets cause the    |
+   |                                              |                | server to respond. There are       |
+   |                                              |                | exceptions (e.g. server receiving  |
+   |                                              |                | a REQUEST with server-id matching  |
+   |                                              |                | another server), so do not worry   |
+   |                                              |                | if it is less than pkt6-received.  |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-advertise-sent                          | integer        | Number of ADVERTISE packets sent.  |
+   |                                              |                | This statistic is expected to grow |
+   |                                              |                | in most cases after a SOLICIT is   |
+   |                                              |                | processed. There are certain       |
+   |                                              |                | uncommon, but valid, cases where   |
+   |                                              |                | incoming SOLICIT packets are       |
+   |                                              |                | dropped, but in general this       |
+   |                                              |                | statistic is expected to be close  |
+   |                                              |                | to pkt6-solicit-received.          |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-reply-sent                              | integer        | Number of REPLY packets sent. This |
+   |                                              |                | statistic is expected to grow in   |
+   |                                              |                | most cases after a SOLICIT (with   |
+   |                                              |                | rapid-commit), REQUEST, RENEW,     |
+   |                                              |                | REBIND, RELEASE, DECLINE, or       |
+   |                                              |                | INFORMATION-REQUEST is processed.  |
+   |                                              |                | There are certain cases where      |
+   |                                              |                | there is no response.              |
+   +----------------------------------------------+----------------+------------------------------------+
+   | pkt6-dhcpv4-response-sent                    | integer        | Number of DHCPv4-RESPONSE packets  |
+   |                                              |                | sent. This statistic is expected   |
+   |                                              |                | to grow in most cases after a      |
+   |                                              |                | DHCPv4-QUERY is processed. There   |
+   |                                              |                | are certain cases where there is   |
+   |                                              |                | no response.                       |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].total-nas                         | integer        | Total number of NA addresses       |
+   |                                              |                | available for DHCPv6 management    |
+   |                                              |                | for a given subnet; in other       |
+   |                                              |                | words, this is the sum of all      |
+   |                                              |                | addresses in all configured pools. |
+   |                                              |                | This statistic changes only during |
+   |                                              |                | configuration changes. Note that   |
+   |                                              |                | it does not take into account any  |
+   |                                              |                | addresses that may be reserved due |
+   |                                              |                | to host reservation. The *id* is   |
+   |                                              |                | the subnet-id of a given subnet.   |
+   |                                              |                | This statistic is exposed for each |
+   |                                              |                | subnet separately, and is reset    |
+   |                                              |                | during a reconfiguration event.    |
+   +----------------------------------------------+----------------+------------------------------------+
+   | cumulative-assigned-nas                      | integer        | Cumulative number of NA addresses  |
+   |                                              |                | that have been assigned since      |
+   |                                              |                | server startup. It is incremented  |
+   |                                              |                | each time a NA address is assigned |
+   |                                              |                | and is not reset when the server   |
+   |                                              |                | is reconfigured.                   |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].cumulative-assigned-nas           | integer        | Cumulative number of NA addresses  |
+   |                                              |                | in a given subnet that were        |
+   |                                              |                | assigned. It increases every time  |
+   |                                              |                | a new lease is allocated (as a     |
+   |                                              |                | result of receiving a REQUEST      |
+   |                                              |                | message) and is never decreased.   |
+   |                                              |                | The *id* is the subnet-id of a     |
+   |                                              |                | given subnet. This statistic is    |
+   |                                              |                | exposed for each subnet            |
+   |                                              |                | separately, and is reset during a  |
+   |                                              |                | reconfiguration event.             |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].assigned-nas                      | integer        | Number of NA addresses in a given  |
+   |                                              |                | subnet that are assigned. It       |
+   |                                              |                | increases every time a new lease   |
+   |                                              |                | is allocated (as a result of       |
+   |                                              |                | receiving a REQUEST message) and   |
+   |                                              |                | is decreased every time a lease is |
+   |                                              |                | released (a RELEASE message is     |
+   |                                              |                | received) or expires. The *id* is  |
+   |                                              |                | the subnet-id of a given subnet.   |
+   |                                              |                | This statistic is exposed for each |
+   |                                              |                | subnet separately, and is reset    |
+   |                                              |                | during a reconfiguration event.    |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].total-pds                         | integer        | Total number of PD prefixes        |
+   |                                              |                | available for DHCPv6 management    |
+   |                                              |                | for a given subnet; in other       |
+   |                                              |                | words, this is the sum of all      |
+   |                                              |                | prefixes in all configured pools.  |
+   |                                              |                | This statistic changes only during |
+   |                                              |                | configuration changes. Note it     |
+   |                                              |                | does not take into account any     |
+   |                                              |                | prefixes that may be reserved due  |
+   |                                              |                | to host reservation. The *id* is   |
+   |                                              |                | the subnet-id of a given subnet.   |
+   |                                              |                | This statistic is exposed for each |
+   |                                              |                | subnet separately, and is reset    |
+   |                                              |                | during a reconfiguration event.    |
+   +----------------------------------------------+----------------+------------------------------------+
+   | cumulative-assigned-pds                      | integer        | Cumulative number of PD prefixes   |
+   |                                              |                | that have been assigned since      |
+   |                                              |                | server startup. It is incremented  |
+   |                                              |                | each time a PD prefix is assigned  |
+   |                                              |                | and is not reset when the server   |
+   |                                              |                | is reconfigured.                   |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].cumulative-assigned-pds           | integer        | Cumulative number of PD prefixes   |
+   |                                              |                | in a given subnet that were        |
+   |                                              |                | assigned. It increases every time  |
+   |                                              |                | a new lease is allocated (as a     |
+   |                                              |                | result of receiving a REQUEST      |
+   |                                              |                | message) and is never decreased.   |
+   |                                              |                | The *id* is the subnet-id of a     |
+   |                                              |                | given subnet. This statistic is    |
+   |                                              |                | exposed for each subnet            |
+   |                                              |                | separately, and is reset during a  |
+   |                                              |                | reconfiguration event.             |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].assigned-pds                      | integer        | Number of PD prefixes in a given   |
+   |                                              |                | subnet that are assigned. It       |
+   |                                              |                | increases every time a new lease   |
+   |                                              |                | is allocated (as a result of       |
+   |                                              |                | receiving a REQUEST message) and   |
+   |                                              |                | is decreased every time a lease is |
+   |                                              |                | released (a RELEASE message is     |
+   |                                              |                | received) or expires. The *id* is  |
+   |                                              |                | the subnet-id of a given subnet.   |
+   |                                              |                | This statistic is exposed for each |
+   |                                              |                | subnet separately, and is reset    |
+   |                                              |                | during a reconfiguration event.    |
+   +----------------------------------------------+----------------+------------------------------------+
+   | reclaimed-leases                             | integer        | Number of expired leases that have |
+   |                                              |                | been reclaimed since server        |
+   |                                              |                | startup. It is incremented each    |
+   |                                              |                | time an expired lease is reclaimed |
+   |                                              |                | (counting both NA and PD           |
+   |                                              |                | reclamations). This statistic      |
+   |                                              |                | never decreases. It can be used as |
+   |                                              |                | a long-term indicator of how many  |
+   |                                              |                | actual leases have been reclaimed. |
+   |                                              |                | This is a global statistic that    |
+   |                                              |                | covers all subnets.                |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].reclaimed-leases                  | integer        | Number of expired leases           |
+   |                                              |                | associated with a given subnet     |
+   |                                              |                | that have been reclaimed since     |
+   |                                              |                | server startup. It is incremented  |
+   |                                              |                | each time an expired lease is      |
+   |                                              |                | reclaimed (counting both NA and PD |
+   |                                              |                | reclamations). The *id* is the     |
+   |                                              |                | subnet-id of a given subnet. This  |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+   | declined-addresses                           | integer        | Number of IPv6 addresses that are  |
+   |                                              |                | currently declined; a count of the |
+   |                                              |                | number of leases currently         |
+   |                                              |                | unavailable. Once a lease is       |
+   |                                              |                | recovered, this statistic will be  |
+   |                                              |                | decreased; ideally, this statistic |
+   |                                              |                | should be zero. If this statistic  |
+   |                                              |                | is non-zero or increasing, a       |
+   |                                              |                | network administrator should       |
+   |                                              |                | investigate whether there is a     |
+   |                                              |                | misbehaving device in the network. |
+   |                                              |                | This is a global statistic that    |
+   |                                              |                | covers all subnets.                |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].declined-addresses                | integer        | Number of IPv6 addresses that are  |
+   |                                              |                | currently declined in a given      |
+   |                                              |                | subnet; a count of the number of   |
+   |                                              |                | leases currently unavailable. Once |
+   |                                              |                | a lease is recovered, this         |
+   |                                              |                | statistic will be decreased;       |
+   |                                              |                | ideally, this statistic should be  |
+   |                                              |                | zero. If this statistic is         |
+   |                                              |                | non-zero or increasing, a network  |
+   |                                              |                | administrator should investigate   |
+   |                                              |                | whether there is a misbehaving     |
+   |                                              |                | device in the network. The *id* is |
+   |                                              |                | the subnet-id of a given subnet.   |
+   |                                              |                | This statistic is exposed for each |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+   | reclaimed-declined-addresses                 | integer        | Number of IPv6 addresses that were |
+   |                                              |                | declined, but have now been        |
+   |                                              |                | recovered. Unlike                  |
+   |                                              |                | declined-addresses, this statistic |
+   |                                              |                | never decreases. It can be used as |
+   |                                              |                | a long-term indicator of how many  |
+   |                                              |                | actual valid declines were         |
+   |                                              |                | processed and recovered from. This |
+   |                                              |                | is a global statistic that covers  |
+   |                                              |                | all subnets.                       |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].reclaimed-declined-addresses      | integer        | Number of IPv6 addresses that were |
+   |                                              |                | declined, but have now been        |
+   |                                              |                | recovered. Unlike                  |
+   |                                              |                | declined-addresses, this statistic |
+   |                                              |                | never decreases. It can be used as |
+   |                                              |                | a long-term indicator of how many  |
+   |                                              |                | actual valid declines were         |
+   |                                              |                | processed and recovered from. The  |
+   |                                              |                | *id* is the subnet-id of a given   |
+   |                                              |                | subnet. This statistic is exposed  |
+   |                                              |                | for each subnet separately.        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v6-allocation-fail                           | integer        | Number of total address allocation |
+   |                                              |                | failures for a particular client.  |
+   |                                              |                | This consists in the number of     |
+   |                                              |                | lease allocation attempts that the |
+   |                                              |                | server made before giving up and   |
+   |                                              |                | was unable to use any of the       |
+   |                                              |                | address pools. This is a global    |
+   |                                              |                | statistic that covers all subnets. |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v6-allocation-fail                | integer        | Number of total address allocation |
+   |                                              |                | failures for a particular client.  |
+   |                                              |                | This consists in the number of     |
+   |                                              |                | lease allocation attempts that the |
+   |                                              |                | server made before giving up and   |
+   |                                              |                | was unable to use any of the       |
+   |                                              |                | address pools. The *id* is the     |
+   |                                              |                | subnet-id of a given subnet. This  |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v6-allocation-fail-shared-network            | integer        | Number of address allocation       |
+   |                                              |                | failures for a particular client   |
+   |                                              |                | connected to a shared network.     |
+   |                                              |                | This is a global statistic that    |
+   |                                              |                | covers all subnets.                |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v6-allocation-fail-shared-network | integer        | Number of address allocation       |
+   |                                              |                | failures for a particular client   |
+   |                                              |                | connected to a shared network.     |
+   |                                              |                | The *id* is the subnet-id of a     |
+   |                                              |                | given subnet. This statistic is    |
+   |                                              |                | exposed for each subnet            |
+   |                                              |                | separately.                        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v6-allocation-fail-subnet                    | integer        | Number of address allocation       |
+   |                                              |                | failures for a particular client   |
+   |                                              |                | connected to a subnet that does    |
+   |                                              |                | not belong to a shared network.    |
+   |                                              |                | This is a global statistic that    |
+   |                                              |                | covers all subnets.                |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v6-allocation-fail-subnet         | integer        | Number of address allocation       |
+   |                                              |                | failures for a particular client   |
+   |                                              |                | connected to a subnet that does    |
+   |                                              |                | not belong to a shared network.    |
+   |                                              |                | The *id* is the subnet-id of a     |
+   |                                              |                | given subnet. This statistic is    |
+   |                                              |                | exposed for each subnet            |
+   |                                              |                | separately.                        |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v6-allocation-fail-no-pools                  | integer        | Number of address allocation       |
+   |                                              |                | failures because the server could  |
+   |                                              |                | not use any configured pools for   |
+   |                                              |                | a particular client. It is also    |
+   |                                              |                | possible that all of the subnets   |
+   |                                              |                | from which the server attempted to |
+   |                                              |                | assign an address lack address     |
+   |                                              |                | pools. In this case, it should be  |
+   |                                              |                | considered misconfiguration if an  |
+   |                                              |                | operator expects that some clients |
+   |                                              |                | should be assigned dynamic         |
+   |                                              |                | addresses. This is a global        |
+   |                                              |                | statistic that covers all subnets. |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v6-allocation-fail-no-pools       | integer        | Number of address allocation       |
+   |                                              |                | failures because the server could  |
+   |                                              |                | not use any configured pools for   |
+   |                                              |                | a particular client. It is also    |
+   |                                              |                | possible that all of the subnets   |
+   |                                              |                | from which the server attempted to |
+   |                                              |                | assign an address lack address     |
+   |                                              |                | pools. In this case, it should be  |
+   |                                              |                | considered misconfiguration if an  |
+   |                                              |                | operator expects that some clients |
+   |                                              |                | should be assigned dynamic         |
+   |                                              |                | addresses. The *id* is the         |
+   |                                              |                | subnet-id of a given subnet. This  |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+   | v6-allocation-fail-classes                   | integer        | Number of address allocation       |
+   |                                              |                | failures when the client's packet  |
+   |                                              |                | belongs to one or more classes.    |
+   |                                              |                | There may be several reasons why a |
+   |                                              |                | lease was not assigned. One of     |
+   |                                              |                | them may be a case when all pools  |
+   |                                              |                | require packet to belong to        |
+   |                                              |                | certain classes and the incoming   |
+   |                                              |                | packet didn't belong to any of     |
+   |                                              |                | them. Another case where this      |
+   |                                              |                | information may be useful is to    |
+   |                                              |                | point out that the pool reserved   |
+   |                                              |                | to a given class has ran out of    |
+   |                                              |                | addresses. This is a global        |
+   |                                              |                | statistic that covers all subnets. |
+   +----------------------------------------------+----------------+------------------------------------+
+   | subnet[id].v6-allocation-fail-classes        | integer        | Number of address allocation       |
+   |                                              |                | failures when the client's packet  |
+   |                                              |                | belongs to one or more classes.    |
+   |                                              |                | There may be several reasons why a |
+   |                                              |                | lease was not assigned. One of     |
+   |                                              |                | them may be a case when all pools  |
+   |                                              |                | require packet to belong to        |
+   |                                              |                | certain classes and the incoming   |
+   |                                              |                | packet didn't belong to any of     |
+   |                                              |                | them. Another case where this      |
+   |                                              |                | information may be useful is to    |
+   |                                              |                | point out that the pool reserved   |
+   |                                              |                | to a given class has ran out of    |
+   |                                              |                | addresses. The *id* is the         |
+   |                                              |                | subnet-id of a given subnet. This  |
+   |                                              |                | statistic is exposed for each      |
+   |                                              |                | subnet separately.                 |
+   +----------------------------------------------+----------------+------------------------------------+
+
+.. note::
+
+   This section describes DHCPv6-specific statistics. For a general
+   overview and usage of statistics, see :ref:`stats`.
+
+The DHCPv6 server provides two global parameters to control the default sample
+limits of statistics:
+
+- ``statistic-default-sample-count`` - determines the default maximum
+  number of samples which are kept. The special value of 0
+  indicates that a default maximum age should be used.
+
+- ``statistic-default-sample-age`` - determines the default maximum
+  age in seconds of samples which are kept.
+
+For instance, to reduce the statistic-keeping overhead, set
+the default maximum sample count to 1 so only one sample is kept:
+
+::
+
+     "Dhcp6": {
+       "statistic-default-sample-count": 1,
+       "subnet6": [ ... ],
+       ...
+   }
+
+Statistics can be retrieved periodically to gain more insight into Kea operations. One tool that
+leverages that capability is ISC Stork. See :ref:`stork` for details.
+
+
+.. _dhcp6-ctrl-channel:
+
+Management API for the DHCPv6 Server
+====================================
+
+The management API allows the issuing of specific management commands,
+such as statistics retrieval, reconfiguration, or shutdown. For more
+details, see :ref:`ctrl-channel`. Currently, the only supported
+communication channel type is the UNIX stream socket. By default there are
+no sockets open; to instruct Kea to open a socket, the following entry
+in the configuration file can be used:
+
+::
+
+   "Dhcp6": {
+       "control-socket": {
+           "socket-type": "unix",
+           "socket-name": "/path/to/the/unix/socket"
+       },
+
+       "subnet6": [
+           ...
+       ],
+       ...
+   }
+
+The length of the path specified by the ``socket-name`` parameter is
+restricted by the maximum length for the UNIX socket name on the administrator's
+operating system, i.e. the size of the ``sun_path`` field in the
+``sockaddr_un`` structure, decreased by 1. This value varies on
+different operating systems, between 91 and 107 characters. Typical
+values are 107 on Linux and 103 on FreeBSD.
+
+Communication over the control channel is conducted using JSON
+structures. See the
+`Control Channel section in the Kea Developer's Guide
+<https://reports.kea.isc.org/dev_guide/d2/d96/ctrlSocket.html>`__
+for more details.
+
+The DHCPv6 server supports the following operational commands:
+
+-  build-report
+-  config-get
+-  config-reload
+-  config-set
+-  config-test
+-  config-write
+-  dhcp-disable
+-  dhcp-enable
+-  leases-reclaim
+-  list-commands
+-  shutdown
+-  status-get
+-  version-get
+
+as described in :ref:`commands-common`. In addition, it supports the
+following statistics-related commands:
+
+-  statistic-get
+-  statistic-reset
+-  statistic-remove
+-  statistic-get-all
+-  statistic-reset-all
+-  statistic-remove-all
+-  statistic-sample-age-set
+-  statistic-sample-age-set-all
+-  statistic-sample-count-set
+-  statistic-sample-count-set-all
+
+as described in :ref:`command-stats`.
+
+.. _dhcp6-user-contexts:
+
+User Contexts in IPv6
+=====================
+
+Kea allows the loading of hook libraries that can sometimes benefit from
+additional parameters. If such a parameter is specific to the whole
+library, it is typically defined as a parameter for the hook library.
+However, sometimes there is a need to specify parameters that are
+different for each pool.
+
+See :ref:`user-context` for additional background regarding the
+user-context idea. See :ref:`user-context-hooks` for a discussion from the
+hooks perspective.
+
+User contexts can be specified at global scope; at the shared-network, subnet,
+pool, client-class, option-data, or definition level; and via host
+reservation. One other useful feature is the ability to store comments or
+descriptions.
+
+Let's consider an example deployment of lightweight 4over6, an
+IPv6 transition technology that allows mapping IPv6 prefixes into full
+or partial IPv4 addresses. In the DHCP context, these are specific
+parameters that are supposed to be delivered to clients in the form of
+additional options. Values of these options are correlated to delegated
+prefixes, so it is reasonable to keep these parameters together with the
+prefix delegation (PD) pool. On the other hand, lightweight 4over6 is not a commonly used
+feature, so it is not a part of the base Kea code. The solution to this
+problem is to specify a user context. For each PD pool that is expected to be
+used for lightweight 4over6, a user context with extra parameters is
+defined. Those extra parameters will be used by a hook library
+and loaded only when dynamic calculation of the lightweight 4over6
+option is actually needed. An example configuration looks as follows:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [ {
+           "pd-pools": [
+           {
+               "prefix":  "2001:db8::",
+               "prefix-len": 56,
+               "delegated-len": 64,
+
+               # This is a pool specific context.
+               "user-context": {
+                   "threshold-percent": 85,
+                   "v4-network": "192.168.0.0/16",
+                   "v4-overflow": "10.0.0.0/16",
+                   "lw4over6-sharing-ratio": 64,
+                   "lw4over6-v4-pool": "192.0.2.0/24",
+                   "lw4over6-sysports-exclude": true,
+                   "lw4over6-bind-prefix-len": 56
+               }
+           } ],
+           "subnet": "2001:db8::/32",
+
+           # This is a subnet-specific context. Any type of
+           # information can be entered here as long as it is valid JSON.
+           "user-context": {
+               "comment": "Those v4-v6 migration technologies are tricky.",
+               "experimental": true,
+               "billing-department": 42,
+               "contacts": [ "Alice", "Bob" ]
+           }
+       } ]
+   }
+
+Kea does not interpret or use the user-context information; it simply
+stores it and makes it available to the hook libraries. It is up to each
+hook library to extract that information and use it. The parser
+translates a ``comment`` entry into a user context with the entry, which
+allows a comment to be attached inside the configuration itself.
+
+.. _dhcp6-std:
+
+Supported DHCPv6 Standards
+==========================
+
+The following standards are currently supported in Kea:
+
+-  *Dynamic Host Configuration Protocol for IPv6*, `RFC
+   3315 <https://tools.ietf.org/html/rfc3315>`__: Supported messages are
+   SOLICIT, ADVERTISE, REQUEST, RELEASE, RENEW, REBIND,
+   INFORMATION-REQUEST, CONFIRM, DECLINE and REPLY. The only
+   unsupported message is RECONFIGURE.
+
+-  *Dynamic Host Configuration Protocol (DHCPv6) Options for
+   Session Initiation Protocol (SIP) Servers*, `RFC 3319
+   <https://tools.ietf.org/html/rfc3319>`__: All defined options are supported.
+
+-  *IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP)
+   version 6*, `RFC 3633 <https://tools.ietf.org/html/rfc3633>`__:
+   Supported options are IA_PD and IA_PREFIX. Also supported is the
+   status code NoPrefixAvail.
+
+-  *DNS Configuration options for Dynamic Host Configuration Protocol for IPv6
+   (DHCPv6)*, `RFC 3646 <https://tools.ietf.org/html/rfc3646>`__: All defined
+   options are supported.
+
+-  *Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6*, `RFC
+   3736 <https://tools.ietf.org/html/rfc3736>`__: Server operation in
+   stateless mode is supported. Kea is currently server-only, so the client side
+   is not implemented.
+
+-  *Information Refresh Time Option for Dynamic Host Configuration Protocol for
+   IPv6 (DHCPv6)*, `RFC 4242 <https://tools.ietf.org/html/rfc4242>`__: The
+   sole defined option (``information-refresh-time``) is supported.
+
+-  *The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay
+   Agent Remote-ID Option*, `RFC
+   4649 <https://tools.ietf.org/html/rfc4649>`__: The REMOTE-ID option is
+   supported.
+
+-  *Resolution of Fully Qualified Domain Name (FQDN) Conflicts among Dynamic Host
+   Configuration Protocol (DHCP) Clients*, `RFC 4703
+   <https://tools.ietf.org/html/rfc4703>`__: The DHCPv6 server uses the DHCP-DDNS
+   server to resolve conflicts.
+
+-  *The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client
+   Fully Qualified Domain Name (FQDN) Option*, `RFC
+   4704 <https://tools.ietf.org/html/rfc4704>`__: The supported option is
+   CLIENT_FQDN.
+
+-  *Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Option for
+   Dual-Stack Lite*, `RFC 6334 <https://tools.ietf.org/html/rfc6334>`__:
+   The AFTR-Name DHCPv6 Option is supported.
+
+-  *Relay-Supplied DHCP Options*, `RFC
+   6422 <https://tools.ietf.org/html/rfc6422>`__: The full functionality is
+   supported: OPTION_RSOO; the ability of the server to echo back the
+   options; verification of whether an option is RSOO-enabled; the ability to mark
+   additional options as RSOO-enabled.
+
+-  *Prefix Exclude Option for DHCPv6-based Prefix Delegation*, `RFC
+   6603 <https://tools.ietf.org/html/rfc6603>`__: The Prefix Exclude option
+   is supported.
+
+-  *Client Link-Layer Address Option in DHCPv6*, `RFC
+   6939 <https://tools.ietf.org/html/rfc6939>`__: The supported option is
+   the client link-layer address option.
+
+-  *Issues and Recommendations with Multiple Stateful DHCPv6 Options*,
+   `RFC 7550 <https://tools.ietf.org/html/rfc7550>`__: All
+   recommendations related to the DHCPv6 server operation are supported.
+
+-  *DHCPv6 Options for Configuration of Softwire Address and Port-Mapped
+   Clients*, `RFC 7598 <https://tools.ietf.org/html/rfc7598>`__: All
+   options indicated in this specification are supported by the DHCPv6
+   server.
+
+-  *Generalized UDP Source Port for DHCP Relay*, `RFC 8357
+   <https://tools.ietf.org/html/rfc8357>`__: The Kea server is able
+   to handle Relay Source Port option in a received Relay-forward
+   message, remembers the UDP port and sends back Relay-reply with a
+   copy of the option to the relay agent using this UDP port.
+
+-  *Dynamic Host Configuration Protocol for IPv6 (DHCPv6)*, `RFC 8415
+   <https://tools.ietf.org/html/rfc8415>`__: This new DHCPv6 protocol specification
+   obsoletes RFC 3315, RFC 3633, RFC 3736, RFC 4242, RFC 7083, RFC 7283,
+   and RFC 7550. All features, with the exception of the RECONFIGURE mechanism and
+   the now-deprecated temporary addresses (IA_TA) mechanism, are supported.
+
+-  *Captive-Portal Identification in DHCP and Router Advertisements (RAs)*, `RFC 8910
+   <https://tools.ietf.org/html/rfc8910>`__: The Kea server can configure both v4
+   and v6 versions of the captive portal options.
+
+.. _dhcp6-limit:
+
+DHCPv6 Server Limitations
+=========================
+
+These are the current limitations of the DHCPv6 server software. Most of
+them are reflections of the current stage of development and should be
+treated as “not implemented yet”, rather than actual limitations.
+
+-  The server will allocate, renew, or rebind a maximum of one lease for
+   a particular IA option (IA_NA or IA_PD) sent by a client. `RFC
+   8415 <https://tools.ietf.org/html/rfc8415>`__ allows for multiple
+   addresses or prefixes to be allocated for a single IA.
+
+-  Temporary addresses are not supported. There is no intention to ever
+   implement this feature, as it is deprecated in `RFC 8415
+   <https://tools.ietf.org/html/rfc8415>`__.
+
+-  Client reconfiguration (RECONFIGURE) is not yet supported.
+
+.. _dhcp6-srv-examples:
+
+Kea DHCPv6 Server Examples
+==========================
+
+A collection of simple-to-use examples for the DHCPv6 component of Kea
+is available with the source files, located in the ``doc/examples/kea6``
+directory.
+
+.. _dhcp6-cb:
+
+Configuration Backend in DHCPv6
+===============================
+
+In the :ref:`config-backend` section we have described the Configuration
+Backend (CB) feature, its applicability, and its limitations. This section focuses
+on the usage of the CB with the DHCPv6 server. It lists the supported
+parameters, describes limitations, and gives examples of DHCPv6
+server configurations to take advantage of the CB. Please also refer to
+the corresponding section :ref:`dhcp4-cb` for DHCPv4-specific usage of
+the CB.
+
+.. _dhcp6-cb-parameters:
+
+Supported Parameters
+--------------------
+
+The ultimate goal for the CB is to serve as a central configuration
+repository for one or multiple Kea servers connected to a database.
+In currently supported Kea versions, only a subset of
+the DHCPv6 server parameters can be stored in the database. All other
+parameters must be specified in the JSON configuration file, if
+required.
+
+All supported parameters can be configured via ``cb_cmds`` hook library
+described in the :ref:`hooks-cb-cmds` section. The general rule is that
+scalar global parameters are set using
+``remote-global-parameter6-set``; shared-network-specific parameters
+are set using ``remote-network6-set``; and subnet- and pool-level
+parameters are set using ``remote-subnet6-set``. Whenever
+there is an exception to this general rule, it is highlighted in the
+table. Non-scalar global parameters have dedicated commands; for example,
+the global DHCPv6 options (``option-data``) are modified using
+``remote-option6-global-set``. Client classes, together with class-specific
+option definitions and DHCPv6 options, are configured using the
+``remote-class6-set`` command.
+
+The :ref:`cb-sharing` section explains the concept of shareable
+and non-shareable configuration elements and the limitations for
+sharing them between multiple servers. In the DHCP configuration (both DHCPv4
+and DHCPv6), the shareable configuration elements are subnets and shared
+networks. Thus, they can be explicitly associated with multiple server tags.
+The global parameters, option definitions, and global options are non-shareable
+and can be associated with only one server tag. This rule does not apply
+to the configuration elements associated with ``all`` servers. Any configuration
+element associated with ``all`` servers (using the ``all`` keyword as a server tag) is
+used by all servers connecting to the configuration database.
+
+The following table lists DHCPv6-specific parameters supported by the
+Configuration Backend, with an indication of the level of the hierarchy
+at which it is currently supported.
+
+.. table:: List of DHCPv6 parameters supported by the Configuration Backend
+
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | Parameter                   | Global                     | Client    | Shared    | Subnet    | Pool      | Prefix     |
+   |                             |                            | Class     | Network   |           |           | Delegation |
+   |                             |                            |           |           |           |           | Pool       |
+   +=============================+============================+===========+===========+===========+===========+============+
+   | cache-max-age               | yes                        | n/a       | no        | no        | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | cache-threshold             | yes                        | n/a       | no        | no        | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | calculate-tee-times         | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | client-class                | n/a                        | n/a       | yes       | yes       | yes       | yes        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | ddns-send-update            | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | ddns-override-no-update     | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | ddns-override-client-update | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | ddns-replace-client-name    | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | ddns-generated-prefix       | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | ddns-qualifying-suffix      | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | decline-probation-period    | yes                        | n/a       | n/a       | n/a       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | delegated-len               | n/a                        | n/a       | n/a       | n/a       | n/a       | yes        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | dhcp4o6-port                | yes                        | n/a       | n/a       | n/a       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | excluded-prefix             | n/a                        | n/a       | n/a       | n/a       | n/a       | yes        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | excluded-prefix-len         | n/a                        | n/a       | n/a       | n/a       | n/a       | yes        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | hostname-char-set           | no                         | n/a       | no        | no        | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | hostname-char-replacement   | no                         | n/a       | no        | no        | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | interface                   | n/a                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | interface-id                | n/a                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | max-preferred-lifetime      | yes                        | yes       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | max-valid-lifetime          | yes                        | yes       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | min-preferred-lifetime      | yes                        | yes       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | min-valid-lifetime          | yes                        | yes       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | option-data                 | yes (via                   | yes       | yes       | yes       | yes       | yes        |
+   |                             | remote-option6-global-set) |           |           |           |           |            |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | option-def                  | yes (via                   | yes       | n/a       | n/a       | n/a       | n/a        |
+   |                             | remote-option-def6-set)    |           |           |           |           |            |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | preferred-lifetime          | yes                        | yes       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | prefix                      | n/a                        | n/a       | n/a       | n/a       | n/a       | yes        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | prefix-len                  | n/a                        | n/a       | n/a       | n/a       | n/a       | yes        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | rapid-commit                | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | rebind-timer                | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | relay                       | n/a                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | renew-timer                 | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | require-client-classes      | n/a                        | n/a       | yes       | yes       | yes       | yes        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | reservation-mode            | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | reservations-global         | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | reservations-in-subnet      | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | reservations-out-of-pool    | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | t1-percent                  | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | t2-percent                  | yes                        | n/a       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+   | valid-lifetime              | yes                        | yes       | yes       | yes       | n/a       | n/a        |
+   +-----------------------------+----------------------------+-----------+-----------+-----------+-----------+------------+
+
+-  ``yes`` - indicates that the parameter is supported at the given
+   level of the hierarchy and can be configured via the Configuration Backend.
+
+-  ``no`` - indicates that a parameter is supported at the given level
+   of the hierarchy but cannot be configured via the Configuration Backend.
+
+-  ``n/a`` -  indicates that a given parameter is not applicable
+   at the particular level of the hierarchy or that the
+   server does not support the parameter at that level.
+
+.. _dhcp6-cb-json:
+
+Enabling the Configuration Backend
+----------------------------------
+
+The following configuration snippet demonstrates how to enable the MySQL
+Configuration Backend for the DHCPv6 server:
+
+::
+
+   {
+       "Dhcp6": {
+       "server-tag": "my DHCPv6 server",
+           "config-control": {
+               "config-databases": [
+                   {
+                       "type": "mysql",
+                       "name": "kea",
+                       "user": "kea",
+                       "password": "kea",
+                       "host": "2001:db8:1::1",
+                       "port": 3302
+                   }
+               ],
+               "config-fetch-wait-time": 20
+           },
+           "hooks-libraries": [
+               {
+                   "library": "/usr/local/lib/kea/hooks/libdhcp_mysql_cb.so"
+               },
+               {
+                   "library": "/usr/local/lib/kea/hooks/libdhcp_cb_cmds.so"
+               }
+           ],
+           ...
+       }
+   }
+
+The configuration structure is almost identical to that of the DHCPv4 server
+(see :ref:`dhcp4-cb-json` for the detailed description).
+
+.. _dhcp6-compatibility:
+
+Kea DHCPv6 Compatibility Configuration Parameters
+=================================================
+
+ISC's intention is for Kea to follow the RFC documents to promote better standards
+compliance. However, many buggy DHCP implementations already exist that cannot be
+easily fixed or upgraded. Therefore, Kea provides an easy-to-use compatibility
+mode for broken or non-compliant clients. For that purpose, the compatibility option must be
+enabled to permit uncommon practices:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "compatibility": {
+        }
+      }
+    }
+
+
+Lenient Option Parsing
+----------------------
+
+By default, DHCPv6 option 16's ``vendor-class-data`` field is parsed as a set of
+length-value pairs. Same for tuple fields defined in custom options.
+
+With ``"lenient-option-parsing": true``, if a length ever exceeds the rest of
+the option's buffer, previous versions of Kea returned a log message ``unable to
+parse the opaque data tuple, the buffer length is x, but the tuple length is y``
+with ``x < y``; this no longer occurs. Instead, the value is considered to be the rest of the buffer,
+or in terms of the log message above, the tuple length ``y`` becomes ``x``.
+
+Enabling this flag is expected to improve compatibility with devices such as RAD
+MiNID.
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "compatibility": {
+          "lenient-option-parsing": true
+        }
+      }
+    }
diff --git a/doc/sphinx/arm/ext-gss-tsig.rst b/doc/sphinx/arm/ext-gss-tsig.rst
new file mode 100644
index 0000000..0baad37
--- /dev/null
+++ b/doc/sphinx/arm/ext-gss-tsig.rst
@@ -0,0 +1,1296 @@
+.. _gss-tsig:
+
+GSS-TSIG
+========
+
+.. _gss-tsig-overview:
+
+GSS-TSIG Overview
+-----------------
+
+Kea provides support for DNS updates, which can be protected using
+Transaction Signatures (or TSIG). This protection is often adequate.
+However, some systems, in particular Active Directory (AD) on Microsoft
+Windows servers, have chosen to adopt a more complex GSS-TSIG approach that offers
+additional capabilities, such as using negotiated dynamic keys.
+
+Kea supports GSS-TSIG to protect DNS updates sent by
+the Kea DHCP-DDNS (D2) server in a premium hook, called ``gss_tsig``.
+
+GSS-TSIG is defined in `RFC 3645 <https://tools.ietf.org/html/rfc3645>`__.
+The GSS-TSIG protocol itself is an implementation of generic GSS-API v2
+services, defined in `RFC 2743 <https://tools.ietf.org/html/rfc2743>`__.
+
+Many protocols are involved in this mechanism:
+
+ - Kerberos 5 - `RFC 4120 <https://tools.ietf.org/html/rfc4120>`__, which
+   provides the security framework;
+ - GSS-API (Generic Security Services Application Program Interface) -
+   `RFC 2743 <https://tools.ietf.org/html/rfc2743>`__ for the API,
+   `RFC 2744 <https://tools.ietf.org/html/rfc2743>`__ for the C bindings, and
+   `RFC 4121 <https://tools.ietf.org/html/rfc4121>`__ for the application
+   to Kerberos 5;
+ - SPNEGO (Simple and Protected GSS-API Negotiation Mechanism) -
+   `RFC 4178 <https://tools.ietf.org/html/rfc4178>`__ for the negotiation;
+ - DNS update `RFC 2136 <https://tools.ietf.org/html/rfc2136>`__;
+ - TSIG (Secret Key Transaction Authentication for DNS) -
+   `RFC 8945 <https://tools.ietf.org/html/rfc8945>`__, which
+   protects DNS exchanges;
+ - Secure Domain Name System (DNS) Dynamic Update -
+   `RFC 3007 <https://tools.ietf.org/html/rfc3007>`__, which is the
+   application of TSIG to DNS update protection;
+ - TKEY (Secret Key Establishment for DNS) -
+   `RFC 2930 <https://tools.ietf.org/html/rfc2930>`__, which establishes
+   secret keys for TSIG by transmitting crypto payloads between DNS
+   parties; and
+ - GSS-TSIG - `RFC 3645 <https://tools.ietf.org/html/rfc3645>`__, which
+   is the application of GSS-API to TSIG.
+
+To summarize, GSS-API for Kerberos 5 with SPNEGO and TKEY are used to
+negotiate a security context between the Kea D2 server and a DNS server:
+
+.. figure:: ../uml/tkey.*
+
+The security context is then used by GSS-TSIG to protect updates:
+
+.. figure:: ../uml/update.*
+
+The Kea implementation of GSS-TSIG uses a GSS-API for Kerberos 5 with
+the SPNEGO library. Two implementations meet this criteria: MIT Kerberos
+5 and Heimdal.
+
+.. _gss-tsig-install:
+
+GSS-TSIG Compilation
+--------------------
+
+The following procedure was tested on Ubuntu 20.10 and 21.04. A similar
+approach can be applied to other systems.
+
+1.  Obtain the Kea sources and premium packages, extract the Kea sources,
+    and then extract the premium packages into the ``premium/`` directory within the Kea
+    source tree.
+
+2. Run autoreconf:
+
+.. code-block:: console
+
+    autoreconf -i
+
+3. Make sure ``./configure --help`` shows the ``--with-gssapi`` option.
+
+4. Install either the MIT (``libkrb5-dev``) or the Heimdal (``heimdal-dev``) library,
+   for instance:
+
+.. code-block:: console
+
+    sudo apt install libkrb5-dev
+
+5. Run ``configure`` with the ``--with-gssapi`` option:
+
+.. code-block:: console
+
+    ./configure --with-gssapi
+
+.. note:
+
+    It is ``--with-gssapi`` (with no dash between "gss" and "api"), to maintain
+    consistency with the BIND 9 option.
+
+The ``--with-gssapi`` parameter requires the ``krb5-config`` tool to be present. This
+tool is provided by both MIT Kerberos 5 and Heimdal; however, on some systems
+where both Kerberos 5 and Heimdal are installed, it is a symbolic link
+to one of them. If the tool is not in the standard location, it can be specified
+with ``--with-gssapi=/path/to/krb5-config``. It is strongly recommended
+to use the default installation locations provided by the packages.
+
+The ``./configure`` script should complete with a successful GSS-API
+detection, similar to this:
+
+::
+
+    GSS-API support:
+      GSSAPI_CFLAGS:         -isystem /usr/include/mit-krb5
+      GSSAPI_LIBS:           -L/usr/lib/x86_64-linux-gnu/mit-krb5 -Wl,-Bsymbolic-functions -Wl,-z,relro -lgssapi_krb5 -lkrb5 -lk5crypto -lcom_err
+
+6.  Compile ``make -jX``, where X is the number of CPU cores
+    available.
+
+7.  After compilation, the ``gss_tsig`` hook is available in the
+    ``premium/src/hooks/d2/gss_tsig`` directory. It can be loaded by
+    the Kea DHCP-DDNS (D2) daemon.
+
+The ``gss_tsig`` hook library was developed using the MIT Kerberos 5 implementation, but
+Heimdal is also supported. Note that Heimdal is picky about
+security-sensitive file permissions and is known to emit an unclear error message.
+It is a good idea to keep these files plain, with one link and no
+access for the group or other users.
+
+The ``krb5-config`` script should provide an ``--all`` option which
+identifies the implementation.
+
+.. _gss-tsig-deployment:
+
+GSS-TSIG Deployment
+-------------------
+
+Before using GSS-TSIG, a GSS-TSIG capable DNS server, such as BIND 9
+or Microsoft Active Directory (AD), must be deployed. Other
+GSS-TSIG capable implementations may work, but have not been tested.
+
+Kerberos 5 Setup
+~~~~~~~~~~~~~~~~
+
+There are two kinds of key tables (keytab files): the system one used
+by servers, and client tables used by clients. For Kerberos 5, Kea is a
+**client**.
+
+Install the Kerberos 5 client library and ``kadmin`` tool:
+
+.. code-block:: console
+
+    sudo apt install krb5-kdc krb5-admin-server
+
+The following examples use the ``EXAMPLE.ORG`` realm to demonstrate required
+configuration steps and settings.
+
+The Kerberos 5 client library must be configured to accept incoming requests
+for the realm ``EXAMPLE.ORG`` by updating the ``krb5.conf`` file
+(e.g. on Linux: /etc/krb5.conf):
+
+.. code-block:: ini
+
+    [libdefaults]
+        default_realm = EXAMPLE.ORG
+        kdc_timesync = 1
+        ccache_type = 4
+        forwardable = true
+        proxiable = true
+
+    [realms]
+        EXAMPLE.ORG = {
+                kdc = kdc.example.org
+                admin_server = kdc.example.org
+        }
+
+In addition to the ``krb5.conf`` file, the ``kdc.conf`` file can be used
+(e.g. on Linux: /etc/krb5kdc/kdc.conf):
+
+.. code-block:: ini
+
+    [kdcdefaults]
+        kdc_ports = 750,88
+
+    [realms]
+        EXAMPLE.ORG = {
+            database_name = /var/lib/krb5kdc/principal
+            admin_keytab = FILE:/etc/krb5kdc/kadm5.keytab
+            acl_file = /etc/krb5kdc/kadm5.acl
+            key_stash_file = /etc/krb5kdc/stash
+            kdc_ports = 750,88
+            max_life = 10h 0m 0s
+            max_renewable_life = 7d 0h 0m 0s
+            master_key_type = des3-hmac-sha1
+            #supported_enctypes = aes256-cts:normal aes128-cts:normal
+            default_principal_flags = +preauth
+        }
+
+The ``kadmind`` daemon Access Control List (ACL) must be configured to give
+permissions to the DNS client principal to access the Kerberos 5 database
+(e.g. on Linux: /etc/krb5kdc/kadm5.acl):
+
+.. code-block:: ini
+
+    DHCP/admin.example.org@EXAMPLE.ORG       *
+
+The administrator password for the default realm must be set:
+
+.. code-block:: console
+
+    krb5_newrealm
+
+After the following message is displayed, enter
+the password for the default realm:
+
+.. code-block:: console
+
+    This script should be run on the master KDC/admin server to initialize
+    a Kerberos realm.  It will ask you to type in a master key password.
+    This password will be used to generate a key that is stored in
+    /etc/krb5kdc/stash.  You should try to remember this password, but it
+    is much more important that it be a strong password than that it be
+    remembered.  However, if you lose the password and /etc/krb5kdc/stash,
+    you cannot decrypt your Kerberos database.
+    Loading random data
+    Initializing database '/var/lib/krb5kdc/principal' for realm 'EXAMPLE.ORG',
+    master key name 'K/M@EXAMPLE.ORG'
+    You will be prompted for the database Master Password.
+    It is important that you NOT FORGET this password.
+    Enter KDC database master key:
+
+Then retype the password:
+
+.. code-block:: console
+
+    Re-enter KDC database master key to verify:
+
+If successfully applied, the following message is displayed:
+
+.. code-block:: console
+
+    Now that your realm is set up you may wish to create an administrative
+    principal using the addprinc subcommand of the kadmin.local program.
+    Then, this principal can be added to /etc/krb5kdc/kadm5.acl so that
+    you can use the kadmin program on other computers.  Kerberos admin
+    principals usually belong to a single user and end in /admin.  For
+    example, if jruser is a Kerberos administrator, then in addition to
+    the normal jruser principal, a jruser/admin principal should be
+    created.
+
+    Don't forget to set up DNS information so your clients can find your
+    KDC and admin servers.  Doing so is documented in the administration
+    guide.
+
+The next step is to create the principals for the BIND 9 DNS server
+(the service protected by the GSS-TSIG TKEY) and for the DNS client
+(the Kea DHCP-DDNS server).
+
+The BIND 9 DNS server principal (used for authentication) is created the
+following way:
+
+.. code-block:: console
+
+    kadmin.local -q "addprinc -randkey DNS/server.example.org"
+
+If successfully created, the following message is displayed:
+
+.. code-block:: console
+
+    No policy specified for DNS/server.example.org@EXAMPLE.ORG; defaulting to no policy
+    Authenticating as principal root/admin@EXAMPLE.ORG with password.
+    Principal "DNS/server.example.org@EXAMPLE.ORG" created.
+
+The DNS server principal must be exported so that it can be used by the BIND 9
+DNS server. Only this principal is required, and it is exported to the keytab
+file with the name ``dns.keytab``.
+
+.. code-block:: console
+
+    kadmin.local -q "ktadd -k /tmp/dns.keytab DNS/server.example.org"
+
+If successfully exported, the following message is displayed:
+
+.. code-block:: console
+
+    Authenticating as principal root/admin@EXAMPLE.ORG with password.
+    Entry for principal DNS/server.example.org with kvno 2, encryption type aes256-cts-hmac-sha1-96 added to keytab WRFILE:/tmp/dns.keytab.
+    Entry for principal DNS/server.example.org with kvno 2, encryption type aes128-cts-hmac-sha1-96 added to keytab WRFILE:/tmp/dns.keytab.
+
+The DHCP client principal (used by the Kea DHCP-DDNS server) is created the
+following way:
+
+.. code-block:: console
+
+    kadmin.local -q "addprinc -randkey DHCP/admin.example.org"
+
+If successfully created, the following message is displayed:
+
+.. code-block:: console
+
+    No policy specified for DHCP/admin.example.org@EXAMPLE.ORG; defaulting to no policy
+    Authenticating as principal root/admin@EXAMPLE.ORG with password.
+    Principal "DHCP/admin.example.org@EXAMPLE.ORG" created.
+
+The DHCP client principal must be exported so that it can be used by the
+Kea DHCP-DDNS server and the GSS-TSIG hook library. It is exported to the client
+keytab file with the name ``dhcp.keytab``.
+
+.. code-block:: console
+
+    kadmin.local -q "ktadd -k /tmp/dhcp.keytab DHCP/admin.example.org"
+
+Finally, the ``krb5-admin-server`` must be restarted:
+
+.. code-block:: console
+
+    systemctl restart krb5-admin-server.service
+
+BIND 9 with GSS-TSIG Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The BIND 9 DNS server must be configured to use GSS-TSIG, and to use the
+previously exported DNS server principal from the keytab file ``dns.keytab``.
+Updating the ``named.conf`` file is required:
+
+.. code-block:: console
+
+    options {
+        ...
+        directory "/var/cache/bind";
+        dnssec-validation auto;
+        listen-on-v6 { any; };
+        tkey-gssapi-keytab "/etc/bind/dns.keytab";
+    };
+    zone "example.org" {
+        type master;
+        file "/var/lib/bind/db.example.org";
+        update-policy {
+            grant "DHCP/admin.example.org@EXAMPLE.ORG" zonesub any;
+        };
+    };
+    zone "84.102.10.in-addr.arpa" {
+        type master;
+        file "/etc/bind/db.10";
+    };
+
+The zone files should have an entry for the server principal FQDN
+``server.example.org``.
+
+The ``/etc/bind/db.10`` file needs to be created or updated:
+
+.. code-block:: console
+
+    ;
+    ; BIND reverse data file for local loopback interface
+    ;
+    $TTL    604800                      ; 1 week
+    @       IN      SOA      server.example.org. root.example.org. (
+                             2          ; Serial
+                             604800     ; Refresh
+                             86400      ; Retry
+                             2419200    ; Expire
+                             604800     ; Negative Cache TTL
+                             )
+    ;
+    @       IN      NS      ns.
+    40      IN      PTR     ns.example.org.
+
+The ``/var/lib/bind/db.example.org`` file needs to be created or updated:
+
+.. code-block:: console
+
+    $ORIGIN .
+    $TTL                604800             ; 1 week
+    example.org         IN SOA  server.example.org. root.example.org. (
+                                8          ; serial
+                                604800     ; refresh (1 week)
+                                86400      ; retry (1 day)
+                                2419200    ; expire (4 weeks)
+                                604800     ; minimum (1 week)
+                                )
+                        NS      example.org.
+                        A       ${BIND9_IP_ADDR}
+                        AAAA    ::1
+    $ORIGIN example.org.
+    kdc                 A       ${KDC_IP_ADDR}
+    server              A       ${BIND9_IP_ADDR}
+
+After any configuration change the server must be reloaded or
+restarted:
+
+.. code-block:: console
+
+    systemctl restart named.service
+
+It is possible to get the status or restart the logs:
+
+.. code-block:: console
+
+    systemctl status named.service
+    journalctl -u named | tail -n 30
+
+Windows Active Directory Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This sub-section is based on an Amazon AWS provided Microsoft Windows Server
+2016 with Active Directory pre-installed, so it describes only the steps used
+for GSS-TSIG deployment. (For the complete configuration process, please refer to
+Microsoft's documentation or other external resources. We found `this <https://www.tenforums.com/tutorials/51456-windows-server-2016-setup-local-domain-controller.html>`__ tutorial very
+useful during configuration of our internal QA testing systems.)
+
+Two Active Directory (AD) user accounts are needed:
+ - the first account is used to download AD information, such as
+   the client key table of Kea
+ - the second account is mapped to the Kea DHCP client principal
+
+Kea needs to know:
+ - the server IP address
+ - the domain/realm name: the domain is in lower case, the realm in upper
+   case, both without a final dot
+ - the server name
+
+The second account (named ``kea`` below) is used to create a Service
+Principal Name (SPN):
+
+.. code-block:: console
+
+    setspn -S DHCP/kea.<domain> kea
+
+After a shared secret key is generated and put in a key table file:
+
+.. code-block:: console
+
+    ktpass -princ DHCP/kea.<domain>@<REALM> -mapuser kea +rndpass -mapop set -ptype KRB5_NT_PRINCIPAL -out dhcp.keytab
+
+The ``dhcp.keytab`` takes the same usage as for UNIX Kerberos.
+
+GSS-TSIG Troubleshooting
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+While testing GSS-TSIG integration with Active Directory we came across
+one very cryptic error:
+
+.. code-block:: console
+
+   INFO  [kea-dhcp-ddns.gss-tsig-hooks/4678.139690935890624] GSS_TSIG_VERIFY_FAILED GSS-TSIG verify failed: gss_verify_mic failed with GSSAPI error:
+   Major = 'A token had an invalid Message Integrity Check (MIC)' (393216), Minor = 'Packet was replayed in wrong direction' (100002).
+
+In our case, the problem was that the Kea D2 server was trying to perform an update of a reverse
+DNS zone while it was not configured. An easy solution is to add a reverse DNS
+zone similar to the one configured in Kea. To do that, open the "DNS Manager" and choose
+"DNS" from the list; from the dropdown list, choose "Reverse Lookup Zones"; then
+click "Action" and "New Zone"; finally, follow the New Zone Wizard to add a new zone.
+
+The standard requires both anti-replay and sequence services. Experiences with the BIND 9 nsupdate
+showed the sequence service led to problems so it is disabled by default in the hook. It seems
+the anti-replay service can also lead to problems with Microsoft DNS servers so it is now
+configurable. Note that these security services are useless for DNS dynamic update which was
+designed to run over UDP so with out of order and duplicated messages.
+
+.. _gss-tsig-using:
+
+Using GSS-TSIG
+--------------
+
+There are a number of steps required to enable the GSS-TSIG mechanism:
+
+1. The ``gss_tsig`` hook library must be loaded by the D2 server.
+2. The GSS-TSIG-capable DNS servers must be specified with their parameters.
+
+An excerpt from a D2 server configuration is provided below; more examples are available in the
+``doc/examples/ddns`` directory in the Kea sources.
+
+.. code-block:: javascript
+   :linenos:
+   :emphasize-lines: 57-117
+
+
+    {
+    "DhcpDdns": {
+        // The following parameters are used to receive NCRs (NameChangeRequests)
+        // from the local Kea DHCP server. Make sure your kea-dhcp4 and kea-dhcp6
+        // matches this.
+        "ip-address": "127.0.0.1",
+        "port": 53001,
+        "dns-server-timeout" : 1000,
+
+        // Forward zone: secure.example.org. It uses GSS-TSIG. It is served
+        // by two DNS servers, which listen for DDNS requests at 192.0.2.1
+        // and 192.0.2.2.
+        "forward-ddns":
+        {
+            "ddns-domains":
+            [
+                // DdnsDomain for zone "secure.example.org."
+                {
+                    "name": "secure.example.org.",
+                    "comment": "DdnsDomain example",
+                    "dns-servers":
+                    [
+                        { // This server has an entry in gss/servers and
+                          // thus will use GSS-TSIG.
+                            "ip-address": "192.0.2.1"
+                        },
+                        { // This server also has an entry there, so will
+                          // use GSS-TSIG, too.
+                            "ip-address": "192.0.2.2",
+                            "port": 5300
+                        }
+                    ]
+                }
+            ]
+        },
+
+        // Reverse zone: we want to update the reverse zone "2.0.192.in-addr.arpa".
+        "reverse-ddns":
+        {
+            "ddns-domains":
+            [
+                {
+                    "name": "2.0.192.in-addr.arpa.",
+                    "dns-servers":
+                    [
+                        {
+                            // There is a GSS-TSIG definition for this server (see
+                            // DhcpDdns/gss-tsig/servers), so it will use
+                            // Krb/GSS-TSIG.
+                            "ip-address": "192.0.2.1"
+                        }
+                    ]
+                }
+            ]
+        },
+
+        // The GSS-TSIG hook is loaded and its configuration is specified here.
+        "hooks-libraries": [
+        {
+            "library": "/opt/lib/libddns_gss_tsig.so",
+            "parameters": {
+                // This section governs the GSS-TSIG integration. Each server
+                // mentioned in forward-ddns and/or reverse-ddns needs to have
+                // an entry here to be able to use GSS-TSIG defaults (optional,
+                // if specified they apply to all the GSS-TSIG servers, unless
+                // overwritten on specific server level).
+
+                "server-principal": "DNS/server.example.org@EXAMPLE.ORG",
+                "client-principal": "DHCP/admin.example.org@EXAMPLE.ORG",
+
+                // client-keytab and credentials-cache can both be used to
+                // store client keys. As credentials cache is more flexible,
+                // it is recommended to use it. Typically, using both at the
+                // same time may cause problems.
+                //
+                // "client-keytab": "FILE:/etc/dhcp.keytab", // toplevel only
+                "credentials-cache": "FILE:/etc/ccache", // toplevel only
+                "gss-replay-flag": true, // GSS anti replay service
+                "gss-sequence-flag": false, // no GSS sequence service
+                "tkey-lifetime": 3600, // 1 hour
+                "rekey-interval": 2700, // 45 minutes
+                "retry-interval": 120, // 2 minutes
+                "tkey-protocol": "TCP",
+                "fallback": false,
+
+                // The list of GSS-TSIG capable servers
+                "servers": [
+                    {
+                        // First server (identification is required)
+                        "id": "server1",
+                        "domain-names": [ ], // if not specified or empty, will
+                                             // match all domains that want to
+                                             // use this IP+port pair
+                        "ip-address": "192.0.2.1",
+                        "port": 53,
+                        "server-principal": "DNS/server1.example.org@EXAMPLE.ORG",
+                        "client-principal": "DHCP/admin1.example.org@EXAMPLE.ORG",
+                        "gss-replay-flag": false, // no GSS anti replay service
+                        "gss-sequence-flag": false, // no GSS sequence service
+                        "tkey-lifetime": 7200, // 2 hours
+                        "rekey-interval": 5400, // 90 minutes
+                        "retry-interval": 240, // 4 minutes
+                        "tkey-protocol": "TCP",
+                        "fallback": true // if no key is available fallback to the
+                                         // standard behavior (vs skip this server)
+                    },
+                    {
+                        // The second server (it has most of the parameters missing
+                        // as those are using the defaults specified above)
+                        "id": "server2",
+                        "ip-address": "192.0.2.2",
+                        "port": 5300
+                    }
+                ]
+            }
+        }
+        ]
+
+        // Additional parameters, such as logging, control socket and
+        // others omitted for clarity.
+    }
+
+    }
+
+This configuration file contains a number of extra elements.
+
+First, a list of forward and/or reverse domains with related DNS servers
+identified by their IP+port pairs is defined. If the port is not
+specified, the default of 53 is assumed. This is similar to basic mode, with no
+authentication done using TSIG keys, with the
+exception that static TSIG keys are not referenced by name.
+
+Second, the ``libddns_gss_tsig.so`` library must be specified on the
+``hooks-libraries`` list. This hook takes many parameters. The most important
+one is ``servers``, which is a list of GSS-TSIG-capable servers. If there are
+several servers and they share some characteristics, the values can be specified
+in the ``parameters`` scope as defaults. In the example above, the defaults that apply
+to all servers, unless otherwise specified on a per-server scope, are defined in
+lines 63 through 68. The defaults can be skipped if there is only one server
+defined, or if all servers have different values.
+
+.. table:: List of available parameters
+
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | Name              | Scope    | Type    | Default value       | Description                    |
+   |                   |          |         |                     |                                |
+   +===================+==========+=========+=====================+================================+
+   | client-keytab     | global / | string  | empty               | the Kerberos **client** key    |
+   |                   | server   |         |                     | table                          |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | credentials-cache | global / | string  | empty               | the Kerberos credentials cache |
+   |                   | server   |         |                     |                                |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | server-principal  | global / | string  | empty               | the Kerberos principal name of |
+   |                   | server   |         |                     | the DNS server that will       |
+   |                   |          |         |                     | receive updates                |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | client-principal  | global / | string  | empty               | the Kerberos principal name of |
+   |                   | server   |         |                     | the Kea D2 service             |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | gss-replay-flag   | global / | true /  | true                | require the GSS anti replay    |
+   |                   | server   | false   |                     | service (GSS_C_REPLAY_FLAG)    |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | gss-sequence-flag | global / | true /  | false               | require the GSS sequence       |
+   |                   | server   | false   |                     | service (GSS_C_SEQUENCE_FLAG)  |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | tkey-protocol     | global / | string  | "TCP"               | the protocol used to establish |
+   |                   | server   | "TCP" / |                     | the security context with the  |
+   |                   |          | "UDP"   |                     | DNS servers                    |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | tkey-lifetime     | global / | uint32  | | 3600 seconds      | the lifetime of GSS-TSIG keys  |
+   |                   | server   |         | | ( 1 hour )        |                                |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | rekey-interval    | global / | uint32  | | 2700 seconds      | the time interval the keys are |
+   |                   | server   |         | | ( 45 minutes )    | checked for rekeying           |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | retry-interval    | global / | uint32  | | 120 seconds       | the time interval to retry to  |
+   |                   | server   |         | | ( 2 minutes )     | create a key if any error      |
+   |                   |          |         |                     | occurred previously            |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | fallback          | global / | true /  | false               | the behavior to fallback to    |
+   |                   | server   | false   |                     | non-GSS-TSIG when GSS-TSIG     |
+   |                   |          |         |                     | should be used but no GSS-TSIG |
+   |                   |          |         |                     | key is available.              |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | exchange-timeout  | global / | uint32  | | 3000 milliseconds | the time used to wait for the  |
+   |                   | server   |         | | ( 3 seconds )     | GSS-TSIG TKEY exchange to      |
+   |                   |          |         |                     | finish before it timeouts      |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | user-context      | global / | string  | empty               | the user-provided data in JSON |
+   |                   | server   |         |                     | format (not used by            |
+   |                   |          |         |                     | the GSS-TSIG hook)             |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | comment           | global / | string  | empty               | ignored                        |
+   |                   | server   |         |                     |                                |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | id                | server   | string  | empty               | identifier to a DNS server     |
+   |                   |          |         |                     | (required)                     |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | domain-names      | server   | list of | empty               | the many-to-one relationship   |
+   |                   |          | strings |                     | between D2 DNS servers and     |
+   |                   |          |         |                     | GSS-TSIG DNS servers           |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | ip-address        | server   | IPv4 /  | empty               | the IP address at which the    |
+   |                   |          | IPv6    |                     | GSS-TSIG DNS server listens    |
+   |                   |          | address |                     | for DDNS and TKEY requests     |
+   |                   |          |         |                     | (required)                     |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+   | port              | server   | uint16  | 53                  | the DNS transport port at      |
+   |                   |          |         |                     | which the GSS-TSIG DNS server  |
+   |                   |          |         |                     | listens for DDNS and TKEY      |
+   |                   |          |         |                     | requests                       |
+   +-------------------+----------+---------+---------------------+--------------------------------+
+
+The global parameters are described below:
+
+- ``client-keytab`` specifies the Kerberos **client** key table.
+  For instance, ``FILE:<filename>`` can be used to point to a specific file.
+  This parameter can be specified only once, in the parameters scope,
+  and is the equivalent of setting the ``KRB5_CLIENT_KTNAME`` environment
+  variable. An empty value is silently ignored.
+
+- ``credentials-cache`` specifies the Kerberos credentials cache.
+  For instance, ``FILE:<filename>`` can be used to point to a file or,
+  if using a directory which supports more than one principal,
+  ``DIR:<directory-path>``.
+  This parameter can be specified only once, in the parameters scope,
+  and is the equivalent of setting the ``KRB5CCNAME`` environment
+  variable. An empty value is silently ignored.
+
+- ``server-principal`` is the Kerberos principal name of the DNS
+  server that receives updates. In other words, this is the
+  DNS server's name in the Kerberos system. This parameter is
+  mandatory, and uses the typical Kerberos notation:
+  ``<SERVICE-NAME>/<server-domain-name>@<REALM>``.
+
+- ``client-principal`` is the Kerberos principal name of the Kea D2
+  service. It is optional, and uses the typical Kerberos notation:
+  ``<SERVICE-NAME>/<server-domain-name>@<REALM>``.
+
+- ``gss-replay-flag`` determines if the GSS anti replay service is
+  required. It is by default but this can be disabled.
+
+- ``gss-sequence-flag`` determines if the GSS sequence service is
+  required. It is not by default but is required by the standard
+  so it can be enabled.
+
+- ``tkey-protocol`` determines which protocol is used to establish the
+  security context with the DNS servers. Currently, the only supported
+  values are TCP (the default) and UDP.
+
+- ``tkey-lifetime`` determines the lifetime of GSS-TSIG keys in the
+  TKEY protocol. The value must be greater than the ``rekey-interval``
+  value. It is expressed in seconds and defaults to 3600 (one hour).
+
+- ``rekey-interval`` governs the time interval at which the keys for each configured
+  server are checked for rekeying, i.e. when a new key is created to replace the
+  current usable one if its age is greater than the ``rekey-interval`` value.
+  The value must be smaller than the ``tkey-lifetime`` value (it is recommended
+  to be set between 50% and 80% of the ``tkey-lifetime`` value). It is expressed in
+  seconds and defaults to 2700 (45 minutes, or 75% of one hour).
+
+- ``retry-interval`` governs the time interval at which to retry to create a key if any
+  error occurred previously for any configured server. The value must be smaller
+  than the ``rekey-interval`` value, and should be at most 1/3 of the difference
+  between ``tkey-lifetime`` and ``rekey-interval``. It is expressed in seconds
+  and defaults to 120 (2 minutes).
+
+- ``fallback`` governs the behavior when GSS-TSIG should be used (a
+  matching DNS server is configured) but no GSS-TSIG key is available.
+  If set to ``false`` (the default), this server is skipped; if
+  set to ``true``, the DNS server is ignored and the DNS update
+  is sent with the configured DHCP-DDNS protection (e.g. TSIG key), or
+  without any protection when none was configured.
+
+- ``exchange-timeout`` governs the amount of time to wait for the GSS-TSIG TKEY
+  exchange to finish before the process times out. It is expressed in milliseconds and
+  defaults to 3000 (3 seconds).
+
+- ``user-context`` is an optional parameter (see :ref:`user-context`
+  for a general description of user contexts in Kea).
+
+- ``comment`` is allowed but currently ignored.
+
+- ``servers`` specifies the list of DNS servers where GSS-TSIG is enabled.
+
+The server map parameters are described below:
+
+- ``id`` assigns an identifier to a DNS server. It is used for statistics
+  and commands. It is required, and must be both not empty and unique.
+
+- ``domain-names`` governs the many-to-one relationship between D2 DNS
+  servers and GSS-TSIG DNS servers: for each domain name on this list,
+  Kea looks for a D2 DNS server for this domain with the specified IP address
+  and port. An empty list (the default) means that all domains
+  match.
+
+- ``ip-address`` specifies the IP address at which the GSS-TSIG DNS server
+  listens for DDNS and TKEY requests. It is a mandatory parameter.
+
+- ``port`` specifies the DNS transport port on which the GSS-TSIG DNS server
+  listens for DDNS and TKEY requests. It defaults to 53.
+
+- ``server-principal`` is the Kerberos principal name of the DNS server
+  that receives updates. The ``server-principal`` parameter set at the per-server
+  level takes precedence over one set at the global level. It is a mandatory parameter which must be specified at
+  either the global or the server level.
+
+- ``client-principal`` is the Kerberos principal name of the Kea D2
+  service for this DNS server. The ``client-principal`` parameter set at the per-server
+  level takes precedence over one set at the global level. It is an optional parameter.
+
+- ``gss-replay-flag`` determines if the GSS anti replay service is
+  required. The ``gss-replay-flag`` parameter set at the per-server
+  level takes precedence over one set at the global level. It is an optional parameter
+  which defaults to true.
+
+- ``gss-sequence-flag`` determines if the GSS sequence service is
+  required. The ``gss-sequence-flag`` parameter set at the per-server
+  level takes precedence over one set at the global level. It is an optional parameter
+  which defaults to false.
+
+- ``tkey-protocol`` determines which protocol is used to establish the
+  security context with the DNS server. The ``tkey-protocol`` parameter set at the per-server
+  level takes precedence over one set at the global level. The default and supported values
+  for the per-server level parameter are the same as
+  for the global-level parameter.
+
+- ``tkey-lifetime`` determines the lifetime of GSS-TSIG keys in the
+  TKEY protocol for the DNS server. The ``tkey-lifetime`` parameter set at the per-server
+  level takes precedence over one set at the global level. The default and supported values
+  for the per-server level parameter are the same as
+  for the global-level parameter.
+
+- ``rekey-interval`` governs the time interval at which the keys for this particular
+  server are checked for rekeying, i.e. when a new key is created to replace the
+  current usable one if its age is greater than the ``rekey-interval`` value.
+  The value must be smaller than the ``tkey-lifetime`` value (it is recommended
+  to be set between 50% and 80% of the ``tkey-lifetime`` value). The ``rekey-interval``
+  parameter set at the per-server level takes precedence over one set at the global
+  level. The default and supported values for the per-server level parameter are the same as
+  for the global-level parameter.
+
+- ``retry-interval`` governs the time interval at which to retry to create a key if any
+  error occurred previously for this particular server. The value must be
+  smaller than the ``rekey-interval`` value, and should be at most 1/3 of the
+  difference between ``tkey-lifetime`` and ``rekey-interval``. The
+  ``retry-interval`` parameter set at the per-server level takes precedence over one set at the global
+  level. The default and supported values for the per-server level parameter are the same as
+  for the global-level parameter.
+
+- ``fallback`` governs the behavior when GSS-TSIG should be used (a
+  matching DNS server is configured) but no GSS-TSIG key is available.
+  The ``fallback`` parameter set at the per-server level takes precedence over one set at the global
+  level. The default and supported values for the per-server level parameter are the same as
+  for the global-level parameter..
+
+- ``exchange-timeout`` governs the amount of time to wait for the GSS-TSIG TKEY
+  exchange to finish before the process times out. The ``exchange-timeout`` parameter
+  set at the per-server level takes precedence over one set at the global
+  level. The default and supported values for the per-server level parameter are the same as
+  for the global-level parameter.
+
+- ``user-context`` is an optional parameter (see :ref:`user-context`
+  for a general description of user contexts in Kea).
+
+- ``comment`` is allowed but currently ignored.
+
+.. note::
+
+    Generally it is not recommended to specify both the client keytab (``client-keytab``)
+    and the credentials cache (``credentials-cache``), although this may
+    differ between Kerberos implementations. The client keytab is just for
+    the client key and is typically used to specify the key explicitly in more
+    static manner, while the credentials cache can be used to store multiple
+    credentials and can be dynamically updated by the Kerberos library. As such,
+    the credentials-cache is more flexible and thus the recommended alternative.
+
+    Also note that only the read access right is needed to use the cache.
+    Fetching credentials and updating the cache requires the write access
+    right.
+
+
+GSS-TSIG Automatic Key Removal
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The server periodically deletes keys after they have been expired more than three times the
+length of the maximum key lifetime (the ``tkey-lifetime`` parameter).
+The user has the option to purge keys on demand by using the ``gss-tsig-purge-all``
+command (see :ref:`command-gss-tsig-purge-all`) or the ``gss-tsig-purge`` command
+(see :ref:`command-gss-tsig-purge`).
+
+
+GSS-TSIG Configuration for Deployment
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When using Kerberos 5 and BIND 9 as described in :ref:`gss-tsig-deployment`,
+the local resolver must point to the BIND 9 ``named`` server address. The
+local Kerberos must also be configured by putting the following text into the ``krb5.conf`` file:
+
+.. code-block:: ini
+
+    [libdefaults]
+        default_realm = EXAMPLE.ORG
+        kdc_timesync = 1
+        ccache_type = 4
+        forwardable = true
+        proxiable = true
+    [realms]
+        EXAMPLE.ORG = {
+                kdc = kdc.example.org
+                admin_server = kdc.example.org
+        }
+
+With Windows AD, the DNS service is provided by AD, which also provides
+the Kerberos service. The required text in the ``krb5.conf`` file becomes:
+
+.. code-block:: ini
+
+    [libdefaults]
+        default_realm = <REALM>
+        kdc_timesync = 1
+        ccache_type = 4
+        forwardable = true
+        proxiable = true
+    [realms]
+        ${REALM} = {
+                kdc = <AD_IP_ADDR>
+                admin_server = <AD_IP_ADDR>
+        }
+
+Even when the GSS-API library can use the secret from the client key
+table, it is far better for performance to get and cache credentials.
+
+This can be done manually via the command:
+
+.. code-block:: console
+
+    kinit -k -t /tmp/dhcp.keytab DHCP/admin.example.org
+
+or, when using AD:
+
+.. code-block:: console
+
+    kinit -k -t /tmp/dhcp.keytab DHCP/kea.<domain>
+
+The credential cache can be displayed using ``klist``.
+
+In production, it is better to rely on a Kerberos Credential Manager as
+the System Security Services Daemon (``sssd``).
+
+When using BIND 9, the server principal is in the form "DNS/server.example.org@EXAMPLE.ORG¨;
+with AD, the format is "DNS/<server>.<domain>@<REALM>".
+
+.. _stats-gss-tsig:
+
+GSS-TSIG Statistics
+-------------------
+
+The GSS-TSIG hook library introduces new statistics at global and
+per-DNS-server levels:
+
+-  ``gss-tsig-key-created`` - the number of created GSS-TSIG keys
+-  ``tkey-sent`` - the number of sent TKEY exchange initial requests
+-  ``tkey-success`` - the number of TKEY exchanges which completed with a success
+-  ``tkey-timeout`` - the number of TKEY exchanges which completed on timeout
+-  ``tkey-error`` - the number of TKEY exchanges which completed with an error other than
+   a timeout
+
+The relationship between keys and DNS servers is very different between
+the D2 code and static TSIG keys, and GSS-TSIG keys and DNS servers:
+
+ - a static TSIG key can be shared between many DNS servers;
+ - a GSS-TSIG key is only used by one DNS server inside a dedicated
+   set of keys.
+
+.. _commands-gss-tsig:
+
+GSS-TSIG Commands
+-----------------
+
+The GSS-TSIG hook library supports some commands, which are described below.
+
+.. _command-gss-tsig-get-all:
+
+The ``gss-tsig-get-all`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command lists all the GSS-TSIG servers and keys.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-get-all"
+    }
+
+Here is an example of a response returning one GSS-TSIG server and one key:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "1 GSS-TSIG servers and 1 keys",
+        "arguments": {
+            "gss-tsig-servers": [
+                {
+                    "id": "foo",
+                    "ip-address": "192.1.2.3",
+                    "port": 53,
+                    "server-principal": "DNS/foo.com@FOO.COM",
+                    "key-name-suffix": "foo.com.",
+                    "tkey-lifetime": 3600,
+                    "tkey-protocol": "TCP",
+                    "keys": [
+                        {
+                            "name": "1234.sig-foo.com.",
+                            "inception-date": "2021-09-05 12:23:36.281176",
+                            "server-id": "foo",
+                            "expire-date": "2021-09-05 13:23:36.281176",
+                            "status": "not yet ready",
+                            "tkey-exchange": true
+                        }
+                    ]
+                },
+                {
+                    "id": "bar",
+                    "ip-address": "192.1.2.4",
+                    "port": 53,
+                    "server-principal": "DNS/bar.com@FOO.COM",
+                    "key-name-suffix": "bar.com.",
+                    "tkey-lifetime": 7200,
+                    "tkey-protocol": "UDP",
+                    "keys": [ ]
+                }
+            ]
+        }
+    }
+
+.. _command-gss-tsig-get:
+
+The ``gss-tsig-get`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command retrieves information about the specified GSS-TSIG server.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-get",
+        "arguments": {
+            "server-id": "foo"
+        }
+    }
+
+Here is an example of a response returning information about the server "foo":
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "GSS-TSIG server[foo] found",
+        "arguments": {
+            "id": "foo",
+            "ip-address": "192.1.2.3",
+            "port": 53,
+            "server-principal": "DNS/foo.com@FOO.COM",
+            "key-name-suffix": "foo.com.",
+            "tkey-lifetime": 3600,
+            "tkey-protocol": "TCP",
+            "keys": [
+                {
+                    "name": "1234.sig-foo.com.",
+                    "server-id": "foo",
+                    "inception-date": "2021-09-05 12:23:36.281176",
+                    "expire-date": "2021-09-05 13:23:36.281176",
+                    "status": "not yet ready",
+                    "tkey-exchange": true
+                }
+            ]
+        }
+    }
+
+.. _command-gss-tsig-list:
+
+The ``gss-tsig-list`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command generates a list of GSS-TSIG server IDs and key names.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-list"
+    }
+
+Here is an example of a response returning two GSS-TSIG servers and three keys:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "2 GSS-TSIG servers and 3 keys",
+        "arguments": {
+            "gss-tsig-servers": [
+                "foo",
+                "bar"
+            ],
+            "gss-tsig-keys": [
+                "1234.example.com.",
+                "5678.example.com.",
+                "43888.example.org."
+            ]
+        }
+    }
+
+.. _command-gss-tsig-key-get:
+
+The ``gss-tsig-key-get`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command retrieves information about the specified GSS-TSIG key.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-key-get",
+        "arguments": {
+            "key-name": "1234.sig-foo.com."
+        }
+    }
+
+Here is an example of a response returning information about GSS-TSIG key "1234.sig-foo.com.":
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "GSS-TSIG key '1234.sig-foo.com.' found",
+        "arguments": {
+            "name": "1234.sig-foo.com.",
+            "server-id": "foo",
+            "inception-date": "2021-09-05 12:23:36.281176",
+            "expire-date": "2021-09-05 13:23:36.281176",
+            "status": "not yet ready",
+            "tkey-exchange": true
+        }
+    }
+
+.. _command-gss-tsig-key-expire:
+
+The ``gss-tsig-key-expire`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command expires the specified GSS-TSIG key.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-key-expire",
+        "arguments": {
+            "key-name": "1234.sig-foo.com."
+        }
+    }
+
+Here is an example of a response indicating that GSS-TSIG key "1234.sig-foo.com." has been expired:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "GSS-TSIG key '1234.sig-foo.com.' expired"
+    }
+
+.. _command-gss-tsig-key-del:
+
+The ``gss-tsig-key-del`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command deletes the specified GSS-TSIG key.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-key-del",
+        "arguments": {
+            "key-name": "1234.sig-foo.com."
+        }
+    }
+
+Here is an example of a response indicating that GSS-TSIG key "1234.sig-foo.com." has been deleted:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "GSS-TSIG key '1234.sig-foo.com.' deleted"
+    }
+
+.. _command-gss-tsig-purge-all:
+
+The ``gss-tsig-purge-all`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command removes all unusable GSS-TSIG keys.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-purge-all"
+    }
+
+Here is an example of a response indicating that two GSS-TSIG keys have been purged:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "2 purged GSS-TSIG keys"
+    }
+
+.. _command-gss-tsig-purge:
+
+The ``gss-tsig-purge`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command removes unusable GSS-TSIG keys for the specified server.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-purge",
+        "arguments": {
+            "server-id": "foo"
+        }
+    }
+
+Here is an example of a response indicating that two GSS-TSIG keys for server "foo" have been purged:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "2 purged keys for GSS-TSIG server[foo]"
+    }
+
+.. _command-gss-tsig-rekey-all:
+
+The ``gss-tsig-rekey-all`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command unconditionally creates new GSS-TSIG keys (rekeys) for
+all DNS servers.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-rekey-all"
+    }
+
+Here is an example of a response indicating that a rekey was performed:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "rekeyed"
+    }
+
+This command is useful when, for instance, the DHCP-DDNS server is
+reconnected to the network.
+
+.. _command-gss-tsig-rekey:
+
+The ``gss-tsig-rekey`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command unconditionally creates new GSS-TSIG keys (rekeys) for
+a specified DNS server.
+
+An example command invocation looks like this:
+
+.. code-block:: json
+
+    {
+        "command": "gss-tsig-rekey",
+        "arguments": {
+            "server-id": "foo"
+        }
+    }
+
+Here is an example of a response indicating that a rekey was performed:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "GSS-TSIG server[foo] rekeyed"
+    }
+
+This command is typically used when a DNS server has been rebooted, so
+that existing GSS-TSIG keys shared with this server can no longer be used.
diff --git a/doc/sphinx/arm/ext-netconf.rst b/doc/sphinx/arm/ext-netconf.rst
new file mode 100644
index 0000000..46725e1
--- /dev/null
+++ b/doc/sphinx/arm/ext-netconf.rst
@@ -0,0 +1,1058 @@
+.. _netconf:
+
+YANG/NETCONF
+============
+
+.. _netconf-overview:
+
+Overview
+--------
+
+The Network Configuration Protocol, or NETCONF, is a network management protocol defined
+in `RFC 4741 <https://tools.ietf.org/html/rfc4741>`__. It uses YANG modeling language,
+defined in `RFC 6020 <https://tools.ietf.org/html/rfc6020>`__, to provide a uniform way
+of handling the configuration syntax of varied networking devices. Kea provides optional
+support for a YANG/NETCONF interface with the ``kea-netconf`` agent.
+
+.. _netconf-install:
+
+Installing NETCONF
+------------------
+
+To get its NETCONF capabilities, Kea uses libyang v1.0.240 and Sysrepo v1.4.140.
+Use packages if they are provided by the system. If not, users can
+build from sources, which should work on all popular OSes:
+
+.. _libyang-install-sources:
+
+Installing libyang From Sources
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: console
+
+    $ git clone https://github.com/CESNET/libyang.git
+    $ cd libyang
+    $ git checkout v1.0.240
+    $ mkdir build
+    $ cd build
+    $ cmake .. -DGEN_CPP_BINDINGS=ON -DGEN_LANGUAGE_BINDINGS=ON -DGEN_PYTHON_BINDINGS=OFF
+    $ make
+    $ make install  # without sudo if you're doing development and want to run unit tests
+
+.. _sysrepo-install-sources:
+
+Installing Sysrepo From Sources
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: console
+
+    $ git clone https://github.com/sysrepo/sysrepo.git
+    $ cd sysrepo
+    $ git checkout v1.4.140
+    $ mkdir build
+    $ cd build
+    $ cmake .. -DGEN_CPP_BINDINGS=ON -DGEN_LANGUAGE_BINDINGS=ON -DGEN_PYTHON_BINDINGS=OFF
+    $ make
+    $ make install  # without sudo if you're doing development and want to run unit tests
+
+.. _sysrepo-overview:
+
+Quick Sysrepo Overview
+----------------------
+
+This section offers a brief overview of a subset of available
+functions in Sysrepo. For more complete information, see the `Sysrepo
+homepage <https://www.sysrepo.org>`__.
+
+In YANG, configurations and state data are described in the YANG syntax
+in module files named: ``"module-name"``\``[@"revision"]``.yang
+
+The revision part is optional and has YYYY-MM-DD format. An alternate
+XML syntax YIN is defined but less user-friendly. Top-level modules are
+named in Kea models (a short version of schema models).
+
+There are two major modules that Kea is able to support: ``kea-dhcp4-server`` and
+``kea-dhcp6-server``. While there is an active effort in the DHC working group at
+IETF to develop a DHCPv6 YANG model, a similar initiative in the past for DHCPv4
+failed. Therefore, Kea uses its own dedicated models for DHCPv4 and DHCPv6 but
+partially supports the IETF model for DHCPv6.
+
+All of the models have extra modules as dependencies. The dependency modules are
+also provided in ``src/share/yang/modules`` in sources and in
+``share/kea/yang/modules`` in the installation directory.
+
+To install modules from sources, do the following to install all modules:
+
+.. code-block:: console
+
+    $ ./src/share/yang/modules/utils/reinstall.sh
+
+If Sysrepo is installed in a custom path, use:
+
+.. code-block:: console
+
+    $ ./src/share/yang/modules/utils/reinstall.sh -s /path/to/sysrepo
+
+To individually install all modules:
+
+.. code-block:: console
+
+    $ cd ./src/share/yang/modules
+    $ sysrepoctl -i ./ietf-dhcpv6-server*.yang
+    $ sysrepoctl -i ./kea-dhcp4-server*.yang
+    $ sysrepoctl -i ./kea-dhcp6-server*.yang
+    ...
+
+The installation should look similar to the following:
+
+.. code-block:: console
+
+    $ ./src/share/yang/modules/utils/reinstall.sh
+    [INF]: Libyang internal module "yang" was installed.
+    [INF]: File "ietf-datastores@2018-02-14.yang" was installed.
+    [INF]: Sysrepo internal dependency module "ietf-datastores" was installed.
+    [INF]: File "ietf-yang-library@2019-01-04.yang" was installed.
+    [INF]: Sysrepo internal module "ietf-yang-library" was installed.
+    [INF]: File "sysrepo-monitoring@2021-01-15.yang" was installed.
+    [INF]: Sysrepo internal module "sysrepo-monitoring" was installed.
+    [INF]: File "sysrepo-plugind@2020-12-10.yang" was installed.
+    [INF]: Sysrepo internal module "sysrepo-plugind" was installed.
+    [INF]: File "ietf-netconf@2011-06-01.yang" was installed.
+    [INF]: Sysrepo internal dependency module "ietf-netconf" was installed.
+    [INF]: File "ietf-netconf-with-defaults@2011-06-01.yang" was installed.
+    [INF]: Sysrepo internal module "ietf-netconf-with-defaults" was installed.
+    [INF]: File "ietf-netconf-notifications@2012-02-06.yang" was installed.
+    [INF]: Sysrepo internal module "ietf-netconf-notifications" was installed.
+    [INF]: File "ietf-origin@2018-02-14.yang" was installed.
+    [INF]: Sysrepo internal module "ietf-origin" was installed.
+    [INF]: Connection 20 created.
+    [INF]: Module "keatest-module" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: File "keatest-module@2018-11-20.yang" was installed.
+    [INF]: Module "keatest-module" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 21 created.
+    [INF]: Module "ietf-interfaces" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: File "ietf-interfaces@2018-02-20.yang" was installed.
+    [INF]: Module "ietf-interfaces" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 22 created.
+    [INF]: Module "ietf-dhcpv6-client" scheduled for installation.
+    [INF]: File "ietf-dhcpv6-options@2018-09-04.yang" was installed.
+    [INF]: File "ietf-dhcpv6-types@2018-09-04.yang" was installed.
+    [INF]: Applying scheduled changes.
+    [INF]: File "ietf-dhcpv6-client@2018-09-04.yang" was installed.
+    [INF]: Module "ietf-dhcpv6-client" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 23 created.
+    [INF]: Module "ietf-dhcpv6-relay" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: File "ietf-dhcpv6-relay@2018-09-04.yang" was installed.
+    [INF]: Module "ietf-dhcpv6-relay" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 24 created.
+    [INF]: Module "ietf-dhcpv6-server" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: File "ietf-dhcpv6-server@2018-09-04.yang" was installed.
+    [INF]: Module "ietf-dhcpv6-server" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 25 created.
+    [INF]: Module "ietf-yang-types" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: Module "ietf-yang-types" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 26 created.
+    [INF]: Module "ietf-dhcpv6-options" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: Module "ietf-dhcpv6-options" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 27 created.
+    [INF]: Module "ietf-dhcpv6-types" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: Module "ietf-dhcpv6-types" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 28 created.
+    [INF]: Module "ietf-inet-types" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: Module "ietf-inet-types" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 29 created.
+    [INF]: Module "kea-types" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: File "kea-types@2019-08-12.yang" was installed.
+    [INF]: Module "kea-types" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 30 created.
+    [INF]: Module "kea-dhcp-types" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: File "kea-dhcp-types@2019-08-12.yang" was installed.
+    [INF]: Module "kea-dhcp-types" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 31 created.
+    [INF]: Module "kea-dhcp-ddns" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: File "kea-dhcp-ddns@2019-08-12.yang" was installed.
+    [INF]: Module "kea-dhcp-ddns" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 32 created.
+    [INF]: Module "kea-ctrl-agent" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: File "kea-ctrl-agent@2019-08-12.yang" was installed.
+    [INF]: Module "kea-ctrl-agent" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 33 created.
+    [INF]: Module "kea-dhcp4-server" scheduled for installation.
+    [INF]: Applying scheduled changes.
+    [INF]: File "kea-dhcp4-server@2019-08-12.yang" was installed.
+    [INF]: Module "kea-dhcp4-server" was installed.
+    [INF]: Scheduled changes applied.
+    [INF]: Connection 34 created.
+    [INF]: Module "kea-dhcp6-server" scheduled for installation.
+
+It is possible to confirm whether the models are imported correctly.
+To list the currently installed YANG modules:
+
+.. code-block:: console
+
+     $ sysrepoctl -l
+
+After installation the result should be similar to this:
+
+::
+
+    Sysrepo repository: /etc/sysrepo
+
+    Module Name                | Revision   | Flags | Owner         | Permissions | Submodules | Features
+    -----------------------------------------------------------------------------------------------------
+    ietf-datastores            | 2018-02-14 | I     | user:user     | 664         |            |
+    ietf-dhcpv6-client         | 2018-09-04 | I     | user:user     | 600         |            |
+    ietf-dhcpv6-options        | 2018-09-04 | I     | user:user     | 600         |            |
+    ietf-dhcpv6-relay          | 2018-09-04 | I     | user:user     | 600         |            |
+    ietf-dhcpv6-server         | 2018-09-04 | I     | user:user     | 600         |            |
+    ietf-dhcpv6-types          | 2018-09-04 | I     | user:user     | 600         |            |
+    ietf-inet-types            | 2013-07-15 | I     | user:user     | 664         |            |
+    ietf-interfaces            | 2018-02-20 | I     | user:user     | 600         |            |
+    ietf-netconf               | 2011-06-01 | I     | user:user     | 664         |            |
+    ietf-netconf-notifications | 2012-02-06 | I     | user:user     | 664         |            |
+    ietf-netconf-with-defaults | 2011-06-01 | I     | user:user     | 664         |            |
+    ietf-origin                | 2018-02-14 | I     | user:user     | 664         |            |
+    ietf-yang-library          | 2019-01-04 | I     | user:user     | 664         |            |
+    ietf-yang-metadata         | 2016-08-05 | i     |               |             |            |
+    ietf-yang-types            | 2013-07-15 | I     | user:user     | 664         |            |
+    kea-ctrl-agent             | 2019-08-12 | I     | user:user     | 600         |            |
+    kea-dhcp-ddns              | 2019-08-12 | I     | user:user     | 600         |            |
+    kea-dhcp-types             | 2019-08-12 | I     | user:user     | 600         |            |
+    kea-dhcp4-server           | 2019-08-12 | I     | user:user     | 600         |            |
+    kea-dhcp6-server           | 2019-08-12 | I     | user:user     | 600         |            |
+    kea-types                  | 2019-08-12 | I     | user:user     | 600         |            |
+    keatest-module             | 2018-11-20 | I     | user:user     | 600         |            |
+    sysrepo-monitoring         | 2021-01-15 | I     | user:user     | 600         |            |
+    sysrepo-plugind            | 2020-12-10 | I     | user:user     | 664         |            |
+    yang                       | 2017-02-20 | I     | user:user     | 664         |            |
+
+    Flags meaning: I - Installed/i - Imported; R - Replay support; N - New/X - Removed/U - Updated; F - Feature changes
+    Features: ! - Means that the feature is effectively disabled because of its false if-feature(s)
+
+To reinstall a module, if the revision YANG entry was bumped, simply installing
+it will update it automatically. Otherwise, it must first be uninstalled:
+
+.. code-block:: console
+
+    $ sysrepoctl -u kea-dhcp4-server
+
+If the module is used (i.e. imported) by other modules, it can be uninstalled
+only after the dependent modules have first been uninstalled.
+Installation and uninstallation must be done in dependency order and
+reverse-dependency order accordingly.
+
+.. _netconf-models:
+
+Supported YANG Models
+---------------------
+
+The only currently supported models are ``kea-dhcp4-server`` and
+``kea-dhcp6-server``. There is partial support for
+``ietf-dhcpv6-server``, but the primary focus of testing has been on Kea DHCP
+servers. Other models (``kea-dhcp-ddns`` and ``kea-ctrl-agent``)
+are currently not supported.
+
+.. _using-netconf:
+
+Using the NETCONF Agent
+-----------------------
+
+The NETCONF agent follows this algorithm:
+
+-  For each managed server, get the initial configuration from the
+   server through the control socket.
+
+-  Open a connection with the Sysrepo environment and establish two
+   sessions with the startup and running datastores.
+
+-  Check that the used (not-essential) and required (essential) modules are
+   installed in the Sysrepo repository at the right revision. If an
+   essential module - that is, a module where the configuration schema for a
+   managed server is defined - is not installed, raise a fatal error.
+
+-  For each managed server, get the YANG configuration from the startup
+   datastore, translate it to JSON, and load it onto the server being
+   configured.
+
+-  For each managed server, subscribe a module change callback using its
+   model name.
+
+-  When a running configuration is changed, try to validate or load the
+   updated configuration via the callback to the managed server.
+
+.. _netconf-configuration:
+
+Configuration
+-------------
+
+The behavior described in :ref:`using-netconf`
+is controlled by several configuration flags, which can be set in the
+global scope or in a specific managed-server scope. If the latter,
+the value defined in the managed-server scope takes precedence. These
+flags are:
+
+-  ``boot-update`` - controls the initial configuration phase; when
+   ``true`` (the default), the initial configuration retrieved from the
+   classic Kea server JSON configuration file is loaded first, and then
+   the startup YANG model is loaded. This setting lets administrators
+   define a control socket in the local JSON file and then download the
+   configuration from YANG. When set to ``false``, this phase is skipped.
+
+-  ``subscribe-changes`` - controls the module change
+   subscription; when ``true`` (the default), a module change callback is
+   subscribed, but when ``false`` the phase is skipped and running
+   configuration updates are disabled. When set to ``true``, the running
+   datastore is used to subscribe for changes.
+
+-  ``validate-changes`` - controls how Kea monitors changes in
+   the Sysrepo configuration. Sysrepo offers two stages where Kea can
+   interact: validation and application. At the validation (or
+   ``SR_EV_CHANGE`` event, in the Sysrepo naming convention) stage, Kea
+   retrieves the newly committed configuration and verifies it. If the
+   configuration is incorrect for any reason, the Kea servers reject it
+   and the error is propagated back to the Sysrepo, which then returns
+   an error. This step only takes place if ``validate-changes`` is set to
+   ``true``. In the application (or ``SR_EV_UPDATE`` event in the Sysrepo naming
+   convention) stage, the actual configuration is applied. At this stage
+   Kea can receive the configuration, but it is too late to signal back
+   any errors as the configuration has already been committed.
+
+The idea behind the initial configuration phase is to boot Kea servers
+with a minimal configuration which includes only a control socket,
+making them manageable. For instance, for the DHCPv4 server:
+
+.. code-block:: json
+
+    {
+        "Dhcp4": {
+            "control-socket": {
+               "socket-name": "/tmp/kea-dhcp4-ctrl.sock",
+               "socket-type": "unix"
+            }
+        }
+    }
+
+With module change subscriptions enabled, the ``kea-netconf`` daemon
+monitors any configuration changes as they appear in the Sysrepo. Such
+changes can be done using the ``sysrepocfg`` tool or remotely using any
+NETCONF client. For details, please see the Sysrepo documentation or
+:ref:`operation-example`.
+Those tools can be used to modify YANG configurations in the running
+datastore. Note that committed configurations are only updated in the
+running datastore; to keep them between server reboots they must be
+copied to the startup datastore.
+
+When module changes are tracked (using ``subscribe-changes`` set to
+``true``) and the running configuration has changed (e.g. using
+``sysrepocfg`` or any NETCONF client), the callback validates the
+modified configuration (if ``validate-changes`` was not set to ``false``)
+and runs a second time to apply the new configuration. If the validation
+fails, the callback is still called again but with an ``SR_EV_ABORT``
+(vs. ``SR_EV_DONE``) event with rollback changes.
+
+The returned code of the callback on an ``SR_EV_DONE`` event is ignored, as it is
+too late to refuse a bad configuration.
+
+There are four ways in which a modified YANG configuration might
+be incorrect:
+
+1. It could be non-compliant with the schema, e.g. an unknown entry, missing a
+   mandatory entry, a value with a bad type, or not matching a constraint.
+
+2. It could fail to be translated from YANG to JSON, e.g. an invalid user
+   context.
+
+3. It could fail Kea server sanity checks, e.g. an out-of-subnet-pool range
+   or an unsupported database type.
+
+4. The syntax may be correct and pass server sanity checks but the
+   configuration could fail to run, e.g. the configuration specifies database
+   credentials but the database refuses the connection.
+
+The first case is handled by Sysrepo. The second and third cases are
+handled by ``kea-netconf`` in the validation phase (if not disabled by
+setting ``validate-changes`` to ``true``). The last case causes the
+application phase to fail without a sensible report to Sysrepo.
+
+The managed Kea servers and agents are described in the
+``managed-servers`` section. Each sub-section begins with the service
+name: ``dhcp4``, ``dhcp6``, ``d2`` (the DHCP-DDNS server does not
+support the control-channel feature yet), and ``ca`` (the control
+agent).
+
+Each managed server entry may contain:
+
+-  control flags - ``boot-update``, ``subscribe-changes``, and/or ``validate-changes``.
+
+-  ``model`` - specifies the YANG model/module name. For each service,
+   the default is the corresponding Kea YANG model, e.g. for ``"dhcp4"``
+   it is ``"kea-dhcp4-server"``.
+
+-  ``control-socket`` - specifies the control socket for managing the
+   service configuration.
+
+A control socket is specified by:
+
+-  ``socket-type`` - the socket type is either ``stdout``, ``unix``, or ``http``.
+   ``stdout`` is the default;
+   it is not really a socket, but it allows ``kea-netconf`` to run in
+   debugging mode where everything is printed on stdout, and it can also be
+   used to redirect commands easily. ``unix`` is the standard direct
+   server control channel, which uses UNIX sockets; ``http`` uses
+   a control agent, which accepts HTTP connections.
+
+-  ``socket-name`` - the local socket name for the ``unix`` socket type
+   (default empty string).
+
+-  ``socket-url`` - the HTTP URL for the ``http`` socket type (default
+   ``http://127.0.0.1:8000/``).
+
+User contexts can store arbitrary data as long as they are in valid JSON
+syntax and their top-level element is a map (i.e. the data must be
+enclosed in curly brackets). They are accepted at the NETCONF entry,
+i.e. below the top-level, managed-service entry, and control-socket
+entry scopes.
+
+Hook libraries can be loaded by the NETCONF agent just as with other
+servers or agents; however, currently no hook points are defined. The
+``hooks-libraries`` list contains the list of hook libraries that
+should be loaded by ``kea-netconf``, along with their configuration
+information specified with ``parameters``.
+
+Please consult :ref:`logging` for details on how to configure
+logging. The name of the NETCONF agent's main logger is ``kea-netconf``, as
+given in the example above.
+
+.. _netconf-example:
+
+A ``kea-netconf`` Configuration Example
+---------------------------------------
+
+The following example demonstrates the basic NETCONF configuration. More
+examples are available in the ``doc/examples/netconf`` directory in the
+Kea sources.
+
+.. code-block:: javascript
+
+   // This is a simple example of a configuration for the NETCONF agent.
+   // This server provides a YANG interface for all Kea servers and the agent.
+   {
+       "Netconf":
+       {
+           // Control flags can be defined in the global scope or
+           // in a managed server scope. Precedences are:
+           // - use the default value (true)
+           // - use the global value
+           // - use the local value.
+           // So this overwrites the default value:
+           "boot-update": false,
+
+           // This map specifies how each server is managed. For each server there
+           // is a name of the YANG model to be used and the control channel.
+           //
+           // Currently three control channel types are supported:
+           // "stdout" which outputs the configuration on the standard output,
+           // "unix" which uses the local control channel supported by the
+           // "dhcp4" and "dhcp6" servers ("d2" support is not yet available),
+           // and "http" which uses the Control Agent "ca" to manage itself or
+           // to forward commands to "dhcp4" or "dhcp6".
+           "managed-servers":
+           {
+               // This is how kea-netconf can communicate with the DHCPv4 server.
+               "dhcp4":
+               {
+                   "comment": "DHCP4 server",
+                   "model": "kea-dhcp4-server",
+                   "control-socket":
+                   {
+                       "socket-type": "unix",
+                       "socket-name": "/tmp/kea4-ctrl-socket"
+                   }
+               },
+
+               // DHCPv6 parameters.
+               "dhcp6":
+               {
+                   "model": "kea-dhcp6-server",
+                   "control-socket":
+                   {
+                       "socket-type": "unix",
+                       "socket-name": "/tmp/kea6-ctrl-socket"
+                   }
+               },
+
+               // Currently the DHCP-DDNS (nicknamed D2) server does not support
+               // a command channel.
+               "d2":
+               {
+                   "model": "kea-dhcp-ddns",
+                   "control-socket":
+                   {
+                       "socket-type": "stdout",
+                       "user-context": { "in-use": false }
+                   }
+               },
+
+               // Of course the Control Agent (CA) supports HTTP.
+               "ca":
+               {
+                   "model": "kea-ctrl-agent",
+                   "control-socket":
+                   {
+                       "socket-type": "http",
+                       "socket-url": "http://127.0.0.1:8000/"
+                   }
+               }
+           },
+
+           // kea-netconf is able to load hook libraries that augment its operation.
+           // Currently there are no hook points defined in kea-netconf
+           // processing.
+           "hooks-libraries": [
+               // The hooks libraries list may contain more than one library.
+               {
+                   // The only necessary parameter is the library filename.
+                   "library": "/opt/local/netconf-commands.so",
+
+                   // Some libraries may support parameters. Make sure you
+                   // type this section carefully, as kea-netconf does not
+                   // validate it (because the format is library-specific).
+                   "parameters": {
+                       "param1": "foo"
+                   }
+               }
+           ],
+
+           // Similar to other Kea components, NETCONF also uses logging.
+           "loggers": [
+               {
+                   "name": "kea-netconf",
+                   "output_options": [
+                       {
+                           "output": "/var/log/kea-netconf.log",
+                           // Several additional parameters are possible in
+                           // addition to the typical output.
+                           // Flush determines whether logger flushes output
+                           //  to a file.
+                           // Maxsize determines maximum filesize before
+                           // the file is being rotated.
+                           // Maxver specifies the maximum number of
+                           //  rotated files being kept.
+                           "flush": true,
+                           "maxsize": 204800,
+                           "maxver": 4
+                       }
+                   ],
+                   "severity": "INFO",
+                   "debuglevel": 0
+               }
+           ]
+       }
+   }
+
+.. _netconf-start-stop:
+
+Starting and Stopping the NETCONF Agent
+---------------------------------------
+
+``kea-netconf`` accepts the following command-line switches:
+
+-  ``-c file`` - specifies the configuration file.
+
+-  ``-d`` - specifies whether the agent logging should be switched to
+   debug/verbose mode. In verbose mode, the logging severity and
+   debuglevel specified in the configuration file are ignored and
+   "debug" severity and the maximum debuglevel (99) are assumed. The
+   flag is convenient for temporarily switching the server into maximum
+   verbosity, e.g. when debugging.
+
+-  ``-t file`` - specifies the configuration file to be tested.
+   ``kea-netconf`` attempts to load it and conducts sanity checks;
+   certain checks are possible only while running the actual server. The
+   actual status is reported with exit code (0 = configuration appears valid,
+   1 = error encountered). Kea prints out log messages to standard
+   output and error to standard error when testing the configuration.
+
+-  ``-v`` - displays the version of ``kea-netconf`` and exits.
+
+-  ``-V`` - displays the extended version information for ``kea-netconf``
+   and exits. The listing includes the versions of the libraries
+   dynamically linked to Kea.
+
+-  ``-W`` - displays the Kea configuration report and exits. The report
+   is a copy of the ``config.report`` file produced by ``./configure``;
+   it is embedded in the executable binary.
+
+.. _operation-example:
+
+A Step-by-Step NETCONF Agent Operation Example
+----------------------------------------------
+
+.. note::
+
+   Copies of example configurations presented within this section can be
+   found in the Kea source code, under
+   ``doc/examples/netconf/kea-dhcp6-operations``.
+
+.. _operation-example-setup:
+
+Setup of NETCONF Agent Operation Example
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The test box has an Ethernet interface named eth1. On some systems it is
+possible to rename interfaces; for instance, on Linux with an ens38
+interface:
+
+.. code-block:: console
+
+    # ip link set down dev ens38
+    # ip link set name eth1 dev ens38
+    # ip link set up dev eth1
+
+The interface must have an address in the test prefix:
+
+.. code-block:: console
+
+    # ip -6 addr add 2001:db8::1/64 dev eth1
+
+The Kea DHCPv6 server must be launched with the configuration specifying
+a control socket used to receive control commands. The ``kea-netconf``
+process uses this socket to communicate with the DHCPv6 server, i.e. it
+pushes translated configurations to that server using control commands.
+The following is an example control socket specification for the Kea
+DHCPv6 server:
+
+.. code-block:: json
+
+    {
+        "Dhcp6": {
+            "control-socket": {
+               "socket-name": "/tmp/kea-dhcp6-ctrl.sock",
+               "socket-type": "unix"
+            }
+        }
+    }
+
+In order to launch the Kea DHCPv6 server using the configuration
+contained within the ``boot.json`` file, run:
+
+.. code-block:: console
+
+    # kea-dhcp6 -d -c boot.json
+
+The current configuration of the server can be fetched via a control
+socket by running:
+
+.. code-block:: console
+
+    # echo '{ "command": "config-get" }' | socat UNIX:/tmp/kea-dhcp6-ctrl.sock '-,ignoreeof'
+
+The following is the example ``netconf.json`` configuration for
+``kea-netconf``, to manage the Kea DHCPv6 server:
+
+.. code-block:: json
+
+    {
+      "Netconf": {
+        "loggers": [
+          {
+            "debuglevel": 99,
+            "name": "kea-netconf",
+            "output_options": [
+              {
+                "output": "stderr"
+              }
+            ],
+            "severity": "DEBUG"
+          }
+        ],
+        "managed-servers": {
+          "dhcp6": {
+            "control-socket": {
+              "socket-name": "/tmp/kea-dhcp6-ctrl.sock",
+              "socket-type": "unix"
+            }
+          }
+        }
+      }
+    }
+
+Note that in production there should not be a need to log at the DEBUG level.
+
+The Kea NETCONF agent is launched by:
+
+.. code-block:: console
+
+    # kea-netconf -d -c netconf.json
+
+Now that both ``kea-netconf`` and ``kea-dhcp6`` are running, it is
+possible to populate updates to the configuration to the DHCPv6 server.
+The following is the configuration extracted from ``startup.xml``:
+
+.. code-block:: xml
+
+   <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
+     <subnet6>
+       <id>1</id>
+       <pool>
+         <start-address>2001:db8::1:0</start-address>
+         <end-address>2001:db8::1:ffff</end-address>
+         <prefix>2001:db8::1:0/112</prefix>
+       </pool>
+       <subnet>2001:db8::/64</subnet>
+     </subnet6>
+     <interfaces-config>
+       <interfaces>eth1</interfaces>
+     </interfaces-config>
+     <control-socket>
+       <socket-name>/tmp/kea-dhcp6-ctrl.sock</socket-name>
+       <socket-type>unix</socket-type>
+     </control-socket>
+   </config>
+
+To populate this new configuration:
+
+.. code-block:: console
+
+    $ sysrepocfg -d startup -f xml -m kea-dhcp6-server --edit=startup.xml
+
+``kea-netconf`` pushes the configuration found in the Sysrepo startup
+datastore to all Kea servers during its initialization phase, after it
+subscribes to module changes in the Sysrepo running datastore. This
+action copies the configuration from the startup datastore to the
+running datastore and enables the running datastore, making it
+available.
+
+Changes to the running datastore are applied after validation to the Kea
+servers. Note that they are not by default copied back to the startup
+datastore, i.e. changes are not permanent.
+
+.. _operation-example-errors:
+
+Error Handling in NETCONF Operation Example
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are four classes of issues with configurations applied via
+NETCONF:
+
+1. The configuration does not comply with the YANG schema.
+
+2. The configuration cannot be translated from YANG to the Kea JSON.
+
+3. The configuration is rejected by the Kea server.
+
+4. The configuration was validated by the Kea server but cannot be
+   applied.
+
+In the first case, consider the following ``BAD-schema.xml``
+configuration file:
+
+.. code-block:: xml
+
+   <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
+     <subnet4>
+       <id>1</id>
+       <pool>
+         <start-address>2001:db8::1:0</start-address>
+         <end-address>2001:db8::1:ffff</end-address>
+         <prefix>2001:db8::1:0/112</prefix>
+       </pool>
+       <subnet>2001:db8::/64</subnet>
+     </subnet6>
+     <interfaces-config>
+       <interfaces>eth1</interfaces>
+     </interfaces-config>
+     <control-socket>
+       <socket-name>/tmp/kea-dhcp6-ctrl.sock</socket-name>
+       <socket-type>unix</socket-type>
+     </control-socket>
+   </config>
+
+It is directly rejected by ``sysrepocfg``:
+
+.. code-block:: console
+
+    $ sysrepocfg -d running -f xml -m kea-dhcp6-server --edit=BAD-schema.xml
+
+In the second case, the configuration is rejected by ``kea-netconf``.
+For example, consider this ``BAD-translator.xml`` file:
+
+.. code-block:: xml
+
+   <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
+     <subnet6>
+       <id>1</id>
+       <pool>
+         <start-address>2001:db8::1:0</start-address>
+         <end-address>2001:db8::1:ffff</end-address>
+         <prefix>2001:db8::1:0/112</prefix>
+       </pool>
+       <subnet>2001:db8::/64</subnet>
+     </subnet6>
+     <interfaces-config>
+       <interfaces>eth1</interfaces>
+     </interfaces-config>
+     <control-socket>
+       <socket-name>/tmp/kea-dhcp6-ctrl.sock</socket-name>
+       <socket-type>unix</socket-type>
+     </control-socket>
+     <user-context>bad</user-context>
+   </config>
+
+In the third case, the configuration is presented to the Kea DHCPv6
+server and fails to validate, as in this ``BAD-config.xml`` file:
+
+.. code-block:: xml
+
+   <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
+     <subnet6>
+       <id>1</id>
+       <pool>
+         <start-address>2001:db8:1::0</start-address>
+         <end-address>2001:db8:1::ffff</end-address>
+         <prefix>2001:db8:1::0/112</prefix>
+       </pool>
+       <subnet>2001:db8::/64</subnet>
+     </subnet6>
+     <interfaces-config>
+       <interfaces>eth1</interfaces>
+     </interfaces-config>
+     <control-socket>
+       <socket-name>/tmp/kea-dhcp6-ctrl.sock</socket-name>
+       <socket-type>unix</socket-type>
+     </control-socket>
+   </config>
+
+In the last case, the misconfiguration is detected too late and the
+change must be reverted in Sysrepo, e.g. using the startup datastore as
+a backup.
+
+.. _operation-example-2pools:
+
+NETCONF Operation Example with Two Pools
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This example adds a second pool to the initial (i.e. startup)
+configuration in the ``twopools.xml`` file:
+
+.. code-block:: xml
+
+   <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
+     <subnet6>
+       <id>1</id>
+       <pool>
+         <start-address>2001:db8::1:0</start-address>
+         <end-address>2001:db8::1:ffff</end-address>
+         <prefix>2001:db8::1:0/112</prefix>
+       </pool>
+       <pool>
+         <start-address>2001:db8::2:0</start-address>
+         <end-address>2001:db8::2:ffff</end-address>
+         <prefix>2001:db8::2:0/112</prefix>
+       </pool>
+       <subnet>2001:db8::/64</subnet>
+     </subnet6>
+     <interfaces-config>
+       <interfaces>eth1</interfaces>
+     </interfaces-config>
+     <control-socket>
+       <socket-name>/tmp/kea-dhcp6-ctrl.sock</socket-name>
+       <socket-type>unix</socket-type>
+     </control-socket>
+   </config>
+
+This configuration is installed by:
+
+.. code-block:: console
+
+    $ sysrepocfg -d running -f xml -m kea-dhcp6-server --edit=twopools.xml
+
+.. _operation-example-2subnets:
+
+NETCONF Operation Example with Two Subnets
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This example specifies two subnets in the ``twosubnets.xml`` file:
+
+.. code-block:: xml
+
+   <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
+     <subnet6>
+       <id>1</id>
+       <pool>
+         <start-address>2001:db8:1::</start-address>
+         <end-address>2001:db8:1::ffff</end-address>
+         <prefix>2001:db8:1::/112</prefix>
+       </pool>
+       <subnet>2001:db8:1::/64</subnet>
+     </subnet6>
+     <subnet6>
+       <id>2</id>
+       <pool>
+         <start-address>2001:db8:2::</start-address>
+         <end-address>2001:db8:2::ffff</end-address>
+         <prefix>2001:db8:2::/112</prefix>
+       </pool>
+       <subnet>2001:db8:2::/64</subnet>
+     </subnet6>
+     <interfaces-config>
+       <interfaces>eth1</interfaces>
+     </interfaces-config>
+     <control-socket>
+       <socket-name>/tmp/kea-dhcp6-ctrl.sock</socket-name>
+       <socket-type>unix</socket-type>
+     </control-socket>
+   </config>
+
+This configuration is installed by:
+
+.. code-block:: console
+
+    $ sysrepocfg -d running -f xml -m kea-dhcp6-server --edit=twosubnets.xml
+
+.. _operation-example-logging:
+
+NETCONF Operation Example with Logging
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This example adds a logger entry to the initial (i.e. startup)
+configuration in the ``logging.xml`` file:
+
+.. code-block:: xml
+
+   <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
+     <interfaces-config>
+       <interfaces>eth1</interfaces>
+     </interfaces-config>
+     <subnet6>
+       <id>1</id>
+       <pool>
+         <start-address>2001:db8::1:0</start-address>
+         <end-address>2001:db8::1:ffff</end-address>
+         <prefix>2001:db8::1:0/112</prefix>
+       </pool>
+       <subnet>2001:db8::/64</subnet>
+     </subnet6>
+     <control-socket>
+       <socket-name>/tmp/kea-dhcp6-ctrl.sock</socket-name>
+       <socket-type>unix</socket-type>
+     </control-socket>
+     <logger>
+       <name>kea-dhcp6</name>
+       <output-option>
+         <output>stderr</output>
+       </output-option>
+       <debuglevel>99</debuglevel>
+       <severity>DEBUG</severity>
+     </logger>
+   </config>
+
+The corresponding Kea configuration in JSON is:
+
+.. code-block:: json
+
+   {
+     "Dhcp6": {
+       "control-socket": {
+         "socket-name": "/tmp/kea-dhcp6-ctrl.sock",
+         "socket-type": "unix"
+       },
+       "interfaces-config": {
+         "interfaces": [ "eth1" ]
+       },
+       "subnet6": [
+         {
+           "id": 1,
+           "pools": [
+             {
+               "pool": "2001:db8::1:0/112"
+             }
+           ],
+           "subnet": "2001:db8::/64"
+         }
+       ],
+       "loggers": [
+         {
+           "name": "kea-dhcp6",
+           "output_options": [
+             {
+               "output": "stderr"
+             }
+           ],
+           "severity": "DEBUG",
+           "debuglevel": 99
+         }
+      ]
+    }
+   }
+
+Finally, any of the previous examples can be replayed by using
+``sysrepocfg`` in edit mode as follows:
+
+.. code-block:: console
+
+    $ sysrepocfg -d running -f xml -m kea-dhcp6-server --edit
+
+or by using a NETCONF client like ``netopeer2-cli`` from the
+`Netopeer2 <https://github.com/CESNET/Netopeer2>`__ NETCONF Toolset.
+
+.. _migrating-yang-v0-to-v1:
+
+Migrating YANG Data from Sysrepo v0.x to v1.x
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Start the migration after turning off ``kea-netconf`` to make sure that backups
+for both datastores are done at the same configuration state and no change
+happens between exporting them.
+
+Unfortunately, Sysrepo v0.x does not support import/export of all YANG modules.
+This was added in Sysrepo v1.x, so users of earlier versions will need to do per-module backup.
+This has the added benefit of isolating potential failures and preventing them from
+affecting all modules.
+
+With Sysrepo v0.x:
+
+.. code-block:: console
+
+    $ sysrepocfg --datastore running --export=save.xml --format=xml kea-dhcp6-server
+    $ sysrepocfg --datastore startup --export=save.xml --format=xml kea-dhcp6-server
+
+Install Sysrepo v1.x and then:
+
+.. code-block:: console
+
+    $ sysrepocfg --datastore running --edit=save.xml
+    $ sysrepocfg --datastore startup --edit=save.xml
+
+Module name and format are optional for v1.x; they are detected automatically.
+If necessary, they can be provided with the ``--format xml`` and
+``--module kea-dhcp6-server`` flags.
+
+If upgrading from a very old version of Sysrepo, there may also be changes to the YANG
+modules themselves. In that case, the backups will need some minor massaging, as would
+be required with normal periodic maintenance.
diff --git a/doc/sphinx/arm/hammer.rst b/doc/sphinx/arm/hammer.rst
new file mode 100644
index 0000000..b8a5318
--- /dev/null
+++ b/doc/sphinx/arm/hammer.rst
@@ -0,0 +1,130 @@
+.. _hammer:
+
+Hammer Building Tool
+====================
+
+Hammer is a Python 3 script that lets users automate tasks related to building
+Kea, such as setting up virtual machines, installing Kea dependencies,
+compiling Kea with various options, running unit-tests and more. This
+tool was created primarily for internal QA purposes at ISC and it is not
+included in the Kea distribution; however, it is available in the Kea
+git repository. This tool was developed primarily for internal purposes
+and ISC cannot guarantee its proper operation. Administrators who decide to use it
+should do so with care.
+
+.. note::
+
+   Use of this tool is completely optional. Everything it does can be
+   done manually.
+
+The first-time user is strongly encouraged to look at Hammer's built-in
+help:
+
+.. code-block:: console
+
+   $ ./hammer.py --help
+
+It will list available parameters.
+
+Hammer is able to set up various operating systems running either in LXC
+or in VirtualBox. For a list of supported systems, use the
+``supported-systems`` command:
+
+.. code-block:: console
+
+   $ ./hammer.py supported-systems
+   fedora:
+     - 27: lxc, virtualbox
+     - 28: lxc, virtualbox
+     - 29: lxc, virtualbox
+   centos:
+     - 7: lxc, virtualbox
+   rhel:
+     - 8: virtualbox
+   ubuntu:
+     - 16.04: lxc, virtualbox
+     - 18.04: lxc, virtualbox
+     - 18.10: lxc, virtualbox
+   debian:
+     - 8: lxc, virtualbox
+     - 9: lxc, virtualbox
+   freebsd:
+     - 11.2: virtualbox
+     - 12.0: virtualbox
+
+It is also possible to run the build locally, in the current system (if the OS
+is supported).
+
+First, the Hammer dependencies must be installed: Vagrant
+and either VirtualBox or LXC. Hammer can install
+Vagrant and the required Vagrant plugins using the command:
+
+.. code-block:: console
+
+   $ ./hammer.py ensure-hammer-deps
+
+VirtualBox and LXC must be installed manually.
+
+The basic functions provided by Hammer are to prepare the build environment
+and perform the actual build, and to run the unit tests locally in the current
+system. This can be achieved by running the command:
+
+.. code-block:: console
+
+   $ ./hammer.py build -p local
+
+The scope of the process can be defined using the ``--with`` (``-w``) and ``--without``
+(``-x``) options. By default, the ``build`` command builds Kea with
+documentation, installs it locally, and runs unit tests.
+
+To exclude the installation and generation of docs, type:
+
+.. code-block:: console
+
+   $ ./hammer.py build -p local -x install docs
+
+The basic scope can be extended by mysql, pgsql, native-pkg,
+radius, shell, and forge.
+
+.. note::
+
+   If building Kea locally, Hammer dependencies like Vagrant are
+   not needed.
+
+Hammer can be told to set up a new virtual machine with a specified
+operating system, without the build:
+
+.. code-block:: console
+
+   $ ./hammer.py prepare-system -p virtualbox -s freebsd -r 12.0
+
+This way, a system can be prepared for our own use. To get to such a system
+using SSH, invoke:
+
+.. code-block:: console
+
+   $ ./hammer.py ssh -p virtualbox -s freebsd -r 12.0
+
+It is possible to speed up subsequent Hammer builds via
+`ccache <https://ccache.samba.org/>`__. During
+compilation, ccache stores objects in a shared folder. In subsequent runs,
+instead of doing an actual compilation, ccache returns the stored earlier
+objects. The cache with these objects for reuse must be stored outside of VM
+or LXC. To indicate the folder, the ``--ccache-dir``
+parameter for Hammer must be included. In the indicated folder, there are separate stored objects for each target
+operating system.
+
+.. code-block:: console
+
+   $ ./hammer.py build -p lxc -s ubuntu -r 18.04 --ccache-dir ~/kea-ccache
+
+.. note::
+
+   ccache is currently only supported for LXC in Hammer; support
+   for VirtualBox may be added later.
+
+For more information check:
+
+.. code-block:: console
+
+   $ ./hammer.py --help
diff --git a/doc/sphinx/arm/hooks-bootp.rst b/doc/sphinx/arm/hooks-bootp.rst
new file mode 100644
index 0000000..629d429
--- /dev/null
+++ b/doc/sphinx/arm/hooks-bootp.rst
@@ -0,0 +1,87 @@
+.. _hooks-bootp:
+
+``bootp``: Support for BOOTP Clients
+====================================
+
+This hook library adds support for BOOTP with vendor-information extensions
+(`RFC 1497 <https://tools.ietf.org/html/rfc1497>`__). Received BOOTP
+requests are recognized, translated into DHCPREQUEST packets by adding
+a ``dhcp-message-type`` option, and put into the "BOOTP" client class.
+Members of this class get infinite lifetime leases but the class can
+also be used to guard a pool of addresses.
+
+The DHCP-specific options, such as ``dhcp-message-type``, are removed from
+the server's responses; responses shorter than the BOOTP minimum
+size of 300 octets are padded to this size.
+
+This open source library is loaded
+similarly to other hook libraries by the ``kea-dhcp4`` process, and
+it takes no parameters.
+
+::
+
+    "Dhcp4": {
+        "hooks-libraries": [
+            {   "library": "/usr/local/lib/libdhcp_bootp.so" },
+            ...
+        ]
+    }
+
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` process,
+   as there is no BOOTP protocol for IPv6.
+
+.. note::
+
+   A host reservation for a BOOTP client should use the hardware address
+   as the identifier (the ``client-id`` option is a DHCP-specific option).
+
+.. _hooks-bootp-config:
+
+Incoming BOOTP packets are added to the BOOTP class, allowing administrators
+to segregate BOOTP clients into separate pools. For example:
+
+::
+
+   "Dhcp4": {
+       "client-classes": [
+           {
+               // The DHCP class is the complement of the BOOTP class
+               "name": "DHCP",
+               "test": "not member('BOOTP')"
+           }
+       ],
+       "subnet4": [
+           {
+               "subnet": "192.0.2.0/24",
+               "pools": [
+               {
+                   // BOOTP clients will be handled here
+                   "pool": "192.0.2.200 - 192.0.2.254",
+                   "client-class": "BOOTP"
+               },
+               {
+                   // Regular DHCP clients will be handled here
+                   "pool": "192.0.2.1 - 192.0.2.199",
+                   "client-class": "DHCP"
+               }],
+               ...
+           },
+           ...
+       ],
+       ...
+   }
+
+
+.. _hooks-bootp-limitations:
+
+BOOTP Hooks Limitations
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Currently the BOOTP library has the following limitation:
+
+- Basic BOOTP, as defined in `RFC 951
+  <https://tools.ietf.org/html/rfc951>`__, is not supported. Kea only
+  supports BOOTP with vendor-information extensions.
diff --git a/doc/sphinx/arm/hooks-cb-cmds.rst b/doc/sphinx/arm/hooks-cb-cmds.rst
new file mode 100644
index 0000000..68fdc82
--- /dev/null
+++ b/doc/sphinx/arm/hooks-cb-cmds.rst
@@ -0,0 +1,2181 @@
+.. _hooks-cb-cmds:
+
+``cb_cmds``: Configuration Backend Commands
+===========================================
+
+This hook library is used to manage Kea
+servers' configurations in a configuration backend database. This library must
+be used in conjunction with the available CB hooks libraries implementing
+the common APIs to create, read, update, and delete (CRUD) the
+configuration information in the respective databases. For example:
+the ``mysql_cb`` hooks library implements this API for MySQL while the
+``pgsql_cg`` hooks library implements this API for PostgreSQL.
+To manage the configuration information in a MySQL database, both the
+``mysql_cb`` and ``cb_cmds`` libraries must be loaded by the server used for the
+configuration management.
+To manage the configuration information in a PostgreSQL database, both the
+``pgsql_cb`` and ``cb_cmds`` libraries must be loaded by the server used for the
+configuration management.
+
+More information on how to configure the Configuration Backend hook library for
+use with a MySQL or PostgreSQL database can be found in the :ref:`dhcp4-cb`
+and :ref:`dhcp6-cb` sections.
+
+The ``cb_cmds`` library is only available to ISC customers with a paid
+support contract.
+
+.. note::
+
+   This library may only be loaded by the ``kea-dhcp4`` or
+   ``kea-dhcp6`` process.
+
+.. note::
+
+   Please read about :ref:`cb-limitations` before using the commands
+   described in this section.
+
+Command Structure
+~~~~~~~~~~~~~~~~~
+
+There are 5 types of commands supported by this library:
+
+-  ``del`` - delete the selected object from the database, e.g.
+   ``remote-global-parameter4-del``.
+
+-  ``get`` - fetch the selected object from the database, e.g.
+   ``remote-subnet4-get``.
+
+-  ``get-all`` - fetch all objects of the particular type from the
+   database, e.g. ``remote-option-def4-get-all``.
+
+-  ``list`` - list all objects of the particular type in the database,
+   e.g. ``remote-network4-list``; this class of commands returns brief
+   information about each object compared to the output of ``get-all``.
+
+-  ``set`` - creates or replaces an object of the given type in the
+   database, e.g. ``remote-option4-global-set``.
+
+All types of commands accept an optional ``remote`` map which selects the
+database instance to which the command refers. For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-subnet4-list",
+       "arguments": {
+           "remote": {
+               "type": "mysql",
+               "host": "192.0.2.33",
+               "port": 3302
+           }
+       }
+   }
+
+selects the MySQL database, running on host 192.0.2.33 and port 3302, to
+fetch the list of subnets from. All parameters in the ``remote`` argument are
+optional. The ``port`` parameter can be only specified in conjunction
+with the ``host``. If no options in the ``remote`` parameter are to
+be specified, the parameter should be omitted. In this case, the server
+will use the first backend listed in the ``config-control`` map within
+the configuration of the server receiving the command.
+
+The ``cb_cmds`` library is only available to ISC customers with a paid
+support contract.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or
+   ``kea-dhcp6`` process.
+
+.. note::
+
+   Please read about :ref:`cb-limitations` before using the commands
+   described in this section.
+
+.. note::
+
+   In the current Kea release, it is only possible to configure the Kea server
+   to use a single configuration backend. Strictly speaking, it is
+   possible to point the Kea server to at most one database (either MySQL or
+   PostgreSQL) using the ``config-control`` parameter. Therefore, the ``remote``
+   parameter may be omitted in the commands and the ``cb_cmds`` hook library
+   uses the sole backend by default.  The example commands below most often show a
+   value of "mysql" for the ``type`` parameter; it should be assumed that the
+   value is "postgresql" for installations using a PostgreSQL database.
+
+.. _cb-cmds-dhcp:
+
+Control Commands for DHCP Servers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This section describes and gives some examples of the control commands
+implemented by the ``cb_cmds`` hooks library, to manage the
+configuration information of the DHCPv4 and DHCPv6 servers. Many of the
+commands are almost identical between DHCPv4 and DHCPv6; they only
+differ by the command name. Other commands differ slightly by the
+structure of the inserted data; for example, the structure of the IPv4 subnet
+information is different than that of the IPv6 subnet.
+Nevertheless, they still share the structure of their command arguments
+and thus it makes sense to describe them together.
+
+In the following sections, various commands are described and some usage
+examples are provided. In the sections jointly describing the DHCPv4 and
+DHCPv6 variants of the particular command, we sometimes use the following
+notation: the ``remote-subnet[46]-set`` is the wildcard name for the
+two commands: ``remote-subnet4-set`` and ``remote-subnet6-set``.
+
+In addition, whenever the text in the subsequent sections refers to a
+DHCP command or DHCP parameter, it refers to both DHCPv4 and DHCPv6
+variants. The text specific to the particular server type refers to them
+as: DHCPv4 command, DHCPv4 parameter, DHCPv6 command, DHCPv6 parameter,
+etc.
+
+.. _cb-cmds-metadata:
+
+Metadata
+~~~~~~~~
+
+The typical response to the ``get`` or ``list`` command includes a list
+of returned objects (e.g. subnets), and each such object contains the
+``metadata`` map with some database-specific information describing this
+object. In other words, the metadata contains any information about the
+fetched object which may be useful for an administrator but which is not
+part of the object specification from the DHCP server standpoint. In the
+present Kea release, the metadata is limited to the ``server-tag``. It
+describes the association of the object with a particular server or
+all servers.
+
+The following is the example response to the ``remote-network4-list``
+command, which includes the metadata:
+
+.. code-block:: json
+
+   {
+       "result": 0,
+       "text": "1 IPv4 shared network(s) found.",
+       "arguments": {
+           "shared-networks": [
+               {
+                   "name": "level3",
+                   "metadata": {
+                       "server-tags": [ "all" ]
+                   }
+               }
+           ],
+           "count": 1
+       }
+   }
+
+
+Client implementations must not assume that the metadata contains only
+the ``server-tags`` parameter. In future releases, it is expected that this
+map will be extended with additional information, e.g. object modification
+time, log message created during the last modification, etc.
+
+.. _command-remote-server4-del:
+.. _command-remote-server6-del:
+
+The ``remote-server4-del``, ``remote-server6-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to delete the information about a selected DHCP server from
+the configuration database. The server is identified by a unique case
+insensitive server tag. For example:
+
+.. code-block:: json
+
+    {
+        "command": "remote-server4-del",
+        "arguments": {
+            "servers": [
+                {
+                    "server-tag": "server1"
+                }
+            ],
+            "remote": {
+                "type": "postgresql"
+            }
+        }
+    }
+
+As a result of this command, all associations of the configuration for the
+user-defined server called "server1" are removed from the database, including
+non-shareable configuration information, such as global parameters, option
+definitions, and global options. Any shareable configuration information,
+i.e. the configuration elements which may
+be associated with more than one server, is preserved. In particular, the
+subnets and shared networks associated with the deleted servers are
+preserved. If any of the shareable configuration elements was associated only
+with the deleted server, this object becomes unassigned (orphaned). For
+example: if a subnet has been created and associated with "server1" using
+the ``remote-subnet4-set`` command and "server1" is subsequently deleted, the
+subnet remains in the database but no servers can use this subnet. The
+subnet can be updated using the ``remote-subnet4-set`` command, and can be
+associated with either another server or with all servers, using the special
+server tag "all". Such a subnet can be also deleted from the database
+using the ``remote-subnet4-del-by-id`` or
+``remote-subnet4-del-by-prefix`` command, if it is no longer needed.
+
+The following is the successful response to the ``remote-server4-del`` command:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "1 DHCPv4 server(s) deleted."
+        "arguments": {
+            "count": 1
+        }
+    }
+
+
+.. warning::
+
+   The ``remote-server4-del`` and ``remote-server6-del`` commands must be used with
+   care, because an accidental deletion of the server can cause some parts of the
+   existing configurations to be lost permanently from the database. This
+   operation is not reversible. Re-creation of the accidentally deleted server
+   does not revert the lost configuration for that server and such configuration
+   must be re-created manually by the user.
+
+.. _command-remote-server4-get:
+.. _command-remote-server6-get:
+
+The ``remote-server4-get``, ``remote-server6-get`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to fetch the information about the selected DHCP server
+from the configuration database. For example:
+
+.. code-block:: json
+
+    {
+        "command": "remote-server6-get"
+        "arguments": {
+            "servers": [
+                {
+                    "server-tag": "server1"
+                }
+            ],
+            "remote": {
+                "type": "mysql"
+            }
+        }
+    }
+
+
+This command fetches the information about the DHCPv6 server identified by the
+server tag "server1". The server tag is case-insensitive. A successful response
+returns basic information about the server, such as the server tag and the user's
+description of the server:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "DHCP server server1 found.",
+        "arguments": {
+            "servers": [
+                {
+                    "server-tag": "server1",
+                    "description": "A DHCPv6 server located on the first floor."
+                }
+            ],
+            "count": 1
+        }
+    }
+
+.. _command-remote-server4-get-all:
+.. _command-remote-server6-get-all:
+
+The ``remote-server4-get-all``, ``remote-server6-get-all`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to fetch all user-defined DHCPv4 or DHCPv6 servers from the
+database. The command structure is very simple:
+
+.. code-block:: json
+
+    {
+        "command": "remote-server4-get-all"
+        "arguments": {
+            "remote": {
+                "type": "mysql"
+            }
+        }
+    }
+
+The response includes basic information about each server, such as its server
+tag and description:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "DHCPv4 servers found.",
+        "arguments": {
+            "servers": [
+                {
+                    "server-tag": "server1",
+                    "description": "A DHCP server located on the first floor."
+                },
+                {
+                    "server-tag": "server2",
+                    "description": "An old DHCP server to be soon replaced."
+                }
+            ],
+           "count": 2
+        }
+    }
+
+.. _command-remote-server4-set:
+.. _command-remote-server6-set:
+
+The ``remote-server4-set``, ``remote-server6-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to create or replace an information about a DHCP server in
+the database. The information about the server must be created when there is a
+need to differentiate the configurations used by various Kea instances
+connecting to the same database. Various configuration elements, e.g. global
+parameters, subnets, etc. may be explicitly associated with the selected servers
+(using server tags as identifiers), allowing only these servers to use the
+respective configuration elements. Using the particular server tag to make such
+associations is only possible when the server information has been stored in the
+database via the ``remote-server4-set`` or ``remote-server6-set`` commands. The
+following command creates a new (or updates an existing) DHCPv6 server in the
+database:
+
+.. code-block:: json
+
+    {
+        "command": "remote-server6-set"
+        "arguments": {
+            "servers": [
+                {
+                    "server-tag": "server1",
+                    "description": "A DHCP server on the ground floor."
+                }
+            ],
+            "remote": {
+                "type": "mysql"
+            }
+        }
+    }
+
+The server tag must be unique across all servers in the database. When the
+server information under the given server tag already exists, it is replaced
+with the new information. The specified server tag is case-insensitive, and the
+maximum length of the server tag is 256 characters. The following keywords are
+reserved and cannot be used as server tags: "all" and "any".
+
+The following is the example response to the above command:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "DHCPv6 server successfully set.",
+        "arguments": {
+            "servers": [
+                {
+                    "server-tag": "server1",
+                    "description": "A DHCP server on the ground floor."
+                }
+            ]
+        }
+    }
+
+
+.. _command-remote-global-parameter4-del:
+
+.. _command-remote-global-parameter6-del:
+
+The ``remote-global-parameter4-del``, ``remote-global-parameter6-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to delete a global DHCP parameter from the
+configuration database. When the parameter is deleted from the database,
+the server uses the value specified in the configuration file for
+this parameter, or a default value if the parameter is not specified in
+the configuration file.
+
+The following command attempts to delete the DHCPv4 ``renew-timer``
+parameter common for all servers from the database:
+
+.. code-block:: json
+
+   {
+       "command": "remote-global-parameter4-del",
+       "arguments": {
+           "parameters": [ "renew-timer" ],
+           "remote": {
+               "type": "mysql"
+            },
+           "server-tags": [ "all" ]
+       }
+   }
+
+If a server-specific parameter is to be deleted, the
+``server-tags`` list must contain the tag of the appropriate
+server. There must be exactly one server tag specified in this list.
+
+.. _command-remote-global-parameter4-get:
+
+.. _command-remote-global-parameter6-get:
+
+The ``remote-global-parameter4-get``, ``remote-global-parameter6-get`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to fetch a scalar global DHCP parameter from the
+configuration database.
+
+The following command attempts to fetch the ``boot-file-name``
+parameter for "server1":
+
+.. code-block:: json
+
+   {
+       "command": "remote-global-parameter4-get",
+       "arguments": {
+           "parameters": [ "boot-file-name" ],
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "server1" ]
+       }
+   }
+
+
+The returned value has one of the four scalar types: string, integer,
+real, or boolean. Non-scalar global configuration parameters, such as map
+or list, are not returned by this command.
+
+In the case of the example above, the string value is returned, e.g.:
+
+.. code-block:: json
+
+   {
+       "result": 0,
+       "text": "1 DHCPv4 global parameter found.",
+       "arguments": {
+           "parameters": {
+               "boot-file-name": "/dev/null",
+               "metadata": {
+                   "server-tags": [ "all" ]
+               }
+           },
+           "count": 1
+       }
+   }
+
+
+Note that the response above indicates that the returned parameter is associated
+with "all" servers rather than "server1", used in the command. This indicates
+that there is no "server1"-specific value in the database and therefore, the value
+shared by all servers is returned. If there were a "server1"-specific value
+in the database, that value would be returned instead.
+
+The example response for the integer value is:
+
+.. code-block:: json
+
+   {
+       "result": 0,
+       "text": "1 DHCPv4 global parameter found.",
+       "arguments": {
+           "parameters": {
+               "renew-timer": 2000,
+               "metadata": {
+                   "server-tags": [ "server1" ]
+               }
+           },
+           "count": 1
+       }
+   }
+
+
+The real value:
+
+.. code-block:: json
+
+   {
+       "result": 0,
+       "text": "1 DHCPv4 global parameter found.",
+       "arguments": {
+           "parameters": {
+               "t1-percent": 0.85,
+               "metadata": {
+                   "server-tags": [ "all" ]
+               }
+           },
+           "count": 1
+       }
+   }
+
+
+Finally, the boolean value:
+
+.. code-block:: json
+
+   {
+       "result": 0,
+       "text": "1 DHCPv4 global parameter found.",
+       "arguments": {
+           "parameters": {
+               "match-client-id": true,
+               "metadata": {
+                   "server-tags": [ "server2" ]
+               }
+           },
+           "count": 1
+       }
+   }
+
+
+.. _command-remote-global-parameter4-get-all:
+
+.. _command-remote-global-parameter6-get-all:
+
+The ``remote-global-parameter4-get-all``, ``remote-global-parameter6-get-all`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to fetch all global DHCP parameters from the database
+for the specified server. The following example demonstrates how to fetch all
+global parameters to be used by the server "server1":
+
+.. code-block:: json
+
+    {
+        "command": "remote-global-parameter4-get-all",
+        "arguments": {
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "server1" ]
+        }
+    }
+
+The example response may look as follows:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "DHCPv4 global parameters found.",
+        "arguments": {
+            "parameters": [
+                {
+                    "boot-file-name": "/dev/null",
+                    "metadata": {
+                        "server-tags": [ "server1" ]
+                    }
+                },
+                {
+                    "match-client-id": true,
+                    "metadata": {
+                        "server-tags": [ "all" ]
+                    }
+                }
+            ],
+            "count": 2
+        }
+    }
+
+
+The example response contains two parameters: one string parameter and one
+boolean parameter. The metadata returned for each parameter indicates
+whether this parameter is specific to "server1" or applies to all servers. Since the
+``match-client-id`` value is associated with "all" servers,
+it indicates that there is no "server1"-specific setting for this parameter.
+Each parameter always has exactly one server tag associated with it, because
+global parameters are non-shareable configuration elements.
+
+.. note::
+
+   If the server tag is set to "all" in the command, the response will
+   contain only the global parameters associated with the logical server
+   "all". When the server tag points to the specific server (as in the
+   example above), the returned list combines parameters associated with
+   this server and all servers, but the former take precedence.
+
+.. _command-remote-global-parameter4-set:
+
+.. _command-remote-global-parameter6-set:
+
+The ``remote-global-parameter4-set``, ``remote-global-parameter6-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to create scalar global DHCP parameters in the
+database. If any of the parameters already exists, its value is replaced
+as a result of this command. It is possible to set multiple parameters
+within a single command, each having one of the four types: string,
+integer, real, or boolean. For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-global-parameter4-set"
+       "arguments": {
+           "parameters": {
+               "boot-file-name": "/dev/null",
+               "renew-timer": 2000,
+               "t1-percent": 0.85,
+               "match-client-id": true
+           },
+           "remote": {
+               "type": "mysql"
+           },
+           "server-tags": [ "server1" ]
+       }
+   }
+
+An error is returned if any of the parameters is not supported by the DHCP
+server or its type does not match. Care should be taken when multiple parameters
+are specified in a single command, because it is possible that only some of the
+parameters will be stored successfully and some will fail. If an error occurs when
+processing this command, it is recommended to use
+``remote-global-parameter[46]-get-all`` to check which of the parameters have
+been stored/updated successfully and which have failed.
+
+The ``server-tags`` list is mandatory and must contain a single server tag or
+the keyword "all". In the example above, all specified parameters are associated
+with the "server1" server.
+
+.. _command-remote-network4-del:
+
+.. _command-remote-network6-del:
+
+The ``remote-network4-del``, ``remote-network6-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to delete an IPv4 or IPv6 shared network from
+the database. The optional parameter ``subnets-action`` determines
+whether the subnets belonging to the deleted shared network should also
+be deleted or preserved. The ``subnets-action`` parameter defaults to ``keep``,
+which preserves the subnets. If it is set to ``delete``, the subnets are
+deleted along with the shared network.
+
+The following command:
+
+.. code-block:: json
+
+   {
+       "command": "remote-network6-del",
+       "arguments": {
+           "shared-networks": [
+               {
+                   "name": "level3"
+               }
+           ],
+           "subnets-action": "keep",
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+
+deletes the "level3" IPv6 shared network. The subnets are preserved, but
+they are disassociated from the deleted shared network and become
+global. This behavior corresponds to the behavior of the
+``network[46]-del`` commands with respect to the ``subnets-action`` parameter.
+
+Note that the ``server-tags`` parameter cannot be used for this command.
+
+.. _command-remote-network4-get:
+
+.. _command-remote-network6-get:
+
+The ``remote-network4-get``, ``remote-network6-get`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to retrieve information about an IPv4 or
+IPv6 shared network. The optional parameter ``subnets-include`` denotes
+whether the subnets belonging to the shared network should also be
+returned. This parameter defaults to ``no``, in which case the subnets
+are not returned. If this parameter is set to ``full``, the subnets are
+returned together with the shared network.
+
+The following command fetches the "level3" IPv6 shared network along
+with the full information about the subnets belonging to it:
+
+.. code-block:: json
+
+   {
+       "command": "remote-network6-get",
+       "arguments": {
+           "shared-networks": [
+               {
+                   "name": "level3"
+               }
+           ],
+           "subnets-include": "full",
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+Note that the ``server-tags`` parameter cannot be used for this command.
+
+.. _command-remote-network4-list:
+
+.. _command-remote-network6-list:
+
+The ``remote-network4-list``, ``remote-network6-list`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to list all IPv4 or IPv6 shared networks for a server.
+
+The following command retrieves all shared networks to be used by
+"server1" and "server2":
+
+.. code-block:: json
+
+    {
+        "command": "remote-network4-list"
+        "arguments": {
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "server1", "server2" ]
+        }
+    }
+
+The ``server-tags`` parameter is mandatory and contains one or more server
+tags. It may contain the keyword "all" to fetch the shared networks associated
+with all servers. When the ``server-tags`` list contains the
+``null`` value, the returned response contains a list of unassigned shared
+networks, i.e. the networks which are associated with no servers. For example:
+
+.. code-block:: json
+
+    {
+        "command": "remote-network4-list"
+        "arguments": {
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ null ]
+        }
+    }
+
+The example response to this command when non-null server tags are specified
+looks similar to this:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "3 IPv4 shared network(s) found.",
+        "arguments": {
+            "shared-networks": [
+                {
+                    "name": "ground floor",
+                    "metadata": {
+                        "server-tags": [ "all" ]
+                    }
+                },
+                {
+                    "name": "floor2",
+                    "metadata": {
+                        "server-tags": [ "server1" ]
+                    }
+                },
+                {
+                    "name": "floor3",
+                    "metadata": {
+                        "server-tags": [ "server2" ]
+                    }
+                }
+            ],
+            "count": 3
+        }
+    }
+
+The returned information about each shared network merely contains the shared
+network name and the metadata. To fetch detailed information about
+the selected shared network, use the ``remote-network[46]-get`` command.
+
+The example response above contains three shared networks. One of the
+shared networks is associated with all servers, so it is included in
+the list of shared networks to be used by "server1" and "server2".
+The remaining two shared networks are returned because one of them
+is associated with "server1" and another one is associated with
+"server2".
+
+When listing unassigned shared networks, the response looks similar
+to this:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "1 IPv4 shared network(s) found.",
+        "arguments": {
+            "shared-networks": [
+                {
+                    "name": "fancy",
+                    "metadata": {
+                        "server-tags": [ null ]
+                    }
+                }
+            ],
+            "count": 1
+        }
+    }
+
+The ``null`` value in the metadata indicates that the
+returned shared network is unassigned.
+
+.. _command-remote-network4-set:
+
+.. _command-remote-network6-set:
+
+The ``remote-network4-set``, ``remote-network6-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands create a new or replace an existing IPv4 or IPv6 shared
+network in the database. The structure of the shared network information
+is the same as in the Kea configuration file (see
+:ref:`shared-network4` and :ref:`shared-network6` for details),
+except that specifying subnets along with the shared
+network information is not allowed. Including the ``subnet4`` or ``subnet6`` parameter
+within the shared network information results in an error.
+
+These commands are intended to be used for managing the shared
+network-specific information and DHCP options. To associate and
+disassociate the subnets with the shared networks, the
+``remote-subnet[46]-set`` commands should be used.
+
+The following command adds the IPv6 shared network "level3" to the
+database:
+
+.. code-block:: json
+
+   {
+       "command": "remote-network6-set",
+       "arguments": {
+           "shared-networks": [
+               {
+                   "name": "level3",
+                   "interface": "eth0",
+                   "option-data": [ {
+                       "name": "sntp-servers",
+                       "data": "2001:db8:1::1"
+                   } ],
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           },
+           "server-tags": [ "all" ]
+       }
+   }
+
+
+This command includes the ``interface`` parameter, which sets the shared
+network-level interface name. Any remaining shared network-level parameters,
+which are not specified with the command, will be marked as
+"unspecified" in the database. The DHCP server uses the global
+values for unspecified parameters or, if the global values are not
+specified, the default values are used.
+
+The ``server-tags`` list is mandatory for this command and must include one or
+more server tags. As a result, the shared network is associated with all listed
+servers. The shared network may be associated with all servers connecting to the
+database when the keyword "all" is included.
+
+.. note::
+
+   As with other "set" commands, this command replaces all the
+   information about the given shared network in the database, if the
+   shared network already exists. Therefore, when sending this command,
+   make sure to always include all parameters that must be specified for
+   the updated shared-network instance. Any unspecified parameter will
+   be marked unspecified in the database, even if its value was present
+   prior to sending the command.
+
+.. _command-remote-option-def4-del:
+
+.. _command-remote-option-def6-del:
+
+The ``remote-option-def4-del``, ``remote-option-def6-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to delete a DHCP option definition from the
+database. The option definition is identified by an option code and
+option space. For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-option-def6-del",
+       "arguments": {
+           "option-defs": [
+               {
+                   "code": 1,
+                   "space": "isc"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           },
+           "server-tags": [ "server1" ]
+       }
+   }
+
+
+deletes the definition of the option associated with "server1", having the
+code of 1 and belonging to the option space "isc". The default option spaces are
+"dhcp4" and "dhcp6" for the DHCPv4 and DHCPv6 top-level options, respectively. If
+there is no such option explicitly associated with "server1", no option is
+deleted. To delete an option belonging to "all" servers, the keyword
+"all" must be used as the server tag. The ``server-tags`` list must contain exactly
+one tag and cannot include the ``null`` value.
+
+.. _command-remote-option-def4-get:
+
+.. _command-remote-option-def6-get:
+
+The ``remote-option-def4-get``, ``remote-option-def6-get`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to fetch a specified DHCP option definition from
+the database. The option definition is identified by the option code and
+option space. The default option spaces are "dhcp4" and "dhcp6" for the
+DHCPv4 and DHCPv6 top-level options, respectively.
+
+The following command retrieves a DHCPv4 option definition associated with all
+servers, having the code of 1 and belonging to the option space "isc":
+
+.. code-block:: json
+
+   {
+       "command": "remote-option-def4-get"
+       "arguments": {
+           "option-defs": [
+               {
+                   "code": 1,
+                   "space": "isc"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           },
+           "server-tags": [ "all" ]
+       }
+   }
+
+The ``server-tags`` list must include exactly one server tag or the keyword
+"all", and cannot contain the `null` value.
+
+.. _command-remote-option-def4-get-all:
+
+.. _command-remote-option-def6-get-all:
+
+The ``remote-option-def4-get-all``, ``remote-option-def6-get-all`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to fetch all DHCP option definitions from the database
+for the given server or all servers. For example:
+
+.. code-block:: json
+
+    {
+        "command": "remote-option-def6-get-all"
+        "arguments": {
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "all" ]
+        }
+    }
+
+This command attempts to fetch all DHCPv6 option definitions associated
+with "all" servers. The ``server-tags`` list is mandatory for
+this command and must include exactly one server tag or the keyword "all".
+It cannot include the ``null`` value.
+
+The following is the example response to this command:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "1 DHCPv6 option definition(s) found.",
+        "arguments": {
+            "option-defs": [
+                {
+                    "name": "bar",
+                    "code": 1012,
+                    "space": "dhcp6",
+                    "type": "record",
+                    "array": true,
+                    "record-types": "ipv6-address, uint16",
+                    "encapsulate": "",
+                    "metadata": {
+                        "server-tags": [ "all" ]
+                    }
+                }
+            ],
+            "count": 1
+        }
+    }
+
+The response contains an option definition associated with all servers, as
+indicated by the metadata.
+
+.. _command-remote-option-def4-set:
+
+.. _command-remote-option-def6-set:
+
+The ``remote-option-def4-set``, ``remote-option-def6-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands create a new DHCP option definition or replace an
+existing option definition in the database. The structure of the option
+definition information is the same as in the Kea configuration file (see
+:ref:`dhcp4-custom-options` and :ref:`dhcp6-custom-options`).
+The following command creates the DHCPv4 option definition at the
+top-level "dhcp4" option space and associates it with "server1":
+
+.. code-block:: json
+
+   {
+       "command": "remote-option-def4-set",
+       "arguments": {
+           "option-defs": [
+               {
+                   "name": "foo",
+                   "code": 222,
+                   "type": "uint32",
+                   "array": false,
+                   "record-types": "",
+                   "space": "dhcp4",
+                   "encapsulate": ""
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           },
+           "server-tags": [ "server1" ]
+       }
+   }
+
+The ``server-tags`` list must include exactly one
+server tag or the keyword "all", and cannot contain the
+``null`` value.
+
+.. _command-remote-option4-global-del:
+
+.. _command-remote-option6-global-del:
+
+The ``remote-option4-global-del``, ``remote-option6-global-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to delete a global DHCP option from the
+database. The option is identified by an option code and option space.
+For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-option4-global-del",
+       "arguments": {
+           "options": [
+               {
+                   "code": 5
+                   "space": "dhcp4"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           },
+           "server-tags": [ "server1" ]
+       }
+   }
+
+"dhcp4" is the top-level option space where the standard DHCPv4 options
+belong. The ``server-tags`` parameter is mandatory and must include a
+single option tag or the keyword "all". If the explicit server tag is specified,
+this command attempts to delete a global option associated with this
+server. If there is no such option associated with the given server, no option
+is deleted. To delete an option associated with all servers, the
+keyword "all" must be specified.
+
+.. _command-remote-option4-global-get:
+
+.. _command-remote-option6-global-get:
+
+The ``remote-option4-global-get``, ``remote-option6-global-get`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to fetch a global DHCP option from the database.
+The option is identified by the code and option space. The top-level
+option spaces where DHCP standard options belong are called "dhcp4" and
+"dhcp6" for the DHCPv4 and DHCPv6 servers, respectively.
+
+The following command retrieves the IPv6 "DNS Servers" (code 23) option
+associated with all servers:
+
+.. code-block:: json
+
+   {
+       "command": "remote-option6-global-get",
+       "arguments": {
+           "options": [
+               {
+                   "code": 23,
+                   "space": "dhcp6"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           },
+           "server-tags": [ "all" ]
+       }
+   }
+
+The ``server-tags`` parameter is mandatory and must include exactly one
+server tag or the keyword "all". It cannot contain the ``null``
+value.
+
+.. _command-remote-option4-global-get-all:
+
+.. _command-remote-option6-global-get-all:
+
+The ``remote-option4-global-get-all``, ``remote-option6-global-get-all`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to fetch all global DHCP options from the configuration
+database for the given server or for all servers. The following command
+fetches all global DHCPv4 options for "server1":
+
+.. code-block:: json
+
+    {
+        "command": "remote-option6-global-get-all",
+        "arguments": {
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "server1" ]
+        }
+    }
+
+The ``server-tags`` list is mandatory for this command and
+must contain exactly one server tag or a keyword "all"; it cannot contain
+the ``null`` value.
+
+The following is a example response to this
+command with a single option being associated with "server1" returned:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "DHCPv4 options found.",
+        "arguments": {
+            "options": [
+                {
+                    "name": "domain-name-servers",
+                    "code": 6,
+                    "space": "dhcp4",
+                    "csv-format": false,
+                    "data": "192.0.2.3",
+                    "metadata": {
+                        "server-tags": [ "server1" ]
+                    }
+                }
+            ],
+            "count": 1
+        }
+    }
+
+.. _command-remote-option4-global-set:
+
+.. _command-remote-option6-global-set:
+
+The ``remote-option4-global-set``, ``remote-option6-global-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands create a new global DHCP option or replace an existing
+option in the database. The structure of the option information is the
+same as in the Kea configuration file (see :ref:`dhcp4-std-options`
+and :ref:`dhcp6-std-options`). For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-option6-global-set",
+       "arguments": {
+           "options": [
+               {
+                   "name": "dns-servers",
+                   "data": "2001:db8:1::1"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           },
+           "server-tags": [ "server1" ]
+       }
+   }
+
+The ``server-tags`` list is mandatory for this command
+and must include exactly one server tag or the keyword "all"; it cannot
+include the ``null`` value. The command above associates
+the option with the "server1" server.
+
+Note that specifying an option name instead of the option code only
+works reliably for standard DHCP options. When specifying a value
+for a user-defined DHCP option, the option code should be indicated
+instead of the name. For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-option6-global-set",
+       "arguments": {
+           "options": [
+               {
+                   "code": 1,
+                   "space": "isc",
+                   "data": "2001:db8:1::1"
+               }
+           ],
+           "server-tags": [ "server1" ]
+       }
+   }
+
+.. _command-remote-option4-network-del:
+
+.. _command-remote-option6-network-del:
+
+The ``remote-option4-network-del``, ``remote-option6-network-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to delete a shared-network-specific DHCP
+option from the database. The option is identified by an option code
+and option space and these two parameters are passed within the
+``options`` list. Another list, ``shared-networks``, contains a map
+with the name of the shared network from which the option is to
+be deleted. If the option is not explicitly specified for this
+shared network, no option is deleted. In particular, the given
+option may be present for a subnet belonging to the shared network.
+Such an option instance is not affected by this command as this
+command merely deletes the shared-network-level option. To
+delete a subnet-level option, the ``remote-option[46]-subnet-del``
+command must be used instead.
+
+The following command attempts to delete an option having the
+option code 5 in the top-level option space from the shared
+network "fancy".
+
+.. code-block:: json
+
+   {
+       "command": "remote-option4-network-del",
+       "arguments": {
+           "shared-networks": [
+               {
+                   "name": "fancy"
+               }
+           ],
+           "options": [
+               {
+                   "code": 5,
+                   "space": "dhcp4"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+"dhcp4" is the top-level option space where the standard DHCPv4 options
+belong. The ``server-tags`` parameter cannot be specified for this command.
+
+.. _command-remote-option4-network-set:
+
+.. _command-remote-option6-network-set:
+
+The ``remote-option4-network-set``, ``remote-option6-network-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands create a new shared-network-specific DHCP option or replace
+an existing option in the database. The structure of the option information
+is the same as in the Kea configuration file (see :ref:`dhcp4-std-options`
+and :ref:`dhcp6-std-options`). The option information is carried in the
+``options`` list. Another list, ``shared-networks``, contains a map with the
+name of the shared network for which the option is to be set. If such an option
+already exists for the shared network, it is replaced with the new instance.
+
+.. code-block:: json
+
+   {
+       "command": "remote-option6-network-set",
+       "arguments": {
+           "shared-networks": [
+               {
+                   "name": "fancy"
+               }
+           ],
+           "options": [
+               {
+                   "name": "dns-servers",
+                   "data": "2001:db8:1::1"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+The ``server-tags`` parameter cannot be specified for this command.
+
+Specifying an option name instead of the option code only works reliably
+for standard DHCP options. When specifying a value for a user-defined
+DHCP option, the option code should be indicated instead of the name.
+
+.. _command-remote-option6-pd-pool-del:
+
+The ``remote-option6-pd-pool-del`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to delete a prefix delegation pool-specific DHCPv6
+option from the database. The option is identified by an option code
+and option space, and these two parameters are passed within the
+``options`` list. Another list, ``pd-pools``, contains a map with the
+prefix-delegation-pool prefix and length identifying the pool. If the
+option is not explicitly specified for this pool, no option is deleted.
+In particular, the given option may exist for a subnet containing
+the specified pool. Such an option instance is not affected by this
+command, as this command merely deletes a prefix delegation pool-level
+option. To delete a subnet level option, the
+``remote-option6-subnet-del`` command must be used instead.
+
+.. code-block:: json
+
+   {
+       "command": "remote-option6-pd-pool-del",
+       "arguments": {
+           "pd-pools": [
+               {
+                   "prefix": "3000::",
+                   "prefix-len": 64
+               }
+           ],
+           "options": [
+               {
+                   "code": 23,
+                   "space": "dhcp6"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+"dhcp6" is the top-level option space where the standard DHCPv6 options
+belong. The ``server-tags`` parameter cannot be specified for this command.
+
+.. _command-remote-option6-pd-pool-set:
+
+The ``remote-option6-pd-pool-set`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command creates a new prefix delegation pool-specific DHCPv6 option or
+replaces an existing option in the database. The structure of the option
+information is the same as in the Kea configuration file (see :ref:`dhcp4-std-options`
+and :ref:`dhcp6-std-options`). The option information is carried in the
+``options`` list. Another list, ``pd-pools``, contains a map with the
+prefix-delegation-pool prefix and the prefix length identifying the pool. If such an
+option already exists for the prefix delegation pool, it is replaced with
+the new instance.
+
+For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-option6-pd-pool-set",
+       "arguments": {
+           "pd-pools": [
+               {
+                   "prefix": "3001:1::",
+                   "length": 64
+               }
+           ],
+           "options": [
+               {
+                   "name": "dns-servers",
+                   "data": "2001:db8:1::1"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+The ``server-tags`` parameter cannot be specified for this command.
+
+Specifying an option name instead of the option code only works reliably
+for standard DHCP options. When specifying a value for a user-defined
+DHCP option, the option code should be indicated instead of the name.
+
+.. _command-remote-option4-pool-del:
+
+.. _command-remote-option6-pool-del:
+
+The ``remote-option4-pool-del``, ``remote-option6-pool-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to delete an address-pool-specific DHCP
+option from the database. The option is identified by an option code
+and option space, and these two parameters are passed within the
+``options`` list. Another list, ``pools``, contains a map with the
+IP address range or prefix identifying the pool. If the option
+is not explicitly specified for this pool, no option is deleted.
+In particular, the given option may exist for a subnet containing
+the specified pool. Such an option instance is not affected by this
+command, as this command merely deletes a pool-level option. To
+delete a subnet-level option, the ``remote-option[46]-subnet-del``
+command must be used instead.
+
+The following command attempts to delete an option having the
+option code 5 in the top-level option space from an IPv4 address
+pool:
+
+.. code-block:: json
+
+   {
+       "command": "remote-option4-pool-del",
+       "arguments": {
+           "pools": [
+               {
+                   "pool": "192.0.2.10 - 192.0.2.100"
+               }
+           ],
+           "options": [
+               {
+                   "code": 5,
+                   "space": "dhcp4"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+"dhcp4" is the top-level option space where the standard DHCPv4 options
+belong. The ``server-tags`` parameter cannot be specified for this command.
+
+.. _command-remote-option4-pool-set:
+
+.. _command-remote-option6-pool-set:
+
+The ``remote-option4-pool-set``, ``remote-option6-pool-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands create a new address-pool-specific DHCP option or replace
+an existing option in the database. The structure of the option information
+is the same as in the Kea configuration file (see :ref:`dhcp4-std-options`
+and :ref:`dhcp6-std-options`). The option information is carried in the
+``options`` list. Another list, ``pools``, contains a map with the IP address
+range or prefix identifying the pool. If such an option already exists for
+the pool, it is replaced with the new instance.
+
+For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-option4-pool-set",
+       "arguments": {
+           "pools": [
+               {
+                   "pool": "192.0.2.10 - 192.0.2.100"
+               }
+           ],
+           "options": [
+               {
+                   "name": "domain-name-servers",
+                   "data": "10.0.0.1"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+The ``server-tags`` parameter cannot be specified for this command.
+
+Specifying an option name instead of the option code only works reliably
+for standard DHCP options. When specifying a value for a user-defined
+DHCP option, the option code should be indicated instead of the name.
+
+.. _command-remote-option4-subnet-del:
+
+.. _command-remote-option6-subnet-del:
+
+The ``remote-option4-subnet-del``, ``remote-option6-subnet-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to delete a subnet-specific DHCP option
+from the database. The option is identified by an option code
+and option space, and these two parameters are passed within the
+``options`` list. Another list, ``subnets``, contains a map with the
+identifier of the subnet from which the option is to be deleted.
+If the option is not explicitly specified for this subnet, no
+option is deleted.
+
+The following command attempts to delete an option having the
+option code 5 in the top-level option space from the subnet
+having an identifier of 123.
+
+.. code-block:: json
+
+   {
+       "command": "remote-option4-subnet-del",
+       "arguments": {
+           "subnets": [
+               {
+                   "id": 123
+               }
+           ],
+           "options": [
+               {
+                   "code": 5,
+                   "space": "dhcp4"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+"dhcp4" is the top-level option space where the standard DHCPv4 options
+belong. The ``server-tags`` parameter cannot be specified for this command.
+
+.. _command-remote-option4-subnet-set:
+
+.. _command-remote-option6-subnet-set:
+
+The ``remote-option4-subnet-set``, ``remote-option6-subnet-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands create a new subnet-specific DHCP option or replace an existing
+option in the database. The structure of the option information is the same as
+in the Kea configuration file (see :ref:`dhcp4-std-options`
+and :ref:`dhcp6-std-options`). The option information is carried in the
+``options`` list. Another list, ``subnets``, contains a map with the identifier of
+the subnet for which the option is to be set. If such an option already exists
+for the subnet, it is replaced with the new instance.
+
+.. code-block:: json
+
+   {
+       "command": "remote-option6-subnet-set",
+       "arguments": {
+           "subnets": [
+               {
+                   "id": 123
+               }
+           ],
+           "options": [
+               {
+                   "name": "dns-servers",
+                   "data": "2001:db8:1::1"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+The ``server-tags`` parameter cannot be specified for this command.
+
+Specifying an option name instead of the option code only works reliably
+for the standard DHCP options. When specifying a value for the user-defined
+DHCP option, the option code should be indicated instead of the name.
+
+.. _command-remote-subnet4-del-by-id:
+
+.. _command-remote-subnet6-del-by-id:
+
+The ``remote-subnet4-del-by-id``, ``remote-subnet6-del-by-id`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This is the first variant of the commands used to delete an IPv4 or IPv6
+subnet from the database. It uses the subnet ID to identify the subnet. For
+example, to delete the IPv4 subnet with an ID of 5:
+
+.. code-block:: json
+
+   {
+       "command": "remote-subnet4-del-by-id",
+       "arguments": {
+           "subnets": [
+               {
+                   "id": 5
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+The ``server-tags`` parameter cannot be used with this command.
+
+.. _command-remote-subnet4-del-by-prefix:
+
+.. _command-remote-subnet6-del-by-prefix:
+
+The ``remote-subnet4-del-by-prefix``, ``remote-subnet6-del-by-prefix`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This is the second variant of the commands used to delete an IPv4 or
+IPv6 subnet from the database. It uses the subnet prefix to identify the
+subnet. For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-subnet6-del-by-prefix",
+       "arguments": {
+           "subnets": [
+               {
+                   "subnet": "2001:db8:1::/64"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+The ``server-tags`` parameter cannot be used with this command.
+
+.. _command-remote-subnet4-get-by-id:
+
+.. _command-remote-subnet6-get-by-id:
+
+The ``remote-subnet4-get-by-id``, ``remote-subnet6-get-by-id`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This is the first variant of the commands used to fetch an IPv4 or IPv6
+subnet from the database. It uses a subnet ID to identify the subnet.
+For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-subnet4-get-by-id",
+       "arguments": {
+           "subnets": [
+               {
+                   "id": 5
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+The ``server-tags`` parameter cannot be used with this command.
+
+.. _command-remote-subnet4-get-by-prefix:
+
+.. _command-remote-subnet6-get-by-prefix:
+
+The ``remote-subnet4-get-by-prefix``, ``remote-subnet6-get-by-prefix`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This is the second variant of the commands used to fetch an IPv4 or IPv6
+subnet from the database. It uses a subnet prefix to identify the
+subnet. For example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-subnet6-get-by-prefix",
+       "arguments": {
+           "subnets": [
+               {
+                   "subnet": "2001:db8:1::/64"
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           }
+       }
+   }
+
+The ``server-tags`` parameter cannot be used with this command.
+
+.. _command-remote-subnet4-list:
+
+.. _command-remote-subnet6-list:
+
+The ``remote-subnet4-list``, ``remote-subnet6-list`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to list all IPv4 or IPv6 subnets from the database for
+selected servers or all servers. The following command retrieves all servers to
+be used by "server1" and "server2":
+
+.. code-block:: json
+
+    {
+        "command": "remote-subnet4-list"
+        "arguments": {
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "server1", "server2" ]
+        }
+    }
+
+The ``server-tags`` parameter is mandatory and contains one or
+more server tags. It may contain the keyword "all", to fetch the subnets
+associated with all servers. When the ``server-tags`` list
+contains the ``null`` value, the returned response contains a list
+of unassigned subnets, i.e. the subnets which are associated with no servers.
+For example:
+
+.. code-block:: json
+
+    {
+        "command": "remote-subnet4-list"
+        "arguments": {
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ null ]
+        }
+    }
+
+The example response to this command when non-null server tags are specified
+looks similar to this:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "2 IPv4 subnet(s) found.",
+        "arguments": {
+            "subnets": [
+                {
+                    "id": 1,
+                    "subnet": "192.0.2.0/24",
+                    "shared-network-name": null,
+                    "metadata": {
+                        "server-tags": [ "server1", "server2" ]
+                    }
+                },
+                {
+                    "id": 2,
+                    "subnet": "192.0.3.0/24",
+                    "shared-network-name": null,
+                    "metadata": {
+                        "server-tags": [ "all" ]
+                    }
+                }
+            ],
+            "count": 2
+        }
+    }
+
+The returned information about each subnet is limited to the subnet identifier,
+prefix, and associated shared network name. To retrieve full
+information about the selected subnet, use
+``remote-subnet[46]-get-by-id`` or
+``remote-subnet[46]-get-by-prefix``.
+
+The example response above contains two subnets. One of the subnets is
+associated with both servers: "server1" and "server2". The second subnet is
+associated with all servers, so it is also present in the configurations for
+"server1" and "server2".
+
+When listing unassigned subnets, the response will look similar to this:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "1 IPv4 subnet(s) found.",
+        "arguments": {
+            "subnets": [
+                {
+                    "id": 3,
+                    "subnet": "192.0.4.0/24",
+                    "shared-network-name": null,
+                    "metadata": {
+                        "server-tags": [ null ]
+                    }
+                }
+            ],
+            "count": 1
+        }
+    }
+
+The ``null`` value in the metadata indicates that the
+returned subnet is unassigned.
+
+.. _command-remote-subnet4-set:
+
+.. _command-remote-subnet6-set:
+
+The ``remote-subnet4-set``, ``remote-subnet6-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to create a new IPv4 or IPv6 subnet or replace
+an existing subnet in the database. Setting the subnet also associates
+or disassociates the subnet with a shared network.
+
+The structure of the subnet information is similar to the structure used
+in the configuration file (see :ref:`dhcp4-configuration` and
+:ref:`dhcp6-configuration`). The subnet information conveyed in the
+``remote-subnet[46]-set`` command must include the additional parameter
+``shared-network-name``, which denotes whether the subnet belongs to a
+shared network.
+
+Consider the following example:
+
+.. code-block:: json
+
+   {
+       "command": "remote-subnet4-set",
+       "arguments": {
+           "subnets": [
+               {
+                   "id": 5,
+                   "subnet": "192.0.2.0/24",
+                   "shared-network-name": "level3",
+                   "pools": [ { "pool": "192.0.2.100-192.0.2.200" } ],
+                   "option-data": [ {
+                       "name": "routers",
+                       "data": "192.0.2.1"
+                   } ]
+               }
+           ],
+           "remote": {
+               "type": "mysql"
+           },
+           "server-tags": [ "all" ]
+       }
+   }
+
+It creates the subnet and associates it with the "level3" shared
+network. The "level3" shared network must be created with the ``remote-network4-set``
+command prior to creating the subnet.
+
+If the created subnet must be global - that is, not associated with any shared
+network - the ``shared-network-name`` must be explicitly set to
+``null``:
+
+.. code-block:: json
+
+   {
+       "command": "remote-subnet4-set",
+       "arguments": {
+           "subnets": [
+               {
+                   "id": 5,
+                   "subnet": "192.0.2.0/24",
+                   "shared-network-name": null,
+                   "pools": [ { "pool": "192.0.2.100-192.0.2.200" } ],
+                   "option-data": [ {
+                       "name": "routers",
+                       "data": "192.0.2.1"
+                   } ]
+              }
+           ],
+           "server-tags": [ "all" ]
+       }
+   }
+
+The subnet created in the previous example is replaced with the new
+subnet having the same parameters, but it becomes global.
+
+The ``shared-network-name`` parameter is mandatory for the
+``remote-subnet4-set`` command. The ``server-tags`` list is mandatory and must
+include one or more server tags. As a result, the subnet is associated with all
+of the listed servers. It may also be associated with all servers connecting
+to the database when the keyword "all" is used as the server tag.
+
+.. note::
+
+   As with other "set" commands, this command replaces all the
+   information about the particular subnet in the database, if the
+   subnet information is already present. Therefore, when sending this
+   command, make sure to always include all parameters that must be
+   specified for the updated subnet instance. Any unspecified parameter
+   will be marked as unspecified in the database, even if its value was
+   present prior to sending the command.
+
+.. _command-remote-class4-del:
+
+.. _command-remote-class6-del:
+
+The ``remote-class4-del``, ``remote-class6-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands delete a DHCPv4 or DHCPv6 client class by name. If any client
+classes in the database depend on the deleted class, an error is returned in
+response to this command. In this case, to successfully delete the class,
+the dependent client classes must be deleted first. Use the
+``remote-class4-get-all`` command to fetch all client classes and find
+the dependent ones.
+
+.. code-block:: json
+
+    {
+        "command": "remote-class4-del",
+        "arguments": {
+            "client-classes": [
+                {
+                    "name": "foo"
+                }
+            ],
+            "remote": {
+                "type": "mysql"
+            }
+        }
+    }
+
+The ``server-tags`` parameter cannot be used for this command because client
+classes are uniquely identified by name.
+
+.. _command-remote-class4-get:
+
+.. _command-remote-class6-get:
+
+The ``remote-class4-get``, ``remote-class6-get`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands retrieve DHCPv4 or DHCPv6 client class information by a
+client-class name.
+
+.. code-block:: json
+
+    {
+        "command": "remote-class4-get",
+        "arguments": {
+            "client-classes": [
+                {
+                    "name": "foo"
+                }
+            ],
+            "remote": {
+                "type": "mysql"
+            }
+        }
+    }
+
+The ``server-tags`` parameter cannot be used for this command because client
+classes are uniquely identified by name.
+
+A response to the command looks similar to this:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "DHCPv4 client class 'foo' found.",
+        "arguments": {
+            "client-classes": [
+                {
+                    "name": "foo",
+                    "metadata": {
+                        "server-tags": [ "all" ]
+                    }
+                }
+            ],
+            "count": 1
+        }
+    }
+
+.. _command-remote-class4-get-all:
+
+.. _command-remote-class6-get-all:
+
+The ``remote-class4-get-all``, ``remote-class6-get-all`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands retrieve all DHCPv4 or DHCPv6 client classes for a particular server,
+multiple explicitly listed servers, and/or all servers. A given server has its own
+server-specific tag and also has the "all" server tag; these commands retrieve
+the classes for both an individual server and for "all" servers. For example, the
+following command retrieves all client classes defined for "server1" as well as
+the client classes defined for "all" servers:
+
+.. code-block:: json
+
+    {
+        "command": "remote-class4-get-all",
+        "arguments": {
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "server1" ]
+        }
+    }
+
+The ``server-tags`` parameter is mandatory and contains one or more server
+tags. If other server tags are specified, "all" does not need to be included
+in ``server-tags``, as every server automatically also has the "all" server tag.
+If ``server-tags`` contains only the keyword "all", only the client classes associated
+with "all" servers are returned. When the ``server-tags`` list contains the
+``null`` value, the returned response contains a list of unassigned client
+classes, i.e. the networks which are associated with no servers.
+
+A response to the command looks similar to this:
+
+.. code-block:: json
+
+    {
+        "result": 0,
+        "text": "2 DHCPv4 client class(es) found.",
+        "arguments": {
+            "client-classes": [
+                {
+                    "name": "foo",
+                    "metadata": {
+                        "server-tags": [ "all" ]
+                    }
+                },
+                {
+                    "name": "bar",
+                    "test": "member('foo')",
+                    "metadata": {
+                        "server-tags": [ "all" ]
+                    }
+                }
+            ],
+            "count": 2
+        }
+    }
+
+.. _command-remote-class4-set:
+
+.. _command-remote-class6-set:
+
+The ``remote-class4-set``, ``remote-class6-set`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands insert a new or replace an existing DHCPv4 or DHCPv6 client class in
+the database. The client class information structure is the same as in the Kea
+configuration file (see :ref:`dhcp4-client-classifier` and
+:ref:`dhcp6-client-classifier` for details).
+
+.. code-block:: json
+
+    {
+        "command": "remote-class4-set",
+        "arguments": {
+            "client-classes": [
+                {
+                    "name": "foo",
+                    "test": "member('KNOWN') or member('bar')",
+                    "option-def": [
+                        {
+                            "name": "configfile",
+                            "code": 224,
+                            "type": "string"
+                        }
+                    ],
+                    "option-data": [
+                        {
+                            "name": "configfile",
+                            "data": "1APC"
+                        }
+                    ]
+                }
+            ],
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "all" ]
+        }
+    }
+
+
+Client-class ordering rules described in :ref:`classification-using-expressions`
+apply to the classes inserted into the database. They imply that the class `bar`
+referenced in the test expression must exist in the database when issuing the
+above command.
+
+By default, a new client class is inserted at the end of the class hierarchy in
+the database and can reference any class associated with the same server tag or
+with the special server tag "all". If an existing class is updated, it remains
+at its current position within the class hierarchy.
+
+However, the class commands allow the position of the inserted
+or updated client class to be specified. The optional ``follow-class-name`` parameter can be
+included in the command to indicate the name of the existing class after which
+the managed class should be placed. Suppose there are two DHCPv6 classes in the
+database: `first-class` and `second-class`. To add a new class, `third-class`,
+between these two, use a command similar to the following:
+
+.. code-block:: json
+
+    {
+        "command": "remote-class6-set",
+        "arguments": {
+            "client-classes": [
+                {
+                    "name": "third-class",
+                    "test": "member('first-class')"
+                }
+            ],
+            "follow-class-name": "first-class",
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "all" ]
+        }
+    }
+
+Note that `third-class` can depend on `first-class` because it is placed
+after `first-class`; `third-class` cannot depend on `second-class`
+because it is placed before it. However, `second-class` could be updated to
+depend on `third-class`.
+
+The ``follow-class-name`` parameter can be explicitly set to ``null``, e.g.:
+
+.. code-block:: json
+
+    {
+        "command": "remote-class6-set",
+        "arguments": {
+            "client-classes": [
+                {
+                    "name": "third-class",
+                    "test": "member('first-class')"
+                }
+            ],
+            "follow-class-name": null,
+            "remote": {
+                "type": "mysql"
+            },
+            "server-tags": [ "all" ]
+        }
+    }
+
+It yields the same behavior as if the ``follow-class-name`` parameter were not included,
+i.e. the new class is appended at the end of the class hierarchy, and the updated
+class remains at the current position.
diff --git a/doc/sphinx/arm/hooks-cb-mysql.rst b/doc/sphinx/arm/hooks-cb-mysql.rst
new file mode 100644
index 0000000..16111ff
--- /dev/null
+++ b/doc/sphinx/arm/hooks-cb-mysql.rst
@@ -0,0 +1,9 @@
+.. _hooks-cb-mysql:
+
+``mysql_cb``: Configuration Backend for MySQL
+=============================================
+
+This hook library works in conjunction with the ``cb_cmds`` library to
+implement the API to create, read, update, and delete (CRUD) the
+configuration in a MySQL database. Please see :ref:`hooks-cb-cmds`
+for more details.
diff --git a/doc/sphinx/arm/hooks-cb-pgsql.rst b/doc/sphinx/arm/hooks-cb-pgsql.rst
new file mode 100644
index 0000000..cf8decc
--- /dev/null
+++ b/doc/sphinx/arm/hooks-cb-pgsql.rst
@@ -0,0 +1,9 @@
+.. _hooks-cb-pgsql:
+
+``pgsql_cb``: Configuration Backend for PostgreSQL
+==================================================
+
+This hook library works in conjunction with the ``cb_cmds`` library to
+implement the API to create, read, update, and delete (CRUD) the
+configuration in a PostgreSQL database. Please see :ref:`hooks-cb-cmds`
+for more details.
diff --git a/doc/sphinx/arm/hooks-class-cmds.rst b/doc/sphinx/arm/hooks-class-cmds.rst
new file mode 100644
index 0000000..d98c398
--- /dev/null
+++ b/doc/sphinx/arm/hooks-class-cmds.rst
@@ -0,0 +1,239 @@
+.. _hooks-class-cmds:
+
+``class_cmds``: Class Commands
+==============================
+
+This hook library exposes
+several control commands for manipulating client classes (part of the
+Kea DHCP servers' configurations) without the need to restart those
+servers. Using these commands it is possible to add, update, delete, and
+list the client classes configured for a given server.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or
+   ``kea-dhcp6`` process.
+
+The Class Commands hook library is currently available only to ISC
+customers with a paid support contract.
+
+.. _command-class-add:
+
+The ``class-add`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``class-add`` command adds a new client class to the DHCP server
+configuration. This class is appended at the end of the list of classes
+used by the server and may depend on any of the already-configured
+client classes.
+
+The following example demonstrates how to add a new client class to the
+DHCPv4 server configuration:
+
+::
+
+   {
+       "command": "class-add",
+       "arguments": {
+           "client-classes": [
+               {
+                   "name": "ipxe_efi_x64",
+                   "test": "option[93].hex == 0x0009",
+                   "next-server": "192.0.2.254",
+                   "server-hostname": "hal9000",
+                   "boot-file-name": "/dev/null"
+               }
+           ]
+       }
+   }
+
+Note that the ``client-classes`` parameter is a JSON list, but it allows
+only a single client class to be present.
+
+Here is the response to the ``class-add`` command in our example:
+
+::
+
+   {
+       "result": 0,
+       "text": "Class 'ipxe_efi_x64' added."
+   }
+
+.. _command-class-update:
+
+The ``class-update`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``class-update`` command updates an existing client class in the
+DHCP server configuration. If the client class with the given name
+does not exist, the server returns the result code of 3, which means that
+the server configuration is not modified and the client class does not
+exist. The ``class-add`` command must be used instead to create the new
+client class.
+
+The ``class-update`` command has the same argument structure as the
+``class-add`` command:
+
+::
+
+   {
+       "command": "class-update",
+       "arguments": {
+           "client-classes": [
+               {
+                   "name": "ipxe_efi_x64",
+                   "test": "option[93].hex == 0x0017",
+                   "next-server": "0.0.0.0",
+                   "server-hostname": "xfce",
+                   "boot-file-name": "/dev/null"
+               }
+           ]
+       }
+   }
+
+Here is the response for our example:
+
+::
+
+   {
+       "result": 0,
+       "text": "Class 'ipxe_efi_x64' updated."
+   }
+
+Any parameter of the client class can be modified with this command,
+except ``name``. There is currently no way to rename the class, because
+the class name is used as a key for searching the class to be updated.
+To achieve a similar effect to renaming the class, an existing class can
+be removed with the ``class-del`` command and then added again with a
+different name using ``class-add``. Note, however, that the class with
+the new name will be added at the end of the list of configured classes.
+
+.. _command-class-del:
+
+The ``class-del`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+The ``class-del`` command is used to remove a particular class from the server
+configuration. The class to be removed is identified by name. The class
+is not removed if there are other classes depending on it; to remove
+such a class, the dependent classes must be removed first.
+
+The following is a sample command removing the ``ipxe_efi_x64`` class:
+
+::
+
+   {
+       "command": "class-del",
+       "arguments": {
+           {
+               "name": "ipxe_efi_x64"
+           }
+       }
+   }
+
+Here is the response to the ``class-del`` command in our example, when
+the specified client class has been found:
+
+::
+
+   {
+       "result": 0,
+       "text": "Class 'ipxe_efi_x64' deleted."
+   }
+
+If the class does not exist, the result of 3 is returned.
+
+.. _command-class-list:
+
+The ``class-list`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+``class-list`` is used to retrieve a list of all client classes. This
+command includes no arguments:
+
+::
+
+   {
+       "command": "class-list"
+   }
+
+Here is the response of the server in our example, including the list of
+client classes:
+
+::
+
+   {
+       "result": 0,
+       "text": "2 classes found",
+       "arguments": {
+           "client-classes": [
+               {
+                   "name": "ipxe_efi_x64"
+               },
+               {
+                   "name": "pxeclient"
+               }
+           ]
+       }
+   }
+
+Note that the returned list does not contain full class definitions, but
+merely class names. To retrieve full class information, the
+``class-get`` command should be used.
+
+.. _command-class-get:
+
+The ``class-get`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``class-get`` is used to retrieve detailed information about a specified
+class. The command structure is very simple:
+
+::
+
+   {
+       "command": "class-get",
+       "arguments": {
+           "name": "pxeclient"
+       }
+   }
+
+If the class with the specified name does not exist, the status code of
+3 is returned. If the specified client class exists, the class details
+are returned in the following format:
+
+::
+
+   {
+       "result": 0,
+       "text": "Class 'pxeclient' definition returned",
+       "arguments": {
+           "client-classes": [
+               {
+                   "name": "pxeclient",
+                   "only-if-required": true,
+                   "test": "option[vendor-class-identifier].text == 'PXEClient'",
+                   "option-def": [
+                       {
+                           "name": "configfile",
+                           "code": 209,
+                           "type": "string"
+                       }
+                   ],
+                   "option-data": [ ],
+                   "next-server": "0.0.0.0",
+                   "server-hostname": "xfce",
+                   "boot-file-name": "/dev/null"
+               }
+           ]
+       }
+   }
+
+Note that the example above is DHCPv4-specific; the last three
+parameters are only returned by the DHCPv4 server and are never returned
+by the DHCPv6 server. Also, some of the parameters provided in this
+example may not be returned if they are not specified for the class.
+Specifically, ``only-if-required``, ``test``, and ``option-def`` are not
+returned if they are not specified for the class.
diff --git a/doc/sphinx/arm/hooks-ddns-tuning.rst b/doc/sphinx/arm/hooks-ddns-tuning.rst
new file mode 100644
index 0000000..7b081bb
--- /dev/null
+++ b/doc/sphinx/arm/hooks-ddns-tuning.rst
@@ -0,0 +1,210 @@
+.. _hooks-ddns-tuning:
+
+``ddns_tuning``: DDNS Tuning
+============================
+
+This hook library adds support for fine-tuning various DNS update aspects.
+It currently supports procedural host-name generation and the ability to skip
+performing DDNS updates for select clients.
+
+The DDNS Tuning hook library is only available to ISC customers with a paid
+support contract.
+
+The library, which was added in Kea 2.1.5, can be loaded by the ``kea-dhcp4``
+and ``kea-dhcp6`` daemons by adding it to the ``hooks-libraries`` element of the
+server's configuration:
+
+.. code-block:: javascript
+
+    {
+        "hooks-libraries": [
+            :
+            ,
+            {
+                "library": "/usr/local/lib/libdhcp_ddns_tuning.so",
+                "parameters": {
+                    :
+                }
+            },
+            :
+        ]
+    }
+
+Procedural Host-Name Generation
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This hook library provides the ability to generate host names procedurally, based on
+an expression. The expression can be defined globally in the hook parameters, using
+`hostname-expr`. If defined globally, it applies to all hosts in all subnets. The
+expressions can use all tokens defined in :ref:`classify`. An example of a global
+expression is shown below:
+
+.. code-block:: javascript
+
+    {
+        "hooks-libraries": [
+            :
+            ,
+            {
+                "library": "/usr/local/lib/libdhcp_ddns_tuning.so",
+                "parameters": {
+                    :
+                    "hostname-expr": "'host-'+hexstring(pkt4.mac,'-')"
+                }
+            },
+            :
+        ]
+    }
+
+It is also possible to define this parameter in a subnet, using the user-context mechanism.
+If defined at the subnet level, the expression applies to a specific subnet only. If the
+subnet expression is defined as empty, ``""``, it suppresses (or disables) the use of a
+global expression for that subnet. An example subnet expression is shown below:
+
+.. code-block:: javascript
+
+    "subnet4": [{
+        "subnet": "192.0.2.0/24",
+        "pools": [{
+            "pool": "192.0.2.10 - 192.0.2.20",
+        } ],
+
+        // This is a subnet-specific user context.
+        "user-context": {
+            "ddns-tuning:" {
+                "hostname-expr": "'guest-'+Int8ToText(substring(pkt4.yiaddr, 0,1))+'-' \
+                                          +Int8ToText(substring(pkt4.yiaddr, 1,2))+'-' \
+                                          +Int8ToText(substring(pkt4.yiaddr, 2,3))+'-' \
+                                          +Int8ToText(substring(pkt4.yiaddr, 3,4))",
+            },
+            "last-modified": "2017-09-04 13:32",
+            "description": "you can put anything you like here",
+            "phones": [ "x1234", "x2345" ],
+            "devices-registered": 42,
+            "billing": false
+        }
+    }]
+
+.. note::
+
+   The expression value above uses a slash, '\', to show line continuation. This is for
+   clarity only and is not valid JSON supported by Kea parsing. The actual value must
+   be expressed on a single line.
+
+.. note::
+
+   Privacy should be taken into consideration when generating a host name. The host name
+   is usually inserted into the DNS, which is a public system. Exposing identifiers that
+   can be used to track devices, such as a MAC address, are usually a very bad idea.
+   The global expression example here used a MAC address for simplicity.
+
+DHCPv4 Host-Name Generation
+---------------------------
+
+With this library installed, the behavior for ``kea-dhcp4`` when forming host names in
+response to a client query (e.g. DISCOVER, REQUEST) is as follows:
+
+  1. If a host name is supplied via a host reservation, use it with the DDNS
+  behavioral parameters to form the final host name. Go to step 4.
+
+  2. If the client supplied an FQDN option (option 81), use the domain name value
+  specified within it, with the DDNS behavioral parameters, to form the final
+  host name. Go to step 4.
+
+  3. If the client supplied a host-name option (option 12), use the host name specified
+  within it, with the DDNS behavioral parameters, to form the final host name.
+
+  4. If there is a ``ddns-tuning`` in-scope host-name expression (either global or subnet),
+  calculate the host name using the expression. If the calculated value is not a fully
+  qualified name and there is an in-scope ``ddns-qualifying-suffix``, append the suffix.
+
+  5. If the value calculated by the hook is not an empty string and is different than
+  the host name formed in steps 1 or 2, the calculated value becomes the
+  final host name.
+
+DHCPv6 Host-Name Generation
+---------------------------
+
+With this library installed, the behavior for ``kea-dhcp6`` when forming host names in
+response to a client query (e.g. SOLICIT, REQUEST, RENEW, REBIND) is as follows:
+
+  1. If the client supplied an FQDN option (option 39), use the domain name value
+  specified within it, with the DDNS behavioral parameters, to form the final
+  host name. Go to step 4.
+
+  2. If the client did not supply an FQDN but ``ddns-replace-client-name`` is either
+  ``always`` or ``when-not-present``, then calculate the final form of the host
+  name and use it to create an outbound FQDN. Go to step 4.
+
+  3. If there is no outbound FQDN at this point, client-name processing for this
+  packet stops. Without an outbound FQDN there is no way to communicate a host
+  name to the client.
+
+  4. If a host name is supplied via a host reservation, use it along with the DDNS
+  behavioral parameters to form the final host name; it supersedes the FQDN value
+  calculated in steps 1 or 2.
+
+  5. If there is a ``ddns-tuning`` in-scope host name expression (either global or subnet),
+  calculate the host name using the expression. If the calculated value is not a fully
+  qualified name and there is an in-scope ``ddns-qualifying-suffix``, append the suffix.
+
+  6. If the value calculated by the hook is not an empty string and is different than
+  the host name formed in steps 1 or 2, the calculated value becomes the
+  final host name.
+
+
+Skipping DDNS Updates
+~~~~~~~~~~~~~~~~~~~~~
+
+The ``ddns-tuning`` library also provides the ability to skip DDNS updates on a
+per-client basis. The library recognizes a special client class, "SKIP_DDNS"; when a
+client is matched to this class, the Kea servers (``kea-dhcp4`` and ``kea-dhcp6``) do not
+send DDNS update requests (NCRs) to ``kea-dhcp-ddns``. A common use case would be
+to skip DDNS updates for fixed-address host reservations. This is done easily by
+simply assigning the class to the host reservation as shown below:
+
+.. code-block:: javascript
+
+    {
+        "reservations": [
+        {
+            "hw-address": "01:02:03:04:05:06",
+            "ip-address": "192.0.2.1",
+            "client-classes": [ "SKIP_DDNS", "foo", "bar" ]
+        }]
+    }
+
+The ``ddns-tuning`` library notes the presence of the "SKIP_DDNS" class in the
+client's class list each time the client requests, renews, or releases its lease,
+and instructs ``kea-dhcp4`` to bypass sending DDNS updates. A similar workflow is
+supported for ``kea-dhcp6``:
+
+.. code-block:: javascript
+
+    {
+        "reservations": [
+        {
+            "duid": "01:02:03:04:05:06",
+            "ip-address": "2001:db8::1",
+            "client-classes": [ "SKIP_DDNS", "foo", "bar" ]
+        }]
+    }
+
+Although "SKIP_DDNS" is a special class, it can be defined with a test
+expression. Defining it as shown below would omit DDNS updates for all KNOWN
+clients:
+
+.. code-block:: javascript
+
+    {
+        "client-classes":[
+        {
+            "name": "SKIP_DDNS",
+            "test": "member('KNOWN')"
+        }]
+    }
+
+.. note::
+
+    The ``ddns-tuning`` hook library must be loaded for the "SKIP_DDNS" class
+    to have an effect.
diff --git a/doc/sphinx/arm/hooks-flex-id.rst b/doc/sphinx/arm/hooks-flex-id.rst
new file mode 100644
index 0000000..cbc0739
--- /dev/null
+++ b/doc/sphinx/arm/hooks-flex-id.rst
@@ -0,0 +1,225 @@
+.. _hooks-flex-id:
+
+``flex_id``: Flexible Identifier for Host Reservations
+======================================================
+
+The Kea software provides a way to handle
+host reservations that include addresses, prefixes, options, client
+classes, and other features. The reservation can be based on hardware
+address, DUID, circuit-id, or client-id in DHCPv4 and on hardware
+address or DUID in DHCPv6. However, there are sometimes scenarios where
+the reservation is more complex; it may use options other than those mentioned
+above, use parts of specific options, or perhaps even use a combination of
+several options and fields to uniquely identify a client. Those
+scenarios are addressed by the Flexible Identifiers hook application.
+
+The Flexible Identifier library is only available to ISC customers with a paid support
+contract.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or ``kea-dhcp6``
+   process.
+
+The ``flex_id`` library allows the definition of an expression, using notation initially
+used only for client classification. (See
+:ref:`classification-using-expressions` for a detailed description of
+the syntax available.) One notable difference is that for client
+classification, the expression currently has to evaluate to either ``true``
+or ``false``, while the flexible identifier expression is expected to
+evaluate to a string that will be used as an identifier. It is a valid case
+for the expression to evaluate to an empty string (e.g. in cases where a
+client does not send specific options). This expression is then
+evaluated for each incoming packet, and this evaluation generates an
+identifier that is used to identify the client. In particular, there may
+be host reservations that are tied to specific values of the flexible
+identifier.
+
+The library can be loaded similarly to other hook libraries. It
+takes a mandatory parameter ``identifier-expression`` and an optional boolean
+parameter ``replace-client-id``:
+
+::
+
+   "Dhcp6": {
+       "hooks-libraries": [
+           {
+               "library": "/path/libdhcp_flex_id.so",
+               "parameters": {
+                   "identifier-expression": "expression",
+                   "replace-client-id": false
+               }
+           },
+           ...
+       ]
+   }
+
+The flexible identifier library supports both DHCPv4 and DHCPv6.
+
+Let's consider a case of an IPv6 network that has an
+independent interface for each of its connected customers. Customers are
+able to plug in whatever device they want, so any type of identifier
+(e.g. a client-id) is unreliable. Therefore, the operator may decide to
+use an option inserted by a relay agent to differentiate between
+clients. In this particular deployment, the operator has verified that the
+interface-id is unique for each customer-facing interface, so it
+is suitable for usage as a reservation. However, only the first six bytes of
+the interface-id are interesting, because the remaining bytes are either
+randomly changed or not unique between devices. Therefore, the customer
+decides to use the first six bytes of the interface-id option inserted by the
+relay agent. After adding ``flex-id``, the ``host-reservation-identifiers`` goal
+can be achieved by using the following configuration:
+
+::
+
+   "Dhcp6": {
+       "subnet6": [{ ..., # subnet definition starts here
+       "reservations": [
+           "flex-id": "'port1234'", # value of the first 8 bytes of the interface-id
+           "ip-addresses": [ "2001:db8::1" ]
+       ],
+       }], # end of subnet definitions
+       "host-reservation-identifiers": ["duid", "flex-id"], # add "flex-id" to reservation identifiers
+       "hooks-libraries": [
+           {
+               "library": "/path/libdhcp_flex_id.so",
+               "parameters": {
+                   "identifier-expression": "substring(relay6[0].option[18].hex,0,8)"
+               }
+           },
+           ...
+       ]
+   }
+
+.. note::
+
+  Care should be taken when adjusting the expression. If the expression
+  changes, then all the ``flex-id`` values may change, possibly rendering
+  all reservations based on ``flex-id`` unusable until they are manually updated.
+  It is strongly recommended that administrators start with the expression and a
+  handful of reservations, and then adjust the expression as needed. Once
+  the desired result is obtained with the expression, host reservations
+  can be deployed on a broader scale.
+
+``flex-id`` values in host reservations can be specified in two ways. First,
+they can be expressed as a hex string, e.g. the string "bar" can be represented
+as 626174. Alternatively, it can be expressed as a quoted value (using
+double and single quotes), e.g. "'bar'". The former is more convenient
+for printable characters, while hex string values are more convenient
+for non-printable characters and do not require the use of the
+``hexstring`` operator.
+
+::
+
+   "Dhcp6": {
+       "subnet6": [{ ..., # subnet definition starts here
+       "reservations": [
+           "flex-id": "01:02:03:04:05:06", # value of the first 8 bytes of the interface-id
+           "ip-addresses": [ "2001:db8::1" ]
+       ],
+       }], # end of subnet definitions
+       "host-reservation-identifiers": ["duid", "flex-id"], # add "flex-id" to reservation identifiers
+       "hooks-libraries": [
+           {
+               "library": "/path/libdhcp_flex_id.so",
+               "parameters": {
+                   "identifier-expression": "vendor[4491].option[1026].hex"
+               }
+           },
+           ...
+       ]
+   }
+
+When ``replace-client-id`` is set to ``false`` (which is the default setting),
+the ``flex-id`` hook library uses the evaluated flexible identifier solely for
+identifying host reservations, i.e. searching for reservations within a
+database. This is the functional equivalent of other identifiers, similar
+to hardware address or circuit-id. However, this mode of operation
+implies that if a client device is replaced, it may cause a
+conflict between an existing lease (allocated to the old device) and the
+new lease being allocated to the new device. The conflict arises
+because the same flexible identifier is computed for the replaced device,
+so the server will try to allocate the same lease. The mismatch between
+client identifiers sent by the new device and the old device causes the server
+to refuse this new allocation until the old lease expires. A
+manifestation of this problem is dependent on the specific expression used
+as the flexible identifier, and is likely to appear if only options
+and other parameters are used that identify where the device is connected
+(e.g. circuit-id), rather than the device identification itself (e.g.
+MAC address).
+
+The ``flex-id`` library offers a way to overcome the problem with lease
+conflicts by dynamically replacing the client identifier (or DUID in DHCPv6)
+with a value derived from the flexible identifier. The server
+processes the client's query as if the flexible identifier were sent in the
+client identifier (or DUID) option. This guarantees that a returning
+client (for which the same flexible identifier is evaluated) will be
+assigned the same lease, despite the client identifier and/or MAC address
+change.
+
+The following is a stub configuration that enables this behavior:
+
+::
+
+   "Dhcp4": {
+       "hooks-libraries": [
+           {
+               "library": "/path/libdhcp_flex_id.so",
+               "parameters": {
+                   "identifier-expression": "expression",
+                   "replace-client-id": true
+               }
+           },
+           ...
+       ]
+   }
+
+In the DHCPv4 case, the value derived from the flexible identifier is
+formed by prepending one byte with a value of zero to the flexible identifier.
+In the DHCPv6 case, it is formed by prepending two zero bytes before the
+flexible identifier.
+
+Note that for this mechanism to take effect, the DHCPv4 server must be
+configured to respect the client identifier option value during lease
+allocation, i.e. ``match-client-id`` must be set to ``true``. See
+:ref:`dhcp4-match-client-id` for details. No additional settings are
+required for DHCPv6.
+
+If the ``replace-client-id`` option is set to ``true``, the value of the
+``echo-client-id`` parameter (which governs whether to send back a
+client-id option) is ignored.
+
+The :ref:`hooks-lease-cmds` section describes commands used to retrieve,
+update, and delete leases using various identifiers, such as ``hw-address`` and
+``client-id``. The ``lease_cmds`` library does not natively support querying
+for leases by flexible identifier. However, when ``replace-client-id`` is
+set to ``true``, it makes it possible to query for leases using a value
+derived from the flexible identifier. In DHCPv4, the query
+looks similar to this:
+
+::
+
+   {
+       "command": "lease4-get",
+       "arguments": {
+           "identifier-type": "client-id",
+           "identifier": "00:54:64:45:66",
+           "subnet-id": 44
+       }
+   }
+
+where the hexadecimal value of "54:64:45:66" is a flexible identifier
+computed for the client.
+
+In DHCPv6, the corresponding query looks something like this:
+
+::
+
+   {
+       "command": "lease6-get",
+       "arguments": {
+           "identifier-type": "duid",
+           "identifier": "00:00:54:64:45:66",
+           "subnet-id": 10
+       }
+   }
diff --git a/doc/sphinx/arm/hooks-flex-option.rst b/doc/sphinx/arm/hooks-flex-option.rst
new file mode 100644
index 0000000..7597d9f
--- /dev/null
+++ b/doc/sphinx/arm/hooks-flex-option.rst
@@ -0,0 +1,162 @@
+.. _hooks-flex-option:
+
+``flex_option``: Flexible Option Actions for Option Value Settings
+==================================================================
+
+This library allows administrators to define an action to take, for a given
+option, based upon on the result of an expression. These actions are carried
+out during the final stages of constructing a query response packet, just
+before it is sent to the client. The three actions currently supported are
+``add``, ``supersede``, and ``remove``.
+
+The syntax used for the action expressions is the same syntax used
+for client classification and the Flexible Identifier hook library;
+see either :ref:`classification-using-expressions` or :ref:`hooks-flex-id`
+for a detailed description of the syntax.
+
+The ``add`` and ``supersede`` actions use an expression returning a
+string, and do nothing if the string is empty. The
+``remove`` application uses an expression returning ``true`` or ``false``,
+and does nothing on ``false``. When it is necessary to set an option to the
+empty value this mechanism does not work, but a client class can be
+used instead.
+
+The ``add`` action adds an option only when the option does not already
+exist and the expression does not evaluate to the empty string.
+The ``supersede`` action is similar, but it overwrites the option value
+if it already exists. The ``remove`` action removes the option from
+the response packet if it already exists and the expression evaluates to
+true.
+
+The option to which an action applies may be specified by either its
+numeric code or its name; either the code or the name must be
+specified. The option space is DHCPv4 or DHCPv6, depending
+on the server where the hook library is loaded.
+
+Similar to other hook libraries, the ``flex_option`` library can be loaded
+by either the ``kea-dhcp4`` or `kea-dhcp6``
+process. It takes a mandatory ``options`` parameter with a list of
+per-option parameter maps, with ``code``, ``name``, ``add``, ``supersede``, and
+``remove`` actions. Action entries take a string value representing an
+expression.
+
+::
+
+    "Dhcp4": {
+        "hooks-libraries": [
+            {   "library": "/usr/local/lib/libdhcp_flex_option.so",
+                "parameters": {
+                    "options": [
+                            {
+                            "code": 67,
+                            "add":
+  "ifelse(option[host-name].exists,concat(option[host-name].text,'.boot'),'')"
+                        }
+                    ]
+                }
+            },
+            ...
+        ]
+    }
+
+If (and only if) the **query** includes a ``host-name`` option (code 12), a
+``boot-file-name`` option (code 67) is added to the response with the host name
+followed by ``.boot`` for content.
+
+The flexible option library supports both DHCPv4 and DHCPv6.
+
+Since Kea 1.9.0, the ``add`` and ``supersede`` actions take an optional
+```csv-format``` boolean parameter. If not specified or set to ``false``, the
+option data is set using the raw value of the evaluated expression. When it is
+configured to ``true``, this value is parsed using the option definition from
+the option data specified in the configuration file. This eases option setting
+for options using complex record formats or fully qualified domain names.
+
+For instance, if the expression evaluation returns "example.com" and
+the option is defined with the ``fqdn`` type, the domain name will be
+encoded into DNS binary format.
+
+Since Kea 2.1.4, the ``client-class`` parameter specifies a class guard.
+It takes a client class name. If not empty, the client's packet needs to
+belong to specified class for this entry to be used.
+
+Since Kea 2.1.4, it is allowed to have multiple entries for the same option,
+but each entry must have exactly one action. If the option is not defined
+in the ``dhcp4`` for DHCPv4 or ``dhcp6`` for DHCPv6 you can specify the
+space where to find the option definition using its name with the new
+``space`` parameter.
+
+Since Kea 2.1.4, sub-options are supported with a new entry ``sub-options``
+which replaces the action in the configuration of the container option,
+i.e. the option where sub-options are located.
+
+The ``sub-options`` entry takes a list of sub-option configuration similar
+to the option one with:
+
+- ``code`` - specifies the sub-option code, either the ``code`` or ``name``
+  must be specified. When both are given they must match or the configuration
+  is rejected at load time.
+
+- ``name`` - specifies the sub-option name, either the ``code`` or ``name``
+  must be specified. When both are given they must match or the configuration
+  is rejected at load time.
+
+- ``space`` - specifies the space where the sub-option can be defined. This
+  parameter is optional because it can be found in the container option
+  definition. The configuration is rejected if no valid space name is
+  available at load time. Note that vendor spaces are supported for the
+  DHCPv4 ``vivso-suboptions`` and for the DHCPv6 ``vendor-opts``, both
+  pre-defined (e.g. DoCSIS vendor id 4491) or custom.
+
+- ``add`` - (action) adds a sub-option only if it does not already exist
+  and the expression does not evaluate to the empty string.
+
+- ``supersede`` - (action) adds or overwrites a sub-option if the expression
+  does not evaluate to the empty string.
+
+- ``remove`` - (action) removes a sub-option if it already exists and the
+  expression evaluates to true.
+
+- ``container-add`` - boolean value which specifies if the container option
+  should be created if it does not exit in the ``add`` and ``supersede``
+  action. When not specified, it defaults to true.
+
+- ``container-remove`` - boolean value which specifies if the container option
+  should be deleted if it remains empty after the removal of a sub-option by
+  the ``remove`` action. When not specified, it defaults to true.
+
+- ``csv-format`` - boolean value which specifies if the raw value of the
+  evaluated expression is used (false, default) or parsed using the sub-option
+  definition (true).
+
+- ``client-class`` - specifies if the sub-option entry must be skipped when
+  the **query** does not belong to the specified client class. Note the similar
+  parameter in the container option entry applies to the whole ``sub-options``
+  list.
+
+For instance this configuration adds a string sub-option in the DHCPv4
+``vendor-encapsulated-options`` (code 43) option. Note this option
+in last resort encapsulates the ``vendor-encapsulated-options`` space.
+
+::
+
+    "Dhcp4": {
+        "hooks-libraries": [
+            {   "library": "/usr/local/lib/libdhcp_flex_option.so",
+                "parameters": {
+                    "options": [
+                            {
+                            "code": 43,
+                            "sub-options": [
+                                {
+                                   "code": 1,
+                                   "add": "'foobar'"
+                                }
+                            ]
+                        }
+                    ]
+                }
+            },
+            ...
+        ]
+    }
diff --git a/doc/sphinx/arm/hooks-gss-tsig.rst b/doc/sphinx/arm/hooks-gss-tsig.rst
new file mode 100644
index 0000000..651b7c9
--- /dev/null
+++ b/doc/sphinx/arm/hooks-gss-tsig.rst
@@ -0,0 +1,8 @@
+.. _hooks-gss-tsig:
+
+``gss-tsig``: Sign DNS Updates With GSS-TSIG
+============================================
+
+This hook library allows the ``kea-dhcp-ddns`` server to use
+GSS-TSIG to sign DNS updates. For a full discussion of GSS-TSIG in Kea,
+please see :ref:`gss-tsig`.
diff --git a/doc/sphinx/arm/hooks-ha.rst b/doc/sphinx/arm/hooks-ha.rst
new file mode 100644
index 0000000..80f66f2
--- /dev/null
+++ b/doc/sphinx/arm/hooks-ha.rst
@@ -0,0 +1,2341 @@
+.. _hooks-high-availability:
+
+``ha``: High Availability Outage Resilience for Kea Servers
+===========================================================
+
+This hook library can be loaded on a pair of DHCPv4 or DHCPv6 servers, to
+increase the reliability of the DHCP service in the event of an outage on one
+server. This library was previously only available to ISC's paid subscribers,
+but is now part of the open source Kea, available to all users.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or ``kea-dhcp6`` process.
+
+High Availability (HA) of the DHCP service is provided by running multiple
+cooperating server instances. If any of these instances becomes unavailable for
+any reason (DHCP software crash, Control Agent software crash, power outage,
+hardware failure), a surviving server instance can continue providing reliable
+service to clients. Many DHCP server implementations include the "DHCP Failover"
+protocol, whose most significant features are communication between the servers,
+partner failure detection, and lease synchronization between the servers.
+However, the DHCPv4 failover standardization process was never completed by the
+IETF. The DHCPv6 failover standard (RFC 8156) was published, but it is complex
+and difficult to use, has significant operational constraints, and is different
+from its v4 counterpart. Although it may be useful to use a "standard" failover
+protocol, most Kea users are simply interested in a working solution which
+guarantees high availability of the DHCP service. Therefore, the Kea HA hook
+library derives major concepts from the DHCP failover protocol but uses its own
+solutions for communication and configuration. It offers its own state machine,
+which greatly simplifies its implementation and generally fits better into Kea,
+and it provides the same features in both DHCPv4 and DHCPv6. This document
+intentionally uses the term "high availability" rather than "failover" to
+emphasize that it is not the failover protocol implementation.
+
+The following sections describe the configuration and operation of the Kea HA
+hook library.
+
+.. _ha-supported-configurations:
+
+Supported Configurations
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The Kea HA hook library supports three configurations, also known as HA modes:
+``load-balancing``, ``hot-standby``, and ``passive-backup``. In the
+``load-balancing`` mode, two servers respond to DHCP requests. The
+``load-balancing`` function is implemented as described in `RFC
+3074 <https://tools.ietf.org/html/rfc3074>`__, with each server responding to
+half the received DHCP queries. When one of the servers allocates a lease for a
+client, it notifies the partner server over the control channel (via the RESTful
+API), so the partner can save the lease information in its own database. If the
+communication with the partner is unsuccessful, the DHCP query is dropped and
+the response is not returned to the DHCP client. If the lease update is
+successful, the response is returned to the DHCP client by the server which has
+allocated the lease. By exchanging lease updates, both servers get a copy of all
+leases allocated by the entire HA setup, and either server can be switched to
+handle the entire DHCP traffic if its partner becomes unavailable.
+
+In the ``load-balancing`` configuration, one of the servers must be designated
+as ``primary`` and the other as ``secondary``. Functionally, there is no
+difference between the two during normal operation. However, this distinction is
+required when the two servers are started at (nearly) the same time and have to
+synchronize their lease databases. The primary server synchronizes the database
+first. The secondary server waits for the primary server to complete the lease
+database synchronization before it starts the synchronization.
+
+In the ``hot-standby`` configuration, one of the servers is designated as
+``primary`` and the other as ``standby``. During normal operation, the primary
+server is the only one that responds to DHCP requests. The standby server
+receives lease updates from the primary over the control channel; however, it
+does not respond to any DHCP queries as long as the primary is running or, more
+accurately, until the standby considers the primary to be offline. If the
+standby server detects the failure of the primary, it starts responding to all
+DHCP queries.
+
+.. note::
+
+   Operators often wonder whether to use ``load-balancing`` or ``hot-standby``
+   mode. The ``load-balancing`` mode has the benefit of splitting the DHCP load
+   between two instances, reducing the traffic processed by each of them.
+   However, it is not always clear to the operators that using the
+   ``load-balancing`` mode requires manually splitting the address pools between
+   two Kea instances using client classification, to preclude both servers from
+   allocating the same address to different clients.
+   Such a split is not needed in the ``hot-standby`` mode. Thus, the benefit
+   of using ``hot-standby`` over ``load-balancing`` is that the former has a
+   simpler configuration. Conversely, ``load-balancing`` has higher performance
+   potential at the cost of more complex configuration.
+   See :ref:`ha-load-balancing-config` for details on how to split the pools
+   using client classification.
+
+In the configurations described above, both the primary and secondary/standby
+are referred to as ``active`` servers, because they receive lease updates and
+can automatically react to the partner's failures by responding to the DHCP
+queries which would normally be handled by the partner. The HA hook library
+supports another server type/role: ``backup``. The use of a backup server is
+optional, and can be implemented in both ``load-balancing`` and ``hot-standby``
+setup, in addition to the active servers. There is no limit on the number of
+backup servers in the HA setup; however, the presence of backup servers may
+increase the latency of DHCP responses, because not only do active servers send
+lease updates to each other, but also to the backup servers. The active servers
+do not expect acknowledgments from the backup servers before responding to the
+DHCP clients, so the overhead of sending lease updates to the backup servers is
+minimized.
+
+In the last supported configuration, ``passive-backup``, there is only one
+active server and typically one or more backup servers. A ``passive-backup``
+configuration with no backup servers is also accepted, but it is no different
+than running a single server with no HA function at all.
+
+The ``passive-backup`` configuration is used in situations when an administrator
+wants to take advantage of the backup server(s) as an additional storage for
+leases without running the full-blown failover setup. In this case, if the
+primary server fails, the DHCP service is lost; it requires the administrator to
+manually restart the primary to resume DHCP service. The administrator may also
+configure one of the backup servers to provide DHCP service to the clients, as
+these servers should have accurate or nearly accurate information about the
+allocated leases. The major advantage of the ``passive-backup`` mode is that it
+provides some redundancy of the lease information but with better performance of
+the primary server responding to the DHCP queries.
+The primary server does not have to wait for acknowledgments to the lease
+updates from the backup servers before it sends a response to the DHCP client.
+This reduces the response time compared to the ``load-balancing`` and
+``hot-standby`` cases, in which the server responding to the DHCP query has to
+wait for the acknowledgment from the other active server before it can respond
+to the client.
+
+.. note::
+
+   An interesting use case for a single active server running in the
+   ``passive-backup`` mode is a notification service, in which software
+   pretending to be a backup server receives live notifications about allocated
+   and deleted leases from the primary server and can display them on a
+   monitoring screen, trigger alerts, etc.
+
+Clocks on Active Servers
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Synchronized clocks are essential for the HA setup to operate reliably.
+The servers share lease information - via lease updates and during
+synchronization of the databases - including the time when the lease was
+allocated and when it expires. Some clock skew between the servers participating
+in the HA setup usually exists; this is acceptable as long as the clock skew is
+relatively low, compared to the lease lifetimes. However, if the clock skew
+becomes too high, the different lease expiration times on different servers may
+cause the HA system to malfunction. For example, one server may consider a lease
+to be expired when it is actually still valid. The lease reclamation process may
+remove a name associated with this lease from the DNS, causing problems when the
+client later attempts to renew the lease.
+
+Each active server monitors the clock skew by comparing its current time with
+the time returned by its partner in response to the heartbeat command. This
+gives a good approximation of the clock skew, although it does not take into
+account the time between the partner sending the response and the receipt of
+this response by the server which sent the heartbeat command. If the clock skew
+exceeds 30 seconds, a warning log message is issued. The administrator may
+correct this problem by synchronizing the clocks (e.g. using NTP); the servers
+should notice the clock skew correction and stop issuing the warning.
+
+If the clock skew is not corrected and exceeds 60 seconds, the HA service on
+each of the servers is terminated, i.e. the state machine enters the
+``terminated`` state. The servers will continue to respond to DHCP clients (as
+in the ``load-balancing`` or ``hot-standby`` mode), but will exchange neither
+lease updates nor heartbeats and their lease databases will diverge. In this
+case, the administrator should synchronize the clocks and restart the servers.
+
+.. note::
+
+   It is possible to restart the servers one at a time, in no particular order.
+   The clocks must be in sync before restarting the servers.
+
+.. note::
+
+   The clock skew is only assessed between two active servers, and only the
+   active servers enter the ``terminated`` state if the skew is too high. The
+   clock skew between active and backup servers is not assessed, because active
+   servers do not exchange heartbeat messages with backup servers.
+
+.. _ha-https-support:
+
+HTTPS Support
+~~~~~~~~~~~~~
+
+Since Kea 1.9.7, the High Availability hook library supports HTTPS via TLS, as
+described in :ref:`tls`.
+
+The HTTPS configuration parameters are:
+
+-  ``trust-anchor`` - specifies the name of a file or directory where the
+   certification authority certificate of a Control Agent can be found.
+
+-  ``cert-file`` - specifies the name of the file containing the end-entity
+   certificate to use.
+
+-  ``key-file`` - specifies the private key of the end-entity certificate to use.
+
+These parameters can be configured at the global and peer levels. When
+configured at both levels the peer value is used, allowing common values to be
+shared.
+
+The three parameters must be either all not specified (HTTPS disabled) or all
+specified (HTTPS enabled). Specification of the empty string is considered not
+specified; this can be used, for instance, to disable HTTPS for a particular
+peer when it is enabled at the global level.
+
+As the High Availability hook library is an HTTPS client, there is no
+``cert-required`` parameter in this hook configuration.
+This parameter can be set in the Control Agent to require and verify a client
+certificate in client-server communication. It does not affect communication
+between HA peers at the client side; see below for information on the server
+side.
+
+Before Kea 2.1.7 using HTTPS in the HA setup required use of the Control Agent
+on all peers. (See :ref:`tls` for Control Agent TLS configuration).
+
+Since Kea 2.1.7 the HTTPS server side is supported:
+
+-  the peer entry for the server name is used for the TLS setting.
+
+-  the new ``require-client-certs`` parameter specifies whether client
+   certificates are required and verified, i.e. like ``cert-required``. It
+   defaults to ``true`` and is an HA config (vs. peer config) parameter.
+
+Kea 2.1.7 added a new security feature with the ``restrict-commands`` HA config
+parameter: when set to ``true``, commands which are not used by the hook are
+rejected. The default is ``false``.
+
+The following is an example of an HA server pair and Control Agent configuration
+for ``hot-standby`` with TLS.
+
+Server 1:
+::
+
+   "Dhcp4": {
+       "hooks-libraries": [{
+           "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+           "parameters": { }
+       }, {
+           "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+           "parameters": {
+               "high-availability": [{
+                   "this-server-name": "server1",
+                   "trust-anchor": /usr/lib/kea/CA.pem,
+                   "cert-file": /usr/lib/kea/server1_cert.pem,
+                   "key-file": /usr/lib/kea/server1_key.pem
+                   "mode": "hot-standby",
+                   "heartbeat-delay": 10000,
+                   "max-response-delay": 60000,
+                   "max-ack-delay": 5000,
+                   "max-unacked-clients": 5,
+                   "peers": [{
+                       "name": "server1",
+                       "url": "http://192.168.56.33:8000/",
+                       "role": "primary",
+                       "auto-failover": true
+                   }, {
+                       "name": "server2",
+                       "url": "http://192.168.56.66:8000/",
+                       "role": "standby",
+                       "auto-failover": true
+                   }]
+               }]
+           }
+       }],
+
+       "subnet4": [{
+           "subnet": "192.0.3.0/24",
+           "pools": [{
+               "pool": "192.0.3.100 - 192.0.3.250",
+               }]
+       }]
+   }
+
+Server 2:
+::
+
+   "Dhcp4": {
+       "hooks-libraries": [{
+           "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+           "parameters": { }
+       }, {
+           "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+           "parameters": {
+               "high-availability": [{
+                   "this-server-name": "server2",
+                   "trust-anchor": /usr/lib/kea/CA.pem,
+                   "cert-file": /usr/lib/kea/server2_cert.pem,
+                   "key-file": /usr/lib/kea/server2_key.pem
+                   "mode": "hot-standby",
+                   "heartbeat-delay": 10000,
+                   "max-response-delay": 60000,
+                   "max-ack-delay": 5000,
+                   "max-unacked-clients": 5,
+                   "peers": [{
+                       "name": "server1",
+                       "url": "http://192.168.56.33:8000/",
+                       "role": "primary",
+                       "auto-failover": true
+                   }, {
+                       "name": "server2",
+                       "url": "http://192.168.56.66:8000/",
+                       "role": "standby",
+                       "auto-failover": true
+                   }]
+               }]
+           }
+       }],
+
+       "subnet4": [{
+           "subnet": "192.0.3.0/24",
+           "pools": [{
+               "pool": "192.0.3.100 - 192.0.3.250",
+               }]
+       }]
+   }
+
+Control Agent on Server 1:
+::
+
+    {
+        "Control-agent": {
+            "http-host": "192.168.56.33",
+            "http-port": 8000,
+            "control-sockets": {
+                "dhcp4": {
+                    "socket-type": "unix",
+                    "socket-name": "/var/run/kea/control_socket"
+                }
+            },
+            "trust-anchor": "/var/lib/kea/CA.pem",
+            "cert-file": "/var/lib/kea/server1_cert.pem",
+            "key-file": "/var/lib/kea/server1_key.pem",
+            "cert-required": true
+        }
+    }
+
+Control Agent on Server 2:
+::
+
+    {
+        "Control-agent": {
+            "http-host": "192.168.56.66",
+            "http-port": 8000,
+            "control-sockets": {
+                "dhcp4": {
+                    "socket-type": "unix",
+                    "socket-name": "/var/run/kea/control_socket"
+                }
+            },
+            "trust-anchor": "/var/lib/kea/CA.pem",
+            "cert-file": "/var/lib/kea/server2_cert.pem",
+            "key-file": "/var/lib/kea/server2_key.pem",
+            "cert-required": true
+        }
+    }
+
+.. _ha-server-states:
+
+Server States
+~~~~~~~~~~~~~
+
+A DHCP server operating within an HA setup runs a state machine, and the state
+of the server can be retrieved by its peers using the ``ha-heartbeat`` command
+sent over the RESTful API. If the partner server does not respond to the
+``ha-heartbeat`` command within the specified amount of time, the communication
+is considered interrupted and the server may, depending on the configuration,
+use additional measures (described later in this document) to verify that the
+partner is still operating. If it finds that the partner is not operating, the
+server transitions to the ``partner-down`` state to handle all the DHCP traffic
+directed to the system.
+
+In this case, the surviving server continues to send the ``ha-heartbeat``
+command to detect when the partner wakes up. At that time, the partner
+synchronizes the lease database. When it is again ready to operate, the
+surviving server returns to normal operation, i.e. the ``load-balancing`` or
+``hot-standby`` state.
+
+The following is the list of all possible server states:
+
+-  ``backup`` - normal operation of the backup server. In this state it receives
+   lease updates from the active server(s).
+
+-  ``communication-recovery`` - an active server running in ``load-balancing``
+   mode may transition to this state when it experiences communication issues
+   with a partner server over the control channel. This is an intermediate state
+   between the ``load-balancing`` and ``partner-down`` states. In this state the
+   server continues to respond to DHCP queries but does not send lease updates
+   to the partner; lease updates are queued and are sent when normal
+   communication is resumed. If communication does not resume within the time
+   specified, the primary server then transitions to the ``partner-down`` state.
+   The ``communication-recovery`` state was introduced to ensure reliable DHCP
+   service when both active servers remain operational but the communication
+   between them is interrupted for a prolonged period of time. Either server can
+   be configured to never enter this state by setting the
+   ``delayed-updates-limit`` to 0 (please refer to
+   :ref:`ha-load-balancing-config`, later in this chapter, for details on this
+   parameter). Disabling entry into the ``communication-recovery`` state causes
+   the server to begin testing for the ``partner-down`` state as soon as the
+   server is unable to communicate with its partner.
+
+.. note::
+
+   In Kea 1.9.4, with the introduction of ``delayed-updates-limit``, the default
+   server's behavior in ``load-balancing`` mode changed. When a server
+   experiences communication issues with its partner, it now enters the
+   ``communication-recovery`` state and queues lease updates until communication
+   is resumed. Prior to Kea 1.9.4, a server that could not communicate with its
+   partner in ``load-balancing`` mode would immediately begin the transition to
+   the ``partner-down`` state.
+
+-  ``hot-standby`` - normal operation of the active server running in the
+   ``hot-standby`` mode; both the primary and the standby server are in this
+   state during their normal operation. The primary server responds to DHCP
+   queries and sends lease updates to the standby server and to any backup
+   servers that are present.
+
+-  ``load-balancing`` - normal operation of the active server running in the
+   ``load-balancing`` mode; both the primary and the secondary server are in
+   this state during their normal operation. Both servers respond to DHCP
+   queries and send lease updates to each other and to any backup servers that
+   are present.
+
+-  ``in-maintenance`` - an active server transitions to this state as a result
+   of being notified by its partner that the administrator requested maintenance
+   of the HA setup. The administrator requests the maintenance by sending the
+   ``ha-maintenance-start`` command to the server which is supposed to take over
+   the responsibility for responding to the DHCP clients while the other server
+   is taken offline for maintenance. If the server is in the ``in-maintenance``
+   state it can be safely shut down. The partner transitions to the
+   ``partner-down`` state immediately after discovering that the server in
+   maintenance has been shut down.
+
+-  ``partner-down`` - an active server transitions to this state after detecting
+   that its partner (another active server) is offline. The server does not
+   transition to this state if only a backup server is unavailable. In the
+   ``partner-down`` state the active server responds to all DHCP queries,
+   including those queries which are normally handled by the server that is now
+   unavailable.
+
+-  ``partner-in-maintenance`` - an active server transitions to this state
+   after receiving a ``ha-maintenance-start`` command from the administrator.
+   The server in this state becomes responsible for responding to all DHCP
+   requests. The server sends a ``ha-maintenance-notify`` command to the partner,
+   which should enter the ``in-maintenance`` state. The server remaining in the
+   ``partner-in-maintenance`` state keeps sending lease updates to the partner
+   until it finds that the partner has stopped responding to those lease updates,
+   heartbeats, or any other commands. In this case, the server in the
+   ``partner-in-maintenance`` state transitions to the ``partner-down`` state
+   and keeps responding to the queries, but no longer sends lease updates.
+
+-  ``passive-backup`` - a primary server running in the ``passive-backup`` HA
+   mode transitions to this state immediately after it boots up. The primary
+   server in this state responds to all DHCP traffic and sends lease updates to
+   the backup servers it is connected to. By default, the primary server does
+   not wait for acknowledgments from the backup servers and responds to a DHCP
+   query right after sending lease updates to all backup servers. If any of the
+   lease updates fail, a backup server misses the lease update but the DHCP
+   client is still provisioned. This default configuration can be changed by
+   setting the ``wait-backup-ack`` configuration parameter to ``true``, in which
+   case the primary server always waits for the acknowledgements and drops the
+   DHCP query if sending any of the corresponding lease updates fails. This
+   improves lease database consistency between the primary and the secondary.
+   However, if a communication failure between the active server and any of the
+   backups occurs, it effectively causes the failure of the DHCP service from
+   the DHCP clients' perspective.
+
+-  ``ready`` - an active server transitions to this state after synchronizing
+   its lease database with an active partner. This state indicates to the
+   partner (which may be in the ``partner-down`` state) that it should return to
+   normal operation. If and when it does, the server in the ``ready`` state also
+   starts normal operation.
+
+-  ``syncing`` - an active server transitions to this state to fetch leases from
+   the active partner and update the local lease database. When in this state,
+   the server issues the ``dhcp-disable`` command to disable the DHCP service of
+   the partner from which the leases are fetched. The DHCP service is disabled
+   for a maximum time of 60 seconds, after which it is automatically re-enabled,
+   in case the syncing partner was unable to re-enable the service. If the
+   synchronization completes successfully, the synchronizing server issues the
+   ``ha-sync-complete-notify`` command to notify the partner. In most states,
+   the partner re-enables its DHCP service to continue responding to the DHCP
+   queries. In the ``partner-down`` state, the partner first ensures that
+   communication between the servers is re-established before enabling the DHCP
+   service. The syncing operation is synchronous; the server waits for an answer
+   from the partner and does nothing else while the lease synchronization takes
+   place. A server that is configured not to synchronize the lease database with
+   its partner, i.e. when the ``sync-leases`` configuration parameter is set to
+   ``false``, will never transition to this state. Instead, it transitions
+   directly from the ``waiting`` state to the ``ready`` state.
+
+-  ``terminated`` - an active server transitions to this state when the High
+   Availability hook library is unable to further provide reliable service and a
+   manual intervention of the administrator is required to correct the problem.
+   Various issues with the HA setup may cause the server to transition to this
+   state. While in this state, the server continues responding to DHCP clients
+   based on the HA mode selected (``load-balancing`` or ``hot-standby``), but
+   lease updates are not exchanged and heartbeats are not sent. Once a server
+   has entered the ``terminated`` state, it remains in this state until it is
+   restarted. The administrator must correct the issue which caused this
+   situation prior to restarting the server (e.g. synchronize the clocks);
+   otherwise, the server will return to the ``terminated`` state once it finds
+   that the issue persists.
+
+-  ``waiting`` - each started server instance enters this state. A backup server
+   transitions directly from this state to the ``backup`` state. An active
+   server sends a heartbeat to its partner to check its state; if the partner
+   appears to be unavailable, the server transitions to the ``partner-down``
+   state. If the partner is available, the server transitions to the ``syncing``
+   or ``ready`` state, depending on the setting of the ``sync-leases``
+   configuration parameter. If both servers appear to be in the ``waiting``
+   state (concurrent startup), the primary server transitions to the next state
+   first. The secondary or standby server remains in the ``waiting`` state until
+   the primary transitions to the ``ready`` state.
+
+.. note::
+
+   Currently, restarting the HA service from the ``terminated`` state requires
+   restarting the DHCP server or reloading its configuration.
+
+Whether the server responds to DHCP queries and which queries it responds to is
+a matter of the server's state, if no administrative action is performed to
+configure the server otherwise. The following table provides the default
+behavior for various states.
+
+The ``DHCP Service Scopes`` denote which group of received DHCP queries the
+server responds to in the given state. The HA configuration must specify a
+unique name for each server within the HA setup. This document uses the
+following convention within the provided examples: "server1" for a primary
+server, "server2" for the secondary or standby server, and "server3" for the
+backup server. In real life any names can be used as long as they remain unique.
+
+An in-depth explanation of the scopes can be found below.
+
+.. table:: Default behavior of the server in various HA states
+
+   +------------------------+-----------------+-----------------+----------------+
+   | State                  | Server Type     | DHCP Service    | DHCP Service   |
+   |                        |                 |                 | Scopes         |
+   +========================+=================+=================+================+
+   | backup                 | backup server   | disabled        | none           |
+   +------------------------+-----------------+-----------------+----------------+
+   | communication-recovery | primary or      | enabled         | "HA_server1"   |
+   |                        | secondary       |                 | or             |
+   |                        | (load-balancing |                 | "HA_server2"   |
+   |                        | mode only)      |                 |                |
+   +------------------------+-----------------+-----------------+----------------+
+   | hot-standby            | primary or      | enabled         | "HA_server1"   |
+   |                        | standby         |                 | if primary,    |
+   |                        | (hot-standby    |                 | none otherwise |
+   |                        | mode)           |                 |                |
+   +------------------------+-----------------+-----------------+----------------+
+   | load-balancing         | primary or      | enabled         | "HA_server1"   |
+   |                        | secondary       |                 | or             |
+   |                        | (load-balancing |                 | "HA_server2"   |
+   |                        | mode)           |                 |                |
+   +------------------------+-----------------+-----------------+----------------+
+   | in-maintenance         | active server   | disabled        | none           |
+   +------------------------+-----------------+-----------------+----------------+
+   | partner-down           | active server   | enabled         | all scopes     |
+   +------------------------+-----------------+-----------------+----------------+
+   | partner-in-maintenance | active server   | enabled         | all scopes     |
+   +------------------------+-----------------+-----------------+----------------+
+   | passive-backup         | active server   | enabled         | all scopes     |
+   +------------------------+-----------------+-----------------+----------------+
+   | ready                  | active server   | disabled        | none           |
+   +------------------------+-----------------+-----------------+----------------+
+   | syncing                | active server   | disabled        | none           |
+   +------------------------+-----------------+-----------------+----------------+
+   | terminated             | active server   | enabled         | same as in the |
+   |                        |                 |                 | load-balancing |
+   |                        |                 |                 | or hot-standby |
+   |                        |                 |                 | state          |
+   +------------------------+-----------------+-----------------+----------------+
+   | waiting                | any server      | disabled        | none           |
+   +------------------------+-----------------+-----------------+----------------+
+
+In the ``load-balancing`` mode there are two scopes specified for the active
+servers: "HA_server1" and "HA_server2". The DHCP queries load-balanced to
+``server1`` belong to the "HA_server1" scope and the queries load-balanced to
+``server2`` belong to the "HA_server2" scope. If either server is in the
+``partner-down`` state, the active partner is responsible for serving both
+scopes.
+
+In the ``hot-standby`` mode, there is only one scope - "HA_server1" - because
+only ``server1`` is responding to DHCP queries. If that server becomes
+unavailable, ``server2`` becomes responsible for this scope.
+
+The backup servers do not have their own scopes. In some cases they can be used
+to respond to queries belonging to the scopes of the active servers. Also, a
+backup server which is neither in the ``partner-down`` state nor in normal
+operation serves no scopes.
+
+The scope names can be used to associate pools, subnets, and networks with
+certain servers, so that only these servers can allocate addresses or prefixes
+from those pools, subnets, or networks. This is done via the client
+classification mechanism (see :ref:`ha-load-balancing-advanced-config` for more
+details).
+
+.. _ha-scope-transition:
+
+Scope Transition in a Partner-Down Case
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When one of the servers finds that its partner is unavailable, it starts serving
+clients from both its own scope and the scope of the unavailable partner. This
+is straightforward for new clients, i.e. those sending DHCPDISCOVER (DHCPv4) or
+Solicit (DHCPv6), because those requests are not sent to any particular server.
+The available server responds to all such queries when it is in the
+``partner-down`` state.
+
+When a client renews a lease, it sends its DHCPREQUEST (DHCPv4) or Renew (DHCPv6)
+message directly to the server which has allocated the lease being renewed. If
+this server is no longer available, the client will get no response. In that
+case, the client continues to use its lease and attempts to renew until the
+rebind timer (T2) elapses. The client then enters the rebinding phase, in which
+it sends a DHCPREQUEST (DHCPv4) or Rebind (DHCPv6) message to any available
+server. The surviving server receives the rebinding request and typically
+extends the lifetime of the lease. The client then continues to contact that new
+server to renew its lease as appropriate.
+
+If and when the other server once again becomes available, both active servers
+will eventually transition to the ``load-balancing`` or ``hot-standby`` state,
+in which they will again be responsible for their own scopes. Some clients
+belonging to the scope of the restarted server will try to renew their leases
+via the surviving server, but this server will no longer respond to them; the
+client will eventually transition back to the correct server via the rebinding
+mechanism.
+
+.. _ha-load-balancing-config:
+
+Load-Balancing Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following is the configuration snippet to enable high availability on the
+primary server within the ``load-balancing`` configuration. The same
+configuration should be applied on the secondary and backup servers, with the
+only difference that ``this-server-name`` should be set to "server2" and
+"server3" on those servers, respectively.
+
+.. note::
+
+   Remember that ``load-balancing`` mode requires the address pools and
+   delegated prefix pools to be split between the active servers. During normal
+   operation, the servers use non-overlapping pools to avoid allocating the same
+   lease to different clients by both instances. A server only uses the pool
+   fragments owned by the partner when the partner is not running. See the notes
+   in :ref:`ha-supported-configurations` highlighting differences between the
+   ``load-balancing`` and ``hot-standby`` modes. The semantics of pool
+   partitioning is explained further in this section.
+   The :ref:`ha-load-balancing-advanced-config` section provides advanced
+   pool-partitioning examples.
+
+::
+
+   "Dhcp4": {
+       "hooks-libraries": [{
+           "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+           "parameters": { }
+       }, {
+           "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+           "parameters": {
+               "high-availability": [{
+                   "this-server-name": "server1",
+                   "mode": "load-balancing",
+                   "heartbeat-delay": 10000,
+                   "max-response-delay": 60000,
+                   "max-ack-delay": 5000,
+                   "max-unacked-clients": 5,
+                   "delayed-updates-limit": 100,
+                   "peers": [{
+                       "name": "server1",
+                       "url": "http://192.168.56.33:8000/",
+                       "role": "primary",
+                       "auto-failover": true
+                   }, {
+                       "name": "server2",
+                       "url": "http://192.168.56.66:8000/",
+                       "role": "secondary",
+                       "auto-failover": true
+                   }, {
+                       "name": "server3",
+                       "url": "http://192.168.56.99:8000/",
+                       "role": "backup",
+                       "basic-auth-user": "foo",
+                       "basic-auth-password": "bar",
+                       "auto-failover": false
+                   }]
+               }]
+           }
+       }],
+
+       "subnet4": [{
+           "subnet": "192.0.3.0/24",
+           "pools": [{
+               "pool": "192.0.3.100 - 192.0.3.150",
+               "client-class": "HA_server1"
+            }, {
+               "pool": "192.0.3.200 - 192.0.3.250",
+               "client-class": "HA_server2"
+            }],
+
+            "option-data": [{
+               "name": "routers",
+               "data": "192.0.3.1"
+            }],
+
+            "relay": { "ip-address": "10.1.2.3" }
+       }]
+   }
+
+Two hook libraries must be loaded to enable HA: ``libdhcp_lease_cmds.so`` and
+``libdhcp_ha.so``. The latter implements the HA feature, while the former
+enables control commands required by HA to fetch and manipulate leases on the
+remote servers. In the example provided above, it is assumed that Kea libraries
+are installed in the ``/usr/lib`` directory. If Kea is not installed in the
+``/usr`` directory, the hook libraries' locations must be updated accordingly.
+
+The HA configuration is specified within the scope of ``libdhcp_ha.so``.
+Note that while the top-level parameter ``high-availability`` is a list, only a
+single entry is currently supported.
+
+The following are the global parameters which control the server's behavior with
+respect to HA:
+
+-  ``this-server-name`` - is a unique identifier of the server within this HA
+   setup. It must match one of the servers specified within the ``peers`` list.
+
+-  ``mode`` - specifies an HA mode of operation. The currently supported modes
+   are ``load-balancing`` and ``hot-standby``.
+
+-  ``heartbeat-delay`` - specifies a duration in milliseconds between sending
+   the last heartbeat (or other command sent to the partner) and the next
+   heartbeat. Heartbeats are sent periodically to gather the status of the
+   partner and to verify whether the partner is still operating. The default
+   value of this parameter is 10000 ms.
+
+-  ``max-response-delay`` - specifies a duration in milliseconds since the last
+   successful communication with the partner, after which the server assumes
+   that communication with the partner is interrupted. This duration should be
+   greater than the ``heartbeat-delay``; typically it should be a multiple of
+   ``heartbeat-delay``. When the server detects that communication is
+   interrupted, it may transition to the ``partner-down`` state (when
+   ``max-unacked-clients`` is 0) or trigger the failure-detection procedure
+   using the values of the two parameters below. The default value of this
+   parameter is 60000 ms.
+
+-  ``max-ack-delay`` - is one of the parameters controlling partner
+   failure-detection. When communication with the partner is interrupted, the
+   server examines the values of the "secs" field (DHCPv4) or "elapsed time"
+   option (DHCPv6), which denote how long the DHCP client has been trying to
+   communicate with the DHCP server. This parameter specifies the maximum time
+   in milliseconds for the client to try to communicate with the DHCP server,
+   after which this server assumes that the client failed to communicate with
+   the DHCP server (is unacknowledged or "unacked"). The default value of this
+   parameter is 10000.
+
+-  ``max-unacked-clients`` - specifies how many "unacked" clients are allowed
+   (see ``max-ack-delay``) before this server assumes that the partner is
+   offline and transitions to the ``partner-down`` state. The special value of 0
+   is allowed for this parameter, which disables the failure-detection mechanism.
+   In this case, a server that cannot communicate with its partner over the
+   control channel assumes that the partner server is down and transitions to
+   the ``partner-down`` state immediately. The default value of this parameter
+   is 10.
+
+-  ``delayed-updates-limit`` - specifies the maximum number of lease updates
+   which can be queued while the server is in the ``communication-recovery``
+   state. This parameter was introduced in Kea 1.9.4. The special value of 0
+   configures the server to never transition to the ``communication-recovery``
+   state and the server behaves as in earlier Kea versions, i.e. if the server
+   cannot reach its partner, it goes straight into the ``partner-down`` state.
+   The default value of this parameter is 100.
+
+The values of ``max-ack-delay`` and ``max-unacked-clients`` must be selected
+carefully, taking into account the specifics of the network in which the DHCP
+servers are operating. The server in question may not respond to some DHCP
+clients following administrative policy, or the server may drop malformed
+queries from clients. Therefore, selecting too low a value for the
+``max-unacked-clients`` parameter may result in a transition to the
+``partner-down`` state even though the partner is still operating. On the other
+hand, selecting too high a value may result in never transitioning to the
+``partner-down`` state if the DHCP traffic in the network is very low (e.g. at
+night), because the number of distinct clients trying to communicate with the
+server could be lower than the ``max-unacked-clients`` setting.
+
+In some cases it may be useful to disable the failure-detection mechanism
+altogether, if the servers are located very close to each other and network
+partitioning is unlikely, i.e. failure to respond to heartbeats is only possible
+when the partner is offline. In such cases, set ``max-unacked-clients`` to 0.
+
+The ``delayed-updates-limit`` parameter is used to enable or disable the
+``communication-recovery`` procedure, and controls the server's behavior in the
+``communication-recovery`` state. This parameter can only be used in the
+``load-balancing`` mode.
+
+If a server in the ``load-balancing`` state experiences communication issues
+with its partner (a heartbeat or lease-update failure), the server transitions
+to the ``communication-recovery`` state. In this state, the server keeps
+responding to DHCP queries but does not send lease updates to the partner. The
+lease updates are queued until communication is re-established, to ensure that
+DHCP service remains available even in the event of the communication loss
+between the partners. There may appear to be communication loss when either one
+of the servers has terminated, or when both servers remain available but cannot
+communicate with each other. In the former case, the surviving server will
+follow the normal procedure and should eventually transition to the
+``partner-down`` state. In the latter case, both servers should transition to
+the ``communication-recovery`` state and should never transition to the
+``partner-down`` state (if ``max-unacked-clients`` is set to a non-zero value),
+because all DHCP queries are answered and neither server would see any unacked
+DHCP queries.
+
+Introduction of the ``communication-recovery`` procedure was motivated by issues
+which may appear when two servers remain online but the communication between
+them remains interrupted for a period of time. In earlier Kea versions, the
+servers having communication issues used to drop DHCP packets before
+transitioning to the ``partner-down`` state. In some cases they both
+transitioned to the ``partner-down`` state, which could potentially result in
+allocations of the same IP addresses or delegated prefixes to different clients
+by both servers. By entering the intermediate ``communication-recovery`` state,
+these problems are avoided.
+
+If a server in the ``communication-recovery`` state re-establishes communication
+with its partner, it tries to send the partner all of the outstanding lease
+updates it has queued. This is done synchronously and may take a considerable
+amount of time before the server transitions to the ``load-balancing`` state and
+resumes normal operation.
+The maximum number of lease updates which can be queued in the
+``communication-recovery`` state is controlled by ``delayed-updates-limit``.
+If the limit is exceeded, the server stops queuing lease updates and performs a
+full database synchronization after re-establishing the connection with the
+partner, instead of sending outstanding lease updates before transitioning to
+the ``load-balancing`` state. Even if the limit is exceeded, the server in the
+``communication-recovery`` state remains responsive to DHCP clients.
+
+It may be preferable to set higher values of ``delayed-updates-limit`` when
+there is a risk of prolonged communication interruption between the servers and
+when the lease database is large, to avoid costly lease-database synchronization.
+On the other hand, if the lease database is small, the time required to send
+outstanding lease updates may be longer than the lease-database synchronization.
+In such cases it may be better to use a lower value, e.g. 10. The default value
+of 100 is a reasonable compromise and should work well in most deployments with
+moderate traffic.
+
+.. note::
+
+   This parameter is new and values for it that work well in some environments
+   may not work well in others. Feedback from users will help us build a better
+   working set of recommendations.
+
+The ``peers`` parameter contains a list of servers within this HA setup.
+This configuration must contain at least one primary and one secondary server.
+It may also contain an unlimited number of backup servers. In this example,
+there is one backup server which receives lease updates from the active servers.
+
+Since Kea version 1.9.0, basic HTTP authentication is available
+to protect the Kea control agent against local attackers.
+
+These are the parameters specified for each of the peers within this
+list:
+
+-  ``name`` - specifies a unique name for the server.
+
+-  ``url`` - specifies the URL to be used to contact this server over the
+   control channel. Other servers use this URL to send control commands to that
+   server.
+
+-  ``basic-auth-user`` - specifies the user ID for basic HTTP authentication. If
+   not specified or specified as an empty string, no authentication header is
+   added to HTTP transactions. It must not contain the colon (:) character.
+
+-  ``basic-auth-password`` - specifies the password for basic HTTP
+   authentication. This parameter is ignored when the user ID is not specified
+   or is empty. The password is optional; if not specified, an empty password is
+   used.
+
+-  ``basic-auth-password-file`` - is an alternative to ``basic-auth-password``:
+   instead of presenting the password in the configuration file it is specified
+   in the file indicated by this parameter.
+
+-  ``role`` - denotes the role of the server in the HA setup. The following
+   roles are supported in the ``load-balancing`` configuration: ``primary``,
+   ``secondary``, and ``backup``. There must be exactly one primary and one
+   secondary server in the ``load-balancing`` setup.
+
+-  ``auto-failover`` - a boolean value which denotes whether a server detecting
+   a partner's failure should automatically start serving the partner's clients.
+   The default value of this parameter is ``true``.
+
+In our example configuration above, both active servers can allocate leases from
+the subnet "192.0.3.0/24". This subnet contains two address pools:
+"192.0.3.100 - 192.0.3.150" and "192.0.3.200 - 192.0.3.250", which are
+associated with HA server scopes using client classification. When ``server1``
+processes a DHCP query, it uses the first pool for lease allocation. Conversely,
+when ``server2`` processes a DHCP query it uses the second pool. If either of
+the servers is in the ``partner-down`` state, the other can serve leases from
+both pools; it selects the pool which is appropriate for the received query. In
+other words, if the query would normally be processed by ``server2`` but this
+server is not available, ``server1`` allocates the lease from the pool of
+"192.0.3.200 - 192.0.3.250". The Kea control agent in front of ``server3``
+requires basic HTTP authentication, and authorizes the user ID "foo" with the
+password "bar".
+
+.. note::
+
+   The ``url`` schema can be ``http`` or ``https``, but since Kea version 1.9.6
+   the ``https`` schema requires a TLS setup. The hostname part must be an IPv4
+   address or an IPv6 address between square brackets, e.g.
+   ``http://[2001:db8::1]:8080/``. Names are not accepted.
+
+.. _ha-load-balancing-advanced-config:
+
+Load Balancing With Advanced Classification
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In the previous section, we provided an example of a ``load-balancing``
+configuration with client classification limited to the "HA_server1" and
+"HA_server2" classes, which are dynamically assigned to the received DHCP
+queries. In many cases, HA is needed in deployments which already use some other
+client classification.
+
+Suppose there is a system which classifies devices into two groups: "phones" and
+"laptops", based on some classification criteria specified in the Kea
+configuration file. Both types of devices are allocated leases from different
+address pools. Introducing HA in ``load-balancing`` mode results in a further
+split of each of those pools, as each server allocates leases for some phones
+and some laptops. This requires each of the existing pools to be split between
+"HA_server1" and "HA_server2", so we end up with the following classes:
+
+-  "phones_server1"
+-  "laptops_server1"
+-  "phones_server2"
+-  "laptops_server2"
+
+The corresponding server configuration, using advanced classification (and the
+``member`` expression), is provided below. For brevity's sake, the HA hook
+library configuration has been removed from this example.
+
+::
+
+   "Dhcp4": {
+       "client-classes": [{
+           "name": "phones",
+           "test": "substring(option[60].hex,0,6) == 'Aastra'",
+       }, {
+           "name": "laptops",
+           "test": "not member('phones')"
+       }, {
+           "name": "phones_server1",
+           "test": "member('phones') and member('HA_server1')"
+       }, {
+           "name": "phones_server2",
+           "test": "member('phones') and member('HA_server2')"
+       }, {
+           "name": "laptops_server1",
+           "test": "member('laptops') and member('HA_server1')"
+       }, {
+           "name": "laptops_server2",
+           "test": "member('laptops') and member('HA_server2')"
+       }],
+
+       "hooks-libraries": [{
+           "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+           "parameters": { }
+       }, {
+           "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+           "parameters": {
+               "high-availability": [{
+                  ...
+               }]
+           }
+       }],
+
+       "subnet4": [{
+           "subnet": "192.0.3.0/24",
+           "pools": [{
+               "pool": "192.0.3.100 - 192.0.3.125",
+               "client-class": "phones_server1"
+           }, {
+               "pool": "192.0.3.126 - 192.0.3.150",
+               "client-class": "laptops_server1"
+           }, {
+               "pool": "192.0.3.200 - 192.0.3.225",
+               "client-class": "phones_server2"
+           }, {
+               "pool": "192.0.3.226 - 192.0.3.250",
+               "client-class": "laptops_server2"
+           }],
+
+           "option-data": [{
+               "name": "routers",
+               "data": "192.0.3.1"
+           }],
+
+           "relay": { "ip-address": "10.1.2.3" }
+       }],
+   }
+
+The configuration provided above splits the address range into four pools: two
+pools dedicated to "HA_server1" and two to "HA_server2". Each server can assign
+leases to both phones and laptops. Both groups of devices are assigned addresses
+from different pools. The "HA_server1" and "HA_server2" classes are built-in
+(see :ref:`classification-using-vendor`) and do not need to be declared.
+They are assigned dynamically by the HA hook library as a result of the
+``load-balancing`` algorithm. "phones_*" and "laptop_*" evaluate to ``true``
+when the query belongs to a given combination of other classes, e.g. "HA_server1"
+and "phones". The pool is selected accordingly as a result of such an evaluation.
+
+Consult :ref:`classify` for details on how to use the ``member`` expression and
+class dependencies.
+
+.. _ha-hot-standby-config:
+
+Hot-Standby Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following is an example configuration of the primary server in a
+``hot-standby`` configuration:
+
+::
+
+   "Dhcp4": {
+       "hooks-libraries": [{
+           "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+           "parameters": { }
+       }, {
+           "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+           "parameters": {
+               "high-availability": [{
+                   "this-server-name": "server1",
+                   "mode": "hot-standby",
+                   "heartbeat-delay": 10000,
+                   "max-response-delay": 60000,
+                   "max-ack-delay": 5000,
+                   "max-unacked-clients": 5,
+                   "peers": [{
+                       "name": "server1",
+                       "url": "http://192.168.56.33:8000/",
+                       "role": "primary",
+                       "auto-failover": true
+                   }, {
+                       "name": "server2",
+                       "url": "http://192.168.56.66:8000/",
+                       "role": "standby",
+                       "auto-failover": true
+                   }, {
+                       "name": "server3",
+                       "url": "http://192.168.56.99:8000/",
+                       "basic-auth-user": "foo",
+                       "basic-auth-password": "bar",
+                       "role": "backup",
+                       "auto-failover": false
+                   }]
+               }]
+           }
+       }],
+
+       "subnet4": [{
+           "subnet": "192.0.3.0/24",
+           "pools": [{
+               "pool": "192.0.3.100 - 192.0.3.250",
+               "client-class": "HA_server1"
+           }],
+
+           "option-data": [{
+               "name": "routers",
+               "data": "192.0.3.1"
+           }],
+
+           "relay": { "ip-address": "10.1.2.3" }
+       }]
+   }
+
+This configuration is very similar to the ``load-balancing`` configuration
+described in :ref:`ha-load-balancing-config`, with a few notable differences.
+
+The ``mode`` is now set to ``hot-standby``, in which only one server responds to
+DHCP clients. If the primary server is online, it responds to all DHCP queries.
+The ``standby`` server takes over all DHCP traffic only if it discovers that the
+primary is unavailable.
+
+In this mode, the non-primary active server is called ``standby`` and that is
+its role.
+
+Finally, because there is always only one server responding to DHCP queries,
+there is only one scope - "HA_server1" - in use within pool definitions. In fact,
+the ``client-class`` parameter could be removed from this configuration without
+harm, because there can be no conflicts in lease allocations by different
+servers as they do not allocate leases concurrently. The ``client-class``
+remains in this example mostly for demonstration purposes, to highlight the
+differences between the ``hot-standby`` and ``load-balancing`` modes of
+operation.
+
+.. _ha-passive-backup-config:
+
+Passive-Backup Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following is an example configuration file for the primary server in a
+``passive-backup`` configuration:
+
+::
+
+   "Dhcp4": {
+       "hooks-libraries": [{
+           "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+           "parameters": { }
+       }, {
+           "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+           "parameters": {
+               "high-availability": [{
+                   "this-server-name": "server1",
+                   "mode": "passive-backup",
+                   "wait-backup-ack": false,
+                   "peers": [{
+                       "name": "server1",
+                       "url": "http://192.168.56.33:8000/",
+                       "role": "primary"
+                   }, {
+                       "name": "server2",
+                       "url": "http://192.168.56.66:8000/",
+                       "role": "backup"
+                   }, {
+                       "name": "server3",
+                       "url": "http://192.168.56.99:8000/",
+                       "basic-auth-user": "foo",
+                       "basic-auth-password": "bar",
+                       "role": "backup"
+                   }]
+               }]
+           }
+       }],
+
+       "subnet4": [{
+           "subnet": "192.0.3.0/24",
+           "pools": [{
+               "pool": "192.0.3.100 - 192.0.3.250",
+           }],
+
+           "option-data": [{
+               "name": "routers",
+               "data": "192.0.3.1"
+           }],
+
+           "relay": { "ip-address": "10.1.2.3" }
+       }]
+   }
+
+The configurations of three peers are included: one for the primary and two for
+the backup servers.
+
+Many of the parameters present in the ``load-balancing`` and ``hot-standby``
+configuration examples are not relevant in the ``passive-backup`` mode, thus
+they are not specified here. For example: ``heartbeat-delay``,
+``max-unacked-clients``, and others related to the automatic failover mechanism
+should not be specified in the ``passive-backup`` mode.
+
+The ``wait-backup-ack`` is a boolean parameter not present in previous examples.
+It defaults to ``false`` and must not be modified in the ``load-balancing`` and
+``hot-standby`` modes. In the ``passive-backup`` mode this parameter can be set
+to ``true``, which causes the primary server to expect acknowledgments to the
+lease updates from the backup servers prior to responding to the DHCP client. It
+ensures that the lease has propagated to all servers before the client is given
+the lease, but it poses a risk of losing a DHCP service if there is a
+communication problem with one of the backup servers. This setting also
+increases the latency of the DHCP response, because of the time that the primary
+spends waiting for the acknowledgements. We recommend that the
+``wait-backup-ack`` setting be left at its default value (``false``) if the DHCP
+service reliability is more important than consistency of the lease information
+between the primary and the backups, and in all cases when the DHCP service
+latency should be minimal.
+
+.. note::
+
+   Currently, active servers place lease updates to be sent to peers onto
+   internal queues (one queue per peer/URL). In ``passive-backup`` mode, active
+   servers do not wait for lease updates to be acknowledged; thus during times
+   of heavy client traffic it is possible for the number of lease updates queued
+   for transmission to accumulate faster than they can be delivered. As client
+   traffic lessens the queues begin to empty. Since Kea 2.0.0, active servers
+   monitor the size of these queues and emit periodic warnings (see
+   HTTP_CLIENT_QUEUE_SIZE_GROWING in :ref:`kea-messages`) if they perceive a
+   queue as growing too quickly. The warnings cease once the queue size begins
+   to shrink. These messages are intended as a bellwether and seeing them
+   sporadically during times of heavy traffic load does not necessarily indicate
+   a problem. If, however, they occur continually during times of routine
+   traffic load, they likely indicate potential mismatches in server
+   capabilities and/or configuration; this should be investigated, as the size
+   of the queues may eventually impair an active server's ability to respond to
+   clients in a timely manner.
+
+.. _ha-sharing-lease-info:
+
+Lease Information Sharing
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+An HA-enabled server informs its active partner about allocated or renewed
+leases by sending appropriate control commands, and the partner updates the
+lease information in its own database. When the server starts up for the first
+time or recovers after a failure, it synchronizes its lease database with its
+partner. These two mechanisms guarantee consistency of the lease information
+between the servers and allow the designation of one of the servers to handle
+the entire DHCP traffic load if the other server becomes unavailable.
+
+In some cases, though, it is desirable to disable lease updates and/or database
+synchronization between the active servers, if the exchange of information about
+the allocated leases is performed using some other mechanism. Kea supports
+various database types that can be used to store leases, including MySQL and
+PostgreSQL. Those databases include built-in solutions for data replication
+which are often used by Kea administrators to provide redundancy.
+
+The HA hook library supports such scenarios by disabling lease updates over the
+control channel and/or lease-database synchronization, leaving the server to
+rely on the database replication mechanism. This is controlled by the two
+boolean parameters ``send-lease-updates`` and ``sync-leases``, whose values
+default to ``true``:
+
+::
+
+   {
+   "Dhcp4": {
+
+       ...
+
+       "hooks-libraries": [
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+               "parameters": { }
+           },
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+               "parameters": {
+                   "high-availability": [ {
+                       "this-server-name": "server1",
+                       "mode": "load-balancing",
+                       "send-lease-updates": false,
+                       "sync-leases": false,
+                       "peers": [
+                           {
+                               "name": "server1",
+                               "url": "http://192.168.56.33:8000/",
+                               "role": "primary"
+                           },
+                           {
+                               "name": "server2",
+                               "url": "http://192.168.56.66:8000/",
+                               "role": "secondary"
+                           }
+                       ]
+                   } ]
+               }
+           }
+       ],
+
+       ...
+
+   }
+
+In the most typical use case, both parameters are set to the same value, i.e.
+both are ``false`` if database replication is in use, or both are ``true``
+otherwise. Introducing two separate parameters to control lease updates and
+lease-database synchronization is aimed at possible special use cases; for
+example, when synchronization is performed by copying a lease file (therefore
+``sync-leases`` is set to ``false``), but lease updates should be conducted as
+usual (``send-lease-updates`` is set to ``true``). It should be noted that Kea
+does not natively support such use cases, but users may develop their own
+scripts and tools around Kea to provide such mechanisms. The HA hook library
+configuration is designed to maximize flexibility of administration.
+
+.. _ha-syncing-page-limit:
+
+Controlling Lease-Page Size Limit
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+An HA-enabled server initiates synchronization of the lease database after
+downtime or upon receiving the ``ha-sync`` command. The server uses commands
+described in :ref:`command-lease4-get-page` and :ref:`command-lease6-get-page`
+to fetch leases from its partner server (lease queries). The size of the results
+page (the maximum number of leases to be returned in a single response to one of
+these commands) can be controlled via configuration of the HA hook library.
+Increasing the page size decreases the number of lease queries sent to the
+partner server, but it causes the partner server to generate larger responses,
+which lengthens transmission time as well as increases memory and CPU
+utilization on both servers. Decreasing the page size helps to decrease resource
+utilization, but requires more lease queries to be issued to fetch the entire
+lease database.
+
+The default value of the ``sync-page-limit`` command controlling the page size
+is 10000. This means that the entire lease database can be fetched with a single
+command if the size of the database is equal to or less than 10000 lines.
+
+.. _ha-syncing-timeouts:
+
+Timeouts
+~~~~~~~~
+
+In deployments with a large number of clients connected to the network,
+lease-database synchronization after a server failure may be a time-consuming
+operation. The synchronizing server must gather all leases from its partner,
+which yields a large response over the RESTful interface. The server receives
+leases using the paging mechanism described in :ref:`ha-syncing-page-limit`.
+Before the page of leases is fetched, the synchronizing server sends a
+``dhcp-disable`` command to disable the DHCP service on the partner server. If
+the service is already disabled, this command resets the timeout for the DHCP
+service being disabled, which by default is set to 60 seconds. If fetching a
+single page of leases takes longer than the specified time, the partner server
+assumes that the synchronizing server has died and resumes its DHCP service. The
+connection of the synchronizing server with its partner is also protected by the
+timeout. If the synchronization of a single page of leases takes longer than the
+specified time, the synchronizing server terminates the connection and the
+synchronization fails. Both timeout values are controlled by a single
+configuration parameter, ``sync-timeout``. The following configuration snippet
+demonstrates how to modify the timeout for automatic re-enabling of the DHCP
+service on the partner server and how to increase the timeout for fetching a
+single page of leases from 60 seconds to 90 seconds:
+
+::
+
+   {
+   "Dhcp4": {
+
+       ...
+
+       "hooks-libraries": [
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+               "parameters": { }
+           },
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+               "parameters": {
+                   "high-availability": [ {
+                       "this-server-name": "server1",
+                       "mode": "load-balancing",
+                       "sync-timeout": 90000,
+                       "peers": [
+                           {
+                               "name": "server1",
+                               "url": "http://192.168.56.33:8000/",
+                               "role": "primary"
+                           },
+                           {
+                               "name": "server2",
+                               "url": "http://192.168.56.66:8000/",
+                               "role": "secondary"
+                           }
+                       ]
+                   } ]
+               }
+           }
+       ],
+
+       ...
+
+   }
+
+It is important to note that extending this ``sync-timeout`` value may sometimes
+be insufficient to prevent issues with timeouts during lease-database
+synchronization. The control commands travel via the Control Agent, which also
+monitors incoming (with a synchronizing server) and outgoing (with a DHCP server)
+connections for timeouts. The DHCP server also monitors the connection from the
+Control Agent for timeouts. Those timeouts cannot currently be modified via
+configuration; extending these timeouts is only possible by modifying them in
+the Kea code and recompiling the server. The relevant constants are located in
+the Kea source at: ``src/lib/config/timeouts.h``.
+
+.. _ha-pause-state-machine:
+
+Pausing the HA State Machine
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``high-availability`` state machine includes many different states described
+in detail in :ref:`ha-server-states`. The server enters each state when certain
+conditions are met, most often taking into account the partner server's state.
+In some states the server performs specific actions, e.g. synchronization of the
+lease database in the ``syncing`` state, or responding to DHCP queries according
+to the configured mode of operation in the ``load-balancing`` and ``hot-standby``
+states.
+
+By default, transitions between the states are performed automatically and the
+server administrator has no direct control over when the transitions take place;
+in most cases, the administrator does not need such control. In some situations,
+however, the administrator may want to "pause" the HA state machine in a
+selected state to perform some additional administrative actions before the
+server transitions to the next state.
+
+Consider a server failure which results in the loss of the entire lease database.
+Typically, the server rebuilds its lease database when it enters the ``syncing``
+state by querying the partner server for leases, but it is possible that the
+partner was also experiencing a failure and lacks lease information. In this
+case, it may be required to reconstruct lease databases on both servers from
+some external source, e.g. a backup server. If the lease database is to be
+reconstructed via the RESTful API, the servers should be started in the initial,
+i.e. ``waiting``, state and remain in this state while leases are being added.
+In particular, the servers should not attempt to synchronize their lease
+databases nor start serving DHCP clients.
+
+The HA hook library provides configuration parameters and a command to control
+pausing and resuming the HA state machine. The following configuration causes
+the HA state machine to pause in the ``waiting`` state after server startup.
+
+::
+
+   "Dhcp4": {
+
+       ...
+
+       "hooks-libraries": [
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+               "parameters": { }
+           },
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+               "parameters": {
+                   "high-availability": [ {
+                       "this-server-name": "server1",
+                       "mode": "load-balancing",
+                       "peers": [
+                           {
+                               "name": "server1",
+                               "url": "http://192.168.56.33:8000/",
+                               "role": "primary"
+                           },
+                           {
+                               "name": "server2",
+                               "url": "http://192.168.56.66:8000/",
+                               "role": "secondary"
+                           }
+                       ],
+                       "state-machine": {
+                           "states": [
+                               {
+                                   "state": "waiting",
+                                   "pause": "once"
+                               }
+                           ]
+                       }
+                   } ]
+               }
+           }
+       ],
+
+       ...
+
+   }
+
+The ``pause`` parameter value ``once`` denotes that the state machine should be
+paused upon the first transition to the ``waiting`` state; later transitions to
+this state will not cause the state machine to pause. Two other supported values
+of the ``pause`` parameter are ``always`` and ``never``. The latter is the
+default value for each state, which instructs the server never to pause the
+state machine.
+
+In order to "unpause" the state machine, the ``ha-continue`` command must be
+sent to the paused server. This command does not take any arguments. See
+:ref:`ha-control-commands` for details about commands specific to the HA hook
+library.
+
+It is possible to configure the state machine to pause in more than one state.
+Consider the following configuration:
+
+::
+
+   "Dhcp4": {
+
+       ...
+
+       "hooks-libraries": [
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+               "parameters": { }
+           },
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+               "parameters": {
+                   "high-availability": [ {
+                       "this-server-name": "server1",
+                       "mode": "load-balancing",
+                       "peers": [
+                           {
+                               "name": "server1",
+                               "url": "http://192.168.56.33:8000/",
+                               "role": "primary"
+                           },
+                           {
+                               "name": "server2",
+                               "url": "http://192.168.56.66:8000/",
+                               "role": "secondary"
+                           }
+                       ],
+                       "state-machine": {
+                           "states": [
+                               {
+                                   "state": "ready",
+                                   "pause": "always"
+                               },
+                               {
+                                   "state": "partner-down",
+                                   "pause": "once"
+                               }
+                           ]
+                       }
+                   } ]
+               }
+           }
+       ],
+
+       ...
+
+   }
+
+This configuration instructs the server to pause the state machine every time it
+transitions to the ``ready`` state and upon the first transition to the
+``partner-down`` state.
+
+Refer to :ref:`ha-server-states` for a complete list of server states. The state
+machine can be paused in any of the supported states; however, it is not
+practical to pause in the ``backup`` or ``terminated`` states because the server
+never transitions out of these states anyway.
+
+.. note::
+
+   In the ``syncing`` state the server is paused before it makes an attempt to
+   synchronize the lease database with a partner. To pause the state machine
+   after lease-database synchronization, use the ``ready`` state instead.
+
+.. note::
+
+   The state of the HA state machine depends on the state of the cooperating
+   server. Therefore, pausing the state machine of one server may affect the
+   operation of the partner server. For example: if the primary server is paused
+   in the ``waiting`` state, the partner server will also remain in the
+   ``waiting`` state until the state machine of the primary server is resumed
+   and that server transitions to the ``ready`` state.
+
+.. _ha-ctrl-agent-config:
+
+Control Agent Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The :ref:`kea-ctrl-agent` describes in detail the Kea daemon, which provides a
+RESTful interface to control the Kea servers. The same functionality is used by
+the High Availability hook library to establish communication between the HA
+peers. Therefore, the HA library requires that the Control Agent (CA) be started
+for each DHCP instance within the HA setup. If the Control Agent is not started,
+the peers cannot communicate with a particular DHCP server (even if the DHCP
+server itself is online) and may eventually consider this server to be offline.
+
+The following is an example configuration for the CA running on the same
+machine as the primary server. This configuration is valid for both the
+``load-balancing`` and the ``hot-standby`` cases presented in previous sections.
+
+::
+
+   {
+   "Control-agent": {
+       "http-host": "192.168.56.33",
+
+        // If enabling HA and multi-threading, the 8000 port is used by the HA
+        // hook library http listener. When using HA hook library with
+        // multi-threading to function, make sure the port used by dedicated
+        // listener is different (e.g. 8001) than the one used by CA. Note
+        // the commands should still be sent via CA. The dedicated listener
+        // is specifically for HA updates only.
+       "http-port": 8000,
+
+       "control-sockets": {
+           "dhcp4": {
+               "socket-type": "unix",
+               "socket-name": "/tmp/kea-dhcp4-ctrl.sock"
+           },
+           "dhcp6": {
+               "socket-type": "unix",
+               "socket-name": "/tmp/kea-dhcp6-ctrl.sock"
+           }
+       }
+   }
+   }
+
+Since Kea 1.9.0, basic HTTP authentication is supported.
+
+.. _ha-mt-config:
+
+Multi-Threaded Configuration (HA+MT)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+HA peer communication consists of specialized API commands sent between HA peers.
+Prior to Kea 1.9.7, each peer had to be paired with a local instance of
+``kea-ctrl-agent`` in order to exchange commands. The agent received HA commands
+via HTTP, communicated via Linux socket with the local peer to carry out the
+command, and then sent the response back to the requesting peer via HTTP. To
+send HA commands, each peer opened its own HTTP client connection to the URL of
+each of its peers.
+
+In Kea 1.9.7 and newer, it is possible to configure HA to use direct
+multi-threaded communication between peers. We refer to this mode as HA+MT.
+With HA+MT enabled, each peer runs its own dedicated, internal HTTP listener
+(i.e. server) which receives and responds to commands directly, thus eliminating
+the need for an agent to carry out HA protocol between peers. In addition, both
+the listener and client components use multi-threading to support multiple,
+concurrent connections between peers. By eliminating the agent and executing
+multiple command exchanges in parallel, HA throughput between peers should
+improve considerably in most situations.
+
+The following parameters have been added to the HA configuration, to support
+HA+MT operation:
+
+-  ``enable-multi-threading`` - enables or disables multi-threading HA peer
+   communication (HA+MT). Kea core multi-threading must be enabled for HA+MT to
+   operate. When ``false`` (the default), the server operates as in earlier
+   versions, relying on ``kea-ctrl-agent`` and using single-threaded HTTP client
+   processing.
+
+-  ``http-dedicated-listener`` - enables or disables the creation of a dedicated,
+   internal HTTP listener through which the server receives HA messages from its
+   peers. The internal listener replaces the role of ``kea-ctrl-agent`` traffic,
+   allowing peers to send their HA commands directly to each other. The listener
+   listens on the peer's ``url``. When ``false`` (the default), the server
+   relies on ``kea-ctrl-agent``. This parameter has been provided largely for
+   flexibility and testing; running HA+MT without dedicated listeners enabled
+   will substantially limit HA throughput.
+
+-  ``http-listener-threads`` - indicates the maximum number of threads the
+   dedicated listener should use. A value of 0 instructs the server to use the
+   same number of threads that the Kea core is using for DHCP multi-threading.
+   The default is 0.
+
+-  ``http-client-threads`` - indicates the maximum number of threads that should
+   be used to send HA messages to its peers. A value of 0 instructs the server
+   to use the same number of threads that the Kea core is using for DHCP
+   multi-threading. The default is 0.
+
+These parameters are grouped together under a map element, ``multi-threading``,
+as illustrated below:
+
+::
+
+   "Dhcp4": {
+
+       ...
+       "hooks-libraries": [
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+               "parameters": { }
+           },
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+               "parameters": {
+                   "high-availability": [ {
+                       "this-server-name": "server1",
+                       ...
+                       "multi-threading": {
+                           "enable-multi-threading": true,
+                           "http-dedicated-listener": true,
+                           "http-listener-threads": 4,
+                           "http-client-threads": 4
+                       },
+                       ...
+                       "peers": [
+                         // This is the configuration of this server instance.
+                         {
+                             "name": "server1",
+                             // This specifies the URL of our server instance.
+                             // Since the HA+MT uses a direct connection, the
+                             // DHCPv4 server open its own socket. Note that it
+                             // must be different than the one used by the CA
+                             // (typically 8000). In this example, 8001 is used.
+                             "url": "http://192.0.2.1:8001/",
+                             // This server is primary. The other one must be
+                             // secondary.
+                             "role": "primary"
+                         },
+                         // This is the configuration of our HA peer.
+                         {
+                             "name": "server2",
+                             // This specifies the URL of our server instance.
+                             // Since the HA+MT uses a direct connection, the
+                             // DHCPv4 server open its own socket. Note that it
+                             // must be different than the one used by the CA
+                             // (typically 8000). In this example, 8001 is used.
+                             "url": "http://192.0.2.2:8001/",
+                             // The partner is a secondary. This server is a
+                             // primary as specified in the previous "peers"
+                             // entry and in "this-server-name" before that.
+                             "role": "secondary"
+                         }
+                       ...
+
+
+In the example above, HA+MT is enabled with four threads for the listener and
+four threads for the client.
+
+.. note::
+
+   It is essential to configure the ports correctly. One common mistake is to
+   configure CA to listen on port 8000 and also configure dedicated listeners on
+   port 8000. In such a configuration, the communication will still work over CA,
+   but it will be slow and the DHCP server will fail to bind sockets.
+   Administrators should ensure that dedicated listeners use a different port
+   (8001 is a suggested alternative); if ports are misconfigured or the ports
+   dedicated to CA are used, the performance bottlenecks caused by the
+   single-threaded nature of CA and the sequential nature of the UNIX socket
+   that connects CA to DHCP servers will nullify any performance gains offered
+   by HA+MT.
+
+.. _ha-parked-packet-limit:
+
+Parked-Packet Limit
+~~~~~~~~~~~~~~~~~~~
+
+Kea servers contain a mechanism by which the response to a client packet may
+be held, pending completion of hook library work. We refer to this as "parking"
+the packet. The HA hook library makes use of this mechanism. When an HA server
+needs to send a lease update to its peer(s) to notify it of the change to the
+lease, it will "park" the client response until the peer acknowledges the lease
+update. At that point, the server will "unpark" the response and send it to the
+client. This applies to client queries which cause lease changes, such as
+DHCPREQUEST for DHCPv4 and Request, Renew, and Rebind for DHCPv6. It does not
+apply to DHPCDISCOVERs (v4) or Solicits (v6).
+
+There is a global parameter, ``parked-packet-limit``, that may be used to limit
+the number of responses that may be parked at any given time. This acts as a
+form of congestion handling and protects the server from being swamped when the
+volume of client queries is outpacing the server's ability to respond. Once the
+limit is reached, the server emits a log and drops any new responses until
+parking spaces are available.
+
+In general, smaller values for the parking lot limit are likely to cause more
+drops but with shorter response times. Larger values are likely to result in
+fewer drops but with longer response times. Currently, the default value for
+``parked-packet-limit`` is 256.
+
+.. warning::
+
+   Using too small a value may result in an unnecessarily high drop rate, while
+   using too large a value may lead to response times that are simply too long
+   to be useful. A value of 0, while allowed, disables the limit altogether, but
+   this is highly discouraged as it may lead to Kea servers becoming
+   unresponsive to clients. Choosing the best value is very site-specific; we
+   recommend users initially leave it at the default value of 256 and observe
+   how the system behaves over time with varying load conditions.
+
+::
+
+   "Dhcp6": {
+
+       ...
+       // Limit the number of concurrently parked packets to 128.
+       "parked-packet-limit": 128,
+       "hooks-libraries": [
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_lease_cmds.so",
+               "parameters": { }
+           },
+           {
+               "library": "/usr/lib/kea/hooks/libdhcp_ha.so",
+               "parameters": {
+                   "high-availability": [ {
+                       "this-server-name": "server1",
+                       ...
+
+.. note::
+
+   While ``parked-packet-limit`` is not specifically tied to HA, currently HA
+   is the only ISC hook that employs packet parking.
+
+.. _ha-maintenance:
+
+Controlled Shutdown and Maintenance of DHCP Servers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Having a pair of servers providing High Availability allows for controlled
+shutdown and maintenance of those servers without disrupting the DHCP service.
+For example, an administrator can perform an upgrade of one of the servers while
+the other one continues to respond to DHCP queries. When the first server is
+upgraded and back online, the upgrade can be performed for the second server.
+
+A typical problem reported with early versions of the High Availability hook
+library was that the administrator did not have direct control over the state of
+the DHCP server. Shutting down one of the servers for maintenance did not
+necessarily cause the other server to start responding to all DHCP queries,
+because the failure-detection algorithm described in :ref:`ha-scope-transition`
+requires that the partner not respond for a configured period of time and,
+depending on the configuration, may also require that a number of DHCP requests
+not be responded to for a specified period of time. The maintenance procedure,
+however, requires that the administrator be able to instruct one of the servers
+to instantly start serving all DHCP clients, and the other server to instantly
+stop serving any DHCP clients, so it can be safely shut down.
+
+The maintenance feature of the High Availability hook library addresses this
+situation. The ``ha-maintenance-start`` command was introduced to allow the
+administrator to put the pair of the active servers in a state in which one of
+them is responding to all DHCP queries and the other one is awaiting shutdown.
+
+Suppose that the HA setup includes two active servers, ``server1`` and
+``server2``, and the latter needs to be shut down for maintenance.
+The administrator can send the ``ha-maintenance-start`` command to ``server1``,
+as this is the server which is going to handle the DHCP traffic while the other
+one is offline. ``server1`` responds with an error if its state or the partner's
+state does not allow for a maintenance shutdown: for example, if maintenance is
+not supported for the backup server or if the server is in the ``terminated``
+state. Also, an error is returned if the ``ha-maintenance-start`` request was
+already sent to the other server.
+
+Upon receiving the ``ha-maintenance-start`` command, ``server1`` sends the
+``ha-maintenance-notify`` command to ``server2`` to put it in the
+``in-maintenance`` state. If ``server2`` confirms, ``server1`` transitions to
+the ``partner-in-maintenance`` state. This is similar to the ``partner-down``
+state, except that in the ``partner-in-maintenance`` state ``server1`` continues
+to send lease updates to ``server2`` until the administrator shuts down
+``server2``. ``server1`` now responds to all DHCP queries.
+
+The administrator can now safely shut down ``server2`` in the ``in-maintenance``
+state and perform any necessary maintenance actions. While ``server2`` is
+offline, ``server1`` will obviously not be able to communicate with its partner,
+so it will immediately transition to the ``partner-down`` state; it will
+continue to respond to all DHCP queries but will no longer send lease updates to
+``server2``. Restarting ``server2`` after the maintenance will trigger normal
+state negotiation, lease-database synchronization, and, ultimately, a transition
+to the normal ``load-balancing`` or ``hot-standby`` state. Maintenance can then
+be performed on ``server1``, after sending the ``ha-maintenance-start`` command
+to ``server2``.
+
+If the ``ha-maintenance-start`` command was sent to the server and the server
+has transitioned to the ``partner-in-maintenance`` state, it is possible to
+transition both it and its partner back to their previous states to resume the
+normal operation of the HA pair. This is achieved by sending the
+``ha-maintenance-cancel`` command to the server that is in the
+``partner-in-maintenance`` state. However, if the server has already
+transitioned to the ``partner-down`` state as a result of detecting that the
+partner is offline, canceling the maintenance is no longer possible. In that
+case, it is necessary to restart the other server and allow it to complete its
+normal state negotiation process.
+
+Upgrading From Older HA Versions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To upgrade from an older HA hook library to the current version, the
+administrator must shut down one of the servers and rely on the failover
+mechanism to force the online server to transition to the ``partner-down`` state,
+where it starts serving all DHCP clients. Once the hook library on the first
+server is upgraded to a current version, the ``ha-maintenance-start`` command
+can be used to upgrade the second server.
+
+In such a case, shut down the server running the old version. Next, send the
+``ha-maintenance-start`` command to the server that has been upgraded. This
+server should immediately transition to the ``partner-down`` state as it cannot
+communicate with its offline partner. In the ``partner-down`` state the first
+(upgraded) server will respond to all DHCP requests, allowing the administrator
+to perform the upgrade on the second server.
+
+.. note::
+
+   Do not send the ``ha-maintenance-start`` command while the server running the
+   old hook library is still online. The server receiving this command will
+   return an error.
+
+
+.. _ha-control-commands:
+
+Control Commands for High Availability
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Even though the HA hook library is designed to automatically resolve issues with
+DHCP service interruptions by redirecting the DHCP traffic to a surviving server
+and synchronizing the lease database as needed, it may be useful for the
+administrator to have more control over both servers' behavior. In particular,
+it may be useful to be able to trigger lease-database synchronization on demand,
+or to manually set the HA scopes that are being served.
+
+The backup server can sometimes be used to handle DHCP traffic if both active
+servers are down. The backup server does not perform the failover function
+automatically; thus, in order to use the backup server to respond to DHCP
+queries, the server administrator must enable this function manually.
+
+The following sections describe commands supported by the HA hook library which
+are available for the administrator.
+
+.. _command-ha-sync:
+
+The ``ha-sync`` Command
+-----------------------
+
+The ``ha-sync`` command instructs the server to synchronize its local lease
+database with the selected peer. The server fetches all leases from the peer and
+updates any locally stored leases which are older than those fetched. It also
+creates new leases when any of those fetched do not exist in the local database.
+All leases that are not returned by the peer but are in the local database are
+preserved. The database synchronization is unidirectional; only the database on
+the server to which the command has been sent is updated. To synchronize the
+peer's database, a separate ``ha-sync`` command must be issued to that peer.
+
+Database synchronization may be triggered for both active and backup server
+types. The ``ha-sync`` command has the following structure (in a DHCPv4 example):
+
+::
+
+   {
+       "command": "ha-sync",
+       "service": [ "dhcp4 "],
+       "arguments": {
+           "server-name": "server2",
+           "max-period": 60
+       }
+   }
+
+When the server receives this command it first disables the DHCP service of the
+server from which it will be fetching leases, by sending the ``dhcp-disable``
+command to that server. The ``max-period`` parameter specifies the maximum
+duration (in seconds) for which the DHCP service should be disabled. If the DHCP
+service is successfully disabled, the synchronizing server fetches leases from
+the remote server by issuing one or more ``lease4-get-page`` commands. When the
+lease-database synchronization is complete, the synchronizing server sends the
+``dhcp-enable`` command to the peer to re-enable its DHCP service.
+
+The ``max-period`` value should be sufficiently long to guarantee that it does
+not elapse before the synchronization is completed. Otherwise, the DHCP server
+will automatically enable its DHCP function while the synchronization is still
+in progress. If the DHCP server subsequently allocates any leases during the
+synchronization, those new (or updated) leases will not be fetched by the
+synchronizing server, leading to database inconsistencies.
+
+.. _command-ha-scopes:
+
+The ``ha-scopes`` Command
+-------------------------
+
+This command allows an administrator to modify the HA scopes being served.
+Consult :ref:`ha-load-balancing-config` and :ref:`ha-hot-standby-config` to
+learn which scopes are available for the different HA modes of operation. The
+``ha-scopes`` command has the following structure (in a DHCPv4 example):
+
+::
+
+   {
+       "command": "ha-scopes",
+       "service": [ "dhcp4" ],
+       "arguments": {
+           "scopes": [ "HA_server1", "HA_server2" ]
+       }
+   }
+
+This command configures the server to handle traffic from both the "HA_server1"
+and "HA_server2" scopes. To disable all scopes specify an empty list:
+
+::
+
+   {
+       "command": "ha-scopes",
+       "service": [ "dhcp4 "],
+       "arguments": {
+           "scopes": [ ]
+       }
+   }
+
+.. _command-ha-continue:
+
+The ``ha-continue`` Command
+---------------------------
+
+This command is used to resume the operation of the paused HA state machine, as
+described in :ref:`ha-pause-state-machine`. It takes no arguments, so the
+command structure is simply:
+
+::
+
+   {
+       "command": "ha-continue",
+       "service": [ "dhcp4" ]
+   }
+
+.. _command-ha-heartbeat:
+
+The ``ha-heartbeat`` Command
+----------------------------
+
+The :ref:`ha-server-states` section describes how the ``ha-heartbeat`` command
+is used by a pair of active HA servers to detect one partner's failure. This
+command, however, can also be sent by the system administrator to one or both
+servers to check their HA state. This allows a monitoring system to be deployed
+on the HA enabled servers to periodically check whether they are operational or
+whether any manual intervention is required. The ``ha-heartbeat`` command takes
+no arguments:
+
+::
+
+   {
+       "command": "ha-heartbeat",
+       "service": [ "dhcp4" ]
+   }
+
+Upon successful communication with the server, a response similar to this should
+be returned:
+
+::
+
+   {
+      "result": 0,
+      "text": "HA peer status returned.",
+      "arguments":
+          {
+              "state": "partner-down",
+              "date-time": "Thu, 07 Nov 2019 08:49:37 GMT",
+              "scopes": [ "server1" ],
+              "unsent-update-count": 123
+          }
+   }
+
+The returned ``state`` value should be one of the values listed in
+:ref:`ha-server-states`. In the example above, the ``partner-down`` state is
+returned, which indicates that the server which responded to the command
+believes that its partner is offline; thus, it is serving all DHCP requests sent
+to the servers. To ensure that the partner is indeed offline, the administrator
+should send the ``ha-heartbeat`` command to the second server. If sending the
+command fails, e.g. due to an inability to establish a TCP connection to the
+Control Agent, or if the Control Agent reports issues with communication with
+the DHCP server, it is very likely that the server is not running.
+
+The ``date-time`` parameter conveys the server's notion of time.
+
+The ``unsent-update-count`` value is a cumulative count of all unsent lease
+updates since the server was booted; its value is set to 0 when the server is
+started. It is never reset to 0 during the server's operation, even after the
+partner synchronizes the database. It is incremented by the partner sending the
+heartbeat response when it cannot send the lease update. For example, suppose
+the failure is a result of a temporary communication interruption. In that case,
+the partner receiving the ``partner-down`` heartbeat response tracks the value
+changes and can determine, once communication is reestablished, whether there
+are any new lease updates that it did not receive. If the values on both servers
+do not match, it is an indication that the partner should synchronize its lease
+database. A non-zero value itself is not an indication of any present issues
+with lease updates, but a constantly incrementing value is.
+
+The typical response returned by one server when both are
+operational is:
+
+::
+
+   {
+      "result": 0,
+      "text": "HA peer status returned.",
+      "arguments":
+          {
+              "state": "load-balancing",
+              "date-time": "Thu, 07 Nov 2019 08:49:37 GMT",
+              "scopes": [ "server1" ],
+              "unsent-update-count": 0
+          }
+   }
+
+In most cases, the ``ha-heartbeat`` command should be sent to both HA-enabled
+servers to verify the state of the entire HA setup. In particular, if one of the
+servers indicates that it is in the ``load-balancing`` state, it means that this
+server is operating as if its partner is functional. When a partner goes down,
+it takes some time for the surviving server to realize it. The
+:ref:`ha-scope-transition` section describes the algorithm which the surviving
+server follows before it transitions to the ``partner-down`` state. If the
+``ha-heartbeat`` command is sent during the time window between the failure of
+one of the servers and the transition of the surviving server to the
+``partner-down`` state, the response from the surviving server does not reflect
+the failure. Resending the command detects the failure once the surviving server
+has entered the ``partner-down`` state.
+
+.. note:
+
+   Always send the ``ha-heartbeat`` command to both active HA servers to check
+   the state of the entire HA setup. Sending it to only one of the servers may
+   not reflect issues that just began with one of the servers.
+
+.. _command-ha-status-get:
+
+The ``status-get`` Command
+--------------------------
+
+``status-get`` is a general-purpose command supported by several Kea daemons,
+not only the DHCP servers. However, when sent to a DHCP server with HA enabled,
+it can be used to get insight into the details of the HA-specific server status.
+Not only does the response contain the status information of the server
+receiving this command, but also the information about its partner if it is
+available.
+
+The following is an example response to the ``status-get`` command, including
+the HA status of two ``load-balancing`` servers:
+
+.. code-block:: json
+
+   {
+       "result": 0,
+       "text": "",
+       "arguments": {
+           "pid": 1234,
+           "uptime": 3024,
+           "reload": 1111,
+           "high-availability": [
+               {
+                   "ha-mode": "load-balancing",
+                   "ha-servers": {
+                       "local": {
+                           "role": "primary",
+                           "scopes": [ "server1" ],
+                           "state": "load-balancing"
+                       },
+                       "remote": {
+                           "age": 10,
+                           "in-touch": true,
+                           "role": "secondary",
+                           "last-scopes": [ "server2" ],
+                           "last-state": "load-balancing",
+                           "communication-interrupted": true,
+                           "connecting-clients": 2,
+                           "unacked-clients": 1,
+                           "unacked-clients-left": 2,
+                           "analyzed-packets": 8
+                       }
+                   }
+               }
+           ],
+           "multi-threading-enabled": true,
+           "thread-pool-size": 4,
+           "packet-queue-size": 64,
+           "packet-queue-statistics": [ 0.2, 0.1, 0.1 ],
+           "sockets": {
+               "status": "ready"
+           }
+       }
+   }
+
+The ``high-availability`` argument is a list which currently comprises only one
+element.
+
+The ``ha-servers`` map contains two structures: ``local`` and ``remote``. The
+former contains the status information of the server which received the command,
+while the latter contains the status information known to the local server about
+the partner. The ``role`` of the partner server is gathered from the local
+configuration file, and thus should always be available. The remaining status
+information, such as ``last-scopes`` and ``last-state``, is not available until
+the local server communicates with the remote by successfully sending the
+``ha-heartbeat`` command. If at least one such communication has taken place,
+the returned value of the ``in-touch`` parameter is set to ``true``. By
+examining this value, the command's sender can determine whether the information
+about the remote server is reliable.
+
+The ``last-scopes`` and ``last-state`` parameters contain information about the
+HA scopes served by the partner and its state. This information is gathered
+during the heartbeat command exchange, so it may not be accurate if a
+communication problem occurs between the partners and this status information is
+not refreshed. In such a case, it may be useful to send the ``status-get``
+command to the partner server directly to check its current state. The ``age``
+parameter specifies the age of the information from the partner, in seconds.
+
+The ``communication-interrupted`` boolean value indicates whether the server
+receiving the ``status-get`` command (the local server) has been unable to
+communicate with the partner longer than the duration specified as
+``max-response-delay``. In such a situation, the active servers are considered
+to be in the ``communication-interrupted`` state. At this point, the local
+server may start monitoring the DHCP traffic directed to the partner to see if
+the partner is responding to this traffic. More about the failover procedure can
+be found in :ref:`ha-load-balancing-config`.
+
+The ``connecting-clients``, ``unacked-clients``, ``unacked-clients-left``, and
+``analyzed-packets`` parameters were introduced along with the
+``communication-interrupted`` parameter and they convey useful information about
+the state of the DHCP traffic monitoring in the ``communication-interrupted``
+state. Once the server leaves the ``communication-interrupted`` state, these
+parameters are all reset to 0.
+
+These parameters have the following meaning in the ``communication-interrupted``
+state:
+
+-  ``connecting-clients`` - this is the number of different clients which have
+   attempted to get a lease from the remote server. These clients are
+   differentiated by their MAC address and client identifier (in DHCPv4) or DUID
+   (in DHCPv6). This number includes "unacked" clients (for which the "secs"
+   field or "elapsed time" value exceeded the ``max-response-delay``).
+
+-  ``unacked-clients`` - this is the number of different clients which have been
+   considered "unacked", i.e. the clients which have been trying to get the
+   lease longer than the value of the "secs" field, or for which the
+   "elapsed time" exceeded the ``max-response-delay`` setting.
+
+-  ``unacked-clients-left`` - this indicates the number of additional clients
+   which have to be considered "unacked" before the server enters the
+   ``partner-down`` state. This value decreases when the ``unacked-clients``
+   value increases. The local server enters the ``partner-down`` state when this
+   value decreases to 0.
+
+-  ``analyzed-packets`` - this is the total number of packets directed to the
+   partner server and analyzed by the local server since entering the
+   communication interrupted state. It includes retransmissions from the same
+   clients.
+
+Monitoring these values helps to predict when the local server will enter the
+``partner-down`` state or to understand why the server has not yet entered this
+state.
+
+The ``ha-mode`` parameter returns the HA mode of operation selected using the
+``mode`` parameter in the configuration file. It can hold one of the following
+values: ``load-balancing``, ``hot-standby``, or ``passive-backup``.
+
+The ``status-get`` response has the format described above only in the
+``load-balancing`` and ``hot-standby`` modes. In the ``passive-backup`` mode the
+``remote`` map is not included in the response because in this mode there is
+only one active server (local). The response includes no information about the
+status of the backup servers.
+
+.. _command-ha-maintenance-start:
+
+The ``ha-maintenance-start`` Command
+------------------------------------
+
+This command is used to initiate the transition of the server's partner into the
+``in-maintenance`` state and the transition of the server receiving the command
+into the ``partner-in-maintenance`` state. See the :ref:`ha-maintenance` section
+for details.
+
+::
+
+   {
+       "command": "ha-maintenance-start",
+       "service": [ "dhcp4" ]
+   }
+
+.. _command-ha-maintenance-cancel:
+
+The ``ha-maintenance-cancel`` Command
+-------------------------------------
+
+This command is used to cancel the maintenance previously initiated using the
+``ha-maintenance-start`` command. The server receiving this command will first
+send ``ha-maintenance-notify``, with the ``cancel`` flag set to ``true``, to its
+partner. Next, the server reverts from the ``partner-in-maintenance`` state to
+its previous state. See the :ref:`ha-maintenance` section for details.
+
+::
+
+   {
+       "command": "ha-maintenance-cancel",
+       "service": [ "dhcp4" ]
+   }
+
+.. _command-ha-maintenance-notify:
+
+The ``ha-maintenance-notify`` Command
+-------------------------------------
+
+This command is sent by the server receiving the ``ha-maintenance-start`` or the
+``ha-maintenance-cancel`` command to its partner, to cause the partner to
+transition to the ``in-maintenance`` state or to revert from this state to a
+previous state. See the :ref:`ha-maintenance` section for details.
+
+::
+
+   {
+       "command": "ha-maintenance-notify",
+       "service": [ "dhcp4" ],
+       "arguments": {
+           "cancel": false
+       }
+   }
+
+.. warning::
+
+   The ``ha-maintenance-notify`` command is not meant to be used by system
+   administrators. It is used for internal communication between a pair of
+   HA-enabled DHCP servers. Direct use of this command is not supported and may
+   produce unintended consequences.
+
+.. _command-ha-reset:
+
+The ``ha-reset`` Command
+------------------------
+
+This command causes the server to reset its High Availability state machine by
+transitioning it to the ``waiting`` state. A partner in the
+``communication-recovery`` state may send this command to cause the server
+to synchronize its lease database. Database synchronization is required when the
+partner has failed to send all lease database updates after re-establishing
+connection after a temporary connection failure. It is also required when the
+``delayed-updates-limit`` is exceeded, when the server is in the
+``communication-recovery`` state.
+
+A server administrator may send this command to reset a misbehaving state
+machine.
+
+This command includes no arguments:
+
+::
+
+   {
+       "command": "ha-reset",
+       "service": [ "dhcp4" ]
+   }
+
+And elicits the response:
+
+::
+
+   {
+       "result": 0,
+       "text": "HA state machine reset."
+   }
+
+If the server receiving this command is already in the ``waiting`` state, the
+command has no effect.
+
+.. _command-ha-sync-complete-notify:
+
+The ``ha-sync-complete-notify`` Command
+---------------------------------------
+
+A server sends this command to its partner to signal that it has completed
+lease-database synchronization. The partner may enable its DHCP service if it
+can allocate new leases in its current state. The partner does not enable the
+DHCP service in the ``partner-down`` state until it sends a successful heartbeat
+test to its partner server. If the connection is still unavailable, the server
+in the ``partner-down`` state enables its own DHCP service to continue
+responding to clients.
+
+This command includes no arguments:
+
+::
+
+   {
+       "command": "ha-sync-complete-notify",
+       "service": [ "dhcp4" ]
+   }
+
+And elicits the response:
+
+::
+
+   {
+       "result": 0,
+       "text": "Server successfully notified about the synchronization completion."
+   }
+
+.. warning::
+
+   The ``ha-sync-complete-notify`` command is not meant to be used by system
+   administrators. It is used for internal communication between a pair of
+   HA-enabled DHCP servers. Direct use of this command is not supported and may
+   produce unintended consequences.
diff --git a/doc/sphinx/arm/hooks-host-cache.rst b/doc/sphinx/arm/hooks-host-cache.rst
new file mode 100644
index 0000000..e1ee411
--- /dev/null
+++ b/doc/sphinx/arm/hooks-host-cache.rst
@@ -0,0 +1,306 @@
+.. _hooks-host-cache:
+
+``host_cache``: Host Cache Reservations for Improved Performance
+================================================================
+
+Some database backends, such as RADIUS, are slow and may take
+a long time to respond. Since Kea in general is synchronous, backend
+performance directly affects DHCP performance. To minimize the
+impact and improve performance, the Host Cache library provides a way to
+cache information from the database locally. This includes negative
+caching, i.e. the ability to remember that there is no client
+information in the database.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or
+   ``kea-dhcp6`` process.
+
+In principle, this hook library can be used with any backend that may
+introduce performance degradation (MySQL, PostgreSQL or RADIUS). Host Cache
+must be loaded for the RADIUS accounting mechanism to work.
+
+The Host Cache hook library is very simple. It takes only one
+optional parameter (``maximum``), which defines the maximum number of hosts
+to be cached. If not specified, the default value of 0 is used, which
+means there is no limit. This hook library can be loaded the same way as
+any other hook library; for example, this configuration could be used:
+
+::
+
+     "Dhcp4": {
+
+     # Your regular DHCPv4 configuration parameters here.
+
+     "hooks-libraries": [
+     {
+         "library": "/usr/local/lib/kea/hooks/libdhc_host_cache.so",
+         "parameters": {
+
+             # Tells Kea to never cache more than 1000 hosts.
+             "maximum": 1000
+
+         }
+     } ]
+
+Once loaded, the Host Cache hook library provides a number of new
+commands which can be used either over the control channel (see
+:ref:`ctrl-channel-client`) or the RESTful API (see
+:ref:`agent-overview`). An example RESTful API client is described in
+:ref:`shell-overview`. The following sections describe the commands
+available.
+
+.. _command-cache-flush:
+
+The ``cache-flush`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command allows removal of a specified number of cached host
+entries. It takes one parameter, which defines the number of hosts to be
+removed. An example usage looks as follows:
+
+::
+
+   {
+       "command": "cache-flush",
+       "arguments": 1000
+   }
+
+This command removes 1000 hosts; to delete *all* cached
+hosts, use ``cache-clear`` instead. The hosts are stored in FIFO
+(first-in, first-out) order, so the oldest entries are always removed.
+
+.. _command-cache-clear:
+
+The ``cache-clear`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command allows removal of all cached host entries. An example usage
+looks as follows:
+
+::
+
+   {
+       "command": "cache-clear"
+   }
+
+This command removes all hosts. To delete only a certain
+number of cached hosts, please use ``cache-flush`` instead.
+
+.. _command-cache-size:
+
+The ``cache-size`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command returns the number of host entries. An example usage looks
+as follows:
+
+::
+
+   {
+       "command": "cache-size"
+   }
+
+.. _command-cache-write:
+
+The ``cache-write`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In general, the cache content is considered a runtime state and the
+server can be shut down or restarted as usual; the cache is then
+repopulated after restart. However, there are some cases when it is
+useful to store the contents of the cache. One such case is RADIUS,
+where the cached hosts also retain additional cached RADIUS attributes;
+there is no easy way to obtain this information again, because renewing
+clients send their packet to the DHCP server directly. Another use case
+is when an administrator wants to restart the server and, for performance reasons,
+wants it to start with a hot (populated) cache.
+
+This command allows writing the contents of the in-memory cache to a
+file on disk. It takes one parameter, which defines the filename. An
+example usage looks as follows:
+
+::
+
+   {
+       "command": "cache-write",
+       "arguments": "/tmp/kea-host-cache.json"
+   }
+
+This causes the contents to be stored in the ``/tmp/kea-host-cache.json``
+file. That file can then be loaded with the ``cache-load`` command or
+processed by any other tool that is able to understand JSON format.
+
+.. _command-cache-load:
+
+The ``cache-load`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+See the previous section for a discussion of use cases where it may be
+useful to write and load contents of the host cache to disk.
+
+This command allows the contents of a file on disk to be loaded into an
+in-memory cache. It takes one parameter, which defines the filename. An
+example usage looks as follows:
+
+::
+
+   {
+       "command": "cache-load",
+       "arguments": "/tmp/kea-host-cache.json"
+   }
+
+This command stores the contents to the ``/tmp/kea-host-cache.json``
+file. That file can then be loaded with the ``cache-load`` command or
+processed by any other tool that is able to understand JSON format.
+
+.. _command-cache-get:
+
+The ``cache-get`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is similar to ``cache-write``, but instead of writing the cache
+contents to disk, it returns the contents to whoever sent the command.
+
+This command allows the contents of a file on disk to be loaded into an
+in-memory cache. It takes one parameter, which defines the filename. An
+example usage looks as follows:
+
+::
+
+   {
+       "command": "cache-get"
+   }
+
+This command returns all the cached hosts; the response
+may be large.
+
+.. _command-cache-get-by-id:
+
+The ``cache-get-by-id`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is similar to ``cache-get``, but instead of returning the whole
+content it returns only the entries matching the given identifier.
+
+It takes one parameter, which defines the identifier of wanted cached
+host reservations. An example usage looks as follows:
+
+::
+
+   {
+       "command": "cache-get-by-id",
+       "arguments": {
+           "hw-address": "01:02:03:04:05:06"
+       }
+   }
+
+This command returns all the cached hosts with the given hardware
+address.
+
+.. _command-cache-insert:
+
+The ``cache-insert`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command may be used to manually insert a host into the cache; there
+are very few use cases when this command might be useful. This command
+expects its arguments to follow the usual syntax for specifying host
+reservations (see :ref:`host-reservation-v4` or
+:ref:`host-reservation-v6`), with one difference: the ``subnet-id``
+value must be explicitly specified.
+
+An example command to insert an IPv4 host into the host cache
+looks as follows:
+
+::
+
+   {
+       "command": "cache-insert",
+       "arguments": {
+           "hw-address": "01:02:03:04:05:06",
+           "subnet-id4": 4,
+           "subnet-id6": 0,
+           "ip-address": "192.0.2.100",
+           "hostname": "somehost.example.org",
+           "client-classes4": [ ],
+           "client-classes6": [ ],
+           "option-data4": [ ],
+           "option-data6": [ ],
+           "next-server": "192.0.0.2",
+           "server-hostname": "server-hostname.example.org",
+           "boot-file-name": "bootfile.efi",
+           "host-id": 0
+       }
+   }
+
+An example command to insert an IPv6 host into the host cache
+looks as follows:
+
+::
+
+   {
+       "command": "cache-insert",
+       "arguments": {
+           "hw-address": "01:02:03:04:05:06",
+           "subnet-id4": 0,
+           "subnet-id6": 6,
+           "ip-addresses": [ "2001:db8::cafe:babe" ],
+           "prefixes": [ "2001:db8:dead:beef::/64" ],
+           "hostname": "",
+           "client-classes4": [ ],
+           "client-classes6": [ ],
+           "option-data4": [ ],
+           "option-data6": [ ],
+           "next-server": "0.0.0.0",
+           "server-hostname": "",
+           "boot-file-name": "",
+           "host-id": 0
+       }
+   }
+
+.. _command-cache-remove:
+
+The ``cache-remove`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Sometimes it is useful to remove a single entry from the host cache: for
+example, consider a situation where the device is active, Kea has already
+provided configuration, and the host entry is in cache. As a result of
+administrative action (e.g. the customer hasn't paid their bills or has
+been upgraded to better service), the information in the backend database
+(e.g. MySQL or RADIUS) is being updated. However, since the cache is in use,
+Kea does not notice the change as the cached values are used. The
+``cache-remove`` command can solve this problem by removing a cached entry
+after administrative changes.
+
+The ``cache-remove`` command works similarly to the ``reservation-get`` command.
+It allows querying by two parameters: either ``subnet-id4`` or ``subnet-id6``;
+or ``ip-address`` (may be an IPv4 or IPv6 address), ``hw-address`` (specifies
+a hardware/MAC address), ``duid``, ``circuit-id``, ``client-id``, or ``flex-id``.
+
+An example command to remove an IPv4 host with reserved address
+192.0.2.1 from a subnet with a ``subnet-id`` 123 looks as follows:
+
+::
+
+   {
+       "command": "cache-remove",
+       "arguments": {
+           "ip-address": "192.0.2.1",
+           "subnet-id": 123
+       }
+   }
+
+Another example that removes an IPv6 host identifier by DUID and
+specific ``subnet-id`` is:
+
+::
+
+   {
+       "command": "cache-remove",
+       "arguments": {
+           "duid": "00:01:ab:cd:f0:a1:c2:d3:e4",
+           "subnet-id": 123
+       }
+   }
diff --git a/doc/sphinx/arm/hooks-host-cmds.rst b/doc/sphinx/arm/hooks-host-cmds.rst
new file mode 100644
index 0000000..27be196
--- /dev/null
+++ b/doc/sphinx/arm/hooks-host-cmds.rst
@@ -0,0 +1,685 @@
+.. _hooks-host-cmds:
+
+``host_cmds``: Host Commands
+============================
+
+Kea can store host reservations in a database; in many larger deployments,
+it is useful to be able to manage that information while the server is
+running. The Host Commands library provides management commands for adding, querying,
+and deleting host reservations in a safe way without restarting the
+server. In particular, it validates the parameters, so an attempt to
+insert incorrect data - such as adding a host with a conflicting identifier in the
+same subnet - is rejected. Those commands are exposed via the command
+channel (JSON over UNIX sockets) and the Control Agent (JSON over a RESTful
+interface).
+
+This library is only available to ISC customers with a paid support
+contract.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or ``kea-dhcp6``
+   process.
+
+Currently, the following commands are supported:
+
+- ``reservation-add``, which adds a new host reservation.
+
+- ``reservation-get``, which returns an existing reservation if specified
+  criteria are matched.
+
+- ``reservation-get-all``, which returns all reservations in a specified subnet.
+
+- ``reservation-get-page``, a variant of ``reservation-get-all`` that returns
+  reservations by pages, either all or in a specified subnet.
+
+- ``reservation-get-by-hostname``, which returns all reservations with a
+  specified hostname and optionally in a subnet.
+
+- ``reservation-get-by-id``, which returns all reservations with a specified
+  identifier (since Kea version 1.9.0).
+
+- ``reservation-del``, which attempts to delete a reservation matching specified
+  criteria.
+
+To use the commands that change reservation information
+(i.e. ``reservation-add`` and ``reservation-del``), the hosts database must be
+specified and it must not operate in read-only mode (for details, see
+the ``hosts-databases`` descriptions in :ref:`hosts-databases-configuration4`
+and :ref:`hosts-databases-configuration6`). If the ``hosts-databases`` are not specified or are
+running in read-only mode, the ``host_cmds`` library will load, but any
+attempts to use ``reservation-add`` or ``reservation-del`` will fail.
+
+For a description of proposed future commands, see the `Control API
+Requirements <https://gitlab.isc.org/isc-projects/kea/wikis/designs/commands>`__
+document.
+
+All host commands use JSON syntax. They can be issued either using the
+control channel (see :ref:`ctrl-channel`) or via the Control Agent (see
+:ref:`kea-ctrl-agent`).
+
+The library can be loaded similarly to other hook libraries. It
+does not take any parameters, and it supports both the DHCPv4 and DHCPv6
+servers.
+
+::
+
+   "Dhcp6": {
+       "hooks-libraries": [
+           {
+               "library": "/path/libdhcp_host_cmds.so"
+           }
+           ...
+       ]
+   }
+
+The ``subnet-id`` Parameter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Before examining the individual commands, it is worth discussing the
+parameter ``subnet-id``. Currently this parameter is mandatory for all of the
+commands supplied by this library, with the exception of
+``reservation-get-by-hostname``, where it is optional. Since Kea 1.9.0,
+``subnet-id`` is also optional in ``reservation-get-page``, and
+it is forbidden in ``reservation-get-by-id``.
+
+Reservations can be specified globally, and are not necessarily specific to any
+subnet. When reservations are supplied via the configuration file, the
+ID of the containing subnet (or lack thereof) is implicit in the
+configuration structure. However, when managing reservations using
+host commands, it is necessary to explicitly identify the scope to which
+the reservation belongs. This is done via the ``subnet-id`` parameter.
+For global reservations, use a value of zero (0). For reservations
+scoped to a specific subnet, use that subnet's ID.
+
+On the other hand, when the ``subnet-id`` is not specified in the command
+parameters, it is added to each host in responses. If the ``subnet-id``
+has the unused special value, this means the host entry belongs only
+to the other IP version (i.e. IPv6 in DHCPv4 server or IPv4 in DHCPv6
+server) and this entry is ignored.
+
+.. _command-reservation-add:
+
+The ``reservation-add`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``reservation-add`` allows for the insertion of a new host. It takes a
+set of arguments that vary depending on the nature of the host
+reservation. Any parameters allowed in the configuration file that
+pertain to host reservation are permitted here. For details regarding
+IPv4 reservations, see :ref:`host-reservation-v4`; for IPv6 reservations, see
+:ref:`host-reservation-v6`. The ``subnet-id`` is mandatory. Use a
+value of zero (0) to add a global reservation, or the ID of the subnet
+to which the reservation should be added. An example command can be as
+simple as:
+
+.. code-block:: json
+
+   {
+       "command": "reservation-add",
+       "arguments": {
+           "reservation": {
+               "subnet-id": 1,
+               "hw-address": "1a:1b:1c:1d:1e:1f",
+               "ip-address": "192.0.2.202"
+           }
+       }
+   }
+
+but it can also take many more parameters, for example:
+
+.. code-block:: json
+
+   {
+       "command": "reservation-add",
+       "arguments": {
+           "reservation": {
+               "subnet-id": 1,
+               "client-id": "01:0a:0b:0c:0d:0e:0f",
+               "ip-address": "192.0.2.205",
+               "next-server": "192.0.2.1",
+               "server-hostname": "hal9000",
+               "boot-file-name": "/dev/null",
+               "option-data": [
+                   {
+                       "name": "domain-name-servers",
+                       "data": "10.1.1.202,10.1.1.203"
+                   }
+               ],
+               "client-classes": [ "special_snowflake", "office" ]
+           }
+       }
+   }
+
+Here is an example of a complex IPv6 reservation:
+
+.. code-block:: json
+
+   {
+       "command": "reservation-add",
+       "arguments": {
+           "reservation": {
+               "subnet-id": 1,
+               "duid": "01:02:03:04:05:06:07:08:09:0A",
+               "ip-addresses": [ "2001:db8:1:cafe::1" ],
+               "prefixes": [ "2001:db8:2:abcd::/64" ],
+               "hostname": "foo.example.com",
+               "option-data": [
+                   {
+                       "name": "vendor-opts",
+                       "data": "4491"
+                   },
+                   {
+                       "name": "tftp-servers",
+                       "space": "vendor-4491",
+                       "data": "3000:1::234"
+                   }
+               ]
+           }
+       }
+   }
+
+The command returns a status that indicates either success (result 0)
+or failure (result 1). A failed command always includes a text parameter
+that explains the cause of the failure. Here's an example of a successful
+addition:
+
+::
+
+   { "result": 0, "text": "Host added." }
+
+And here's an example of a failure:
+
+::
+
+   { "result": 1, "text": "Mandatory 'subnet-id' parameter missing." }
+
+As ``reservation-add`` is expected to store the host, the ``hosts-databases``
+parameter must be specified in the configuration, and databases must not
+run in read-only mode.
+
+.. _command-reservation-get:
+
+The ``reservation-get`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``reservation-get`` can be used to query the host database and retrieve
+existing reservations. This command supports two types of parameters:
+(``subnet-id``, ``address``) or (``subnet-id``, ``identifier-type``,
+``identifier``). The first type of query is used when the address (either
+IPv4 or IPv6) is known, but the details of the reservation are not. One
+common use for this type of query is to find out whether a given
+address is reserved. The second query uses identifiers. For
+maximum flexibility, Kea stores the host identifying information as a
+pair of values: the type and the actual identifier. Currently supported
+identifiers are ``"hw-address"``, ``"duid"``, ``"circuit-id"``, ``"client-id"``, and
+``"flex-id"``. The ``subnet-id`` is mandatory. Use a value
+of zero (0) to fetch a global reservation, or the ID of the subnet to
+which the reservation belongs.
+
+An example command for getting a host reservation by a (``subnet-id``,
+``address``) pair looks as follows:
+
+::
+
+   {
+       "command": "reservation-get",
+       "arguments": {
+           "subnet-id": 1,
+           "ip-address": "192.0.2.202"
+       }
+   }
+
+An example query by (``subnet-id``, ``identifier-type``, ``identifier``) looks as
+follows:
+
+::
+
+   {
+       "command": "reservation-get",
+       "arguments": {
+           "subnet-id": 4,
+           "identifier-type": "hw-address",
+           "identifier": "01:02:03:04:05:06"
+       }
+   }
+
+``reservation-get`` typically returns the result 0 when a query was
+conducted properly. In particular, 0 is returned when the host was not
+found. If the query was successful, the host parameters are
+returned. An example of a query that did not find the host looks as
+follows:
+
+::
+
+   { "result": 0, "text": "Host not found." }
+
+Here's an example of a result returned when the host was found successfully:
+
+::
+
+   {
+     "arguments": {
+       "boot-file-name": "bootfile.efi",
+       "client-classes": [
+
+       ],
+       "hostname": "somehost.example.org",
+       "hw-address": "01:02:03:04:05:06",
+       "ip-address": "192.0.2.100",
+       "next-server": "192.0.0.2",
+       "option-data": [
+
+       ],
+       "server-hostname": "server-hostname.example.org"
+     },
+     "result": 0,
+     "text": "Host found."
+   }
+
+An example result returned when the query was malformed might look like this:
+
+::
+
+   { "result": 1, "text": "No 'ip-address' provided and 'identifier-type'
+                           is either missing or not a string." }
+
+.. _command-reservation-get-all:
+
+The ``reservation-get-all`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``reservation-get-all`` can be used to query the host database and
+retrieve all reservations in a specified subnet. This command uses
+parameters providing the mandatory ``subnet-id``. Global host reservations
+can be retrieved by using a ``subnet-id`` value of zero (0).
+
+For instance, retrieving host reservations for the subnet 1:
+
+::
+
+   {
+       "command": "reservation-get-all",
+       "arguments": {
+           "subnet-id": 1
+        }
+   }
+
+returns some IPv4 hosts:
+
+::
+
+   {
+       "arguments": {
+           "hosts": [
+               {
+                   "boot-file-name": "bootfile.efi",
+                   "client-classes": [ ],
+                   "hostname": "somehost.example.org",
+                   "hw-address": "01:02:03:04:05:06",
+                   "ip-address": "192.0.2.100",
+                   "next-server": "192.0.0.2",
+                   "option-data": [ ],
+                   "server-hostname": "server-hostname.example.org"
+               },
+               ...
+               {
+                   "boot-file-name": "bootfile.efi",
+                   "client-classes": [ ],
+                   "hostname": "otherhost.example.org",
+                   "hw-address": "01:02:03:04:05:ff",
+                   "ip-address": "192.0.2.200",
+                   "next-server": "192.0.0.2",
+                   "option-data": [ ],
+                   "server-hostname": "server-hostname.example.org"
+               }
+           ]
+       },
+       "result": 0,
+       "text": "72 IPv4 host(s) found."
+   }
+
+The response returned by ``reservation-get-all`` can be very long. The
+DHCP server does not handle DHCP traffic while preparing a response to
+``reservation-get-all``, so if there are many reservations in a subnet, this
+may be disruptive; use with caution. For larger deployments, please
+consider using ``reservation-get-page`` instead (see
+:ref:`command-reservation-get-page`).
+
+For more information, see :ref:`command-reservation-get-all`.
+
+.. _command-reservation-get-page:
+
+The ``reservation-get-page`` command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``reservation-get-page`` can be used to query the host database and
+retrieve all reservations in a specified subnet, by pages. This command
+uses parameters providing the mandatory ``subnet-id``. Use a value of zero
+(0) to fetch global reservations. The second mandatory parameter is the
+page size limit. The optional ``source-index`` and ``from-host-id`` parameters, both
+of which default to 0, are used to chain page queries.
+Since Kea version 1.9.0, the ``subnet-id`` parameter is optional.
+
+The usage of the ``from`` and ``source-index`` parameters requires additional
+explanation. For the first call, those parameters should not be specified
+(or should be specified as zeros). For any follow-up calls, they should be set to
+the values returned in previous calls, in a next map holding ``from`` and
+``source-index`` values. Subsequent calls should be issued until all
+reservations are returned. The end is reached once the returned list is
+empty, the count is 0, no next map is present, and result status 3 (empty) is
+returned.
+
+.. note::
+
+   The ``from`` and ``source-index`` parameters reflect the internal state of
+   the search. There is no need to understand what they represent; it is
+   simply a value that should be copied from one response to the
+   next query. However, for those who are curious, the ``from`` field represents a
+   64-bit representation of the host identifier used by a host backend. The
+   ``source-index`` is an internal representation of multiple host
+   backends: 0 is used to represent hosts defined in a configuration
+   file, and 1 represents the first database backend. In some uncommon cases
+   there may be more than one database backend configured, so
+   potentially there may be a 2. In any case, Kea iterates over all
+   backends configured.
+
+For instance, retrieving host reservations for the subnet 1 and
+requesting the first page can be done by:
+
+::
+
+   {
+       "command": "reservation-get-page",
+       "arguments": {
+           "subnet-id": 1,
+           "limit": 10
+        }
+   }
+
+Since this is the first call, ``source-index`` and ``from`` should not be
+specified. They are set to their zero default values.
+
+Some hosts are returned with information to get the next page:
+
+::
+
+   {
+       "arguments": {
+           "count": 72,
+           "hosts": [
+               {
+                   "boot-file-name": "bootfile.efi",
+                   "client-classes": [ ],
+                   "hostname": "somehost.example.org",
+                   "hw-address": "01:02:03:04:05:06",
+                   "ip-address": "192.0.2.100",
+                   "next-server": "192.0.0.2",
+                   "option-data": [ ],
+                   "server-hostname": "server-hostname.example.org"
+               },
+               ...
+               {
+                   "boot-file-name": "bootfile.efi",
+                   "client-classes": [ ],
+                   "hostname": "otherhost.example.org",
+                   "hw-address": "01:02:03:04:05:ff",
+                   "ip-address": "192.0.2.200",
+                   "next-server": "192.0.0.2",
+                   "option-data": [ ],
+                   "server-hostname": "server-hostname.example.org"
+               }
+           ],
+           "next": {
+               "from": 1234567,
+               "source-index": 1
+           }
+       },
+       "result": 0,
+       "text": "72 IPv4 host(s) found."
+   }
+
+Note that the ``from`` and ``source-index`` fields were specified in the response in
+the next map. Those two must be copied to the next command, so Kea
+continues from the place where the last command finished. To get the
+next page the following command can be sent:
+
+::
+
+   {
+       "command": "reservation-get-page",
+       "arguments": {
+           "subnet-id": 1,
+           "source-index": 1,
+           "from": 1234567,
+           "limit": 10
+        }
+   }
+
+The response will contain a list of hosts with updated ``source-index``
+and ``from`` fields. Continue calling the command until the last
+page is received. Its response will look like this:
+
+::
+
+   {
+       "arguments": {
+           "count": 0,
+           "hosts": [ ],
+       },
+       "result": 3,
+       "0 IPv4 host(s) found."
+   }
+
+This command is more complex than ``reservation-get-all``, but lets
+users retrieve larger host reservations lists in smaller chunks. For
+small deployments with few reservations, it is easier to use
+``reservation-get-all`` (see :ref:`command-reservation-get-all`).
+
+.. _command-reservation-get-by-hostname:
+
+The ``reservation-get-by-hostname`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``reservation-get-by-hostname`` can be used to query the host database and
+retrieve all reservations with a specified hostname or in
+a specified subnet. This command uses parameters providing the mandatory
+``hostname`` and the optional ``subnet-id``. Global host reservations
+can be retrieved by using a ``subnet-id`` value of zero (0).
+Hostname matching is case-insensitive.
+
+For instance, retrieving host reservations for "foobar" in the subnet 1:
+
+::
+
+   {
+       "command": "reservation-get-by-hostname",
+       "arguments": {
+           "hostname": "foobar.example.org",
+           "subnet-id": 1
+        }
+   }
+
+returns some IPv4 hosts:
+
+::
+
+   {
+       "arguments": {
+           "hosts": [
+               {
+                   "boot-file-name": "bootfile.efi",
+                   "client-classes": [ ],
+                   "hostname": "foobar.example.org",
+                   "hw-address": "01:02:03:04:05:06",
+                   "ip-address": "192.0.2.100",
+                   "next-server": "192.0.0.2",
+                   "option-data": [ ],
+                   "server-hostname": "server-hostname.example.org"
+               },
+               ...
+               {
+                   "boot-file-name": "bootfile.efi",
+                   "client-classes": [ ],
+                   "hostname": "foobar.example.org",
+                   "hw-address": "01:02:03:04:05:ff",
+                   "ip-address": "192.0.2.200",
+                   "next-server": "192.0.0.2",
+                   "option-data": [ ],
+                   "server-hostname": "server-hostname.example.org"
+               }
+           ]
+       },
+       "result": 0,
+       "text": "5 IPv4 host(s) found."
+   }
+
+The response returned by ``reservation-get-by-hostname`` can be long,
+particularly when responses are not limited to a subnet.
+
+For more information, see :ref:`command-reservation-get-by-hostname`.
+
+.. note::
+
+   When using MySQL as the host backend, this command relies on the fact
+   that the hostname column in the hosts table uses a case-insensitive
+   collation, as explained in the :ref:`mysql-database` section of
+   :ref:`admin`.
+
+.. _command-reservation-get-by-id:
+
+The ``reservation-get-by-id`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``reservation-get-by-id`` can be used to query the host database and
+retrieve all reservations with a specified identifier (``identifier-type``
+and ``identifier`` parameters), independently of subnets. The syntax for
+parameters is the same as for ref:`command-reservation-get`.
+The ``subnet-id`` parameter cannot be used, to avoid confusion.
+This command is available since Kea version 1.9.0.
+
+For instance, retrieving host reservations for the 01:02:03:04:05:06 MAC
+address:
+
+::
+
+   {
+       "command": "reservation-get-by-id",
+       "arguments": {
+           "identifier-type": "hw-address",
+           "identifier": "01:02:03:04:05:06"
+        }
+    }
+
+returns some IPv4 hosts:
+
+::
+
+   {
+       "arguments": {
+           "hosts": [
+               {
+                   "boot-file-name": "bootfile.efi",
+                   "client-classes": [ ],
+                   "hostname": "foo.example.org",
+                   "hw-address": "01:02:03:04:05:06",
+                   "ip-address": "192.0.2.100",
+                   "next-server": "192.0.0.2",
+                   "option-data": [ ],
+                   "server-hostname": "server-hostname.example.org",
+                   "subnet-id": 123
+               },
+               ...
+               {
+                   "boot-file-name": "bootfile.efi",
+                   "client-classes": [ ],
+                   "hostname": "bar.example.org",
+                   "hw-address": "01:02:03:04:05:06",
+                   "ip-address": "192.0.2.200",
+                   "next-server": "192.0.0.2",
+                   "option-data": [ ],
+                   "server-hostname": "server-hostname.example.org",
+                   "subnet-id": 345
+               }
+           ]
+       },
+       "result": 0,
+       "text": "5 IPv4 host(s) found."
+   }
+
+The response returned by ``reservation-get-by-id`` can be long,
+particularly when responses are not limited to a subnet.
+
+For more information, see :ref:`command-reservation-get-by-id`.
+
+.. _command-reservation-del:
+
+The ``reservation-del`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``reservation-del`` can be used to delete a reservation from the host
+database. This command supports two types of parameters:
+(``subnet-id``, ``address``) or (``subnet-id``, ``identifier-type``, ``identifier``). The
+first type of query is used when the address (either IPv4 or IPv6) is
+known, but the details of the reservation are not. One common use for
+this type of query is to remove a reservation (e.g. a specific
+address should no longer be reserved). The second query uses identifiers.
+For maximum flexibility, Kea stores the host identifying information as
+a pair of values: the type and the actual identifier. Currently supported
+identifiers are ``"hw-address"``, ``"duid"``, ``"circuit-id"``, ``"client-id"``, and
+``"flex-id"``. The ``subnet-id`` is mandatory. Use a value
+of zero (0) to delete a global reservation, or the ID of the subnet from
+which the reservation should be deleted.
+
+An example command for deleting a host reservation by (``subnet-id``,
+``address``) pair looks as follows:
+
+::
+
+   {
+       "command": "reservation-del",
+       "arguments": {
+           "subnet-id": 1,
+           "ip-address": "192.0.2.202"
+       }
+   }
+
+An example deletion by (``subnet-id``, ``identifier-type``, ``identifier``) looks as
+follows:
+
+::
+
+   {
+       "command": "reservation-del",
+       "arguments":
+           "subnet-id": 4,
+           "identifier-type": "hw-address",
+           "identifier": "01:02:03:04:05:06"
+       }
+   }
+
+``reservation-del`` returns a result of 0 when the host deletion was
+successful, or 1 if it failed. Descriptive text is provided in the event of
+an error. Here are some examples of possible results:
+
+::
+
+   {
+       "result": 1,
+       "text": "Host not deleted (not found)."
+   }
+
+::
+
+   {
+       "result": 0,
+       "text": "Host deleted."
+   }
+
+::
+
+   {
+       "result": 1,
+       "text": "Unable to delete a host because there is no hosts-database
+                configured."
+   }
diff --git a/doc/sphinx/arm/hooks-lease-cmds.rst b/doc/sphinx/arm/hooks-lease-cmds.rst
new file mode 100644
index 0000000..f4ee018
--- /dev/null
+++ b/doc/sphinx/arm/hooks-lease-cmds.rst
@@ -0,0 +1,1005 @@
+.. _hooks-lease-cmds:
+
+``lease_cmds``: Lease Commands for Easier Lease Management
+==========================================================
+
+Kea allows users to store lease information in several
+backends (memfile, MySQL, and PostgreSQL), and the Lease Commands library provides an
+interface that can manipulate leases in a unified, safe way.
+In particular, it allows things that were previously impossible: lease
+manipulation in memfile while Kea is running, sanity check changes,
+lease existence checks, and removal of all leases belonging to a
+specific subnet. The hook library can also catch more obscure errors, like an attempt
+to add a lease with a ``subnet-id`` that does not exist in the
+configuration, or configuring a lease to use an address that is outside
+of the subnet to which it is supposed to belong. The library also
+provides a non-programmatic way to manage user contexts associated with
+leases.
+
+The Lease Commands library is part of the open source code and is
+available to every Kea user.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or the
+   ``kea-dhcp6`` process.
+
+There are many situations where an administrative command may be useful;
+for example, during migration between servers or different vendors, when
+a certain network is being retired, or when a device has been
+disconnected and the system administrator knows that it will not be coming
+back. The ``get`` queries may be useful for automating certain management
+and monitoring tasks, and they can also act as preparatory steps for lease
+updates and removals.
+
+This library provides the following commands:
+
+-  ``lease4-add`` - adds a new IPv4 lease.
+
+-  ``lease6-add`` - adds a new IPv6 lease.
+
+-  ``lease6-bulk-apply`` - creates, updates, and/or deletes multiple
+   IPv6 leases in a single transaction.
+
+-  ``lease4-get`` - checks whether an IPv4 lease with the specified
+   parameters exists and returns it if it does.
+
+-  ``lease6-get`` - checks whether an IPv6 lease with the specified
+   parameters exists and returns it if it does.
+
+-  ``lease4-get-all`` - returns all IPv4 leases or all IPv4 leases for
+   the specified subnets.
+
+-  ``lease6-get-all`` - returns all IPv6 leases or all IPv6 leases for
+   the specified subnets.
+
+-  ``lease4-get-page`` - returns a set ("page") of leases from the list
+   of all IPv4 leases in the database. By iterating through the pages it
+   is possible to retrieve all the leases.
+
+-  ``lease6-get-page`` - returns a set ("page") of leases from the list
+   of all IPv6 leases in the database. By iterating through the pages it
+   is possible to retrieve all the leases.
+
+-  ``lease4-get-by-hw-address`` - returns all IPv4 leases with the specified
+   hardware address.
+
+-  ``lease4-get-by-client-id`` - returns all IPv4 leases with the specified
+   ``client-id``.
+
+-  ``lease6-get-by-duid`` - returns all IPv6 leases with the specified DUID.
+
+-  ``lease4-get-by-hostname`` - returns all IPv4 leases with the specified
+   hostname.
+
+-  ``lease6-get-by-hostname`` - returns all IPv6 leases with the specified
+   hostname.
+
+-  ``lease4-del`` - deletes an IPv4 lease with the specified parameters.
+
+-  ``lease6-del`` - deletes an IPv6 lease with the specified parameters.
+
+-  ``lease4-update`` - updates an IPv4 lease.
+
+-  ``lease6-update`` - updates an IPv6 lease.
+
+-  ``lease4-wipe`` - removes all leases from a specific IPv4 subnet or
+   from all subnets.
+
+-  ``lease6-wipe`` - removes all leases from a specific IPv6 subnet or
+   from all subnets.
+
+-  ``lease4-resend-ddns`` - resends a request to update DNS entries for
+   an existing lease.
+
+-  ``lease6-resend-ddns`` - resends a request to update DNS entries for
+   an existing lease.
+
+All commands use JSON syntax and can be issued either using the control
+channel (see :ref:`ctrl-channel`) or Control Agent (see
+:ref:`kea-ctrl-agent`).
+
+The library can be loaded in the same way as other hook libraries, and
+it does not take any parameters. It supports both the DHCPv4 and DHCPv6
+servers.
+
+::
+
+   "Dhcp6": {
+       "hooks-libraries": [
+           {
+               "library": "/path/libdhcp_lease_cmds.so"
+           }
+           ...
+       ]
+   }
+
+.. _command-lease4-add:
+
+.. _command-lease6-add:
+
+The ``lease4-add``, ``lease6-add`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``lease4-add`` and ``lease6-add`` commands allow a new lease
+to be created. Typically Kea creates a lease when it first sees a new
+device; however, sometimes it may be convenient to create the lease
+manually. The ``lease4-add`` command requires at least two parameters:
+an IPv4 address and an identifier, i.e. hardware (MAC) address. A third
+parameter, ``subnet-id``, is optional. If the ``subnet-id`` is not specified or
+the specified value is 0, Kea tries to determine the value by running
+a subnet-selection procedure. If specified, however, its value must
+match the existing subnet. The simplest successful call might look as
+follows:
+
+::
+
+   {
+       "command": "lease4-add",
+       "arguments": {
+           "ip-address": "192.0.2.202",
+           "hw-address": "1a:1b:1c:1d:1e:1f"
+       }
+   }
+
+The ``lease6-add`` command requires three parameters: an IPv6 address,
+an IAID value (identity association identifier, a value sent by
+clients), and a DUID. As with ``lease4-add``, the ``subnet-id`` parameter is
+optional. If the ``subnet-id`` is not specified or the provided value is 0,
+Kea tries to determine the value by running a subnet-selection
+procedure. If specified, however, its value must match the existing
+subnet. For example:
+
+::
+
+   {
+       "command": "lease6-add",
+       "arguments": {
+           "subnet-id": 66,
+           "ip-address": "2001:db8::3",
+           "duid": "1a:1b:1c:1d:1e:1f:20:21:22:23:24",
+           "iaid": 1234
+       }
+   }
+
+``lease6-add`` can also be used to add leases for IPv6 prefixes. In this
+case there are three additional parameters that must be specified:
+``subnet-id``, ``type`` (set to "IA_PD"), and prefix length. The actual
+prefix is set using the ``ip-address`` field. Note that Kea cannot guess
+``subnet-id`` values for prefixes; they must be specified explicitly. For
+example, to configure a lease for prefix 2001:db8:abcd::/48, the
+following command can be used:
+
+::
+
+   {
+       "command": "lease6-add",
+       "arguments": {
+           "subnet-id": 66,
+           "type": "IA_PD",
+           "ip-address": "2001:db8:abcd::",
+           "prefix-len": 48,
+           "duid": "1a:1b:1c:1d:1e:1f:20:21:22:23:24",
+           "iaid": 1234
+       }
+   }
+
+The commands can take several additional optional parameters:
+
+-  ``valid-lft`` - specifies the lifetime of the lease, expressed in
+   seconds. If not specified, the value configured in the subnet related
+   to the specified ``subnet-id`` is used.
+
+-  ``expire`` - creates a timestamp of the lease expiration time,
+   expressed in UNIX format (seconds since 1 Jan 1970). If not
+   specified, the default value is the current time plus the lease lifetime (the value
+   of ``valid-lft``).
+
+-  ``fqdn-fwd`` - specifies whether the lease should be marked as if a
+   forward DNS update were conducted. This only affects the
+   data stored in the lease database, and no DNS update will be
+   performed. If configured, a DNS update to remove the A or AAAA
+   records will be conducted when the lease is removed due to expiration
+   or being released by a client. If not specified, the default value is
+   ``false``. The hostname parameter must be specified if ``fqdn-fwd`` is set to
+   ``true``.
+
+-  ``fqdn-rev`` - specifies whether the lease should be marked as if
+   reverse DNS update were conducted. This only affects the
+   data stored in the lease database, and no DNS update will be
+   performed.. If configured, a DNS update to remove the PTR record will
+   be conducted when the lease is removed due to expiration or being
+   released by a client. If not specified, the default value is ``false``.
+   The hostname parameter must be specified if ``fqdn-fwd`` is set to ``true``.
+
+-  ``hostname`` - specifies the hostname to be associated with this
+   lease. Its value must be non-empty if either ``fqdn-fwd`` or ``fqdn-rev`` are
+   set to ``true``. If not specified, the default value is an empty string.
+
+-  ``hw-address`` - optionally specifies a hardware (MAC) address for an
+   IPv6 lease. It is a mandatory parameter for an IPv4 lease.
+
+-  ``client-id`` - optionally specifies a client identifier for an IPv4
+   lease.
+
+-  ``preferred-lft`` - optionally specifies a preferred lifetime for
+   IPv6 leases. If not specified, the value configured for the subnet
+   corresponding to the specified ``subnet-id`` is used. This parameter is
+   not used when adding an IPv4 lease.
+
+-  ``state`` - specifies the state of an added lease, which can be 0 for ``default``,
+   1 for ``declined``, and 2 for the ``expired-reclaimed`` state. Any other
+   value causes an error. Using 1 for a ``"IA_PD"`` lease type is
+   illegal and will be rejected.
+
+-  ``user-context`` - specifies the user context to be associated with
+   this lease. It must be a JSON map.
+
+Here is an example of a fairly complex lease addition:
+
+::
+
+   {
+       "command": "lease6-add",
+       "arguments": {
+           "subnet-id": 66,
+           "ip-address": "2001:db8::3",
+           "duid": "01:02:03:04:05:06:07:08",
+           "iaid": 1234,
+           "hw-address": "1a:1b:1c:1d:1e:1f",
+           "preferred-lft": 500,
+           "valid-lft": 1000,
+           "expire": 12345678,
+           "fqdn-fwd": true,
+           "fqdn-rev": true,
+           "state": 0,
+           "hostname": "urania.example.org",
+           "user-context": { "version": 1 }
+       }
+   }
+
+The command returns a status that indicates either success (result 0)
+or failure (result 1). A failed command always includes a text
+parameter that explains the cause of failure. For example:
+
+::
+
+   { "result": 0, "text": "Lease added." }
+
+Example failure:
+
+::
+
+   { "result": 1, "text": "missing parameter 'ip-address' (<string>:3:19)" }
+
+
+.. _command-lease6-bulk-apply:
+
+The ``lease6-bulk-apply`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``lease6-bulk-apply`` was implemented to address
+the performance penalty in High-Availability mode when a single DHCPv6
+transaction resulted in multiple lease updates sent to the partner, if
+multiple address and/or prefix leases were allocated. Consider the case
+when a DHCPv6 client requests the assignment of two IPv6 addresses and two IPv6
+prefixes: it may result in the allocation of four leases. In addition,
+DHCPv6 may assign a different address than the one requested by the client during
+the renew or rebind stage, and delete the leases previously used by this client.
+There are six lease changes sent between the HA partners in this case.
+Sending these updates as individual commands, e.g. via ``lease6-update``,
+is highly inefficient and produces unnecessary delays in communication,
+both between the HA partners and in sending the response to the DHCPv6 client.
+
+The ``lease6-bulk-apply`` command deals with this
+problem by aggregating all lease changes - both deleted leases and
+new or updated leases - in a single command.
+The receiving server iterates over the deleted leases and deletes them
+from its lease database. Next, it iterates over the new/updated leases
+and adds them to the database or updates them if they already exist.
+
+Even though High Availability is the major application for
+this command, it can be freely used in all cases when it is desirable to
+send multiple lease changes in a single command.
+
+In the following example, we delete two leases and add
+or update two other leases in the database:
+
+
+::
+
+    {
+      "command": "lease6-bulk-apply",
+      "arguments": {
+          "deleted-leases": [
+              {
+                  "ip-address": "2001:db8:abcd::",
+                  "type": "IA_PD",
+                  ...
+              },
+              {
+                  "ip-address": "2001:db8:abcd::234",
+                  "type": "IA_NA",
+                  ...
+              }
+          ],
+          "leases": [
+              {
+                  "subnet-id": 66,
+                  "ip-address": "2001:db8:cafe::",
+                  "type": "IA_PD",
+                   ...
+              },
+              {
+                  "subnet-id": 66,
+                  "ip-address": "2001:db8:abcd::333",
+                  "type": "IA_NA",
+                  ...
+              }
+          ]
+       }
+   }
+
+If any of the leases are malformed, no lease changes are applied
+to the lease database. If the leases are well-formed but there is a
+failure to apply any of the lease changes to the database, the command
+continues to be processed for other leases. All the leases for which
+the command was unable to apply the changes in the database are
+listed in the response. For example:
+
+::
+
+    {
+        "result": 0,
+        "text": "Bulk apply of 2 IPv6 leases completed".
+        "arguments": {
+            "failed-deleted-leases": [
+                {
+                    "ip-address": "2001:db8:abcd::",
+                    "type": "IA_PD",
+                    "result": 3,
+                    "error-message": "no lease found"
+                }
+            ],
+            "failed-leases": [
+                {
+                    "ip-address": "2001:db8:cafe::",
+                    "type": "IA_PD",
+                    "result": 1,
+                    "error-message": "unable to communicate with the lease database"
+                }
+            ]
+        }
+    }
+
+The response above indicates that the hook library was unable to
+delete the lease for prefix "2001:db8:abcd::" and add or update the lease
+for prefix "2001:db8:cafe::". However, there are two other lease changes
+which have been applied as indicated by the text message. The
+``result`` is the status constant that indicates the type
+of the error experienced for the particular lease. The meanings of the
+returned codes are the same as the results returned for the commands.
+In particular, the result of 1 indicates an error while processing the
+lease, e.g. a communication error with the database. The result of 3
+indicates that an attempt to delete the lease was unsuccessful because
+such a lease doesn't exist (an empty result).
+
+.. _command-lease4-get:
+
+.. _command-lease6-get:
+
+The ``lease4-get``, ``lease6-get`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``lease4-get`` and ``lease6-get`` can be used to query the lease database
+and retrieve existing leases. There are two types of parameters the
+``lease4-get`` command supports: (``address``) or (``subnet-id``,
+``identifier-type``, ``identifier``). There are also two types for
+``lease6-get``: (``address``, ``type``) or (``subnet-id``, ``identifier-type``,
+``identifier``, ``IAID``, ``type``). The first type of query is used when the
+address (either IPv4 or IPv6) is known, but the details of the lease are
+not; one common use case of this type of query is to find out whether a
+given address is being used. The second query uses identifiers;
+currently supported identifiers for leases are: ``"hw-address"`` (IPv4
+only), ``"client-id"`` (IPv4 only), and ``"duid"`` (IPv6 only).
+
+An example ``lease4-get`` command for getting a lease using an IPv4
+address is:
+
+::
+
+   {
+       "command": "lease4-get",
+       "arguments": {
+           "ip-address": "192.0.2.1"
+       }
+   }
+
+An example of the ``lease6-get`` query is:
+
+::
+
+   {
+     "command": "lease6-get",
+     "arguments": {
+       "ip-address": "2001:db8:1234:ab::",
+       "type": "IA_PD"
+     }
+   }
+
+An example query by ``"hw-address"`` for an IPv4 lease looks as follows:
+
+::
+
+   {
+       "command": "lease4-get",
+       "arguments": {
+           "identifier-type": "hw-address",
+           "identifier": "08:08:08:08:08:08",
+           "subnet-id": 44
+       }
+   }
+
+An example query by ``"client-id"`` for an IPv4 lease looks as follows:
+
+::
+
+   {
+       "command": "lease4-get",
+       "arguments": {
+           "identifier-type": "client-id",
+           "identifier": "01:01:02:03:04:05:06",
+           "subnet-id": 44
+       }
+   }
+
+An example query by (``subnet-id``, ``identifier-type``, ``identifier``, ``iaid``, ``type``)
+for an IPv6 lease is:
+
+::
+
+   {
+       "command": "lease4-get",
+       "arguments": {
+           "identifier-type": "duid",
+           "identifier": "08:08:08:08:08:08",
+           "iaid": 1234567,
+           "type": "IA_NA",
+           "subnet-id": 44
+       }
+   }
+
+The ``type`` is an optional parameter. Supported values are: ``IA_NA``
+(non-temporary address) and ``IA_PD`` (IPv6 prefix). If not specified, ``IA_NA``
+is assumed.
+
+``lease4-get`` and ``lease6-get`` return an indication of the result of the operation
+and lease details, if found. The result has one of the following values: 0
+(success), 1 (error), or 3 (empty). An empty result means that a query
+has been completed properly, but the object (a lease in this case) has
+not been found.
+The lease parameters, if found, are returned as arguments.
+``client-id`` is not returned if empty.
+
+An example result returned when the host was found:
+
+::
+
+   {
+     "arguments": {
+       "client-id": "42:42:42:42:42:42:42:42",
+       "cltt": 12345678,
+       "fqdn-fwd": false,
+       "fqdn-rev": true,
+       "hostname": "myhost.example.com.",
+       "hw-address": "08:08:08:08:08:08",
+       "ip-address": "192.0.2.1",
+       "state": 0,
+       "subnet-id": 44,
+       "valid-lft": 3600
+     },
+     "result": 0,
+     "text": "IPv4 lease found."
+   }
+
+.. note::
+
+   The client last transaction time (``cltt`` field) is bound to the
+   valid lifetime (``valid-lft``) and to the expire date (not reported
+   here but stored in databases) by the equation
+   :math:`cltt + valid\_lft = expire`
+
+   at the exception of the infinite valid lifetime coded by the
+   0xfffffff (4294967295) special value which makes the expire value
+   to overflow on MySQL and old PostgreSQL backends where timestamps
+   are 32 bit long. So in these lease databases the expire date is the
+   same as the cltt i.e.
+   :math:`cltt = expire` when :math:`valid\_lft = 4294967295` and the
+   lease backend is MySQL or PostgreSQL.
+
+.. _command-lease4-get-all:
+
+.. _command-lease6-get-all:
+
+The ``lease4-get-all``, ``lease6-get-all`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``lease4-get-all`` and ``lease6-get-all`` are used to retrieve all IPv4
+or IPv6 leases, or all leases for the specified set of subnets. All
+leases are returned when there are no arguments specified with the
+command, as in the following example:
+
+::
+
+   {
+       "command": "lease4-get-all"
+   }
+
+If arguments are provided, it is expected that they contain the
+``"subnets"`` parameter, which is a list of subnet identifiers for which
+leases should be returned. For example, to retrieve all IPv6
+leases belonging to the subnets with identifiers 1, 2, 3, and 4:
+
+::
+
+   {
+       "command": "lease6-get-all",
+       "arguments": {
+           "subnets": [ 1, 2, 3, 4 ]
+       }
+   }
+
+The returned response contains a detailed list of leases in the
+following format:
+
+::
+
+   {
+       "arguments": {
+           "leases": [
+               {
+                   "cltt": 12345678,
+                   "duid": "42:42:42:42:42:42:42:42",
+                   "fqdn-fwd": false,
+                   "fqdn-rev": true,
+                   "hostname": "myhost.example.com.",
+                   "hw-address": "08:08:08:08:08:08",
+                   "iaid": 1,
+                   "ip-address": "2001:db8:2::1",
+                   "preferred-lft": 500,
+                   "state": 0,
+                   "subnet-id": 44,
+                   "type": "IA_NA",
+                   "valid-lft": 3600
+               },
+               {
+                   "cltt": 12345678,
+                   "duid": "21:21:21:21:21:21:21:21",
+                   "fqdn-fwd": false,
+                   "fqdn-rev": true,
+                   "hostname": "",
+                   "iaid": 1,
+                   "ip-address": "2001:db8:0:0:2::",
+                   "preferred-lft": 500,
+                   "prefix-len": 80,
+                   "state": 0,
+                   "subnet-id": 44,
+                   "type": "IA_PD",
+                   "valid-lft": 3600
+               }
+           ]
+       },
+       "result": 0,
+       "text": "2 IPv6 lease(s) found."
+   }
+
+.. warning::
+
+   The ``lease4-get-all`` and ``lease6-get-all`` commands may result in
+   very large responses. This may have a negative impact on the DHCP
+   server's responsiveness while the response is generated and
+   transmitted over the control channel, as the server imposes no
+   restriction on the number of leases returned as a result of this
+   command.
+
+.. _command-lease4-get-page:
+
+.. _command-lease6-get-page:
+
+The ``lease4-get-page``, ``lease6-get-page`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``lease4-get-all`` and ``lease6-get-all`` commands may result in
+very large responses; generating such a response may consume CPU
+bandwidth as well as memory. It may even cause the server to become
+unresponsive. In the case of large lease databases it is usually better to
+retrieve leases in chunks, using the paging mechanism.
+``lease4-get-page`` and ``lease6-get-page`` implement a paging mechanism
+for DHCPv4 and DHCPv6 servers, respectively. The following command
+retrieves the first 1024 IPv4 leases:
+
+::
+
+   {
+       "command": "lease4-get-page",
+       "arguments": {
+           "from": "start",
+           "limit": 1024
+       }
+   }
+
+The keyword ``start`` denotes that the first page of leases should be
+retrieved. Alternatively, an IPv4 zero address can be specified to
+retrieve the first page:
+
+::
+
+   {
+       "command": "lease4-get-page",
+       "arguments": {
+           "from": "0.0.0.0",
+           "limit": 1024
+       }
+   }
+
+Similarly, the IPv6 zero address can be specified in the
+``lease6-get-page`` command:
+
+::
+
+   {
+       "command": "lease6-get-page",
+       "arguments": {
+           "from": "::",
+           "limit": 6
+       }
+   }
+
+The response has the following structure:
+
+::
+
+   {
+       "arguments": {
+           "leases": [
+               {
+                   "ip-address": "2001:db8:2::1",
+                   ...
+               },
+               {
+                   "ip-address": "2001:db8:2::9",
+                   ...
+               },
+               {
+                   "ip-address": "2001:db8:3::1",
+                   ...
+               },
+               {
+                   "ip-address": "2001:db8:5::3",
+                   ...
+               }
+               {
+                   "ip-address": "2001:db8:4::1",
+                   ...
+               },
+               {
+                   "ip-address": "2001:db8:2::7",
+                   ...
+               }
+
+           ],
+           "count": 6
+       },
+       "result": 0,
+       "text": "6 IPv6 lease(s) found."
+   }
+
+Note that the leases' details were excluded from the response above for
+brevity.
+
+Generally, the returned list is not sorted in any particular order. Some
+lease database backends may sort leases in ascending order of addresses,
+but the controlling client must not rely on this behavior.
+
+The ``count`` parameter contains the number of returned leases on the
+page.
+
+To fetch the next page, the client must use the last address of the
+current page as an input to the next ``lease4-get-page`` or
+``lease6-get-page`` command call. In this example it is:
+
+::
+
+   {
+       "command": "lease6-get-page",
+       "arguments": {
+           "from": "2001:db8:2::7",
+           "count": 6
+       }
+   }
+
+because 2001:db8:2::7 is the last address on the current page.
+
+The client may assume that it has reached the last page when the
+``count`` value is lower than that specified in the command; this
+includes the case when the ``count`` is equal to 0, meaning that no
+leases were found.
+
+.. _command-lease4-get-by-hw-address:
+
+.. _command-lease4-get-by-client-id:
+
+.. _command-lease6-get-by-duid:
+
+.. _command-lease4-get-by-hostname:
+
+.. _command-lease6-get-by-hostname:
+
+The ``lease4-get-by-*``, ``lease6-get-by-*`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``lease4-get-by-*`` and ``lease6-get-by-*`` can be used to query the lease database and
+retrieve all existing leases matching a given feature (denoted by the ``*``). These
+can include a specified hardware address (IPv4
+only), ``client-id`` IPv4 only), ``duid`` (IPv6 only) identifiers, or hostname.
+
+An example ``lease4-get-by-hw-address`` command for getting IPv4 leases
+with a given hardware address is:
+
+::
+
+    {
+        "command": "lease4-get-by-hw-address",
+        "arguments": {
+            "hw-address": "08:08:08:08:08:08"
+        }
+    }
+
+An example of the ``lease6-get-by-hostname`` is:
+
+::
+
+    {
+        "command": "lease6-get-by-hostname",
+        "arguments": {
+            "hostname": "myhost.example.org"
+        }
+    }
+
+The ``by`` key is the only parameter. The returned response contains a detailed
+list of leases in the same format as ``lease4-get-all`` or ``lease6-get-all``. This list can be
+empty and is usually not large.
+
+.. _command-lease4-del:
+
+.. _command-lease6-del:
+
+The ``lease4-del``, ``lease6-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``lease4-del`` and ``lease6-del`` can be used to delete a lease from the lease database.
+There are two types of parameters these commands support, similar to the
+``lease4-get``and ``lease6-get`` commands: (``address``) for both v4 and v6, (``subnet-id``,
+``identifier-type``, ``identifier``) for v4, and (``subnet-id``, ``identifier-type``,
+``identifier``, ``type``, ``IAID``) for v6. The first type of query is used when the
+address (either IPv4 or IPv6) is known, but the details of the lease are
+not. One common use case is where an administrator wants a specified
+address to no longer be used. The second form of the command uses
+identifiers. For maximum flexibility, this interface uses identifiers as
+a pair of values: the type and the actual identifier. The currently
+supported identifiers are ``"hw-address"`` (IPv4 only), ``"client-id"`` (IPv4
+only), and ``"duid"`` (IPv6 only).
+
+An example command for deleting a lease by address is:
+
+::
+
+   {
+       "command": "lease4-del",
+       "arguments": {
+           "ip-address": "192.0.2.202"
+       }
+   }
+
+An example IPv4 lease deletion by ``"hw-address"`` is:
+
+::
+
+   {
+     "command": "lease4-del",
+     "arguments": {
+       "identifier": "08:08:08:08:08:08",
+       "identifier-type": "hw-address",
+       "subnet-id": 44
+     }
+   }
+
+
+Another parameter called ``update-ddns``, when ``true``, instructs the server to
+queue a request to ``kea-dhcp-ddns`` to remove DNS entries after the lease is
+successfully deleted if:
+
+- DDNS updating is enabled (i.e. ``"dhcp-ddns":{ "enable-updates": true }``).
+- The lease's hostname is not empty.
+- At least one of the lease's DNS direction flags (``fqdn_fwd`` or ``fqdn_rev``) is true.
+
+This parameter defaults to ``false``. An example of its use is shown below:
+
+::
+
+   {
+       "command": "lease4-del",
+       "arguments": {
+           "ip-address": "192.0.2.202",
+           "update-ddns": true
+       }
+   }
+
+
+``lease4-del`` and ``lease6-del`` return a result that indicates the outcome of the
+operation. It has one of the following values: 0 (success), 1 (error),
+or 3 (empty). The empty result means that a query has been completed
+properly, but the object (a lease, in this case) has not been found.
+
+.. _command-lease4-update:
+
+.. _command-lease6-update:
+
+The ``lease4-update``, ``lease6-update`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``lease4-update`` and ``lease6-update`` commands can be used to
+update existing leases. Since all lease database backends are indexed by
+IP addresses, it is not possible to update an address, but all other
+fields may be altered. If an address needs to be changed, please use
+``lease4-del``/``lease6-del`` followed by ``lease4-add``/``lease6-add``.
+
+The ``subnet-id`` parameter is optional. If not specified, or if the
+specified value is 0, Kea tries to determine its value by running a
+subnet-selection procedure. If specified, however, its value must match
+the existing subnet.
+
+The optional boolean parameter ``"force-create"`` specifies whether the
+lease should be created if it does not exist in the database. It defaults
+to ``false``, which indicates that the lease is not created if it does not
+exist. In such a case, an error is returned when trying to
+update a non-existing lease. If the ``"force-create"`` parameter is set to
+``true`` and the updated lease does not exist, the new lease is created as a
+result of receiving the ``lease4-update``/``lease6-update`` command.
+
+An example of a command to update an IPv4 lease is:
+
+::
+
+   {
+     "command": "lease4-update",
+     "arguments": {
+       "ip-address": "192.0.2.1",
+       "hostname": "newhostname.example.org",
+       "hw-address": "1a:1b:1c:1d:1e:1f",
+       "subnet-id": 44,
+       "force-create": true
+     }
+   }
+
+An example of a command to update an IPv6 lease is:
+
+::
+
+   {
+     "command": "lease6-update",
+     "arguments": {
+       "ip-address": "2001:db8::1",
+       "duid": "88:88:88:88:88:88:88:88",
+       "iaid": 7654321,
+       "hostname": "newhostname.example.org",
+       "subnet-id": 66,
+       "force-create": false
+     }
+   }
+
+.. _command-lease4-wipe:
+
+.. _command-lease6-wipe:
+
+The ``lease4-wipe``, ``lease6-wipe`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``lease4-wipe`` and ``lease6-wipe`` are designed to remove all leases
+associated with a given subnet. This administrative task is expected to
+be used when an existing subnet is being retired. The leases
+are not properly expired; no DNS updates are carried out, no log
+messages are created, and hooks are not called for the leases being
+removed.
+
+An example of ``lease4-wipe`` is:
+
+::
+
+   {
+     "command": "lease4-wipe",
+     "arguments": {
+       "subnet-id": 44
+     }
+   }
+
+An example of ``lease6-wipe`` is:
+
+::
+
+   {
+     "command": "lease6-wipe",
+     "arguments": {
+       "subnet-id": 66
+     }
+   }
+
+The commands return a text description of the number of leases removed,
+plus the status code 0 (success) if any leases were removed or 3 (empty)
+if there were no leases. Status code 1 (error) may be returned if the
+parameters are incorrect or some other exception is encountered.
+
+``subnet-id`` 0 has a special meaning; it tells Kea to delete leases from
+all configured subnets. Also, the ``subnet-id`` parameter may be omitted. If
+not specified, leases from all subnets are wiped.
+
+Note: currently only memfile lease storage supports this command.
+
+.. _command-lease4-resend-ddns:
+
+.. _command-lease6-resend-ddns:
+
+The ``lease4-resend-ddns``, ``lease6-resend-ddns`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``lease4-resend-ddns`` and ``lease6-resend-ddns`` can be used to generate
+a request to ``kea-dhcp-ddns`` to update the DNS entries for an existing
+lease.  The desired lease is selected by a single parameter, ``"ip-address"``.
+For an update request to be generated, DDNS updating must be enabled
+and DNS entries must have already been made (or attempted) for the lease.
+In other words, all of the following must be true:
+
+- DDNS updating must be enabled (i.e. ``"dhcp-ddns":{ "enable-updates": true"}``).
+- The lease's hostname must not be empty.
+- At least one of the lease's DNS direction flags (``fqdn_fwd`` or ``fqdn_rev``) must be true.
+
+An example ``lease4-resend-ddns`` command for getting a lease using an IPv4
+address is:
+
+::
+
+   {
+       "command": "lease4-resend-ddns",
+       "arguments": {
+           "ip-address": "192.0.2.1"
+       }
+   }
+
+An example of the ``lease6-resend-ddns`` query is:
+
+::
+
+   {
+     "command": "lease6-resend-ddns",
+     "arguments": {
+       "ip-address": "2001:db8:1::1"
+     }
+   }
+
+``lease4-resend-ddns`` and ``lease6-resend-ddns`` return an indication of the result of the operation.
+It has one of the following values: 0 (success), 1 (error), or 3 (empty). An empty
+result means that a query has been completed properly, but the object (a lease in
+this case) has not been found.
+
+A successful result does not mean that DNS has been successfully updated; it
+indicates that a request to update DNS has been successfully created and
+queued for transmission to ``kea-dhcp-ddns``.
+
+Here's an example of a result returned when the lease was found:
+
+::
+
+   {
+     "result": 0,
+     "text": "NCR generated for: 2001:db8:1::1, hostname: example.com."
+   }
diff --git a/doc/sphinx/arm/hooks-lease-query.rst b/doc/sphinx/arm/hooks-lease-query.rst
new file mode 100644
index 0000000..8aa6f2d
--- /dev/null
+++ b/doc/sphinx/arm/hooks-lease-query.rst
@@ -0,0 +1,331 @@
+.. _hooks-lease-query:
+
+``lease_query``: Leasequery Support
+===================================
+
+This library provides support for DHCPv4 Leasequery as described in
+`RFC 4388 <https://tools.ietf.org/html/rfc4388>`__; and for DHCPv6
+Leasequery (`RFC 5007 <https://tools.ietf.org/html/rfc5007>`__).
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or
+   ``kea-dhcp6`` process.
+
+The Leasequery library is only available to ISC customers with a paid support contract.
+
+.. _lease-query-dhcpv4:
+
+DHCPv4 Leasequery
+~~~~~~~~~~~~~~~~~
+
+DHCPv4 simple Leasequery provides a requester the ability to query for
+active lease information for either a single IP address or a single client.
+RFC 4388 calls for three such queries:
+
+- Query by IP address
+
+    The IP address of interest is contained within the ``ciaddr`` field of
+    the query.
+- Query by hardware address
+
+    The hardware address of interest is contained with the ``chaddr`` field
+    of the query.
+- Query by client identifier
+
+    The client identifier of interest is sent in the ``dhcp-client-identifier``
+    option (61) of the query.
+
+The inbound DHCPLEASEQUERY packet must supply only one of the three values
+above. Queries which supply more than one of these values are dropped.
+
+In addition, the query must contain the IP address of the requester in
+``giaddr``. This value is used not only as the destination for the
+query response but also to validate the requester against a known
+list of IP addresses which are permitted to query. This list of valid
+requester addresses is specified as part of the Leasequery hook library's
+configuration (see the section on configuration below).
+
+In response to a valid query, the server returns one of three message
+types:
+
+- DHCPLEASEUNKNOWN
+
+    Returned when the IP address of interest is not one the server knows
+    about (query by IP address); or there are no active leases for the
+    client of interest (query by hardware address or client ID).
+
+- DHCPLEASEUNASSIGNED
+
+    Returned when the IP address is one the server knows of but for which
+    there are no active leases (applies only to query by IP address).
+
+- DHCPLEASEACTIVE
+
+    Returned when there is at least one active lease found matching the
+    criteria.
+
+For both DHCPLEASEUNKNOWN and DHCPLEASEUNASSIGNED responses, the only
+information sent back to the requester in response is the query parameter
+itself (i.e. one of: IP address, hardware address, or client identifier).
+
+For DHCPLEASEACTIVE the server provides the following information
+for the newest active lease that matches the criteria, in the response:
+
+- ``ciaddr`` - set to the lease's IP address
+- ``chaddr`` - set to the lease's hardware address
+
+In addition, one or more of the following options are included:
+
+.. tabularcolumns:: |p{0.2\linewidth}|p{0.1\linewidth}|p{0.7\linewidth}|
+
+.. table:: DHCPLEASEACTIVE options
+   :class: longtable
+   :widths: 30 10 70
+
+   +------------------------------+-------+-----------------------------------------------+
+   | Option                       | Code  | Content                                       |
+   +==============================+=======+===============================================+
+   | dhcp-client-identifier       |  61   | copied from the lease (if appropriate)        |
+   +------------------------------+-------+-----------------------------------------------+
+   | client-last-transaction-time |  91   | the amount of time that has elapsed since the |
+   |                              |       | lease's client-last-transaction-time (CLTT).  |
+   |                              |       | This value is also used by the server to      |
+   |                              |       | adjust lifetime and timer values.             |
+   +------------------------------+-------+-----------------------------------------------+
+   | dhcp-lease-time              |  51   | lease's lifetime reduced by CLTT              |
+   +------------------------------+-------+-----------------------------------------------+
+   | dhcp-renewal-time            |  58   | as controlled by kea-dhcp4 configuration and  |
+   |                              |       | then reduced by CLTT                          |
+   +------------------------------+-------+-----------------------------------------------+
+   | dhcp-rebind-time             |  59   | as dictated by kea-dhcp4 configuration and    |
+   |                              |       | then reduced by CLTT                          |
+   +------------------------------+-------+-----------------------------------------------+
+   | dhcp-agent-options           |  82   | if stored on the lease. (See                  |
+   |                              |       | :ref:`dhcp4-store-extended-info`)             |
+   +------------------------------+-------+-----------------------------------------------+
+   | associated-ip                |  92   | a list of all other IP addresses for which    |
+   |                              |       | the client has active leases. (Does not apply |
+   |                              |       | to query by IP address)                       |
+   +------------------------------+-------+-----------------------------------------------+
+
+The ``dhcp-server-identifier`` option (54) is returned in all responses in keeping with
+RFC 2131, section 4.3.1.
+
+RFC 4388 allows requesters to ask for specific options via the
+``dhcp-parameter-request-list`` (PRL, option 55). This is not currently supported in Kea.
+
+.. _lease-query-dhcpv4-config:
+
+DHCPv4 Leasequery Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Configuring the Leasequery hook library for use is straightforward. It
+supports a single parameter, ``requesters``, which is a list of IP addresses from
+which DHCPLEASEQUERY packets are accepted. In other words, it is a list of
+known requesters. The following code shows an example configuration with two requester
+addresses:
+
+::
+
+ :
+    "hooks-libraries": [
+        {
+            "library": "lib/kea/hooks/libdhcp_lease_query.so",
+            "parameters": {
+                "requesters": [ "192.0.1.1", "10.0.0.2" ]
+            }
+        }
+    ],
+ :
+
+.. note::
+
+    For security purposes, there is no way to specify wildcards. Each requester address
+    must be explicitly listed.
+
+.. _lease-query-dhcpv6:
+
+DHCPv6 Leasequery
+~~~~~~~~~~~~~~~~~
+
+DHCPv6 simple Leasequery gives a requester the ability to query for
+active lease information for either a single IP address or a single client
+DUID. The query type and parameters are conveyed in an ``lq-query`` option (44)
+attached to a ``DHCPV6_LEASEQUERY`` message:
+
+- ``query-type``
+
+    This is either ``query-by-address`` (1) or ``query-by-clientid`` (2)
+
+- ``link-address``
+
+    The global link address, when not empty, instructs the query to be
+    limited to leases within that "link." Kea uses this value to
+    select only leases that belong to subnets whose prefix matches
+    this value. Active leases for prefix delegations for
+    a matched subnet are included in the query reply, even if the
+    delegated prefix itself falls outside the subnet prefix.
+
+- ``query-options``
+
+    A single ``iaaddr`` option (12) must be supplied when querying by address.
+    When querying by client ID, a single ``clientid`` option (1) must be
+    supplied. RFC 5007 also calls for an optional, ``oro`` option (6), to
+    request specific options be returned for matched leases. This is
+    not currently implemented.
+
+.. note::
+
+    `RFC 5007, Section 3.3 <https://tools.ietf.org/html/rfc5007#section-3.3>`__
+    states that querying by IP address should return either a lease (e.g.
+    binding) for the address itself or a lease for a delegated prefix that
+    contains the address. The latter is not currently implemented. Leases for
+    delegated prefixes may only be returned when querying by client ID. See
+    `GitLab issue #1275 <https://gitlab.isc.org/isc-projects/kea/-/issues/1275>`__
+
+``DHCPV6_LEASEQUERY`` queries are only honored if the source address of
+the query matches an entry in a list of known IP addresses which are
+permitted to query. This list of valid requester addresses is specified
+as part of the Leasequery hook library’s configuration (see the section
+on configuration below). Queries received from unknown requesters are
+logged and dropped.
+
+In response to a valid query, the server carries out the requisite
+activities and returns a ``DHCPV6_LEASEQUERY_REPLY``. All replies contain
+at least a ``status-code`` option (13) that indicates the outcome of the query
+as detailed in the following table:
+
+.. tabularcolumns:: |p{0.5\linewidth}|p{0.3\linewidth}|p{0.1\linewidth}|p{0.3\linewidth}|
+
+.. table:: DHCPV6_LEASEQUERY_REPLY status option values per query outcome
+   :class: longtable
+   :widths: 50 30 10 30
+
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   |                                      | Status                  | Status |  Status                      |
+   | Query Outcome                        | Label                   | Code   |  Text                        |
+   +======================================+=========================+========+==============================+
+   | Invalid query type field             | STATUS_UnknownQueryType |   7    | "unknown query-type"         |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   | Query by IP address that does not    | STATUS_Malformed        |   10   | "missing D6O_IAADDR"         |
+   | contain an address option            |                         |        |                              |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   | Query by IP address for an address   | STATUS_NotConfigured    |    9   | "address not in a configured |
+   | that does fall within any configured |                         |        | pool"                        |
+   | pools                                |                         |        |                              |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   | Query by IP address which found only | STATUS_Success          |    0   | "inactive lease exists"      |
+   | an inactive lease (e.g. expired,     |                         |        |                              |
+   | declined, reclaimed-expired)         |                         |        |                              |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   | Query by IP address that found no    | STATUS_Success          |    0   | "no active lease"            |
+   | leases (active or otherwise)         |                         |        |                              |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   | Query by IP address that found an    | STATUS_Success          |    0   | "active lease found"         |
+   | active lease for the address         |                         |        |                              |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   | Query by Client ID that does not     | STATUS_Malformed        |   10   | "missing D6O_CLIENTID"       |
+   | contain a client ID option           |                         |        |                              |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   | Query by Client ID with a link       | STATUS_NotConfigured    |    9   | "not a configured link"      |
+   | address that does not match any      |                         |        |                              |
+   | configured subnets                   |                         |        |                              |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   | Query by client ID which found no    | STATUS_Success          |    0   | "no active leases"           |
+   | matching leases                      |                         |        |                              |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+   | Query by client ID which found one   | STATUS_Success          |    0   | "active lease(s) found"      |
+   | or more active leases                |                         |        |                              |
+   +--------------------------------------+-------------------------+--------+------------------------------+
+
+For those scenarios where the query was either invalid or for which no matching active
+leases were found, the ``DHCPV6_LEASEQUERY_REPLY`` only contains the ``status-code``
+option (12) per the above table.
+
+When a query finds active leases in more than one subnet and the query's ``link-address``
+is empty, then, in addition to the status-code, the ``DHCPV6_LEASEQUERY_REPLY``
+contains an ``lq-client-link`` option (48). The ``lq-client-link`` contains a list of
+IPv6 addresses, one for each subnet in which a lease was found (see
+`RFC 5007, Section 4.1.2.5 <https://tools.ietf.org/html/rfc5007#section-4.1.2.5>`__)
+If, however, the query's ``link-address`` is not empty, the list of queries is
+pruned to contain only leases that belong to that subnet.
+
+When the query results in one or more active leases which all belong to a single
+subnet, in addition to the ``status-code``, the ``DHCPV6_LEASEQUERY_REPLY`` contains a
+``client-data`` option (45) (see
+`RFC 5007, Section 4.1.2.2 <https://tools.ietf.org/html/rfc5007#section-4.1.2.2>`__).
+The client-data option encapsulates the following options:
+
+.. tabularcolumns:: |p{0.2\linewidth}|p{0.1\linewidth}|p{0.7\linewidth}|
+
+.. table:: OPTION_CLIENT_DATA returned when active lease(s) are found
+   :class: longtable
+   :widths: 30 10 70
+
+   +------------------------------+-------+-----------------------------------------------+
+   | Option                       | Code  | Content                                       |
+   +==============================+=======+===============================================+
+   | clientid                     |   1   | copied from the lease (if one exists)         |
+   +------------------------------+-------+-----------------------------------------------+
+   | clt-time                     |  46   | amount of time that has elapsed since the     |
+   |                              |       | lease's client-last-transaction-time (CLTT).  |
+   |                              |       | This value will also be used by the server to |
+   |                              |       | adjust lifetime and timer values.             |
+   +------------------------------+-------+-----------------------------------------------+
+   | iaaddr                       |   5   | One option per matched address. Fields in     |
+   |                              |       | each option:                                  |
+   |                              |       | - lease address                               |
+   |                              |       | - valid lifetime reduced by CLTT              |
+   |                              |       | - preferred lifetime reduced by CLTT          |
+   +------------------------------+-------+-----------------------------------------------+
+   | iaprefix                     |   26  | One option per matched prefix. Fields in      |
+   |                              |       | each option:                                  |
+   |                              |       | - prefix                                      |
+   |                              |       | - prefix length                               |
+   |                              |       | - valid lifetime reduced by CLTT              |
+   |                              |       | - preferred lifetime reduced by CLTT          |
+   +------------------------------+-------+-----------------------------------------------+
+
+If the lease with the most recent client-last-transaction-time (CLTT)
+value has relay information in its user-context (see
+:ref:`store-extended-info-v6`), then an ``OPTION_LQ_RELAY_DATA`` option is
+added to the reply (see
+`RFC 5007, Section 4.1.2.4 <https://tools.ietf.org/html/rfc5007#section-4.1.2.4>`__).
+
+The relay information on the lease is a list with an entry for each
+relay layer the client packet (e.g. ``DHCPV6_REQUEST``) traversed, with the
+first entry in the list being the outermost layer (closest to the server). The
+``peer-address`` field of the ``lq-rely-option`` is set to the peer address of this
+relay. The list of relays is then used to construct a ``DHCPV6_RELAY_FORW`` message
+equivalent to that which contained the client packet, minus the client packet.
+This message is stored in the ``DHCP-relay-message`` field of the ``lq-relay-data`` option.
+
+.. _lease-query-dhcpv6-config:
+
+DHCPv6 Leasequery Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Configuring the Leasequery hook library for use is straightforward. It
+supports a single parameter, ``requesters``, which is a list of IP addresses from
+which DHCPV6_LEASEQUERY packets are accepted. In other words, it is a list of
+known requesters. The following code shows an example configuration with two requester
+addresses:
+
+::
+
+ :
+    "hooks-libraries": [
+        {
+            "library": "lib/kea/hooks/libdhcp_lease_query.so",
+            "parameters": {
+                "requesters": [ "2001:db8:1::1", "2001:db8:2::1" ]
+            }
+        }
+    ],
+ :
+
+.. note::
+
+    For security purposes, there is no way to specify wildcards. Each requester address
+    must be explicitly listed.
diff --git a/doc/sphinx/arm/hooks-legal-log.rst b/doc/sphinx/arm/hooks-legal-log.rst
new file mode 100644
index 0000000..961431e
--- /dev/null
+++ b/doc/sphinx/arm/hooks-legal-log.rst
@@ -0,0 +1,1030 @@
+.. _hooks-legal-log:
+
+``legal_log``: Forensic Logging
+===============================
+
+The Forensic Logging hook library provides
+hooks that record a detailed log of assignments, renewals, releases, and other
+lease events into a set of log files.
+
+Currently this library is only available to ISC customers with a paid support
+contract.
+
+.. note::
+
+   This library may only be loaded by the ``kea-dhcp4`` or ``kea-dhcp6``
+   process.
+
+In many legal jurisdictions, companies - especially ISPs - must record
+information about the addresses they have leased to DHCP clients. This
+library is designed to help with that requirement. If the information
+that it records is sufficient, it may be used directly.
+
+If a jurisdiction requires that different information be saved, users
+may use the custom formatting capability to extract information from the inbound
+request packet, or from the outbound response packet. Administrators are advised
+to use this feature with caution, as it may affect server performance.
+The custom format cannot be used for control channel commands.
+
+Alternatively, this library may be used as a template or an example for the
+user's own custom logging hook. The logging is done as a set of hooks to allow
+it to be customized to any particular need; modifying a hook library is easier
+and safer than updating the core code. In addition, by using the hooks features,
+users who do not need to log this information can leave it out and avoid
+any performance penalties.
+
+Log File Naming
+~~~~~~~~~~~~~~~
+
+The names of the log files follow a set pattern.
+
+If using ``day``, ``month``, or ``year`` as the time unit, the file name follows
+the format:
+
+::
+
+   path/base-name.CCYYMMDD.txt
+
+where ``CC`` represents the century, ``YY`` represents the year,
+``MM`` represents the month, and ``DD`` represents the day.
+
+If using ``second`` as the time unit the file name follows the format:
+
+::
+
+   path/base-name.TXXXXXXXXXXXXXXXXXXXX.txt
+
+where ``XXXXXXXXXXXXXXXXXXXX`` represents the time in seconds since the beginning
+of the UNIX epoch.
+
+When using ``second`` as the time unit, the file is rotated when
+the ``count`` number of seconds pass. In contrast, when using ``day``, ``month``,
+or ``year`` as the time unit, the file is rotated whenever the ``count`` of day,
+month, or year starts, as applicable.
+
+The ``"path"`` and ``"base-name"`` are supplied in the configuration as
+described below; see :ref:`forensic-log-configuration`.
+
+.. note::
+
+   When running Kea servers for both DHCPv4 and DHCPv6, the log names
+   must be distinct. See the examples in :ref:`forensic-log-configuration`.
+
+.. _forensic-log-configuration:
+
+Configuring the Forensic Logging Hooks
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To use this functionality, the hook library must be included in the
+configuration of the desired DHCP server modules. The ``legal_log`` library
+can save logs to a text file or to a database (created using
+``kea-admin``; see :ref:`mysql-database-create` and :ref:`pgsql-database-create`).
+The library is installed alongside the Kea libraries in
+``[kea-install-dir]/var/lib/kea``, where ``kea-install-dir`` is determined
+by the ``--prefix`` option of the configure script; it defaults to
+``/usr/local``. Assuming the default value, ``kea-dhcp4`` can be configured to load
+the ``legal_log`` library like this:
+
+.. code-block:: json
+
+    {
+        "Dhcp4": {
+            "hooks-libraries": [
+                {
+                    "library": "/usr/local/lib/kea/hooks/libdhcp_legal_log.so",
+                    "parameters": {
+                        "path": "/var/lib/kea/log",
+                        "base-name": "kea-forensic4"
+                    }
+                }
+            ]
+        }
+    }
+
+For ``kea-dhcp6``, the configuration is:
+
+.. code-block:: json
+
+    {
+        "Dhcp6": {
+            "hooks-libraries": [
+                {
+                    "library": "/usr/local/lib/kea/hooks/libdhcp_legal_log.so",
+                    "parameters": {
+                        "path": "/var/lib/kea/log",
+                        "base-name": "kea-forensic6"
+                    }
+                }
+            ]
+        }
+    }
+
+The hook library parameters for the text file configuration are:
+
+-  ``path`` - the directory in which the forensic file(s) will be written.
+   The default value is ``[prefix]/var/lib/kea``. The directory must exist.
+
+-  ``base-name`` - an arbitrary value which is used in conjunction with the
+   current system date to form the current forensic file name. It
+   defaults to ``kea-legal``.
+
+-  ``time-unit`` - configures the time unit used to rotate the log file. Valid
+   values are ``second``, ``day``, ``month``, or ``year``. It defaults to
+   ``day``.
+
+-  ``count`` - configures the number of time units that need to pass until the
+   log file is rotated. It can be any positive number, or 0, which disables log
+   rotation. It defaults to 1.
+
+If log rotation is disabled, a new file is created when the library is
+loaded; the new file name is different from any previous file name.
+
+Additional actions can be performed just before closing the old file and after
+opening the new file. These actions must point to an external executable or
+script and are configured with the following settings:
+
+-  ``prerotate`` - an external executable or script called with the name of the
+   file that will be closed. Kea does not wait for the process to finish.
+
+-  ``postrotate`` - an external executable or script called with the name of the
+   file that was opened. Kea does not wait for the process to finish.
+
+Custom formatting can be enabled for logging information that can be extracted
+either from the client's request packet or from the server's response packet.
+Use with caution as this might affect server performance.
+The custom format cannot be used for control channel commands.
+Two parameters can be used towards this goal, either together or separately:
+
+-  ``request-parser-format`` - an evaluated parsed expression used to extract and
+   log data from the incoming packet.
+
+-  ``response-parser-format`` - an evaluated parsed expression used to extract and
+   log data from the server response packet.
+
+See :ref:`classification-using-expressions` for a list of expressions.
+If either ``request-parser-format`` or ``response-parser-format`` is
+configured, the default logging format is not used. If both of them are
+configured, the resulting log message is constructed by concatenating the
+data extracted from the request and the data extracted from the response.
+
+The custom formatting permits logging on multiple lines using the hexstring 0x0a
+(ASCII code for new line). In the log file, each line is prepended
+with the log timestamp. For the database backend, the data is stored
+(including the newline character) in the same entry.
+
+Examples:
+
+.. code-block:: json
+
+    {
+        "Dhcp6": {
+            "hooks-libraries": [
+                {
+                    "library": "/usr/local/lib/kea/hooks/libdhcp_legal_log.so",
+                    "parameters": {
+                        "path": "/var/lib/kea/log",
+                        "base-name": "kea-forensic6",
+                        "request-parser-format": "'first line' + 0x0a + 'second line'",
+                        "response-parser-format": "'also second line' + 0x0a + 'third line'"
+                    }
+                }
+            ]
+        }
+    }
+
+Some data might be available in the request or only in the response; the
+data in the request packet might differ from that in the response packet.
+
+The lease-client context can only be printed using the default format, as this
+information is not directly stored in the request packet or in the response
+packet.
+
+The ``timestamp-format`` parameter can be used to change the timestamp logged
+at the beginning of each line. Permissible formatting is the one supported by
+strftime plus the '%Q' extra format which adds the microseconds subunits. The
+default is: "%Y-%m-%d %H:%M:%S %Z". This parameter has no effect for the
+database backends, where the timestamp is defined at the schema level.
+
+Examples:
+
+.. code-block:: json
+
+    {
+        "Dhcp6": {
+            "hooks-libraries": [
+                {
+                    "library": "/usr/local/lib/kea/hooks/libdhcp_legal_log.so",
+                    "parameters": {
+                        "path": "/var/lib/kea/log",
+                        "base-name": "kea-forensic6",
+                        "timestamp-format": "%H%t%w %F%%"
+                    }
+                }
+            ]
+        }
+    }
+
+Additional parameters for the database connection can be specified, e.g:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "hooks-libraries": [
+          {
+            "library": "/usr/local/lib/kea/hooks/libdhcp_legal_log.so",
+            "parameters": {
+              "name": "database-name",
+              "password": "passwd",
+              "type": "mysql",
+              "user": "user-name"
+            }
+          }
+        ]
+      }
+    }
+
+For more specific information about database-related parameters, please refer to
+:ref:`database-configuration4` and :ref:`database-configuration6`.
+
+If it is desired to restrict forensic logging to certain subnets, the
+``"legal-logging"`` boolean parameter can be specified within a user context
+of these subnets. For example:
+
+.. code-block:: json
+
+    {
+        "Dhcp4": {
+            "subnet4": [
+                {
+                    "subnet": "192.0.2.0/24",
+                    "pools": [
+                        {
+                            "pool": "192.0.2.1 - 192.0.2.200"
+                        }
+                    ],
+                    "user-context": {
+                        "legal-logging": false
+                    }
+                }
+            ]
+        }
+    }
+
+This configuration disables legal logging for the subnet "192.0.2.0/24". If the
+``"legal-logging"`` parameter is not specified, it defaults to ``true``, which
+enables legal logging for the subnet.
+
+The following example demonstrates how to selectively disable legal
+logging for an IPv6 subnet:
+
+.. code-block:: json
+
+    {
+        "Dhcp6": {
+            "subnet6": [
+                {
+                    "subnet": "2001:db8:1::/64",
+                    "pools": [
+                        {
+                            "pool": "2001:db8:1::1-2001:db8:1::ffff"
+                        }
+                    ],
+                    "user-context": {
+                        "legal-logging": false
+                    }
+                }
+            ]
+        }
+    }
+
+See :ref:`dhcp4-user-contexts` and :ref:`dhcp6-user-contexts` to
+learn more about user contexts in Kea configuration.
+
+DHCPv4 Log Entries
+~~~~~~~~~~~~~~~~~~
+
+For DHCPv4, the library creates entries based on DHCPREQUEST, DHCPDECLINE,
+and DHCPRELEASE messages, et al., and their responses. The resulting packets and
+leases are taken into account, intercepted through the following hook points:
+
+* ``pkt4_receive``
+* ``leases4_committed``
+* ``pkt4_send``
+* ``lease4_release``
+* ``lease4_decline``
+
+An entry is a single string with no embedded end-of-line markers and a
+prepended timestamp, and has the following sections:
+
+::
+
+   timestamp address duration device-id {client-info} {relay-info} {user-context}
+
+Where:
+
+-  ``timestamp`` - the date and time the log entry was written, in
+   "%Y-%m-%d %H:%M:%S %Z" strftime format ("%Z" is the time zone name).
+
+-  ``address`` - the leased IPv4 address given out, and whether it was
+   assigned, renewed, or released.
+
+-  ``duration`` - the lease lifetime expressed in days (if present), hours,
+   minutes, and seconds. A lease lifetime of 0xFFFFFFFF will be denoted
+   with the text "infinite duration." This information is not given
+   when the lease is released.
+
+-  ``device-id`` - the client's hardware address shown as a numerical type and
+   hex-digit string.
+
+-  ``client-info`` - the DHCP client id option (61) if present, shown as a
+   hex string. When its content is printable it is displayed.
+
+-  ``relay-info`` - for relayed packets, the ``giaddr`` and the RAI ``circuit-id``,
+   ``remote-id``, and ``subscriber-id`` options (option 82 sub options: 1, 2 and 6),
+   if present. The ``circuit-id`` and ``remote-id`` are presented as hex
+   strings. When their content is printable it is displayed.
+
+-  ``user-context`` - the optional user context associated with the lease.
+
+For instance (line breaks are added here for readability; they are not
+present in the log file):
+
+::
+
+   2018-01-06 01:02:03 CET Address: 192.2.1.100 has been renewed for 1 hrs 52 min 15 secs to a device with hardware address:
+   hwtype=1 08:00:2b:02:3f:4e, client-id: 17:34:e2:ff:09:92:54 connected via relay at address: 192.2.16.33,
+   identified by circuit-id: 68:6f:77:64:79 (howdy) and remote-id: 87:f6:79:77:ef
+
+or for a release:
+
+::
+
+   2018-01-06 01:02:03 CET Address: 192.2.1.100 has been released from a device with hardware address:
+   hwtype=1 08:00:2b:02:3f:4e, client-id: 17:34:e2:ff:09:92:54 connected via relay at address: 192.2.16.33,
+   identified by circuit-id: 68:6f:77:64:79 (howdy) and remote-id: 87:f6:79:77:ef
+
+In addition to logging lease activity driven by DHCPv4 client traffic,
+the hook library also logs entries for the following lease management control
+channel commands: ``lease4-add``, ``lease4-update``, and ``lease4-del``. These cannot have
+custom formatting. Each entry is a single string with no embedded end-of-line
+markers, and it will typically have the following form:
+
+``lease4-add:``
+
+::
+
+   *timestamp* Administrator added a lease of address: *address* to a device with hardware address: *device-id*
+
+Depending on the arguments of the add command, it may also include the
+client-id and duration.
+
+Example:
+
+::
+
+   2018-01-06 01:02:03 CET Administrator added a lease of address: 192.0.2.202 to a device with hardware address:
+   1a:1b:1c:1d:1e:1f for 1 days 0 hrs 0 mins 0 secs
+
+``lease4-update:``
+
+::
+
+   *timestamp* Administrator updated information on the lease of address: *address* to a device with hardware address: *device-id*
+
+Depending on the arguments of the update command, it may also include
+the client-id and lease duration.
+
+Example:
+
+::
+
+   2018-01-06 01:02:03 CET Administrator updated information on the lease of address: 192.0.2.202 to a device
+   with hardware address: 1a:1b:1c:1d:1e:1f, client-id: 1234567890
+
+``lease4-del:`` deletes have two forms, one by address and one by
+identifier and identifier type:
+
+::
+
+   *timestamp* Administrator deleted the lease for address: *address*
+
+or
+
+::
+
+   *timestamp* Administrator deleted a lease for a device identified by: *identifier-type* of *identifier*
+
+Currently only a type of ``@b hw-address`` (hardware address) is supported.
+
+Examples:
+
+::
+
+   2018-01-06 01:02:03 CET Administrator deleted the lease for address: 192.0.2.202
+
+   2018-01-06 01:02:12 CET Administrator deleted a lease for a device identified by: hw-address of 1a:1b:1c:1d:1e:1f
+
+The ``request-parser-format`` and ``response-parser-format`` options can be used to
+extract and log data from the incoming packet and server response packet,
+respectively. The configured value is an evaluated parsed expression returning a
+string. A list of tokens is described in the server classification process.
+Use with caution as this might affect server performance.
+If either of them is configured, the default logging format is not used.
+If both of them are configured, the resulting log message is constructed by
+concatenating the logged data extracted from the request and the logged data
+extracted from the response.
+
+The custom formatting permits logging on multiple lines using the hexstring 0x0a
+(ASCII code for new line). In the case of the log file, each line is prepended
+with the log timestamp. For the database backend, the data is stored
+(including the newline character) in the same entry.
+
+Examples:
+
+.. code-block:: json
+
+    {
+      "Dhcp4": {
+        "hooks-libraries": [
+          {
+            "library": "/usr/local/lib/kea/hooks/libdhcp_legal_log.so",
+            "parameters": {
+              "name": "database-name",
+              "password": "passwd",
+              "type": "mysql",
+              "user": "user-name",
+              "request-parser-format": "'log entry' + 0x0a + 'same log entry'",
+              "response-parser-format": "'also same log entry' + 0x0a + 'again same log entry'"
+            }
+          }
+        ]
+      }
+    }
+
+Some data might be available in the request or in the response only, and some
+data might differ in the incoming packet from the one in the response packet.
+
+Examples:
+
+.. code-block:: json
+
+    {
+        "request-parser-format": "ifelse(pkt4.msgtype == 4 or pkt4.msgtype == 7, 'Address: ' + ifelse(option[50].exists, addrtotext(option[50].hex), addrtotext(pkt4.ciaddr)) + ' has been released from a device with hardware address: hwtype=' + substring(hexstring(pkt4.htype, ''), 7, 1) + ' ' + hexstring(pkt4.mac, ':') + ifelse(option[61].exists, ', client-id: ' + hexstring(option[61].hex, ':'), '') + ifelse(pkt4.giaddr == 0.0.0.0, '', ' connected via relay at address: ' + addrtotext(pkt4.giaddr) + ifelse(option[82].option[1].exists, ', circuit-id: ' + hexstring(option[82].option[1].hex, ':'), '') + ifelse(option[82].option[2].exists, ', remote-id: ' + hexstring(option[82].option[2].hex, ':'), '') + ifelse(option[82].option[6].exists, ', subscriber-id: ' + hexstring(option[82].option[6].hex, ':'), '')), '')",
+        "response-parser-format": "ifelse(pkt4.msgtype == 5, 'Address: ' + addrtotext(pkt4.yiaddr) + ' has been assigned for ' + uint32totext(option[51].hex) + ' seconds to a device with hardware address: hwtype=' + substring(hexstring(pkt4.htype, ''), 7, 1) + ' ' + hexstring(pkt4.mac, ':') + ifelse(option[61].exists, ', client-id: ' + hexstring(option[61].hex, ':'), '') + ifelse(pkt4.giaddr == 0.0.0.0, '', ' connected via relay at address: ' + addrtotext(pkt4.giaddr) + ifelse(option[82].option[1].exists, ', circuit-id: ' + hexstring(option[82].option[1].hex, ':'), '') + ifelse(option[82].option[2].exists, ', remote-id: ' + hexstring(option[82].option[2].hex, ':'), '') + ifelse(option[82].option[6].exists, ', subscriber-id: ' + hexstring(option[82].option[6].hex, ':'), '')), '')"
+    }
+
+.. raw:: html
+
+    <details><summary>Expand here!</summary>
+    <pre>{
+        "request-parser-format":
+            "ifelse(pkt4.msgtype == 4 or pkt4.msgtype == 7,
+                'Address: ' +
+                ifelse(option[50].exists,
+                    addrtotext(option[50].hex),
+                    addrtotext(pkt4.ciaddr)) +
+                ' has been released from a device with hardware address: hwtype=' + substring(hexstring(pkt4.htype, ''), 7, 1) + ' ' + hexstring(pkt4.mac, ':') +
+                ifelse(option[61].exists,
+                    ', client-id: ' + hexstring(option[61].hex, ':'),
+                    '') +
+                ifelse(pkt4.giaddr == 0.0.0.0,
+                    '',
+                    ' connected via relay at address: ' + addrtotext(pkt4.giaddr) +
+                    ifelse(option[82].option[1].exists,
+                        ', circuit-id: ' + hexstring(option[82].option[1].hex, ':'),
+                        '') +
+                    ifelse(option[82].option[2].exists,
+                        ', remote-id: ' + hexstring(option[82].option[2].hex, ':'),
+                        '') +
+                    ifelse(option[82].option[6].exists,
+                        ', subscriber-id: ' + hexstring(option[82].option[6].hex, ':'),
+                        '')),
+                '')",
+        "response-parser-format":
+            "ifelse(pkt4.msgtype == 5,
+                'Address: ' + addrtotext(pkt4.yiaddr) + ' has been assigned for ' + uint32totext(option[51].hex) + ' seconds to a device with hardware address: hwtype=' + substring(hexstring(pkt4.htype, ''), 7, 1) + ' ' + hexstring(pkt4.mac, ':') +
+                ifelse(option[61].exists,
+                    ', client-id: ' + hexstring(option[61].hex, ':'),
+                    '') +
+                ifelse(pkt4.giaddr == 0.0.0.0,
+                    '',
+                    ' connected via relay at address: ' + addrtotext(pkt4.giaddr) +
+                    ifelse(option[82].option[1].exists,
+                        ', circuit-id: ' + hexstring(option[82].option[1].hex, ':'),
+                        '') +
+                    ifelse(option[82].option[2].exists,
+                        ', remote-id: ' + hexstring(option[82].option[2].hex, ':'),
+                        '') +
+                    ifelse(option[82].option[6].exists,
+                        ', subscriber-id: ' + hexstring(option[82].option[6].hex, ':'),
+                        '')),
+                '')"
+    }</pre>
+    </details><br>
+
+This will log the following data on request and renew:
+
+::
+
+   Address: 192.2.1.100 has been assigned for 6735 seconds to a device with hardware address: hwtype=1 08:00:2b:02:3f:4e, client-id: 17:34:e2:ff:09:92:54 connected via relay at address: 192.2.16.33, circuit-id: 68:6f:77:64:79, remote-id: 87:f6:79:77:ef, subscriber-id: 1a:2b:3c:4d:5e:6f
+
+This will log the following data on release and decline:
+
+::
+
+   Address: 192.2.1.100 has been released from a device with hardware address: hwtype=1 08:00:2b:02:3f:4e, client-id: 17:34:e2:ff:09:92:54 connected via relay at address: 192.2.16.33, circuit-id: 68:6f:77:64:79, remote-id: 87:f6:79:77:ef, subscriber-id: 1a:2b:3c:4d:5e:6f
+
+A similar result can be obtained by configuring only ``request-parser-format``.
+
+Examples:
+
+.. code-block:: json
+
+    {
+        "request-parser-format": "ifelse(pkt4.msgtype == 3, 'Address: ' + ifelse(option[50].exists, addrtotext(option[50].hex), addrtotext(pkt4.ciaddr)) + ' has been assigned' + ifelse(option[51].exists, ' for ' + uint32totext(option[51].hex) + ' seconds', '') + ' to a device with hardware address: hwtype=' + substring(hexstring(pkt4.htype, ''), 7, 1) + ' ' + hexstring(pkt4.mac, ':') + ifelse(option[61].exists, ', client-id: ' + hexstring(option[61].hex, ':'), '') + ifelse(pkt4.giaddr == 0.0.0.0, '', ' connected via relay at address: ' + addrtotext(pkt4.giaddr) + ifelse(option[82].option[1].exists, ', circuit-id: ' + hexstring(option[82].option[1].hex, ':'), '') + ifelse(option[82].option[2].exists, ', remote-id: ' + hexstring(option[82].option[2].hex, ':'), '') + ifelse(option[82].option[6].exists, ', subscriber-id: ' + hexstring(option[82].option[6].hex, ':'), '')), ifelse(pkt4.msgtype == 4 or pkt4.msgtype == 7, 'Address: ' + ifelse(option[50].exists, addrtotext(option[50].hex), addrtotext(pkt4.ciaddr)) + ' has been released from a device with hardware address: hwtype=' + substring(hexstring(pkt4.htype, ''), 7, 1) + ' ' + hexstring(pkt4.mac, ':') + ifelse(option[61].exists, ', client-id: ' + hexstring(option[61].hex, ':'), '') + ifelse(pkt4.giaddr == 0.0.0.0, '', ' connected via relay at address: ' + addrtotext(pkt4.giaddr) + ifelse(option[82].option[1].exists, ', circuit-id: ' + hexstring(option[82].option[1].hex, ':'), '') + ifelse(option[82].option[2].exists, ', remote-id: ' + hexstring(option[82].option[2].hex, ':'), '') + ifelse(option[82].option[6].exists, ', subscriber-id: ' + hexstring(option[82].option[6].hex, ':'), '')), ''))"
+    }
+
+.. raw:: html
+
+    <details><summary>Expand here!</summary>
+    <pre>{
+        "request-parser-format":
+            "ifelse(pkt4.msgtype == 3,
+                'Address: ' +
+                ifelse(option[50].exists,
+                    addrtotext(option[50].hex),
+                    addrtotext(pkt4.ciaddr)) +
+                ' has been assigned' +
+                ifelse(option[51].exists,
+                    ' for ' + uint32totext(option[51].hex) + ' seconds',
+                    '') +
+                ' to a device with hardware address: hwtype=' + substring(hexstring(pkt4.htype, ''), 7, 1) + ' ' + hexstring(pkt4.mac, ':') +
+                ifelse(option[61].exists,
+                    ', client-id: ' + hexstring(option[61].hex, ':'),
+                    '') +
+                ifelse(pkt4.giaddr == 0.0.0.0,
+                    '',
+                    ' connected via relay at address: ' + addrtotext(pkt4.giaddr) +
+                    ifelse(option[82].option[1].exists,
+                        ', circuit-id: ' + hexstring(option[82].option[1].hex, ':'),
+                        '') +
+                    ifelse(option[82].option[2].exists,
+                        ', remote-id: ' + hexstring(option[82].option[2].hex, ':'),
+                        '') +
+                    ifelse(option[82].option[6].exists,
+                        ', subscriber-id: ' + hexstring(option[82].option[6].hex, ':'),
+                        '')),
+                ifelse(pkt4.msgtype == 4 or pkt4.msgtype == 7,
+                    'Address: ' +
+                    ifelse(option[50].exists,
+                        addrtotext(option[50].hex),
+                        addrtotext(pkt4.ciaddr)) +
+                    ' has been released from a device with hardware address: hwtype=' + substring(hexstring(pkt4.htype, ''), 7, 1) + ' ' + hexstring(pkt4.mac, ':') +
+                    ifelse(option[61].exists,
+                        ', client-id: ' + hexstring(option[61].hex, ':'),
+                        '') +
+                    ifelse(pkt4.giaddr == 0.0.0.0,
+                        '',
+                        ' connected via relay at address: ' + addrtotext(pkt4.giaddr) +
+                        ifelse(option[82].option[1].exists,
+                            ', circuit-id: ' + hexstring(option[82].option[1].hex, ':'),
+                            '') +
+                        ifelse(option[82].option[2].exists,
+                            ', remote-id: ' + hexstring(option[82].option[2].hex, ':'),
+                            '') +
+                        ifelse(option[82].option[6].exists,
+                            ', subscriber-id: ' + hexstring(option[82].option[6].hex, ':'),
+                            '')),
+                    ''))"
+    }</pre>
+    </details><br>
+
+DHCPv6 Log Entries
+~~~~~~~~~~~~~~~~~~
+
+For DHCPv6, the library creates entries based on REQUEST, RENEW, RELEASE,
+and DECLINE messages, et al. and their responses. The resulting packets and leases
+are taken into account, intercepted through the following hook points:
+
+* ``pkt6_receive``
+* ``leases6_committed``
+* ``pkt6_send``
+* ``lease6_release``
+* ``lease6_decline``
+
+An entry is a single string with no embedded end-of-line markers and a
+prepended timestamp, and has the following sections:
+
+::
+
+   timestamp address duration device-id {relay-info}* {user-context}
+
+Where:
+
+-  ``timestamp`` - the date and time the log entry was written, in
+   "%Y-%m-%d %H:%M:%S %Z" strftime format ("%Z" is the time zone name).
+
+-  ``address`` - the leased IPv6 address or prefix given out, and whether it
+   was assigned, renewed, or released.
+
+-  ``duration`` - the lease lifetime expressed in days (if present), hours,
+   minutes, and seconds. A lease lifetime of 0xFFFFFFFF will be denoted
+   with the text "infinite duration." This information is not given
+   when the lease is released.
+
+-  ``device-id`` - the client's DUID and hardware address (if present).
+
+-  ``relay-info`` - for relayed packets the content of relay agent messages, and the
+   ``remote-id`` (code 37), ``subscriber-id`` (code 38), and ``interface-id`` (code 18)
+   options, if present. Note that the ``interface-id`` option, if present,
+   identifies the whole interface on which the relay agent received the message.
+   This typically translates to a single link in the network, but
+   it depends on the specific network topology. Nevertheless, this is
+   useful information to better pinpoint the location of the device,
+   so it is recorded, if present.
+
+-  ``user-context`` - the optional user context associated with the lease.
+
+For instance (line breaks are added here for readability; they are not
+present in the log file):
+
+::
+
+   2018-01-06 01:02:03 PST Address:2001:db8:1:: has been assigned for 0 hrs 11 mins 53 secs
+   to a device with DUID: 17:34:e2:ff:09:92:54 and hardware address: hwtype=1 08:00:2b:02:3f:4e
+   (from Raw Socket) connected via relay at address: fe80::abcd for client on link address: 3001::1,
+   hop count: 1, identified by remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f and subscriber-id: 1a:2b:3c:4d:5e:6f
+
+or for a release:
+
+::
+
+   2018-01-06 01:02:03 PST Address:2001:db8:1:: has been released
+   from a device with DUID: 17:34:e2:ff:09:92:54 and hardware address: hwtype=1 08:00:2b:02:3f:4e
+   (from Raw Socket) connected via relay at address: fe80::abcd for client on link address: 3001::1,
+   hop count: 1, identified by remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f and subscriber-id: 1a:2b:3c:4d:5e:6f
+
+In addition to logging lease activity driven by DHCPv6 client traffic,
+the hook library also logs entries for the following lease management control channel
+commands: ``lease6-add``, ``lease6-update``, and ``lease6-del``. Each entry is a
+single string with no embedded end-of-line markers, and it will
+typically have the following form:
+
+``lease6-add:``
+
+::
+
+   *timestamp* Administrator added a lease of address: *address* to a device with DUID: *DUID*
+
+Depending on the arguments of the add command, it may also include the
+hardware address and duration.
+
+Example:
+
+::
+
+   2018-01-06 01:02:03 PST Administrator added a lease of address: 2001:db8::3 to a device with DUID:
+   1a:1b:1c:1d:1e:1f:20:21:22:23:24 for 1 days 0 hrs 0 mins 0 secs
+
+``lease6-update:``
+
+::
+
+   *timestamp* Administrator updated information on the lease of address: *address* to a device with DUID: *DUID*
+
+Depending on the arguments of the update command, it may also include
+the hardware address and lease duration.
+
+Example:
+
+::
+
+   2018-01-06 01:02:03 PST Administrator updated information on the lease of address: 2001:db8::3 to a device with
+   DUID: 1a:1b:1c:1d:1e:1f:20:21:22:23:24, hardware address: 1a:1b:1c:1d:1e:1f
+
+``lease6-del:`` deletes have two forms, one by address and one by
+identifier and identifier type:
+
+::
+
+   *timestamp* Administrator deleted the lease for address: *address*
+
+or
+
+::
+
+   *timestamp* Administrator deleted a lease for a device identified by: *identifier-type* of *identifier*
+
+Currently only a type of ``DUID`` is supported.
+
+Examples:
+
+::
+
+   2018-01-06 01:02:03 PST Administrator deleted the lease for address: 2001:db8::3
+
+   2018-01-06 01:02:11 PST Administrator deleted a lease for a device identified by: duid of 1a:1b:1c:1d:1e:1f:20:21:22:23:24
+
+The ``request-parser-format`` and ``response-parser-format`` options can be used to
+extract and log data from the incoming packet and server response packet,
+respectively. The configured value is an evaluated parsed expression returning a
+string. A list of tokens is described in the server classification process.
+Use with caution as this might affect server performance.
+If either of them is configured, the default logging format is not used.
+If both of them are configured, the resulting log message is constructed by
+concatenating the logged data extracted from the request and the logged data
+extracted from the response.
+
+The custom formatting permits logging on multiple lines using the hexstring 0x0a
+(ASCII code for new line). In the case of the log file, each line is prepended
+with the log timestamp. For the database backend, the data is stored
+(including the newline character) in the same entry.
+
+Examples:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "hooks-libraries": [
+          {
+            "library": "/usr/local/lib/kea/hooks/libdhcp_legal_log.so",
+            "parameters": {
+              "name": "database-name",
+              "password": "passwd",
+              "type": "mysql",
+              "user": "user-name",
+              "request-parser-format": "'log entry' + 0x0a + 'same log entry'",
+              "response-parser-format": "'also same log entry' + 0x0a + 'again same log entry'"
+            }
+          }
+        ]
+      }
+    }
+
+Some data might be available in the request or in the response only, and some
+data might differ in the incoming packet from the one in the response packet.
+
+Notes:
+
+In the case of IPv6, the packets can contain multiple IA_NA (3) or IA_PD (25)
+options, each containing multiple options, including OPTION_IAADDR (5) or
+OPTION_IAPREFIX (25) suboptions.
+To be able to print the current lease associated with the log entry, the
+forensic log hook library internally isolates the corresponding IA_NA or IA_PD
+option and respective suboption matching the current lease.
+The hook library will iterate over all new allocated addresses and all deleted
+addresses, making each address available for logging as the current lease for
+the respective logged entry.
+
+They are accessible using the following parser expressions:
+
+Current lease associated with OPTION_IAADDR:
+
+::
+
+    addrtotext(substring(option[3].option[5].hex, 0, 16))
+
+Current lease associated with OPTION_IAPREFIX:
+
+::
+
+    addrtotext(substring(option[25].option[26].hex, 9, 16))
+
+All other parameters of the options are available at their respective offsets
+in the option. Please read RFC8415 for more details.
+
+Examples:
+
+.. code-block:: json
+
+    {
+        "request-parser-format": "ifelse(pkt6.msgtype == 8 or pkt6.msgtype == 9, ifelse(option[3].option[5].exists, 'Address: ' + addrtotext(substring(option[3].option[5].hex, 0, 16)) + ' has been released from a device with DUID: ' + hexstring(option[1].hex, ':') + ifelse(relay6[0].peeraddr == '', '', ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) + ifelse(relay6[0].option[37].exists, ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'), '') + ifelse(relay6[0].option[38].exists, ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'), '') + ifelse(relay6[0].option[18].exists, ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'), '')), '') + ifelse(option[25].option[26].exists, 'Prefix: ' + addrtotext(substring(option[25].option[26].hex, 9, 16)) + '/' + uint8totext(substring(option[25].option[26].hex, 8, 1)) + ' has been released from a device with DUID: ' + hexstring(option[1].hex, ':') + ifelse(relay6[0].peeraddr == '', '', ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) + ifelse(relay6[0].option[37].exists, ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'), '') + ifelse(relay6[0].option[38].exists, ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'), '') + ifelse(relay6[0].option[18].exists, ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'), '')), ''), '')",
+        "response-parser-format": "ifelse(pkt6.msgtype == 7, ifelse(option[3].option[5].exists and not (substring(option[3].option[5].hex, 20, 4) == 0), 'Address: ' + addrtotext(substring(option[3].option[5].hex, 0, 16)) + ' has been assigned for ' + uint32totext(substring(option[3].option[5].hex, 20, 4)) + ' seconds to a device with DUID: ' + hexstring(option[1].hex, ':') + ifelse(relay6[0].peeraddr == '', '', ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) + ifelse(relay6[0].option[37].exists, ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'), '') + ifelse(relay6[0].option[38].exists, ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'), '') + ifelse(relay6[0].option[18].exists, ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'), '')), '') + ifelse(option[25].option[26].exists and not (substring(option[25].option[26].hex, 4, 4) == 0), 'Prefix: ' + addrtotext(substring(option[25].option[26].hex, 9, 16)) + '/' + uint8totext(substring(option[25].option[26].hex, 8, 1)) + ' has been assigned for ' + uint32totext(substring(option[25].option[26].hex, 4, 4)) + ' seconds to a device with DUID: ' + hexstring(option[1].hex, ':') + ifelse(relay6[0].peeraddr == '', '', ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) + ifelse(relay6[0].option[37].exists, ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'), '') + ifelse(relay6[0].option[38].exists, ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'), '') + ifelse(relay6[0].option[18].exists, ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'), '')), ''), '')"
+    }
+
+.. raw:: html
+
+    <details><summary>Expand here!</summary>
+    <pre>{
+        "request-parser-format":
+            "ifelse(pkt6.msgtype == 8 or pkt6.msgtype == 9,
+                ifelse(option[3].option[5].exists,
+                    'Address: ' + addrtotext(substring(option[3].option[5].hex, 0, 16)) + ' has been released from a device with DUID: ' + hexstring(option[1].hex, ':') +
+                    ifelse(relay6[0].peeraddr == '',
+                        '',
+                        ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) +
+                        ifelse(relay6[0].option[37].exists,
+                            ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[38].exists,
+                            ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[18].exists,
+                            ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'),
+                            '')),
+                    '') +
+                ifelse(option[25].option[26].exists,
+                    'Prefix: ' + addrtotext(substring(option[25].option[26].hex, 9, 16)) + '/' + uint8totext(substring(option[25].option[26].hex, 8, 1)) + ' has been released from a device with DUID: ' + hexstring(option[1].hex, ':') +
+                    ifelse(relay6[0].peeraddr == '',
+                        '',
+                        ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) +
+                        ifelse(relay6[0].option[37].exists,
+                            ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[38].exists,
+                            ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[18].exists,
+                            ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'),
+                            '')),
+                    ''),
+                '')",
+        "response-parser-format":
+            "ifelse(pkt6.msgtype == 7,
+                ifelse(option[3].option[5].exists and not (substring(option[3].option[5].hex, 20, 4) == 0),
+                    'Address: ' + addrtotext(substring(option[3].option[5].hex, 0, 16)) + ' has been assigned for ' + uint32totext(substring(option[3].option[5].hex, 20, 4)) + ' seconds to a device with DUID: ' + hexstring(option[1].hex, ':') +
+                    ifelse(relay6[0].peeraddr == '',
+                        '',
+                        ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) +
+                        ifelse(relay6[0].option[37].exists,
+                            ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[38].exists,
+                            ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[18].exists,
+                            ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'),
+                            '')),
+                    '') +
+                ifelse(option[25].option[26].exists and not (substring(option[25].option[26].hex, 4, 4) == 0),
+                    'Prefix: ' + addrtotext(substring(option[25].option[26].hex, 9, 16)) + '/' + uint8totext(substring(option[25].option[26].hex, 8, 1)) + ' has been assigned for ' + uint32totext(substring(option[25].option[26].hex, 4, 4)) + ' seconds to a device with DUID: ' + hexstring(option[1].hex, ':') +
+                    ifelse(relay6[0].peeraddr == '',
+                        '',
+                        ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) +
+                        ifelse(relay6[0].option[37].exists,
+                            ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[38].exists,
+                            ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[18].exists,
+                            ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'),
+                            '')),
+                    ''),
+                '')"
+    }</pre>
+    </details><br>
+
+This will log the following data on request, renew, and rebind for NA:
+
+::
+
+   Address: 2001:db8:1:: has been assigned for 713 seconds to a device with DUID: 17:34:e2:ff:09:92:54 connected via relay at address: fe80::abcd for client on link address: 3001::1, remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f, subscriber-id: 1a:2b:3c:4d:5e:6f, connected at location interface-id: 72:65:6c:61:79:31:3a:65:74:68:30
+
+This will log the following data on request, renew and rebind for PD:
+
+::
+
+   Prefix: 2001:db8:1::/64 has been assigned for 713 seconds to a device with DUID: 17:34:e2:ff:09:92:54 connected via relay at address: fe80::abcd for client on link address: 3001::1, remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f, subscriber-id: 1a:2b:3c:4d:5e:6f, connected at location interface-id: 72:65:6c:61:79:31:3a:65:74:68:30
+
+This will log the following data on release and decline for NA:
+
+::
+
+   Address: 2001:db8:1:: has been released from a device with DUID: 17:34:e2:ff:09:92:54 connected via relay at address: fe80::abcd for client on link address: 3001::1, remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f, subscriber-id: 1a:2b:3c:4d:5e:6f, connected at location interface-id: 72:65:6c:61:79:31:3a:65:74:68:30
+
+This will log the following data on release and decline for PD:
+
+::
+
+   Prefix: 2001:db8:1::/64 has been released from a device with DUID: 17:34:e2:ff:09:92:54 connected via relay at address: fe80::abcd for client on link address: 3001::1, remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f, subscriber-id: 1a:2b:3c:4d:5e:6f, connected at location interface-id: 72:65:6c:61:79:31:3a:65:74:68:30
+
+A similar result can be obtained by configuring only ``request-parser-format``.
+
+Examples:
+
+.. code-block:: json
+
+    {
+        "request-parser-format": "ifelse(pkt6.msgtype == 3 or pkt6.msgtype == 5 or pkt6.msgtype == 6, ifelse(option[3].option[5].exists, 'Address: ' + addrtotext(substring(option[3].option[5].hex, 0, 16)) + ' has been assigned for ' + uint32totext(substring(option[3].option[5].hex, 20, 4)) + ' seconds to a device with DUID: ' + hexstring(option[1].hex, ':') + ifelse(relay6[0].peeraddr == '', '', ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) + ifelse(relay6[0].option[37].exists, ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'), '') + ifelse(relay6[0].option[38].exists, ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'), '') + ifelse(relay6[0].option[18].exists, ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'), '')), '') + ifelse(option[25].option[26].exists, 'Prefix: ' + addrtotext(substring(option[25].option[26].hex, 9, 16)) + '/' + uint8totext(substring(option[25].option[26].hex, 8, 1)) + ' has been assigned for ' + uint32totext(substring(option[25].option[26].hex, 4, 4)) + ' seconds to a device with DUID: ' + hexstring(option[1].hex, ':') + ifelse(relay6[0].peeraddr == '', '', ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) + ifelse(relay6[0].option[37].exists, ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'), '') + ifelse(relay6[0].option[38].exists, ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'), '') + ifelse(relay6[0].option[18].exists, ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'), '')), ''), ifelse(pkt6.msgtype == 8 or pkt6.msgtype == 9, ifelse(option[3].option[5].exists, 'Address: ' + addrtotext(substring(option[3].option[5].hex, 0, 16)) + ' has been released from a device with DUID: ' + hexstring(option[1].hex, ':') + ifelse(relay6[0].peeraddr == '', '', ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) + ifelse(relay6[0].option[37].exists, ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'), '') + ifelse(relay6[0].option[38].exists, ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'), '') + ifelse(relay6[0].option[18].exists, ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'), '')), '') + ifelse(option[25].option[26].exists, 'Prefix: ' + addrtotext(substring(option[25].option[26].hex, 9, 16)) + '/' + uint8totext(substring(option[25].option[26].hex, 8, 1)) + ' has been released from a device with DUID: ' + hexstring(option[1].hex, ':') + ifelse(relay6[0].peeraddr == '', '', ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) + ifelse(relay6[0].option[37].exists, ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'), '') + ifelse(relay6[0].option[38].exists, ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'), '') + ifelse(relay6[0].option[18].exists, ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'), '')), ''), ''))"
+    }
+
+.. raw:: html
+
+    <details><summary>Expand here!</summary>
+    <pre>{
+        "request-parser-format":
+            "ifelse(pkt6.msgtype == 3 or pkt6.msgtype == 5 or pkt6.msgtype == 6,
+                ifelse(option[3].option[5].exists,
+                    'Address: ' + addrtotext(substring(option[3].option[5].hex, 0, 16)) + ' has been assigned for ' + uint32totext(substring(option[3].option[5].hex, 20, 4)) + ' seconds to a device with DUID: ' + hexstring(option[1].hex, ':') +
+                    ifelse(relay6[0].peeraddr == '',
+                        '',
+                        ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) +
+                        ifelse(relay6[0].option[37].exists,
+                            ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[38].exists,
+                            ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[18].exists,
+                            ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'),
+                            '')),
+                    '') +
+                ifelse(option[25].option[26].exists,
+                    'Prefix: ' + addrtotext(substring(option[25].option[26].hex, 9, 16)) + '/' + uint8totext(substring(option[25].option[26].hex, 8, 1)) + ' has been assigned for ' + uint32totext(substring(option[25].option[26].hex, 4, 4)) + ' seconds to a device with DUID: ' + hexstring(option[1].hex, ':') +
+                    ifelse(relay6[0].peeraddr == '',
+                        '',
+                        ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) +
+                        ifelse(relay6[0].option[37].exists,
+                            ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[38].exists,
+                            ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'),
+                            '') +
+                        ifelse(relay6[0].option[18].exists,
+                            ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'),
+                            '')),
+                    ''),
+                ifelse(pkt6.msgtype == 8 or pkt6.msgtype == 9,
+                    ifelse(option[3].option[5].exists,
+                        'Address: ' + addrtotext(substring(option[3].option[5].hex, 0, 16)) + ' has been released from a device with DUID: ' + hexstring(option[1].hex, ':') +
+                        ifelse(relay6[0].peeraddr == '',
+                            '',
+                            ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) +
+                            ifelse(relay6[0].option[37].exists,
+                                ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'),
+                                '') +
+                            ifelse(relay6[0].option[38].exists,
+                                ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'),
+                                '') +
+                            ifelse(relay6[0].option[18].exists,
+                                ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'),
+                                '')),
+                        '') +
+                    ifelse(option[25].option[26].exists,
+                        'Prefix: ' + addrtotext(substring(option[25].option[26].hex, 9, 16)) + '/' + uint8totext(substring(option[25].option[26].hex, 8, 1)) + ' has been released from a device with DUID: ' + hexstring(option[1].hex, ':') +
+                        ifelse(relay6[0].peeraddr == '',
+                            '',
+                            ' connected via relay at address: ' + addrtotext(relay6[0].peeraddr) + ' for client on link address: ' + addrtotext(relay6[0].linkaddr) +
+                            ifelse(relay6[0].option[37].exists,
+                                ', remote-id: ' + hexstring(relay6[0].option[37].hex, ':'),
+                                '') +
+                            ifelse(relay6[0].option[38].exists,
+                                ', subscriber-id: ' + hexstring(relay6[0].option[38].hex, ':'),
+                                '') +
+                            ifelse(relay6[0].option[18].exists,
+                                ', connected at location interface-id: ' + hexstring(relay6[0].option[18].hex, ':'),
+                                '')),
+                        ''),
+                    ''))"
+    }</pre>
+    </details><br>
+
+.. _forensic-log-database:
+
+Database Backend
+~~~~~~~~~~~~~~~~
+
+Log entries can be inserted into a database when Kea is configured with
+database backend support. Kea uses a table named ``logs``, that includes a
+timestamp generated by the database software, and a text log with the same
+format as files without the timestamp.
+
+Please refer to :ref:`mysql-database` for information on using a MySQL database;
+or to :ref:`pgsql-database` for PostgreSQL database information. The ``logs``
+table is part of the Kea database schemas.
+
+Configuration parameters are extended by standard lease database
+parameters as defined in :ref:`database-configuration4`. The ``type``
+parameter should be ``mysql``, ``postgresql`` or ``logfile``; when
+it is absent or set to ``logfile``, files are used.
+
+This database feature is experimental. No specific tools are provided
+to operate the database, but standard tools may be used, for example,
+to dump the logs table from a MYSQL database:
+
+::
+
+   $ mysql --user keatest --password keatest -e "select * from logs;"
+   +---------------------+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+----+
+   | timestamp           | address      | log                                                                                                                                                             | id |
+   +---------------------+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+----+
+   | 2022-03-30 17:38:41 | 192.168.50.1 | Address: 192.168.50.1 has been assigned for 0 hrs 10 mins 0 secs to a device with hardware address: hwtype=1 ff:01:02:03:ff:04, client-id: 00:01:02:03:04:05:06 | 31 |
+   | 2022-03-30 17:38:43 | 192.168.50.1 | Address: 192.168.50.1 has been assigned for 0 hrs 10 mins 0 secs to a device with hardware address: hwtype=1 ff:01:02:03:ff:04, client-id: 00:01:02:03:04:05:06 | 32 |
+   | 2022-03-30 17:38:45 | 192.168.50.1 | Address: 192.168.50.1 has been assigned for 0 hrs 10 mins 0 secs to a device with hardware address: hwtype=1 ff:01:02:03:ff:04, client-id: 00:01:02:03:04:05:06 | 33 |
+   +---------------------+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+----+
+
+Like all the other database-centric features, forensic logging supports database
+connection recovery, which can be enabled by setting the ``on-fail`` parameter.
+If not specified, the ``on-fail`` parameter in forensic logging defaults to
+``serve-retry-continue``;
+this is a change from its behavior in the Lease Commands, Host Commands, and
+Configuration Backend hook libraries, where
+``on-fail`` defaults to ``stop-retry-exit``. In this case, the server continues
+serving clients and does not shut down even if the recovery mechanism fails.
+If ``on-fail`` is set to ``serve-retry-exit``, the server will shut down if
+the connection to the database backend is not restored according to the
+``max-reconnect-tries`` and ``reconnect-wait-time`` parameters, but it
+continues serving clients while this mechanism is activated.
diff --git a/doc/sphinx/arm/hooks-limits.rst b/doc/sphinx/arm/hooks-limits.rst
new file mode 100644
index 0000000..25cf916
--- /dev/null
+++ b/doc/sphinx/arm/hooks-limits.rst
@@ -0,0 +1,199 @@
+.. _hooks-limits:
+
+``limits``: Limits to Manage Lease Allocation and Packet Processing
+===================================================================
+
+This hook library enables two types of limits:
+
+1. Lease limiting: allow a maximum of ``n`` leases assigned at any one time.
+2. Rate limiting: allow a maximum of ``n`` packets per ``time_unit`` to receive a response.
+
+The Limits hook library is only available to ISC customers with a paid support contract.
+
+.. _hooks-limits-configuration:
+
+Configuration
+~~~~~~~~~~~~~
+
+The following examples are for ``kea-dhcp6``, but they apply equally to
+``kea-dhcp4``. The wildcards ``"<limit-type>"`` and ``"<limit-value>"`` need to be replaced
+with the respective keys and values for each limit type described in the sections following this
+one.
+
+The library can be loaded by both ``kea-dhcp4`` and ``kea-dhcp6`` servers by adding its path in the
+``"hooks-libraries"`` element of the server's configuration.
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "hooks-libraries": [
+          {
+            "library": "/usr/local/lib/libdhcp_limits.so"
+          }
+        ]
+      }
+    }
+
+This alone does not limit anything. The desired limits are added to the user context in the
+configuration portion of the element that identifies the clients to be limited: a client class or a
+subnet. Upon reconfiguration, if Kea picked up on the configured limits, it logs one line for
+each configured limit. The log message contains ``LIMITS_CONFIGURED`` in its identifier.
+
+This is how a lease limit is defined for a client class:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "client-classes": [
+          {
+            "name": "cable-modem-1",
+            "test": "option[123].hex == 0x000C4B1E",
+            "user-context": {
+              "limits": {
+                "<limit>": "<limit-value>"
+              }
+            }
+          }
+        ]
+      }
+    }
+
+This is how a lease limit is defined for a global subnet:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "subnet6": [
+          {
+            "id": 1,
+            "subnet": "2001:db8::/64",
+            "user-context": {
+              "limits": {
+                "<limit>": "<limit-value>"
+              }
+            }
+          }
+        ]
+      }
+    }
+
+This is how a lease limit is defined for a subnet inside a shared network:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "shared-networks": [
+          {
+            "subnet6": [
+              {
+                "id": 1,
+                "subnet": "2001:db8::/64",
+                "user-context": {
+                  "limits": {
+                    "<limit>": "<limit-value>"
+                  }
+                }
+              }
+            ]
+          }
+        ]
+      }
+    }
+
+.. note::
+
+    The Limits hook library uses the class name to identify a client class and the subnet ID to
+    identify a subnet.  Changing a test expression in a client class or the network range of a
+    subnet while leaving the name or ID unchanged does not reset the lease count for the
+    respective client class or subnet. To reset the lease count, change the client class name
+    or the subnet ID.
+
+.. _hooks-limits-lease-limiting:
+
+Lease Limiting
+~~~~~~~~~~~~~~
+
+It is possible to limit the number of leases that a group of clients can get from a Kea DHCP server
+or from a set of collaborating Kea DHCP servers.
+
+The value of a lease limit can be specified as an unsigned integer in 32 bits, i.e. between ``0`` and
+``4,294,967,295``. Each lease type can be limited individually. IPv4 leases and IPv6 IA_NA leases
+are limited through the ``"address-limit"`` configuration entry. IPv6 IA_PD leases are limited
+through the ``"prefix-limit"`` configuration entry. Here are some examples:
+
+* ``"address-limit": 4``
+* ``"prefix-limit": 2``
+
+For lease limiting, client classes and the associated lease counts - which are
+checked against the configured limits - are updated for each lease in the following hook callouts:
+
+* ``lease4_select``
+* ``lease4_renew``
+* ``lease6_select``
+* ``lease6_renew``
+* ``lease6_rebind``
+
+As a result, classes for which ``"only-if-required"`` is "true" cannot be lease-limited.
+Please refer to :ref:`the classification steps <classify-classification-steps>` for more information on which
+client classes can be used to limit the number of leases.
+
+.. note::
+
+    Under load, a Kea DHCP server may allocate more leases than the limit strictly allows. This only has a chance of
+    happening during high traffic surges, coming from clients belonging to the same class or the
+    same subnet, depending on what is limited. Users may be interested in following the development of
+    `atomic lease limits <https://gitlab.isc.org/isc-projects/kea/-/issues/2449>`__ in ISC's GitLab instance.
+
+.. _hooks-limits-rate-limiting:
+
+Rate Limiting
+~~~~~~~~~~~~~
+
+It is possible to limit the frequency or rate at which inbound packets receive a response.
+
+The value of a rate limit can be specified in the format ``"<p> packets per <time-unit>"``. ``<p>``
+is any number that can be represented by an unsigned integer in 32 bits, i.e. between ``0`` and
+``4,294,967,295``. ``<time-unit>`` can be any of ``second``, ``minute``, ``hour``, ``day``,
+``week``, ``month``, or ``year``. A ``month`` is considered to be 30 days for
+simplicity; similarly, a ``year`` is 365 days for limiting purposes. This syntax
+covers a wide range of rates, from one lease per year to four billion leases per
+second. This value is assigned to the ``"rate-limit"`` configuration entry.
+Here are some examples:
+
+* ``"rate-limit": 1 packet per second``
+* ``"rate-limit": 4 packets per minute``
+* ``"rate-limit": 16 packets per hour``
+
+The configured value of ``0`` packets is a convenient way of disabling packet processing for certain
+clients entirely. As such, it means its literal value and is not a special value for disabling
+limiting altogether, as might be imagined. Disabling limiting entirely is achieved by removing
+the ``"rate-limit"`` leaf configuration entry, the ``"limits"`` map or user context
+around it, or the hook library configuration. The same applies to the value of ``0`` in lease
+limiting. However, that use case is best achieved with rate limiting; it puts less computational
+strain on Kea, since the action of dropping the request or sending a NAK is decided earlier.
+
+In terms of rate limiting, client classes are evaluated at the ``pkt4_receive`` and the
+``pkt6_receive`` callout, respectively, so that rate limits are checked as early as possible in the
+packet-processing cycle. Thus, only those classes which are assigned to the packet solely via an
+independent test expression can be used. Classes that depend on host reservations or the special
+``BOOTP`` or ``KNOWN`` classes, and classes that are marked with ``"only-if-required": true``,
+cannot be rate limited. See :ref:`the classification steps <classify-classification-steps>` for
+more details on which client classes can be used to limit the packet rate.
+
+Rate limits based on subnet are enforced only on the initially selected subnet for a given packet.
+If the selected subnet is subsequently changed, as may be the case for subnets in a
+shared network or when reselection is enabled in libraries such as the RADIUS hook, rate
+limits on the newly selected subnet are ignored. In other words, packets are gated only by
+the rate limit on the original subnet.
+
+.. note::
+
+    It may seem logical to think that assigning a rate limit of ``n`` packets per time unit results
+    in ``n`` DORA or ``n`` SARR exchanges. However, by default, all inbound packets are counted - meaning
+    that a full message exchange accounts for two packets. To achieve the effect of counting an
+    exchange only once, use client-class rate-limiting with a test expression that binds
+    ``pkt4.msgtype`` to DHCPDISCOVER messages or ``pkt6.msgtype`` to SOLICIT messages.
diff --git a/doc/sphinx/arm/hooks-radius.rst b/doc/sphinx/arm/hooks-radius.rst
new file mode 100644
index 0000000..fc8c44d
--- /dev/null
+++ b/doc/sphinx/arm/hooks-radius.rst
@@ -0,0 +1,604 @@
+.. _hooks-radius:
+
+``radius``: RADIUS Server Support
+=================================
+
+This hook library allows Kea to interact with two types of RADIUS
+servers: access and accounting. Although the most common DHCP and RADIUS
+integration is done on the DHCP relay-agent level (DHCP clients send
+DHCP packets to DHCP relays; those relays contact the RADIUS server and
+depending on the response either send the packet to the DHCP server or
+drop it), it does require DHCP relay hardware to support RADIUS
+communication. Also, even if the relay has the necessary support, it is
+often not flexible enough to send and receive additional RADIUS
+attributes. As such, the alternative looks more appealing: to extend the
+DHCP server to talk to RADIUS directly. That is the goal of this library.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or the
+   ``kea-dhcp6`` process.
+
+The major feature of this hook library is the ability to use RADIUS
+authorization. When a DHCP packet is received, the Kea server sends an
+Access-Request to the RADIUS server and waits for a response. The server
+then sends back either an Access-Accept with specific client attributes,
+or an Access-Reject. There are two cases supported here: first, the
+Access-Accept includes a Framed-IP-Address attribute (for DHCPv4) or a
+Framed-IPv6-Address attribute (for DHCPv6), which are interpreted by Kea as
+instructions to assign the specified IPv4 or IPv6 address. This
+effectively means RADIUS can act as an address-reservation database.
+
+The second supported case is the ability to assign clients to specific
+pools based on a RADIUS response. In this case, the RADIUS server sends
+back an Access-Accept with a Framed-Pool attribute.
+For both DHCPv4 and DHCPv6, Kea interprets this attribute as a client class.
+With the addition of the ability to limit access to pools to
+specific classes (see :ref:`classification-pools`), RADIUS can be
+used to force the client to be assigned a dynamic address from a
+specific pool. Furthermore, the same mechanism can be used to control
+what kind of options the client gets if there are DHCP options
+specified for a particular class.
+
+.. _hooks-radius-install:
+
+Compilation and Installation of the RADIUS Hook
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following section describes how to compile and install the software
+on CentOS 7.0. Other systems may differ slightly.
+
+.. note::
+
+   ISC provides Kea software and hooks in convenient-to-use
+   native Alpine, deb, and RPM packages. This includes the RADIUS hook and the required patched version
+   of the FreeRADIUS client library. The software compilation for RADIUS is complicated; unless
+   there are specific reasons to compile it, administrators should seriously consider using
+   native packages.
+
+STEP 1: Install dependencies
+
+Several tools are needed to build the dependencies and Kea itself. The
+following commands should install them:
+
+.. code-block:: console
+
+   $ sudo rpm -Uvh https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
+   $ sudo yum install gcc-g++ openssl-devel log4cplus-devel wget git
+
+STEP 2: Install FreeRADIUS
+
+The Kea RADIUS hook library uses the FreeRADIUS client library to
+conduct RADIUS communication. Unfortunately, the standard 1.1.7 release
+available from the project website https://freeradius.org/sub_projects/
+has several serious deficiencies; ISC engineers observed a segmentation
+fault during testing. Also, the base version of the library does not
+offer asynchronous transmissions, which are essential for effective
+accounting implementation. Both of these issues were addressed by ISC
+engineers, and the changes have been reported to the FreeRADIUS client
+project. Acceptance of those changes is outside of ISC's control, so
+until those are processed, it is strongly recommended to use the
+FreeRADIUS client with ISC's patches. To download and compile this
+version, please use the following steps:
+
+.. code-block:: console
+
+   $ git clone https://github.com/fxdupont/freeradius-client.git
+   $ cd freeradius-client/
+   $ git checkout iscdev
+   $ ./configure
+   $ make
+   $ sudo make install
+
+Additional parameters may be passed to the configure script, if needed.
+The FreeRADIUS client will be installed in
+/usr/local, which is the default path where Kea will look for it.
+It can be installed in a different directory; if so,
+make sure to add that path to the configure script when compiling Kea.
+
+STEP 3: Install a recent Boost version
+
+Kea requires a reasonably recent Boost version. Unfortunately, the
+version available in CentOS 7 is too old, so a newer Boost version is
+necessary. Furthermore, CentOS 7 has an old version of the g++ compiler
+that does not handle the latest Boost versions. Fortunately, Boost 1.65
+meets both requirements; it is both recent enough for Kea and can be
+compiled using the g++ 4.8 version in CentOS.
+
+To download and compile Boost 1.65, please use the following commands:
+
+.. code-block:: console
+
+   $ wget -nd https://boostorg.jfrog.io/artifactory/main/release/1.65.1/source/boost_1_65_1.tar.gz
+   $ tar -zxvf boost_1_65_1.tar.gz
+   $ cd boost_1_65_1/
+   $ ./bootstrap.sh
+   $ ./b2 --without-python
+   $ sudo ./b2 install
+
+Note that the ``b2`` script may optionally take extra parameters; one of
+them specifies the destination path where the sources are to be
+compiled.
+
+Alternatively, some systems provide newer Boost packages. For example,
+CentOS 7 provides ``boost169-devel``. If it is installed with
+``yum install boost169-devel``, Kea must be pointed to it with:
+
+.. code-block:: console
+
+   $ ./configure --with-boost-include=/usr/include/boost169 --with-boost-lib-dir=/usr/lib64/boost169
+
+STEP 4: Compile and install Kea
+
+Obtain the Kea sources either by downloading them from the git
+repository or extracting the tarball. Use one of these commands
+to obtain the Kea sources.
+
+Choice 1: Retrieve from GitHub
+
+.. code-block:: console
+
+   $ git clone https://github.com/isc-projects/kea.git
+
+Choice 2: Retrieve a tarball and extract it
+
+.. parsed-literal::
+
+   $ tar -zxvf kea-|release|.tar.gz
+
+The next step is to extract the premium Kea package that contains the
+RADIUS repository into the Kea sources. After the tarball is extracted,
+the Kea sources should have a premium/ subdirectory.
+
+.. parsed-literal::
+
+     $ cd kea
+     $ tar -zxvf ../kea-premium-radius-|release|.tar.gz
+
+Once this is done, verify that the Kea sources look similar to this:
+
+.. code-block:: console
+
+   $ ls -l
+   total 952
+   -rw-r--r--   1 thomson  staff    6192 Apr 25 17:38 AUTHORS
+   -rw-r--r--   1 thomson  staff   29227 Apr 25 17:38 COPYING
+   -rw-r--r--   1 thomson  staff  360298 Apr 25 20:00 ChangeLog
+   -rw-r--r--   1 thomson  staff     645 Apr 25 17:38 INSTALL
+   -rw-r--r--   1 thomson  staff    5015 Apr 25 17:38 Makefile.am
+   -rw-r--r--   1 thomson  staff     587 Apr 25 17:38 README
+   -rw-r--r--   1 thomson  staff   62323 Apr 25 17:38 configure.ac
+   drwxr-xr-x  12 thomson  staff     408 Apr 26 19:04 doc
+   drwxr-xr-x   7 thomson  staff     238 Apr 25 17:38 examples
+   drwxr-xr-x   5 thomson  staff     170 Apr 26 19:04 ext
+   drwxr-xr-x   8 thomson  staff     272 Apr 26 19:04 m4macros
+   drwxr-xr-x  20 thomson  staff     680 Apr 26 11:22 premium
+   drwxr-xr-x  10 thomson  staff     340 Apr 26 19:04 src
+   drwxr-xr-x  14 thomson  staff     476 Apr 26 19:04 tools
+
+The makefiles must be regenerated using ``autoreconf``.
+
+The next step is to configure Kea, and there are several essential steps
+necessary here. Running ``autoreconf -if`` is necessary to compile the
+premium package that contains RADIUS. Also, the ``--with-freeradius`` option
+is necessary to tell Kea where the FreeRADIUS client sources can be
+found. Also, since the non-standard Boost is used, the path to it must
+be specified.
+
+.. code-block:: console
+
+   $ autoreconf -i
+   $ ./configure --with-freeradius=/path/to/freeradius --with-boost-include=/path/to/boost --with-boost-lib-dir=/path/to/boost/state/lib
+
+For example, assuming the FreeRADIUS client was installed in the default
+directory (/usr/local) and the Boost 1.65 sources were compiled in
+/home/thomson/devel/boost1_65_1, the configure path should look as
+follows:
+
+.. code-block:: console
+
+   $ ./configure --with-freeradius=/usr/local \
+         --with-boost-include=/home/thomson/devel/boost_1_65_1 \
+         --with-boost-lib-dir=/home/thomson/devel/boost_1_65_1/stage/lib
+
+After some checks, the configure script should print a report similar to
+the following:
+
+.. parsed-literal::
+
+          Kea source configure results:
+       -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
+
+   Package:
+     Name:              kea
+     Version:           |release|
+     Extended version:  |release| (tarball)
+     OS Family:         Linux
+
+     Hooks directory:   /usr/local/lib/kea/hooks
+     Premium hooks:     yes
+     Included Hooks:    forensic_log flex_id host_cmds subnet_cmds radius host_cache
+
+   C++ Compiler:
+     CXX:             g++ --std=c++11
+     CXX_VERSION:     g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16)
+     CXX_STANDARD:    201103
+     DEFS:            -DHAVE_CONFIG_H
+     CPPFLAGS:         -DOS_LINUX  -DBOOST_ASIO_HEADER_ONLY
+     CXXFLAGS:        -g -O2
+     LDFLAGS:          -lpthread
+     KEA_CXXFLAGS:     -Wall -Wextra -Wnon-virtual-dtor -Wwrite-strings -Woverloaded-virtual -Wno-sign-compare -pthread -Wno-missing-field-initializers -fPIC
+
+   Python:
+     PYTHON_VERSION:  not needed (because kea-shell is disabled)
+
+   Boost:
+     BOOST_VERSION:   1.65.1
+     BOOST_INCLUDES:  -I/home/thomson/devel/boost_1_65_1
+     BOOST_LIBS:      -L/home/thomson/devel/boost_1_65_1/stage/lib  -lboost_system
+
+   OpenSSL:
+     CRYPTO_VERSION:  OpenSSL 1.0.2k  26 Jan 2017
+     CRYPTO_CFLAGS:
+     CRYPTO_INCLUDES:
+     CRYPTO_LDFLAGS:
+     CRYPTO_LIBS:     -lcrypto
+
+   Botan: no
+
+   Log4cplus:
+     LOG4CPLUS_VERSION:  1.1.3
+     LOG4CPLUS_INCLUDES: -I/usr/include
+     LOG4CPLUS_LIBS:     -L/usr/lib -L/usr/lib64 -llog4cplus
+
+   Flex/bison:
+     FLEX:  flex
+     BISON: bison -y
+
+   MySQL:
+     no
+
+   PostgreSQL:
+     no
+
+   Google Test:
+     no
+
+   FreeRADIUS client:
+     FREERADIUS_INCLUDE:    -I/usr/local/include
+     FREERADIUS_LIB:        -L/usr/local/lib -lfreeradius-client
+     FREERADIUS_DICTIONARY: /usr/local/etc/radiusclient/dictionary
+
+   Developer:
+     Enable Debugging:       no
+     Google Tests:           no
+     Valgrind:               not found
+     C++ Code Coverage:      no
+     Logger checks:          no
+     Generate Documentation: no
+     Parser Generation:      no
+     Kea-shell:              no
+     Perfdhcp:               no
+
+Please make sure that the compilation includes the following:
+
+-  RADIUS listed in Included Hooks;
+-  FreeRADIUS client directories printed and pointing to the right
+   directories;
+-  Boost version at least 1.65.1. The versions available in CentOS 7
+   (1.48 and 1.53) are too old.
+
+Once the configuration is complete, compile Kea using ``make``. If the
+system has more than one core, using the ``-jN``
+option is recommended to speed up the build.
+
+.. code-block:: console
+
+       $ make -j5
+       $ sudo make install
+
+.. _hooks-radius-config:
+
+RADIUS Hook Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The RADIUS hook is a library that must be loaded by either DHCPv4 or
+DHCPv6 Kea servers. Unlike some other available hook libraries, this one
+takes many parameters. For example, this configuration could be used:
+
+::
+
+     "Dhcp4": {
+
+     # Your regular DHCPv4 configuration parameters here.
+
+     "hooks-libraries": [
+     {
+         # Note that RADIUS requires host-cache for proper operation,
+         # so that library is loaded as well.
+         "library": "/usr/local/lib/kea/hooks/libdhcp_host_cache.so"
+     },
+     {
+         "library": "/usr/local/lib/kea/hooks/libdhc_radius.so",
+         "parameters": {
+
+             # Specify where FreeRADIUS dictionary could be located
+             "dictionary": "/usr/local/etc/freeradius/dictionary",
+
+             # Specify which address to use to communicate with RADIUS servers
+             "bindaddr": "*",
+
+             # more RADIUS parameters here
+         }
+     } ]
+
+RADIUS is a complicated environment. As such, it is not feasible
+to provide a default configuration that works for everyone.
+However, we do have an example that showcases some of the more common
+features. Please see ``doc/examples/kea4/hooks-radius.json`` in the Kea
+sources.
+
+The RADIUS hook library supports the following global configuration
+flags, which correspond to FreeRADIUS client library options:
+
+-  ``bindaddr`` (default ``*``) - specifies the address to be used by the
+   hook library in communication with RADIUS servers. The ``*`` special
+   value tells the kernel to choose the address.
+
+-  ``canonical-mac-address`` (default ``false``) - specifies whether MAC
+   addresses in attributes follow the canonical RADIUS format (lowercase
+   pairs of hexadecimal digits separated by ``-``).
+
+-  ``client-id-pop0`` (default ``false``) - used with ``flex-id``, removes the
+   leading zero (or pair of zeroes in DHCPv6) type in ``client-id``
+   (``duid`` in DHCPv6). Implied by ``client-id-printable``.
+
+-  ``client-id-printable`` (default ``false``) - checks whether the
+   ``client-id``/``duid`` content is printable and uses it as is instead of in
+   hexadecimal. Implies ``client-id-pop0`` and ``extract-duid`` as 0 and 255 are
+   not printable.
+
+-  ``deadtime`` (default ``0``) - is a mechanism to try unresponsive servers
+   after responsive servers. Its value specifies the number of seconds
+   after which a server is considered not to have answered, so 0
+   disables the mechanism. As the asynchronous communication does not
+   use locks or atomics, it is recommended not to use this
+   feature when running in this mode.
+
+-  ``dictionary`` (default set by configure at build time) - is the
+   attribute and value dictionary. Note that it is a critical parameter.
+   Dictionary examples can be found in the FreeRADIUS repository under the etc/
+   directory.
+
+-  ``extract-duid`` (default ``true``) - extracts the embedded ``duid`` from an
+   RFC 4361-compliant DHCPv4 ``client-id``. Implied by ``client-id-printable``.
+
+-  ``identifier-type4`` (default ``client-id``) - specifies the identifier
+   type to build the User-Name attribute. It should be the same as the
+   host identifier, and when the ``flex-id`` hook library is used the
+   ``replace-client-id`` must be set to ``true``; ``client-id`` is used with
+   ``client-id-pop0``.
+
+-  ``identifier-type6`` (default ``duid``) - specifies the identifier type to
+   build the User-Name attribute. It should be the same as the host
+   identifier, and when the ``flex-id`` hook library is used the
+   ``replace-client-id`` must be set to ``true``; ``duid`` is used with
+   ``client-id-pop0``.
+
+-  ``realm`` (default ``""``) - is the default realm.
+
+-  ``reselect-subnet-address`` (default ``false``) - uses the Kea reserved
+   address/RADIUS Framed-IP-Address or Framed-IPv6-Address to reselect
+   subnets where the address is not in the subnet range.
+
+-  ``reselect-subnet-pool`` (default ``false``) - uses the Kea
+   ``client-class``/RADIUS Frame-Pool to reselect subnets where no available
+   pool can be found.
+
+-  ``retries`` (default ``3``) - is the number of retries before trying the
+   next server. Note that it is not supported for asynchronous
+   communication.
+
+-  ``session-history`` (default ``""``) - is the name of the file providing
+   persistent storage for accounting session history.
+
+-  ``timeout`` (default ``10``) - is the number of seconds during which a
+   response is awaited.
+
+When ``reselect-subnet-pool`` or ``reselect-subnet-address`` is set to
+``true`` at the reception of RADIUS Access-Accept, the selected subnet is
+checked against the ``client-class`` name or the reserved address; if it
+does not match, another subnet is selected among matching subnets.
+
+Two services are supported:
+
+-  ``access`` - the authentication service.
+
+-  ``accounting`` - the accounting service.
+
+Configuration of services is divided into two parts:
+
+-  Servers that define RADIUS servers that the library is expected to
+   contact. Each server may have the following items specified:
+
+   -  ``name`` - specifies the IP address of the server (it is
+      possible to use a name which will be resolved, but it is not
+      recommended).
+
+   -  ``port`` (default RADIUS authentication or accounting service) -
+      specifies the UDP port of the server. Note that the
+      FreeRADIUS client library by default uses ports 1812
+      (authorization) and 1813 (accounting). Some server implementations
+      use 1645 (authorization) and 1646 (accounting). The
+      ``port`` parameter may be used to adjust as needed.
+
+   -  ``secret`` - authenticates messages.
+
+   There may be up to eight servers. Note that when no server is
+   specified, the service is disabled.
+
+-  Attributes which define additional information that the Kea server
+   sends to a RADIUS server. The parameter must be identified either
+   by a name or type. Its value can be specified in one of three
+   possible ways: ``data`` (which defines a plain text value), ``raw`` (which
+   defines the value in hex), or ``expr`` (which defines an expression
+   that is evaluated for each incoming packet independently).
+
+   -  ``name`` - the name of the attribute.
+
+   -  ``type`` - the type of the attribute. Either the type or the name must be
+      provided, and the attribute must be defined in the dictionary.
+
+   -  ``data`` - the first of three ways to specify the attribute
+      content. The data entry is parsed by the FreeRADIUS library, so
+      values defined in the dictionary of the attribute may be used.
+
+   -  ``raw`` - the second of three ways to specify the attribute
+      content; it specifies the content in hexadecimal. Note that it
+      does not work with integer-content attributes (date, integer, and
+      IPv4 address); a string-content attribute (string, IPv6 address,
+      and IPv6 prefix) is required.
+
+   -  ``expr`` - the last way to specify the attribute content. It
+      specifies an evaluation expression which must return a not-empty
+      string when evaluated with the DHCP query packet. Currently this
+      is restricted to the access service.
+
+For example, to specify a single access server available on localhost
+that uses "xyz123" as a secret, and tell Kea to send three additional
+attributes (Password, Connect-Info, and Configuration-Token), the
+following snippet could be used:
+
+::
+
+   "parameters": {
+
+       # Other RADIUS parameters here
+
+       "access": {
+
+           # This starts the list of access servers
+           "servers": [
+           {
+               # These are parameters for the first (and only) access server
+               "name": "127.0.0.1",
+               "port": 1812,
+               "secret": "xyz123"
+           }
+           # Additional access servers could be specified here
+           ],
+
+           # This defines a list of additional attributes Kea will send to each
+           # access server in Access-Request.
+           "attributes": [
+           {
+               # This attribute is identified by name (must be present in the
+               # dictionary) and has static value (i.e. the same value will be
+               # sent to every server for every packet)
+               "name": "Password",
+               "data": "mysecretpassword"
+           },
+           {
+               # It is also possible to specify an attribute using its type,
+               # rather than a name. 77 is Connect-Info. The value is specified
+               # using hex. Again, this is a static value. It will be sent the
+               # same for every packet and to every server.
+               "type": 77,
+               "raw": "65666a6a71"
+           },
+           {
+               # This example shows how an expression can be used to send dynamic
+               # value. The expression (see Section 13) may take any value from
+               # the incoming packet or even its metadata (e.g. the interface
+               # it was received over from)
+               "name": "Configuration-Token",
+               "expr": "hexstring(pkt4.mac,':')"
+           }
+           ] # End of attributes
+       }, # End of access
+
+       # Accounting parameters.
+       "accounting": {
+           # This starts the list of accounting servers
+           "servers": [
+           {
+               # These are parameters for the first (and only) accounting server
+               "name": "127.0.0.1",
+               "port": 1813,
+               "secret": "sekret"
+           }
+           # Additional accounting servers could be specified here
+           ]
+       }
+
+   }
+
+Customization is sometimes required for certain attributes by devices belonging
+to various vendors. This is a great way to leverage the expression evaluation
+mechanism. For example, MAC addresses which might be used as a convenience
+value for the User-Name attribute are most likely to appear in colon-hexadecimal
+notation (``de:ad:be:ef:ca:fe``), but they might need to be expressed in
+hyphen-hexadecimal notation (``de-ad-be-ef-ca-fe``). Here's how to specify that:
+
+.. code-block:: json
+
+   {
+      "parameters": {
+         "access": {
+            "attributes": [
+               {
+                  "name": "User-Name",
+                  "expr": "hexstring(pkt4.mac, '-')"
+               }
+            ]
+         }
+      }
+   }
+
+And here's how to specify period-separated hexadecimal notation (``dead.beef.cafe``), preferred by Cisco devices:
+
+.. code-block:: json
+
+   {
+      "parameters": {
+         "access": {
+            "attributes": [
+               {
+                  "name": "User-Name",
+                  "expr": "concat(concat(concat(substring(hexstring(pkt4.mac, ''), 0, 4), '.'), concat(substring(hexstring(pkt4.mac, ''), 4, 4), '.'), concat(substring(hexstring(pkt4.mac, ''), 8, 4), '.'))"
+               }
+            ]
+         }
+      }
+   }
+
+
+For the RADIUS hook library to operate properly in DHCPv4,
+the Host Cache hook library must also be loaded. The reason for this
+is somewhat complex. In a typical deployment, the DHCP clients send
+their packets via DHCP relay, which inserts certain Relay Agent
+Information options, such as ``circuit-id`` or ``remote-id``. The values of
+those options are then used by the Kea DHCP server to formulate the
+necessary attributes in the Access-Request message sent to the RADIUS
+server. However, once the DHCP client gets its address, it then renews
+by sending packets directly to the DHCP server. As a result, the relays
+are not able to insert their RAI options, and the DHCP server cannot send
+the Access-Request queries to the RADIUS server by using just the
+information from incoming packets. Kea needs to keep the information
+received during the initial Discover/Offer exchanges and use it again
+later when sending accounting messages.
+
+This mechanism is implemented based on user context in host
+reservations. (See :ref:`user-context` and :ref:`user-context-hooks` for
+details.) The host-cache mechanism allows the information retrieved by
+RADIUS to be stored and later used for sending accounting and access
+queries to the RADIUS server. In other words, the host-cache mechanism
+is mandatory, unless administrators do not want RADIUS communication for messages
+other than Discover and the first Request from each client.
+
+.. note::
+
+   Currently the RADIUS hook library is incompatible with the
+   ``early-global-reservations-lookup`` global parameter i.e.
+   setting the parameter to ``true`` raises an error when the
+   hook library is loaded.
diff --git a/doc/sphinx/arm/hooks-rbac.rst b/doc/sphinx/arm/hooks-rbac.rst
new file mode 100644
index 0000000..d1c0b9c
--- /dev/null
+++ b/doc/sphinx/arm/hooks-rbac.rst
@@ -0,0 +1,439 @@
+.. _hooks-RBAC:
+
+``rbac``: Role-Based Access Control
+===================================
+
+.. _hooks-RBAC-overview:
+
+Role-Based Access Control (RBAC) Overview
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Before the processing of commands in received HTTP requests, the ``rbac`` hook
+takes specific parameters, e.g. the common name part of the client
+certificate subject name, to assign a role to the request.
+The configuration associated with this role is used to accept or reject
+the command. After processing, the response can be rewritten, e.g.
+parts can be removed.
+
+Here is a summary of the steps in processing a request:
+ - The HTTP library records some information to be used later, e.g.
+   the remote address.
+ - When TLS is required but the request was not protected by TLS,
+   the request is rejected by sending an "unauthorized" response.
+ - The command is extracted from the request.
+ - A role is assigned using recorded information in the request.
+ - The role is used to accept (pass through) or reject (send
+   a forbidden response) the command.
+
+Here is a summary of the steps in processing a response:
+ - The information attached to the request is retrieved during the
+   request processing (when the request was accepted).
+ - Request filters are applied to the response.
+
+.. _hooks-RBAC-config:
+
+Role-Based Access Control Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Role Assignment
+---------------
+
+Role assignment is governed by the configured role-assignment method.
+
+.. table:: Role assignment methods
+
+   +----------------------+---------------------------------------------------------+
+   | Name                 | Description                                             |
+   +----------------------+---------------------------------------------------------+
+   | remote-address       | remote/client IP address                                |
+   +----------------------+---------------------------------------------------------+
+   | cert-subject         | common name part of the client certificate subject name |
+   +----------------------+---------------------------------------------------------+
+   | cert-issuer          | common name part of the client certificate issuer name  |
+   +----------------------+---------------------------------------------------------+
+   | basic-authentication | user ID of basic HTTP authentication                    |
+   +----------------------+---------------------------------------------------------+
+   | custom-value         | for extension                                           |
+   +----------------------+---------------------------------------------------------+
+
+Role Configuration
+------------------
+
+.. table:: Role configuration parameters
+
+   +------------------+----------------------------------------------------+
+   | Name             | Description                                        |
+   +------------------+----------------------------------------------------+
+   | name             | the role name (at the exception of the default     |
+   |                  | and unknown roles)                                 |
+   +------------------+----------------------------------------------------+
+   | accept-commands  | the accept access list                             |
+   +------------------+----------------------------------------------------+
+   | reject-commands  | the reject access list                             |
+   +------------------+----------------------------------------------------+
+   | other-commands   | specifies what to do for commands not matching     |
+   |                  | accept and reject lists (default reject)           |
+   +------------------+----------------------------------------------------+
+   | list-match-first | specifies what to do for commands matching both    |
+   |                  | accept and reject list by giving the list to check |
+   |                  | and apply first (default accept)                   |
+   +------------------+----------------------------------------------------+
+   | response-filters | the filters to apply to responses                  |
+   +------------------+----------------------------------------------------+
+
+.. note::
+
+   The role assignment can fail, for instance with ``cert-subject`` when
+   the client certificate was not required, or it has no subject common
+   name and instead a DNS alternative subject name. In this case the role
+   assignment returns the empty role and the ``default-role`` entry is used.
+
+   The role assignment can return an unexpected value e.g. with an
+   unregistered role name or a typing error. In this case the ``unknown-role``
+   entry is used.
+
+   Both ``default-role`` and ``unknown-role`` default to reject all commands.
+
+API Commands
+------------
+
+All commands of the REST API are described in files in the source directory
+``src/share/api``, or in installed Kea
+in ``.../share/kea/api``. The ``rbac`` hook reads these files to take the name,
+the access right (i.e. ``read`` or ``write``), and the hook name.
+
+.. table:: Extra command-definition parameters
+
+   +--------+---------------------------------------------------------+
+   | Name   | Description                                             |
+   +--------+---------------------------------------------------------+
+   | name   | (mandatory) the command name                            |
+   +--------+---------------------------------------------------------+
+   | access | (mandatory) the access right i.e. ``read`` or ``write`` |
+   +--------+---------------------------------------------------------+
+   | hook   | (optional) the hook name (empty or not-present for      |
+   |        | commands of servers or agents)                          |
+   +--------+---------------------------------------------------------+
+
+.. note::
+
+   These command description files are security-sensitive, e.g. with
+   too-permissive access rights a local attacker may modify them and
+   defeat the RBAC goal.
+
+Access Control Lists
+--------------------
+
+Access control lists can be specified using a name (string) or a
+single entry map.
+
+.. table:: Predefined named access list
+
+   +-------+----------------------------------------------+
+   | Name  | Description                                  |
+   +-------+----------------------------------------------+
+   | ALL   | matches everything                           |
+   +-------+----------------------------------------------+
+   | NONE  | matches nothing                              |
+   +-------+----------------------------------------------+
+   | READ  | matches commands with the read-access right  |
+   +-------+----------------------------------------------+
+   | WRITE | matches commands with the write-access right |
+   +-------+----------------------------------------------+
+
+Map access list specifications use a list type in the name of the single entry
+and parameter in the value.
+
+.. table:: Access list types
+
+   +---------+-----------------+--------------------------------------+
+   | Name    | Description     | Parameter                            |
+   +---------+-----------------+--------------------------------------+
+   | not     | logical not     | access list                          |
+   +---------+-----------------+--------------------------------------+
+   | and     | logical and     | list of access lists                 |
+   +---------+-----------------+--------------------------------------+
+   | or      | logical or      | list of access lists                 |
+   +---------+-----------------+--------------------------------------+
+   | command | explicit list   | list of command names                |
+   +---------+-----------------+--------------------------------------+
+   | access  | by access right | access right (``read`` or ``write``) |
+   +---------+-----------------+--------------------------------------+
+   | hook    | by hook         | hook name (can be empty)             |
+   +---------+-----------------+--------------------------------------+
+
+Response Filters
+----------------
+
+.. table:: Predefined response filters
+
+   +---------------+---------------------------------------+
+   | Name          | Description                           |
+   +---------------+---------------------------------------+
+   | list-commands | Removes not-allowed commands from the |
+   |               | list-commands response                |
+   +---------------+---------------------------------------+
+
+Global Parameters
+-----------------
+
+The global parameters are:
+
+-  ``assign-role-method``: the name of the method
+   which is used for role assignment. This parameter is mandatory.
+
+-  ``api-files``: the path of the directory where
+   the API files describing commands can be found. This parameter is mandatory.
+
+-  ``require-tls``: the specification of whether received requests on HTTP (vs HTTPS) are
+   rejected. It defaults to ``false`` when the role-assignment method is not
+   based on certificates.
+
+-  ``commands``: the list of extra command configurations.
+
+-  ``access-control-lists``: the named access control list definitions
+   (each definition is a single entry map; the name of the entry is
+   the name of the access list, and the value is the specification).
+
+-  ``roles``: the role configurations.
+
+-  ``default-role``: the configuration of the default role (used
+   when "" is assigned).
+
+-  ``unknown-role``: the configuration of the unknown role
+   (used when the not-empty assigned role has no configuration).
+
+Sample Configuration
+~~~~~~~~~~~~~~~~~~~~
+
+A sample configuration is available in ``doc/examples/agent/rbac.json``
+in the Kea source and is copied below.
+
+.. code-block:: javascript
+   :linenos:
+   :emphasize-lines: 31-85
+
+    {
+    "Control-agent": {
+        // We need to specify where the agent should listen to incoming HTTP
+        // queries.
+        "http-host": "127.0.0.1",
+
+        // If enabling HA and multi-threading, the 8000 port is used by the HA
+        // hook library http listener. When using HA hook library with
+        // multi-threading to function, make sure the port used by dedicated
+        // listener is different (e.g. 8001) than the one used by CA. Note
+        // the commands should still be sent via CA. The dedicated listener
+        // is specifically for HA updates only.
+        "http-port": 8000,
+
+        // TLS trust anchor (Certificate Authority). This is a file name or
+        // (for OpenSSL only) a directory path.
+        "trust-anchor": "my-ca",
+
+        // TLS server certificate file name.
+        "cert-file": "my-cert",
+
+        // TLS server private key file name.
+        "key-file": "my-key",
+
+        // TLS require client certificates flag. Default is true and means
+        // require client certificates. False means they are optional.
+        "cert-required": true,
+
+        // Add hooks here.
+        "hooks-libraries": [
+        {
+            "library": "/opt/lib/libca_rbac.so",
+            "parameters": {
+                // This section configures the RBAC hook library.
+                // Mandatory parameters.
+                "assign-role-method": "cert-subject",
+                "api-files": "/opt/share/kea/api",
+                // Optional parameters.
+                "require-tls": true,
+                "commands": [
+                {
+                    "name": "my-command",
+                    "access": "read",
+                    "hook": "my-hook"
+                } ],
+                "access-control-lists": [
+                {
+                    "my-none": { "not": "ALL" }
+                },{
+                    "another-none": { "and": [ "ALL", "NONE" ] }
+                },{
+                    "my-read": { "access": "read" }
+                } ],
+                "roles": [
+                {
+                    "name": "kea-client",
+                    "accept-commands":
+                    {
+                        "commands": [ "list-commands", "status-get" ]
+                    },
+                    "reject-commands": "NONE",
+                    "other-commands": "reject",
+                    "list-match-first": "accept",
+                    "response-filters": [ "list-commands" ]
+                },{
+                    "name": "admin",
+                    "accept-commands": "ALL",
+                    "reject-commands":
+                    {
+                        "hook": "cb_cmds"
+                    },
+                    "list-match-first": "reject"
+                } ],
+                "default-role":
+                {
+                    "accept-commands": "NONE",
+                    "reject-commands": "ALL"
+                },
+                "unknown-role":
+                {
+                    "accept-commands": "READ",
+                    "reject-commands": "WRITE"
+                }
+            }
+        } ]
+
+        // Additional parameters, such as logging and others
+        // omitted for clarity.
+
+    }
+    }
+
+Accept/Reject Algorithm
+~~~~~~~~~~~~~~~~~~~~~~~
+
+This is the pseudo-code of the accept/reject decision algorithm which returns
+``true`` (accept) or ``false`` (reject).
+
+.. code-block:: c
+
+   bool match(command) {
+       if (list-match-first == accept) {
+           if (accept_list && accept_list->match(command)) {
+               return (true);
+           }
+           if (reject_list && reject_list->match(command)) {
+               return (false);
+           }
+       } else {
+           if (reject_list && reject_list->match(command)) {
+               return (false);
+           }
+           if (accept_list && accept_list->match(command)) {
+               return (true);
+           }
+       }
+       if (others == reject) {
+          return (false);
+       } else {
+          return (true);
+       }
+   }
+
+Extensive Example
+~~~~~~~~~~~~~~~~~
+
+Here is an extensive example for a role accepting all read commands, with
+the exception of ``config-get``, e.g. for hiding passwords. For any remote
+user who is not recognized as "user1", all commands should be rejected.
+
+The first option is to put the allowed commands in the "accept-commands"
+list and to reject anything else:
+
+.. code-block:: javascript
+
+   ...
+   "roles": [
+   {
+       "name": "user1",
+       "accept-commands":
+       {
+           "and": [
+               "READ",
+               { "not":
+                   { "commands": [ "config-get" ] }
+               }
+           ]
+       },
+       "reject-commands": "ALL",
+       // This is the default but as the config relies on it
+       // it is explicitly set.
+       "list-match-first": "accept"
+    },
+    ...
+    ],
+    ...
+
+A common alternative is to not set the "reject-commands" list, i.e. leave
+it empty and rely on "other-commands" to reject anything else.
+
+.. code-block:: javascript
+
+   ...
+   "roles": [
+   {
+       "name": "user2",
+       "accept-commands":
+       {
+           "and": [
+               "READ",
+               { "not":
+                   { "commands": [ "config-get" ] }
+               }
+           ]
+       },
+       // This is the default but as the config relies on it
+       // it is explicitly set.
+       "other-commands": "reject"
+    },
+    ...
+    ],
+    ...
+
+It is also possible to do the opposite, i.e. to set only the "reject-commands" list:
+
+.. code-block:: javascript
+
+   ...
+   "roles": [
+   {
+       "name": "user3",
+       "reject-commands":
+       {
+           "or": [
+               "WRITE",
+               { "commands": [ "config-get" ] }
+           ]
+       },
+       "other-commands": "accept"
+    },
+    ...
+    ],
+    ...
+
+Or use both lists with the exception in the "reject-commands" list,
+which must be checked first as "config-get" has the read-access right.
+
+.. code-block:: javascript
+
+   ...
+   "roles": [
+   {
+       "name": "user4",
+       "accept-commands": "READ",
+       "reject-commands": { "commands": [ "config-get" ] },
+       "list-match-first": "reject"
+    },
+    ...
+    ],
+    ...
+
+To check any configuration, it is a good idea to use the "list-commands"
+response filter, which shows errors such as missing (rejected) commands
+and extra (accepted) commands.
diff --git a/doc/sphinx/arm/hooks-run-script.rst b/doc/sphinx/arm/hooks-run-script.rst
new file mode 100644
index 0000000..7eade15
--- /dev/null
+++ b/doc/sphinx/arm/hooks-run-script.rst
@@ -0,0 +1,620 @@
+.. _hooks-run-script:
+
+``run_script``: Run Script Support for External Hook Scripts
+============================================================
+
+The Run Script hook library adds support for calling an external script for specific
+packet-processing hook points.
+
+The library, which was added in Kea 1.9.5, can be loaded in a
+similar way to other hook libraries by the ``kea-dhcp4`` and
+``kea-dhcp6`` processes.
+
+.. code-block:: json
+
+    {
+        "hooks-libraries": [
+            {
+                "library": "/usr/local/lib/libdhcp_run_script.so",
+                "parameters": {
+                    "name": "/full_path_to/script_name.sh",
+                    "sync": false
+                }
+            }
+        ]
+    }
+
+The parameters contain the ``name``, which indicates the full path to the external
+script to be called on each hook point, and also the ``sync`` option, to be able
+to wait synchronously for the script to finish execution.
+If the ``sync`` parameter is ``false``, then the script will launch and Kea
+will not wait for the execution to finish, causing all the OUT parameters of
+the script (including the next step) to be ignored.
+
+.. note::
+
+   The script inherits all privileges from the server which calls it.
+
+.. note::
+
+   Currently, enabling synchronous calls to external scripts is not supported.
+
+.. _hooks-run-script-hook-points:
+
+This library has several hook-point functions implemented, which are
+called at the specific packet-processing stage.
+
+The dhcpv4 hook points:
+
+::
+
+   lease4_renew
+   lease4_expire
+   lease4_recover
+   leases4_committed
+   lease4_release
+   lease4_decline
+
+
+The dhcpv6 hook points:
+
+::
+
+   lease6_renew
+   lease6_rebind
+   lease6_expire
+   lease6_recover
+   leases6_committed
+   lease6_release
+   lease6_decline
+
+Each hook point extracts the Kea internal data and exports it as string
+environment variables. These parameters are shared with the target script
+using the child process environment.
+The only parameter passed to the call of the target script is the name of
+the hook point.
+
+An example of a script implementing all hook points is presented below:
+
+::
+
+   #!/bin/bash
+
+   unknown_handle() {
+       echo "Unhandled function call ${*}"
+       exit 123
+   }
+
+
+   lease4_renew () {
+       ...
+   }
+
+   lease4_expire () {
+       ...
+   }
+
+   lease4_recover () {
+       ...
+   }
+
+   leases4_committed () {
+       ...
+   }
+
+   lease4_release () {
+       ...
+   }
+
+   lease4_decline () {
+       ...
+   }
+
+   lease6_renew () {
+       ...
+   }
+
+   lease6_rebind () {
+       ...
+   }
+
+   lease6_expire () {
+       ...
+   }
+
+   lease6_recover () {
+       ...
+   }
+
+   leases6_committed () {
+       ...
+   }
+
+   lease6_release () {
+       ...
+   }
+
+   lease6_decline () {
+       ...
+   }
+
+   case "$1" in
+       "lease4_renew")
+           lease4_renew
+           ;;
+       "lease4_expire")
+           lease4_expire
+           ;;
+       "lease4_recover")
+           lease4_recover
+           ;;
+       "leases4_committed")
+           leases4_committed
+           ;;
+       "lease4_release")
+           lease4_release
+           ;;
+       "lease4_decline")
+           lease4_decline
+           ;;
+       "lease6_renew")
+           lease6_renew
+           ;;
+       "lease6_rebind")
+           lease6_rebind
+           ;;
+       "lease6_expire")
+           lease6_expire
+           ;;
+       "lease6_recover")
+           lease6_recover
+           ;;
+       "leases6_committed")
+           leases6_committed
+           ;;
+       "lease6_release")
+           lease6_release
+           ;;
+       "lease6_decline")
+           lease6_decline
+           ;;
+       *)
+           unknown_handle "${@}"
+           ;;
+   esac
+
+
+.. _hooks-run-script-exported-environment-variables:
+
+Available parameters for each hook point are presented below.
+
+DHCPv4:
+
+``lease4_renew``
+
+::
+
+   QUERY4_TYPE
+   QUERY4_TXID
+   QUERY4_LOCAL_ADDR
+   QUERY4_LOCAL_PORT
+   QUERY4_REMOTE_ADDR
+   QUERY4_REMOTE_PORT
+   QUERY4_IFACE_INDEX
+   QUERY4_IFACE_NAME
+   QUERY4_HOPS
+   QUERY4_SECS
+   QUERY4_FLAGS
+   QUERY4_CIADDR
+   QUERY4_SIADDR
+   QUERY4_YIADDR
+   QUERY4_GIADDR
+   QUERY4_RELAYED
+   QUERY4_HWADDR
+   QUERY4_HWADDR_TYPE
+   QUERY4_LOCAL_HWADDR
+   QUERY4_LOCAL_HWADDR_TYPE
+   QUERY4_REMOTE_HWADDR
+   QUERY4_REMOTE_HWADDR_TYPE
+   QUERY4_OPTION_82
+   QUERY4_OPTION_82_SUB_OPTION_1
+   QUERY4_OPTION_82_SUB_OPTION_2
+   SUBNET4_ID
+   SUBNET4_NAME
+   SUBNET4_PREFIX
+   SUBNET4_PREFIX_LEN
+   PKT4_CLIENT_ID
+   PKT4_HWADDR
+   PKT4_HWADDR_TYPE
+   LEASE4_ADDRESS
+   LEASE4_CLTT
+   LEASE4_HOSTNAME
+   LEASE4_HWADDR
+   LEASE4_HWADDR_TYPE
+   LEASE4_STATE
+   LEASE4_SUBNET_ID
+   LEASE4_VALID_LIFETIME
+   LEASE4_CLIENT_ID
+
+``lease4_expire``
+
+::
+
+   LEASE4_ADDRESS
+   LEASE4_CLTT
+   LEASE4_HOSTNAME
+   LEASE4_HWADDR
+   LEASE4_HWADDR_TYPE
+   LEASE4_STATE
+   LEASE4_SUBNET_ID
+   LEASE4_VALID_LIFETIME
+   LEASE4_CLIENT_ID
+   REMOVE_LEASE
+
+``lease4_recover``
+
+::
+
+   LEASE4_ADDRESS
+   LEASE4_CLTT
+   LEASE4_HOSTNAME
+   LEASE4_HWADDR
+   LEASE4_HWADDR_TYPE
+   LEASE4_STATE
+   LEASE4_SUBNET_ID
+   LEASE4_VALID_LIFETIME
+   LEASE4_CLIENT_ID
+
+``leases4_committed``
+
+::
+
+   QUERY4_TYPE
+   QUERY4_TXID
+   QUERY4_LOCAL_ADDR
+   QUERY4_LOCAL_PORT
+   QUERY4_REMOTE_ADDR
+   QUERY4_REMOTE_PORT
+   QUERY4_IFACE_INDEX
+   QUERY4_IFACE_NAME
+   QUERY4_HOPS
+   QUERY4_SECS
+   QUERY4_FLAGS
+   QUERY4_CIADDR
+   QUERY4_SIADDR
+   QUERY4_YIADDR
+   QUERY4_GIADDR
+   QUERY4_RELAYED
+   QUERY4_HWADDR
+   QUERY4_HWADDR_TYPE
+   QUERY4_LOCAL_HWADDR
+   QUERY4_LOCAL_HWADDR_TYPE
+   QUERY4_REMOTE_HWADDR
+   QUERY4_REMOTE_HWADDR_TYPE
+   QUERY4_OPTION_82
+   QUERY4_OPTION_82_SUB_OPTION_1
+   QUERY4_OPTION_82_SUB_OPTION_2
+   LEASES4_SIZE
+   DELETED_LEASES4_SIZE
+
+If ``LEASES4_SIZE`` or ``DELETED_LEASES4_SIZE`` is non-zero, then each lease
+has its own unique identifier, as shown below. The first index starts
+at 0.
+
+::
+
+   LEASES4_AT0_ADDRESS
+   LEASES4_AT0_CLTT
+   LEASES4_AT0_HOSTNAME
+   LEASES4_AT0_HWADDR
+   LEASES4_AT0_HWADDR_TYPE
+   LEASES4_AT0_STATE
+   LEASES4_AT0_SUBNET_ID
+   LEASES4_AT0_VALID_LIFETIME
+   LEASES4_AT0_CLIENT_ID
+   DELETED_LEASES4_AT0_ADDRESS
+   DELETED_LEASES4_AT0_CLTT
+   DELETED_LEASES4_AT0_HOSTNAME
+   DELETED_LEASES4_AT0_HWADDR
+   DELETED_LEASES4_AT0_HWADDR_TYPE
+   DELETED_LEASES4_AT0_STATE
+   DELETED_LEASES4_AT0_SUBNET_ID
+   DELETED_LEASES4_AT0_VALID_LIFETIME
+   DELETED_LEASES4_AT0_CLIENT_ID
+
+``lease4_release``
+
+::
+
+   QUERY4_TYPE
+   QUERY4_TXID
+   QUERY4_LOCAL_ADDR
+   QUERY4_LOCAL_PORT
+   QUERY4_REMOTE_ADDR
+   QUERY4_REMOTE_PORT
+   QUERY4_IFACE_INDEX
+   QUERY4_IFACE_NAME
+   QUERY4_HOPS
+   QUERY4_SECS
+   QUERY4_FLAGS
+   QUERY4_CIADDR
+   QUERY4_SIADDR
+   QUERY4_YIADDR
+   QUERY4_GIADDR
+   QUERY4_RELAYED
+   QUERY4_HWADDR
+   QUERY4_HWADDR_TYPE
+   QUERY4_LOCAL_HWADDR
+   QUERY4_LOCAL_HWADDR_TYPE
+   QUERY4_REMOTE_HWADDR
+   QUERY4_REMOTE_HWADDR_TYPE
+   QUERY4_OPTION_82
+   QUERY4_OPTION_82_SUB_OPTION_1
+   QUERY4_OPTION_82_SUB_OPTION_2
+   LEASE4_ADDRESS
+   LEASE4_CLTT
+   LEASE4_HOSTNAME
+   LEASE4_HWADDR
+   LEASE4_HWADDR_TYPE
+   LEASE4_STATE
+   LEASE4_SUBNET_ID
+   LEASE4_VALID_LIFETIME
+   LEASE4_CLIENT_ID
+
+``lease4_decline``
+
+::
+
+   QUERY4_TYPE
+   QUERY4_TXID
+   QUERY4_LOCAL_ADDR
+   QUERY4_LOCAL_PORT
+   QUERY4_REMOTE_ADDR
+   QUERY4_REMOTE_PORT
+   QUERY4_IFACE_INDEX
+   QUERY4_IFACE_NAME
+   QUERY4_HOPS
+   QUERY4_SECS
+   QUERY4_FLAGS
+   QUERY4_CIADDR
+   QUERY4_SIADDR
+   QUERY4_YIADDR
+   QUERY4_GIADDR
+   QUERY4_RELAYED
+   QUERY4_HWADDR
+   QUERY4_HWADDR_TYPE
+   QUERY4_LOCAL_HWADDR
+   QUERY4_LOCAL_HWADDR_TYPE
+   QUERY4_REMOTE_HWADDR
+   QUERY4_REMOTE_HWADDR_TYPE
+   QUERY4_OPTION_82
+   QUERY4_OPTION_82_SUB_OPTION_1
+   QUERY4_OPTION_82_SUB_OPTION_2
+   LEASE4_ADDRESS
+   LEASE4_CLTT
+   LEASE4_HOSTNAME
+   LEASE4_HWADDR
+   LEASE4_HWADDR_TYPE
+   LEASE4_STATE
+   LEASE4_SUBNET_ID
+   LEASE4_VALID_LIFETIME
+   LEASE4_CLIENT_ID
+
+DHCPv6:
+
+``lease6_renew``
+
+::
+
+   QUERY6_TYPE
+   QUERY6_TXID
+   QUERY6_LOCAL_ADDR
+   QUERY6_LOCAL_PORT
+   QUERY6_REMOTE_ADDR
+   QUERY6_REMOTE_PORT
+   QUERY6_IFACE_INDEX
+   QUERY6_IFACE_NAME
+   QUERY6_REMOTE_HWADDR
+   QUERY6_REMOTE_HWADDR_TYPE
+   QUERY6_PROTO
+   QUERY6_CLIENT_ID
+   LEASE6_ADDRESS
+   LEASE6_CLTT
+   LEASE6_HOSTNAME
+   LEASE6_HWADDR
+   LEASE6_HWADDR_TYPE
+   LEASE6_STATE
+   LEASE6_SUBNET_ID
+   LEASE6_VALID_LIFETIME
+   LEASE6_DUID
+   LEASE6_IAID
+   LEASE6_PREFERRED_LIFETIME
+   LEASE6_PREFIX_LEN
+   LEASE6_TYPE
+   PKT6_IA_IAID
+   PKT6_IA_IA_TYPE
+   PKT6_IA_IA_T1
+   PKT6_IA_IA_T2
+
+``lease6_rebind``
+
+::
+
+   QUERY6_TYPE
+   QUERY6_TXID
+   QUERY6_LOCAL_ADDR
+   QUERY6_LOCAL_PORT
+   QUERY6_REMOTE_ADDR
+   QUERY6_REMOTE_PORT
+   QUERY6_IFACE_INDEX
+   QUERY6_IFACE_NAME
+   QUERY6_REMOTE_HWADDR
+   QUERY6_REMOTE_HWADDR_TYPE
+   QUERY6_PROTO
+   QUERY6_CLIENT_ID
+   LEASE6_ADDRESS
+   LEASE6_CLTT
+   LEASE6_HOSTNAME
+   LEASE6_HWADDR
+   LEASE6_HWADDR_TYPE
+   LEASE6_STATE
+   LEASE6_SUBNET_ID
+   LEASE6_VALID_LIFETIME
+   LEASE6_DUID
+   LEASE6_IAID
+   LEASE6_PREFERRED_LIFETIME
+   LEASE6_PREFIX_LEN
+   LEASE6_TYPE
+   PKT6_IA_IAID
+   PKT6_IA_IA_TYPE
+   PKT6_IA_IA_T1
+   PKT6_IA_IA_T2
+
+``lease6_expire``
+
+::
+
+   LEASE6_ADDRESS
+   LEASE6_CLTT
+   LEASE6_HOSTNAME
+   LEASE6_HWADDR
+   LEASE6_HWADDR_TYPE
+   LEASE6_STATE
+   LEASE6_SUBNET_ID
+   LEASE6_VALID_LIFETIME
+   LEASE6_DUID
+   LEASE6_IAID
+   LEASE6_PREFERRED_LIFETIME
+   LEASE6_PREFIX_LEN
+   LEASE6_TYPE
+   REMOVE_LEASE
+
+``lease6_recover``
+
+::
+
+   LEASE6_ADDRESS
+   LEASE6_CLTT
+   LEASE6_HOSTNAME
+   LEASE6_HWADDR
+   LEASE6_HWADDR_TYPE
+   LEASE6_STATE
+   LEASE6_SUBNET_ID
+   LEASE6_VALID_LIFETIME
+   LEASE6_DUID
+   LEASE6_IAID
+   LEASE6_PREFERRED_LIFETIME
+   LEASE6_PREFIX_LEN
+   LEASE6_TYPE
+
+``leases6_committed``
+
+::
+
+   QUERY6_TYPE
+   QUERY6_TXID
+   QUERY6_LOCAL_ADDR
+   QUERY6_LOCAL_PORT
+   QUERY6_REMOTE_ADDR
+   QUERY6_REMOTE_PORT
+   QUERY6_IFACE_INDEX
+   QUERY6_IFACE_NAME
+   QUERY6_REMOTE_HWADDR
+   QUERY6_REMOTE_HWADDR_TYPE
+   QUERY6_PROTO
+   QUERY6_CLIENT_ID
+   LEASES6_SIZE
+   DELETED_LEASES6_SIZE
+
+If ``LEASES6_SIZE`` or ``DELETED_LEASES6_SIZE`` is non-zero, then each lease
+has its own unique identifier, as shown below. The first index starts
+at 0.
+
+::
+
+   LEASES6_AT0_ADDRESS
+   LEASES6_AT0_CLTT
+   LEASES6_AT0_HOSTNAME
+   LEASES6_AT0_HWADDR
+   LEASES6_AT0_HWADDR_TYPE
+   LEASES6_AT0_STATE
+   LEASES6_AT0_SUBNET_ID
+   LEASES6_AT0_VALID_LIFETIME
+   LEASES6_AT0_DUID
+   LEASES6_AT0_IAID
+   LEASES6_AT0_PREFERRED_LIFETIME
+   LEASES6_AT0_PREFIX_LEN
+   LEASES6_AT0_TYPE
+   DELETED_LEASES6_AT0_ADDRESS
+   DELETED_LEASES6_AT0_CLTT
+   DELETED_LEASES6_AT0_HOSTNAME
+   DELETED_LEASES6_AT0_HWADDR
+   DELETED_LEASES6_AT0_HWADDR_TYPE
+   DELETED_LEASES6_AT0_STATE
+   DELETED_LEASES6_AT0_SUBNET_ID
+   DELETED_LEASES6_AT0_VALID_LIFETIME
+   DELETED_LEASES6_AT0_DUID
+   DELETED_LEASES6_AT0_IAID
+   DELETED_LEASES6_AT0_PREFERRED_LIFETIME
+   DELETED_LEASES6_AT0_PREFIX_LEN
+   DELETED_LEASES6_AT0_TYPE
+
+``lease6_release``
+
+::
+
+   QUERY6_TYPE
+   QUERY6_TXID
+   QUERY6_LOCAL_ADDR
+   QUERY6_LOCAL_PORT
+   QUERY6_REMOTE_ADDR
+   QUERY6_REMOTE_PORT
+   QUERY6_IFACE_INDEX
+   QUERY6_IFACE_NAME
+   QUERY6_REMOTE_HWADDR
+   QUERY6_REMOTE_HWADDR_TYPE
+   QUERY6_PROTO
+   QUERY6_CLIENT_ID
+   LEASE6_ADDRESS
+   LEASE6_CLTT
+   LEASE6_HOSTNAME
+   LEASE6_HWADDR
+   LEASE6_HWADDR_TYPE
+   LEASE6_STATE
+   LEASE6_SUBNET_ID
+   LEASE6_VALID_LIFETIME
+   LEASE6_DUID
+   LEASE6_IAID
+   LEASE6_PREFERRED_LIFETIME
+   LEASE6_PREFIX_LEN
+   LEASE6_TYPE
+
+``lease6_decline``
+
+::
+
+   QUERY6_TYPE
+   QUERY6_TXID
+   QUERY6_LOCAL_ADDR
+   QUERY6_LOCAL_PORT
+   QUERY6_REMOTE_ADDR
+   QUERY6_REMOTE_PORT
+   QUERY6_IFACE_INDEX
+   QUERY6_IFACE_NAME
+   QUERY6_REMOTE_HWADDR
+   QUERY6_REMOTE_HWADDR_TYPE
+   QUERY6_PROTO
+   QUERY6_CLIENT_ID
+   LEASE6_ADDRESS
+   LEASE6_CLTT
+   LEASE6_HOSTNAME
+   LEASE6_HWADDR
+   LEASE6_HWADDR_TYPE
+   LEASE6_STATE
+   LEASE6_SUBNET_ID
+   LEASE6_VALID_LIFETIME
+   LEASE6_DUID
+   LEASE6_IAID
+   LEASE6_PREFERRED_LIFETIME
+   LEASE6_PREFIX_LEN
+   LEASE6_TYPE
diff --git a/doc/sphinx/arm/hooks-stat-cmds.rst b/doc/sphinx/arm/hooks-stat-cmds.rst
new file mode 100644
index 0000000..7cbe654
--- /dev/null
+++ b/doc/sphinx/arm/hooks-stat-cmds.rst
@@ -0,0 +1,243 @@
+.. _hooks-stat-cmds:
+
+``stat_cmds``: Statistics Commands for Supplemental Lease Statistics
+====================================================================
+
+This library provides additional commands for retrieving lease
+statistics from Kea DHCP servers. These commands were added to address
+an issue with obtaining accurate lease statistics in deployments running
+multiple Kea servers that use a shared lease backend. The in-memory
+statistics kept by individual servers only track lease changes made by
+that server; thus, in a deployment with multiple servers (e.g. two
+``kea-dhcp6`` servers using the same PostgreSQL database for lease storage),
+these statistics are incomplete. The MySQL and PostgreSQL backends in
+Kea track lease allocation changes as they occur via database triggers.
+Additionally, all the lease backends were extended to support
+retrieving lease statistics for a single subnet, a range
+of subnets, or all subnets. Finally, this library provides commands
+for retrieving these statistics.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or
+   ``kea-dhcp6`` process.
+
+The commands provided by this library are:
+
+-  ``stat-lease4-get`` - fetches DHCPv4 lease statistics.
+
+-  ``stat-lease6-get`` - fetches DHCPv6 lease statistics.
+
+The Statistics Commands library is part of the open source code and is
+available to every Kea user.
+
+All commands use JSON syntax and can be issued directly to the servers
+via either the control channel (see :ref:`ctrl-channel`) or the
+Control Agent (see :ref:`kea-ctrl-agent`).
+
+This library may be loaded by both the ``kea-dhcp4`` and ``kea-dhcp6`` servers. It
+is loaded in the same way as other libraries and currently has no
+parameters:
+
+::
+
+   "Dhcp6": {
+       "hooks-libraries": [
+           {
+               "library": "/path/libdhcp_stat_cmds.so"
+           }
+           ...
+       ]
+   }
+
+In a deployment with multiple Kea DHCP servers sharing a common lease
+storage, this hook library may be loaded by any or all of the servers. However,
+a server's response to a
+``stat-lease[46]-get`` command will only contain data for subnets known to
+that server. In other words, if a subnet does not appear in a server's
+configuration, Kea will not retrieve statistics for it.
+
+.. _command-stat-lease4-get:
+
+.. _command-stat-lease6-get:
+
+The ``stat-lease4-get``, ``stat-lease6-get`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``stat-lease4-get`` and ``stat-lease6-get`` commands fetch lease
+statistics for a range of known subnets. The range of subnets is
+determined through the use of optional command input parameters:
+
+-  ``subnet-id`` - the ID of the subnet for which lease statistics
+   should be fetched; used to get statistics for a single subnet. If
+   the subnet does not exist, the command result code is 3 (i.e.
+   ``CONTROL_RESULT_EMPTY``).
+
+-  ``subnet-range`` - a pair of subnet IDs which describe an inclusive
+   range of subnets for which statistics should be retrieved. The range
+   may include one or more IDs that correspond to no subnet; in this
+   case, the command only outputs lease statistics for those that
+   exist. However, if the range does not include any known subnets, the
+   command result code is 3 (i.e. ``CONTROL_RESULT_EMPTY``).
+
+   -  ``first-subnet-id`` - the ID of the first subnet in the range.
+
+   -  ``last-subnet-id`` - the ID of the last subnet in the range.
+
+The use of ``subnet-id`` and ``subnet-range`` are mutually exclusive. If no
+parameters are given, the result will contain data for all known
+subnets. Note that in configurations with many subnets, this
+can result in a large response.
+
+The following command fetches lease statistics for all known subnets
+from a ``kea-dhcp4`` server:
+
+::
+
+   {
+     "command": "stat-lease4-get"
+   }
+
+The following command fetches lease statistics for subnet ID 10 from a
+``kea-dhcp6`` server:
+
+::
+
+   {
+     "command": "stat-lease6-get",
+     "arguments": {
+       "subnet-id" : 10
+     }
+   }
+
+The following command fetches lease statistics for all subnets with IDs
+in the range 10 through 50 from a ``kea-dhcp4`` server:
+
+::
+
+   {
+     "command": "stat-lease4-get",
+     "arguments": {
+       "subnet-range" {
+         "first-subnet-id": 10,
+         "last-subnet-id": 50,
+       }
+     }
+   }
+
+The response to either command will contain three elements:
+
+-  ``result`` - a numeric value indicating the outcome of the command
+   where:
+
+   -  ``0`` - the command was successful;
+
+   -  ``1`` - an error occurred, and an explanation is the "text"
+      element; or
+
+   -  ``2`` - the fetch found no matching data.
+
+-  ``text`` - an explanation of the command outcome. When the command
+   succeeds, it contains the command name along with the number of
+   rows returned.
+
+-  ``arguments`` - a map containing the data returned by the command as
+   the element "result-set", which is patterned after SQL statement
+   responses:
+
+   -  ``columns`` - a list of text column labels. The columns returned
+      for DHCPv4 are:
+
+      -  ``subnet-id`` - the ID of the subnet.
+
+      -  ``total-addresses`` - the total number of addresses available for
+         DHCPv4 management in the subnet. In other words, this is the
+         sum of all addresses in all the configured pools in the subnet.
+
+      - ``cumulative-assigned-addresses`` - the cumulative number of addresses
+        in the subnet that have been assigned to a client by the server
+        since it started.
+
+      -  ``assigned-addresses`` - the number of addresses in the subnet that
+         are currently assigned to a client.
+
+      -  ``declined-addresses`` - the number of addresses in the subnet that
+         are currently declined and are thus unavailable for assignment.
+
+   -  The columns returned for DHCPv6 are:
+
+      -  ``subnet-id`` - the ID of the subnet.
+
+      -  ``total-nas`` - the number of NA addresses available for DHCPv6
+         management in the subnet. In other words, this is the sum of
+         all the NA addresses in all the configured NA pools in the
+         subnet.
+
+      - ``cumulative-assigned-nas`` - the cumulative number of NA addresses
+        in the subnet that have been assigned to a client by the server
+        since it started.
+
+      -  ``assigned-nas`` - the number of NA addresses in the subnet that
+         are currently assigned to a client.
+
+      -  ``declined-nas`` - the number of NA addresses that are currently
+         declined and are thus unavailable for assignment.
+
+      -  ``total-pds`` - the total number of PD prefixes available of DHCPv6
+         management in the subnet. In other words, this is the sum of
+         all prefixes in all the configured prefix pools in the subnet.
+
+      - ``cumulative-assigned-pds`` - the cumulative number of PD prefixes
+        in the subnet that have been assigned to a client by the server
+        since it started.
+
+      -  ``assigned-pds`` - the number of PD prefixes in the subnet that are
+         currently assigned to a client.
+
+   -  ``rows`` - a list of rows, one per subnet ID. Each row contains a
+      data value corresponding to and in the same order as each column
+      listed in "columns" for a given subnet.
+
+   -  ``timestamp`` - the textual date and time the data were fetched,
+      expressed as GMT.
+
+The response to a DHCPv4 command might look as follows:
+
+::
+
+     {
+       "result": 0,
+       "text": "stat-lease4-get: 2 rows found",
+       "arguments": {
+         "result-set": {
+           "columns": [ "subnet-id", "total-addresses", "cumulative-assigned-addresses", "assigned-addresses", "declined-addresses" ]
+           "rows": [
+             [ 10, 256, 300, 111, 0 ],
+             [ 20, 4098, 2034, 2034, 4 ]
+           ],
+         "timestamp": "2018-05-04 15:03:37.000000"
+         }
+       }
+     }
+
+The response to a DHCPv6 command might look as follows, assuming subnet 10 has no
+prefix pools, subnet 20 has no NA pools, and subnet 30 has both NA and
+PD pools:
+
+::
+
+     {
+       "result": 0,
+       "text": "stat-lease6-get: 2 rows found",
+       "arguments": {
+         "result-set": {
+           "columns": [ "subnet-id", "total-nas", "cumulative-assigned-nas", "assigned-nas", "declined-nas", "total-pds", "cumulative-assigned-pds", "assigned-pds" ]
+           "rows": [
+             [ 10, 4096, 5000, 2400, 3, 0, 0, 0],
+             [ 20, 0, 0, 0, 0, 1048, 300, 233 ]
+             [ 30, 256, 60, 60, 0, 1048, 15, 15 ]
+           ],
+         "timestamp": "2018-05-04 15:03:37.000000"
+         }
+       }
+     }
diff --git a/doc/sphinx/arm/hooks-subnet-cmds.rst b/doc/sphinx/arm/hooks-subnet-cmds.rst
new file mode 100644
index 0000000..4601069
--- /dev/null
+++ b/doc/sphinx/arm/hooks-subnet-cmds.rst
@@ -0,0 +1,1272 @@
+.. _hooks-subnet-cmds:
+
+``subnet_cmds``: Subnet Commands to Manage Subnets and Shared Networks
+======================================================================
+
+This library offers commands used to query and manipulate subnet and shared network
+configurations in Kea. These can be very useful in deployments
+with a large number of subnets being managed by the DHCP servers,
+when those subnets are frequently updated. The commands offer a lightweight
+approach for manipulating subnets without needing to fully reconfigure
+the server, and without affecting existing servers' configurations. An
+ability to manage shared networks (listing, retrieving details, adding
+new ones, removing existing ones, and adding subnets to and removing them from
+shared networks) is also provided.
+
+This library is only available to ISC customers with a paid support
+contract.
+
+.. note::
+
+   This library can only be loaded by the ``kea-dhcp4`` or ``kea-dhcp6``
+   process.
+
+The following commands are currently supported:
+
+-  ``subnet4-list``/``subnet6-list`` - lists all configured subnets.
+
+-  ``subnet4-get``/``subnet6-get`` - retrieves detailed information about a
+   specified subnet.
+
+-  ``subnet4-add``/``subnet6-add`` - adds a new subnet into the server's
+   configuration.
+
+-  ``subnet4-update``/``subnet6-update`` - updates (replaces) a single subnet in
+   the server's configuration.
+
+-  ``subnet4-del``/``subnet6-del`` - removes a subnet from the server's
+   configuration.
+
+-  ``subnet4-delta-add``/``subnet6-delta-add`` - updates (replaces) parts of a
+   single subnet in the server's configuration.
+
+-  ``subnet4-delta-del``/``subnet6-delta-del`` - removes parts of a single subnet in
+   the server's configuration.
+
+-  ``network4-list``/``network6-list`` - lists all configured shared networks.
+
+-  ``network4-get``/``network6-get`` - retrieves detailed information about a
+   specified shared network.
+
+-  ``network4-add``/``network6-add`` - adds a new shared network to the
+   server's configuration.
+
+-  ``network4-del``/``network6-del`` - removes a shared network from the
+   server's configuration.
+
+-  ``network4-subnet-add``/``network6-subnet-add`` - adds an existing subnet to
+   an existing shared network.
+
+-  ``network4-subnet-del``/``network6-subnet-del`` - removes a subnet from
+   an existing shared network and demotes it to a plain subnet.
+
+.. _command-subnet4-list:
+
+The ``subnet4-list`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to list all currently configured subnets. Each
+subnet is returned with a subnet identifier and
+subnet prefix. To retrieve
+detailed information about the subnet, use the ``subnet4-get`` command.
+
+This command has a simple structure:
+
+::
+
+   {
+       "command": "subnet4-list"
+   }
+
+The list of subnets is returned in the following format:
+
+::
+
+   {
+       "result": 0,
+       "text": "2 IPv4 subnets found",
+       "arguments": {
+       "subnets": [
+           {
+               "id": 10,
+               "subnet": "10.0.0.0/8"
+           },
+           {
+               "id": 100,
+               "subnet": "192.0.2.0/24"
+           }
+       ]
+   }
+
+If no IPv4 subnets are found, an error code is returned along with the
+error description.
+
+.. _command-subnet6-list:
+
+The ``subnet6-list`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to list all currently configured subnets. Each
+subnet is returned with a subnet identifier and
+subnet prefix. To retrieve
+detailed information about the subnet, use the ``subnet6-get`` command.
+
+This command has a simple structure:
+
+::
+
+   {
+       "command": "subnet6-list"
+   }
+
+The list of subnets is returned in the following format:
+
+::
+
+   {
+       "result": 0,
+       "text": "2 IPv6 subnets found",
+       "arguments": {
+       "subnets": [
+           {
+               "id": 11,
+               "subnet": "2001:db8:1::/64"
+           },
+           {
+               "id": 233,
+               "subnet": "3000::/16"
+           }
+       ]
+   }
+
+If no IPv6 subnets are found, an error code is returned along with the
+error description.
+
+.. _command-subnet4-get:
+
+The ``subnet4-get`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to retrieve detailed information about the
+specified subnet. This command usually follows ``subnet4-list``,
+which is used to discover available subnets with their respective subnet
+identifiers and prefixes. Any of those parameters can then be used in
+``subnet4-get`` to fetch subnet information:
+
+::
+
+   {
+       "command": "subnet4-get",
+       "arguments": {
+           "id": 10
+       }
+   }
+
+or
+
+::
+
+   {
+       "command": "subnet4-get",
+       "arguments": {
+           "subnet": "10.0.0.0/8"
+       }
+   }
+
+If the subnet exists, the response will be similar to this:
+
+::
+
+   {
+       "result": 0,
+       "text": "Info about IPv4 subnet 10.0.0.0/8 (id 10) returned",
+       "arguments": {
+           "subnets": [
+               {
+                   "subnet": "10.0.0.0/8",
+                   "id": 1,
+                   "option-data": [
+                       ....
+                   ]
+                   ...
+               }
+           ]
+       }
+   }
+
+.. _command-subnet6-get:
+
+The ``subnet6-get`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to retrieve detailed information about the
+specified subnet. This command usually follows ``subnet6-list``,
+which is used to discover available subnets with their respective subnet
+identifiers and prefixes. Any of those parameters can be then used in
+``subnet6-get`` to fetch subnet information:
+
+::
+
+   {
+       "command": "subnet6-get",
+       "arguments": {
+           "id": 11
+       }
+   }
+
+or
+
+::
+
+   {
+       "command": "subnet6-get",
+       "arguments": {
+           "subnet": "2001:db8:1::/64"
+       }
+   }
+
+If the subnet exists, the response will be similar to this:
+
+::
+
+   {
+       "result": 0,
+       "text": "Info about IPv6 subnet 2001:db8:1::/64 (id 11) returned",
+       "arguments": {
+           "subnets": [
+               {
+                   "subnet": "2001:db8:1::/64",
+                   "id": 1,
+                   "option-data": [
+                       ...
+                   ]
+                   ....
+               }
+           ]
+       }
+   }
+
+.. _command-subnet4-add:
+
+The ``subnet4-add`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to create and add a new subnet to the existing server
+configuration. This operation has no impact on other subnets. The subnet
+identifier must be specified and must be unique among all subnets. If
+the identifier or a subnet prefix is not unique, an error is reported and
+the subnet is not added.
+
+The subnet information within this command has the same structure as the
+subnet information in the server configuration file, with the exception
+that static host reservations cannot be specified within
+``subnet4-add``. The commands described in :ref:`hooks-host-cmds` should be used to
+add, remove, and modify static reservations.
+
+::
+
+   {
+       "command": "subnet4-add",
+       "arguments": {
+           "subnet4": [ {
+               "id": 123,
+               "subnet": "10.20.30.0/24",
+               ...
+           } ]
+       }
+   }
+
+The response to this command has the following structure:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv4 subnet added",
+       "arguments": {
+           "subnet4": [
+               {
+                   "id": 123,
+                   "subnet": "10.20.30.0/24"
+               }
+           ]
+       }
+   }
+
+.. _command-subnet6-add:
+
+The ``subnet6-add`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to create and add a new subnet to the existing server
+configuration. This operation has no impact on other subnets. The subnet
+identifier must be specified and must be unique among all subnets. If
+the identifier or a subnet prefix is not unique, an error is reported and
+the subnet is not added.
+
+The subnet information within this command has the same structure as the
+subnet information in the server configuration file, with the exception
+that static host reservations cannot be specified within
+``subnet6-add``. The commands described in :ref:`hooks-host-cmds` should be used
+to add, remove, and modify static reservations.
+
+::
+
+   {
+       "command": "subnet6-add",
+       "arguments": {
+           "subnet6": [ {
+               "id": 234,
+               "subnet": "2001:db8:1::/64",
+               ...
+           } ]
+       }
+   }
+
+The response to this command has the following structure:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv6 subnet added",
+       "arguments": {
+           "subnet6": [
+               {
+                   "id": 234,
+                   "subnet": "2001:db8:1::/64"
+               }
+           ]
+       }
+   }
+
+It is recommended, but not mandatory, to specify the subnet ID. If not
+specified, Kea will try to assign the next ``subnet-id`` value. This
+automatic ID value generator is simple; it returns the previous
+automatically assigned value, increased by 1. This works well, unless
+a subnet is manually created with a larger value than one previously used. For
+example, if ``subnet4-add`` is called five times, each without an ID, Kea will
+assign IDs 1, 2, 3, 4, and 5 and it will work just fine. However, if
+``subnet4-add`` is called five times, with the first subnet having the
+``subnet-id`` of value 3 and the remaining ones having no ``subnet-id``, the operation will
+fail. The first command (with the explicit value) will use ``subnet-id`` 3; the
+second command will create a subnet with and ID of 1; the third will use a
+value of 2; and finally the fourth will have its ``subnet-id`` value
+auto-generated as 3. However, since there is already a subnet with that
+ID, the process will fail.
+
+The general recommendation is either never to use explicit values, so
+that auto-generated values will always work; or always use explicit
+values, so that auto-generation is never used. The two
+approaches can be mixed only if the administrator understands how internal
+automatic ``subnet-id`` generation works in Kea.
+
+.. note::
+
+   Subnet IDs must be greater than zero and less than 4294967295.
+
+.. _command-subnet4-update:
+
+The ``subnet4-update`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to update (overwrite) a single subnet in the existing
+server configuration. This operation has no impact on other subnets. The
+subnet identifier is used to identify the subnet to replace; it must be
+specified and must be unique among all subnets. The subnet prefix should
+not be updated.
+
+The subnet information within this command has the same structure as the
+subnet information in the server configuration file, with the exception
+that static host reservations cannot be specified within
+``subnet4-update``. The commands described in :ref:`hooks-host-cmds` should be
+used to update, remove, and modify static reservations.
+
+::
+
+   {
+       "command": "subnet4-update",
+       "arguments": {
+           "subnet4": [ {
+               "id": 123,
+               "subnet": "10.20.30.0/24",
+               ...
+           } ]
+       }
+   }
+
+The response to this command has the following structure:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv4 subnet updated",
+       "arguments": {
+           "subnet4": [
+               {
+                   "id": 123,
+                   "subnet": "10.20.30.0/24"
+               }
+           ]
+       }
+   }
+
+.. _command-subnet6-update:
+
+The ``subnet6-update`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to update (overwrite) a single subnet in the existing
+server configuration. This operation has no impact on other subnets. The
+subnet identifier is used to identify the subnet to replace; it must be
+specified and must be unique among all subnets. The subnet prefix should
+not be updated.
+
+The subnet information within this command has the same structure as the
+subnet information in the server configuration file, with the exception
+that static host reservations cannot be specified within
+``subnet6-update``. The commands described in :ref:`hooks-host-cmds` should be
+used to update, remove, and modify static reservations.
+
+::
+
+   {
+       "command": "subnet6-update",
+       "arguments": {
+           "subnet6": [ {
+               "id": 234,
+               "subnet": "2001:db8:1::/64",
+               ...
+           } ]
+       }
+   }
+
+The response to this command has the following structure:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv6 subnet updated",
+       "arguments": {
+           "subnet6": [
+               {
+                   "id": 234,
+                   "subnet": "2001:db8:1::/64"
+               }
+           ]
+       }
+   }
+
+.. _command-subnet4-del:
+
+The ``subnet4-del`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to remove a subnet from the server's configuration.
+This command has no effect on other configured subnets, but removing a
+subnet does have certain implications.
+
+In most cases the server has assigned some leases to the clients
+belonging to the subnet. The server may also be configured with static
+host reservations which are associated with this subnet. The current
+implementation of the ``subnet4-del`` command removes neither the leases nor
+the host reservations associated with a subnet. This is the safest approach
+because the server does not lose track of leases assigned to the clients
+from this subnet. However, removal of the subnet may still cause
+configuration errors and conflicts. For example: after removal of the
+subnet, the server administrator may update a new subnet with the ID
+used previously for the removed subnet. This means that the existing
+leases and static reservations will be in conflict with this new subnet.
+Thus, we recommend that this command be used with extreme caution.
+
+This command can also be used to completely delete an IPv4 subnet that
+is part of a shared network. To simply remove the subnet
+from a shared network and keep the subnet configuration, use the
+``network4-subnet-del`` command instead.
+
+The command has the following structure:
+
+::
+
+   {
+       "command": "subnet4-del",
+       "arguments": {
+           "id": 123
+       }
+   }
+
+A successful response may look like this:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv4 subnet 192.0.2.0/24 (id 123) deleted",
+       "arguments": {
+           "subnets": [
+               {
+                   "id": 123,
+                   "subnet": "192.0.2.0/24"
+               }
+           ]
+       }
+   }
+
+.. _command-subnet6-del:
+
+The ``subnet6-del`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to remove a subnet from the server's configuration.
+This command has no effect on other configured subnets, but removing a
+subnet does have certain implications.
+
+In most cases the server has assigned some leases to the clients
+belonging to the subnet. The server may also be configured with static
+host reservations which are associated with this subnet. The current
+implementation of the ``subnet6-del`` command removes neither the leases nor
+the host reservations associated with a subnet. This is the safest approach
+because the server does not lose track of leases assigned to the clients
+from this subnet. However, removal of the subnet may still cause
+configuration errors and conflicts. For example: after removal of the
+subnet, the server administrator may add a new subnet with the ID used
+previously for the removed subnet. This means that the existing leases
+and static reservations will be in conflict with this new subnet. Thus,
+we recommend that this command be used with extreme caution.
+
+This command can also be used to completely delete an IPv6 subnet that
+is part of a shared network. To simply remove the subnet
+from a shared network and keep the subnet configuration, use the
+``network6-subnet-del`` command instead.
+
+The command has the following structure:
+
+::
+
+   {
+       "command": "subnet6-del",
+       "arguments": {
+           "id": 234
+       }
+   }
+
+A successful response may look like this:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv6 subnet 2001:db8:1::/64 (id 234) deleted",
+       "subnets": [
+           {
+               "id": 234,
+               "subnet": "2001:db8:1::/64"
+           }
+       ]
+   }
+
+.. _command-subnet4-delta-add:
+
+The ``subnet4-delta-add`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to update a subnet by adding or overwriting its parts in
+the existing server configuration. This operation has no impact on other
+subnets. The subnet identifier is used to identify the subnet to update; it must
+be specified and must be unique among all subnets. The subnet prefix should not
+be updated.
+
+The subnet information within this command has the same structure as the
+subnet information in the server configuration file, with the exception
+that static host reservations cannot be specified within
+``subnet4-delta-add``. The commands described in :ref:`hooks-host-cmds` should
+be used to update, remove, and modify static reservations.
+
+::
+
+   {
+       "command": "subnet4-delta-add",
+       "arguments": {
+           "subnet4": [ {
+               "valid-lifetime": 120,
+               "id": 123,
+               "subnet": "10.20.30.0/24",
+               "option-data": [
+                   {
+                       "always-send": false,
+                       "code": 3,
+                       "csv-format": true,
+                       "data": "192.0.3.1",
+                       "name": "routers",
+                       "space": "dhcp4"
+                   }
+               ],
+               "pools": [
+                   {
+                       "pool": "10.20.30.1-10.20.30.10",
+                       "option-data": [
+                           {
+                               "always-send": false,
+                               "code": 4,
+                               "csv-format": true,
+                               "data": "192.0.4.1",
+                               "name": "time-servers",
+                               "space": "dhcp4"
+                           }
+                       ]
+                   }
+               ]
+           } ]
+       }
+   }
+
+The response to this command has the following structure:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv4 subnet updated",
+       "arguments": {
+           "subnet4": [
+               {
+                   "id": 123,
+                   "subnet": "10.20.30.0/24"
+               }
+           ]
+       }
+   }
+
+The command updates subnet "10.20.30.0/24" with id 123 by changing the valid
+lifetime, adding or changing the subnet level option 3 ("routers"), by adding
+or changing the pool "10.20.30.1-10.20.30.10" and by adding or changing the pool
+level option 4 ("time-servers").
+
+.. _command-subnet6-delta-add:
+
+The ``subnet6-delta-add`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to update a subnet by adding or overwriting its parts in
+the existing server configuration. This operation has no impact on other
+subnets. The subnet identifier is used to identify the subnet to update; it must
+be specified and must be unique among all subnets. The subnet prefix should not
+be updated.
+
+The subnet information within this command has the same structure as the
+subnet information in the server configuration file, with the exception
+that static host reservations cannot be specified within
+``subnet6-delta-add``. The commands described in :ref:`hooks-host-cmds` should
+be used to update, remove, and modify static reservations.
+
+::
+
+   {
+       "command": "subnet6-delta-add",
+       "arguments": {
+           "subnet6": [ {
+               "valid-lifetime": 120,
+               "id": 243,
+               "subnet": "2001:db8:1::/64",
+               "option-data": [
+                   {
+                       "always-send": false,
+                       "code": 23,
+                       "csv-format": true,
+                       "data": "3000::3:1",
+                       "name": "dns-servers",
+                       "space": "dhcp6"
+                   }
+               ],
+               "pd-pools": [
+                   {
+                       "prefix": "2001:db8:2::",
+                       "prefix-len": 48,
+                       "delegated-len": 64,
+                       "option-data": [
+                           {
+                               "always-send": false,
+                               "code": 22,
+                               "csv-format": true,
+                               "data": "3000::4:1",
+                               "name": "sip-server-addr",
+                               "space": "dhcp6"
+                           }
+                       ]
+                   }
+               ],
+               "pools": [
+                   {
+                       "pool": "2001:db8:1::1-2001:db8:1::10",
+                       "option-data": [
+                           {
+                               "always-send": false,
+                               "code": 31,
+                               "csv-format": true,
+                               "data": "3000::5:1",
+                               "name": "sntp-servers",
+                               "space": "dhcp6"
+                           }
+                       ]
+                   }
+               ]
+           } ]
+       }
+   }
+
+The response to this command has the following structure:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv6 subnet updated",
+       "arguments": {
+           "subnet6": [
+               {
+                   "id": 234,
+                   "subnet": "2001:db8:1::/64"
+               }
+           ]
+       }
+   }
+
+The command updates subnet "2001:db8:1::/64" with id 243 by changing the valid
+lifetime, adding or changing the subnet level option 23 ("dns-servers"), by
+adding or changing the pool "2001:db8:1::1-2001:db8:1::10", by adding or
+changing the pool level option 31 ("sntp-servers"), by adding or changing the
+pd-pool "2001:db8:2::" with prefix-len 48 and by adding or changing the pd-pool
+level option 22 ("sip-server-addr").
+
+.. _command-subnet4-delta-del:
+
+The ``subnet4-delta-del`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to update a subnet by removing its parts in the existing
+server configuration. This operation has no impact on other subnets.
+The subnet identifier is used to identify the subnet to update; it must be
+specified and must be unique among all subnets. The subnet prefix should not be
+updated.
+
+The subnet information within this command has the same structure as the
+subnet information in the server configuration file, with the exception
+that static host reservations cannot be specified within
+``subnet4-delta-del``. The commands described in :ref:`hooks-host-cmds` should
+be used to update, remove, and modify static reservations.
+
+The command is flexible and can delete the part of the subnet by either
+specifying the entire object that needs to be deleted, or just the keys
+identifying the respective object. The address pools are identified by the
+'pool' parameter, the options are identified by the 'name' or 'code' and
+'space' parameters. The 'space' parameter can be omitted if the option belongs
+to the default 'dhcp4' space.
+
+::
+
+   {
+       "command": "subnet4-delta-del",
+       "arguments": {
+           "subnet4": [ {
+               "valid-lifetime": 0,
+               "id": 123,
+               "subnet": "10.20.30.0/24",
+               "option-data" [
+                   { "name": "routers" }
+               ]
+               "pools": [
+                   {
+                       "option-data": [
+                           { "code": 4 }
+                       ]
+                       "pool": "10.20.30.11-10.20.30.20"
+                   },
+                   {
+                       "pool": "10.20.30.21-10.20.30.30"
+                   }
+               ]
+           } ]
+       }
+   }
+
+The response to this command has the following structure:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv4 subnet updated",
+       "arguments": {
+           "subnet4": [
+               {
+                   "id": 123,
+                   "subnet": "10.20.30.0/24"
+               }
+           ]
+       }
+   }
+
+The command updates subnet "10.20.30.0/24" with id 123 by removing the valid
+lifetime, removing the subnet level option 3 ("routers"), by removing the pool
+"10.20.30.21-10.20.30.30" and by removing the pool level option 4
+("time-servers") in pool "10.20.30.11-10.20.30.20".
+The scalar values don't need to match what is configured, but still need to be
+present to maintain a valid json structure and to be a valid value to be able to
+be parsed.
+
+.. _command-subnet6-delta-del:
+
+The ``subnet6-delta-del`` Command
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This command is used to update a subnet by removing its parts in the existing
+server configuration. This operation has no impact on other subnets.
+The subnet identifier is used to identify the subnet to update; it must be
+specified and must be unique among all subnets. The subnet prefix should not be
+updated.
+
+The subnet information within this command has the same structure as the
+subnet information in the server configuration file, with the exception
+that static host reservations cannot be specified within
+``subnet6-delta-del``. The commands described in :ref:`hooks-host-cmds` should
+be used to update, remove, and modify static reservations.
+
+The command is flexible and can delete the part of the subnet by either
+specifying the entire object that needs to be deleted, or just the keys
+identifying the respective object. The address pools are identified by the
+'pool' parameter, the prefix pools are identified by the "prefix", "prefix-len"
+and "delegated-len" parameters, the options are identified by the 'name' or
+'code' and 'space' parameters. The 'space' parameter can be omitted if the
+option belongs to the default 'dhcp6' space.
+
+::
+
+   {
+       "command": "subnet6-delta-del",
+       "arguments": {
+           "subnet6": [ {
+               "valid-lifetime": 0,
+               "id": 234,
+               "subnet": "2001:db8:1::/64",
+               "option-data" [
+                   { "name": "dns-servers" }
+               ]
+               "pd-pools": [
+                   {
+                       "prefix": "2001:db8:3::",
+                       "prefix-len": 48,
+                       "delegated-len": 64,
+                       "option-data": [
+                           { "code": 22 }
+                       ]
+                   },
+                   {
+                       "prefix": "2001:db8:4::",
+                       "prefix-len": 48,
+                       "delegated-len": 64,
+                   }
+               ],
+               "pools": [
+                   {
+                       "option-data": [
+                           { "code": 31 }
+                       ]
+                       "pool": "2001:db8:1::11-2001:db8:1::20"
+                   },
+                   {
+                       "pool": "2001:db8:1::21-2001:db8:1::30"
+                   }
+               ]
+           } ]
+       }
+   }
+
+The response to this command has the following structure:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv6 subnet updated",
+       "arguments": {
+           "subnet6": [
+               {
+                   "id": 234,
+                   "subnet": "2001:db8:1::/64"
+               }
+           ]
+       }
+   }
+
+The command updates subnet "2001:db8:1::/64" with id 243 by removing the valid
+lifetime, removing the subnet level option 23 ("dns-servers"), by removing the
+pool "2001:db8:1::21-2001:db8:1::30", by removing the pool level option 31
+("sntp-servers") in pool "2001:db8:1::11-2001:db8:1::20", by removing the
+pd-pool "2001:db8:4::" with prefix-len 48, by removing the pd-pool level option
+22 ("sip-server-addr") in pd-pool "2001:db8:3::" with prefix-len 48.
+The scalar values don't need to match what is configured, but still need to be
+present to maintain a valid json structure and to be a valid value to be able to
+be parsed.
+
+.. _command-network4-list:
+
+.. _command-network6-list:
+
+The ``network4-list``, ``network6-list`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to retrieve the full list of currently configured
+shared networks. The list contains only very basic information about
+each shared network. If more details are needed, please use
+``network4-get`` or ``network6-get`` to retrieve all information
+available. This command does not require any parameters and its
+invocation is very simple:
+
+::
+
+   {
+       "command": "network4-list"
+   }
+
+An example response for ``network4-list`` looks as follows:
+
+::
+
+   {
+       "arguments": {
+           "shared-networks": [
+               { "name": "floor1" },
+               { "name": "office" }
+           ]
+       },
+       "result": 0,
+       "text": "2 IPv4 network(s) found"
+   }
+
+The ``network6-list`` command uses exactly the same syntax for both the
+command and the response.
+
+.. _command-network4-get:
+
+.. _command-network6-get:
+
+The ``network4-get``, ``network6-get`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to retrieve detailed information about shared
+networks, including subnets that are currently part of a given network.
+Both commands take one mandatory parameter, ``name``, which specifies the
+name of the shared network. An example command to retrieve details about
+an IPv4 shared network with the name "floor13" looks as follows:
+
+::
+
+   {
+       "command": "network4-get",
+       "arguments": {
+           "name": "floor13"
+       }
+   }
+
+An example response could look as follows:
+
+::
+
+   {
+       "result": 0,
+       "text": "Info about IPv4 shared network 'floor13' returned",
+       "arguments": {
+           "shared-networks": [
+           {
+               "match-client-id": true,
+               "name": "floor13",
+               "option-data": [ ],
+               "rebind-timer": 90,
+               "relay": {
+                   "ip-address": "0.0.0.0"
+               },
+               "renew-timer": 60,
+               # "reservation-mode": "all",
+               # It is replaced by the "reservations-global"
+               # "reservations-in-subnet" and "reservations-out-of-pool"
+               # parameters.
+               # Specify if the server should lookup global reservations.
+               "reservations-global": false,
+               # Specify if the server should lookup in-subnet reservations.
+               "reservations-in-subnet": true,
+               # Specify if the server can assume that all reserved addresses
+               # are out-of-pool.
+               "reservations-out-of-pool": false,
+               "subnet4": [
+                   {
+                       "subnet": "192.0.2.0/24",
+                       "id": 5,
+                       # many other subnet-specific details here
+                   },
+                   {
+                       "id": 6,
+                       "subnet": "192.0.3.0/31",
+                       # many other subnet-specific details here
+                   }
+               ],
+               "valid-lifetime": 120
+           }
+           ]
+       }
+   }
+
+The actual response contains many additional fields that are
+omitted here for clarity. The response format is exactly the same as
+used in ``config-get``, just limited to returning the shared network's
+information.
+
+.. _command-network4-add:
+
+.. _command-network6-add:
+
+The ``network4-add``, ``network6-add`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to add a new shared network, which must
+have a unique name. This command requires one parameter,
+``shared-networks``, which is a list and should contain exactly one
+entry that defines the network. The only mandatory element for a network
+is its name. Although it does not make operational sense, it is possible
+to add an empty shared network that does not have any subnets in it.
+That is allowed for testing purposes, but having empty networks (or networks with
+only one subnet) is discouraged in production environments. For details
+regarding syntax, see :ref:`shared-network4` and
+:ref:`shared-network6`.
+
+.. note::
+
+   As opposed to parameter inheritance during the processing of a full new
+   configuration, this command does not fully handle parameter inheritance.
+   Any missing parameters will be filled with default values, rather
+   than inherited from the global scope.
+
+An example that showcases how to add a new IPv4 shared network looks as
+follows:
+
+::
+
+   {
+       "command": "network4-add",
+       "arguments": {
+           "shared-networks": [ {
+               "name": "floor13",
+               "subnet4": [
+               {
+                   "id": 100,
+                   "pools": [ { "pool": "192.0.2.2-192.0.2.99" } ],
+                   "subnet": "192.0.2.0/24",
+                   "option-data": [
+                       {
+                           "name": "routers",
+                           "data": "192.0.2.1"
+                       }
+                   ]
+               },
+               {
+                   "id": 101,
+                   "pools": [ { "pool": "192.0.3.2-192.0.3.99" } ],
+                   "subnet": "192.0.3.0/24",
+                   "option-data": [
+                       {
+                           "name": "routers",
+                           "data": "192.0.3.1"
+                       }
+                   ]
+               } ]
+           } ]
+       }
+   }
+
+Assuming there was no shared network with a name "floor13" and no subnets
+with IDs 100 and 101 previously configured, the command will be
+successful and will return the following response:
+
+::
+
+   {
+       "arguments": {
+           "shared-networks": [ { "name": "floor13" } ]
+       },
+       "result": 0,
+       "text": "A new IPv4 shared network 'floor13' added"
+   }
+
+The ``network6-add`` command uses the same syntax for both the query and the
+response. However, there are some parameters that are IPv4-only (e.g.
+``match-client-id``) and some that are IPv6-only (e.g. ``interface-id``). The same
+applies to subnets within the network.
+
+.. _command-network4-del:
+
+.. _command-network6-del:
+
+The ``network4-del``, ``network6-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to delete existing shared networks. Both
+commands take exactly one parameter, ``name``, that specifies the name of
+the network to be removed. An example invocation of the ``network4-del``
+command looks as follows:
+
+::
+
+   {
+       "command": "network4-del",
+       "arguments": {
+           "name": "floor13"
+       }
+   }
+
+Assuming there was such a network configured, the response will look
+similar to the following:
+
+::
+
+   {
+       "arguments": {
+           "shared-networks": [
+               {
+                   "name": "floor13"
+               }
+           ]
+       },
+       "result": 0,
+       "text": "IPv4 shared network 'floor13' deleted"
+   }
+
+The ``network6-del`` command uses exactly the same syntax for both the
+command and the response.
+
+If there are any subnets belonging to the shared network being deleted,
+they will be demoted to a plain subnet. There is an optional parameter
+called ``subnets-action`` that, if specified, takes one of two possible
+values: ``keep`` (which is the default) and ``delete``. It controls
+whether the subnets are demoted to plain subnets or removed. An example
+usage in the ``network6-del`` command that deletes the shared network and all
+subnets in it could look as follows:
+
+::
+
+   {
+       "command": "network4-del",
+       "arguments": {
+           "name": "floor13",
+           "subnets-action": "delete"
+       }
+   }
+
+Alternatively, to completely remove the subnets, it is possible to use the
+``subnet4-del`` or ``subnet6-del`` commands.
+
+.. _command-network4-subnet-add:
+
+.. _command-network6-subnet-add:
+
+The ``network4-subnet-add``, ``network6-subnet-add`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to add existing subnets to existing shared
+networks. There are several ways to add a new shared network. The system
+administrator can add the whole shared network at once, either by
+editing a configuration file or by calling the ``network4-add`` or
+``network6-add`` command with the desired subnets in it. This approach
+works well for completely new shared subnets. However, there may be
+cases when an existing subnet is running out of addresses and needs to
+be extended with additional address space; in other words, another subnet
+needs to be added on top of it. For this scenario, a system administrator
+can use ``network4-add`` or ``network6-add``, and then add an existing
+subnet to this newly created shared network using
+``network4-subnet-add`` or ``network6-subnet-add``.
+
+The ``network4-subnet-add`` and ``network6-subnet-add`` commands take
+two parameters: ``id``, which is an integer and specifies the ID of
+an existing subnet to be added to a shared network; and ``name``, which
+specifies the name of the shared network to which the subnet will be added. The
+subnet must not belong to any existing network; to
+reassign a subnet from one shared network to another, use the
+``network4-subnet-del`` or ``network6-subnet-del`` commands first.
+
+An example invocation of the ``network4-subnet-add`` command looks as
+follows:
+
+::
+
+   {
+       "command": "network4-subnet-add",
+       "arguments": {
+           "name": "floor13",
+           "id": 5
+       }
+   }
+
+Assuming there is a network named "floor13", and there is a subnet with
+``subnet-id`` 5 that is not a part of the existing network, the command will
+return a response similar to the following:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now part of shared network 'floor13'"
+   }
+
+The ``network6-subnet-add`` command uses exactly the same syntax for both the
+command and the response.
+
+.. note::
+
+   As opposed to parameter inheritance during the processing of a full new
+   configuration or when adding a new shared network with new subnets,
+   this command does not fully handle parameter inheritance.
+   Any missing parameters will be filled with default values, rather
+   than inherited from the global scope or from the shared network.
+
+.. _command-network4-subnet-del:
+
+.. _command-network6-subnet-del:
+
+The ``network4-subnet-del``, ``network6-subnet-del`` Commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These commands are used to remove a subnet that is part of an existing
+shared network and demote it to a plain, stand-alone subnet.
+To remove a subnet completely, use the ``subnet4-del`` or ``subnet6-del``
+commands instead. The ``network4-subnet-del`` and
+``network6-subnet-del`` commands take two parameters: ``id``, which is
+an integer and specifies the ID of an existing subnet to be removed from
+a shared network; and ``name``, which specifies the name of the shared
+network from which the subnet will be removed.
+
+An example invocation of the ``network4-subnet-del`` command looks as
+follows:
+
+::
+
+    {
+       "command": "network4-subnet-del",
+       "arguments": {
+           "name": "floor13",
+           "id": 5
+       }
+    }
+
+Assuming there was a subnet with ``subnet-id`` 5, that was part of a
+shared network named "floor13", the response would look similar to the
+following:
+
+::
+
+   {
+       "result": 0,
+       "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now removed from shared network 'floor13'"
+   }
+
+The ``network6-subnet-del`` command uses exactly the same syntax for both the
+command and the response.
diff --git a/doc/sphinx/arm/hooks-user-chk.rst b/doc/sphinx/arm/hooks-user-chk.rst
new file mode 100644
index 0000000..a7d2ba2
--- /dev/null
+++ b/doc/sphinx/arm/hooks-user-chk.rst
@@ -0,0 +1,79 @@
+.. _hooks-user-chk:
+
+``user_chk``: User Check
+========================
+
+This library serves several purposes:
+
+-  To assign "new" or "unregistered" users to a restricted subnet, while
+   "known" or "registered" users are assigned to unrestricted subnets.
+
+-  To allow DHCP response options or vendor option values to be
+   customized based on user identity.
+
+-  To provide a real-time record of user registration activity, which
+   can be sampled by an external consumer.
+
+-  To serve as a demonstration of various capabilities possible using
+   the hooks interface.
+
+This library is part of the Kea open source and is available to all users.
+
+Once loaded, the library allows the separation of incoming requests into known
+and unknown clients. For known clients, packets are processed
+as usual, although it is possible to override the sending of certain options
+on a per-host basis. Clients that are not on the known
+hosts list are treated as unknown and are assigned to the last
+subnet defined in the configuration file.
+
+As an example of a use case, this behavior may be implemented to put unknown users
+into a separate subnet that leads to a "walled garden," where they can
+only access a registration portal. Once they fill in necessary data,
+their details are added to the known clients file and they get a proper
+address after their device is restarted.
+
+.. note::
+
+   This library was developed several years before the host reservation
+   mechanism became available. Host reservation is much
+   more powerful and flexible, but the ability of ``user_chk``
+   to consult an external source of information about clients and alter
+   Kea's behavior remains useful and of educational value.
+
+The library reads the ``/tmp/user_chk_registry.txt`` file while being loaded
+and each time an incoming packet is processed. Each line of the file is expected to
+contain a self-contained JSON snippet which must have the
+following two entries:
+
+-  ``type`` - whose value is ``"HW_ADDR"`` for IPv4 users or ``"DUID"`` for IPv6
+   users.
+
+-  ``id`` - whose value is either the hardware address or the DUID from
+   the request formatted as a string of hex digits, with or without ":"
+   delimiters.
+
+and may have zero or more of the following entries:
+
+-  ``bootfile`` - whose value is the pathname of the desired file.
+
+-  ``tftp_server`` - whose value is the hostname or IP address of the
+   desired server.
+
+A sample user registry file is shown below:
+
+::
+
+   { "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:04", "bootfile" : "/tmp/v4bootfile" }
+   { "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:06", "tftp_server" : "tftp.v4.example.com" }
+   { "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:04", "bootfile" : "/tmp/v6bootfile" }
+   { "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:06", "tftp_server" : "tftp.v6.example.com" }
+
+As with any other hook libraries provided by ISC, internals of the
+``user_chk`` code are well-documented. Users may refer to the `user_chk
+library section of the Kea Developer's Guide
+<https://reports.kea.isc.org/dev_guide/d8/db2/libdhcp_user_chk.html>`__
+for information on how the code works internally. That, together with the
+`Hooks Framework section of the Kea Developer's Guide
+<https://reports.kea.isc.org/dev_guide/index.html#hooksFramework>`__ should give users
+some pointers on how to extend this library and perhaps even write one
+from scratch.
diff --git a/doc/sphinx/arm/hooks.rst b/doc/sphinx/arm/hooks.rst
new file mode 100644
index 0000000..45aae38
--- /dev/null
+++ b/doc/sphinx/arm/hooks.rst
@@ -0,0 +1,624 @@
+.. _hooks-libraries:
+
+**************
+Hook Libraries
+**************
+
+.. _hooks-libraries-introduction:
+
+Introduction
+============
+
+Kea is both flexible and customizable, via the use of "hooks." This feature
+lets Kea load one or more
+dynamically linked libraries (known as "hook libraries") and call functions
+in them at various points in its processing ("hook points").
+Those functions perform whatever custom processing is required.
+
+The hooks concept allows the core Kea code to remain reasonably small
+by moving features that only some, but not all, users find useful to
+external libraries. Those with no need for certain functions can simply choose not
+to load those libraries.
+
+Hook libraries are loaded by individual Kea processes, not by Kea as a
+whole. This means, among other things, that it is possible to associate one set
+of libraries with the DHCP4 server and a different set with the DHCP6
+server.
+
+It is also possible for a process to load
+multiple libraries. When processing reaches a hook point, Kea calls the
+hook library functions attached to it. If multiple libraries have
+attached a function to a given hook point, Kea calls all of them, in the
+order in which the libraries are specified in the configuration file.
+The order may be important; consult the documentation of the libraries
+for specifics.
+
+When a Kea process unloads a library, it expects the ``dlclose`` function
+to remove all library symbols, as well as the library code, from address space.
+Although most OSes implement the ``dlclose`` function, this behavior is not
+required by the POSIX standard and not all systems support it; for example, the musl
+library, used by default by Alpine Linux, implements the ``dlclose`` function
+as a no operation. On such systems a library actually remains loaded for the
+lifetime of the process, which means that it must be restarted
+to update libraries with newer versions; it is not sufficient to simply
+reconfigure or reload the Kea process.
+
+The next sections describe how to install and configure hook libraries. Users who are
+interested in writing their own hook library can find information
+in the `Hooks Developer's Guide section of the Kea Developer's
+Guide <https://reports.kea.isc.org/dev_guide/df/d46/hooksdgDevelopersGuide.html>`__.
+
+Note that some libraries are available under different licenses.
+
+Please also note that some libraries may require additional dependencies and/or
+compilation switches to be enabled, e.g. the RADIUS library
+requires the FreeRadius-client library to be present. If
+the ``--with-freeradius`` option is not specified, the RADIUS library is not
+built.
+
+Installing Hook Packages
+========================
+
+.. note::
+
+   For more details about installing the Kea Premium Hooks package, please read
+   `this Knowledgebase article <https://kb.isc.org/docs/aa-01587>`__.
+
+Some hook packages are included in the base Kea sources. There is no
+need to do anything special to compile or install them, as they are covered
+by the usual building and installation procedures. Please
+refer to :ref:`installation` for a general overview of the installation process.
+
+ISC provides several additional premium hooks in the form of packages, which
+follow a similar installation procedure but with several additional steps.
+For our users' convenience, the premium hooks installation procedure is described in this section.
+
+1. Download the package; detailed instructions are provided in the KB article
+above. The package will be a file with a name similar to
+``kea-premium-|release|.tar.gz``. (The name may vary depending on the package
+purchased.)
+
+2. Administrators who have the sources for the corresponding version of the
+open-source Kea package on their system from the initial Kea installation
+should skip this step. Otherwise, extract the Kea source from the original
+tarball that was downloaded. For example, with a download of Kea |release|,
+there should be a tarball called ``kea-|release|.tar.gz`` on the system.
+Unpack this tarball:
+
+.. parsed-literal::
+
+   $ tar -zxvf kea-|release|.tar.gz
+
+This will unpack the tarball into the ``kea-|release|`` subdirectory of
+the current working directory.
+
+3. Unpack the Kea premium hooks tarball into the same directory where the
+original Kea source is located. Once Kea |release| has been unpacked into a ``kea-|release|``
+subdirectory and the Kea premium tarball is in the current directory, the following
+steps will unpack the premium tarball into the correct location:
+
+.. parsed-literal::
+
+     $ cd kea-|release|
+     $ tar -xvf ../kea-premium-|release|.tar.gz
+
+Note that unpacking the Kea premium package puts the files into a
+directory named ``premium``. Regardless of the name of the package, the
+directory is always called ``premium``, although its contents will vary
+depending on the hooks package.
+
+4. Run the ``autoreconf`` tools. This step is necessary to update Kea's build
+script to include the additional directory. If this tool is not already
+available on the system, install the ``automake`` and ``autoconf``
+tools. To generate the configure script, please use:
+
+::
+
+     $ autoreconf -i
+
+5. Rerun ``configure``, using the same configuration options that were used when
+originally building Kea. It is possible to verify that ``configure`` has detected the
+premium package by inspecting the summary printed when it exits. The
+first section of the output should look something like this:
+
+.. parsed-literal::
+
+   Package:
+     Name:             kea
+     Version:          |release|
+     Extended version: |release| (tarball)
+     OS Family:        Linux
+     Using GNU sed:    yes
+     Premium package:  yes
+     Included Hooks:   forensic_log flex_id host_cmds
+
+The last line indicates which specific hooks were detected. Note that
+some hooks may require their own dedicated switches, e.g. the RADIUS hook
+requires extra switches for FreeRADIUS. Please consult later sections of
+this chapter for details.
+
+6. Rebuild Kea.
+
+::
+
+     $ make
+
+If the machine has multiple CPU cores, an interesting option to consider
+here is using the argument ``-j X``, where ``X`` is the number of available cores.
+
+7. Install Kea sources along with the hooks:
+
+::
+
+   $ sudo make install
+
+Note that as part of the installation procedure, the install script
+places additional hook libraries and associated files into the ``premium/`` directory.
+
+The installation location of the hook libraries depends on whether the
+``--prefix`` parameter was specified in the ``configure`` script. If not,
+the default location is ``/usr/local/lib/kea/hooks``. The proper installation
+of the libraries can be verified with this command:
+
+::
+
+   $ ls -l /usr/local/lib/kea/hooks/*.so
+   /usr/local/lib/kea/hooks/libdhcp_class_cmds.so
+   /usr/local/lib/kea/hooks/libdhcp_flex_id.so
+   /usr/local/lib/kea/hooks/libdhcp_flex_option.so
+   /usr/local/lib/kea/hooks/libdhcp_host_cmds.so
+   /usr/local/lib/kea/hooks/libdhcp_lease_cmds.so
+   /usr/local/lib/kea/hooks/libdhcp_legal_log.so
+   /usr/local/lib/kea/hooks/libdhcp_subnet_cmds.so
+
+The exact list returned depends on the packages installed. If the
+directory was specified via ``--prefix``, the hook libraries will be located in
+``{prefix directory}/lib/kea/hooks``.
+
+Configuring Hook Libraries
+===========================
+
+The hook libraries for a given process are configured using the
+``hooks-libraries`` keyword in the configuration for that process. (Note
+that the word "hooks" is plural.) The value of the keyword is an array
+of map structures, with each structure corresponding to a hook library. For
+example, to set up two hook libraries for the DHCPv4 server, the
+configuration would be:
+
+::
+
+   "Dhcp4": {
+       :
+       "hooks-libraries": [
+           {
+               "library": "/opt/charging.so"
+           },
+           {
+               "library": "/opt/local/notification.so",
+               "parameters": {
+                   "mail": "spam@example.com",
+                   "floor": 13,
+                   "debug": false,
+                   "users": [ "alice", "bob", "charlie" ],
+                   "languages": {
+                       "french": "bonjour",
+                       "klingon": "yl'el"
+                   }
+               }
+           }
+       ]
+       :
+   }
+
+.. note::
+
+   Libraries are reloaded even if their lists have not changed,
+   because the parameters specified for the library (or the files those
+   parameters point to) may have changed.
+
+Libraries may have additional parameters that are not mandatory, in the
+sense that there may be libraries that do not require them. However, for any
+given library there is often a requirement to specify a certain
+set of parameters. Please consult the documentation for each individual library for
+details. In the example above, the first library (``/opt/charging.so``) has no parameters. The
+second library (``/opt/local/notification.so``) has five parameters: specifying mail (string parameter),
+floor (integer parameter), debug (boolean parameter), lists
+(list of strings), and maps (containing strings). Nested parameters can
+be used if the library supports it. This topic is explained in detail in
+the `Hooks Developer's Guide section of the Kea Developer's Guide
+<https://reports.kea.isc.org/dev_guide/df/d46/hooksdgDevelopersGuide.html>`__.
+
+Some hooks use user context to set the parameters. See :ref:`user-context-hooks`.
+
+Notes:
+
+-  The full path to each library should be given.
+
+-  As noted above, the order in which the hooks are called may be important;
+   consult the documentation for each library for specifics.
+
+-  An empty list has the same effect as omitting the ``hooks-libraries``
+   configuration element altogether.
+
+   .. note::
+
+      There is one case where this is not true: if Kea is running with a
+      configuration that contains a ``hooks-libraries`` item, and that
+      item is removed and the configuration reloaded, the removal will
+      be ignored and the libraries remain loaded. As a workaround,
+      instead of removing the ``hooks-libraries`` item, change it to an
+      empty list.
+
+At the moment, only the ``kea-dhcp4`` and ``kea-dhcp6`` processes support
+hook libraries.
+
+.. _order-of-configuration-hooks:
+
+Order of Configuration:
+~~~~~~~~~~~~~~~~~~~~~~~
+
+It is important to recognize that the order in which hook libraries are
+configured determines the order in which their callouts will be executed,
+in cases where more than one hook library implements the same callout.  For
+example, if you wish to use the flex-id hook library to formulate the client
+IDs in conjunction with HA hook library for load-balanced HA, it is essential
+that the flex-id library be specified first in your server's ``hooks-libraries``
+section.  This ensures that the client ID is formulated by the flex-id library
+before the HA library uses it for load-balancing. Similarly it would be best to
+specify forensic logging last, to ensure any other install hooks have made
+their contributions to the packet processing.
+
+.. _user-context-hooks:
+
+User Contexts in Hooks
+~~~~~~~~~~~~~~~~~~~~~~
+
+Hook libraries can have their own configuration parameters, which is
+convenient if the parameter applies to the whole library. However,
+sometimes it is useful to extend certain configuration entities
+with additional configuration data. This is where the concept
+of user contexts comes in. A system administrator can define an arbitrary set of
+data and attach it to Kea structures, as long as the data is specified
+as a JSON map. In particular, it is possible to define fields that are
+integers, strings, boolean, lists, or maps. It is possible to define
+nested structures of arbitrary complexity. Kea does not use that data on
+its own; it simply stores it and makes it available for the hook libraries.
+
+Another use case for user contexts may be storing comments and other
+information that will be retained by Kea. Regular comments are discarded
+when the configuration is loaded, but user contexts are retained. This is
+useful if administrators want their comments to survive ``config-set`` or ``config-get``
+operations, for example.
+
+If user context is supported in a given context, the parser translates
+"comment" entries into user context with a "comment" entry.
+
+User context can store configuration for multiple hooks and comments at once.
+
+Some hooks use user context for a configuration that can be easily edited
+without the need to restart the server.
+
+The DDNS-Tuning Hook uses user-context to configure per subnet behavior. Example:
+
+::
+
+    "subnet4": [{
+        "subnet": "192.0.2.0/24",
+        "pools": [{
+            "pool": "192.0.2.10 - 192.0.2.20",
+        } ],
+        "user-context": {
+            "ddns-tuning:" {
+                "hostname-expr": "'guest-'+Int8ToText(substring(pkt4.yiaddr, 0,1))+'-' \
+                                          +Int8ToText(substring(pkt4.yiaddr, 1,2))+'-' \
+                                          +Int8ToText(substring(pkt4.yiaddr, 2,3))+'-' \
+                                          +Int8ToText(substring(pkt4.yiaddr, 3,4))",
+            },
+            "last-modified": "2017-09-04 13:32",
+            "phones": [ "x1234", "x2345" ],
+            "devices-registered": 42,
+            "billing": false
+        }
+    }]
+
+
+The Limits hook uses user-context in classes and subnets to set parameters. For example:
+
+.. code-block:: json
+
+    {
+      "Dhcp6": {
+        "client-classes": [
+          {
+            "name": "gold",
+            "user-context": {
+              "limits": {
+                "address-limit": 2,
+                "prefix-limit": 1,
+                "rate-limit": "1000 packets per second"
+              }
+            }
+          }
+        ],
+        "hooks-libraries": [
+          {
+            "library": "/usr/local/lib/libdhcp_limits.so"
+          }
+        ],
+        "subnet6": [
+          {
+            "id": 1,
+            "pools": [
+              {
+                "pool": "2001:db8::/64"
+              }
+            ],
+            "subnet": "2001:db8::/64",
+            "user-context": {
+              "limits": {
+                "address-limit": 4,
+                "prefix-limit": 2,
+                "rate-limit": "10 packets per minute"
+              }
+            }
+          }
+        ]
+      }
+    }
+
+Available Hook Libraries
+========================
+
+As described above, the hook functionality provides a way to customize
+a Kea server without modifying the core code. ISC has chosen to take
+advantage of this feature to provide functions that may only be useful
+to a subset of Kea users. To this end, ISC has created some hook
+libraries, discussed in the following sections.
+
+.. note::
+
+   Some of these libraries are available with the base code, while
+   others are only shared with organizations who contribute to Kea's development
+   through paid ISC support contracts. Paid support
+   includes professional engineering assistance, advance security notifications, input
+   into ISC's roadmap planning, and many other benefits, while helping
+   keep Kea sustainable in the long term. ISC encourages companies and organizations
+   to consider purchasing a paid support contract; further information can be
+   obtained by completing the form at https://www.isc.org/contact.
+
+The following table provides a list of hook libraries currently available
+from ISC. It is important to pay attention to which libraries may be
+loaded by which Kea processes. It is a common mistake to configure the
+``kea-ctrl-agent`` process to load libraries that should, in fact, be
+loaded by the ``kea-dhcp4`` or ``kea-dhcp6`` processes. If a library
+from ISC does not work as expected, please make sure that it has been
+loaded by the correct process per the table below.
+
+.. warning::
+
+   While the Kea Control Agent includes the "hooks" functionality, (i.e.
+   hook libraries can be loaded by this process), none of ISC's current
+   hook libraries should be loaded by the Control Agent.
+
+.. tabularcolumns:: |p{0.1\linewidth}|p{0.1\linewidth}|p{0.8\linewidth}|
+
+.. table:: List of available hook libraries
+   :class: longtable
+   :widths: 10 10 80
+
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | Name                                                      | Availability | Description                                                  |
+   +===========================================================+==============+==============================================================+
+   | :ref:`BOOTP <hooks-bootp>`                                | Kea open     | This hook library adds BOOTP support, as defined in          |
+   |                                                           | source       | RFC 1497. It recognizes received BOOTP requests:             |
+   |                                                           |              | they are translated into DHCPREQUEST packets, put into the   |
+   |                                                           |              | BOOTP client class, and receive infinite lifetime leases.    |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Class Commands <hooks-class-cmds>`                  | ISC support  | This hook library allows configured DHCP client classes to   |
+   |                                                           | customers    | be added, updated, deleted, and fetched without              |
+   |                                                           |              | needing to restart the DHCP server.                          |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Configuration Backend Commands <hooks-cb-cmds>`     | ISC support  | This hook                                                    |
+   |                                                           | customers    | library implements a collection of commands to manage        |
+   |                                                           |              | Kea configuration information in a                           |
+   |                                                           |              | database. This library may only be used in conjunction with  |
+   |                                                           |              | one of the supported Configuration Backend implementations.  |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`DDNS Tuning <hooks-ddns-tuning>`                    | ISC support  | This hook library adds custom behaviors related to Dynamic   |
+   |                                                           | customers    | DNS updates on a per-client basis. Its primary feature is to |
+   |                                                           |              | allow the host name used for DNS to be                       |
+   |                                                           |              | calculated using an expression.                              |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Flexible Identifier <hooks-flex-id>`                | ISC support  | Kea software provides a way to handle host reservations that |
+   |                                                           | customers    | include addresses, prefixes, options, client classes and     |
+   |                                                           |              | other features. The reservation can be based on hardware     |
+   |                                                           |              | address, DUID, circuit-id, or client-id in DHCPv4 and on     |
+   |                                                           |              | hardware address or DUID in DHCPv6. However, there are       |
+   |                                                           |              | sometimes scenarios where the reservation is more complex,   |
+   |                                                           |              | e.g. uses other options than mentioned above, uses parts of  |
+   |                                                           |              | specific options, or perhaps uses a combination of several   |
+   |                                                           |              | options and fields to uniquely identify a client. Those      |
+   |                                                           |              | scenarios are addressed by the Flexible Identifier hook      |
+   |                                                           |              | application. It allows defining an expression, similar to    |
+   |                                                           |              | the one used in client classification,                       |
+   |                                                           |              | e.g. ``substring(relay6[0].option[37],0,6)``. Each incoming  |
+   |                                                           |              | packet is evaluated against that expression and its value is |
+   |                                                           |              | then searched in the reservations database.                  |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Flexible Option <hooks-flex-option>`                | Kea open     | This library provides hooks that compute option values       |
+   |                                                           | source       | instead of static configured values. An expression is        |
+   |                                                           |              | evaluated on the query packet. Defined add, supersede, and   |
+   |                                                           |              | remove actions are applied on the response packet before     |
+   |                                                           |              | it is sent using the evaluation result.                      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Forensic Logging <hooks-legal-log>`                 | ISC support  | This library provides hooks that record a detailed log of    |
+   |                                                           | customers    | lease assignments and renewals in a set of log files. In     |
+   |                                                           |              | many legal jurisdictions, companies - especially ISPs - must |
+   |                                                           |              | record information about the addresses they have leased to   |
+   |                                                           |              | DHCP clients. This library is designed to help with that     |
+   |                                                           |              | requirement. If the information that it records is           |
+   |                                                           |              | sufficient, it may be used directly. If a jurisdiction       |
+   |                                                           |              | requires a different set of information to be saved, it can  |
+   |                                                           |              | be used as a template or example to create                   |
+   |                                                           |              | custom logging hooks. In Kea 1.9.8, additional parameters    |
+   |                                                           |              | were added to give users more flexibility regarding          |
+   |                                                           |              | what information should be logged.                           |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`GSS-TSIG <hooks-gss-tsig>`                          | ISC support  | This hook library adds support to the Kea D2 server          |
+   |                                                           | customers    | (kea-dhcp-ddns) for using GSS-TSIG to sign DNS updates.      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`High Availability <hooks-high-availability>`        | Kea open     | The risk of DHCP service unavailability can be minimized     |
+   |                                                           | source       | by setting up a pair of DHCP servers in a network. Two       |
+   |                                                           |              | modes of operation are supported. The first one is called    |
+   |                                                           |              | load-balancing, and is sometimes referred to as              |
+   |                                                           |              | "active-active." Each server can handle selected groups of   |
+   |                                                           |              | clients in this network, or all clients if it detects that   |
+   |                                                           |              | its partner has become unavailable. It is also possible to   |
+   |                                                           |              | designate one server to serve all DHCP clients, and leave    |
+   |                                                           |              | another server as standby. This mode is called "hot standby" |
+   |                                                           |              | and is sometimes referred to as "active-passive." This       |
+   |                                                           |              | server activates its DHCP function only when it detects that |
+   |                                                           |              | its partner is not available. Such cooperation between the   |
+   |                                                           |              | DHCP servers requires that these servers constantly          |
+   |                                                           |              | communicate with each other to send updates about allocated  |
+   |                                                           |              | leases, and to periodically test whether their partners are  |
+   |                                                           |              | still operational. The hook library also provides an ability |
+   |                                                           |              | to send lease updates to external backup servers, making it  |
+   |                                                           |              | much easier to have a replacement that is up-to-date.        |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Host Cache <hooks-host-cache>`                      | ISC support  | Some database backends, such as RADIUS,                      |
+   |                                                           | customers    | may take a long time to respond. Since                       |
+   |                                                           |              | Kea in general is synchronous, backend performance           |
+   |                                                           |              | directly affects DHCP performance. To minimize               |
+   |                                                           |              | performance impact, this library                             |
+   |                                                           |              | provides a way to cache responses from other hosts. This     |
+   |                                                           |              | includes negative caching, i.e. the ability to remember that |
+   |                                                           |              | there is no client information in the database.              |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Host Commands <hooks-host-cmds>`                    | ISC support  | Kea provides a way to store host reservations in a           |
+   |                                                           | customers    | database. In many larger deployments it is useful to be able |
+   |                                                           |              | to manage that information while the server is running. This |
+   |                                                           |              | library provides management commands for adding, querying,   |
+   |                                                           |              | and deleting host reservations in a safe way without         |
+   |                                                           |              | restarting the server. In particular, it validates the       |
+   |                                                           |              | parameters, so an attempt to insert incorrect data, e.g. add |
+   |                                                           |              | a host with conflicting identifier in the same subnet, is    |
+   |                                                           |              | rejected. Those commands are exposed via the command channel |
+   |                                                           |              | (JSON over UNIX sockets) and the Control Agent (JSON over    |
+   |                                                           |              | RESTful interface).                                          |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Lease Commands <hooks-lease-cmds>`                  | Kea open     | This hook library offers a number of  commands used to       |
+   |                                                           | source       | manage leases. Kea can store lease information in various    |
+   |                                                           |              | backends: memfile, MySQL, PostgreSQL. This library provides  |
+   |                                                           |              | a unified interface to manipulate leases in an unified, safe |
+   |                                                           |              | way. In particular, it allows manipulation of memfile leases |
+   |                                                           |              | while Kea is running, sanity check changes, lease existence  |
+   |                                                           |              | checks, and removal of all leases belonging to a specific    |
+   |                                                           |              | subnet. It can also catch obscure errors, like the addition  |
+   |                                                           |              | of a lease with subnet-id that does not exist in the         |
+   |                                                           |              | configuration, or configuration of a lease to use an address |
+   |                                                           |              | that is outside of the subnet to which it is supposed to     |
+   |                                                           |              | belong. This library allows easy management of user contexts |
+   |                                                           |              | associated with leases.                                      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Leasequery <hooks-lease-query>`                     | ISC support  | This library adds support for DHCPv4                         |
+   |                                                           | customers    | Leasequery as described in RFC 4388; and for DHCPv6          |
+   |                                                           |              | Leasequery as described in RFC 5007.                         |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Limits <hooks-limits>`                              | ISC support  | With this hook library, ``kea-dhcp4`` and ``kea-dhcp6``      |
+   |                                                           | customers    | servers can apply a limit to the rate at which packets       |
+   |                                                           |              | receive a response. The limit can be applied per-client      |
+   |                                                           |              | class or per-subnet.                                         |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`MySQL Configuration Backend <hooks-cb-mysql>`       | Kea open     | This hook library is an implementation of the Kea            |
+   |                                                           | source       | Configuration Backend for MySQL. It uses a MySQL database as |
+   |                                                           |              | a repository for the Kea configuration information. Kea      |
+   |                                                           |              | servers use this library to fetch their configurations.      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`PostgreSQL Configuration Backend <hooks-cb-pgsql>`  | Kea open     | This hook library is an implementation of the Kea            |
+   |                                                           | source       | Configuration Backend for PostgreSQL. It uses a PostgreSQL   |
+   |                                                           |              | database as a repository for the Kea configuration           |
+   |                                                           |              | information. Kea servers use this library to fetch their     |
+   |                                                           |              | configurations.                                              |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`RADIUS <hooks-radius>`                              | ISC support  | The RADIUS hook library allows Kea to interact with          |
+   |                                                           | customers    | RADIUS servers using access and accounting mechanisms. The   |
+   |                                                           |              | access mechanism may be used for access control, assigning   |
+   |                                                           |              | specific IPv4 or IPv6 addresses reserved by RADIUS,          |
+   |                                                           |              | dynamically assigning addresses from designated pools chosen |
+   |                                                           |              | by RADIUS, or rejecting the client's messages altogether.    |
+   |                                                           |              | The accounting mechanism allows a RADIUS server to keep      |
+   |                                                           |              | track of device activity over time.                          |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`RBAC <hooks-rbac>`                                  | ISC support  | This hook library adds support to the Kea Control Agent      |
+   |                                                           | customers    | (kea-ctrl-agent) for Role-Based Access Control filtering     |
+   |                                                           |              | of commands.                                                 |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Run Script <hooks-run-script>`                      | Kea open     | This hook library adds support to run external               |
+   |                                                           | source       | scripts for specific packet-processing hook points. There    |
+   |                                                           |              | are several exported environment variables available for     |
+   |                                                           |              | the script.                                                  |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Statistics Commands <hooks-stat-cmds>`              | Kea open     | This library provides additional                             |
+   |                                                           | source       | commands for retrieving accurate DHCP lease statistics, for  |
+   |                                                           |              | Kea DHCP servers that share the same lease database. This    |
+   |                                                           |              | setup is common in deployments where DHCP service redundancy |
+   |                                                           |              | is required and a shared lease database is used to avoid     |
+   |                                                           |              | lease-data replication between the DHCP servers.             |
+   |                                                           |              | This hook library returns lease statistics                   |
+   |                                                           |              | for each subnet.                                             |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`Subnet Commands <hooks-subnet-cmds>`                | ISC support  | In deployments in which subnet configuration needs to be     |
+   |                                                           | customers    | frequently updated, it is a hard requirement that such       |
+   |                                                           |              | updates be performed without the need for a full DHCP server |
+   |                                                           |              | reconfiguration or restart. This hook library allows for     |
+   |                                                           |              | incremental changes to the subnet configuration such as      |
+   |                                                           |              | adding or removing a subnet. It also allows for              |
+   |                                                           |              | listing all available subnets and fetching detailed          |
+   |                                                           |              | information about a selected subnet. The commands exposed by |
+   |                                                           |              | this library do not affect other subnets or configuration    |
+   |                                                           |              | parameters currently used by the server.                     |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+   | :ref:`User Check <hooks-user-chk>`                        | Kea open     | Reads known users list from a file. Unknown users will be    |
+   |                                                           | source       | assigned a lease from the last subnet defined in the         |
+   |                                                           |              | configuration file, e.g. to redirect them to a captive       |
+   |                                                           |              | portal. This demonstrates how an external source of          |
+   |                                                           |              | information can be used to influence the Kea allocation      |
+   |                                                           |              | engine. This hook is part of the Kea source code and is      |
+   |                                                           |              | available in the ``src/hooks/dhcp/user_chk`` directory.      |
+   +-----------------------------------------------------------+--------------+--------------------------------------------------------------+
+
+ISC hopes to see more hook libraries become available as time
+progresses, developed both internally and externally. Since this list
+may evolve dynamically, it is maintained on a wiki page, available
+at https://gitlab.isc.org/isc-projects/kea/wikis/Hooks-available.
+Developers or others who are aware of any hook libraries not listed there
+are asked to please send a note to the kea-users or kea-dev mailing lists for
+updating. (Information on all of ISC's public mailing lists can be found
+at https://www.isc.org/mailinglists/.)
+
+The libraries developed by ISC are described in detail in the following
+sections.
+
+.. include:: hooks-bootp.rst
+.. include:: hooks-cb-cmds.rst
+.. include:: hooks-class-cmds.rst
+.. include:: hooks-ddns-tuning.rst
+.. include:: hooks-flex-id.rst
+.. include:: hooks-flex-option.rst
+.. include:: hooks-gss-tsig.rst
+.. include:: hooks-ha.rst
+.. include:: hooks-host-cache.rst
+.. include:: hooks-host-cmds.rst
+.. include:: hooks-lease-cmds.rst
+.. include:: hooks-lease-query.rst
+.. include:: hooks-legal-log.rst
+.. include:: hooks-limits.rst
+.. include:: hooks-cb-mysql.rst
+.. include:: hooks-cb-pgsql.rst
+.. include:: hooks-radius.rst
+.. include:: hooks-rbac.rst
+.. include:: hooks-run-script.rst
+.. include:: hooks-stat-cmds.rst
+.. include:: hooks-subnet-cmds.rst
+.. include:: hooks-user-chk.rst
diff --git a/doc/sphinx/arm/install.rst b/doc/sphinx/arm/install.rst
new file mode 100644
index 0000000..5482812
--- /dev/null
+++ b/doc/sphinx/arm/install.rst
@@ -0,0 +1,566 @@
+.. _installation:
+
+************
+Installation
+************
+
+Packages
+========
+
+ISC publishes native RPM, deb, and APK packages, along with the tarballs
+with the source code. The packages are available on
+`Cloudsmith <https://cloudsmith.io/~isc/repos/>`_ at
+https://cloudsmith.io/~isc/repos. The native packages can be downloaded
+and installed using the system available in a specific distribution (such
+as dpkg or rpm). The Kea repository can also be added to the system,
+making it easier to install updates. For details, please
+go to https://cloudsmith.io/~isc/repos, choose the repository of
+interest, and then click the ``Set Me Up`` button for detailed
+instructions.
+
+.. _install-hierarchy:
+
+Installation Hierarchy
+======================
+
+The following is the directory layout of the complete Kea installation.
+(All directory paths are relative to the installation directory.)
+
+-  ``etc/kea/`` — configuration files.
+
+-  ``include/`` — C++ development header files.
+
+-  ``lib/`` — libraries.
+
+-  ``lib/kea/hooks`` — additional hooks libraries.
+
+-  ``sbin/`` — server software and commands used by the system administrator.
+
+-  ``share/doc/kea/`` — this guide, other supplementary documentation, and examples.
+
+-  ``share/kea/`` — API command examples and database schema scripts.
+
+-  ``share/man/`` — manual pages (online documentation).
+
+-  ``var/lib/kea/`` — server identification and lease database files.
+
+-  ``var/log/`` - log files.
+
+-  ``var/run/kea`` - PID file and logger lock file.
+
+.. _build-requirements:
+
+Build Requirements
+==================
+
+In addition to the runtime requirements (listed in
+:ref:`required-software`), building Kea from source code requires
+various development include headers and program development tools.
+
+.. note::
+
+   Some operating systems have split their distribution packages into a
+   runtime and a development package. The
+   development package versions, which include header files and
+   libraries, must be installed to build Kea from the source code.
+
+Building from source code requires the following software installed on
+the system:
+
+-  Boost C++ libraries (https://www.boost.org/). The oldest Boost version
+   used for testing is 1.57 (although Kea may also work with older
+   versions). The Boost system library must also be installed.
+   Installing a header-only version of Boost is not recommended.
+
+-  OpenSSL (at least version 1.0.2) or Botan (at least version 2).
+   OpenSSL version 1.1.1 or later is strongly recommended.
+
+-  log4cplus (at least version 1.0.3) development include headers.
+
+-  A C++ compiler (with C++11 support) and standard development headers.
+   The Kea build has been checked with GCC g++ 4.8.5 and some later versions,
+   and Clang 800.0.38 and some later versions.
+
+-  The development tools automake, libtool, and pkg-config.
+
+-  The MySQL client and the client development libraries, when using the
+   ``--with-mysql`` configuration flag to build the Kea MySQL database
+   backend. In this case, an instance of the MySQL server running locally
+   or on a machine reachable over a network is required. Note that running
+   the unit tests requires a local MySQL server.
+
+-  The PostgreSQL client and the client development libraries, when using the
+   ``--with-pgsql`` configuration flag to build the Kea PostgreSQL database
+   backend. In this case an instance of the PostgreSQL server running locally
+   or on a machine reachable over a network is required. Note that running
+   the unit tests requires a local PostgreSQL server.
+
+-  The FreeRADIUS client library is required to connect to a RADIUS server.
+   This is specified using the ``--with-freeradius`` configuration switch.
+
+-  Sysrepo v1.4.140 and libyang v1.0.240 are needed to connect to a Sysrepo
+   datastore. Earlier versions are no longer supported. When compiling from
+   sources, the configure switches that can be used are ``--with-libyang`` and
+   ``--with-sysrepo`` without any parameters. If these dependencies were
+   installed in custom paths, point the switches to them.
+
+-  The MIT Kerberos 5 or Heimdal libraries are needed by Kea DDNS server to sign
+   and verify DNS updates using GSS-TSIG. The configuration switch which enables
+   this functionality is ``--with-gssapi`` without any parameters. If these
+   dependencies were installed in custom paths, point the switch to them.
+
+-  googletest (version 1.8 or later) is required when using the ``--with-gtest``
+   configuration option to build the unit tests.
+
+-  The documentation generation tools `Sphinx <https://www.sphinx-doc.org/>`_,
+   texlive with its extensions, and Doxygen, if using the ``--enable-generate-docs``
+   configuration option to create the documentation. Specifically,
+   with Fedora, python3-sphinx, texlive, and texlive-collection-latexextra are necessary;
+   with Ubuntu, python3-sphinx, python3-sphinx-rtd-theme, and texlive-binaries
+   are needed. If LaTeX packages are missing, Kea skips PDF generation and produces
+   only HTML documents.
+
+Visit ISC's Knowledgebase at https://kb.isc.org/docs/installing-kea for
+system-specific installation tips.
+
+.. _install:
+
+Installation From Source
+========================
+
+Although Kea may be available in pre-compiled, ready-to-use packages
+from operating system vendors, it is open source software written in
+C++. As such, it is freely available in source code form from ISC as a
+downloadable tar file. The source code can also be obtained from the Kea
+GitLab repository at https://gitlab.isc.org/isc-projects/kea. This
+section describes how to build Kea from the source code.
+
+Download Tar File
+-----------------
+
+The Kea release tarballs may be downloaded from:
+https://downloads.isc.org/isc/kea/.
+
+Retrieve From Git
+-----------------
+
+The latest development code is available on GitLab (see
+https://gitlab.isc.org/isc-projects/kea). The Kea source is public and
+development is done in the “master” branch.
+
+Downloading this "bleeding edge" code is recommended only for developers
+or advanced users. Using development code in a production environment is
+not recommended.
+
+.. note::
+
+   When building from source code retrieved via git, additional software
+   is required: automake (v1.11 or later), libtoolize, and autoconf
+   (v2.69 or later). These may need to be installed.
+
+The code can be checked out from
+``https://gitlab.isc.org/isc-projects/kea.git``:
+
+.. code-block:: console
+
+   $ git clone https://gitlab.isc.org/isc-projects/kea.git
+
+The code checked out from the git repository does not include the
+generated configure script or the Makefile.in files, nor their related build
+files. They can be created by running ``autoreconf`` with the
+``--install`` switch. This will run ``autoconf``, ``aclocal``,
+``libtoolize``, ``autoheader``, ``automake``, and related commands.
+
+Write access to the Kea repository is only granted to ISC staff.
+Developers planning to contribute to Kea should check our
+`Contributor's
+Guide <https://gitlab.isc.org/isc-projects/kea/blob/master/contributors-guide.md>`__.
+The `Kea Developer's
+Guide <https://reports.kea.isc.org/dev_guide/>`__ contains more
+information about the process, and describes the requirements for
+contributed code to be accepted by ISC.
+
+.. _configure:
+
+Configure Before the Build
+--------------------------
+
+Kea uses the GNU Build System to discover build environment details. To
+generate the makefiles using the defaults, simply run:
+
+.. code-block:: console
+
+   $ ./configure
+
+Run ``./configure`` with the ``--help`` switch to view the different
+options. Some commonly used options are:
+
+ - ``--prefix``
+   Define the installation location (the default is ``/usr/local``).
+
+ - ``--with-mysql``
+   Build Kea with code to allow it to store leases and host reservations
+   in a MySQL database.
+
+ - ``--with-pgsql``
+   Build Kea with code to allow it to store leases and host reservations
+   in a PostgreSQL database.
+
+ - ``--with-log4cplus``
+   Define the path to find the Log4cplus headers and libraries. Normally
+   this is not necessary.
+
+ - ``--with-boost-include``
+   Define the path to find the Boost headers. Normally this is not
+   necessary.
+
+ - ``--with-botan-config``
+   Specify the path to the botan-config script to build with Botan for
+   cryptographic functions. It is preferable to use OpenSSL (see below).
+
+ - ``--with-openssl``
+   Use the OpenSSL cryptographic library instead of Botan. By default
+   ``configure`` searches for a valid Botan installation; if one is not
+   found, Kea searches for OpenSSL. Normally this is not necessary.
+
+ - ``--enable-shell``
+   Build the optional ``kea-shell`` tool (more in :ref:`kea-shell`).
+   The default is to not build it.
+
+ - ``--with-site-packages``
+   Only useful when ``kea-shell`` is enabled, this switch causes the kea-shell
+   Python packages to be installed in the specified directory. This is
+   mostly useful for Debian-related distributions. While most systems store
+   Python packages in ``${prefix}/usr/lib/pythonX/site-packages``, Debian
+   introduced a separate directory for packages installed from DEB. Such
+   Python packages are expected to be installed in
+   ``/usr/lib/python3/dist-packages``.
+
+ - ``--enable-perfdhcp``
+   Build the optional ``perfdhcp`` DHCP benchmarking tool. The default
+   is to not build it.
+
+ - ``--with-freeradius``
+   Build the optional ``RADIUS`` hook. This option specifies the path to the
+   patched version of the FreeRADIUS client. This feature is available in
+   the subscriber-only version of Kea, and requires the subscription-only RADIUS hook.
+
+ - ``--with-freeradius-dictionary``
+   Specify a non-standard location for a FreeRADIUS dictionary file, which
+   contains a list of supported RADIUS attributes. This feature is available in
+   the subscriber-only version of Kea, and requires the subscription-only RADIUS hook.
+
+If the RADIUS options are not available, ensure that the RADIUS hook sources are in
+the ``premium`` directory and rerun ``autoreconf -i``.
+
+.. note::
+
+   For instructions concerning the installation and configuration of
+   database backends for Kea, see :ref:`dhcp-install-configure`.
+
+There are many options that are typically not necessary for
+regular users. However, they may be useful for package maintainers,
+developers, or people who want to extend Kea code or send patches:
+
+ - ``--with-gtest``, ``--with-gtest-source``
+   Enable the building of C++ unit tests using the Google Test
+   framework. This option specifies the path to the gtest source. (If
+   the framework is not installed on the system, it can be downloaded
+   from https://github.com/google/googletest.)
+
+ - ``--enable-generate-docs``
+   Enable the rebuilding of Kea documentation. ISC publishes Kea
+   documentation for each release; however, in some cases it may be
+   desirable to rebuild it: for example, to change something in the
+   docs, or to generate new ones from git sources that are not yet
+   released.
+
+ - ``--enable-generate-parser``
+   Enable the generation of parsers using flex or bison. Kea sources include
+   .cc and .h parser files, pre-generated for users' convenience. By
+   default Kea does not use flex or bison, to avoid
+   requiring installation of unnecessary dependencies for users.
+   However, if anything in the parsers is changed (such as adding a new
+   parameter), flex and bison are required to regenerate
+   parsers. This option permits that.
+
+ - ``--enable-generate-messages``
+   Enable the regeneration of messages files from their messages source
+   files, e.g. regenerate xxx_messages.h and xxx_messages.cc from
+   xxx_messages.mes using the Kea message compiler. By default Kea is
+   built using these .h and .cc files from the distribution. However, if
+   anything in a .mes file is changed (such as adding a new message),
+   the Kea message compiler needs to be built and used. This option
+   permits that.
+
+As an example, the following command configures Kea to find the Boost
+headers in /usr/pkg/include, specifies that PostgreSQL support should be
+enabled, and sets the installation location to /opt/kea:
+
+.. code-block:: console
+
+   $ ./configure \
+         --with-boost-include=/usr/pkg/include \
+         --with-pgsql=/usr/local/bin/pg_config \
+         --prefix=/opt/kea
+
+Users who have any problems with building Kea using the header-only Boost
+code, or who would like to use the Boost system library (assumed for the
+sake of this example to be located in /usr/pkg/lib), should issue these
+commands:
+
+.. code-block:: console
+
+   $ ./configure \
+         --with-boost-libs=-lboost_system \
+         --with-boost-lib-dir=/usr/pkg/lib
+
+If ``configure`` fails, it may be due to missing or old dependencies.
+
+When ``configure`` succeeds, it displays a report with the parameters used
+to build the code. This report is saved into the file ``config.report``
+and is also embedded into the executable binaries, e.g., ``kea-dhcp4``.
+
+Build
+-----
+
+After the configure step is complete, build the executables from the C++
+code and prepare the Python scripts by running the command:
+
+.. code-block:: console
+
+   $ make
+
+Install
+-------
+
+To install the Kea executables, support files, and documentation, issue
+the command:
+
+.. code-block:: console
+
+   $ make install
+
+Do not use any form of parallel or job server options (such as GNU
+make's ``-j`` option) when performing this step; doing so may cause
+errors.
+
+.. note::
+
+   The install step may require superuser privileges.
+
+If required, run ``ldconfig`` as root with ``/usr/local/lib`` (or with
+prefix/lib if configured with ``--prefix``) in ``/etc/ld.so.conf`` (or the
+relevant linker cache configuration file for the OS):
+
+.. code-block:: console
+
+   $ ldconfig
+
+.. note::
+
+   If ``ldconfig`` is not run where required, users may see
+   errors like the following:
+
+   ::
+
+       program: error while loading shared libraries: libkea-something.so.1:
+       cannot open shared object file: No such file or directory
+
+
+Cross-Building
+--------------
+
+It is possible to cross-build Kea, i.e. to create binaries in a separate
+system (the ``build`` system) from the one where Kea runs
+(the ``host`` system).
+
+It is outside of the scope of common administrator operations and requires
+some developer skills, but the Developer Guide explains how to do that
+using an x86_64 Linux system to build Kea for a Raspberry Pi box running
+Raspbian: `Kea Cross-Compiling Example
+<https://reports.kea.isc.org/dev_guide/de/d9a/crossCompile.html>`__.
+
+.. _dhcp-install-configure:
+
+DHCP Database Installation and Configuration
+============================================
+
+Kea stores its leases in a lease database. The software has been written
+in a way that makes it possible to choose which database product should
+be used to store the lease information. Kea supports three
+database backends: MySQL, PostgreSQL and memfile. To limit external
+dependencies, MySQL and PostgreSQL support are disabled by default and only
+memfile is available. Support for the optional external database backend must
+be explicitly included when Kea is built.
+This section covers the building of Kea with one of the optional backends and
+the creation of the lease database.
+
+.. note::
+
+   When unit tests are built with Kea (i.e. the ``--with-gtest`` configuration
+   option is specified), the databases must be manually pre-configured
+   for the unit tests to run. The details of this configuration can be
+   found in the `Kea Developer's
+   Guide <https://reports.kea.isc.org/dev_guide/>`__.
+
+Building with MySQL Support
+---------------------------
+
+Install MySQL according to the instructions for the system. The client
+development libraries must be installed.
+
+Build and install Kea as described in :ref:`installation`,
+with the following modification. To enable the MySQL database code, at the
+"configure" step (see :ref:`configure`), the ``--with-mysql`` switch should be
+specified:
+
+.. code-block:: console
+
+   $ ./configure [other-options] --with-mysql
+
+If MySQL was not installed in the default location, the location of the
+MySQL configuration program "mysql_config" should be included with the
+switch:
+
+.. code-block:: console
+
+   $ ./configure [other-options] --with-mysql=path-to-mysql_config
+
+See :ref:`mysql-database-create` for details regarding MySQL
+database configuration.
+
+Building with PostgreSQL support
+--------------------------------
+
+Install PostgreSQL according to the instructions for the system. The
+client development libraries must be installed. Client development
+libraries are often packaged as "libpq".
+
+Build and install Kea as described in :ref:`installation`,
+with the following modification. To enable the PostgreSQL database code, at the
+"configure" step (see :ref:`configure`), the ``--with-pgsql`` switch should be
+specified:
+
+.. code-block:: console
+
+   $ ./configure [other-options] --with-pgsql
+
+If PostgreSQL was not installed in the default location, the location of
+the PostgreSQL configuration program "pg_config" should be included with
+the switch:
+
+.. code-block:: console
+
+   $ ./configure [other-options] --with-pgsql=path-to-pg_config
+
+See :ref:`pgsql-database-create` for details regarding PostgreSQL
+database configuration.
+
+
+
+.. include:: hammer.rst
+
+.. _non-root:
+
+Running Kea From a Non-root Account on Linux
+============================================
+
+Both Kea DHCPv4 and DHCPv6 servers perform operations that in general require root access
+privileges. In particular, DHCPv4 opens raw sockets and both DHCPv4 and DHCPv6 open UDP sockets on
+privileged ports. However, with some extra system configuration, it is possible to run Kea from
+non-root accounts.
+
+First, a regular user account must be created:
+
+.. code-block:: console
+
+   useradd admin
+
+Then, change the binaries' ownership and group to the new user. Note that
+the specific path may be different. Please refer to the ``--prefix``
+parameter passed to the configure script:
+
+.. code-block:: console
+
+   chown -R admin /opt/kea
+   chgrp -R admin /opt/kea
+   chown -R admin /var/log/kea-dhcp4.log
+   chgrp -R admin /var/log/kea-dhcp4.log
+   chown -R admin /var/log/kea-dhcp6.log
+   chgrp -R admin /var/log/kea-dhcp6.log
+
+If using systemd, modify its service file
+(e.g. /etc/systemd/system/kea-dhcp6.service):
+
+.. code-block:: console
+
+   User=admin
+   Group=admin
+
+The most important step is to set the capabilities of the binaries. Refer to `man capabilities` to get
+more information.
+
+.. code-block:: console
+
+   setcap 'cap_net_bind_service,cap_net_raw=+ep' /opt/kea/sbin/kea-dhcp4
+   setcap 'cap_net_bind_service=+ep' /opt/kea/sbin/kea-dhcp6
+
+If using systemd, also add this to the service file
+(e.g. /etc/systemd/system/kea-dhcp6.service):
+
+.. code-block:: console
+
+   ExecStartPre=setcap 'cap_net_bind_service=+ep' /opt/kea/sbin/kea-dhcp6
+
+After this step is complete, the admin user should be able to run Kea. Note that the DHCPv4 server by
+default opens raw sockets. If the network is only using relayed traffic, Kea can be instructed to
+use regular UDP sockets (refer to ``dhcp-socket-type`` parameter in the
+:ref:`dhcp4-interface-configuration` section) and the ``cap_net_raw`` capability can be skipped.
+
+.. note::
+
+   It is possible to avoid running Kea with root privileges by instructing Kea to
+   use non-privileged (greater than 1024) ports and redirecting traffic. This, however, only works
+   for relayed traffic. This approach in general is considered experimental and has not been tested
+   for deployment in production environments. Use with caution!
+
+   To use this approach, configure the server to listen on other non-privileged ports (e.g. 1547
+   and 1548) by running the process with the ``-p`` option in ``/etc/systemd/system/kea-dhcp4.service``:
+
+.. code-block:: console
+
+   ExecStart=/opt/kea/sbin/kea-dhcp4 -d -c /etc/kea/kea-dhcp4.conf -p 2067
+
+and ``/etc/systemd/system/kea-dhcp4.service``:
+
+.. code-block:: console
+
+   ExecStart=/opt/kea/sbin/kea-dhcp6 -d -c /etc/kea/kea-dhcp6.conf -p 1547
+
+Then configure port redirection with iptables and ip6tables for new ports (e.g. 1547
+and 1548). Be sure to replace ``ens4`` with the specific interface name.
+
+.. code-block:: console
+
+   iptables -t nat -A PREROUTING -i ens4 -p udp --dport 67 -j REDIRECT --to-port 2067
+   iptables -t nat -A PREROUTING -i ens4 -p udp --dport 2068 -j REDIRECT --to-port 68
+   ip6tables -t nat -A PREROUTING -i ens4 -p udp --dport 547 -j REDIRECT --to-port 1547
+   ip6tables -t nat -A PREROUTING -i ens4 -p udp --dport 1548 -j REDIRECT --to-port 548
+
+.. _deprecated:
+
+Deprecated Features
+===================
+
+This section lists significant features that have been or will be removed. We try to
+deprecate features before removing them to signal
+to current users to plan a migration. New users should not rely on deprecated features.
+
+Sysrepo 0.x
+-----------
+
+Kea versions 1.9.9 and earlier required Sysrepo 0.7.x to run, when optional support for NETCONF was
+enabled. Kea versions 1.9.10 and later now require Sysrepo 1.4.x and the related libyang 1.x library to
+run. The earlier Sysrepo versions are no longer supported. The latest Sysrepo 2.x version does not
+provide C++ bindings, and as such, is not usable for Kea.
diff --git a/doc/sphinx/arm/integrations.rst b/doc/sphinx/arm/integrations.rst
new file mode 100644
index 0000000..8436588
--- /dev/null
+++ b/doc/sphinx/arm/integrations.rst
@@ -0,0 +1,10 @@
+*********************************
+Integration With External Systems
+*********************************
+
+Kea provides optional support for a variety of external systems, such as RADIUS, NETCONF,
+YANG, and GSS-TSIG. The following sections describe how to compile Kea with those additional
+capabilities and how to configure them.
+
+.. include:: ext-netconf.rst
+.. include:: ext-gss-tsig.rst
diff --git a/doc/sphinx/arm/intro.rst b/doc/sphinx/arm/intro.rst
new file mode 100644
index 0000000..b9f221d
--- /dev/null
+++ b/doc/sphinx/arm/intro.rst
@@ -0,0 +1,64 @@
+.. _intro:
+
+************
+Introduction
+************
+
+Kea is the next generation of DHCP software, developed by Internet Systems Consortium (ISC). It
+supports both the DHCPv4 and DHCPv6 protocols along with their extensions,
+e.g. prefix delegation and dynamic updates to DNS.
+
+This guide covers Kea version |release|.
+
+For information about supported platforms see :ref:`platforms`.
+
+.. include:: platforms.rst
+
+.. _kea_software:
+
+Kea Software
+============
+
+Kea is a modular DHCP server solution. This modularity is accomplished using multiple
+cooperating processes which, together, provide the server functionality.
+The following software is included with Kea:
+
+-  ``keactrl`` — This tool starts, stops, reconfigures, and reports the status of
+   the Kea servers.
+
+-  ``kea-dhcp4`` — The DHCPv4 server process. This process responds to
+   DHCPv4 queries from clients.
+
+-  ``kea-dhcp6`` — The DHCPv6 server process. This process responds to
+   DHCPv6 queries from clients.
+
+-  ``kea-dhcp-ddns`` — The DHCP Dynamic DNS process. This process acts
+   as an intermediary between the DHCP servers and external DNS servers. It
+   receives name update requests from the DHCP servers and sends DNS
+   update messages to the DNS servers.
+
+-  ``kea-admin`` — This is a useful tool for database backend maintenance
+   (creating a new database, checking versions, upgrading, etc.).
+
+-  ``kea-lfc`` — This process removes redundant information from the
+   files used to provide persistent storage for the memfile database
+   backend. While it can be run standalone, it is normally run as and
+   when required by the Kea DHCP servers.
+
+-  ``kea-ctrl-agent`` — The Kea Control Agent (CA) is a daemon that exposes
+   a RESTful control interface for managing Kea servers.
+
+-  ``kea-netconf`` - kea-netconf is an agent that provides a
+   YANG/NETCONF interface for configuring Kea.
+
+-  ``kea-shell`` — This simple text client uses the REST interface to
+   connect to the Kea Control Agent.
+
+-  ``perfdhcp`` — This is a DHCP benchmarking tool which simulates multiple
+   clients to test both DHCPv4 and DHCPv6 server performance.
+
+The tools and modules are covered in full detail in this guide. In
+addition, manual pages are also provided in the default installation.
+
+Kea also provides C++ libraries and programmer interfaces for DHCP.
+These include detailed developer documentation and code examples.
diff --git a/doc/sphinx/arm/keactrl.rst b/doc/sphinx/arm/keactrl.rst
new file mode 100644
index 0000000..f2b382e
--- /dev/null
+++ b/doc/sphinx/arm/keactrl.rst
@@ -0,0 +1,358 @@
+.. _keactrl:
+
+*****************************
+Managing Kea with ``keactrl``
+*****************************
+
+.. _keactrl-overview:
+
+Overview
+========
+
+``keactrl`` is a shell script which controls the startup, shutdown, and
+reconfiguration of the Kea servers (``kea-dhcp4``, ``kea-dhcp6``,
+``kea-dhcp-ddns``, ``kea-ctrl-agent``, and ``kea-netconf``). It also
+provides the means for checking the current status of the servers and
+determining the configuration files in use.
+
+``keactrl`` is available only when Kea is built from sources. When installing
+Kea using native packages, the native ``systemd`` scripts are provided. See
+:ref:`systemd` Section for details.
+
+.. _keactrl-usage:
+
+Command Line Options
+====================
+
+``keactrl`` is run as follows:
+
+.. code-block:: console
+
+   # keactrl <command> [-c keactrl-config-file] [-s server[,server,...]]
+
+``<command>`` is one of the commands described in :ref:`keactrl-commands`.
+
+The optional ``-c keactrl-config-file`` switch allows specification of
+an alternate ``keactrl`` configuration file. (``--ctrl-config`` is a
+synonym for ``-c``.) In the absence of ``-c``, ``keactrl`` uses the
+default configuration file ``[kea-install-dir]/etc/kea/keactrl.conf``.
+
+The optional ``-s server[,server,...]`` switch selects the servers to
+which the command is issued. (``--server`` is a synonym for ``-s``.) If
+absent, the command is sent to all servers enabled in the ``keactrl``
+configuration file. If multiple servers are specified, they should be
+separated by commas with no intervening spaces.
+
+.. _keactrl-config-file:
+
+The ``keactrl`` Configuration File
+==================================
+
+Depending on the administrator's requirements, it may not be
+necessary to run all of the available servers.
+The ``keactrl`` configuration file sets which servers are enabled and
+which are disabled. The default configuration file is
+``[kea-install-dir]/etc/kea/keactrl.conf``, but this can be overridden
+on a per-command basis using the ``-c`` switch.
+
+The contents of ``keactrl.conf`` are:
+
+.. code-block:: bash
+
+   # This is a configuration file for keactrl script which controls
+   # the startup, shutdown, reconfiguration and gathering the status
+   # of the Kea processes.
+
+   # prefix holds the location where the Kea is installed.
+   prefix=@prefix@
+
+   # Location of Kea configuration file.
+   kea_dhcp4_config_file=@sysconfdir@/@PACKAGE@/kea-dhcp4.conf
+   kea_dhcp6_config_file=@sysconfdir@/@PACKAGE@/kea-dhcp6.conf
+   kea_dhcp_ddns_config_file=@sysconfdir@/@PACKAGE@/kea-dhcp-ddns.conf
+   kea_ctrl_agent_config_file=@sysconfdir@/@PACKAGE@/kea-ctrl-agent.conf
+   kea_netconf_config_file=@sysconfdir@/@PACKAGE@/kea-netconf.conf
+
+   # Location of Kea binaries.
+   exec_prefix=@exec_prefix@
+   dhcp4_srv=@sbindir@/kea-dhcp4
+   dhcp6_srv=@sbindir@/kea-dhcp6
+   dhcp_ddns_srv=@sbindir@/kea-dhcp-ddns
+   ctrl_agent_srv=@sbindir@/kea-ctrl-agent
+   netconf_srv=@sbindir@/kea-netconf
+
+   # Start DHCPv4 server?
+   dhcp4=yes
+
+   # Start DHCPv6 server?
+   dhcp6=yes
+
+   # Start DHCP DDNS server?
+   dhcp_ddns=no
+
+   # Start Control Agent?
+   ctrl_agent=yes
+
+   # Start Netconf?
+   netconf=no
+
+   # Be verbose?
+   kea_verbose=no
+
+.. note::
+
+   In the example above, strings of the form @something@ are replaced by
+   the appropriate values when Kea is installed.
+
+Setting the ``dhcp4``, ``dhcp6``, ``dhcp_ddns``, ``ctrl_agent``, and ``netconf``
+parameters set to "yes" configures ``keactrl`` to manage (start,
+reconfigure) all servers, i.e. ``kea-dhcp4``, ``kea-dhcp6``,
+``kea-dhcp-ddns``, ``kea-ctrl-agent``, and ``kea-netconf``. When any of
+these parameters is set to "no", ``keactrl`` ignores the
+corresponding server when starting or reconfiguring Kea. Some daemons
+(dhcp_ddns and netconf) are disabled by default.
+
+By default, Kea servers managed by ``keactrl`` are located in
+``[kea-install-dir]/sbin``. This should work for most installations. If
+the default location needs to be altered, the paths
+specified with the ``dhcp4_srv``, ``dhcp6_srv``, ``dhcp_ddns_srv``,
+``ctrl_agent_srv``, and ``netconf_srv`` parameters should be modified.
+
+The ``kea_verbose`` parameter specifies the verbosity of the servers
+being started. When ``kea_verbose`` is set to "yes," the logging level of
+the server is set to DEBUG. Modification of the logging severity in a
+configuration file, as described in :ref:`logging`, will have no
+effect as long as ``kea_verbose`` is set to "yes." Setting it to
+"no" causes the server to use the logging levels specified in the
+Kea configuration file. If no logging configuration is specified, the
+default settings are used.
+
+.. note::
+
+   The verbosity for the server is set when it is started. Once started,
+   the verbosity can only be changed by stopping the server and starting
+   it again with the new value of the ``kea_verbose`` parameter.
+
+.. _keactrl-commands:
+
+Commands
+========
+
+The following commands are supported by ``keactrl``:
+
+-  ``start`` - starts the selected servers.
+
+-  ``stop`` - stops all running servers.
+
+-  ``reload`` - triggers reconfiguration of the selected servers by
+   sending the SIGHUP signal to them.
+
+-  ``status`` - returns the status of the servers (active or inactive)
+   and the names of the configuration files in use.
+
+-  ``version`` - prints out the version of the ``keactrl`` tool itself,
+   together with the versions of the Kea daemons.
+
+Typical output from ``keactrl`` when starting the servers looks similar
+to the following:
+
+.. code-block:: console
+
+   $ keactrl start
+   INFO/keactrl: Starting kea-dhcp4 -c /usr/local/etc/kea/kea-dhcp4.conf -d
+   INFO/keactrl: Starting kea-dhcp6 -c /usr/local/etc/kea/kea-dhcp6.conf -d
+   INFO/keactrl: Starting kea-dhcp-ddns -c /usr/local/etc/kea/kea-dhcp-ddns.conf -d
+   INFO/keactrl: Starting kea-ctrl-agent -c /usr/local/etc/kea/kea-ctrl-agent.conf -d
+   INFO/keactrl: Starting kea-netconf -c /usr/local/etc/kea/kea-netconf.conf -d
+
+Kea's servers create PID files upon startup. These files are used by
+``keactrl`` to determine whether a given server is running. If one or more
+servers are running when the start command is issued, the output
+looks similar to the following:
+
+.. code-block:: console
+
+   $ keactrl start
+   INFO/keactrl: kea-dhcp4 appears to be running, see: PID 10918, PID file: /usr/local/var/run/kea/kea.kea-dhcp4.pid.
+   INFO/keactrl: kea-dhcp6 appears to be running, see: PID 10924, PID file: /usr/local/var/run/kea/kea.kea-dhcp6.pid.
+   INFO/keactrl: kea-dhcp-ddns appears to be running, see: PID 10930, PID file: /usr/local/var/run/kea/kea.kea-dhcp-ddns.pid.
+   INFO/keactrl: kea-ctrl-agent appears to be running, see: PID 10931, PID file: /usr/local/var/run/kea/kea.kea-ctrl-agent.pid.
+   INFO/keactrl: kea-netconf appears to be running, see: PID 10123, PID file: /usr/local/var/run/kea/kea.kea-netconf.pid.
+
+During normal shutdowns, these PID files are deleted; they may, however,
+be left over as remnants following a system crash. It is possible,
+though highly unlikely, that upon system restart the PIDs they contain
+may actually refer to processes unrelated to Kea. This condition will
+cause ``keactrl`` to decide that the servers are running, when in fact they
+are not. In such a case the PID files listed in the ``keactrl`` output
+must be manually deleted.
+
+The following command stops all servers:
+
+.. code-block:: console
+
+   $ keactrl stop
+   INFO/keactrl: Stopping kea-dhcp4...
+   INFO/keactrl: Stopping kea-dhcp6...
+   INFO/keactrl: Stopping kea-dhcp-ddns...
+   INFO/keactrl: Stopping kea-ctrl-agent...
+   INFO/keactrl: Stopping kea-netconf...
+
+Note that the ``stop`` command attempts to stop all servers
+regardless of whether they are "enabled" in ``keactrl.conf``. If any
+of the servers are not running, an informational message is displayed as
+in the ``stop`` command output below.
+
+.. code-block:: console
+
+   $ keactrl stop
+   INFO/keactrl: kea-dhcp4 isn't running.
+   INFO/keactrl: kea-dhcp6 isn't running.
+   INFO/keactrl: kea-dhcp-ddns isn't running.
+   INFO/keactrl: kea-ctrl-agent isn't running.
+   INFO/keactrl: kea-netconf isn't running.
+
+As already mentioned, the reconfiguration of each Kea server is
+triggered by the SIGHUP signal. The ``reload`` command sends the SIGHUP
+signal to any servers that are enabled in the ``keactrl`` configuration
+file and that are currently running. When a server receives the SIGHUP signal
+it rereads its configuration file and, if the new configuration is
+valid, uses the new configuration. A reload is executed as follows:
+
+.. code-block:: console
+
+   $ keactrl reload
+   INFO/keactrl: Reloading kea-dhcp4...
+   INFO/keactrl: Reloading kea-dhcp6...
+   INFO/keactrl: Reloading kea-dhcp-ddns...
+   INFO/keactrl: Reloading kea-ctrl-agent...
+
+If any of the servers are not running, an informational message is
+displayed as in the ``reload`` command output below.
+``kea-netconf`` does not support the SIGHUP signal. If its
+configuration has changed, please stop and restart it for the change to
+take effect.
+
+.. code-block:: console
+
+   $ keactrl stop
+   INFO/keactrl: kea-dhcp4 isn't running.
+   INFO/keactrl: kea-dhcp6 isn't running.
+   INFO/keactrl: kea-dhcp-ddns isn't running.
+   INFO/keactrl: kea-ctrl-agent isn't running.
+   INFO/keactrl: kea-netconf isn't running.
+
+.. note::
+
+   NETCONF is an optional feature that is disabled by default and can be
+   enabled during compilation. If Kea was compiled without NETCONF
+   support, ``keactrl`` does not provide
+   information about it. The NETCONF entries are still present in
+   the ``keactrl.conf`` file, but NETCONF status is not shown and other
+   commands ignore it.
+
+.. note::
+
+   Currently ``keactrl`` does not report configuration failures when the
+   server is started or reconfigured. To check if the server's
+   configuration succeeded, the Kea log must be examined for errors. By
+   default, the log is written to the `syslog` file.
+
+Sometimes it is useful to check which servers are running. The
+``status`` command reports this, with typical output that looks like:
+
+.. code-block:: console
+
+   $ keactrl status
+   DHCPv4 server: active
+   DHCPv6 server: inactive
+   DHCP DDNS: active
+   Control Agent: active
+   Netconf agent: inactive
+   Kea configuration file: /usr/local/etc/kea/kea.conf
+   Kea DHCPv4 configuration file: /usr/local/etc/kea/kea-dhcp4.conf
+   Kea DHCPv6 configuration file: /usr/local/etc/kea/kea-dhcp6.conf
+   Kea DHCP DDNS configuration file: /usr/local/etc/kea/kea-dhcp-ddns.conf
+   Kea Control Agent configuration file: /usr/local/etc/kea/kea-ctrl-agent.conf
+   Kea Netconf configuration file: /usr/local/etc/kea/kea-netconf.conf
+   keactrl configuration file: /usr/local/etc/kea/keactrl.conf
+
+``keactrl status`` offers basic reporting capabilities. For more extensive insight
+into Kea's health and status, consider deploying Stork. For details, see :ref:`stork`.
+
+.. _keactrl-overriding-servers:
+
+Overriding the Server Selection
+===============================
+
+The optional ``-s`` switch allows the selection of the server(s) to which
+the ``keactrl`` command is issued. For example, the following instructs
+``keactrl`` to stop the ``kea-dhcp4`` and ``kea-dhcp6`` servers and
+leave the ``kea-dhcp-ddns`` and ``kea-ctrl-agent`` running:
+
+.. code-block:: console
+
+   $ keactrl stop -s dhcp4,dhcp6
+
+Similarly, the following starts only the ``kea-dhcp4`` and
+``kea-dhcp-ddns`` servers, but not ``kea-dhcp6`` or ``kea-ctrl-agent``.
+
+.. code-block:: console
+
+   $ keactrl start -s dhcp4,dhcp_ddns
+
+Note that the behavior of the ``-s`` switch with the ``start`` and
+``reload`` commands is different from its behavior with the ``stop``
+command. On ``start`` and ``reload``, ``keactrl`` checks whether the
+servers given as parameters to the ``-s`` switch are enabled in the
+``keactrl`` configuration file; if not, the server is ignored. For
+``stop``, however, this check is not made; the command is applied to all
+listed servers, regardless of whether they have been enabled in the
+file.
+
+The following keywords can be used with the ``-s`` command-line option:
+
+-  ``dhcp4`` for ``kea-dhcp4``.
+
+-  ``dhcp6`` for ``kea-dhcp6``.
+
+-  ``dhcp_ddns`` for ``kea-dhcp-ddns``.
+
+-  ``ctrl_agent`` for ``kea-ctrl-agent``.
+
+-  ``netconf`` for ``kea-netconf``.
+
+-  ``all`` for all servers (default).
+
+.. _systemd:
+
+Native Packages and ``systemd``
+===============================
+
+``keactrl`` is a script that was developed to assist in managing Kea processes.
+However, all modern operating systems have their own process-management scripts,
+such as ``systemd``. In general, these native scripts should be used,
+as they have several advantages. ``systemd`` scripts handle processes in a uniform
+way, so Kea is handled in a similar fashion to HTTP or a mail
+server. Second and more importantly, ``systemd`` allows dependencies to be defined
+between services. For example, it is easy to specify that the Kea server should not start
+until the network interfaces are operational. Using native scripts also has other benefits, such as
+the ability to enable or disable services using commands, and the ability to temporarily start a disabled
+service.
+
+Thus, it is recommended to use ``systemctl`` commands if they are available. Native
+Kea packages do not provide ``keactrl``; ``systemctl`` service definitions are
+provided instead. Consult the system documentation for details.
+
+Briefly, here are example commands to check status, start, stop, and restart various Kea daemons:
+
+.. code-block:: console
+
+   # systemctl status isc-kea-ctrl-agent
+   # systemctl start isc-kea-dhcp4-server
+   # systemctl stop isc-kea-dhcp6-server
+   # systemctl restart isc-kea-dhcp-ddns-server
+
+Note that the service names may be slightly different between Linux distributions; in general,
+we have followed the naming conventions in third-party packages. In particular,
+some systems may not have the `isc-` prefix.
diff --git a/doc/sphinx/arm/lease-expiration.rst b/doc/sphinx/arm/lease-expiration.rst
new file mode 100644
index 0000000..9deaa3b
--- /dev/null
+++ b/doc/sphinx/arm/lease-expiration.rst
@@ -0,0 +1,330 @@
+.. _lease-expiration:
+
+****************
+Lease Expiration
+****************
+
+The primary role of the DHCP server is to assign addresses and/or
+delegate prefixes to DHCP clients. These addresses and prefixes are
+often referred to as "leases." Leases are typically assigned to clients
+for a finite amount of time, known as the "valid lifetime." DHCP clients
+who wish to continue using their assigned leases periodically renew
+them by sending the appropriate message to the DHCP server. The DHCP
+server records the time when these leases are renewed and calculates new
+expiration times for them.
+
+If the client does not renew a lease before its valid lifetime elapses,
+the lease is considered expired. There are many situations when the
+client may cease lease renewals; common scenarios include when the machine
+running the client shuts down for an extended period of time, or when a
+mobile device leaves the vicinity of a network.
+
+The process through which the DHCP server makes expired leases available
+for reassignment is referred to as "lease reclamation," and expired
+leases returned to availability through this process are referred to as
+"reclaimed." The DHCP server attempts to reclaim an expired lease as
+soon as it detects that it has expired. The server has several possible
+ways to detect expiration: it may attempt to allocate a lease to a
+client but find this lease already present in the database and expired;
+or it can periodically query the lease database for expired leases.
+Regardless of how an expired lease is detected, it must be reclaimed
+before it can be assigned to a client.
+
+This chapter explains how to configure the server to periodically query
+for the expired leases, and how to minimize the impact of the periodic
+lease-reclamation process on the server's responsiveness. Finally, it
+explains "lease affinity," which provides the means to assign the same
+lease to a returning client after its lease has expired.
+
+Although all configuration examples in this section are provided for the
+DHCPv4 server, the same parameters may be used for DHCPv6 server
+configuration.
+
+.. _lease-reclamation:
+
+Lease Reclamation
+=================
+
+Lease reclamation is the process through which an expired lease becomes
+available for assignment to the same or a different client. This process
+involves the following steps for each reclaimed lease:
+
+-  Invoke callouts for the ``lease4_expire`` or ``lease6_expire`` hook
+   points, if hook libraries supporting those callouts are currently
+   loaded.
+
+-  Update the DNS, i.e. remove any DNS entries associated with the
+   expired lease.
+
+-  Update lease information in the lease database to indicate that the
+   lease is now available for reassignment.
+
+-  Update counters on the server, a process that includes increasing the
+   number of reclaimed leases and decreasing the number of assigned
+   addresses or delegated prefixes.
+
+Please refer to :ref:`dhcp-ddns-server` to see how to configure DNS
+updates in Kea, and to :ref:`hooks-libraries` for information about
+using hooks libraries.
+
+.. _lease-reclamation-defaults:
+
+Lease Reclamation Configuration Parameters
+==========================================
+
+The following list presents all the configuration parameters pertaining to
+processing expired leases, with their default values:
+
+-  ``reclaim-timer-wait-time`` - this parameter governs intervals
+   between the completion of the previous reclamation cycle and the start of the
+   next one. Specified in seconds; the default value is 10.
+
+-  ``flush-reclaimed-timer-wait-time`` - this parameter controls how
+   often the server initiates the lease reclamation procedure. Expressed in
+   seconds; the default value is 25.
+
+-  ``hold-reclaimed-time`` - this parameter governs how long the lease
+   should be kept after it is reclaimed. This enables lease affinity
+   when set to a non-zero value. Expressed in seconds; the default value
+   is 3600.
+
+-  ``max-reclaim-leases`` - this parameter specifies the maximum number
+   of reclaimed leases that can be processed at one time. Zero means
+   unlimited (i.e. process all reclaimed leases). The default value is
+   100.
+
+-  ``max-reclaim-time`` - this parameter specifies an upper limit to the
+   length of time a lease reclamation procedure can take. Zero means no time
+   limit. Expressed in milliseconds; the default value is 250.
+
+-  ``unwarned-reclaim-cycles`` - if lease reclamation limits are
+   specified (``max-reclaim-leases`` and/or ``max-reclaim-time``), then
+   under certain circumstances the server may not be able to deal with
+   the leases to be reclaimed fast enough. This parameter specifies how many
+   consecutive clean-up cycles must end with remaining leases to be
+   processed before a warning is printed. The default is 5 cycles.
+
+The parameters are explained in more detail in the rest of this chapter.
+
+The default value for any parameter is used when the parameter is not
+explicitly specified in the configuration. If the
+``expired-leases-processing`` map is omitted entirely in the
+configuration, the default values are used for all
+parameters listed above.
+
+.. _lease-reclaim-config:
+
+Configuring Lease Reclamation
+=============================
+
+Kea can be configured to periodically detect and reclaim expired leases.
+During this process the lease entries in the database are modified or
+removed. While this is happening the server does not process incoming
+DHCP messages, to avoid issues with concurrent access to database
+information. As a result, the server is unresponsive while lease
+reclamation is performed and DHCP queries will accumulate; responses
+will be sent once the lease-reclamation cycle is complete.
+
+In deployments where response time is critical, administrators may wish
+to minimize the interruptions in service caused by lease reclamation.
+To this end, Kea provides configuration parameters to control the
+frequency of lease reclamation cycles, the maximum number of leases
+processed in a single reclamation cycle, and the maximum amount of time
+a single reclamation cycle is allowed to run before being interrupted.
+The following examples demonstrate how these parameters can be used:
+
+::
+
+   "Dhcp4": {
+       ...
+
+       "expired-leases-processing": {
+           "reclaim-timer-wait-time": 5,
+           "max-reclaim-leases": 0,
+           "max-reclaim-time": 0,
+       },
+
+       ...
+   }
+
+The first parameter is expressed in seconds and specifies an interval
+between the two consecutive lease reclamation cycles. This is explained
+by the following diagram:
+
+::
+
+
+   |  c1  |            | c2 |            |c3|            | c4 |
+   |<---->|<---------->|<-->|<---------->|<>|<---------->|<-->|<--
+   ------------------------------------------------------------------>
+   |      |     5s     |    |     5s     |  |     5s     |    | time
+
+This diagram shows four lease-reclamation cycles (c1 through c4) of
+variable duration. The duration of the reclamation cycle
+depends on the number of expired leases detected and processed in a
+particular cycle. This duration is usually significantly shorter than
+the interval between the cycles.
+
+According to the ``reclaim-timer-wait-time``, the server keeps fixed
+intervals of five seconds between the end of one cycle and the start of
+the next cycle. This guarantees the presence of 5-second-long periods during
+which the server remains responsive to DHCP queries and does not perform
+lease reclamation. The ``max-reclaim-leases`` and ``max-reclaim-time``
+are set to 0, which sets no restriction on the maximum number of leases
+reclaimed in the particular cycle, or on the maximum duration of each
+cycle.
+
+In deployments with high lease-pool utilization, relatively short valid
+lifetimes, and frequently disconnecting clients which allow leases to
+expire, the number of expired leases requiring reclamation at any given
+time may rise significantly. In this case, it is often desirable to
+apply restrictions to the maximum duration of a reclamation cycle or the
+maximum number of leases reclaimed in a cycle. The following
+configuration demonstrates how this can be done:
+
+::
+
+   "Dhcp4": {
+       ...
+
+       "expired-leases-processing": {
+           "reclaim-timer-wait-time": 3,
+           "max-reclaim-leases": 100,
+           "max-reclaim-time": 50,
+           "unwarned-reclaim-cycles": 10,
+       },
+
+       ...
+   }
+
+In this example, the ``max-reclaim-leases`` parameter limits the number of leases
+reclaimed in a single cycle to 100, and the ``max-reclaim-time`` limits the
+maximum duration of each cycle to 50ms. The lease-reclamation cycle will
+be interrupted if either of these limitations is reached. The
+reclamation of any unreclaimed leases will be attempted in subsequent
+cycles.
+
+The following diagram illustrates the behavior of the system in the
+presence of many expired leases, when the limits are applied for the
+reclamation cycles:
+
+::
+
+
+   | c1 |                | c2 |                | c3 |                | c4 |
+   |<-->|<-------------->|<-->|<-------------->|<-->|<-------------->|<-->|<--
+   ------------------------------------------------------------------------------>
+   |50ms|       3s       |50ms|       3s       |50ms|       3s       |50ms|  time
+
+In this case, if any reclamation cycle takes
+more than 50ms, it is interrupted according to the value of the
+``max-reclaim-time``. This results in equal durations of all reclamation
+cycles over time. In this example, the limitation of the
+maximum 100 leases is not reached. This may be the case when database
+transactions or callouts in the hook libraries attached to the
+server are slow. Regardless, the chosen values for either the maximum
+number of leases or a maximum cycle time strongly depend on the
+particular deployment, the lease database backend being used, any
+hook libraries, etc. Administrators may need to experiment to tune the
+system to suit the dynamics of their deployment.
+
+It is important to realize that with the use of these limits, there is a
+risk that expired leases will accumulate faster than the server can
+reclaim them. This should not be a problem if the server is dealing with
+a temporary burst of expirations, because it should be able to
+eventually deal with them over time. However, if leases expire at a high
+rate for a long period of time, the unreclaimed leases will pile up in
+the database. To notify the administrator that the current configuration
+does not satisfy the needs for reclamation of expired leases, the server
+issues a warning message in the log if it is unable to reclaim all
+leases within several reclamation cycles. The number of cycles after
+which such a warning is issued is specified with the
+``unwarned-reclaim-cycles`` configuration parameter.
+
+Setting the ``reclaim-timer-wait-time`` to 0 disables periodic
+reclamation of the expired leases.
+
+.. _lease-affinity:
+
+Configuring Lease Affinity
+==========================
+
+Suppose that a laptop goes into sleep mode after a period of user
+inactivity. While the laptop is in sleep mode, its DHCP client does not
+renew leases obtained from the server and these leases will eventually
+expire. When the laptop wakes up, it is often desirable for it to
+continue using its previous assigned IP addresses. To facilitate this,
+the server needs to correlate returning clients with their expired
+leases. When the client returns, the server first checks for those
+leases and reassigns them if they have not been assigned to another
+client. The ability of the server to reassign the same lease to a
+returning client is referred to as "lease affinity."
+
+When lease affinity is enabled (i.e. when ``hold-reclaimed-time`` is
+configured to a value greater than zero), the server still reclaims
+leases according to the parameters described in :ref:`lease-reclaim-config`,
+but the reclaimed leases are
+held in the database for a specified amount of
+time rather than removed. When the client returns, the server first verifies whether
+there are any reclaimed leases associated with this client and then
+reassigns them if possible. However, it is important to note that any
+reclaimed lease may be assigned to another client if that client
+specifically asks for it. Therefore, lease affinity does not guarantee
+that the reclaimed lease will be available for the client who used it
+before; it merely increases the chances of the client being assigned
+the same lease. If the lease pool is small - namely, in
+DHCPv4, for which address space is limited - there is an increased
+likelihood that the expired lease will be assigned to another client.
+
+Consider the following configuration:
+
+::
+
+   "Dhcp4": {
+       ...
+
+       "expired-leases-processing": {
+           "reclaim-timer-wait-time": 3,
+           "hold-reclaimed-time": 1800,
+           "flush-reclaimed-timer-wait-time": 5
+       },
+
+       ...
+   }
+
+The ``hold-reclaim-time`` specifies how many seconds after an expiration
+a reclaimed lease should be held in the database for reassignment to
+the same client. In the example given above, reclaimed leases are
+held for 30 minutes (1800 seconds) after their expiration. During this time,
+the server will likely be able to reassign the same lease to the
+returning client, unless another client specifically requests this lease and the
+server assigns it.
+
+The server must periodically remove reclaimed leases for which the time
+indicated by ``hold-reclaim-time`` has elapsed. The
+``flush-reclaimed-timer-wait-time`` parameter controls how often the
+server removes such leases. In the example provided above, the server
+initiates removal of such leases five seconds after the previous
+removal attempt was completed. Setting this value to 0 disables lease
+affinity, meaning leases are removed from the lease database
+when they are reclaimed. If lease affinity is enabled, it is recommended
+that the ``hold-reclaim-time`` be set to a value significantly higher than
+the ``reclaim-timer-wait-time``, as timely removal of expired-reclaimed
+leases is less critical than the removal process, which may impact
+server responsiveness.
+
+There is no guarantee that lease affinity will work every time; if a
+server is running out of addresses, it will reassign expired addresses
+to new clients. Also, clients can request specific addresses and the
+server tries to honor such requests if possible. Administrators who want to
+ensure a client keeps its address, even after periods of inactivity,
+should consider using host reservations or leases with very long lifetimes.
+
+.. _leases-reclamation-using-command:
+
+Reclaiming Expired Leases via Command
+=====================================
+
+The ``leases-reclaim`` command can be used to trigger lease reclamation at
+any time. Please consult the :ref:`command-leases-reclaim` section
+for details about using this command.
diff --git a/doc/sphinx/arm/lfc.rst b/doc/sphinx/arm/lfc.rst
new file mode 100644
index 0000000..dfe3e24
--- /dev/null
+++ b/doc/sphinx/arm/lfc.rst
@@ -0,0 +1,73 @@
+.. _kea-lfc:
+
+***************
+The LFC Process
+***************
+
+.. _kea-lfc-overview:
+
+Overview
+========
+
+``kea-lfc`` is a service process that removes redundant information from
+the files used to provide persistent storage for the memfile database
+backend. This service is written to run as a standalone process.
+
+While ``kea-lfc`` can be started externally, there is usually no need to
+do so. ``kea-lfc`` is run on a periodic basis by the Kea DHCP servers.
+
+The process operates on a set of files, using them to receive input and
+output of the lease entries and to indicate what stage the process is
+in, in the event of an interruption. Currently the caller must supply
+names for all of the files.
+
+.. _kea-lfc-usage:
+
+Command-Line Options
+====================
+
+``kea-lfc`` is run as follows:
+
+::
+
+   kea-lfc [-4 | -6] -c config-file -p pid-file -x previous-file -i copy-file -o output-file -f finish-file
+
+The argument ``-4`` or ``-6`` selects the protocol version of the lease
+files.
+
+The ``-c`` argument specifies the configuration file. This is required,
+but is not currently used by the process.
+
+The ``-p`` argument specifies the PID file. When the ``kea-lfc`` process
+starts, it attempts to determine whether another instance of the process
+is already running by examining the PID file. If one is already running,
+the new process is terminated; if one is not running, Kea writes its PID
+into the PID file.
+
+The other filenames specify where the ``kea-lfc`` process should look
+for input, write its output, and perform its bookkeeping:
+
+-  ``previous`` — when ``kea-lfc`` starts, this is the result of any
+   previous run of ``kea-lfc``. When ``kea-lfc`` finishes, it is the
+   result of this run. If ``kea-lfc`` is interrupted before completing,
+   this file may not exist.
+
+-  ``input`` — before the DHCP server invokes ``kea-lfc``, it moves
+   the current lease file here and then calls ``kea-lfc`` with this file.
+
+-  ``output`` — this is the temporary file where ``kea-lfc`` writes the
+   leases. Once the file has finished writing, it is moved to the
+   ``finish`` file (see below).
+
+-  ``finish`` — this is another temporary file ``kea-lfc`` uses for
+   bookkeeping. When ``kea-lfc`` completes writing the ``output`` file, it
+   moves the contents to the file of this name. After ``kea-lfc`` finishes deleting the
+   other files (``previous`` and ``input``), it moves this file to the ``previous``
+   lease file. By moving the files in this fashion, ``kea-lfc`` and
+   the DHCP server processes can determine the correct file to use even
+   if one of the processes is interrupted before completing its task.
+
+There are several additional arguments, mostly for debugging purposes.
+``-d`` sets the logging level to debug. ``-v`` and ``-V`` print out
+version stamps, with ``-V`` providing a longer form. ``-h`` prints out
+the usage string.
diff --git a/doc/sphinx/arm/logging.rst b/doc/sphinx/arm/logging.rst
new file mode 100644
index 0000000..8847545
--- /dev/null
+++ b/doc/sphinx/arm/logging.rst
@@ -0,0 +1,912 @@
+.. _logging:
+
+*******
+Logging
+*******
+
+Logging Configuration
+=====================
+
+During its operation Kea may produce many log messages. They differ in
+severity (some are more important than others) and source (different
+components, like hooks, produce different messages). It is useful to
+understand which log messages are critical and which are not, and to
+configure logging appropriately. For example, debug-level messages
+can be safely ignored in a typical deployment. They are, however, very
+useful when debugging a problem.
+
+The logging system in Kea is configured through the ``loggers`` entry in the
+server section of the configuration file.
+
+Loggers
+-------
+
+Within Kea, a message is logged through an entity called a "logger."
+Different components log messages through different loggers, and each
+logger can be configured independently of the others. Some components,
+in particular the DHCP server processes, may use multiple loggers to log
+messages pertaining to different logical functions of the component. For
+example, the DHCPv4 server uses one logger for messages about packet
+reception and transmission, another logger for messages related to lease
+allocation, and so on. Some of the libraries used by the Kea server,
+such as libdhcpsrv, use their own loggers.
+
+Users implementing hook libraries (code attached to the server at
+runtime) are responsible for creating the loggers used by those
+libraries. Such loggers should have unique names, different from the
+logger names used by Kea. That way, the messages produced by the hook
+library can be distinguished from messages issued by the core Kea code.
+Unique names also allow the hook loggers to be configured independently of
+loggers used by Kea. Whenever it makes sense, a hook library can use
+multiple loggers to log messages pertaining to different logical parts
+of the library.
+
+In the server section of a configuration file, the
+configuration for zero or more loggers (including loggers used by the
+proprietary hook libraries) can be specified. If there are no loggers specified, the
+code uses default values; these cause Kea to log messages of INFO
+severity or greater to standard output. There is a small time window
+after Kea has been started but before it has read its configuration;
+logging in this short period can be controlled using environment
+variables. For details, see :ref:`logging-during-startup`.
+
+The three main elements of a logger configuration are: ``name`` (the
+component that is generating the messages), ``severity`` (what to log),
+and ``output_commands`` (where to log). There is also a ``debuglevel``
+element, which is only relevant if debug-level logging has been
+selected.
+
+The ``name`` (string) Logger
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Each logger in the system has a name: that of the component binary file
+using it to log messages. For instance, to configure logging
+for the DHCPv4 server, add an entry for a logger named “kea-dhcp4”.
+This configuration will then be used by the loggers in the DHCPv4
+server and all the libraries used by it, unless a library defines its
+own logger and there is a specific logger configuration that applies to
+that logger.
+
+When tracking down an issue with the server's operation, use of DEBUG
+logging is required to obtain the verbose output needed for problem
+diagnosis. However, the high verbosity is likely to overwhelm the
+logging system in cases where the server is processing high-volume
+traffic. To mitigate this problem, Kea can use multiple loggers, for
+different functional parts of the server, that can each be configured
+independently. If the user is reasonably confident that a problem
+originates in a specific function of the server, or that the problem is
+related to a specific type of operation, they may enable high verbosity
+only for the relevant logger, thereby limiting the DEBUG messages to the
+required minimum.
+
+The loggers are associated with a particular library or binary of Kea.
+However, each library or binary may (and usually does) include multiple
+loggers. For example, the DHCPv4 server binary contains separate loggers
+for packet parsing, dropped packets, callouts, etc.
+
+The loggers form a hierarchy. For each program in Kea, there is a "root"
+logger, named after the program (e.g. the root logger for ``kea-dhcp4``, the
+DHCPv4 server, is named ``kea-dhcp4``). All other loggers are children of
+this logger and are named accordingly, e.g. the allocation engine in the
+DHCPv4 server logs messages using a logger called
+``kea-dhcp4.alloc-engine``.
+
+This relationship is important, as each child logger derives its default
+configuration from its parent root logger. In the typical case, the root
+logger configuration is the only logging configuration specified in the
+configuration file and so applies to all loggers. If an entry is made
+for a given logger, any attributes specified override those of the root
+logger, whereas any not specified are inherited from it.
+
+To illustrate this, suppose we are using the DHCPv4 server with the
+root logger ``kea-dhcp4`` logging at the INFO level. In order to enable
+DEBUG verbosity for DHCPv4 packet drops, we must create a configuration
+entry for the logger called "kea-dhcp4.bad-packets” and specify severity
+DEBUG for this logger. All other configuration parameters may be omitted
+for this logger if the logger should use the default values specified in
+the root logger's configuration.
+
+If there are multiple logger specifications in the configuration that
+might match a particular logger, the specification with the more
+specific logger name takes precedence. For example, if there are entries
+for both ``kea-dhcp4`` and ``kea-dhcp4.dhcpsrv``, the main DHCPv4 server
+program — and all libraries it uses other than the ``dhcpsrv`` library
+(libdhcpsrv) — logs messages according to the configuration in the
+first entry (``kea-dhcp4``). Messages generated by the ``dhcpsrv`` library
+are logged according to the configuration set by the second entry.
+
+Currently defined loggers are listed in the following table. The
+"Software Package" column of this table specifies whether the particular
+loggers belong to the core Kea code (open source Kea binaries and
+libraries), or hook libraries (open source or premium).
+
+.. tabularcolumns:: |p{0.2\linewidth}|p{0.2\linewidth}|p{0.6\linewidth}|
+
+.. table:: List of loggers supported by Kea servers and hook libraries shipped with Kea/premium packages
+   :class: longtable
+   :widths: 20 20 60
+
+   +----------------------------------+------------------------+--------------------------------+
+   | Logger Name                      | Software Package       | Description                    |
+   +==================================+========================+================================+
+   | ``kea-ctrl-agent``               | core                   | The root logger for            |
+   |                                  |                        | the Control Agent              |
+   |                                  |                        | exposing the RESTful           |
+   |                                  |                        | control API. All               |
+   |                                  |                        | components used by             |
+   |                                  |                        | the Control Agent              |
+   |                                  |                        | inherit the settings           |
+   |                                  |                        | from this logger.              |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-ctrl-agent.auth``          | core                   | A logger which covers          |
+   |                                  |                        | access control details, such as|
+   |                                  |                        | a result of the basic HTTP     |
+   |                                  |                        | authentication.                |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-ctrl-agent.http``          | core                   | A logger which                 |
+   |                                  |                        | outputs log messages           |
+   |                                  |                        | related to receiving,          |
+   |                                  |                        | parsing, and sending           |
+   |                                  |                        | HTTP messages.                 |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4``                    | core                   | The root logger for            |
+   |                                  |                        | the DHCPv4 server.             |
+   |                                  |                        | All components used            |
+   |                                  |                        | by the DHCPv4 server           |
+   |                                  |                        | inherit the settings           |
+   |                                  |                        | from this logger.              |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp6``                    | core                   | The root logger for            |
+   |                                  |                        | the DHCPv6 server.             |
+   |                                  |                        | All components used            |
+   |                                  |                        | by the DHCPv6 server           |
+   |                                  |                        | inherit the settings           |
+   |                                  |                        | from this logger.              |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.alloc-engine``,      | core                   | Used by the lease              |
+   | ``kea-dhcp6.alloc-engine``       |                        | allocation engine,             |
+   |                                  |                        | which is responsible           |
+   |                                  |                        | for managing leases            |
+   |                                  |                        | in the lease                   |
+   |                                  |                        | database, i.e.                 |
+   |                                  |                        | creating, modifying,           |
+   |                                  |                        | and removing DHCP              |
+   |                                  |                        | leases as a result of          |
+   |                                  |                        | processing messages            |
+   |                                  |                        | from clients.                  |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.bad-packets``,       | core                   | Used by the DHCP               |
+   | ``kea-dhcp6.bad-packets``        |                        | servers for logging            |
+   |                                  |                        | inbound client                 |
+   |                                  |                        | packets that were              |
+   |                                  |                        | dropped or to which            |
+   |                                  |                        | the server responded           |
+   |                                  |                        | with a DHCPNAK. It             |
+   |                                  |                        | allows administrators          |
+   |                                  |                        | to configure a                 |
+   |                                  |                        | separate log output            |
+   |                                  |                        | that contains only             |
+   |                                  |                        | packet drop and                |
+   |                                  |                        | reject entries.                |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.bootp-hooks``        | libdhcp_bootp          | This logger is used to log     |
+   |                                  | hook library           | messages related to the        |
+   |                                  |                        | operation of the BOOTP hook    |
+   |                                  |                        | library.                       |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.callouts``,          | core                   | Used to log messages           |
+   | ``kea-dhcp6.callouts``           |                        | pertaining to the              |
+   |                                  |                        | callouts registration          |
+   |                                  |                        | and execution for the          |
+   |                                  |                        | particular hook                |
+   |                                  |                        | point.                         |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.commands``,          | core                   | Used to log messages           |
+   | ``kea-dhcp6.commands``           |                        | relating to the                |
+   |                                  |                        | handling of commands           |
+   |                                  |                        | received by the DHCP           |
+   |                                  |                        | server over the                |
+   |                                  |                        | command channel.               |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.database``,          | core                   | Used to log messages           |
+   | ``kea-dhcp6.database``           |                        | relating to general            |
+   |                                  |                        | operations on the              |
+   |                                  |                        | relational databases.          |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.ddns``,              | core                   | Used by the DHCP               |
+   | ``kea-dhcp6.ddns``               |                        | server to log                  |
+   |                                  |                        | messages related to            |
+   |                                  |                        | Client FQDN and                |
+   |                                  |                        | Hostname option                |
+   |                                  |                        | processing. It also            |
+   |                                  |                        | includes log messages          |
+   |                                  |                        | related to the                 |
+   |                                  |                        | relevant DNS updates.          |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.dhcp4``              | core                   | Used by the DHCPv4             |
+   |                                  |                        | server daemon to log           |
+   |                                  |                        | basic operations.              |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.dhcpsrv``,           | core                   | The base loggers for           |
+   | ``kea-dhcp6.dhcpsrv``            |                        | the ``libkea-dhcpsrv``         |
+   |                                  |                        | library.                       |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.eval``,              | core                   | Used to log messages           |
+   | ``kea-dhcp6.eval``               |                        | relating to the                |
+   |                                  |                        | client classification          |
+   |                                  |                        | expression evaluation          |
+   |                                  |                        | code.                          |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.host-cache-hooks``,  | libdhcp_host_cache     | Used                           |
+   | ``kea-dhcp6.host-cache-hooks``   | premium hook library   | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the Host          |
+   |                                  |                        | Cache hook library.            |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.flex-id-hooks``,     | libdhcp_flex_id        | Used                           |
+   | ``kea-dhcp6.flex-id-hooks``      | premium hook library   | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the               |
+   |                                  |                        | Flexible Identifier            |
+   |                                  |                        | hook library.                  |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.ha-hooks``,          | libdhcp_ha hook        | Used                           |
+   | ``kea-dhcp6.ha-hooks``           | library                | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the High          |
+   |                                  |                        | Availability hook              |
+   |                                  |                        | library.                       |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.hooks``,             | core                   | Used to log messages           |
+   | ``kea-dhcp6.hooks``              |                        | related to the                 |
+   |                                  |                        | management of hook             |
+   |                                  |                        | libraries, e.g.                |
+   |                                  |                        | registration and               |
+   |                                  |                        | deregistration of the          |
+   |                                  |                        | libraries, and to the          |
+   |                                  |                        | initialization of the          |
+   |                                  |                        | callouts execution             |
+   |                                  |                        | for various hook               |
+   |                                  |                        | points within the              |
+   |                                  |                        | DHCP server.                   |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.host-cmds-hooks``,   | libdhcp_host_cmds      | Used                           |
+   | ``kea-dhcp6.host-cmds-hooks``    | premium hook library   | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the Host          |
+   |                                  |                        | Commands hook                  |
+   |                                  |                        | library. In general,           |
+   |                                  |                        | these pertain to               |
+   |                                  |                        | the loading and                |
+   |                                  |                        | unloading of the               |
+   |                                  |                        | library and the                |
+   |                                  |                        | execution of commands          |
+   |                                  |                        | by the library.                |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.hosts``,             | core                   | Used within                    |
+   | ``kea-dhcp6.hosts``              |                        | ``libdhcpsrv``, it logs        |
+   |                                  |                        | messages related to            |
+   |                                  |                        | the management of              |
+   |                                  |                        | DHCP host                      |
+   |                                  |                        | reservations, i.e.             |
+   |                                  |                        | retrieving                     |
+   |                                  |                        | reservations and               |
+   |                                  |                        | adding new                     |
+   |                                  |                        | reservations.                  |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.lease-cmds-hooks``,  | libdhcp_lease_cmds     | Used                           |
+   | ``kea-dhcp6.lease-cmds-hooks``   | hook library           | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the               |
+   |                                  |                        | Lease Commands hook            |
+   |                                  |                        | library. In general,           |
+   |                                  |                        | these pertain to               |
+   |                                  |                        | the loading and                |
+   |                                  |                        | unloading of the               |
+   |                                  |                        | library and the                |
+   |                                  |                        | execution of commands          |
+   |                                  |                        | by the library.                |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.leases``,            | core                   | Used by the DHCP               |
+   | ``kea-dhcp6.leases``             |                        | server to log                  |
+   |                                  |                        | messages related to            |
+   |                                  |                        | lease allocation. The          |
+   |                                  |                        | messages include               |
+   |                                  |                        | detailed information           |
+   |                                  |                        | about the allocated            |
+   |                                  |                        | or offered leases,             |
+   |                                  |                        | errors during the              |
+   |                                  |                        | lease allocation,              |
+   |                                  |                        | etc.                           |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.legal-log-hooks``,   | libdhcp_legal_log      | Used                           |
+   | ``kea-dhcp6.legal-log-hooks``    | premium hook library   | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the               |
+   |                                  |                        | Forensic Logging               |
+   |                                  |                        | hook library.                  |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.options``,           | core                   | Used by the DHCP               |
+   | ``kea-dhcp6.options``            |                        | server to log                  |
+   |                                  |                        | messages related to            |
+   |                                  |                        | the processing of              |
+   |                                  |                        | options in the DHCP            |
+   |                                  |                        | messages, i.e.                 |
+   |                                  |                        | parsing options,               |
+   |                                  |                        | encoding options into          |
+   |                                  |                        | on-wire format, and            |
+   |                                  |                        | packet classification          |
+   |                                  |                        | using options                  |
+   |                                  |                        | contained in the               |
+   |                                  |                        | received packets.              |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.packets``,           | core                   | Mostly                         |
+   | ``kea-dhcp6.packets``            |                        | used to log messages           |
+   |                                  |                        | related to                     |
+   |                                  |                        | transmission of the            |
+   |                                  |                        | DHCP packets, i.e.             |
+   |                                  |                        | packet reception and           |
+   |                                  |                        | the sending of a               |
+   |                                  |                        | response. Such                 |
+   |                                  |                        | messages include               |
+   |                                  |                        | information about the          |
+   |                                  |                        | source and                     |
+   |                                  |                        | destination IP                 |
+   |                                  |                        | addresses and                  |
+   |                                  |                        | interfaces used to             |
+   |                                  |                        | transmit packets. The          |
+   |                                  |                        | logger is also used            |
+   |                                  |                        | to log messages                |
+   |                                  |                        | related to subnet              |
+   |                                  |                        | selection, as this             |
+   |                                  |                        | selection is usually           |
+   |                                  |                        | based on the IP                |
+   |                                  |                        | addresses, relay               |
+   |                                  |                        | addresses, and/or              |
+   |                                  |                        | interface names,               |
+   |                                  |                        | which can be                   |
+   |                                  |                        | retrieved from the             |
+   |                                  |                        | received packet even           |
+   |                                  |                        | before the DHCP                |
+   |                                  |                        | message carried in             |
+   |                                  |                        | the packet is parsed.          |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.radius-hooks``,      | libdhcp_radius         | Used                           |
+   | ``kea-dhcp6.radius-hooks``       | premium hook library   | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the               |
+   |                                  |                        | RADIUS hook library.           |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.stat-cmds-hooks``,   | libdhcp_stat_cmds      | Used                           |
+   | ``kea-dhcp6.stat-cmds-hooks``    | hook library           | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the               |
+   |                                  |                        | Statistics Commands            |
+   |                                  |                        | hook library. In               |
+   |                                  |                        | general, these                 |
+   |                                  |                        | pertain to loading             |
+   |                                  |                        | and unloading the              |
+   |                                  |                        | library and the                |
+   |                                  |                        | execution of commands          |
+   |                                  |                        | by the library.                |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.subnet-cmds-hooks``, | libdhcp_subnet_cmds    | Used                           |
+   | ``kea-dhcp6.subnet-cmds-hooks``  | hook library           | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the               |
+   |                                  |                        | Subnet Commands hook           |
+   |                                  |                        | library. In general,           |
+   |                                  |                        | these pertain to               |
+   |                                  |                        | loading and unloading          |
+   |                                  |                        | the library and the            |
+   |                                  |                        | execution of commands          |
+   |                                  |                        | by the library.                |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.mysql-cb-hooks``,    | libdhcp_mysql_cb_hooks | Used                           |
+   | ``kea-dhcp6.mysql-cb-hooks``     | hook library           | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the               |
+   |                                  |                        | MySQL Configuration            |
+   |                                  |                        | Backend hook                   |
+   |                                  |                        | library.                       |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp-ddns``                | core                   | The root logger for            |
+   |                                  |                        | the ``kea-dhcp-ddns``          |
+   |                                  |                        | daemon. All                    |
+   |                                  |                        | components used by             |
+   |                                  |                        | this daemon inherit            |
+   |                                  |                        | the settings from              |
+   |                                  |                        | this logger unless             |
+   |                                  |                        | there are                      |
+   |                                  |                        | configurations for             |
+   |                                  |                        | more specialized               |
+   |                                  |                        | loggers.                       |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp-ddns.dctl``           | core                   | Used by                        |
+   |                                  |                        | the ``kea-dhcp-ddns``          |
+   |                                  |                        | daemon to log                  |
+   |                                  |                        | basic information              |
+   |                                  |                        | about the process,             |
+   |                                  |                        | received signals, and          |
+   |                                  |                        | triggered                      |
+   |                                  |                        | reconfigurations.              |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp-ddns.dhcpddns``       | core                   | Used by                        |
+   |                                  |                        | the ``kea-dhcp-ddns``          |
+   |                                  |                        | daemon to log                  |
+   |                                  |                        | events related to              |
+   |                                  |                        | DDNS operations.               |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp-ddns.dhcp-to-d2``     | core                   | Used by the                    |
+   |                                  |                        | ``kea-dhcp-ddns`` daemon       |
+   |                                  |                        | to log                         |
+   |                                  |                        | information about              |
+   |                                  |                        | events dealing with            |
+   |                                  |                        | receiving messages             |
+   |                                  |                        | from the DHCP servers          |
+   |                                  |                        | and adding them to             |
+   |                                  |                        | the queue for                  |
+   |                                  |                        | processing.                    |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp-ddns.d2-to-dns``      | core                   | Used by the                    |
+   |                                  |                        | ``kea-dhcp-ddns`` daemon       |
+   |                                  |                        | to log                         |
+   |                                  |                        | information about              |
+   |                                  |                        | events dealing with            |
+   |                                  |                        | sending and receiving          |
+   |                                  |                        | messages to and from           |
+   |                                  |                        | the DNS servers.               |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-netconf``                  | core                   | The root logger for            |
+   |                                  |                        | the NETCONF agent.             |
+   |                                  |                        | All components used            |
+   |                                  |                        | by NETCONF inherit             |
+   |                                  |                        | the settings from              |
+   |                                  |                        | this logger if there           |
+   |                                  |                        | is no specialized              |
+   |                                  |                        | logger provided.               |
+   +----------------------------------+------------------------+--------------------------------+
+   | ``kea-dhcp4.lease-query-hooks``, | libdhcp_lease_query    | Used                           |
+   | ``kea-dhcp6.lease-query-hooks``  | hook library           | to log messages                |
+   |                                  |                        | related to the                 |
+   |                                  |                        | operation of the               |
+   |                                  |                        | Leasequery hook library.       |
+   +----------------------------------+------------------------+--------------------------------+
+
+Note that user-defined hook libraries should not use any of the loggers
+mentioned above, but should instead define new loggers with names that
+correspond to the libraries using them. Suppose that a user created
+a library called “libdhcp-packet-capture” to dump packets received and
+transmitted by the server to a file. An appropriate name for the
+logger could be ``kea-dhcp4.packet-capture-hooks``. (Note that the hook
+library implementer only specifies the second part of this name, i.e.
+“packet-capture”. The first part is a root-logger name and is prepended
+by the Kea logging system.) It is also important to note that since this
+new logger is a child of a root logger, it inherits the configuration
+from the root logger, something that can be overridden by an entry in
+the configuration file.
+
+The easiest way to find a logger name is to configure all logging to go
+to a single destination and look there for specific logger names. See
+:ref:`logging-message-format` for details.
+
+The ``severity`` (string) Logger
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This specifies the category of messages logged. Each message is logged
+with an associated severity, which may be one of the following (in
+descending order of severity):
+
+-  FATAL - associated with messages generated by a condition that is so
+   serious that the server cannot continue executing.
+
+-  ERROR - associated with messages generated by an error condition. The
+   server continues executing, but the results may not be as
+   expected.
+
+-  WARN - indicates an out-of-the-ordinary condition. However, the
+   server continues executing normally.
+
+-  INFO - an informational message marking some event.
+
+-  DEBUG - messages produced for debugging purposes.
+
+When the severity of a logger is set to one of these values, it
+only logs messages of that severity and above (e.g. setting the logging
+severity to INFO logs INFO, WARN, ERROR, and FATAL messages). The
+severity may also be set to NONE, in which case all messages from that
+logger are inhibited.
+
+.. note::
+
+   The ``keactrl`` tool, described in :ref:`keactrl`, can be configured
+   to start the servers in verbose mode. If this is the case, the
+   settings of the logging severity in the configuration file have
+   no effect; the servers use a logging severity of DEBUG
+   regardless of the logging settings specified in the configuration
+   file. To control severity via the configuration file,
+   please make sure that the ``kea_verbose`` value is set to "no" within
+   the ``keactrl`` configuration.
+
+.. _debuglevel:
+
+The ``debuglevel`` (integer) Logger
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When a logger's severity is set to DEBUG, this value specifies the
+level of debug messages to be printed. It ranges from 0 (least
+verbose) to 99 (most verbose). If severity for the logger is not DEBUG,
+this value is ignored.
+
+The ``output_options`` (list) Logger
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Each logger can have zero or more ``output_options``. These specify
+where log messages are sent and are explained in detail below.
+
+The ``output`` (string) Option
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This value determines the type of output. There are several special
+values allowed here: ``stdout`` (messages are printed on standard
+output), ``stderr`` (messages are printed on stderr), ``syslog``
+(messages are logged to syslog using the default name), ``syslog:name``
+(messages are logged to syslog using a specified name). Any other value is
+interpreted as a filename to which messages should be written.
+
+The ``flush`` (boolean) Option
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This flushes the buffers after each log message. Doing this reduces performance
+but ensures that if the program terminates abnormally, all messages
+up to the point of termination are output. The default is ``true``.
+
+The ``maxsize`` (integer) Option
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This option is only relevant when the destination is a file; this is the maximum size
+in bytes that a log file may reach. When the maximum size is reached,
+the file is renamed and a new file created. Initially, a ".1" is
+appended to the name; if a ".1" file exists, it is renamed ".2", etc.
+This is referred to as rotation.
+
+The default value is 10240000 (10MB). The smallest value that can be
+specified without disabling rotation is 204800. Any value less than
+this, including 0, disables rotation. The greatest possible value is INT_MAX MB, which is
+approximately 2PB.
+
+.. note::
+
+   Due to a limitation of the underlying logging library (log4cplus),
+   rolling over the log files (from ".1" to ".2", etc.) may show odd
+   results; there can be multiple small files at the timing of rollover.
+   This can happen when multiple processes try to roll over the
+   files simultaneously. Version 1.1.0 of log4cplus solved this problem,
+   so if this version or later of log4cplus is used to build Kea, the
+   issue should not occur. Even with older versions, it is normally
+   expected to happen rarely unless the log messages are produced very
+   frequently by multiple different processes.
+
+The ``maxver`` (integer) Option
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This option is only relevant when the destination is a file and rotation is enabled
+(i.e. maxsize is large enough). This is the maximum number of rotated
+versions that will be kept. Once that number of files has been reached,
+the oldest file, "log-name.maxver", is discarded each time the log
+rotates. In other words, at most there will be the active log file plus
+maxver rotated files. The minimum and default value is 1.
+
+The ``pattern`` (string) Option
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This option can be used to specify the layout pattern of messages for
+a logger. Kea logging is implemented using the log4cplus library and its
+output formatting is based, conceptually, on the printf formatting from C;
+this is discussed in detail in the next section,
+:ref:`logging-message-format`.
+
+Each output type (``stdout``, file, or ``syslog``) has a default ``pattern`` which
+describes the content of its log messages. This parameter can be used to
+specify a desired pattern. The pattern for each logger is governed
+individually, so each configured logger can have its own pattern. Omitting
+the ``pattern`` parameter or setting it to an empty string, "", causes
+Kea to use the default pattern for that logger's output type.
+
+In addition to the log text itself, the default patterns used for ``stdout``
+and files contain information such as date and time, logger level, and
+process information. The default pattern for ``syslog`` is limited primarily
+to log level, source, and the log text. This avoids duplicating information
+which is usually supplied by syslog.
+
+.. warning::
+    Users are strongly encouraged to test their pattern(s) on a local,
+    non-production instance of Kea, running in the foreground and
+    logging to ``stdout``.
+
+.. _logging-message-format:
+
+Logging Message Format
+----------------------
+
+As mentioned above, Kea log message content is controlled via a scheme similar
+to the C language's printf formatting. The "pattern" used for each message is
+described by a string containing one or more format components as part of a
+text string.  In addition to the components, the string may contain any other
+useful text for the administrator.
+
+The behavior of Kea's format strings is determined by log4cplus. The following
+format options are possible:
+
+.. table:: List of supported format string components by Kea's logger
+   :class: longtable
+   :widths: 8 40
+
+   +-----------+-----------------------------------------------+
+   | Component | Value                                         |
+   +===========+===============================================+
+   | ``%a``    | Abbreviated weekday name                      |
+   +-----------+-----------------------------------------------+
+   | ``%A``    | Full weekday name                             |
+   +-----------+-----------------------------------------------+
+   | ``%b``    | Abbreviated month name                        |
+   +-----------+-----------------------------------------------+
+   | ``%B``    | Full month name                               |
+   +-----------+-----------------------------------------------+
+   | ``%c``    | Standard date and time string                 |
+   +-----------+-----------------------------------------------+
+   | ``%d``    | Day of month as a decimal(1-31)               |
+   +-----------+-----------------------------------------------+
+   | ``%H``    | Hour(0-23)                                    |
+   +-----------+-----------------------------------------------+
+   | ``%I``    | Hour(1-12)                                    |
+   +-----------+-----------------------------------------------+
+   | ``%j``    | Day of year as a decimal(1-366)               |
+   +-----------+-----------------------------------------------+
+   | ``%m``    | Month as decimal(1-12)                        |
+   +-----------+-----------------------------------------------+
+   | ``%M``    | Minute as decimal(0-59)                       |
+   +-----------+-----------------------------------------------+
+   | ``%p``    | Locale's equivalent of AM or PM               |
+   +-----------+-----------------------------------------------+
+   | ``%q``    | milliseconds as decimal(0-999)                |
+   +-----------+-----------------------------------------------+
+   | ``%Q``    | microseconds as decimal(0-999.999)            |
+   +-----------+-----------------------------------------------+
+   | ``%S``    | Second as decimal(0-59)                       |
+   +-----------+-----------------------------------------------+
+   | ``%U``    | Week of year, Sunday being first day(0-53)    |
+   +-----------+-----------------------------------------------+
+   | ``%w``    | Weekday as a decimal(0-6, Sunday being 0)     |
+   +-----------+-----------------------------------------------+
+   | ``%W``    | Week of year, Monday being first day(0-53)    |
+   +-----------+-----------------------------------------------+
+   | ``%x``    | Standard date string                          |
+   +-----------+-----------------------------------------------+
+   | ``%X``    | Standard time string                          |
+   +-----------+-----------------------------------------------+
+   | ``%y``    | Year in decimal without century(0-99)         |
+   +-----------+-----------------------------------------------+
+   | ``%Y``    | Year including century as decimal             |
+   +-----------+-----------------------------------------------+
+   | ``%Z``    | Time zone name                                |
+   +-----------+-----------------------------------------------+
+   | ``%%``    | The percent sign                              |
+   +-----------+-----------------------------------------------+
+
+Refer to the documentation for the ``strftime()`` function found in the
+``<ctime>`` header or the ``strftime(3)`` UNIX manual page for more
+information.
+
+It is probably easiest to understand this by examining the default pattern
+for stdout and files; currently they are the same. That pattern is shown
+below:
+
+::
+
+    "%D{%Y-%m-%d %H:%M:%S.%q} %-5p [%c/%i.%t] %m\n";
+
+and a typical log produced by this pattern looks something like this:
+
+::
+
+    2019-08-05 14:27:45.871 DEBUG [kea-dhcp4.dhcpsrv/8475.12345] DHCPSRV_TIMERMGR_START_TIMER starting timer: reclaim-expired-leases
+
+That breaks down to:
+
+  - ``%D{%Y-%m-%d %H:%M:%S.%q}``
+    "%D" is the local date and time when the log message is generated,
+    while everything between the curly braces, "{}", are date and time components.
+    From the example log above this produces:
+    ``2019-08-05 14:27:45.871``
+
+  - ``%-5p``
+    The severity of the message, output as a minimum of five characters,
+    using right-padding with spaces. In our example log: ``DEBUG``
+
+  - ``%c``
+    The log source. This includes two elements: the Kea process generating the
+    message, in this case, ``kea-dhcp4``; and the component within the program
+    from which the message originated, ``dhcpsrv`` (e.g.  the name of the
+    library used by DHCP server implementations).
+
+  - ``%i``
+    The process ID. From the example log: ``8475``.
+
+  - ``%t``
+    The thread ID. From the example log: ``12345``.
+    The format of the thread ID is OS-dependent: e.g. on some systems
+    it is an address, so it is displayed in hexadecimal.
+
+  - ``%m``
+    The log message itself. Kea log messages all begin with a message identifier
+    followed by arbitrary log text. Every message in Kea has a unique
+    identifier, which can be used as an index to the :ref:`kea-messages`, where
+    more information can be obtained. In our example log above, the identifier
+    is ``DHCPSRV_TIMERMGR_START_TIMER``. The log text is typically a brief
+    description detailing the condition that caused the message to be logged. In
+    our example, the information logged,
+    ``starting timer: reclaim-expired-leases``, explains that the timer for the
+    expired lease reclamation cycle has been started.
+
+.. Warning::
+
+    Omitting ``%m`` omits the log message text from the output, making it
+    rather useless. ``%m`` should be considered mandatory.
+
+Finally, note that spacing between components, the square brackets around the
+log source and PID, and the final carriage return ``\n`` are all literal text
+specified as part of the pattern.
+
+.. Warning::
+
+    To ensure that each log entry is a separate line, patterns
+    must end with an ``\n``. There may be use cases where it is not desired
+    so we do not enforce its inclusion. If it is omitted from
+    the pattern, the log entries will run together in one long "line".
+
+The default pattern for ``syslog`` output is:
+
+::
+
+    "%-5p [%c.%t] %m\n";
+
+It omits the date and time as well as the process ID, as this
+information is typically output by ``syslog``. Note that Kea uses the pattern
+to construct the text it sends to ``syslog`` (or any other destination). It has
+no influence on the content ``syslog`` may add or formatting it may do.
+
+Consult the OS documentation for ``syslog`` behavior, as there are multiple
+implementations.
+
+
+Example Logger Configurations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In this example, we want to set the server logging to write to the
+console using standard output.
+
+::
+
+   "Server": {
+       "loggers": [
+           {
+               "name": "kea-dhcp4",
+               "output_options": [
+                   {
+                       "output": "stdout"
+                   }
+               ],
+               "severity": "WARN"
+           }
+       ]
+   }
+
+As a second example, we want to store DEBUG log messages in a file
+that is at most 2MB and keep up to eight copies of old log files. Once the
+logfile grows to 2MB, it should be renamed and a new file should be created.
+
+::
+
+   "Server": {
+       "loggers": [
+           {
+               "name": "kea-dhcp6",
+               "output_options": [
+                   {
+                       "output": "/var/log/kea-debug.log",
+                       "maxver": 8,
+                       "maxsize": 204800,
+                       "flush": true
+                       "pattern": "%d{%j %H:%M:%S.%q} %c %m\n"
+                   }
+               ],
+               "severity": "DEBUG",
+               "debuglevel": 99
+           }
+      ]
+   }
+
+Notice that the above configuration uses a custom pattern which produces output like this:
+
+::
+
+    220 13:50:31.783 kea-dhcp4.dhcp4 DHCP4_STARTED Kea DHCPv4 server version 1.6.0-beta2-git started
+
+
+.. _logging-during-startup:
+
+Logging During Kea Startup
+--------------------------
+
+The logging configuration is specified in the configuration file.
+However, when Kea starts, the configuration file is not read until partway into the
+initialization process. Prior to that, the logging settings are set to
+default values, although it is possible to modify some aspects of the
+settings by means of environment variables. In the absence of
+any logging configuration in the configuration file, the settings of the
+(possibly modified) default configuration will persist while the program
+is running.
+
+The following environment variables can be used to control the behavior
+of logging during startup:
+
+``KEA_LOCKFILE_DIR``
+
+   Specifies a directory where the logging system should create its lock
+   file. If not specified, it is prefix/var/run/kea, where "prefix"
+   defaults to /usr/local. This variable must not end with a slash.
+   There is one special value: "none", which instructs Kea not to create
+   a lock file at all. This may cause issues if several processes log to
+   the same file.
+
+``KEA_LOGGER_DESTINATION``
+
+   Specifies logging output. There are several special values:
+
+   ``stdout``
+   Log to standard output.
+
+   ``stderr``
+   Log to standard error.
+
+   ``syslog[:fac]``
+   Log via syslog. The optional "fac" (which is separated from the word
+   "syslog" by a colon) specifies the facility to be used for the log
+   messages. Unless specified, messages are logged using the
+   facility "local0".
+
+   Any other value is treated as a name of the output file. If not
+   otherwise specified, Kea logs to standard output.
+
+Logging Levels
+==============
+
+All Kea servers follow the overall intention to let the user
+know what is going on while not overloading the logging system with too much information, as that
+could easily be used as a denial-of-service attack.
+
+Unlike the FATAL, ERROR, WARN and
+INFO levels, DEBUG has additional parameters. The following list details
+the basic information that is logged on each level. Sometimes the circumstances
+determine whether a piece of information is logged on a higher
+or lower level. For example, if a packet is being dropped due to configured classification, that
+is an execution of the configured policy and would be logged on debuglevel 15. However, if the
+packet is dropped due to an exception being thrown, it is much more important, as it may indicate
+a software bug, serious problems with memory, or database connectivity problems. As such it may
+be logged on much higher levels, such as WARN or even ERROR.
+
+- 0 - singular messages printed during startup or shutdown of the server.
+- 10 - log information about received API commands.
+- 15 - information about reasons why a packet was dropped.
+- 40 - tracing information, including processing decisions, results
+  of expression evaluations, and more.
+- 45 - similar to level 40, but with more details, e.g. the subnet being
+  selected for an incoming packet.
+- 50 - evaluations of expressions, status received from hook points, lease
+  processing, packet processing details, including unpacking, packing, sending, etc.
+- 55 - includes all details available, including full packet contents
+  with all options printed.
+
+The debug levels apply only to messages logged on DEBUG, and are configured using
+the ``debuglevel`` option. See the :ref:`debuglevel` section for details.
diff --git a/doc/sphinx/arm/quickstart.rst b/doc/sphinx/arm/quickstart.rst
new file mode 100644
index 0000000..7433535
--- /dev/null
+++ b/doc/sphinx/arm/quickstart.rst
@@ -0,0 +1,191 @@
+.. _quickstart:
+
+***********
+Quick Start
+***********
+
+This section describes the basic steps needed to get Kea up and running.
+For further details, full customizations, and troubleshooting, see the
+respective chapters elsewhere in this Kea Administrator Reference Manual (ARM).
+
+.. _quick-start-tarball:
+
+Quick Start Guide Using tarball
+===============================
+
+1.  Install required runtime and build dependencies. See
+    :ref:`build-requirements` for details.
+
+2.  Download the Kea source tarball from the `ISC.org downloads
+    page <https://www.isc.org/download/>`__ or the `ISC downloads site
+    <https://downloads.isc.org/isc/kea/>`__.
+
+3.  Extract the tarball. For example:
+
+    .. parsed-literal::
+
+       $ tar -xvzf kea-|release|.tar.gz
+
+4.  Go into the source directory and run the configure script:
+
+    .. parsed-literal::
+
+       $ cd kea-|release|
+       $ ./configure [your extra parameters]
+
+5.  Build it:
+
+    .. code-block:: console
+
+       $ make
+
+6.  Install it (by default it will be placed in ``/usr/local/``, so
+    root privileges are likely required for this step):
+
+    .. code-block:: console
+
+       $ make install
+
+.. _quick-start-repo:
+
+Quick Start Guide Using Native Packages
+=======================================
+
+ISC provides native Alpine, deb, and RPM packages, which make Kea installation
+much easier. Unless specific compilation options are desired, it is usually
+easier to install Kea using native packages.
+
+1. Go to `Kea on cloudsmith.io <https://cloudsmith.io/~isc/repos/>`__,
+   choose the Kea version, and enter the repository.
+
+2. Use ``Set Me Up`` and follow instructions to add the repository
+   to the local system.
+
+3. Update system repositories. For example:
+
+    .. code-block:: console
+
+        $ apt-get update
+
+4. Kea is split into various packages. The entire list is available on
+   `cloudsmith.io <https://cloudsmith.io/~isc/repos/>`__  or using apt/yum/dnf.
+   For example:
+
+    .. code-block:: console
+
+        $ apt-cache search isc-kea
+
+5. Install specific packages:
+
+    .. code-block:: console
+
+        $ sudo apt-get install isc-kea-dhcp6-server
+
+   or all packages:
+
+    .. code-block:: console
+
+        $ sudo apt-get install isc-kea*
+
+   or all packages with a specified version number:
+
+    .. code-block:: console
+
+        $ sudo apt-get install isc-kea*=1.8.1-isc0000920201106154401
+
+6. All installed packages should be now available directly; for example:
+
+    .. code-block:: console
+
+       # kea-dhcp6 -c /path/to/your/kea6/config/file.json
+
+   or using systemd:
+
+    .. code-block:: console
+
+       # systemctl restart isc-kea-dhcp6-server
+
+   ``keactrl`` is not available in packages as similar functionality is provided
+   by the native systemctl scripts.
+
+.. _quick-start-services:
+
+Quick Start Guide for DHCPv4 and DHCPv6 Services
+================================================
+1.  Edit the Kea configuration files, which by default are installed in
+    the ``[kea-install-dir]/etc/kea/`` directory. These are:
+    ``kea-dhcp4.conf``, ``kea-dhcp6.conf``, ``kea-dhcp-ddns.conf`` and
+    ``kea-ctrl-agent.conf``, ``keactrl.conf`` for DHCPv4 server, DHCPv6 server,
+    D2, Control Agent, and the keactrl script, respectively.
+
+2.  To start the DHCPv4 server in the background, run the
+    following command (as root):
+
+    .. code-block:: console
+
+       # keactrl start -s dhcp4
+
+    Or run the following command to start the DHCPv6 server:
+
+    .. code-block:: console
+
+       # keactrl start -s dhcp6
+
+    Note that it is also possible to start all servers simultaneously:
+
+    .. code-block:: console
+
+       # keactrl start
+
+3.  Verify that the Kea server(s) is/are running:
+
+    .. code-block:: console
+
+       # keactrl status
+
+    A server status of "inactive" may indicate a configuration error.
+    Please check the log file (by default named
+    ``[kea-install-dir]/var/log/kea-dhcp4.log``,
+    ``[kea-install-dir]/var/log/kea-dhcp6.log``,
+    ``[kea-install-dir]/var/log/kea-ddns.log``, or
+    ``[kea-install-dir]/var/log/kea-ctrl-agent.log``) for the details of
+    any errors.
+
+4.  If the server has started successfully, test that it is
+    responding to DHCP queries and that the client receives a
+    configuration from the server; for example, use the `ISC DHCP
+    client <https://www.isc.org/download/>`__.
+
+5.  To stop running the server(s):
+
+    .. code-block:: console
+
+       # keactrl stop
+
+For system-specific instructions, please read the
+`system-specific notes <https://kb.isc.org/docs/installing-kea>`__,
+available in the Kea section of `ISC's
+Knowledgebase <https://kb.isc.org/docs>`__.
+
+The details of ``keactrl`` script usage can be found in :ref:`keactrl`.
+
+Once Kea services are up and running, consider deploying a dashboard solution
+to monitor running services. For more details, see :ref:`stork`.
+
+.. _quick-start-direct-run:
+
+Running the Kea Servers Directly
+================================
+
+The Kea servers can be started directly, without the need to use
+``keactrl`` or ``systemctl``. To start the DHCPv4 server run the following command:
+
+.. code-block:: console
+
+   # kea-dhcp4 -c /path/to/your/kea4/config/file.json
+
+Similarly, to start the DHCPv6 server, run the following command:
+
+.. code-block:: console
+
+   # kea-dhcp6 -c /path/to/your/kea6/config/file.json
diff --git a/doc/sphinx/arm/rst_arm_sources.mk b/doc/sphinx/arm/rst_arm_sources.mk
new file mode 100644
index 0000000..77305b7
--- /dev/null
+++ b/doc/sphinx/arm/rst_arm_sources.mk
@@ -0,0 +1,51 @@
+rst_arm_sources += arm/acknowledgments.rst
+rst_arm_sources += arm/admin.rst
+rst_arm_sources += arm/agent.rst
+rst_arm_sources += arm/classify.rst
+rst_arm_sources += arm/config-backend.rst
+rst_arm_sources += arm/config-templates.rst
+rst_arm_sources += arm/config.rst
+rst_arm_sources += arm/congestion-handling.rst
+rst_arm_sources += arm/ctrl-channel.rst
+rst_arm_sources += arm/database-connectivity.rst
+rst_arm_sources += arm/ddns.rst
+rst_arm_sources += arm/dhcp4-srv.rst
+rst_arm_sources += arm/dhcp6-srv.rst
+rst_arm_sources += arm/ext-gss-tsig.rst
+rst_arm_sources += arm/ext-netconf.rst
+rst_arm_sources += arm/hammer.rst
+rst_arm_sources += arm/hooks-bootp.rst
+rst_arm_sources += arm/hooks-cb-cmds.rst
+rst_arm_sources += arm/hooks-class-cmds.rst
+rst_arm_sources += arm/hooks-ddns-tuning.rst
+rst_arm_sources += arm/hooks-flex-id.rst
+rst_arm_sources += arm/hooks-flex-option.rst
+rst_arm_sources += arm/hooks-gss-tsig.rst
+rst_arm_sources += arm/hooks-ha.rst
+rst_arm_sources += arm/hooks-host-cache.rst
+rst_arm_sources += arm/hooks-host-cmds.rst
+rst_arm_sources += arm/hooks-lease-cmds.rst
+rst_arm_sources += arm/hooks-lease-query.rst
+rst_arm_sources += arm/hooks-limits.rst
+rst_arm_sources += arm/hooks-cb-mysql.rst
+rst_arm_sources += arm/hooks-cb-pgsql.rst
+rst_arm_sources += arm/hooks-legal-log.rst
+rst_arm_sources += arm/hooks-radius.rst
+rst_arm_sources += arm/hooks-rbac.rst
+rst_arm_sources += arm/hooks-run-script.rst
+rst_arm_sources += arm/hooks-stat-cmds.rst
+rst_arm_sources += arm/hooks-subnet-cmds.rst
+rst_arm_sources += arm/hooks-user-chk.rst
+rst_arm_sources += arm/hooks.rst
+rst_arm_sources += arm/install.rst
+rst_arm_sources += arm/integrations.rst
+rst_arm_sources += arm/intro.rst
+rst_arm_sources += arm/keactrl.rst
+rst_arm_sources += arm/lease-expiration.rst
+rst_arm_sources += arm/lfc.rst
+rst_arm_sources += arm/logging.rst
+rst_arm_sources += arm/quickstart.rst
+rst_arm_sources += arm/security.rst
+rst_arm_sources += arm/shell.rst
+rst_arm_sources += arm/stats.rst
+rst_arm_sources += arm/stork.rst
diff --git a/doc/sphinx/arm/security.rst b/doc/sphinx/arm/security.rst
new file mode 100644
index 0000000..ec7baa6
--- /dev/null
+++ b/doc/sphinx/arm/security.rst
@@ -0,0 +1,388 @@
+.. _security:
+
+************
+Kea Security
+************
+
+Kea was originally designed to be installed in a protected environment, in a network
+datacenter; it did not offer hardened security features. However, due to customer demand
+and evolving network requirements, support for basic HTTP authentication and Transport
+Layer Security (TLS) have been added to Kea.
+
+.. _tls:
+
+TLS/HTTPS Support
+=================
+
+Since Kea 1.9.6, TLS can be used to secure HTTP communication. There are three levels of
+protection possible:
+
+- No TLS. The connection is plain-text, unencrypted HTTP. (This is
+  the only option available in versions prior to Kea 1.9.6.)
+
+- Encryption, which protects against passive attacks and
+  eavesdropping. In this case, the server is authenticated but the client is
+  not. This is the typical mode when securing a website, where
+  clients and servers are not under the control of a common entity.
+
+- Mutual authentication between the client and the server. This is the
+  strictest security mode and is the default when TLS is
+  enabled.
+
+.. note::
+
+   TLS mutual authentication is for TLS entities only. When TLS and
+   an HTTP authentication scheme are used together, there is no binding between
+   the two security mechanisms, and therefore no proof that the TLS client and server
+   are the same as the HTTP authentication client and server.
+
+.. _tls_config:
+
+Building Kea with TLS/HTTPS Support
+-----------------------------------
+
+TLS/HTTPS support is available with either the OpenSSL or the Botan
+cryptographic library. There are some constraints on the Boost library
+that must be used:
+
+- OpenSSL versions older than 1.0.2 are obsolete and should not be used.
+  Kea TLS support has not been tested with and is not supported on these versions.
+
+- OpenSSL version 1.0.2 has extended support, but only for OpenSSL premium
+  customers. Kea TLS support has been tested but is not supported on this version.
+
+- OpenSSL versions 1.1.x and later have been tested and are supported. Many
+  recent operating system versions include TLS 1.3 support.
+
+- OpenSSL 3.x is not yet released; it is unknown whether Kea will build with it.
+
+- LibreSSL 3.2.4 has been tested. LibreSSL shares the OpenSSL 1.0.2 API, so
+  it should work, but is not supported.
+
+- Botan 1.x versions are obsolete and should not be used.
+  Kea TLS support has not been tested and is not supported with these versions.
+
+- Botan versions 2.14.0 and later have been tested and are supported. Kea TLS
+  support requires the four Asio header files which are included in Botan
+  packages and which are installed only if Botan is configured with the
+  ``--with-boost`` option.
+
+  Many packages provided by operating systems, such as Ubuntu 20.10,
+  do not build Botan with Boost support, making those packages
+  unusable for Kea with TLS.
+
+  It is still possible to take these files from the corresponding
+  Botan distribution and install them manually in the Botan include
+  directory, but this should be a last-resort procedure.
+
+  Without these header files, or with a Botan version prior
+  to 2.14.0, Kea can still build, but the TLS/HTTPS support is disabled;
+  any attempt to use it will fail with a fatal error.
+
+- Very old Boost versions provide SSL support (based on OpenSSL)
+  without offering a choice of the TLS version; Kea can still use them,
+  but they are not recommended.
+
+- Boost versions prior to 1.64 provide SSL support with a fixed
+  choice of the TLS version; Kea enforces the use of TLS 1.2 with them.
+
+- Boost versions 1.64 or newer provide SSL support with a generic
+  TLS version; the best (highest) version available on both peers is
+  selected.
+
+TLS/HTTPS Configuration
+-----------------------
+
+The TLS configuration parameters are:
+
+- ``trust-anchor`` - this string parameter specifies the name of a file
+  or directory where the certification authority (CA) certificate of
+  the other peer can be found. With OpenSSL, the directory must include
+  hash symbolic links. With Botan, the directory is recursively
+  searched for certificates.
+
+- ``cert-file`` - this string parameter specifies the name of the file
+  containing the end-entity certificate of the Kea instance
+  being configured.
+
+- ``key-file`` - this string parameter specifies the private key of the
+  end-entity certificate of the Kea instance being configured.
+  The file must not be encrypted; it is highly recommended to
+  restrict its access.
+
+The three string parameters must be either all unspecified (TLS disabled)
+or all specified (TLS enabled).
+
+TLS is asymmetric: the authentication of the server by the client is
+mandatory but the authentication of the client by the server is optional.
+In TLS terms, this means the server may require the client certificate, or
+may not; there is a server-specific TLS parameter.
+
+- ``cert-required`` - this boolean parameter allows a server to not
+  require the client certificate. Its default value is ``true``, which
+  means the client certificate is required and the
+  client must be authenticated. This flag has no meaning on the client side; the server
+  always provides a certificate which is validated by the client.
+
+Objects in files must be in the PEM format. Files can contain more
+than one certificate, but this has not been tested and is not supported.
+
+Botan requires CA certificates to have the standard CA certificate
+attributes, verifies that end-entity certificates are version 3
+certificates (as required by the TLS standard), and supports only PKCS 8
+files for the private key.
+
+.. note::
+
+   Some cryptographic libraries (e.g. Botan and recent OpenSSL) enforce
+   minimal strength (i.e. key length), e.g. at least 2048 for RSA.
+
+A sample set of certificates and associated objects is available at
+``src/lib/asiolink/testutils/ca`` in the Kea sources, with a ``doc.txt`` file
+explaining how they were generated using the ``openssl`` command. These
+files are for testing purposes only. **Do not use them in production.**
+
+TLS handshake, the phase where the cryptographic parameters are exchanged
+and authentication is verified, can fail in multiple ways. Error messages
+often do not help to pinpoint the source of the problem.
+Both OpenSSL and Botan provide a command-line tool with a ``verify`` command
+which can be used to understand and fix handshake issues.
+
+Securing a Kea Deployment
+=========================
+
+Below is a list of considerations for administrators wishing to improve Kea's
+security. In many cases, there are trade-offs between convenience and security.
+
+Component-Based Design
+----------------------
+
+The Kea architecture is modular, with separate daemons for separate tasks.
+A Kea deployment may include DHCPv4, DHCPv6, and Dynamic DNS daemons; a Control Agent
+daemon run on each application server; the ``kea-lfc utility`` for doing periodic lease
+file cleanup; MySQL and or PostgreSQL databases, run either locally on the application
+servers or accessed over the internal network; and a Stork monitoring system.
+This modular architecture allows the administrator to minimize the attack surface
+by minimizing the code that is loaded and running.
+For example, ``kea-dhcp-ddns`` should not be run unless DNS updates are required.
+Similarly, ``kea-lfc`` is never triggered (and can be safely removed or never installed) if memfile is not used.
+Potential Kea security issues can be minimized by running only those processes required in the local environment.
+
+Limiting Application Permissions
+--------------------------------
+
+The DHCPv4 and DHCPv6 protocols assume the server opens privileged UDP port 67
+(DHCPv4) or 547 (DHCPv6), which requires root access under normal circumstances. However, via the
+capabilities mechanism on Linux systems, Kea can run from an unprivileged account. See
+:ref:`non-root` for details on how to run Kea without root access.
+
+The Control Agent (CA) can accept incoming HTTP or HTTPS connections. The default port is 8000, which
+does not require privileged access.
+
+Securing Kea Administrative Access
+----------------------------------
+
+The three primary Kea daemons (``kea-dhcp4``, ``kea-dhcp6`` and ``kea-dhcp-ddns``) all support a control
+channel, which is implemented as a UNIX socket. The control channel, which opens a UNIX socket, is disabled by default;
+however, many configuration examples have it enabled, as it is a very popular feature. To
+read from or write to this socket, root access is generally required, although if Kea is configured
+to run as non-root, the owner of the process can write to it. Access can be controlled using normal
+file-access control on POSIX systems (owner, group, others, read/write).
+
+Kea configuration is controlled by a JSON file on the Kea server. This file can be viewed or edited
+by anyone with file permissions (which are controlled by the operating system). Note that
+passwords are stored in clear text in the configuration file, so anyone with access to read the
+configuration file can find this information. As a practical matter, anyone with permission to edit
+the configuration file has control over Kea.
+Limiting user permission to read or write the Kea configuration file is an important security step.
+
+Securing Database Connections
+-----------------------------
+
+Kea can use an external MySQL or PostgreSQL database to store configuration, host reservations,
+or/and leases, or/and for forensic logging. The use of databases is a popular feature, but it is optional;
+it is also possible to store data in a flat file on disk.
+
+When using a database, Kea stores and uses the following credentials to authenticate with the database:
+username, password, host, port, and database name. **These are stored in clear text
+in the configuration file.**
+
+Depending on the database configuration, it is also possible to verify whether the system user matches the
+database username. Consult the MySQL or PostgreSQL manual for details.
+
+Information Leakage Through Logging
+-----------------------------------
+
+It is possible for Kea to log an entire configuration file, including passwords and secrets.
+Since Kea 1.9.7, this issue has been resolved by replacing the value of all entries ending in
+``password`` or ``secret`` with asterisks, as was already done for database logs.
+
+Logs are sent to stdout, stderr, files, or syslog; system file permissions system apply to
+stdout/stderr and files. Syslog may export the logs over the network, exposing them further to possible snooping.
+
+Cryptography Components
+-----------------------
+
+Kea supports the use of either of two cryptographic libraries: Botan or OpenSSL.
+The choice is made at compile time, and creates both compile and runtime dependencies
+between the Kea and the selected library. While OpenSSL is the most popular choice for
+deployments, Botan remains a fully supported alternative.
+
+The primary use cases for the cryptographic libraries are:
+
+- TLS support for the Control Agent (CA), introduced in Kea 1.9.6.
+- TSIG signatures when sending DNS updates.
+- calculating DHCID records when sending DNS updates.
+- random number generation (but not for usage requiring a crypto grade generator).
+
+For OpenSSL and Botan, only the low-level crypto interface is used (e.g. libcrypto). Kea does not link
+with libssl. Some dependent software systems, such as database client libraries, can also depend on a crypto
+library.
+
+One way to limit exposure for potential OpenSSL or Botan vulnerabilities is not to use DDNS. The
+libraries would still be needed to build and run Kea, but the code would never be used, so any
+potential bugs in the libraries would not be exploitable.
+
+TSIG Signatures
+---------------
+
+Kea supports the following algorithms when signing DNS updates with TSIG signatures:
+
+- HMAC-MD5
+- HMAC-SHA1
+- HMAC-SHA224
+- HMAC-SHA256
+- HMAC-SHA384
+- HMAC-SHA512
+
+See :ref:`d2-tsig-key-list-config` for an up-to-date list.
+
+Kea uses SHA256 to calculate DHCID records. This is irrelevant from the cryptography perspective, as
+the DHCID record is only used to generate unique identifiers for two devices that may have been
+assigned the same IP address at different times.
+
+Raw Socket Support
+------------------
+
+In principle, Kea DHCPv4 uses raw sockets to receive traffic from clients. The difficulty is with
+receiving packets from devices that do not yet have an IPv4 address. When dealing with direct traffic
+(where both client and server are connected to the same link, not separated by relays), the kernel
+normally drops the packet as the source IP address is 0.0.0.0. Therefore, Kea needs to open raw
+sockets to be able to receive this traffic.
+
+However, this is not necessary if all the traffic is coming via relays, which is often the case in
+many networks. In that case normal UDP sockets can be used instead. There is a ``dhcp-socket-type``
+parameter that controls this behavior.
+
+The default is to permit raw socket usage, as it is more versatile.
+
+When using raw sockets, Kea is able to receive raw layer 2 packets, bypassing most firewalls
+(including iptables). This effectively means that when raw sockets are used, the iptables cannot be
+used to block DHCP traffic. This is a design choice of the Linux kernel.
+
+Kea can be switched to use UDP sockets. This is an option when all traffic is relayed.
+However, it does not work for directly connected devices. If Kea is limited to UDP sockets,
+iptables should work properly.
+
+If raw sockets are not required, disabling this access can improve security.
+
+Remote Administrative Access
+----------------------------
+
+Kea's Control Agent (CA) exposes a RESTful API over HTTP or HTTPS (HTTP over TLS). The CA is an
+optional feature that is disabled by default, but it is very popular. When enabled, it listens on the
+loopback address (127.0.0.1 or ::1) by default, unless configured otherwise. See :ref:`tls`
+for information about protecting the TLS traffic. Limiting the incoming connections with a firewall, such as
+iptables, is generally a good idea.
+
+Note that in High Availability (HA) deployments, DHCP partners connect to each other using a CA
+connection.
+
+Authentication for Kea's RESTful API
+------------------------------------
+
+Kea 1.9.0 added support for basic HTTP authentication (`RFC 7617 <https://tools.ietf.org/html/rfc7617>`_),
+to control access for incoming REST commands over HTTP. The credentials (username, password) are
+stored in a local Kea configuration file on disk. The username is logged with the API command, so it
+is possible to determine which authenticated user performed each command. The access control details
+are logged using a dedicated ``auth`` logger. Basic HTTP
+authentication is weak on its own as there are known dictionary attacks, but those attacks require
+a "man in the middle" to get access to the HTTP traffic. That can be eliminated by using basic HTTP
+authentication exclusively over TLS. In fact, if possible, using client certificates for TLS is better than
+using basic HTTP authentication.
+
+Kea 1.9.2 introduced a new ``auth`` hook point. With this new hook point, it is possible to develop an external
+hook library to extend the access controls, integrate with another authentication authority, or add role-based
+access control to the Control Agent.
+
+Kea Security Processes
+======================
+
+The following sections discuss how the Kea DHCP development team ensures code quality and handles vulnerabilities.
+
+Vulnerability Handling
+----------------------
+
+ISC is an experienced and active participant in the industry-standard vulnerability disclosure
+process and maintains accurate documentation on our process and vulnerabilities in ISC software.
+See https://kb.isc.org/docs/aa-00861 for ISC's Software Defect and Security Vulnerability Disclosure Policy.
+
+In case of a security vulnerability in Kea, ISC notifies support customers ahead of any public
+disclosure, and provides a patch and/or updated installer package to remediate the
+vulnerability.
+
+When a security update is published, both the source tarballs and the ISC-maintained packages are
+published on the same day. This enables users of the native Linux update mechanisms (such as
+Debian's and Ubuntu's apt or RedHat's dnf) to update their systems promptly.
+
+Code Quality and Testing
+------------------------
+
+Kea undergoes extensive tests during its development. The following are some of the
+processes that are used to ensure adequate code quality:
+
+- Each line of code goes through a formal review before it is accepted. The review process is
+  documented and available publicly.
+- Roughly 50% of the source code is dedicated to unit tests. As of December 2020, there were over 6000
+  unit tests and the number is increasing with time. Unit tests are required to commit any new feature.
+- There are around 1500 system tests for Kea. These simulate both correct and invalid
+  situations, covering network packets (mostly DHCP, but also DNS, HTTP, HTTPS and others),
+  command-line usage, API calls, database interactions, scripts, and more.
+- There are performance tests with over 80 scenarios that test Kea overall performance and
+  resiliency to various levels of traffic, and measuring various metrics (latency, leases per seconds,
+  packets per seconds, CPU usage, memory utilization, and others).
+- Kea uses Continuous Integration (CI). This means that the great majority of tests (all unit and system
+  tests, and in some cases also performance tests) are run for every commit. Many "lighter" tests are
+  run on branches, before the code is even accepted.
+- Many unit and system tests check for negative scenarios, such as incomplete,
+  broken, or truncated packets, API commands, and configuration files, as well as incorrect sequences (such as sending
+  packets in an invalid order) and more.
+- The Kea development team uses many tools that perform automatic code quality checks, such as danger, as well as
+  internally developed sanity checkers.
+- The Kea team uses the following static code analyzers: Coverity Scan, shellcheck, and danger.
+- The Kea team uses the following dynamic code analyzers: Valgrind and Thread Sanitizer (TSAN).
+
+Fuzz Testing
+------------
+
+The Kea team has a process for running fuzz testing, using `AFL <https://github.com/google/AFL>`_. There
+are two modes which are run: the first mode fuzzes incoming packets, effectively throwing millions of mostly
+broken packets at Kea per day, while the second mode fuzzes configuration structures and forces Kea to
+attempt to load them. Kea has been fuzzed since around 2018 in both modes. The input seeds
+(the data being used to generate or "fuzz" other input) are changed periodically.
+
+Release Integrity
+-----------------
+
+All ISC software releases are signed with PGP and distributed via the ISC website, which is itself
+DNSSEC-signed, so users can be confident the software has not been tampered with.
+
+Bus Factor
+----------
+
+According to the `Core Infrastructure project <https://bestpractices.coreinfrastructure.org/>`_, a "bus
+factor" or "truck factor" is the minimum number of project members that have to suddenly disappear
+from a project ("be hit by a bus") before the project stalls due to lack of knowledgeable or competent
+personnel. It is hard to estimate precisely, but the bus factor for Kea is somewhere around five. As of
+2021, there are six core developers and two quality assurance engineers, with many additional casual
+contributors (product manager, support team, IT, etc.). The team is geographically dispersed.
diff --git a/doc/sphinx/arm/shell.rst b/doc/sphinx/arm/shell.rst
new file mode 100644
index 0000000..4f6a7e3
--- /dev/null
+++ b/doc/sphinx/arm/shell.rst
@@ -0,0 +1,161 @@
+.. _kea-shell:
+
+*************
+The Kea Shell
+*************
+
+.. _shell-overview:
+
+Overview of the Kea Shell
+=========================
+
+The Kea Control Agent (CA, see
+:ref:`kea-ctrl-agent`) provides a RESTful control interface
+over HTTP. That API is typically expected to be used by various IPAMs
+and similar management systems. Nevertheless, there may be cases when an
+administrator wants to send a command to the CA directly, and the Kea shell
+provides a way to do this. It is a simple command-line,
+scripting-friendly, text client that is able to connect to the CA, send
+it commands with parameters, retrieve the responses, and display them.
+
+As the primary purpose of the Kea shell is as a tool in a scripting
+environment, it is not interactive. However, by following simple guidelines it can
+be run manually.
+
+Kea 1.9.0 introduced basic HTTP authentication support.
+
+Shell Usage
+===========
+
+``kea-shell`` is run as follows:
+
+.. code-block:: console
+
+   $ kea-shell [--host hostname] [--port number] [--path path] [--auth-user] [--auth-password] [--timeout seconds] [--service service-name] [command]
+
+where:
+
+-  ``--host hostname`` specifies the hostname of the CA. If not
+   specified, "localhost" is used.
+
+-  ``--port number`` specifies the TCP port on which the CA listens. If
+   not specified, 8000 is used.
+
+-  ``--path path`` specifies the path in the URL to connect to. If not
+   specified, an empty path is used. As the CA listens at the empty
+   path, this parameter is useful only with a reverse proxy.
+
+-  ``--auth-user`` specifies the user ID for basic HTTP authentication.
+   If not specified or specified as the empty string, authentication is
+   not used.
+
+-  ``--auth-password`` specifies the password for basic HTTP authentication.
+   If not specified but the user ID is specified, an empty password is used.
+
+-  ``--timeout seconds`` specifies the timeout (in seconds) for the
+   connection. If not given, 10 seconds is used.
+
+-  ``--service service-name`` specifies the target of a command. If not
+   given, the CA is used as the target. This may be used more than once
+   to specify multiple targets.
+
+-  ``command`` specifies the command to be sent. If not specified, the
+   ``list-commands`` command is used.
+
+Other switches are:
+
+-  ``-h`` - prints a help message.
+
+-  ``-v`` - prints the software version.
+
+See :ref:`shell-tls` for new command-line arguments associated with TLS/HTTPS support.
+
+Once started, the shell reads the parameters for the command from standard
+input, which are expected to be in JSON format. When all have been read,
+the shell establishes a connection with the CA using HTTP, sends the
+command, and awaits a response. Once that is received, it is displayed
+on standard output.
+
+For a list of available commands, see :ref:`ctrl-channel`;
+additional commands may be provided by hook libraries. For a list of
+all supported commands from the CA, use the ``list-commands`` command.
+
+The following shows a simple example of usage:
+
+.. code-block:: console
+
+   $ kea-shell --host 192.0.2.1 --port 8001 --service dhcp4 list-commands
+   ^D
+
+After the command line is entered, the program waits for command
+parameters to be entered. Since ``list-commands`` does not take any
+arguments, Ctrl-D (represented in the above example by "^D")
+indicates end-of-file and terminates the parameter input. The shell
+then contacts the CA and prints out the list of available commands
+returned for the service named ``dhcp4``.
+
+The Kea shell will likely be most frequently used in
+scripts; the next example shows a simple scripted execution. It sends
+the command ``config-write`` to the CA (the ``--service`` parameter has not
+been used), along with the parameters specified in param.json. The
+result will be stored in result.json.
+
+.. code-block:: console
+
+   $ cat param.json
+   "filename": "my-config-file.json"
+   $ cat param.json | kea-shell --host 192.0.2.1 config-write > result.json
+
+When a reverse proxy is used to de-multiplex requests to different
+servers, the default empty path in the URL is not enough, so the
+``--path`` parameter should be used. For instance, if requests to the
+"/kea" path are forwarded to the CA this can be used:
+
+.. code-block:: console
+
+   $ kea-shell --host 192.0.2.1 --port 8001 --path kea ...
+
+The Kea shell requires Python to be installed on the system. It has been
+tested with Python 2.7 and various versions of Python 3, up to 3.5.
+Since not every Kea deployment uses this feature and there are
+deployments that do not have Python, the Kea shell is not enabled by
+default. To use it, specify ``--enable-shell`` when running ``configure``
+during the installation of Kea. When building on Debian systems,
+``--with-site-packages=...`` may also be useful.
+
+The Kea shell is intended to serve more as a demonstration of the
+RESTful interface's capabilities (and, perhaps, an illustration for
+people interested in integrating their management environments with Kea)
+than as a serious management client. It is not likely to be
+significantly expanded in the future; it is, and will remain, a simple
+tool.
+
+.. note::
+
+   When using this tool with basic HTTP authentication, please keep in
+   mind that command-line arguments are not hidden from local users.
+
+.. _shell-tls:
+
+TLS Support
+===========
+
+Since Kea 1.9.6, ``kea-shell`` supports HTTPS connections. The TLS/HTTPS
+support requires Python 3. The additional command-line arguments are:
+
+-  ``--ca`` specifies the file or directory name of the Certification
+   Authority. If not specified, HTTPS is not used.
+
+-  ``--cert`` specifies the file name of the user end-entity public key
+   certificate. If specified, the file name of the user key must also be specified.
+
+-  ``--key`` specifies the file name of the user key file. If specified,
+   the file name of the user certificate must also be specified.
+   Encrypted key files are not supported.
+
+For example, a basic HTTPS request to get a list of commands could
+look like this:
+
+.. code-block:: console
+
+   $ kea-shell --host 127.0.0.1 --port 8000 --ca ./kea-ca.crt list-commands
diff --git a/doc/sphinx/arm/stats.rst b/doc/sphinx/arm/stats.rst
new file mode 100644
index 0000000..1a05c30
--- /dev/null
+++ b/doc/sphinx/arm/stats.rst
@@ -0,0 +1,578 @@
+.. _stats:
+
+**********
+Statistics
+**********
+
+Statistics Overview
+===================
+
+Both Kea DHCP servers support statistics gathering. A working DHCP
+server encounters various events that can cause certain statistics to be
+collected. For example, a DHCPv4 server may receive a packet
+(the ``pkt4-received`` statistic increases by one) that after parsing is
+identified as a DHCPDISCOVER (``pkt4-discover-received``). The server
+processes it and decides to send a DHCPOFFER representing its answer
+(the ``pkt4-offer-sent`` and ``pkt4-sent statistics`` increase by one). Such
+events happen frequently, so it is not uncommon for the statistics to have
+values in the high thousands. They can serve as an easy and powerful
+tool for observing a server's and a network's health. For example, if
+the ``pkt4-received`` statistic stops growing, it means that the clients'
+packets are not reaching the server.
+
+There are four types of statistics:
+
+-  *integer* - this is the most common type. It is implemented as a
+   64-bit integer (int64_t in C++), so it can hold any value between
+   -2^63 to 2^63-1.
+
+-  *floating point* - this type is intended to store floating-point
+   precision. It is implemented as a C++ double type.
+
+-  *duration* - this type is intended for recording time periods. It
+   uses the \`boost::posix_time::time_duration type, which stores hours,
+   minutes, seconds, and microseconds.
+
+-  *string* - this type is intended for recording statistics in text
+   form. It uses the C++ std::string type.
+
+During normal operation, the DHCPv4 and DHCPv6 servers gather
+statistics. For a list of DHCPv4 and DHCPv6 statistics, see
+:ref:`dhcp4-stats` and :ref:`dhcp6-stats`, respectively.
+
+To extract data from the statistics module, the control channel can be
+used. See :ref:`ctrl-channel` for details. It is possible to
+retrieve a single statistic or all statistics, reset the statistics (i.e.
+set them to a neutral value, typically zero), or even completely remove a
+single statistic or all statistics. See the section :ref:`command-stats`
+for a list of statistics-oriented commands.
+
+Statistics can be used by external tools to monitor Kea. One example of such a tool is Stork.
+See :ref:`stork` for details on how to use it and other data sources to retrieve statistics periodically
+to get better insight into Kea's health and operational status.
+
+.. _stats-lifecycle:
+
+Statistics Lifecycle
+====================
+
+All of the statistics supported by Kea's servers are initialized upon the servers' startup
+and are returned in response to the commands such as
+``statistic-get-all``. The runtime statistics concerning DHCP packets
+processed are initially set to 0 and are reset upon the server
+restart.
+
+Per-subnet statistics are recalculated when reconfiguration takes place.
+
+In general, once a statistic is initialized it is held in the manager until
+explicitly removed, via ``statistic-remove`` or ``statistic-remove-all``,
+or when the server is shut down.
+
+Removing a statistic that is updated frequently makes little sense, as
+it will be re-added when the server code next records that statistic.
+The ``statistic-remove`` and ``statistic-remove-all`` commands are
+intended to remove statistics that are not expected to be observed in
+the near future. For example, a misconfigured device in a network may
+cause clients to report duplicate addresses, so the server will report
+increasing values of ``pkt4-decline-received``. Once the problem is found
+and the device is removed, the system administrator may want to remove
+the ``pkt4-decline-received`` statistic so that it is no longer reported, until
+and unless a duplicate address is again detected.
+
+.. _command-stats:
+
+Commands for Manipulating Statistics
+====================================
+
+There are several commands defined that can be used for accessing
+(``-get``), resetting to zero or a neutral value (``-reset``), or removing a
+statistic completely (``-remove``). The statistics time-based
+limit (``-sample-age-set``) and size-based limit (``-sample-count-set``), which
+control how long or how many samples of a given statistic are retained, can also
+be changed.
+
+The difference between ``-reset`` and ``-remove`` is somewhat subtle.
+The ``-reset`` command sets the value of the statistic to zero or a neutral value,
+so that after this operation, the statistic has a value of 0 (integer),
+0.0 (float), 0h0m0s0us (duration), or "" (string).
+When requested, a statistic with the values mentioned is returned.
+``-remove`` removes a statistic completely, so the statistic is no longer
+reported. However, the server code may add it back if there is a reason
+to record it.
+
+.. note::
+
+   The following sections describe commands that can be sent to the
+   server; the examples are not fragments of a configuration file. For
+   more information on sending commands to Kea, see
+   :ref:`ctrl-channel`.
+
+.. _command-statistic-get:
+
+The ``statistic-get`` Command
+-----------------------------
+
+The ``statistic-get`` command retrieves a single statistic. It takes a
+single-string parameter called ``name``, which specifies the statistic
+name. An example command may look like this:
+
+::
+
+   {
+       "command": "statistic-get",
+       "arguments": {
+           "name": "pkt4-received"
+       }
+   }
+
+The server returns details of the requested statistic, with a result of
+0 indicating success and the specified statistic as the value of the
+``arguments`` parameter. If the requested statistic is not found, the
+response contains an empty map, i.e. only { } as an argument, but
+the status code still indicates success (0).
+
+Here is an example response:
+
+::
+
+   {
+       "command": "statistic-get",
+       "arguments": {
+           "pkt4-received": [ [ 125, "2019-07-30 10:11:19.498739" ], [ 100, "2019-07-30 10:11:19.498662" ] ]
+       },
+       "result": 0
+   }
+
+.. _command-statistic-reset:
+
+The ``statistic-reset`` Command
+-------------------------------
+
+The ``statistic-reset`` command sets the specified statistic to its
+neutral value: 0 for integer, 0.0 for float, 0h0m0s0us for time
+duration, and "" for string type. It takes a single-string parameter
+called ``name``, which specifies the statistic name. An example command
+may look like this:
+
+::
+
+   {
+       "command": "statistic-reset",
+       "arguments": {
+           "name": "pkt4-received"
+       }
+   }
+
+If the specific statistic is found and the reset is successful, the
+server responds with a status of 0, indicating success, and an empty
+parameters field. If an error is encountered (e.g. the requested
+statistic was not found), the server returns a status code of 1 (error)
+and the text field contains the error description.
+
+.. _command-statistic-remove:
+
+The ``statistic-remove`` Command
+--------------------------------
+
+The ``statistic-remove`` command deletes a single statistic. It
+takes a single-string parameter called ``name``, which specifies the
+statistic name. An example command may look like this:
+
+::
+
+   {
+       "command": "statistic-remove",
+       "arguments": {
+           "name": "pkt4-received"
+       }
+   }
+
+If the specific statistic is found and its removal is successful, the
+server responds with a status of 0, indicating success, and an empty
+parameters field. If an error is encountered (e.g. the requested
+statistic was not found), the server returns a status code of 1 (error)
+and the text field contains the error description.
+
+.. _command-statistic-get-all:
+
+The ``statistic-get-all`` Command
+---------------------------------
+
+The ``statistic-get-all`` command retrieves all statistics recorded. An
+example command may look like this:
+
+::
+
+   {
+       "command": "statistic-get-all",
+       "arguments": { }
+   }
+
+The server responds with details of all recorded statistics, with a
+result set to 0 to indicate that it iterated over all statistics (even
+when the total number of statistics is zero).
+
+Here is an example response returning all collected statistics:
+
+::
+
+   {
+       "command": "statistic-get-all",
+       "arguments": {
+           "cumulative-assigned-addresses": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.487569"
+               ]
+           ],
+           "declined-addresses": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.487555"
+               ]
+           ],
+           "pkt4-ack-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455233"
+               ]
+           ],
+           "pkt4-ack-sent": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455256"
+               ]
+           ],
+           "pkt4-decline-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455259"
+               ]
+           ],
+           "pkt4-discover-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455263"
+               ]
+           ],
+           "pkt4-inform-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455265"
+               ]
+           ],
+           "pkt4-nak-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455269"
+               ]
+           ],
+           "pkt4-nak-sent": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455271"
+               ]
+           ],
+           "pkt4-offer-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455274"
+               ]
+           ],
+           "pkt4-offer-sent": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455277"
+               ]
+           ],
+           "pkt4-parse-failed": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455280"
+               ]
+           ],
+           "pkt4-receive-drop": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455284"
+               ]
+           ],
+           "pkt4-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455287"
+               ]
+           ],
+           "pkt4-release-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455290"
+               ]
+           ],
+           "pkt4-request-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455293"
+               ]
+           ],
+           "pkt4-sent": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455296"
+               ]
+           ],
+           "pkt4-unknown-received": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455299"
+               ]
+           ],
+           "reclaimed-declined-addresses": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.487559"
+               ]
+           ],
+           "reclaimed-leases": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.487564"
+               ]
+           ],
+           "subnet[1].assigned-addresses": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.487579"
+               ]
+           ],
+           "subnet[1].cumulative-assigned-addresses": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.487528"
+               ]
+           ],
+           "subnet[1].declined-addresses": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.487585"
+               ]
+           ],
+           "subnet[1].reclaimed-declined-addresses": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.487595"
+               ]
+           ],
+           "subnet[1].reclaimed-leases": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.487604"
+               ]
+           ],
+           "subnet[1].total-addresses": [
+               [
+                   200,
+                   "2022-02-11 17:54:17.487512"
+               ]
+           ],
+           "v4-allocation-fail": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455302"
+               ]
+           ],
+           "v4-allocation-fail-classes": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455306"
+               ]
+           ],
+           "v4-allocation-fail-no-pools": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455310"
+               ]
+           ],
+           "v4-allocation-fail-shared-network": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455319"
+               ]
+           ],
+           "v4-allocation-fail-subnet": [
+               [
+                   0,
+                   "2022-02-11 17:54:17.455323"
+               ]
+           ]
+       },
+       "result": 0
+   }
+
+.. _command-statistic-reset-all:
+
+The ``statistic-reset-all`` Command
+-----------------------------------
+
+The ``statistic-reset`` command sets all statistics to their neutral
+values: 0 for integer, 0.0 for float, 0h0m0s0us for time duration, and
+"" for string type. An example command may look like this:
+
+::
+
+   {
+       "command": "statistic-reset-all",
+       "arguments": { }
+   }
+
+If the operation is successful, the server responds with a status of 0,
+indicating success, and an empty parameters field. If an error is
+encountered, the server returns a status code of 1 (error) and the text
+field contains the error description.
+
+.. _command-statistic-remove-all:
+
+The ``statistic-remove-all`` Command
+------------------------------------
+
+The ``statistic-remove-all`` command attempts to delete all statistics. An
+example command may look like this:
+
+::
+
+   {
+       "command": "statistic-remove-all",
+       "arguments": { }
+   }
+
+If the removal of all statistics is successful, the server responds with
+a status of 0, indicating success, and an empty parameters field. If an
+error is encountered, the server returns a status code of 1 (error) and
+the text field contains the error description.
+
+.. _command-statistic-sample-age-set:
+
+The ``statistic-sample-age-set`` Command
+----------------------------------------
+
+The ``statistic-sample-age-set`` command sets a time-based limit
+on samples for a given statistic. It takes two parameters: a string
+called ``name``, which specifies the statistic name, and an integer value called
+``duration``, which specifies the time limit for the given statistic in seconds.
+An example command may look like this:
+
+::
+
+   {
+       "command": "statistic-sample-age-set",
+       "arguments": {
+           "name": "pkt4-received",
+           "duration": 1245
+       }
+
+   }
+
+If the command is successful, the server responds with a status of
+0, indicating success,
+and an empty parameters field. If an error is encountered (e.g. the
+requested statistic was not found), the server returns a status code
+of 1 (error) and the text field contains the error description.
+
+.. _command-statistic-sample-age-set-all:
+
+The ``statistic-sample-age-set-all`` Command
+--------------------------------------------
+
+The ``statistic-sample-age-set-all`` command sets time-based limits
+on samples for all statistics. It takes a single-integer parameter
+called ``duration``, which specifies the time limit for the statistic
+in seconds. An example command may look like this:
+
+::
+
+   {
+       "command": "statistic-sample-age-set-all",
+       "arguments": {
+           "duration": 1245
+       }
+
+   }
+
+If the command is successful, the server responds with a status of
+0, indicating success,
+and an empty parameters field. If an error is encountered, the server returns
+a status code of 1 (error) and the text field contains the error description.
+
+.. _command-statistic-sample-count-set:
+
+The ``statistic-sample-count-set`` Command
+------------------------------------------
+
+The ``statistic-sample-count-set`` command sets a size-based limit
+on samples for a given statistic. An example command may look
+like this:
+
+::
+
+   {
+       "command": "statistic-sample-count-set",
+       "arguments": {
+           "name": "pkt4-received",
+           "max-samples": 100
+       }
+
+   }
+
+If the command is successful, the server responds with a status of
+0, indicating success,
+and an empty parameters field. If an error is encountered (e.g. the
+requested statistic was not found), the server returns a status code
+of 1 (error) and the text field contains the error description.
+
+.. _command-statistic-sample-count-set-all:
+
+The ``statistic-sample-count-set-all`` Command
+----------------------------------------------
+
+The ``statistic-sample-count-set-all`` command sets size-based limits
+on samples for all statistics. An example command may look
+like this:
+
+::
+
+   {
+       "command": "statistic-sample-count-set-all",
+       "arguments": {
+           "max-samples": 100
+       }
+
+   }
+
+If the command is successful, the server responds with a status of
+0, indicating success,
+and an empty parameters field. If an error is encountered, the server returns
+a status code of 1 (error) and the text field contains the error description.
+
+.. _time-series:
+
+Time Series
+===========
+
+With certain statistics, a single isolated data point may be useful. However,
+some statistics, such as received
+packet size, packet processing time, or number of database queries needed to
+process a packet, are not cumulative and it is useful to keep many data
+points, perhaps to do some statistical analysis afterwards.
+
+
+Each Kea statistic holds 20 data points; setting such
+a limit prevents unlimited memory growth.
+There are two ways to define the limits: time-based (e.g. keep samples from
+the last 5 minutes) and size-based. The size-based
+limit can be changed using one of two commands: ``statistic-sample-count-set``,
+to set a size limit for a single statistic, and ``statistic-sample-count-set-all``,
+to set size-based limits for all statistics. To set time-based
+limits for a single statistic, use ``statistic-sample-age-set``; use
+``statistic-sample-age-set-all`` to set time-based limits for all statistics.
+For a given statistic only one type of limit can be active; storage
+is limited by either time or size, not both.
diff --git a/doc/sphinx/arm/stork.rst b/doc/sphinx/arm/stork.rst
new file mode 100644
index 0000000..bfa4a06
--- /dev/null
+++ b/doc/sphinx/arm/stork.rst
@@ -0,0 +1,50 @@
+.. _stork:
+
+*************************
+Monitoring Kea With Stork
+*************************
+
+Most administrators want to be able to monitor any Kea services that are running. Kea offers so many
+pieces of information - configuration files, API, statistics, logs, open database content, and more -
+that it may sometimes
+be overwhelming to keep up. ISC's Stork project is intended to address this problem for both Kea
+and BIND 9. Stork is useful in a variety of ways:
+
+- Stork can be used as a dashboard. It provides insight into what exactly is happening
+  on the servers. In particular, it allows users to: see up-to-date details regarding pool
+  utilization in subnets and shared networks; monitor the state of the HA pair (and
+  provide extra insight in case of failover and recovery events); list, filter, and
+  search for specific host reservations; and more. Only
+  a single Stork server needs to be deployed, and one Stork agent on each machine to be monitored.
+
+- The Stork agent can integrate Kea with Prometheus and Grafana. Once the Stork
+  agent is active on the server, it serves as a Prometheus exporter. Users who have deployed
+  Prometheus in their networks can visualize statistics as time series using Grafana.
+
+- Stork can act as both a dashboard and an integrator for Prometheus/Grafana. Once Stork
+  is linked to where Grafana is deployed on the network, users can inspect the current status and
+  visit a customized link to Grafana to see how a given property behaves over time.
+
+Stork is available as source code, but also as native deb and RPM packages, which makes it easy
+to install on most popular systems. For more details, please see the
+`Stork ARM <https://stork.readthedocs.io>`_ or the `Stork project page <https://gitlab.isc.org/isc-projects/stork>`_.
+The ARM has a nice collection of screenshots that is frequently updated, to give users
+an idea of what is currently available. Stork is in the midst of full development with
+monthly releases, so please check back frequently.
+
+.. _grafana:
+.. _prometheus:
+
+Kea Statistics in Grafana
+=========================
+
+The ISC Stork project provides an agent that can be deployed alongside Kea. It
+exposes Kea statistics in a format that is accepted by Prometheus.
+One of the major benefits of Prometheus is that it turns repeated one-time observations into time series,
+which lets users monitor how certain behaviors change over time. It is easy to use other tools
+to visualize data available in Prometheus; the most common approach is to use
+Grafana to provide visual dashboards. The Stork project provides dashboard
+definitions for Kea that can be imported into Grafana very easily.
+
+Learn more about Prometheus and Grafana on their websites: `Prometheus <https://prometheus.io/>`
+and `Grafana <https://grafana.com/>`.
diff --git a/doc/sphinx/conf.py b/doc/sphinx/conf.py
new file mode 100644
index 0000000..960f229
--- /dev/null
+++ b/doc/sphinx/conf.py
@@ -0,0 +1,282 @@
+# -*- coding: utf-8 -*-
+#
+# Configuration file for the Sphinx documentation builder.
+#
+# This file does only contain a selection of the most common options. For a
+# full list see the documentation:
+# http://www.sphinx-doc.org/en/master/config
+
+# -- Path setup --------------------------------------------------------------
+
+# If extensions (or modules to document with autodoc) are in another directory,
+# add these directories to sys.path here. If the directory is relative to the
+# documentation root, use os.path.abspath to make it absolute, like shown here.
+#
+import os
+# import sys
+# sys.path.insert(0, os.path.abspath('.'))
+
+# to avoid "sphinx.errors.SphinxParallelError: RecursionError: maximum recursion depth exceeded while pickling an object"
+import sys
+sys.setrecursionlimit(5000)
+
+# -- Project information -----------------------------------------------------
+
+project = 'Kea'
+copyright = '2019-2022, Internet Systems Consortium'
+author = 'Internet Systems Consortium'
+
+# get current kea version
+config_ac_path = '../../configure.ac'
+changelog_path = '../../ChangeLog'
+release = 'UNRELEASED'
+with open(config_ac_path) as f:
+    for line in f.readlines():
+        if line.startswith('AC_INIT(kea'):
+            parts = line.split(',')
+            release = parts[1]
+            # If the first line of the ChangeLog announces release, it means
+            # that this is the final release.
+            dash_parts = release.split('-')
+            candidate_release = dash_parts[0]
+            with open(changelog_path) as changelog_file:
+                first_line = changelog_file.readline()
+                if candidate_release in first_line and "released" in first_line:
+                    release = candidate_release
+            break
+version = release
+
+# -- General configuration ---------------------------------------------------
+
+# If your documentation needs a minimal Sphinx version, state it here.
+#
+# needs_sphinx = '1.0'
+
+# Add any Sphinx extension module names here, as strings. They can be
+# extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
+# ones.
+extensions = [
+    'sphinx.ext.todo',
+    'sphinx.ext.mathjax',
+]
+
+# The suffix(es) of source filenames.
+# You can specify multiple suffix as a list of string:
+#
+# source_suffix = ['.rst', '.md']
+source_suffix = '.rst'
+
+# The master toctree document.
+master_doc = 'index'
+
+# Additional docs
+messages_doc = 'kea-messages'
+
+# The language for content autogenerated by Sphinx. Refer to documentation
+# for a list of supported languages.
+#
+# This is also used if you do content translation via gettext catalogs.
+# Usually you set "language" from the command line for these cases.
+language = "en"
+
+# List of patterns, relative to source directory, that match files and
+# directories to ignore when looking for source files.
+# This pattern also affects html_static_path and html_extra_path.
+exclude_patterns = [
+    '_build', 'Thumbs.db', '.DS_Store',
+    # included files need to be excluded to avoid duplicate labels
+    'arm/platforms.rst',
+    'arm/hooks-bootp.rst',
+    'arm/hooks-class-cmds.rst',
+    'arm/hooks-cb-cmds.rst',
+    'arm/config-backend.rst',
+    'arm/hooks-ha.rst',
+    'arm/hooks-host-cache.rst',
+    'arm/hooks-lease-cmds.rst',
+    'arm/hooks-lease-query.rst',
+    'arm/hooks-limits.rst',
+    'arm/hooks-radius.rst',
+    'arm/hooks-rbac.rst',
+    'arm/hooks-run-script.rst',
+    'arm/hooks-stat-cmds.rst',
+    'arm/hooks-ddns-tuning.rst',
+    'arm/hammer.rst',
+    'arm/ext-netconf.rst',
+    'arm/ext-gss-tsig.rst',
+    'grammar/grammar-ca-parser.rst',
+    'grammar/grammar-d2-parser.rst',
+    'grammar/grammar-dhcp4-parser.rst',
+    'grammar/grammar-dhcp6-parser.rst',
+    'grammar/grammar-netconf-parser.rst',
+    'arm/hooks-flex-id.rst',
+    'arm/hooks-flex-option.rst',
+    'arm/hooks-legal-log.rst',
+    'arm/hooks-gss-tsig.rst',
+    'arm/hooks-host-cmds.rst',
+    'arm/hooks-cb-mysql.rst',
+    'arm/hooks-cb-pgsql.rst',
+    'arm/hooks-limits.rst',
+    'arm/hooks-rbac.rst',
+    'arm/hooks-run-script.rst',
+    'arm/hooks-subnet-cmds.rst',
+    'arm/hooks-user-chk.rst',
+]
+
+# The name of the Pygments (syntax highlighting) style to use.
+pygments_style = None
+
+
+# -- Options for HTML output -------------------------------------------------
+
+# The theme to use for HTML and HTML Help pages.  See the documentation for
+# a list of builtin themes.
+#
+#html_theme = 'alabaster'
+html_theme = 'sphinx_rtd_theme'
+html_logo = 'static/kea-imageonly-100bw.png'
+
+# Theme options are theme-specific and customize the look and feel of a theme
+# further.  For a list of options available for each theme, see the
+# documentation.
+#
+#html_theme_options = {
+#    "logo": "kea-logo-100x70.png",
+#}
+
+# Add any paths that contain custom static files (such as style sheets) here,
+# relative to this directory. They are copied after the builtin static files,
+# so a file named "default.css" will overwrite the builtin "default.css".
+html_static_path = ['static']
+
+# Custom sidebar templates, must be a dictionary that maps document names
+# to template names.
+#
+# The default sidebars (for documents that don't match any pattern) are
+# defined by theme itself.  Builtin themes are using these templates by
+# default: ``['localtoc.html', 'relations.html', 'sourcelink.html',
+# 'searchbox.html']``.
+#
+# html_sidebars = {}
+
+
+# -- Options for HTMLHelp output ---------------------------------------------
+
+# Output file base name for HTML help builder.
+#htmlhelp_basename = 'KeaAdministratorReferenceManualdoc'
+
+
+# -- Options for LaTeX output ------------------------------------------------
+
+latex_elements = {
+    # The paper size ('letterpaper' or 'a4paper').
+    #
+    # 'papersize': 'letterpaper',
+
+    # The font size ('10pt', '11pt' or '12pt').
+    #
+    # 'pointsize': '10pt',
+
+    # Additional stuff for the LaTeX preamble.
+    #
+    # 'preamble': '',
+
+    # Latex figure (float) alignment
+    #
+    # 'figure_align': 'htbp',
+}
+
+# Grouping the document tree into LaTeX files. List of tuples
+# (source start file, target name, title,
+#  author, documentclass [howto, manual, or own class]).
+latex_documents = [
+    (master_doc, 'kea-arm.tex', 'Kea Administrator Reference Manual Documentation', author, 'manual'),
+]
+
+latex_logo = 'static/kea-logo-200.png'
+
+if os.getenv("READTHEDOCS", "False") == "False":
+    latex_documents.append((messages_doc, 'kea-messages.tex', 'Kea Messages Manual', author, 'manual'))
+
+
+# -- Options for manual page output ------------------------------------------
+
+# One entry per manual page. List of tuples
+# (source start file, name, description, authors, manual section).
+man_pages = [
+    (master_doc, 'kea-arm', 'Kea Administrator Reference Manual Documentation', [author], 1),
+    ('man/kea-admin.8', 'kea-admin', 'Shell script for managing Kea databases', author, 8),
+    ('man/keactrl.8', 'keactrl', 'Shell script for managing Kea', author, 8),
+    ('man/kea-ctrl-agent.8', 'kea-ctrl-agent', 'Control Agent process in Kea', author, 8),
+    ('man/kea-dhcp4.8', 'kea-dhcp4', 'DHCPv4 server in Kea', author, 8),
+    ('man/kea-dhcp6.8', 'kea-dhcp6', 'DHCPv6 server in Kea', author, 8),
+    ('man/kea-dhcp-ddns.8', 'kea-dhcp-ddns', 'DHCP-DDNS process in Kea', author, 8),
+    ('man/kea-lfc.8', 'kea-lfc', 'Lease File Cleanup process in Kea', author, 8),
+    ('man/kea-netconf.8', 'kea-netconf', 'NETCONF agent for configuring Kea', author, 8),
+    ('man/kea-shell.8', 'kea-shell', 'Text client for Control Agent process', author, 8),
+    ('man/perfdhcp.8', 'perfdhcp', 'DHCP benchmarking tool', author, 8),
+]
+
+
+# -- Extension configuration -------------------------------------------------
+
+# -- Options for todo extension ----------------------------------------------
+
+# If true, `todo` and `todoList` produce output, else they produce nothing.
+todo_include_todos = True
+
+
+
+# Do generation of api.rst and kea-messages.rst here in conf.py instead of Makefile.am
+# so they are available on ReadTheDocs as there makefiles are not used for building docs.
+def run_generate_docs(_):
+    import os
+    import sys
+    src_dir = os.path.abspath(os.path.dirname(__file__))
+    print(src_dir)
+    sys.path.append(src_dir)
+
+    import api2doc
+    with open(os.path.join(src_dir, 'api-files.txt')) as af:
+        api_files = af.read().split()
+    api_files = [os.path.abspath(os.path.join(src_dir, '../..', af)) for af in api_files]
+    api2doc.generate(api_files, os.path.join(src_dir, 'api.rst'))
+
+    import mes2doc
+    with open(os.path.join(src_dir, 'mes-files.txt')) as mf:
+        mes_files = mf.read().split()
+    mes_files = [os.path.abspath(os.path.join(src_dir, '../..', mf)) for mf in mes_files]
+    mes2doc.generate(mes_files, os.path.join(src_dir, 'kea-messages.rst'))
+
+    # Sphinx has some limitations. It can't import files from outside its directory, which
+    # in our case is src/sphinx. On the other hand, we need to have platforms.rst file
+    # in top level directory, so it's easily accessible by prospective and first time
+    # users. Furthermore, ReadTheDocs does not use the makefile system at all and they rely
+    # on sphinx-build only. As a result we need to conduct some Makefile-like operations
+    # here. This requires us to copy (or link) the file from the top level to sphinx subdir.
+    #
+    # The first entry on this list is the actual file to copy, the second is a unique name
+    # that will be used when copied over to arm/ directory.
+    FILES_TO_COPY = [
+        [ '../../platforms.rst', 'platforms.rst' ],
+        [ '../examples/template-power-user-home/info.md', 'template-power-user-home.md' ],
+        [ '../examples/template-power-user-home/kea-ca-1.conf', 'template-power-user-home-ca-1.conf' ],
+        [ '../examples/template-power-user-home/kea-ca-2.conf', 'template-power-user-home-ca-2.conf' ],
+        [ '../examples/template-power-user-home/kea-dhcp4-1.conf', 'template-power-user-home-dhcp4-1.conf' ],
+        [ '../examples/template-power-user-home/kea-dhcp4-2.conf', 'template-power-user-home-dhcp4-2.conf' ]
+    ]
+
+    from shutil import copyfile
+    for [a, b] in FILES_TO_COPY:
+        src = os.path.join(src_dir, a)
+        dst = os.path.join(src_dir, 'arm', b)
+        print("Copying %s to %s" % (src, dst))
+        copyfile(src, dst)
+
+# custom setup hook
+def setup(app):
+    if hasattr(app, 'add_css_file'):
+        app.add_css_file('kea.css')
+    else:
+        app.add_stylesheet('kea.css')
+
+    app.connect('builder-inited', run_generate_docs)
diff --git a/doc/sphinx/grammar/grammar-ca-parser.rst b/doc/sphinx/grammar/grammar-ca-parser.rst
new file mode 100644
index 0000000..880d44b
--- /dev/null
+++ b/doc/sphinx/grammar/grammar-ca-parser.rst
@@ -0,0 +1,253 @@
+This grammar is generated from ``agent_parser.yy``. See :ref:`kea-ctrl-agent` for more details.
+
+.. code-block:: BNF
+   :linenos:
+
+     Grammar
+
+     $accept ::= start EOF
+
+     start ::= START_JSON json
+
+     start ::= START_AGENT agent_syntax_map
+
+     start ::= START_SUB_AGENT sub_agent
+
+     sub_agent ::= "{" global_params "}"
+
+     json ::= value
+
+     value ::= INTEGER
+          | FLOAT
+          | BOOLEAN
+          | STRING
+          | NULL
+          | map
+          | list_generic
+
+     map ::= "{" map_content "}"
+
+     map_value ::= map
+
+     map_content ::= 
+                | not_empty_map
+
+     not_empty_map ::= STRING ":" value
+                  | not_empty_map "," STRING ":" value
+                  | not_empty_map ","
+
+     list_generic ::= "[" list_content "]"
+
+     list_content ::= 
+                 | not_empty_list
+
+     not_empty_list ::= value
+                   | not_empty_list "," value
+                   | not_empty_list ","
+
+     unknown_map_entry ::= STRING ":"
+
+     agent_syntax_map ::= "{" global_object "}"
+
+     global_object ::= "Control-agent" ":" "{" global_params "}"
+                  | global_object_comma
+
+     global_object_comma ::= global_object ","
+
+     global_params ::= global_param
+                  | global_params "," global_param
+                  | global_params ","
+
+     global_param ::= http_host
+                 | http_port
+                 | trust_anchor
+                 | cert_file
+                 | key_file
+                 | cert_required
+                 | authentication
+                 | control_sockets
+                 | hooks_libraries
+                 | loggers
+                 | user_context
+                 | comment
+                 | unknown_map_entry
+
+     http_host ::= "http-host" ":" STRING
+
+     http_port ::= "http-port" ":" INTEGER
+
+     trust_anchor ::= "trust-anchor" ":" STRING
+
+     cert_file ::= "cert-file" ":" STRING
+
+     key_file ::= "key-file" ":" STRING
+
+     cert_required ::= "cert-required" ":" BOOLEAN
+
+     user_context ::= "user-context" ":" map_value
+
+     comment ::= "comment" ":" STRING
+
+     hooks_libraries ::= "hooks-libraries" ":" "[" hooks_libraries_list "]"
+
+     hooks_libraries_list ::= 
+                         | not_empty_hooks_libraries_list
+
+     not_empty_hooks_libraries_list ::= hooks_library
+                                   | not_empty_hooks_libraries_list "," hooks_library
+                                   | not_empty_hooks_libraries_list ","
+
+     hooks_library ::= "{" hooks_params "}"
+
+     hooks_params ::= hooks_param
+                 | hooks_params "," hooks_param
+                 | hooks_params ","
+                 | unknown_map_entry
+
+     hooks_param ::= library
+                | parameters
+
+     library ::= "library" ":" STRING
+
+     parameters ::= "parameters" ":" map_value
+
+     control_sockets ::= "control-sockets" ":" "{" control_sockets_params "}"
+
+     control_sockets_params ::= control_socket
+                           | control_sockets_params "," control_socket
+                           | control_sockets_params ","
+
+     control_socket ::= dhcp4_server_socket
+                   | dhcp6_server_socket
+                   | d2_server_socket
+                   | unknown_map_entry
+
+     dhcp4_server_socket ::= "dhcp4" ":" "{" control_socket_params "}"
+
+     dhcp6_server_socket ::= "dhcp6" ":" "{" control_socket_params "}"
+
+     d2_server_socket ::= "d2" ":" "{" control_socket_params "}"
+
+     control_socket_params ::= control_socket_param
+                          | control_socket_params "," control_socket_param
+                          | control_socket_params ","
+
+     control_socket_param ::= socket_name
+                         | socket_type
+                         | user_context
+                         | comment
+                         | unknown_map_entry
+
+     socket_name ::= "socket-name" ":" STRING
+
+     socket_type ::= "socket-type" ":" socket_type_value
+
+     socket_type_value ::= "unix"
+
+     authentication ::= "authentication" ":" "{" auth_params "}"
+
+     auth_params ::= auth_param
+                | auth_params "," auth_param
+                | auth_params ","
+
+     auth_param ::= auth_type
+               | realm
+               | directory
+               | clients
+               | comment
+               | user_context
+               | unknown_map_entry
+
+     auth_type ::= "type" ":" auth_type_value
+
+     auth_type_value ::= "basic"
+
+     realm ::= "realm" ":" STRING
+
+     directory ::= "directory" ":" STRING
+
+     clients ::= "clients" ":" "[" clients_list "]"
+
+     clients_list ::= 
+                 | not_empty_clients_list
+
+     not_empty_clients_list ::= basic_auth
+                           | not_empty_clients_list "," basic_auth
+                           | not_empty_clients_list ","
+
+     basic_auth ::= "{" clients_params "}"
+
+     clients_params ::= clients_param
+                   | clients_params "," clients_param
+                   | clients_params ","
+
+     clients_param ::= user
+                  | user_file
+                  | password
+                  | password_file
+                  | user_context
+                  | comment
+                  | unknown_map_entry
+
+     user ::= "user" ":" STRING
+
+     user_file ::= "user-file" ":" STRING
+
+     password ::= "password" ":" STRING
+
+     password_file ::= "password-file" ":" STRING
+
+     loggers ::= "loggers" ":" "[" loggers_entries "]"
+
+     loggers_entries ::= logger_entry
+                    | loggers_entries "," logger_entry
+                    | loggers_entries ","
+
+     logger_entry ::= "{" logger_params "}"
+
+     logger_params ::= logger_param
+                  | logger_params "," logger_param
+                  | logger_params ","
+
+     logger_param ::= name
+                 | output_options_list
+                 | debuglevel
+                 | severity
+                 | user_context
+                 | comment
+                 | unknown_map_entry
+
+     name ::= "name" ":" STRING
+
+     debuglevel ::= "debuglevel" ":" INTEGER
+
+     severity ::= "severity" ":" STRING
+
+     output_options_list ::= "output_options" ":" "[" output_options_list_content "]"
+
+     output_options_list_content ::= output_entry
+                                | output_options_list_content "," output_entry
+                                | output_options_list_content ","
+
+     output_entry ::= "{" output_params_list "}"
+
+     output_params_list ::= output_params
+                       | output_params_list "," output_params
+                       | output_params_list ","
+
+     output_params ::= output
+                  | flush
+                  | maxsize
+                  | maxver
+                  | pattern
+
+     output ::= "output" ":" STRING
+
+     flush ::= "flush" ":" BOOLEAN
+
+     maxsize ::= "maxsize" ":" INTEGER
+
+     maxver ::= "maxver" ":" INTEGER
+
+     pattern ::= "pattern" ":" STRING
+
diff --git a/doc/sphinx/grammar/grammar-d2-parser.rst b/doc/sphinx/grammar/grammar-d2-parser.rst
new file mode 100644
index 0000000..4f02ab0
--- /dev/null
+++ b/doc/sphinx/grammar/grammar-d2-parser.rst
@@ -0,0 +1,310 @@
+This grammar is generated from ``d2_parser.yy``. See :ref:`dhcp-ddns-server` for more details.
+
+.. code-block:: BNF
+   :linenos:
+
+     Grammar
+
+     $accept ::= start EOF
+
+     start ::= TOPLEVEL_JSON sub_json
+
+     start ::= TOPLEVEL_DHCPDDNS syntax_map
+
+     start ::= SUB_DHCPDDNS sub_dhcpddns
+
+     start ::= SUB_TSIG_KEY sub_tsig_key
+
+     start ::= SUB_TSIG_KEYS sub_tsig_keys
+
+     start ::= SUB_DDNS_DOMAIN sub_ddns_domain
+
+     start ::= SUB_DDNS_DOMAINS sub_ddns_domains
+
+     start ::= SUB_DNS_SERVER sub_dns_server
+
+     start ::= SUB_DNS_SERVERS sub_dns_servers
+
+     start ::= SUB_HOOKS_LIBRARY sub_hooks_library
+
+     value ::= INTEGER
+          | FLOAT
+          | BOOLEAN
+          | STRING
+          | NULL
+          | map2
+          | list_generic
+
+     sub_json ::= value
+
+     map2 ::= "{" map_content "}"
+
+     map_value ::= map2
+
+     map_content ::= 
+                | not_empty_map
+
+     not_empty_map ::= STRING ":" value
+                  | not_empty_map "," STRING ":" value
+                  | not_empty_map ","
+
+     list_generic ::= "[" list_content "]"
+
+     list_content ::= 
+                 | not_empty_list
+
+     not_empty_list ::= value
+                   | not_empty_list "," value
+                   | not_empty_list ","
+
+     unknown_map_entry ::= STRING ":"
+
+     syntax_map ::= "{" global_object "}"
+
+     global_object ::= "DhcpDdns" ":" "{" dhcpddns_params "}"
+                  | global_object_comma
+
+     global_object_comma ::= global_object ","
+
+     sub_dhcpddns ::= "{" dhcpddns_params "}"
+
+     dhcpddns_params ::= dhcpddns_param
+                    | dhcpddns_params "," dhcpddns_param
+                    | dhcpddns_params ","
+
+     dhcpddns_param ::= ip_address
+                   | port
+                   | dns_server_timeout
+                   | ncr_protocol
+                   | ncr_format
+                   | forward_ddns
+                   | reverse_ddns
+                   | tsig_keys
+                   | control_socket
+                   | hooks_libraries
+                   | loggers
+                   | user_context
+                   | comment
+                   | unknown_map_entry
+
+     ip_address ::= "ip-address" ":" STRING
+
+     port ::= "port" ":" INTEGER
+
+     dns_server_timeout ::= "dns-server-timeout" ":" INTEGER
+
+     ncr_protocol ::= "ncr-protocol" ":" ncr_protocol_value
+
+     ncr_protocol_value ::= "UDP"
+                       | "TCP"
+
+     ncr_format ::= "ncr-format" ":" "JSON"
+
+     user_context ::= "user-context" ":" map_value
+
+     comment ::= "comment" ":" STRING
+
+     forward_ddns ::= "forward-ddns" ":" "{" ddns_mgr_params "}"
+
+     reverse_ddns ::= "reverse-ddns" ":" "{" ddns_mgr_params "}"
+
+     ddns_mgr_params ::= 
+                    | not_empty_ddns_mgr_params
+
+     not_empty_ddns_mgr_params ::= ddns_mgr_param
+                              | ddns_mgr_params "," ddns_mgr_param
+                              | ddns_mgr_params ","
+
+     ddns_mgr_param ::= ddns_domains
+                   | unknown_map_entry
+
+     ddns_domains ::= "ddns-domains" ":" "[" ddns_domain_list "]"
+
+     sub_ddns_domains ::= "[" ddns_domain_list "]"
+
+     ddns_domain_list ::= 
+                     | not_empty_ddns_domain_list
+
+     not_empty_ddns_domain_list ::= ddns_domain
+                               | not_empty_ddns_domain_list "," ddns_domain
+                               | not_empty_ddns_domain_list ","
+
+     ddns_domain ::= "{" ddns_domain_params "}"
+
+     sub_ddns_domain ::= "{" ddns_domain_params "}"
+
+     ddns_domain_params ::= ddns_domain_param
+                       | ddns_domain_params "," ddns_domain_param
+                       | ddns_domain_params ","
+
+     ddns_domain_param ::= ddns_domain_name
+                      | ddns_key_name
+                      | dns_servers
+                      | user_context
+                      | comment
+                      | unknown_map_entry
+
+     ddns_domain_name ::= "name" ":" STRING
+
+     ddns_key_name ::= "key-name" ":" STRING
+
+     dns_servers ::= "dns-servers" ":" "[" dns_server_list "]"
+
+     sub_dns_servers ::= "[" dns_server_list "]"
+
+     dns_server_list ::= dns_server
+                    | dns_server_list "," dns_server
+                    | dns_server_list ","
+
+     dns_server ::= "{" dns_server_params "}"
+
+     sub_dns_server ::= "{" dns_server_params "}"
+
+     dns_server_params ::= dns_server_param
+                      | dns_server_params "," dns_server_param
+                      | dns_server_params ","
+
+     dns_server_param ::= dns_server_hostname
+                     | dns_server_ip_address
+                     | dns_server_port
+                     | ddns_key_name
+                     | user_context
+                     | comment
+                     | unknown_map_entry
+
+     dns_server_hostname ::= "hostname" ":" STRING
+
+     dns_server_ip_address ::= "ip-address" ":" STRING
+
+     dns_server_port ::= "port" ":" INTEGER
+
+     tsig_keys ::= "tsig-keys" ":" "[" tsig_keys_list "]"
+
+     sub_tsig_keys ::= "[" tsig_keys_list "]"
+
+     tsig_keys_list ::= 
+                   | not_empty_tsig_keys_list
+
+     not_empty_tsig_keys_list ::= tsig_key
+                             | not_empty_tsig_keys_list "," tsig_key
+                             | not_empty_tsig_keys_list ","
+
+     tsig_key ::= "{" tsig_key_params "}"
+
+     sub_tsig_key ::= "{" tsig_key_params "}"
+
+     tsig_key_params ::= tsig_key_param
+                    | tsig_key_params "," tsig_key_param
+                    | tsig_key_params ","
+
+     tsig_key_param ::= tsig_key_name
+                   | tsig_key_algorithm
+                   | tsig_key_digest_bits
+                   | tsig_key_secret
+                   | user_context
+                   | comment
+                   | unknown_map_entry
+
+     tsig_key_name ::= "name" ":" STRING
+
+     tsig_key_algorithm ::= "algorithm" ":" STRING
+
+     tsig_key_digest_bits ::= "digest-bits" ":" INTEGER
+
+     tsig_key_secret ::= "secret" ":" STRING
+
+     control_socket ::= "control-socket" ":" "{" control_socket_params "}"
+
+     control_socket_params ::= control_socket_param
+                          | control_socket_params "," control_socket_param
+                          | control_socket_params ","
+
+     control_socket_param ::= control_socket_type
+                         | control_socket_name
+                         | user_context
+                         | comment
+                         | unknown_map_entry
+
+     control_socket_type ::= "socket-type" ":" STRING
+
+     control_socket_name ::= "socket-name" ":" STRING
+
+     hooks_libraries ::= "hooks-libraries" ":" "[" hooks_libraries_list "]"
+
+     hooks_libraries_list ::= 
+                         | not_empty_hooks_libraries_list
+
+     not_empty_hooks_libraries_list ::= hooks_library
+                                   | not_empty_hooks_libraries_list "," hooks_library
+                                   | not_empty_hooks_libraries_list ","
+
+     hooks_library ::= "{" hooks_params "}"
+
+     sub_hooks_library ::= "{" hooks_params "}"
+
+     hooks_params ::= hooks_param
+                 | hooks_params "," hooks_param
+                 | hooks_params ","
+                 | unknown_map_entry
+
+     hooks_param ::= library
+                | parameters
+
+     library ::= "library" ":" STRING
+
+     parameters ::= "parameters" ":" map_value
+
+     loggers ::= "loggers" ":" "[" loggers_entries "]"
+
+     loggers_entries ::= logger_entry
+                    | loggers_entries "," logger_entry
+                    | loggers_entries ","
+
+     logger_entry ::= "{" logger_params "}"
+
+     logger_params ::= logger_param
+                  | logger_params "," logger_param
+                  | logger_params ","
+
+     logger_param ::= name
+                 | output_options_list
+                 | debuglevel
+                 | severity
+                 | user_context
+                 | comment
+                 | unknown_map_entry
+
+     name ::= "name" ":" STRING
+
+     debuglevel ::= "debuglevel" ":" INTEGER
+
+     severity ::= "severity" ":" STRING
+
+     output_options_list ::= "output_options" ":" "[" output_options_list_content "]"
+
+     output_options_list_content ::= output_entry
+                                | output_options_list_content "," output_entry
+                                | output_options_list_content ","
+
+     output_entry ::= "{" output_params_list "}"
+
+     output_params_list ::= output_params
+                       | output_params_list "," output_params
+                       | output_params_list ","
+
+     output_params ::= output
+                  | flush
+                  | maxsize
+                  | maxver
+                  | pattern
+
+     output ::= "output" ":" STRING
+
+     flush ::= "flush" ":" BOOLEAN
+
+     maxsize ::= "maxsize" ":" INTEGER
+
+     maxver ::= "maxver" ":" INTEGER
+
+     pattern ::= "pattern" ":" STRING
+
diff --git a/doc/sphinx/grammar/grammar-dhcp4-parser.rst b/doc/sphinx/grammar/grammar-dhcp4-parser.rst
new file mode 100644
index 0000000..94e9891
--- /dev/null
+++ b/doc/sphinx/grammar/grammar-dhcp4-parser.rst
@@ -0,0 +1,997 @@
+This grammar is generated from ``dhcp4_parser.yy``. See :ref:`dhcp4` for more details.
+
+.. code-block:: BNF
+   :linenos:
+
+     Grammar
+
+     $accept ::= start EOF
+
+     start ::= TOPLEVEL_JSON sub_json
+
+     start ::= TOPLEVEL_DHCP4 syntax_map
+
+     start ::= SUB_DHCP4 sub_dhcp4
+
+     start ::= SUB_INTERFACES4 sub_interfaces4
+
+     start ::= SUB_SUBNET4 sub_subnet4
+
+     start ::= SUB_POOL4 sub_pool4
+
+     start ::= SUB_RESERVATION sub_reservation
+
+     start ::= SUB_OPTION_DEFS sub_option_def_list
+
+     start ::= SUB_OPTION_DEF sub_option_def
+
+     start ::= SUB_OPTION_DATA sub_option_data
+
+     start ::= SUB_HOOKS_LIBRARY sub_hooks_library
+
+     start ::= SUB_DHCP_DDNS sub_dhcp_ddns
+
+     start ::= SUB_CONFIG_CONTROL sub_config_control
+
+     value ::= INTEGER
+          | FLOAT
+          | BOOLEAN
+          | STRING
+          | NULL
+          | map2
+          | list_generic
+
+     sub_json ::= value
+
+     map2 ::= "{" map_content "}"
+
+     map_value ::= map2
+
+     map_content ::= 
+                | not_empty_map
+
+     not_empty_map ::= STRING ":" value
+                  | not_empty_map "," STRING ":" value
+                  | not_empty_map ","
+
+     list_generic ::= "[" list_content "]"
+
+     list_content ::= 
+                 | not_empty_list
+
+     not_empty_list ::= value
+                   | not_empty_list "," value
+                   | not_empty_list ","
+
+     list_strings ::= "[" list_strings_content "]"
+
+     list_strings_content ::= 
+                         | not_empty_list_strings
+
+     not_empty_list_strings ::= STRING
+                           | not_empty_list_strings "," STRING
+                           | not_empty_list_strings ","
+
+     unknown_map_entry ::= STRING ":"
+
+     syntax_map ::= "{" global_object "}"
+
+     global_object ::= "Dhcp4" ":" "{" global_params "}"
+                  | global_object_comma
+
+     global_object_comma ::= global_object ","
+
+     sub_dhcp4 ::= "{" global_params "}"
+
+     global_params ::= global_param
+                  | global_params "," global_param
+                  | global_params ","
+
+     global_param ::= valid_lifetime
+                 | min_valid_lifetime
+                 | max_valid_lifetime
+                 | renew_timer
+                 | rebind_timer
+                 | decline_probation_period
+                 | subnet4_list
+                 | shared_networks
+                 | interfaces_config
+                 | lease_database
+                 | hosts_database
+                 | hosts_databases
+                 | host_reservation_identifiers
+                 | client_classes
+                 | option_def_list
+                 | option_data_list
+                 | hooks_libraries
+                 | expired_leases_processing
+                 | dhcp4o6_port
+                 | control_socket
+                 | dhcp_queue_control
+                 | dhcp_ddns
+                 | echo_client_id
+                 | match_client_id
+                 | authoritative
+                 | next_server
+                 | server_hostname
+                 | boot_file_name
+                 | user_context
+                 | comment
+                 | sanity_checks
+                 | reservations
+                 | config_control
+                 | server_tag
+                 | reservation_mode
+                 | reservations_global
+                 | reservations_in_subnet
+                 | reservations_out_of_pool
+                 | calculate_tee_times
+                 | t1_percent
+                 | t2_percent
+                 | cache_threshold
+                 | cache_max_age
+                 | loggers
+                 | hostname_char_set
+                 | hostname_char_replacement
+                 | ddns_send_updates
+                 | ddns_override_no_update
+                 | ddns_override_client_update
+                 | ddns_replace_client_name
+                 | ddns_generated_prefix
+                 | ddns_qualifying_suffix
+                 | ddns_update_on_renew
+                 | ddns_use_conflict_resolution
+                 | store_extended_info
+                 | statistic_default_sample_count
+                 | statistic_default_sample_age
+                 | dhcp_multi_threading
+                 | early_global_reservations_lookup
+                 | ip_reservations_unique
+                 | reservations_lookup_first
+                 | compatibility
+                 | parked_packet_limit
+                 | unknown_map_entry
+
+     valid_lifetime ::= "valid-lifetime" ":" INTEGER
+
+     min_valid_lifetime ::= "min-valid-lifetime" ":" INTEGER
+
+     max_valid_lifetime ::= "max-valid-lifetime" ":" INTEGER
+
+     renew_timer ::= "renew-timer" ":" INTEGER
+
+     rebind_timer ::= "rebind-timer" ":" INTEGER
+
+     calculate_tee_times ::= "calculate-tee-times" ":" BOOLEAN
+
+     t1_percent ::= "t1-percent" ":" FLOAT
+
+     t2_percent ::= "t2-percent" ":" FLOAT
+
+     cache_threshold ::= "cache-threshold" ":" FLOAT
+
+     cache_max_age ::= "cache-max-age" ":" INTEGER
+
+     decline_probation_period ::= "decline-probation-period" ":" INTEGER
+
+     server_tag ::= "server-tag" ":" STRING
+
+     parked_packet_limit ::= "parked-packet-limit" ":" INTEGER
+
+     echo_client_id ::= "echo-client-id" ":" BOOLEAN
+
+     match_client_id ::= "match-client-id" ":" BOOLEAN
+
+     authoritative ::= "authoritative" ":" BOOLEAN
+
+     ddns_send_updates ::= "ddns-send-updates" ":" BOOLEAN
+
+     ddns_override_no_update ::= "ddns-override-no-update" ":" BOOLEAN
+
+     ddns_override_client_update ::= "ddns-override-client-update" ":" BOOLEAN
+
+     ddns_replace_client_name ::= "ddns-replace-client-name" ":" ddns_replace_client_name_value
+
+     ddns_replace_client_name_value ::= "when-present"
+                                   | "never"
+                                   | "always"
+                                   | "when-not-present"
+                                   | BOOLEAN
+
+     ddns_generated_prefix ::= "ddns-generated-prefix" ":" STRING
+
+     ddns_qualifying_suffix ::= "ddns-qualifying-suffix" ":" STRING
+
+     ddns_update_on_renew ::= "ddns-update-on-renew" ":" BOOLEAN
+
+     ddns_use_conflict_resolution ::= "ddns-use-conflict-resolution" ":" BOOLEAN
+
+     hostname_char_set ::= "hostname-char-set" ":" STRING
+
+     hostname_char_replacement ::= "hostname-char-replacement" ":" STRING
+
+     store_extended_info ::= "store-extended-info" ":" BOOLEAN
+
+     statistic_default_sample_count ::= "statistic-default-sample-count" ":" INTEGER
+
+     statistic_default_sample_age ::= "statistic-default-sample-age" ":" INTEGER
+
+     early_global_reservations_lookup ::= "early-global-reservations-lookup" ":" BOOLEAN
+
+     ip_reservations_unique ::= "ip-reservations-unique" ":" BOOLEAN
+
+     reservations_lookup_first ::= "reservations-lookup-first" ":" BOOLEAN
+
+     interfaces_config ::= "interfaces-config" ":" "{" interfaces_config_params "}"
+
+     interfaces_config_params ::= interfaces_config_param
+                             | interfaces_config_params "," interfaces_config_param
+                             | interfaces_config_params ","
+
+     interfaces_config_param ::= interfaces_list
+                            | dhcp_socket_type
+                            | outbound_interface
+                            | re_detect
+                            | service_sockets_require_all
+                            | service_sockets_retry_wait_time
+                            | service_sockets_max_retries
+                            | user_context
+                            | comment
+                            | unknown_map_entry
+
+     sub_interfaces4 ::= "{" interfaces_config_params "}"
+
+     interfaces_list ::= "interfaces" ":" list_strings
+
+     dhcp_socket_type ::= "dhcp-socket-type" ":" socket_type
+
+     socket_type ::= "raw"
+                | "udp"
+
+     outbound_interface ::= "outbound-interface" ":" outbound_interface_value
+
+     outbound_interface_value ::= "same-as-inbound"
+                             | "use-routing"
+
+     re_detect ::= "re-detect" ":" BOOLEAN
+
+     service_sockets_require_all ::= "service-sockets-require-all" ":" BOOLEAN
+
+     service_sockets_retry_wait_time ::= "service-sockets-retry-wait-time" ":" INTEGER
+
+     service_sockets_max_retries ::= "service-sockets-max-retries" ":" INTEGER
+
+     lease_database ::= "lease-database" ":" "{" database_map_params "}"
+
+     sanity_checks ::= "sanity-checks" ":" "{" sanity_checks_params "}"
+
+     sanity_checks_params ::= sanity_checks_param
+                         | sanity_checks_params "," sanity_checks_param
+                         | sanity_checks_params ","
+
+     sanity_checks_param ::= lease_checks
+
+     lease_checks ::= "lease-checks" ":" STRING
+
+     hosts_database ::= "hosts-database" ":" "{" database_map_params "}"
+
+     hosts_databases ::= "hosts-databases" ":" "[" database_list "]"
+
+     database_list ::= 
+                  | not_empty_database_list
+
+     not_empty_database_list ::= database
+                            | not_empty_database_list "," database
+                            | not_empty_database_list ","
+
+     database ::= "{" database_map_params "}"
+
+     database_map_params ::= database_map_param
+                        | database_map_params "," database_map_param
+                        | database_map_params ","
+
+     database_map_param ::= database_type
+                       | user
+                       | password
+                       | host
+                       | port
+                       | name
+                       | persist
+                       | lfc_interval
+                       | readonly
+                       | connect_timeout
+                       | max_reconnect_tries
+                       | reconnect_wait_time
+                       | on_fail
+                       | max_row_errors
+                       | trust_anchor
+                       | cert_file
+                       | key_file
+                       | cipher_list
+                       | unknown_map_entry
+
+     database_type ::= "type" ":" db_type
+
+     db_type ::= "memfile"
+            | "mysql"
+            | "postgresql"
+
+     user ::= "user" ":" STRING
+
+     password ::= "password" ":" STRING
+
+     host ::= "host" ":" STRING
+
+     port ::= "port" ":" INTEGER
+
+     name ::= "name" ":" STRING
+
+     persist ::= "persist" ":" BOOLEAN
+
+     lfc_interval ::= "lfc-interval" ":" INTEGER
+
+     readonly ::= "readonly" ":" BOOLEAN
+
+     connect_timeout ::= "connect-timeout" ":" INTEGER
+
+     max_reconnect_tries ::= "max-reconnect-tries" ":" INTEGER
+
+     reconnect_wait_time ::= "reconnect-wait-time" ":" INTEGER
+
+     on_fail ::= "on-fail" ":" on_fail_mode
+
+     on_fail_mode ::= "stop-retry-exit"
+                 | "serve-retry-exit"
+                 | "serve-retry-continue"
+
+     max_row_errors ::= "max-row-errors" ":" INTEGER
+
+     trust_anchor ::= "trust-anchor" ":" STRING
+
+     cert_file ::= "cert-file" ":" STRING
+
+     key_file ::= "key-file" ":" STRING
+
+     cipher_list ::= "cipher-list" ":" STRING
+
+     host_reservation_identifiers ::= "host-reservation-identifiers" ":" "[" host_reservation_identifiers_list "]"
+
+     host_reservation_identifiers_list ::= host_reservation_identifier
+                                      | host_reservation_identifiers_list "," host_reservation_identifier
+                                      | host_reservation_identifiers_list ","
+
+     host_reservation_identifier ::= duid_id
+                                | hw_address_id
+                                | circuit_id
+                                | client_id
+                                | flex_id
+
+     duid_id ::= "duid"
+
+     hw_address_id ::= "hw-address"
+
+     circuit_id ::= "circuit-id"
+
+     client_id ::= "client-id"
+
+     flex_id ::= "flex-id"
+
+     dhcp_multi_threading ::= "multi-threading" ":" "{" multi_threading_params "}"
+
+     multi_threading_params ::= multi_threading_param
+                           | multi_threading_params "," multi_threading_param
+                           | multi_threading_params ","
+
+     multi_threading_param ::= enable_multi_threading
+                          | thread_pool_size
+                          | packet_queue_size
+                          | user_context
+                          | comment
+                          | unknown_map_entry
+
+     enable_multi_threading ::= "enable-multi-threading" ":" BOOLEAN
+
+     thread_pool_size ::= "thread-pool-size" ":" INTEGER
+
+     packet_queue_size ::= "packet-queue-size" ":" INTEGER
+
+     hooks_libraries ::= "hooks-libraries" ":" "[" hooks_libraries_list "]"
+
+     hooks_libraries_list ::= 
+                         | not_empty_hooks_libraries_list
+
+     not_empty_hooks_libraries_list ::= hooks_library
+                                   | not_empty_hooks_libraries_list "," hooks_library
+                                   | not_empty_hooks_libraries_list ","
+
+     hooks_library ::= "{" hooks_params "}"
+
+     sub_hooks_library ::= "{" hooks_params "}"
+
+     hooks_params ::= hooks_param
+                 | hooks_params "," hooks_param
+                 | hooks_params ","
+                 | unknown_map_entry
+
+     hooks_param ::= library
+                | parameters
+
+     library ::= "library" ":" STRING
+
+     parameters ::= "parameters" ":" map_value
+
+     expired_leases_processing ::= "expired-leases-processing" ":" "{" expired_leases_params "}"
+
+     expired_leases_params ::= expired_leases_param
+                          | expired_leases_params "," expired_leases_param
+                          | expired_leases_params ","
+
+     expired_leases_param ::= reclaim_timer_wait_time
+                         | flush_reclaimed_timer_wait_time
+                         | hold_reclaimed_time
+                         | max_reclaim_leases
+                         | max_reclaim_time
+                         | unwarned_reclaim_cycles
+
+     reclaim_timer_wait_time ::= "reclaim-timer-wait-time" ":" INTEGER
+
+     flush_reclaimed_timer_wait_time ::= "flush-reclaimed-timer-wait-time" ":" INTEGER
+
+     hold_reclaimed_time ::= "hold-reclaimed-time" ":" INTEGER
+
+     max_reclaim_leases ::= "max-reclaim-leases" ":" INTEGER
+
+     max_reclaim_time ::= "max-reclaim-time" ":" INTEGER
+
+     unwarned_reclaim_cycles ::= "unwarned-reclaim-cycles" ":" INTEGER
+
+     subnet4_list ::= "subnet4" ":" "[" subnet4_list_content "]"
+
+     subnet4_list_content ::= 
+                         | not_empty_subnet4_list
+
+     not_empty_subnet4_list ::= subnet4
+                           | not_empty_subnet4_list "," subnet4
+                           | not_empty_subnet4_list ","
+
+     subnet4 ::= "{" subnet4_params "}"
+
+     sub_subnet4 ::= "{" subnet4_params "}"
+
+     subnet4_params ::= subnet4_param
+                   | subnet4_params "," subnet4_param
+                   | subnet4_params ","
+
+     subnet4_param ::= valid_lifetime
+                  | min_valid_lifetime
+                  | max_valid_lifetime
+                  | renew_timer
+                  | rebind_timer
+                  | option_data_list
+                  | pools_list
+                  | subnet
+                  | interface
+                  | id
+                  | client_class
+                  | require_client_classes
+                  | reservations
+                  | reservation_mode
+                  | reservations_global
+                  | reservations_in_subnet
+                  | reservations_out_of_pool
+                  | relay
+                  | match_client_id
+                  | authoritative
+                  | next_server
+                  | server_hostname
+                  | boot_file_name
+                  | subnet_4o6_interface
+                  | subnet_4o6_interface_id
+                  | subnet_4o6_subnet
+                  | user_context
+                  | comment
+                  | calculate_tee_times
+                  | t1_percent
+                  | t2_percent
+                  | cache_threshold
+                  | cache_max_age
+                  | ddns_send_updates
+                  | ddns_override_no_update
+                  | ddns_override_client_update
+                  | ddns_replace_client_name
+                  | ddns_generated_prefix
+                  | ddns_qualifying_suffix
+                  | ddns_update_on_renew
+                  | ddns_use_conflict_resolution
+                  | hostname_char_set
+                  | hostname_char_replacement
+                  | store_extended_info
+                  | unknown_map_entry
+
+     subnet ::= "subnet" ":" STRING
+
+     subnet_4o6_interface ::= "4o6-interface" ":" STRING
+
+     subnet_4o6_interface_id ::= "4o6-interface-id" ":" STRING
+
+     subnet_4o6_subnet ::= "4o6-subnet" ":" STRING
+
+     interface ::= "interface" ":" STRING
+
+     client_class ::= "client-class" ":" STRING
+
+     require_client_classes ::= "require-client-classes" ":" list_strings
+
+     reservations_global ::= "reservations-global" ":" BOOLEAN
+
+     reservations_in_subnet ::= "reservations-in-subnet" ":" BOOLEAN
+
+     reservations_out_of_pool ::= "reservations-out-of-pool" ":" BOOLEAN
+
+     reservation_mode ::= "reservation-mode" ":" hr_mode
+
+     hr_mode ::= "disabled"
+            | "out-of-pool"
+            | "global"
+            | "all"
+
+     id ::= "id" ":" INTEGER
+
+     shared_networks ::= "shared-networks" ":" "[" shared_networks_content "]"
+
+     shared_networks_content ::= 
+                            | shared_networks_list
+
+     shared_networks_list ::= shared_network
+                         | shared_networks_list "," shared_network
+                         | shared_networks_list ","
+
+     shared_network ::= "{" shared_network_params "}"
+
+     shared_network_params ::= shared_network_param
+                          | shared_network_params "," shared_network_param
+                          | shared_network_params ","
+
+     shared_network_param ::= name
+                         | subnet4_list
+                         | interface
+                         | renew_timer
+                         | rebind_timer
+                         | option_data_list
+                         | match_client_id
+                         | authoritative
+                         | next_server
+                         | server_hostname
+                         | boot_file_name
+                         | relay
+                         | reservation_mode
+                         | reservations_global
+                         | reservations_in_subnet
+                         | reservations_out_of_pool
+                         | client_class
+                         | require_client_classes
+                         | valid_lifetime
+                         | min_valid_lifetime
+                         | max_valid_lifetime
+                         | user_context
+                         | comment
+                         | calculate_tee_times
+                         | t1_percent
+                         | t2_percent
+                         | cache_threshold
+                         | cache_max_age
+                         | ddns_send_updates
+                         | ddns_override_no_update
+                         | ddns_override_client_update
+                         | ddns_replace_client_name
+                         | ddns_generated_prefix
+                         | ddns_qualifying_suffix
+                         | ddns_update_on_renew
+                         | ddns_use_conflict_resolution
+                         | hostname_char_set
+                         | hostname_char_replacement
+                         | store_extended_info
+                         | unknown_map_entry
+
+     option_def_list ::= "option-def" ":" "[" option_def_list_content "]"
+
+     sub_option_def_list ::= "{" option_def_list "}"
+
+     option_def_list_content ::= 
+                            | not_empty_option_def_list
+
+     not_empty_option_def_list ::= option_def_entry
+                              | not_empty_option_def_list "," option_def_entry
+                              | not_empty_option_def_list ","
+
+     option_def_entry ::= "{" option_def_params "}"
+
+     sub_option_def ::= "{" option_def_params "}"
+
+     option_def_params ::= 
+                      | not_empty_option_def_params
+
+     not_empty_option_def_params ::= option_def_param
+                                | not_empty_option_def_params "," option_def_param
+                                | not_empty_option_def_params ","
+
+     option_def_param ::= option_def_name
+                     | option_def_code
+                     | option_def_type
+                     | option_def_record_types
+                     | option_def_space
+                     | option_def_encapsulate
+                     | option_def_array
+                     | user_context
+                     | comment
+                     | unknown_map_entry
+
+     option_def_name ::= name
+
+     code ::= "code" ":" INTEGER
+
+     option_def_code ::= code
+
+     option_def_type ::= "type" ":" STRING
+
+     option_def_record_types ::= "record-types" ":" STRING
+
+     space ::= "space" ":" STRING
+
+     option_def_space ::= space
+
+     option_def_encapsulate ::= "encapsulate" ":" STRING
+
+     option_def_array ::= "array" ":" BOOLEAN
+
+     option_data_list ::= "option-data" ":" "[" option_data_list_content "]"
+
+     option_data_list_content ::= 
+                             | not_empty_option_data_list
+
+     not_empty_option_data_list ::= option_data_entry
+                               | not_empty_option_data_list "," option_data_entry
+                               | not_empty_option_data_list ","
+
+     option_data_entry ::= "{" option_data_params "}"
+
+     sub_option_data ::= "{" option_data_params "}"
+
+     option_data_params ::= 
+                       | not_empty_option_data_params
+
+     not_empty_option_data_params ::= option_data_param
+                                 | not_empty_option_data_params "," option_data_param
+                                 | not_empty_option_data_params ","
+
+     option_data_param ::= option_data_name
+                      | option_data_data
+                      | option_data_code
+                      | option_data_space
+                      | option_data_csv_format
+                      | option_data_always_send
+                      | user_context
+                      | comment
+                      | unknown_map_entry
+
+     option_data_name ::= name
+
+     option_data_data ::= "data" ":" STRING
+
+     option_data_code ::= code
+
+     option_data_space ::= space
+
+     option_data_csv_format ::= "csv-format" ":" BOOLEAN
+
+     option_data_always_send ::= "always-send" ":" BOOLEAN
+
+     pools_list ::= "pools" ":" "[" pools_list_content "]"
+
+     pools_list_content ::= 
+                       | not_empty_pools_list
+
+     not_empty_pools_list ::= pool_list_entry
+                         | not_empty_pools_list "," pool_list_entry
+                         | not_empty_pools_list ","
+
+     pool_list_entry ::= "{" pool_params "}"
+
+     sub_pool4 ::= "{" pool_params "}"
+
+     pool_params ::= pool_param
+                | pool_params "," pool_param
+                | pool_params ","
+
+     pool_param ::= pool_entry
+               | option_data_list
+               | client_class
+               | require_client_classes
+               | user_context
+               | comment
+               | unknown_map_entry
+
+     pool_entry ::= "pool" ":" STRING
+
+     user_context ::= "user-context" ":" map_value
+
+     comment ::= "comment" ":" STRING
+
+     reservations ::= "reservations" ":" "[" reservations_list "]"
+
+     reservations_list ::= 
+                      | not_empty_reservations_list
+
+     not_empty_reservations_list ::= reservation
+                                | not_empty_reservations_list "," reservation
+                                | not_empty_reservations_list ","
+
+     reservation ::= "{" reservation_params "}"
+
+     sub_reservation ::= "{" reservation_params "}"
+
+     reservation_params ::= 
+                       | not_empty_reservation_params
+
+     not_empty_reservation_params ::= reservation_param
+                                 | not_empty_reservation_params "," reservation_param
+                                 | not_empty_reservation_params ","
+
+     reservation_param ::= duid
+                      | reservation_client_classes
+                      | client_id_value
+                      | circuit_id_value
+                      | flex_id_value
+                      | ip_address
+                      | hw_address
+                      | hostname
+                      | option_data_list
+                      | next_server
+                      | server_hostname
+                      | boot_file_name
+                      | user_context
+                      | comment
+                      | unknown_map_entry
+
+     next_server ::= "next-server" ":" STRING
+
+     server_hostname ::= "server-hostname" ":" STRING
+
+     boot_file_name ::= "boot-file-name" ":" STRING
+
+     ip_address ::= "ip-address" ":" STRING
+
+     ip_addresses ::= "ip-addresses" ":" list_strings
+
+     duid ::= "duid" ":" STRING
+
+     hw_address ::= "hw-address" ":" STRING
+
+     client_id_value ::= "client-id" ":" STRING
+
+     circuit_id_value ::= "circuit-id" ":" STRING
+
+     flex_id_value ::= "flex-id" ":" STRING
+
+     hostname ::= "hostname" ":" STRING
+
+     reservation_client_classes ::= "client-classes" ":" list_strings
+
+     relay ::= "relay" ":" "{" relay_map "}"
+
+     relay_map ::= ip_address
+              | ip_addresses
+
+     client_classes ::= "client-classes" ":" "[" client_classes_list "]"
+
+     client_classes_list ::= client_class_entry
+                        | client_classes_list "," client_class_entry
+                        | client_classes_list ","
+
+     client_class_entry ::= "{" client_class_params "}"
+
+     client_class_params ::= 
+                        | not_empty_client_class_params
+
+     not_empty_client_class_params ::= client_class_param
+                                  | not_empty_client_class_params "," client_class_param
+                                  | not_empty_client_class_params ","
+
+     client_class_param ::= client_class_name
+                       | client_class_test
+                       | only_if_required
+                       | option_def_list
+                       | option_data_list
+                       | next_server
+                       | server_hostname
+                       | boot_file_name
+                       | user_context
+                       | comment
+                       | unknown_map_entry
+                       | valid_lifetime
+                       | min_valid_lifetime
+                       | max_valid_lifetime
+
+     client_class_name ::= name
+
+     client_class_test ::= "test" ":" STRING
+
+     only_if_required ::= "only-if-required" ":" BOOLEAN
+
+     dhcp4o6_port ::= "dhcp4o6-port" ":" INTEGER
+
+     control_socket ::= "control-socket" ":" "{" control_socket_params "}"
+
+     control_socket_params ::= control_socket_param
+                          | control_socket_params "," control_socket_param
+                          | control_socket_params ","
+
+     control_socket_param ::= control_socket_type
+                         | control_socket_name
+                         | user_context
+                         | comment
+                         | unknown_map_entry
+
+     control_socket_type ::= "socket-type" ":" STRING
+
+     control_socket_name ::= "socket-name" ":" STRING
+
+     dhcp_queue_control ::= "dhcp-queue-control" ":" "{" queue_control_params "}"
+
+     queue_control_params ::= queue_control_param
+                         | queue_control_params "," queue_control_param
+                         | queue_control_params ","
+
+     queue_control_param ::= enable_queue
+                        | queue_type
+                        | capacity
+                        | user_context
+                        | comment
+                        | arbitrary_map_entry
+
+     enable_queue ::= "enable-queue" ":" BOOLEAN
+
+     queue_type ::= "queue-type" ":" STRING
+
+     capacity ::= "capacity" ":" INTEGER
+
+     arbitrary_map_entry ::= STRING ":" value
+
+     dhcp_ddns ::= "dhcp-ddns" ":" "{" dhcp_ddns_params "}"
+
+     sub_dhcp_ddns ::= "{" dhcp_ddns_params "}"
+
+     dhcp_ddns_params ::= dhcp_ddns_param
+                     | dhcp_ddns_params "," dhcp_ddns_param
+                     | dhcp_ddns_params ","
+
+     dhcp_ddns_param ::= enable_updates
+                    | server_ip
+                    | server_port
+                    | sender_ip
+                    | sender_port
+                    | max_queue_size
+                    | ncr_protocol
+                    | ncr_format
+                    | dep_override_no_update
+                    | dep_override_client_update
+                    | dep_replace_client_name
+                    | dep_generated_prefix
+                    | dep_qualifying_suffix
+                    | dep_hostname_char_set
+                    | dep_hostname_char_replacement
+                    | user_context
+                    | comment
+                    | unknown_map_entry
+
+     enable_updates ::= "enable-updates" ":" BOOLEAN
+
+     server_ip ::= "server-ip" ":" STRING
+
+     server_port ::= "server-port" ":" INTEGER
+
+     sender_ip ::= "sender-ip" ":" STRING
+
+     sender_port ::= "sender-port" ":" INTEGER
+
+     max_queue_size ::= "max-queue-size" ":" INTEGER
+
+     ncr_protocol ::= "ncr-protocol" ":" ncr_protocol_value
+
+     ncr_protocol_value ::= "udp"
+                       | "tcp"
+
+     ncr_format ::= "ncr-format" ":" "JSON"
+
+     dep_qualifying_suffix ::= "qualifying-suffix" ":" STRING
+
+     dep_override_no_update ::= "override-no-update" ":" BOOLEAN
+
+     dep_override_client_update ::= "override-client-update" ":" BOOLEAN
+
+     dep_replace_client_name ::= "replace-client-name" ":" ddns_replace_client_name_value
+
+     dep_generated_prefix ::= "generated-prefix" ":" STRING
+
+     dep_hostname_char_set ::= "hostname-char-set" ":" STRING
+
+     dep_hostname_char_replacement ::= "hostname-char-replacement" ":" STRING
+
+     config_control ::= "config-control" ":" "{" config_control_params "}"
+
+     sub_config_control ::= "{" config_control_params "}"
+
+     config_control_params ::= config_control_param
+                          | config_control_params "," config_control_param
+                          | config_control_params ","
+
+     config_control_param ::= config_databases
+                         | config_fetch_wait_time
+
+     config_databases ::= "config-databases" ":" "[" database_list "]"
+
+     config_fetch_wait_time ::= "config-fetch-wait-time" ":" INTEGER
+
+     loggers ::= "loggers" ":" "[" loggers_entries "]"
+
+     loggers_entries ::= logger_entry
+                    | loggers_entries "," logger_entry
+                    | loggers_entries ","
+
+     logger_entry ::= "{" logger_params "}"
+
+     logger_params ::= logger_param
+                  | logger_params "," logger_param
+                  | logger_params ","
+
+     logger_param ::= name
+                 | output_options_list
+                 | debuglevel
+                 | severity
+                 | user_context
+                 | comment
+                 | unknown_map_entry
+
+     debuglevel ::= "debuglevel" ":" INTEGER
+
+     severity ::= "severity" ":" STRING
+
+     output_options_list ::= "output_options" ":" "[" output_options_list_content "]"
+
+     output_options_list_content ::= output_entry
+                                | output_options_list_content "," output_entry
+                                | output_options_list_content ","
+
+     output_entry ::= "{" output_params_list "}"
+
+     output_params_list ::= output_params
+                       | output_params_list "," output_params
+                       | output_params_list ","
+
+     output_params ::= output
+                  | flush
+                  | maxsize
+                  | maxver
+                  | pattern
+
+     output ::= "output" ":" STRING
+
+     flush ::= "flush" ":" BOOLEAN
+
+     maxsize ::= "maxsize" ":" INTEGER
+
+     maxver ::= "maxver" ":" INTEGER
+
+     pattern ::= "pattern" ":" STRING
+
+     compatibility ::= "compatibility" ":" "{" compatibility_params "}"
+
+     compatibility_params ::= compatibility_param
+                         | compatibility_params "," compatibility_param
+                         | compatibility_params ","
+
+     compatibility_param ::= lenient_option_parsing
+                        | unknown_map_entry
+
+     lenient_option_parsing ::= "lenient-option-parsing" ":" BOOLEAN
+
diff --git a/doc/sphinx/grammar/grammar-dhcp6-parser.rst b/doc/sphinx/grammar/grammar-dhcp6-parser.rst
new file mode 100644
index 0000000..b9d4b79
--- /dev/null
+++ b/doc/sphinx/grammar/grammar-dhcp6-parser.rst
@@ -0,0 +1,1049 @@
+This grammar is generated from ``dhcp6_parser.yy``. See :ref:`dhcp6` for more details.
+
+.. code-block:: BNF
+   :linenos:
+
+     Grammar
+
+     $accept ::= start EOF
+
+     start ::= TOPLEVEL_JSON sub_json
+
+     start ::= TOPLEVEL_DHCP6 syntax_map
+
+     start ::= SUB_DHCP6 sub_dhcp6
+
+     start ::= SUB_INTERFACES6 sub_interfaces6
+
+     start ::= SUB_SUBNET6 sub_subnet6
+
+     start ::= SUB_POOL6 sub_pool6
+
+     start ::= SUB_PD_POOL sub_pd_pool
+
+     start ::= SUB_RESERVATION sub_reservation
+
+     start ::= SUB_OPTION_DEFS sub_option_def_list
+
+     start ::= SUB_OPTION_DEF sub_option_def
+
+     start ::= SUB_OPTION_DATA sub_option_data
+
+     start ::= SUB_HOOKS_LIBRARY sub_hooks_library
+
+     start ::= SUB_DHCP_DDNS sub_dhcp_ddns
+
+     start ::= SUB_CONFIG_CONTROL sub_config_control
+
+     value ::= INTEGER
+          | FLOAT
+          | BOOLEAN
+          | STRING
+          | NULL
+          | map2
+          | list_generic
+
+     sub_json ::= value
+
+     map2 ::= "{" map_content "}"
+
+     map_value ::= map2
+
+     map_content ::= 
+                | not_empty_map
+
+     not_empty_map ::= STRING ":" value
+                  | not_empty_map "," STRING ":" value
+                  | not_empty_map ","
+
+     list_generic ::= "[" list_content "]"
+
+     list_content ::= 
+                 | not_empty_list
+
+     not_empty_list ::= value
+                   | not_empty_list "," value
+                   | not_empty_list ","
+
+     list_strings ::= "[" list_strings_content "]"
+
+     list_strings_content ::= 
+                         | not_empty_list_strings
+
+     not_empty_list_strings ::= STRING
+                           | not_empty_list_strings "," STRING
+                           | not_empty_list_strings ","
+
+     unknown_map_entry ::= STRING ":"
+
+     syntax_map ::= "{" global_object "}"
+
+     global_object ::= "Dhcp6" ":" "{" global_params "}"
+                  | global_object_comma
+
+     global_object_comma ::= global_object ","
+
+     sub_dhcp6 ::= "{" global_params "}"
+
+     global_params ::= global_param
+                  | global_params "," global_param
+                  | global_params ","
+
+     global_param ::= data_directory
+                 | preferred_lifetime
+                 | min_preferred_lifetime
+                 | max_preferred_lifetime
+                 | valid_lifetime
+                 | min_valid_lifetime
+                 | max_valid_lifetime
+                 | renew_timer
+                 | rebind_timer
+                 | decline_probation_period
+                 | subnet6_list
+                 | shared_networks
+                 | interfaces_config
+                 | lease_database
+                 | hosts_database
+                 | hosts_databases
+                 | mac_sources
+                 | relay_supplied_options
+                 | host_reservation_identifiers
+                 | client_classes
+                 | option_def_list
+                 | option_data_list
+                 | hooks_libraries
+                 | expired_leases_processing
+                 | server_id
+                 | dhcp4o6_port
+                 | control_socket
+                 | dhcp_queue_control
+                 | dhcp_ddns
+                 | user_context
+                 | comment
+                 | sanity_checks
+                 | reservations
+                 | config_control
+                 | server_tag
+                 | reservation_mode
+                 | reservations_global
+                 | reservations_in_subnet
+                 | reservations_out_of_pool
+                 | calculate_tee_times
+                 | t1_percent
+                 | t2_percent
+                 | cache_threshold
+                 | cache_max_age
+                 | loggers
+                 | hostname_char_set
+                 | hostname_char_replacement
+                 | ddns_send_updates
+                 | ddns_override_no_update
+                 | ddns_override_client_update
+                 | ddns_replace_client_name
+                 | ddns_generated_prefix
+                 | ddns_qualifying_suffix
+                 | ddns_update_on_renew
+                 | ddns_use_conflict_resolution
+                 | store_extended_info
+                 | statistic_default_sample_count
+                 | statistic_default_sample_age
+                 | dhcp_multi_threading
+                 | early_global_reservations_lookup
+                 | ip_reservations_unique
+                 | reservations_lookup_first
+                 | compatibility
+                 | parked_packet_limit
+                 | unknown_map_entry
+
+     data_directory ::= "data-directory" ":" STRING
+
+     preferred_lifetime ::= "preferred-lifetime" ":" INTEGER
+
+     min_preferred_lifetime ::= "min-preferred-lifetime" ":" INTEGER
+
+     max_preferred_lifetime ::= "max-preferred-lifetime" ":" INTEGER
+
+     valid_lifetime ::= "valid-lifetime" ":" INTEGER
+
+     min_valid_lifetime ::= "min-valid-lifetime" ":" INTEGER
+
+     max_valid_lifetime ::= "max-valid-lifetime" ":" INTEGER
+
+     renew_timer ::= "renew-timer" ":" INTEGER
+
+     rebind_timer ::= "rebind-timer" ":" INTEGER
+
+     calculate_tee_times ::= "calculate-tee-times" ":" BOOLEAN
+
+     t1_percent ::= "t1-percent" ":" FLOAT
+
+     t2_percent ::= "t2-percent" ":" FLOAT
+
+     cache_threshold ::= "cache-threshold" ":" FLOAT
+
+     cache_max_age ::= "cache-max-age" ":" INTEGER
+
+     decline_probation_period ::= "decline-probation-period" ":" INTEGER
+
+     ddns_send_updates ::= "ddns-send-updates" ":" BOOLEAN
+
+     ddns_override_no_update ::= "ddns-override-no-update" ":" BOOLEAN
+
+     ddns_override_client_update ::= "ddns-override-client-update" ":" BOOLEAN
+
+     ddns_replace_client_name ::= "ddns-replace-client-name" ":" ddns_replace_client_name_value
+
+     ddns_replace_client_name_value ::= "when-present"
+                                   | "never"
+                                   | "always"
+                                   | "when-not-present"
+                                   | BOOLEAN
+
+     ddns_generated_prefix ::= "ddns-generated-prefix" ":" STRING
+
+     ddns_qualifying_suffix ::= "ddns-qualifying-suffix" ":" STRING
+
+     ddns_update_on_renew ::= "ddns-update-on-renew" ":" BOOLEAN
+
+     ddns_use_conflict_resolution ::= "ddns-use-conflict-resolution" ":" BOOLEAN
+
+     hostname_char_set ::= "hostname-char-set" ":" STRING
+
+     hostname_char_replacement ::= "hostname-char-replacement" ":" STRING
+
+     store_extended_info ::= "store-extended-info" ":" BOOLEAN
+
+     statistic_default_sample_count ::= "statistic-default-sample-count" ":" INTEGER
+
+     statistic_default_sample_age ::= "statistic-default-sample-age" ":" INTEGER
+
+     server_tag ::= "server-tag" ":" STRING
+
+     parked_packet_limit ::= "parked-packet-limit" ":" INTEGER
+
+     early_global_reservations_lookup ::= "early-global-reservations-lookup" ":" BOOLEAN
+
+     ip_reservations_unique ::= "ip-reservations-unique" ":" BOOLEAN
+
+     reservations_lookup_first ::= "reservations-lookup-first" ":" BOOLEAN
+
+     interfaces_config ::= "interfaces-config" ":" "{" interfaces_config_params "}"
+
+     sub_interfaces6 ::= "{" interfaces_config_params "}"
+
+     interfaces_config_params ::= interfaces_config_param
+                             | interfaces_config_params "," interfaces_config_param
+                             | interfaces_config_params ","
+
+     interfaces_config_param ::= interfaces_list
+                            | re_detect
+                            | service_sockets_require_all
+                            | service_sockets_retry_wait_time
+                            | service_sockets_max_retries
+                            | user_context
+                            | comment
+                            | unknown_map_entry
+
+     interfaces_list ::= "interfaces" ":" list_strings
+
+     re_detect ::= "re-detect" ":" BOOLEAN
+
+     service_sockets_require_all ::= "service-sockets-require-all" ":" BOOLEAN
+
+     service_sockets_retry_wait_time ::= "service-sockets-retry-wait-time" ":" INTEGER
+
+     service_sockets_max_retries ::= "service-sockets-max-retries" ":" INTEGER
+
+     lease_database ::= "lease-database" ":" "{" database_map_params "}"
+
+     hosts_database ::= "hosts-database" ":" "{" database_map_params "}"
+
+     hosts_databases ::= "hosts-databases" ":" "[" database_list "]"
+
+     database_list ::= 
+                  | not_empty_database_list
+
+     not_empty_database_list ::= database
+                            | not_empty_database_list "," database
+                            | not_empty_database_list ","
+
+     database ::= "{" database_map_params "}"
+
+     database_map_params ::= database_map_param
+                        | database_map_params "," database_map_param
+                        | database_map_params ","
+
+     database_map_param ::= database_type
+                       | user
+                       | password
+                       | host
+                       | port
+                       | name
+                       | persist
+                       | lfc_interval
+                       | readonly
+                       | connect_timeout
+                       | max_reconnect_tries
+                       | reconnect_wait_time
+                       | on_fail
+                       | max_row_errors
+                       | trust_anchor
+                       | cert_file
+                       | key_file
+                       | cipher_list
+                       | unknown_map_entry
+
+     database_type ::= "type" ":" db_type
+
+     db_type ::= "memfile"
+            | "mysql"
+            | "postgresql"
+
+     user ::= "user" ":" STRING
+
+     password ::= "password" ":" STRING
+
+     host ::= "host" ":" STRING
+
+     port ::= "port" ":" INTEGER
+
+     name ::= "name" ":" STRING
+
+     persist ::= "persist" ":" BOOLEAN
+
+     lfc_interval ::= "lfc-interval" ":" INTEGER
+
+     readonly ::= "readonly" ":" BOOLEAN
+
+     connect_timeout ::= "connect-timeout" ":" INTEGER
+
+     reconnect_wait_time ::= "reconnect-wait-time" ":" INTEGER
+
+     on_fail ::= "on-fail" ":" on_fail_mode
+
+     on_fail_mode ::= "stop-retry-exit"
+                 | "serve-retry-exit"
+                 | "serve-retry-continue"
+
+     max_row_errors ::= "max-row-errors" ":" INTEGER
+
+     max_reconnect_tries ::= "max-reconnect-tries" ":" INTEGER
+
+     trust_anchor ::= "trust-anchor" ":" STRING
+
+     cert_file ::= "cert-file" ":" STRING
+
+     key_file ::= "key-file" ":" STRING
+
+     cipher_list ::= "cipher-list" ":" STRING
+
+     sanity_checks ::= "sanity-checks" ":" "{" sanity_checks_params "}"
+
+     sanity_checks_params ::= sanity_checks_param
+                         | sanity_checks_params "," sanity_checks_param
+                         | sanity_checks_params ","
+
+     sanity_checks_param ::= lease_checks
+
+     lease_checks ::= "lease-checks" ":" STRING
+
+     mac_sources ::= "mac-sources" ":" "[" mac_sources_list "]"
+
+     mac_sources_list ::= mac_sources_value
+                     | mac_sources_list "," mac_sources_value
+                     | mac_sources_list ","
+
+     mac_sources_value ::= duid_id
+                      | string_id
+
+     duid_id ::= "duid"
+
+     string_id ::= STRING
+
+     host_reservation_identifiers ::= "host-reservation-identifiers" ":" "[" host_reservation_identifiers_list "]"
+
+     host_reservation_identifiers_list ::= host_reservation_identifier
+                                      | host_reservation_identifiers_list "," host_reservation_identifier
+                                      | host_reservation_identifiers_list ","
+
+     host_reservation_identifier ::= duid_id
+                                | hw_address_id
+                                | flex_id
+
+     hw_address_id ::= "hw-address"
+
+     flex_id ::= "flex-id"
+
+     relay_supplied_options ::= "relay-supplied-options" ":" "[" list_content "]"
+
+     dhcp_multi_threading ::= "multi-threading" ":" "{" multi_threading_params "}"
+
+     multi_threading_params ::= multi_threading_param
+                           | multi_threading_params "," multi_threading_param
+                           | multi_threading_params ","
+
+     multi_threading_param ::= enable_multi_threading
+                          | thread_pool_size
+                          | packet_queue_size
+                          | user_context
+                          | comment
+                          | unknown_map_entry
+
+     enable_multi_threading ::= "enable-multi-threading" ":" BOOLEAN
+
+     thread_pool_size ::= "thread-pool-size" ":" INTEGER
+
+     packet_queue_size ::= "packet-queue-size" ":" INTEGER
+
+     hooks_libraries ::= "hooks-libraries" ":" "[" hooks_libraries_list "]"
+
+     hooks_libraries_list ::= 
+                         | not_empty_hooks_libraries_list
+
+     not_empty_hooks_libraries_list ::= hooks_library
+                                   | not_empty_hooks_libraries_list "," hooks_library
+                                   | not_empty_hooks_libraries_list ","
+
+     hooks_library ::= "{" hooks_params "}"
+
+     sub_hooks_library ::= "{" hooks_params "}"
+
+     hooks_params ::= hooks_param
+                 | hooks_params "," hooks_param
+                 | hooks_params ","
+                 | unknown_map_entry
+
+     hooks_param ::= library
+                | parameters
+
+     library ::= "library" ":" STRING
+
+     parameters ::= "parameters" ":" map_value
+
+     expired_leases_processing ::= "expired-leases-processing" ":" "{" expired_leases_params "}"
+
+     expired_leases_params ::= expired_leases_param
+                          | expired_leases_params "," expired_leases_param
+                          | expired_leases_params ","
+
+     expired_leases_param ::= reclaim_timer_wait_time
+                         | flush_reclaimed_timer_wait_time
+                         | hold_reclaimed_time
+                         | max_reclaim_leases
+                         | max_reclaim_time
+                         | unwarned_reclaim_cycles
+
+     reclaim_timer_wait_time ::= "reclaim-timer-wait-time" ":" INTEGER
+
+     flush_reclaimed_timer_wait_time ::= "flush-reclaimed-timer-wait-time" ":" INTEGER
+
+     hold_reclaimed_time ::= "hold-reclaimed-time" ":" INTEGER
+
+     max_reclaim_leases ::= "max-reclaim-leases" ":" INTEGER
+
+     max_reclaim_time ::= "max-reclaim-time" ":" INTEGER
+
+     unwarned_reclaim_cycles ::= "unwarned-reclaim-cycles" ":" INTEGER
+
+     subnet6_list ::= "subnet6" ":" "[" subnet6_list_content "]"
+
+     subnet6_list_content ::= 
+                         | not_empty_subnet6_list
+
+     not_empty_subnet6_list ::= subnet6
+                           | not_empty_subnet6_list "," subnet6
+                           | not_empty_subnet6_list ","
+
+     subnet6 ::= "{" subnet6_params "}"
+
+     sub_subnet6 ::= "{" subnet6_params "}"
+
+     subnet6_params ::= subnet6_param
+                   | subnet6_params "," subnet6_param
+                   | subnet6_params ","
+
+     subnet6_param ::= preferred_lifetime
+                  | min_preferred_lifetime
+                  | max_preferred_lifetime
+                  | valid_lifetime
+                  | min_valid_lifetime
+                  | max_valid_lifetime
+                  | renew_timer
+                  | rebind_timer
+                  | option_data_list
+                  | pools_list
+                  | pd_pools_list
+                  | subnet
+                  | interface
+                  | interface_id
+                  | id
+                  | rapid_commit
+                  | client_class
+                  | require_client_classes
+                  | reservations
+                  | reservation_mode
+                  | reservations_global
+                  | reservations_in_subnet
+                  | reservations_out_of_pool
+                  | relay
+                  | user_context
+                  | comment
+                  | calculate_tee_times
+                  | t1_percent
+                  | t2_percent
+                  | cache_threshold
+                  | cache_max_age
+                  | hostname_char_set
+                  | hostname_char_replacement
+                  | ddns_send_updates
+                  | ddns_override_no_update
+                  | ddns_override_client_update
+                  | ddns_replace_client_name
+                  | ddns_generated_prefix
+                  | ddns_qualifying_suffix
+                  | ddns_update_on_renew
+                  | ddns_use_conflict_resolution
+                  | store_extended_info
+                  | unknown_map_entry
+
+     subnet ::= "subnet" ":" STRING
+
+     interface ::= "interface" ":" STRING
+
+     interface_id ::= "interface-id" ":" STRING
+
+     client_class ::= "client-class" ":" STRING
+
+     require_client_classes ::= "require-client-classes" ":" list_strings
+
+     reservations_global ::= "reservations-global" ":" BOOLEAN
+
+     reservations_in_subnet ::= "reservations-in-subnet" ":" BOOLEAN
+
+     reservations_out_of_pool ::= "reservations-out-of-pool" ":" BOOLEAN
+
+     reservation_mode ::= "reservation-mode" ":" hr_mode
+
+     hr_mode ::= "disabled"
+            | "out-of-pool"
+            | "global"
+            | "all"
+
+     id ::= "id" ":" INTEGER
+
+     rapid_commit ::= "rapid-commit" ":" BOOLEAN
+
+     shared_networks ::= "shared-networks" ":" "[" shared_networks_content "]"
+
+     shared_networks_content ::= 
+                            | shared_networks_list
+
+     shared_networks_list ::= shared_network
+                         | shared_networks_list "," shared_network
+                         | shared_networks_list ","
+
+     shared_network ::= "{" shared_network_params "}"
+
+     shared_network_params ::= shared_network_param
+                          | shared_network_params "," shared_network_param
+                          | shared_network_params ","
+
+     shared_network_param ::= name
+                         | subnet6_list
+                         | interface
+                         | interface_id
+                         | renew_timer
+                         | rebind_timer
+                         | option_data_list
+                         | relay
+                         | reservation_mode
+                         | reservations_global
+                         | reservations_in_subnet
+                         | reservations_out_of_pool
+                         | client_class
+                         | require_client_classes
+                         | preferred_lifetime
+                         | min_preferred_lifetime
+                         | max_preferred_lifetime
+                         | rapid_commit
+                         | valid_lifetime
+                         | min_valid_lifetime
+                         | max_valid_lifetime
+                         | user_context
+                         | comment
+                         | calculate_tee_times
+                         | t1_percent
+                         | t2_percent
+                         | cache_threshold
+                         | cache_max_age
+                         | hostname_char_set
+                         | hostname_char_replacement
+                         | ddns_send_updates
+                         | ddns_override_no_update
+                         | ddns_override_client_update
+                         | ddns_replace_client_name
+                         | ddns_generated_prefix
+                         | ddns_qualifying_suffix
+                         | ddns_update_on_renew
+                         | ddns_use_conflict_resolution
+                         | store_extended_info
+                         | unknown_map_entry
+
+     option_def_list ::= "option-def" ":" "[" option_def_list_content "]"
+
+     sub_option_def_list ::= "{" option_def_list "}"
+
+     option_def_list_content ::= 
+                            | not_empty_option_def_list
+
+     not_empty_option_def_list ::= option_def_entry
+                              | not_empty_option_def_list "," option_def_entry
+                              | not_empty_option_def_list ","
+
+     option_def_entry ::= "{" option_def_params "}"
+
+     sub_option_def ::= "{" option_def_params "}"
+
+     option_def_params ::= 
+                      | not_empty_option_def_params
+
+     not_empty_option_def_params ::= option_def_param
+                                | not_empty_option_def_params "," option_def_param
+                                | not_empty_option_def_params ","
+
+     option_def_param ::= option_def_name
+                     | option_def_code
+                     | option_def_type
+                     | option_def_record_types
+                     | option_def_space
+                     | option_def_encapsulate
+                     | option_def_array
+                     | user_context
+                     | comment
+                     | unknown_map_entry
+
+     option_def_name ::= name
+
+     code ::= "code" ":" INTEGER
+
+     option_def_code ::= code
+
+     option_def_type ::= "type" ":" STRING
+
+     option_def_record_types ::= "record-types" ":" STRING
+
+     space ::= "space" ":" STRING
+
+     option_def_space ::= space
+
+     option_def_encapsulate ::= "encapsulate" ":" STRING
+
+     option_def_array ::= "array" ":" BOOLEAN
+
+     option_data_list ::= "option-data" ":" "[" option_data_list_content "]"
+
+     option_data_list_content ::= 
+                             | not_empty_option_data_list
+
+     not_empty_option_data_list ::= option_data_entry
+                               | not_empty_option_data_list "," option_data_entry
+                               | not_empty_option_data_list ","
+
+     option_data_entry ::= "{" option_data_params "}"
+
+     sub_option_data ::= "{" option_data_params "}"
+
+     option_data_params ::= 
+                       | not_empty_option_data_params
+
+     not_empty_option_data_params ::= option_data_param
+                                 | not_empty_option_data_params "," option_data_param
+                                 | not_empty_option_data_params ","
+
+     option_data_param ::= option_data_name
+                      | option_data_data
+                      | option_data_code
+                      | option_data_space
+                      | option_data_csv_format
+                      | option_data_always_send
+                      | user_context
+                      | comment
+                      | unknown_map_entry
+
+     option_data_name ::= name
+
+     option_data_data ::= "data" ":" STRING
+
+     option_data_code ::= code
+
+     option_data_space ::= space
+
+     option_data_csv_format ::= "csv-format" ":" BOOLEAN
+
+     option_data_always_send ::= "always-send" ":" BOOLEAN
+
+     pools_list ::= "pools" ":" "[" pools_list_content "]"
+
+     pools_list_content ::= 
+                       | not_empty_pools_list
+
+     not_empty_pools_list ::= pool_list_entry
+                         | not_empty_pools_list "," pool_list_entry
+                         | not_empty_pools_list ","
+
+     pool_list_entry ::= "{" pool_params "}"
+
+     sub_pool6 ::= "{" pool_params "}"
+
+     pool_params ::= pool_param
+                | pool_params "," pool_param
+                | pool_params ","
+
+     pool_param ::= pool_entry
+               | option_data_list
+               | client_class
+               | require_client_classes
+               | user_context
+               | comment
+               | unknown_map_entry
+
+     pool_entry ::= "pool" ":" STRING
+
+     user_context ::= "user-context" ":" map_value
+
+     comment ::= "comment" ":" STRING
+
+     pd_pools_list ::= "pd-pools" ":" "[" pd_pools_list_content "]"
+
+     pd_pools_list_content ::= 
+                          | not_empty_pd_pools_list
+
+     not_empty_pd_pools_list ::= pd_pool_entry
+                            | not_empty_pd_pools_list "," pd_pool_entry
+                            | not_empty_pd_pools_list ","
+
+     pd_pool_entry ::= "{" pd_pool_params "}"
+
+     sub_pd_pool ::= "{" pd_pool_params "}"
+
+     pd_pool_params ::= pd_pool_param
+                   | pd_pool_params "," pd_pool_param
+                   | pd_pool_params ","
+
+     pd_pool_param ::= pd_prefix
+                  | pd_prefix_len
+                  | pd_delegated_len
+                  | option_data_list
+                  | client_class
+                  | require_client_classes
+                  | excluded_prefix
+                  | excluded_prefix_len
+                  | user_context
+                  | comment
+                  | unknown_map_entry
+
+     pd_prefix ::= "prefix" ":" STRING
+
+     pd_prefix_len ::= "prefix-len" ":" INTEGER
+
+     excluded_prefix ::= "excluded-prefix" ":" STRING
+
+     excluded_prefix_len ::= "excluded-prefix-len" ":" INTEGER
+
+     pd_delegated_len ::= "delegated-len" ":" INTEGER
+
+     reservations ::= "reservations" ":" "[" reservations_list "]"
+
+     reservations_list ::= 
+                      | not_empty_reservations_list
+
+     not_empty_reservations_list ::= reservation
+                                | not_empty_reservations_list "," reservation
+                                | not_empty_reservations_list ","
+
+     reservation ::= "{" reservation_params "}"
+
+     sub_reservation ::= "{" reservation_params "}"
+
+     reservation_params ::= 
+                       | not_empty_reservation_params
+
+     not_empty_reservation_params ::= reservation_param
+                                 | not_empty_reservation_params "," reservation_param
+                                 | not_empty_reservation_params ","
+
+     reservation_param ::= duid
+                      | reservation_client_classes
+                      | ip_addresses
+                      | prefixes
+                      | hw_address
+                      | hostname
+                      | flex_id_value
+                      | option_data_list
+                      | user_context
+                      | comment
+                      | unknown_map_entry
+
+     ip_addresses ::= "ip-addresses" ":" list_strings
+
+     prefixes ::= "prefixes" ":" list_strings
+
+     duid ::= "duid" ":" STRING
+
+     hw_address ::= "hw-address" ":" STRING
+
+     hostname ::= "hostname" ":" STRING
+
+     flex_id_value ::= "flex-id" ":" STRING
+
+     reservation_client_classes ::= "client-classes" ":" list_strings
+
+     relay ::= "relay" ":" "{" relay_map "}"
+
+     relay_map ::= ip_address
+              | ip_addresses
+
+     ip_address ::= "ip-address" ":" STRING
+
+     client_classes ::= "client-classes" ":" "[" client_classes_list "]"
+
+     client_classes_list ::= client_class_entry
+                        | client_classes_list "," client_class_entry
+                        | client_classes_list ","
+
+     client_class_entry ::= "{" client_class_params "}"
+
+     client_class_params ::= 
+                        | not_empty_client_class_params
+
+     not_empty_client_class_params ::= client_class_param
+                                  | not_empty_client_class_params "," client_class_param
+                                  | not_empty_client_class_params ","
+
+     client_class_param ::= client_class_name
+                       | client_class_test
+                       | only_if_required
+                       | option_data_list
+                       | user_context
+                       | comment
+                       | preferred_lifetime
+                       | min_preferred_lifetime
+                       | max_preferred_lifetime
+                       | valid_lifetime
+                       | min_valid_lifetime
+                       | max_valid_lifetime
+                       | unknown_map_entry
+
+     client_class_name ::= name
+
+     client_class_test ::= "test" ":" STRING
+
+     only_if_required ::= "only-if-required" ":" BOOLEAN
+
+     server_id ::= "server-id" ":" "{" server_id_params "}"
+
+     server_id_params ::= server_id_param
+                     | server_id_params "," server_id_param
+                     | server_id_params ","
+
+     server_id_param ::= server_id_type
+                    | identifier
+                    | time
+                    | htype
+                    | enterprise_id
+                    | persist
+                    | user_context
+                    | comment
+                    | unknown_map_entry
+
+     server_id_type ::= "type" ":" duid_type
+
+     duid_type ::= "LLT"
+              | "EN"
+              | "LL"
+
+     htype ::= "htype" ":" INTEGER
+
+     identifier ::= "identifier" ":" STRING
+
+     time ::= "time" ":" INTEGER
+
+     enterprise_id ::= "enterprise-id" ":" INTEGER
+
+     dhcp4o6_port ::= "dhcp4o6-port" ":" INTEGER
+
+     control_socket ::= "control-socket" ":" "{" control_socket_params "}"
+
+     control_socket_params ::= control_socket_param
+                          | control_socket_params "," control_socket_param
+                          | control_socket_params ","
+
+     control_socket_param ::= socket_type
+                         | socket_name
+                         | user_context
+                         | comment
+                         | unknown_map_entry
+
+     socket_type ::= "socket-type" ":" STRING
+
+     socket_name ::= "socket-name" ":" STRING
+
+     dhcp_queue_control ::= "dhcp-queue-control" ":" "{" queue_control_params "}"
+
+     queue_control_params ::= queue_control_param
+                         | queue_control_params "," queue_control_param
+                         | queue_control_params ","
+
+     queue_control_param ::= enable_queue
+                        | queue_type
+                        | capacity
+                        | user_context
+                        | comment
+                        | arbitrary_map_entry
+
+     enable_queue ::= "enable-queue" ":" BOOLEAN
+
+     queue_type ::= "queue-type" ":" STRING
+
+     capacity ::= "capacity" ":" INTEGER
+
+     arbitrary_map_entry ::= STRING ":" value
+
+     dhcp_ddns ::= "dhcp-ddns" ":" "{" dhcp_ddns_params "}"
+
+     sub_dhcp_ddns ::= "{" dhcp_ddns_params "}"
+
+     dhcp_ddns_params ::= dhcp_ddns_param
+                     | dhcp_ddns_params "," dhcp_ddns_param
+                     | dhcp_ddns_params ","
+
+     dhcp_ddns_param ::= enable_updates
+                    | server_ip
+                    | server_port
+                    | sender_ip
+                    | sender_port
+                    | max_queue_size
+                    | ncr_protocol
+                    | ncr_format
+                    | dep_override_no_update
+                    | dep_override_client_update
+                    | dep_replace_client_name
+                    | dep_generated_prefix
+                    | dep_qualifying_suffix
+                    | dep_hostname_char_set
+                    | dep_hostname_char_replacement
+                    | user_context
+                    | comment
+                    | unknown_map_entry
+
+     enable_updates ::= "enable-updates" ":" BOOLEAN
+
+     dep_qualifying_suffix ::= "qualifying-suffix" ":" STRING
+
+     server_ip ::= "server-ip" ":" STRING
+
+     server_port ::= "server-port" ":" INTEGER
+
+     sender_ip ::= "sender-ip" ":" STRING
+
+     sender_port ::= "sender-port" ":" INTEGER
+
+     max_queue_size ::= "max-queue-size" ":" INTEGER
+
+     ncr_protocol ::= "ncr-protocol" ":" ncr_protocol_value
+
+     ncr_protocol_value ::= "UDP"
+                       | "TCP"
+
+     ncr_format ::= "ncr-format" ":" "JSON"
+
+     dep_override_no_update ::= "override-no-update" ":" BOOLEAN
+
+     dep_override_client_update ::= "override-client-update" ":" BOOLEAN
+
+     dep_replace_client_name ::= "replace-client-name" ":" ddns_replace_client_name_value
+
+     dep_generated_prefix ::= "generated-prefix" ":" STRING
+
+     dep_hostname_char_set ::= "hostname-char-set" ":" STRING
+
+     dep_hostname_char_replacement ::= "hostname-char-replacement" ":" STRING
+
+     config_control ::= "config-control" ":" "{" config_control_params "}"
+
+     sub_config_control ::= "{" config_control_params "}"
+
+     config_control_params ::= config_control_param
+                          | config_control_params "," config_control_param
+                          | config_control_params ","
+
+     config_control_param ::= config_databases
+                         | config_fetch_wait_time
+
+     config_databases ::= "config-databases" ":" "[" database_list "]"
+
+     config_fetch_wait_time ::= "config-fetch-wait-time" ":" INTEGER
+
+     loggers ::= "loggers" ":" "[" loggers_entries "]"
+
+     loggers_entries ::= logger_entry
+                    | loggers_entries "," logger_entry
+                    | loggers_entries ","
+
+     logger_entry ::= "{" logger_params "}"
+
+     logger_params ::= logger_param
+                  | logger_params "," logger_param
+                  | logger_params ","
+
+     logger_param ::= name
+                 | output_options_list
+                 | debuglevel
+                 | severity
+                 | user_context
+                 | comment
+                 | unknown_map_entry
+
+     debuglevel ::= "debuglevel" ":" INTEGER
+
+     severity ::= "severity" ":" STRING
+
+     output_options_list ::= "output_options" ":" "[" output_options_list_content "]"
+
+     output_options_list_content ::= output_entry
+                                | output_options_list_content "," output_entry
+                                | output_options_list_content ","
+
+     output_entry ::= "{" output_params_list "}"
+
+     output_params_list ::= output_params
+                       | output_params_list "," output_params
+                       | output_params_list ","
+
+     output_params ::= output
+                  | flush
+                  | maxsize
+                  | maxver
+                  | pattern
+
+     output ::= "output" ":" STRING
+
+     flush ::= "flush" ":" BOOLEAN
+
+     maxsize ::= "maxsize" ":" INTEGER
+
+     maxver ::= "maxver" ":" INTEGER
+
+     pattern ::= "pattern" ":" STRING
+
+     compatibility ::= "compatibility" ":" "{" compatibility_params "}"
+
+     compatibility_params ::= compatibility_param
+                         | compatibility_params "," compatibility_param
+                         | compatibility_params ","
+
+     compatibility_param ::= lenient_option_parsing
+                        | unknown_map_entry
+
+     lenient_option_parsing ::= "lenient-option-parsing" ":" BOOLEAN
+
diff --git a/doc/sphinx/grammar/grammar-netconf-parser.rst b/doc/sphinx/grammar/grammar-netconf-parser.rst
new file mode 100644
index 0000000..0594706
--- /dev/null
+++ b/doc/sphinx/grammar/grammar-netconf-parser.rst
@@ -0,0 +1,221 @@
+This grammar is generated from ``netconf_parser.yy``. See :ref:`netconf` for more details.
+
+.. code-block:: BNF
+   :linenos:
+
+     Grammar
+
+     $accept ::= start EOF
+
+     start ::= START_JSON json
+
+     start ::= START_NETCONF netconf_syntax_map
+
+     start ::= START_SUB_NETCONF sub_netconf
+
+     sub_netconf ::= "{" global_params "}"
+
+     json ::= value
+
+     value ::= INTEGER
+          | FLOAT
+          | BOOLEAN
+          | STRING
+          | NULL
+          | map
+          | list_generic
+
+     map ::= "{" map_content "}"
+
+     map_value ::= map
+
+     map_content ::= 
+                | not_empty_map
+
+     not_empty_map ::= STRING ":" value
+                  | not_empty_map "," STRING ":" value
+                  | not_empty_map ","
+
+     list_generic ::= "[" list_content "]"
+
+     list_content ::= 
+                 | not_empty_list
+
+     not_empty_list ::= value
+                   | not_empty_list "," value
+                   | not_empty_list ","
+
+     unknown_map_entry ::= STRING ":"
+
+     netconf_syntax_map ::= "{" global_object "}"
+
+     global_object ::= "Netconf" ":" "{" global_params "}"
+                  | global_object_comma
+
+     global_object_comma ::= global_object ","
+
+     global_params ::= 
+                  | not_empty_global_params
+
+     not_empty_global_params ::= global_param
+                            | not_empty_global_params "," global_param
+                            | not_empty_global_params ","
+
+     global_param ::= boot_update
+                 | subscribe_changes
+                 | validate_changes
+                 | managed_servers
+                 | hooks_libraries
+                 | loggers
+                 | user_context
+                 | comment
+                 | unknown_map_entry
+
+     boot_update ::= "boot-update" ":" BOOLEAN
+
+     subscribe_changes ::= "subscribe-changes" ":" BOOLEAN
+
+     validate_changes ::= "validate-changes" ":" BOOLEAN
+
+     user_context ::= "user-context" ":" map_value
+
+     comment ::= "comment" ":" STRING
+
+     hooks_libraries ::= "hooks-libraries" ":" "[" hooks_libraries_list "]"
+
+     hooks_libraries_list ::= 
+                         | not_empty_hooks_libraries_list
+
+     not_empty_hooks_libraries_list ::= hooks_library
+                                   | not_empty_hooks_libraries_list "," hooks_library
+                                   | not_empty_hooks_libraries_list ","
+
+     hooks_library ::= "{" hooks_params "}"
+
+     hooks_params ::= hooks_param
+                 | hooks_params "," hooks_param
+                 | hooks_params ","
+                 | unknown_map_entry
+
+     hooks_param ::= library
+                | parameters
+
+     library ::= "library" ":" STRING
+
+     parameters ::= "parameters" ":" map_value
+
+     managed_servers ::= "managed-servers" ":" "{" servers_entries "}"
+
+     servers_entries ::= 
+                    | not_empty_servers_entries
+
+     not_empty_servers_entries ::= server_entry
+                              | not_empty_servers_entries "," server_entry
+                              | not_empty_servers_entries ","
+
+     server_entry ::= dhcp4_server
+                 | dhcp6_server
+                 | d2_server
+                 | ca_server
+                 | unknown_map_entry
+
+     dhcp4_server ::= "dhcp4" ":" "{" managed_server_params "}"
+
+     dhcp6_server ::= "dhcp6" ":" "{" managed_server_params "}"
+
+     d2_server ::= "d2" ":" "{" managed_server_params "}"
+
+     ca_server ::= "ca" ":" "{" managed_server_params "}"
+
+     managed_server_params ::= managed_server_param
+                          | managed_server_params "," managed_server_param
+                          | managed_server_params ","
+
+     managed_server_param ::= model
+                         | boot_update
+                         | subscribe_changes
+                         | validate_changes
+                         | control_socket
+                         | user_context
+                         | comment
+                         | unknown_map_entry
+
+     model ::= "model" ":" STRING
+
+     control_socket ::= "control-socket" ":" "{" control_socket_params "}"
+
+     control_socket_params ::= control_socket_param
+                          | control_socket_params "," control_socket_param
+                          | control_socket_params ","
+
+     control_socket_param ::= socket_type
+                         | socket_name
+                         | socket_url
+                         | user_context
+                         | comment
+                         | unknown_map_entry
+
+     socket_type ::= "socket-type" ":" socket_type_value
+
+     socket_type_value ::= "unix"
+                      | "http"
+                      | "stdout"
+
+     socket_name ::= "socket-name" ":" STRING
+
+     socket_url ::= "socket-url" ":" STRING
+
+     loggers ::= "loggers" ":" "[" loggers_entries "]"
+
+     loggers_entries ::= logger_entry
+                    | loggers_entries "," logger_entry
+                    | loggers_entries ","
+
+     logger_entry ::= "{" logger_params "}"
+
+     logger_params ::= logger_param
+                  | logger_params "," logger_param
+                  | logger_params ","
+
+     logger_param ::= name
+                 | output_options_list
+                 | debuglevel
+                 | severity
+                 | user_context
+                 | comment
+                 | unknown_map_entry
+
+     name ::= "name" ":" STRING
+
+     debuglevel ::= "debuglevel" ":" INTEGER
+
+     severity ::= "severity" ":" STRING
+
+     output_options_list ::= "output_options" ":" "[" output_options_list_content "]"
+
+     output_options_list_content ::= output_entry
+                                | output_options_list_content "," output_entry
+                                | output_options_list_content ","
+
+     output_entry ::= "{" output_params_list "}"
+
+     output_params_list ::= output_params
+                       | output_params_list "," output_params
+                       | output_params_list ","
+
+     output_params ::= output
+                  | flush
+                  | maxsize
+                  | maxver
+                  | pattern
+
+     output ::= "output" ":" STRING
+
+     flush ::= "flush" ":" BOOLEAN
+
+     maxsize ::= "maxsize" ":" INTEGER
+
+     maxver ::= "maxver" ":" INTEGER
+
+     pattern ::= "pattern" ":" STRING
+
diff --git a/doc/sphinx/grammar/grammar.rst b/doc/sphinx/grammar/grammar.rst
new file mode 100644
index 0000000..d8f77b0
--- /dev/null
+++ b/doc/sphinx/grammar/grammar.rst
@@ -0,0 +1,44 @@
+..
+   Copyright (C) 2021-2022 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+.. _bnf-grammar:
+
+Kea Configuration File Syntax (BNF)
+===================================
+
+Kea consists of several daemons, each with its own configuration syntax. The following sections
+provide a complete syntax of all possible parameters, written in Backus-Naur Form (BNF).
+See this `Wikipedia article on BNF <https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form>`_ for
+more information.
+
+BNF Grammar for DHCPv4
+----------------------
+
+.. include:: grammar-dhcp4-parser.rst
+
+BNF Grammar for DHCPv6
+----------------------
+
+.. include:: grammar-dhcp6-parser.rst
+
+BNF Grammar for Control Agent
+-----------------------------
+
+.. include:: grammar-ca-parser.rst
+
+BNF Grammar for DHCP-DDNS
+-------------------------
+
+.. include:: grammar-d2-parser.rst
+
+BNF Grammar for the Kea NETCONF Agent
+-------------------------------------
+
+.. include:: grammar-netconf-parser.rst
diff --git a/doc/sphinx/index.rst b/doc/sphinx/index.rst
new file mode 100644
index 0000000..438621e
--- /dev/null
+++ b/doc/sphinx/index.rst
@@ -0,0 +1,62 @@
+.. only:: not latex
+
+    .. image:: static/kea-logo-200.png
+        :align: right
+
+.. _introduction:
+
+##################################
+Kea Administrator Reference Manual
+##################################
+
+Kea is an open source implementation of the Dynamic Host Configuration
+Protocol (DHCP) servers, developed and maintained by Internet Systems
+Consortium (ISC).
+
+This is the reference guide for Kea version |release|.
+Links to the most up-to-date version of this document (in PDF, HTML,
+and plain text formats) can be found on `Read the Docs <https://kea.readthedocs.io>`_.
+Other useful Kea information can be found in our
+`Knowledgebase <https://kb.isc.org>`_.
+
+
+.. toctree::
+   :numbered:
+   :maxdepth: 5
+
+   arm/intro
+   arm/quickstart
+   arm/install
+   arm/admin
+   arm/config
+   arm/keactrl
+   arm/agent
+   arm/dhcp4-srv
+   arm/dhcp6-srv
+   arm/database-connectivity
+   arm/lease-expiration
+   arm/congestion-handling
+   arm/ddns
+   arm/lfc
+   arm/classify
+   arm/hooks
+   arm/stats
+   arm/ctrl-channel
+   arm/logging
+   arm/shell
+   arm/integrations
+   arm/stork
+   arm/security
+
+.. toctree::
+   :caption: Appendices
+   :name: appendices
+   :maxdepth: 1
+
+   api
+   manpages
+   kea-messages
+   arm/config-templates.rst
+   umls
+   grammar/grammar
+   arm/acknowledgments
diff --git a/doc/sphinx/man/kea-admin.8.rst b/doc/sphinx/man/kea-admin.8.rst
new file mode 100644
index 0000000..9de0a0f
--- /dev/null
+++ b/doc/sphinx/man/kea-admin.8.rst
@@ -0,0 +1,159 @@
+..
+   Copyright (C) 2019-2022 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``kea-admin`` - Shell script for managing Kea databases
+-------------------------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`kea-admin` [command] [backend] [**-h** database_host]
+[**-P** database_port] [**-u** database_username]
+[**-p** [database_password]] [**-n** database_name] [**-d** script_directory]
+[**-v**] [**-x** extra_argument [**-x** extra_argument ...]]
+[**-4** | **-6**] [**-i** input_file] [**-o** output_file] [**-y**]
+
+Description
+~~~~~~~~~~~
+
+``kea-admin`` is a shell script that offers database maintenance. In
+particular, it features database initialization, database version
+checking, and database schema upgrading.
+
+Arguments
+~~~~~~~~~
+
+``command``
+   Specifies the command to be issued to the servers. It can be one of the
+   following:
+
+   ``db-init``
+      Initializes a new database schema. This is useful during a new Kea
+      installation. The database is initialized to the latest version
+      supported by the version of the software being installed.
+
+   ``db-version``
+      Reports the database backend version number. This is not necessarily
+      equal to the Kea version number, as each backend has its own
+      versioning scheme.
+
+   ``db-upgrade``
+      Conducts a database schema upgrade. This is useful when upgrading Kea.
+
+   ``lease-dump``
+      Dumps the contents of the lease database (for MySQL or
+      PostgreSQL backends) to a CSV (comma-separated values) text file. (Support
+      for the Cassandra backend has been deprecated.)
+      The first line of the file contains the column names. This can be used
+      as a way to switch from a database backend to a memfile backend.
+      Alternatively, it can be used as a diagnostic tool, so it provides a
+      portable form of the lease data.
+
+   ``lease-upload``
+      Uploads leases from a CSV (comma-separated values) text file to a MySQL or
+      a PostgreSQL lease database. The CSV file needs to be in memfile format.
+
+   ``stats-recount``
+      Recounts lease statistics for a MySQL or PostgreSQL database.
+
+``backend``
+   Specifies the backend type. Currently allowed backends are: memfile,
+   mysql, and pgsql; cql has been deprecated.
+
+``-h|--host hostname``
+   Specifies the hostname when connecting to a database.
+   The default value is ``localhost``.
+
+``-P|--port port``
+   Specifies the port when connecting to a database. If not specified,
+   the default value chosen by the database client is used.
+
+``-u|--user username``
+   Specifies the username when connecting to a database.
+   The default value is ``keatest``.
+
+``-p|--password password``
+   Specifies the password when connecting to a database.
+   If only ``-p`` or ``--password`` is given, the user is prompted for a password.
+   If not specified at all, the ``KEA_ADMIN_DB_PASSWORD`` environment variable
+   is checked for a value and used if it exists.
+   Otherwise the default value of ``keatest`` is used.
+
+``-n|--name database-name``
+   Specifies the name of the database to connect to. The
+   default value is ``keatest``.
+
+``-d|--directory script-directory``
+   Specifies the override scripts directory. That script is used during
+   upgrades, database initialization, and possibly other operations.
+   The default value is ``(prefix)/share/kea/scripts/``.
+
+``-o|--output output_file``
+   Specifies the file to which the lease data will be dumped. Required for
+   ``lease-dump``.
+
+``-v|--version``
+   Prints the ``kea-admin`` version and quits.
+
+``-4``
+   Directs ``kea-admin`` to lease-dump the DHCPv4 leases. Incompatible with
+   the -6 option.
+
+``-6``
+   Directs ``kea-admin`` to lease-dump the DHCPv6 leases. Incompatible with
+   the -4 option.
+
+``-x|--extra``
+   Specifies an extra argument to pass to the database command tool e.g.
+   to invoke ``mysql`` with the ``--ssl`` argument. This can be repeated
+   to pass more than one argument. Quotes are not preserved. Avoid commands
+   containing spaces.
+
+``-y|--yes``
+    Assume yes on overwriting temporary files.
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp4(8)`, :manpage:`kea-dhcp6(8)`,
+:manpage:`kea-dhcp-ddns(8)`, :manpage:`kea-ctrl-agent(8)`,
+:manpage:`keactrl(8)`, :manpage:`perfdhcp(8)`, :manpage:`kea-netconf(8)`,
+Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/kea-ctrl-agent.8.rst b/doc/sphinx/man/kea-ctrl-agent.8.rst
new file mode 100644
index 0000000..48212cc
--- /dev/null
+++ b/doc/sphinx/man/kea-ctrl-agent.8.rst
@@ -0,0 +1,100 @@
+..
+   Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``kea-ctrl-agent`` - Control Agent process in Kea
+-------------------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`kea-ctrl-agent` [**-v**] [**-V**] [**-W**] [**-d**] [**-c** config-file] [**-t** config-file]
+
+Description
+~~~~~~~~~~~
+
+The ``kea-ctrl-agent`` provides a REST service for controlling Kea
+services. The received HTTP requests are decapsulated and forwarded to
+the respective Kea services in JSON format. Received JSON responses are
+encapsulated within HTTP responses and returned to the controlling
+entity. Some commands may be handled by the Control Agent directly, and
+not forwarded to any Kea service.
+
+Arguments
+~~~~~~~~~
+
+The arguments are as follows:
+
+``-v``
+   Displays the version.
+
+``-V``
+   Displays the extended version.
+
+``-W``
+   Displays the configuration report.
+
+``-d``
+   Sets the logging level to debug with extra verbosity. This is primarily for
+   development purposes in stand-alone mode.
+
+``-c config-file``
+   Specifies the file with the configuration for the Control Agent
+   server. It may also contain configuration entries for other Kea
+   services.
+
+``-t config-file``
+   Checks the syntax of the configuration file and reports the first error,
+   if any. Note that not all parameters are completely checked; in
+   particular, service and client sockets are not opened, and hook
+   libraries are not loaded.
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+History
+~~~~~~~
+
+The ``kea-ctrl-agent`` was first coded in December 2016 by Marcin
+Siodelski.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp4(8)`, :manpage:`kea-dhcp6(8)`,
+:manpage:`kea-dhcp-ddns(8)`, :manpage:`kea-admin(8)`, :manpage:`keactrl(8)`,
+:manpage:`perfdhcp(8)`, :manpage:`kea-lfc(8)`, Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/kea-dhcp-ddns.8.rst b/doc/sphinx/man/kea-dhcp-ddns.8.rst
new file mode 100644
index 0000000..4b1841a
--- /dev/null
+++ b/doc/sphinx/man/kea-dhcp-ddns.8.rst
@@ -0,0 +1,100 @@
+..
+   Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``kea-dhcp-ddns`` - DHCP-DDNS process in Kea
+--------------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`kea-dhcp-ddns` [**-v**] [**-V**] [**-W**] [**-d**] [**-c** config-file] [**-t** config-file]
+
+Description
+~~~~~~~~~~~
+
+The ``kea-dhcp-ddns`` service process requests an update of DNS mapping
+based on DHCP lease-change events. It runs as a separate process that
+expects to receive Name Change Requests from Kea DHCP servers.
+
+Arguments
+~~~~~~~~~
+
+The arguments are as follows:
+
+``-v``
+   Displays the version.
+
+``-V``
+   Displays the extended version.
+
+``-W``
+   Displays the configuration report.
+
+``-d``
+   Sets the logging level to debug with extra verbosity. This is primarily for
+   development purposes in stand-alone mode.
+
+``-c config-file``
+   Specifies the configuration file with the configuration for the DHCP-DDNS server. It
+   may also contain configuration entries for other Kea services.
+
+``-t config-file``
+   Checks the syntax of the configuration file and reports the first error,
+   if any. Note that not all parameters are completely checked; in
+   particular, a service socket is not opened.
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+History
+~~~~~~~
+
+The ``b10-dhcp-ddns`` process was first coded in May 2013 by Thomas
+Markwalder.
+
+Kea became a standalone server and the BIND 10 framework was removed. The
+DHCP-DDNS server binary was renamed to kea-dhcp-ddns in July 2014. Kea
+1.0.0 was released in December 2015.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp4(8)`, :manpage:`kea-dhcp6(8)`,
+:manpage:`kea-ctrl-agent(8)`, :manpage:`kea-admin(8)`, :manpage:`keactrl(8)`,
+:manpage:`perfdhcp(8)`, :manpage:`kea-netconf(8)`, :manpage:`kea-lfc(8)`,
+Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/kea-dhcp4.8.rst b/doc/sphinx/man/kea-dhcp4.8.rst
new file mode 100644
index 0000000..be59b0f
--- /dev/null
+++ b/doc/sphinx/man/kea-dhcp4.8.rst
@@ -0,0 +1,106 @@
+..
+   Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``kea-dhcp4`` - DHCPv4 server in Kea
+------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`kea-dhcp4` [**-v**] [**-V**] [**-W**] [**-d**] [**-c** config-file] [**-t** config-file] [**-p** server-port-number] [**-P** client-port-number]
+
+Description
+~~~~~~~~~~~
+
+The ``kea-dhcp4`` daemon provides the DHCPv4 server implementation.
+
+Arguments
+~~~~~~~~~
+
+The arguments are as follows:
+
+``-v``
+   Displays the version.
+
+``-V``
+   Displays the extended version.
+
+``-W``
+   Displays the configuration report.
+
+``-d``
+   Enables the debug mode with extra verbosity.
+
+``-c config-file``
+   Specifies the configuration file with the configuration for the DHCPv4 server. It
+   may also contain configuration entries for other Kea services.
+
+``-t config-file``
+   Checks the configuration file and reports the first error, if any. Note
+   that not all parameters are completely checked; in particular,
+   service and control channel sockets are not opened, and hook
+   libraries are not loaded.
+
+``-p server-port-number``
+   Specifies the server port number (1-65535) on which the server listens. This is
+   useful for testing purposes only.
+
+``-P client-port-number``
+   Specifies the client port number (1-65535) to which the server responds. This is
+   useful for testing purposes only.
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+History
+~~~~~~~
+
+The ``b10-dhcp4`` daemon was first coded in November 2011 by Tomek
+Mrugalski.
+
+In mid-2014, Kea was decoupled from the BIND 10 framework and became a
+standalone DHCP server. The DHCPv4 server binary was renamed to
+``kea-dhcp4``. Kea 1.0.0 was released in December 2015.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp6(8)`, :manpage:`kea-dhcp-ddns(8)`,
+:manpage:`kea-ctrl-agent(8)`, :manpage:`kea-admin(8)`, :manpage:`keactrl(8)`,
+:manpage:`perfdhcp(8)`, :manpage:`kea-netconf(8)`, :manpage:`kea-lfc(8)`,
+Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/kea-dhcp6.8.rst b/doc/sphinx/man/kea-dhcp6.8.rst
new file mode 100644
index 0000000..19ec5e8
--- /dev/null
+++ b/doc/sphinx/man/kea-dhcp6.8.rst
@@ -0,0 +1,106 @@
+..
+   Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``kea-dhcp6`` - DHCPv6 server in Kea
+------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`kea-dhcp6` [**-v**] [**-V**] [**-W**] [**-d**] [**-c** config-file] [**-t** config-file] [**-p** server-port-number] [**-P** client-port-number]
+
+Description
+~~~~~~~~~~~
+
+The ``kea-dhcp6`` daemon provides the DHCPv6 server implementation.
+
+Arguments
+~~~~~~~~~
+
+The arguments are as follows:
+
+``-v``
+   Displays the version.
+
+``-V``
+   Displays the extended version.
+
+``-W``
+   Displays the configuration report.
+
+``-d``
+   Enables the debug mode with extra verbosity.
+
+``-c config-file``
+   Specifies the configuration file with the configuration for the DHCPv6 server. It
+   may also contain configuration entries for other Kea services.
+
+``-t config-file``
+   Checks the configuration file and reports the first error, if any. Note
+   that not all parameters are completely checked; in particular,
+   service and control channel sockets are not opened, and hook
+   libraries are not loaded.
+
+``-p server-port-number``
+   Specifies the server port number (1-65535) on which the server listens. This is
+   useful for testing purposes only.
+
+``-P client-port-number``
+   Specifies the client port number (1-65535) to which the server responds. This is
+   useful for testing purposes only.
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+History
+~~~~~~~
+
+The ``b10-dhcp6`` daemon was first coded in June 2011 by Tomek
+Mrugalski.
+
+In mid-2014, Kea was decoupled from the BIND 10 framework and became a
+standalone DHCP server. The DHCPv6 server binary was renamed to
+``kea-dhcp6``. Kea 1.0.0 was released in December 2015.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp4(8)`, :manpage:`kea-dhcp-ddns(8)`,
+:manpage:`kea-ctrl-agent(8)`, :manpage:`kea-admin(8)`, :manpage:`keactrl(8)`,
+:manpage:`perfdhcp(8)`, :manpage:`kea-netconf(8)`, :manpage:`kea-lfc(8)`,
+Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/kea-lfc.8.rst b/doc/sphinx/man/kea-lfc.8.rst
new file mode 100644
index 0000000..d4082b5
--- /dev/null
+++ b/doc/sphinx/man/kea-lfc.8.rst
@@ -0,0 +1,131 @@
+..
+   Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``kea-lfc`` - Lease File Cleanup process in Kea
+-----------------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`kea-lfc` [**-4**|**-6**] [**-c** config-file] [**-p** pid-file] [**-x** previous-file] [**-i** copy-file] [**-o** output-file] [**-f** finish-file] [**-v**] [**-V**] [**-W**] [**-d**] [**-h**]
+
+Description
+~~~~~~~~~~~
+
+The ``kea-lfc`` service process removes redundant information from the
+files used to provide persistent storage for the memfile database
+backend. The service is written to run as a stand-alone process. While
+it can be started externally, there is usually no need to do this. It
+is run periodically by the Kea DHCP servers.
+
+Arguments
+~~~~~~~~~
+
+The arguments are as follows:
+
+``-4 | -6``
+   Indicates the protocol version of the lease files; must be either 4 or 6.
+
+``-c config-file``
+   Specifies the file with the configuration for the ``kea-lfc``
+   process. It may also contain configuration entries for other Kea
+   services. Currently ``kea-lfc`` gets all of its arguments from the
+   command line.
+
+``-p pid-file``
+   Specifies the PID file. When the ``kea-lfc`` process starts, it attempts to
+   determine if another instance of the process is already running, by
+   examining the PID file. If one is already running, the new process is
+   terminated. If one is not running, Kea writes its PID into the PID file.
+
+``-x previous-file``
+   Specifies the previous or ex-lease file. When ``kea-lfc`` starts, this is the
+   result of any previous run of ``kea-lfc``; when ``kea-lfc`` finishes,
+   it is the result of the current run. If ``kea-lfc`` is interrupted before
+   completing, this file may not exist.
+
+``-i copy-file``
+   Specifies the input or copy of lease file. Before the DHCP server invokes
+   ``kea-lfc``, it moves the current lease file here and then calls
+   ``kea-lfc`` with this file.
+
+``-o output-file``
+   Specifies the output lease file, which is the temporary file ``kea-lfc`` should use to
+   write the leases. Once this file is finished writing, it is
+   moved to the finish file (see below).
+
+``-f finish-file``
+   Specifies the finish or completion file, another temporary file ``kea-lfc`` uses
+   for bookkeeping. When ``kea-lfc`` finishes writing the output file,
+   it moves it to this file name. After ``kea-lfc`` finishes deleting
+   the other files (previous and input), it moves this file to the previous
+   lease file. By moving the files in this fashion, the ``kea-lfc`` and
+   the DHCP server processes can determine the correct file to use even
+   if one of the processes was interrupted before completing its task.
+
+``-v``
+   Causes the version stamp to be printed.
+
+``-V``
+   Causes a longer form of the version stamp to be printed.
+
+``-W``
+   Displays the configuration report.
+
+``-d``
+   Sets the logging level to debug with extra verbosity. This is primarily for
+   development purposes in stand-alone mode.
+
+``-h``
+   Causes the usage string to be printed.
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+History
+~~~~~~~
+
+The ``kea-lfc`` process was first coded in January 2015 by the ISC
+Kea/DHCP team.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp4(8)`, :manpage:`kea-dhcp6(8)`, :manpage:`kea-dhcp-ddns(8)`,
+:manpage:`kea-ctrl-agent(8)`, :manpage:`kea-admin(8)`, :manpage:`keactrl(8)`,
+:manpage:`perfdhcp(8)`, :manpage:`kea-netconf(8)`, Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/kea-netconf.8.rst b/doc/sphinx/man/kea-netconf.8.rst
new file mode 100644
index 0000000..9029d01
--- /dev/null
+++ b/doc/sphinx/man/kea-netconf.8.rst
@@ -0,0 +1,95 @@
+..
+   Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``kea-netconf`` - NETCONF agent for configuring Kea
+---------------------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`kea-netconf` [**-v**] [**-V**] [**-W**] [**-d**] [**-c** config-file] [**-t** config-file]
+
+Description
+~~~~~~~~~~~
+
+The ``kea-netconf`` agent provides a YANG/NETCONF interface for the Kea
+environment.
+
+Arguments
+~~~~~~~~~
+
+The arguments are as follows:
+
+``-v``
+   Displays the version.
+
+``-V``
+   Displays the extended version.
+
+``-W``
+   Displays the configuration report.
+
+``-d``
+   Enables the debug mode with extra verbosity.
+
+``-c config-file``
+   Specifies the file with the configuration for the NETCONF agent.
+
+``-t config-file``
+   Checks the syntax of the configuration file and reports the first error,
+   if any. Note that not all parameters are completely checked; in
+   particular, service and client sockets are not opened, and hook
+   libraries are not loaded.
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+History
+~~~~~~~
+
+Early prototypes of ``kea-netconf`` implementation were written during IETF
+Hackathons in Berlin, London, and Montreal. An actual production-ready
+implementation was started in August 2018 by Tomek Mrugalski and Francis
+Dupont.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp4(8)`, :manpage:`kea-dhcp6(8)`, :manpage:`kea-dhcp-ddns(8)`,
+:manpage:`kea-ctrl-agent(8)`, :manpage:`kea-admin(8)`, :manpage:`keactrl(8)`,
+:manpage:`perfdhcp(8)`, :manpage:`kea-lfc(8)`, Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/kea-shell.8.rst b/doc/sphinx/man/kea-shell.8.rst
new file mode 100644
index 0000000..0f468f1
--- /dev/null
+++ b/doc/sphinx/man/kea-shell.8.rst
@@ -0,0 +1,128 @@
+..
+   Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``kea-shell`` - Text client for Control Agent process
+-----------------------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`kea-shell` [**-h**] [**-v**] [**--host**] [**--port**] [**--path**] [**--ca**] [**--cert**] [**--key**] [**--auth-user**] [**--auth-password**] [**--timeout**] [**--service**] [command]
+
+Description
+~~~~~~~~~~~
+
+The ``kea-shell`` provides a REST client for the Kea Control Agent (CA).
+It takes commands as a command-line parameter that is sent to the CA
+with proper JSON encapsulation. Optional arguments may be specified on
+the standard input. The request is sent via HTTP and a response is
+retrieved, displayed on the standard output. Basic HTTP authentication
+and HTTPS, i.e. TLS transport, are supported.
+
+
+Arguments
+~~~~~~~~~
+
+The arguments are as follows:
+
+``-h``
+   Displays help regarding command-line parameters.
+
+``-v``
+   Displays the version.
+
+``--host``
+   Specifies the host to connect to. The Control Agent must be running at the
+   specified host. If not specified, 127.0.0.1 is used.
+
+``--port``
+   Specifies the TCP port to connect to. Control Agent must be listening
+   at the specified port. If not specified, 8000 is used.
+
+``--path``
+   Specifies the path in the URL to connect to. If not specified, an empty
+   path is used. As Control Agent listens at the empty path, this
+   parameter is useful only with a reverse proxy.
+
+``--ca``
+   Specifies the file or directory name of the Certification Authority.
+   If not specified, HTTPS is not used.
+
+``--cert``
+   Specifies the file name of the user end-entity public key certificate.
+   If specified, the file name of the user key must also be specified.
+
+``--key``
+   Specifies the file name of the user key file. If specified, the file
+   name of the user certificate must also be specified.
+   Encrypted key files are not supported.
+
+``--auth-user``
+   Specifies the user ID for basic HTTP authentication. If not specified,
+   or specified as the empty string, authentication is not used.
+
+``--auth-password``
+   Specifies the password for basic HTTP authentication. If not specified
+   but the user ID is specified, an empty password is used.
+
+``--timeout``
+   Specifies the connection timeout, in seconds. The default is 10.
+
+``--service``
+   Specifies the service that is the target of a command. If not
+   specified, the Control Agent itself is targeted. May be used more than once
+   to specify multiple targets.
+
+``command``
+   Specifies the command to be sent to the CA. If not specified,
+   ``list-commands`` is used.
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+History
+~~~~~~~
+
+The ``kea-shell`` was first coded in March 2017 by Tomek Mrugalski.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp4(8)`, :manpage:`kea-dhcp6(8)`, :manpage:`kea-dhcp-ddns(8)`,
+:manpage:`kea-ctrl-agent(8)`, :manpage:`kea-admin(8)`, :manpage:`keactrl(8)`,
+:manpage:`perfdhcp(8)`, :manpage:`kea-lfc(8)`, Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/keactrl.8.rst b/doc/sphinx/man/keactrl.8.rst
new file mode 100644
index 0000000..67727f3
--- /dev/null
+++ b/doc/sphinx/man/keactrl.8.rst
@@ -0,0 +1,126 @@
+..
+   Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``keactrl`` - Shell script for managing Kea
+-------------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`keactrl` [**command**] [**-c** keactrl-config-file] [**-s** server[,server,...]] [**-v**]
+
+Description
+~~~~~~~~~~~
+
+``keactrl`` is a shell script which controls the startup, shutdown, and
+reconfiguration of the Kea servers (``kea-dhcp4``, ``kea-dhcp6``,
+``kea-dhcp-ddns``, ``kea-ctrl-agent``, and ``kea-netconf``). It also
+provides a way to check the current status of the servers and
+determine the configuration files in use.
+
+Configuration File
+~~~~~~~~~~~~~~~~~~
+
+Depending on the user's requirements, not all of the available servers need be run.
+The ``keactrl`` configuration file specifies which servers are enabled and which
+are disabled. By default the configuration file is
+``[kea-install-dir]/etc/kea/keactrl.conf``.
+
+See the Kea Administrator Reference Manual for documentation of the
+parameters in the ``keactrl`` configuration file.
+
+Options
+~~~~~~~
+
+``command``
+   Specifies the command to be issued to the servers. It can be one of the following:
+
+   ``start``
+      Starts the servers.
+
+   ``stop``
+      Stops the servers.
+
+   ``reload``
+      Instructs the servers to re-read the Kea configuration file. This
+      command is not supported by the NETCONF agent.
+
+   ``status``
+      Prints the status of the servers.
+
+``-c|--ctrl-config keactrl-config-file``
+   Specifies the ``keactrl`` configuration file. Without this switch,
+   ``keactrl`` uses the file
+   ``[kea-install-dir]/etc/kea/keactrl.conf``.
+
+``-s|--server server[,server,...]``
+   Specifies a subset of the enabled servers to which the command should
+   be issued. The list of servers should be separated by commas, with no
+   intervening spaces. Acceptable values are:
+
+   ``dhcp4``
+      DHCPv4 server (``kea-dhcp4``).
+
+   ``dhcp6``
+      DHCPv6 server (``kea-dhcp6``).
+
+   ``dhcp_ddns``
+      DHCP DDNS server (``kea-dhcp-ddns``).
+
+   ``ctrl_agent``
+      Control Agent (``kea-ctrl-agent``).
+
+   ``netconf``
+      NETCONF agent (``kea-netconf``).
+
+   ``all``
+      All servers, including NETCONF if it was configured to be
+      built. This is the default.
+
+``-v|--version``
+   Prints the ``keactrl`` version and quits.
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp4(8)`, :manpage:`kea-dhcp6(8)`, :manpage:`kea-dhcp-ddns(8)`,
+:manpage:`kea-ctrl-agent(8)`, :manpage:`kea-admin(8)`, :manpage:`kea-netconf(8)`,
+:manpage:`perfdhcp(8)`, :manpage:`kea-lfc(8)`, Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/man8s.mk b/doc/sphinx/man/man8s.mk
new file mode 100644
index 0000000..7af7c1f
--- /dev/null
+++ b/doc/sphinx/man/man8s.mk
@@ -0,0 +1,10 @@
+man8s += $(sphinxbuilddir)/man/kea-admin.8
+man8s += $(sphinxbuilddir)/man/kea-ctrl-agent.8
+man8s += $(sphinxbuilddir)/man/kea-dhcp4.8
+man8s += $(sphinxbuilddir)/man/kea-dhcp6.8
+man8s += $(sphinxbuilddir)/man/kea-dhcp-ddns.8
+man8s += $(sphinxbuilddir)/man/kea-lfc.8
+man8s += $(sphinxbuilddir)/man/kea-netconf.8
+man8s += $(sphinxbuilddir)/man/kea-shell.8
+man8s += $(sphinxbuilddir)/man/keactrl.8
+man8s += $(sphinxbuilddir)/man/perfdhcp.8
diff --git a/doc/sphinx/man/perfdhcp.8.rst b/doc/sphinx/man/perfdhcp.8.rst
new file mode 100644
index 0000000..75c371c
--- /dev/null
+++ b/doc/sphinx/man/perfdhcp.8.rst
@@ -0,0 +1,548 @@
+..
+   Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+
+``perfdhcp`` - DHCP benchmarking tool
+-------------------------------------
+
+Synopsis
+~~~~~~~~
+
+:program:`perfdhcp` [**-1**] [**-4** | **-6**] [**-A** encapsulation-level] [**-b** base] [**-B**] [**-c**] [**-C** separator] [**-d** drop-time] [**-D** max-drop] [-e lease-type] [**-E** time-offset] [**-f** renew-rate] [**-F** release-rate] [**-g** thread-mode] [**-h**] [**-i**] [**-I** ip-offset] [**-J** remote-address-list-file] [**-l** local-address|interface] [**-L** local-port] [**-M** mac-list-file] [**-n** num-request] [**-N** remote-port] [**-O** random-offset] [**-o** code,hexstring] [**-p** test-period] [**-P** preload] [**-r** rate] [**-R** num-clients] [**-s** seed] [**-S** srvid-offset] [**--scenario** name] [**-t** report] [**-T** template-file] [**-u**] [**-v**] [**-W** exit-wait-time] [**-w** script_name] [**-x** diagnostic-selector] [**-X** xid-offset] [server]
+
+Description
+~~~~~~~~~~~
+
+``perfdhcp`` is a DHCP benchmarking tool. It provides a way to measure
+the performance of DHCP servers by generating large amounts of traffic
+from multiple simulated clients. It is able to test both IPv4 and IPv6
+servers, and provides statistics concerning response times and the
+number of requests that are dropped.
+
+The tool supports two different scenarios, which offer certain behaviors to be tested.
+By default (the basic scenario), tests are run using the full four-packet exchange sequence
+(DORA for DHCPv4, SARR for DHCPv6). An option is provided to run tests
+using the initial two-packet exchange (DO and SA) instead. It is also
+possible to configure ``perfdhcp`` to send DHCPv6 RENEW and RELEASE messages
+at a specified rate, in parallel with the DHCPv6 four-way exchanges. By
+default, if there is no response received with one second, a response is
+considered lost and ``perfdhcp`` continues with other transactions.
+
+A second scenario, called avalanche, is selected via ``--scenario avalanche``.
+It first sends the number of Discovery or Solicit messages specified by the ``-R`` option; then
+a retransmission (with an exponential back-off mechanism) is used for each simulated client, until all requests are
+answered. It generates a report when all clients receive their addresses, or when
+it is manually stopped. This scenario attempts to replicate a
+case where the server is not able to handle the traffic swiftly
+enough. Real clients will assume the packet or response was lost
+and will retransmit, further increasing DHCP traffic. This is
+sometimes called an avalanche effect, thus the scenario name.
+Option ``-p`` is ignored in the avalanche scenario.
+
+When running a performance test, ``perfdhcp`` exchanges packets with
+the server under test as quickly as possible, unless the ``-r`` parameter is used to
+limit the request rate. The length of the test can be limited by setting
+a threshold on any or all of the number of requests made by
+``perfdhcp``, the elapsed time, or the number of requests dropped by the
+server.
+
+Templates
+~~~~~~~~~
+
+To allow the contents of packets sent to the server to be customized,
+``perfdhcp`` allows the specification of template files that determine
+the contents of the packets. For example, the customized packet may
+contain a DHCPv6 ORO to request a set of options to be returned by the
+server, or it may contain the Client FQDN option to request that the server
+perform DNS updates. This may be used to discover performance
+bottlenecks for different server configurations (e.g. DDNS enabled or
+disabled).
+
+Up to two template files can be specified on the command line, with each file
+representing the contents of a particular type of packet, and the type being
+determined by the test being carried out. For example, if testing
+DHCPv6:
+
+-  With no template files specified on the command line, ``perfdhcp``
+   generates both Solicit and Request packets.
+
+-  With one template file specified, that file is used as the
+   pattern for Solicit packets: ``perfdhcp`` generates the Request
+   packets.
+
+-  With two template files given on the command line, the first is
+   used as the pattern for Solicit packets, and the second as the pattern
+   for Request packets.
+
+(A similar determination applies to DHCPv4's DHCPDISCOVER and DHCPREQUEST
+packets.)
+
+The template file holds the DHCP packet, represented as a stream of ASCII
+hexadecimal digits; it excludes any IP/UDP stack headers. The
+template file must not contain any characters other than hexadecimal
+digits and spaces. Spaces are discarded when the template file is parsed;
+in the file, ``12B4`` is the same as ``12 B4``, which is the same as
+``1 2 B 4``.
+
+The template files should be used in conjunction with the command-line
+parameters which specify offsets of the data fields being modified in
+outbound packets. For example, the ``-E time-offset`` switch specifies
+the offset of the DHCPv6 Elapsed Time option in the packet template.
+If the offset is specified, ``perfdhcp`` injects the current elapsed-time
+value into this field before sending the packet to the server.
+
+In many scenarios, ``perfdhcp`` needs to simulate multiple clients,
+each having a unique client identifier. Since packets for each client are
+generated from the same template file, it is necessary to randomize the
+client identifier (or HW address in DHCPv4) in the packet created from
+it. The ``-O random-offset`` option allows specification of the offset in
+the template where randomization should be performed. It is important to
+note that this offset points to the end (not the beginning) of the
+client identifier (or HW address field). The number of bytes being
+randomized depends on the number of simulated clients. If the number of
+simulated clients is between 1 and 255, only one byte (to which the
+randomization offset points) is randomized. If the number of
+simulated clients is between 256 and 65535, two bytes are
+randomized. Note that the last two bytes of the client identifier are
+randomized in this case: the byte which the randomization offset parameter
+points to, and the one which precedes it (random-offset - 1). If the
+number of simulated clients exceeds 65535, three bytes are
+randomized, and so on.
+
+``perfdhcp`` can simulate traffic from multiple subnets by enabling option
+``-J`` and passing a path to a file that contains v4 or v6 addresses to be
+used as relays in generated messages. That enables testing of vast numbers
+of Kea shared networks. While testing DHCPv4, Kea should be started with the
+``KEA_TEST_SEND_RESPONSES_TO_SOURCE`` environment variable, to force Kea
+to send generated messages to the source address of the incoming packet.
+
+Templates may currently be used to generate packets being sent to the
+server in 4-way exchanges, i.e. Solicit, Request (DHCPv6) and DHCPDISCOVER,
+DHCPREQUEST (DHCPv4). They cannot be used when Renew or DHCPRELEASE packets are
+being sent.
+
+Options
+~~~~~~~
+
+``-1``
+   Takes the ``server-id`` option from the first received message.
+
+``-4``
+   Establishes DHCPv4 operation; this is the default. It is incompatible with the
+   ``-6`` option.
+
+``-6``
+   Establishes DHCPv6 operation. It is incompatible with the ``-4`` option.
+
+``-b basetype=value``
+   Indicates the base MAC or DUID used to simulate different clients. The basetype
+   may be "mac" or "duid". (The keyword "ether" may alternatively used
+   for MAC.) The ``-b`` option can be specified multiple times. The MAC
+   address must consist of six octets separated by single (:) or double
+   (::) colons; for example: mac=00:0c:01:02:03:04. The DUID value is a
+   hexadecimal string; it must be at least six octets long and not
+   longer than 64 bytes, and the length must be less than 128
+   hexadecimal digits. For example: duid=0101010101010101010110111F14.
+
+``-d drop-time``
+   Specifies the time after which a request is treated as having been
+   lost. The value is given in seconds and may contain a fractional
+   component. The default is 1.
+
+``-e lease-type``
+   Specifies the type of lease being requested from the server. It may
+   be one of the following:
+
+   ``address-only``
+      Only regular addresses (v4 or v6) are requested.
+
+   ``prefix-only``
+      Only IPv6 prefixes are requested.
+
+   ``address-and-prefix``
+      Both IPv6 addresses and prefixes are requested.
+
+   The ``-e prefix-only`` and ``-e address-and-prefix`` forms may not be used
+   with the ``-4`` option.
+
+``-F release-rate``
+   Specifies the rate at which DHCPv4 DHCPRELEASE or DHCPv6 Release requests are sent to a server. This value
+   is only valid when used in conjunction with the exchange rate (given
+   by ``-r rate``). Furthermore, the sum of this value and the renew-rate
+   (given by ``-f rate``) must be equal to or less than the exchange
+   rate value.
+
+``-f renew-rate``
+   Specifies the rate at which DHCPv4 DHCPREQUEST or DHCPv6 Renew requests are sent to a server.
+   This value is only valid when used in conjunction with the exchange
+   rate (given by ``-r rate``). Furthermore, the sum of this value and
+   the release-rate (given by ``-F rate``) must be equal to or less than the
+   exchange rate.
+
+``-g thread-mode``
+   Allows selection of thread-mode, which can be either ``single`` or ``multi``. In multi-thread mode,
+   packets are received in a separate thread, which allows better
+   utilisation of CPUs. In a single-CPU system it is better to run in one
+   thread, to avoid threads blocking each other. If more than one CPU is
+   present in the system, multi-thread mode is the default; otherwise
+   single-thread is the default.
+
+``-h``
+   Prints help and exits.
+
+``-i``
+   Performs only the initial part of the exchange: DISCOVER-OFFER if ``-4`` is
+   selected, Solicit-Advertise if ``-6`` is chosen.
+
+   ``-i`` is incompatible with the following options: ``-1``, ``-d``,
+   ``-D``, ``-E``, ``-S``, ``-I`` and ``-F``. In addition, it cannot be
+   used with multiple instances of ``-O``, ``-T``, and ``-X``.
+
+``-J remote-address-list-file``
+    Specifies a text file that includes multiple addresses, and is
+    designed to test shared networks. If provided, ``perfdhcp``
+    randomly chooses one of the addresses for each exchange, to generate traffic
+    from multiple subnets. When testing DHCPv4, it
+    should be started with the ``KEA_TEST_SEND_RESPONSES_TO_SOURCE=ENABLE``
+    environment variable; otherwise, ``perfdhcp`` will not be able to receive responses.
+
+``-l local-addr|interface``
+   For DHCPv4 operation, specifies the local hostname/address to use when
+   communicating with the server. By default, the interface address
+   through which traffic would normally be routed to the server is used.
+   For DHCPv6 operation, specifies the name of the network interface
+   through which exchanges are initiated.
+
+``-L local-port``
+   Specifies the local port to use. This must be zero or a positive
+   integer up to 65535. A value of 0 (the default) allows ``perfdhcp``
+   to choose its own port.
+
+``-M mac-list-file``
+   Specifies a text file containing a list of MAC addresses, one per line. If
+   provided, a MAC address is chosen randomly from this list for
+   every new exchange. In DHCPv6, MAC addresses are used to
+   generate DUID-LLs. This parameter must not be used in conjunction
+   with the ``-b`` parameter.
+
+``-N remote-port``
+   Specifies the remote port to use. This must be zero or a positive
+   integer up to 65535. A value of 0 (the default) allows ``perfdhcp``
+   to choose the standard service port.
+
+``-o code,hexstring``
+   Forces ``perfdhcp`` to insert the specified extra option (or options if
+   used several times) into packets being transmitted. The code
+   specifies the option code and the hexstring is a hexadecimal string that
+   defines the content of the option. Care should be taken as ``perfdhcp``
+   does not offer any kind of logic behind those options; they are simply
+   inserted into packets and sent as is. Be careful not to duplicate
+   options that are already inserted. For example, to insert client
+   class identifier (option code 60) with a string "docsis", use
+   "-o 60,646f63736973". The ``-o`` may be used multiple times. It is
+   necessary to specify the protocol family (either ``-4`` or ``-6``) before
+   using ``-o``.
+
+``-P preload``
+   Initiates preload exchanges back-to-back at startup. Must be 0
+   (the default) or a positive integer.
+
+``-r rate``
+   Initiates the rate of DORA/SARR (or if ``-i`` is given, DO/SA) exchanges per
+   second. A periodic report is generated showing the number of
+   exchanges which were not completed, as well as the average response
+   latency. The program continues until interrupted, at which point a
+   final report is generated.
+
+``-R num-clients``
+   Specifies how many different clients are used. With a value of 1 (the
+   default), all requests appear to come from the same client.
+   Must be a positive number.
+
+``-s seed``
+   Specifies the seed for randomization, making runs of ``perfdhcp``
+   repeatable. This must be 0 or a positive integer. The value 0 means that a
+   seed is not used; this is the default.
+
+``--scenario name``
+   Specifies the type of scenario, and can be ``basic`` (the default) or ``avalanche``.
+
+``-T template-file``
+   Specifies a file containing the template to use as a stream of
+   hexadecimal digits. This may be specified up to two times and
+   controls the contents of the packets sent (see the "Templates"
+   section above).
+
+``-u``
+   Enables checks for address uniqueness. The lease valid-lifetime should not be shorter
+   than the test duration, and clients should not request an address more than once without
+   releasing it.
+
+``-v``
+   Prints the version of this program.
+
+``-W exit-wait-time``
+   Specifies the exit-wait-time parameter, which causes ``perfdhcp`` to wait for
+   a certain amount of time after an exit condition has been met, to receive all
+   packets without sending any new packets. Expressed in microseconds.
+   If not specified, 0 is used (i.e. exit immediately after exit
+   conditions are met).
+
+``-w script_name``
+   Specifies the name of the script to be run before/after ``perfdhcp``.
+   When called, the script is passed a single parameter, either "start" or
+   "stop", indicating whether it is being called before or after ``perfdhcp``.
+
+``-x diagnostic-selector``
+   Includes extended diagnostics in the output. This is a
+   string of single keywords specifying the operations for which verbose
+   output is desired. The selector key letters are:
+
+   ``a``
+      Prints the decoded command-line arguments.
+
+   ``e``
+      Prints the exit reason.
+
+   ``i``
+      Prints the rate-processing details.
+
+   ``l``
+      Prints the received leases.
+
+   ``s``
+      Prints the first server ID.
+
+   ``t``
+      When finished, prints timers of all successful exchanges.
+
+   ``T``
+      When finished, prints templates.
+
+``-y seconds``
+   Time in seconds after which ``perfdhcp`` starts simulating the client waiting longer for server responses. This increases the
+   ``secs`` field in DHCPv4 and sends increased values in the ``Elapsed Time`` option in DHCPv6. Must be used with ``-Y``.
+
+``-Y seconds``
+   Time in seconds during which ``perfdhcp`` simulates the client waiting longer for server responses. This increases
+   the ``secs`` field in DHCPv4 and sends increased values in the ``Elapsed Time`` option in DHCPv6. Must be used with ``-y``.
+
+DHCPv4-Only Options
+~~~~~~~~~~~~~~~~~~~
+
+The following options only apply for DHCPv4 (i.e. when ``-4`` is given).
+
+``-B``
+   Forces broadcast handling.
+
+DHCPv6-Only Options
+~~~~~~~~~~~~~~~~~~~
+
+The following options only apply for DHCPv6 (i.e. when ``-6`` is given).
+
+``-c``
+   Adds a rapid-commit option (exchanges are Solicit-Advertise).
+
+``-A encapsulation-level``
+   Specifies that relayed traffic must be generated. The argument
+   specifies the level of encapsulation, i.e. how many relay agents are
+   simulated. Currently the only supported encapsulation-level value is
+   1, which means that the generated traffic is equivalent to the amount of
+   traffic passing through a single relay agent.
+
+Template-Related Options
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following options may only be used in conjunction with ``-T`` and
+control how ``perfdhcp`` modifies the template. The options may be
+specified multiple times on the command line; each occurrence affects
+the corresponding template file (see "Templates" above).
+
+``-E time-offset``
+   Specifies the offset of the ``secs`` field (DHCPv4) or ``Elapsed Time`` option (DHCPv6) in the
+   second (i.e. Request) template; must be 0 or a positive integer. A
+   value of 0 disables this.
+
+``-I ip-offset``
+   Specifies the offset of the IP address (DHCPv4) in the ``requested-ip``
+   option or ``IA_NA`` option (DHCPv6) in the second (Request) template.
+
+``-O random-offset``
+   Specifies the offset of the last octet to randomize in the template. This
+   must be an integer greater than 3. The ``-T`` switch must be given to
+   use this option.
+
+``-S srvid-offset``
+   Specifies the offset of the ``server-id`` option in the second (Request) template.
+   This must be a positive integer, and the switch can only be used
+   when the template option (``-T``) is also given.
+
+``-X xid-offset``
+   Specifies the offset of the transaction ID (xid) in the template. This must be a
+   positive integer, and the switch can only be used when the template
+   option (``-T``) is also given.
+
+Options Controlling a Test
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``-D max-drop``
+   Aborts the test immediately if "max-drop" requests have been dropped.
+   Use ``-D 0`` to abort if even a single request has
+   been dropped. "max-drop" must be a positive integer. If "max-drop"
+   includes the suffix ``%``, it specifies the maximum percentage of
+   requests that may be dropped before aborting. In this case, testing of
+   the threshold begins after 10 requests are expected to have been
+   received.
+
+``-n num-requests``
+   Initiates "num-request" transactions. No report is generated until all
+   transactions have been initiated/waited-for, after which a report is
+   generated and the program terminates.
+
+``-p test-period``
+   Sends requests for "test-period", which is specified in the same manner
+   as ``-d``. This can be used as an alternative to ``-n``, or both
+   options can be given, in which case the testing is completed when
+   either limit is reached.
+
+``-t interval``
+   Sets the delay (in seconds) between two successive reports.
+
+``-C separator``
+    Suppresses the preliminary output and causes the interim data to
+    only contain the values delimited by ``separator``. Used in
+    conjunction with ``-t`` to produce easily parsable
+    reports at ``-t`` intervals.
+
+Arguments
+~~~~~~~~~
+
+``server``
+   Indicates the server to test, specified as an IP address. In the DHCPv6 case, the
+   special name ``all`` can be used to refer to
+   ``All_DHCP_Relay_Agents_and_Servers`` (the multicast address FF02::1:2),
+   or the special name ``servers`` to refer to ``All_DHCP_Servers`` (the
+   multicast address FF05::1:3). The server is mandatory except where
+   the ``-l`` option is given to specify an interface, in which case it
+   defaults to ``all``.
+
+Errors
+~~~~~~
+
+``perfdhcp`` can report the following errors in the packet exchange:
+
+tooshort
+   A message was received that was too short.
+
+orphans
+   A message was received which does not match one sent to the server (i.e.
+   it is a duplicate message, a message that has arrived after an
+   excessive delay, or one that is just not recognized).
+
+locallimit
+   Local system limits have been reached when sending a message.
+
+Exit Status
+~~~~~~~~~~~
+
+``perfdhcp`` exits with one of the following status codes:
+
+0
+   Success.
+
+1
+   General error.
+
+2
+   Error in command-line arguments.
+
+3
+   No general failures in operation, but one or more exchanges were
+   unsuccessful.
+
+Usage Examples
+~~~~~~~~~~~~~~
+
+Here is an example that simulates regular DHCPv4 traffic of 100 DHCPv4 devices (-R 100),
+10 packets per second (-r 10), shows the query/response rate details (-xi),
+shows a report every 2 seconds (-t 2), and sends the packets to the IP 192.0.2.1:
+
+.. code-block:: console
+
+   sudo perfdhcp -xi -t 2 -r 10 -R 100 192.0.2.1
+
+Here's a similar case, but for DHCPv6. Note that the DHCPv6 protocol uses link-local
+addresses, so the interface (eth0 in this example) must be specified on which to send the
+traffic. ``all`` is a convenience alias for ``All_DHCP_Relay_Agents_and_Servers``
+(the multicast address FF02::1:2). It is also possible to use the ``servers`` alias
+to refer to ``All_DHCP_Servers`` (the multicast address FF05::1:3). The default is ``all``.
+
+.. code-block:: console
+
+   sudo perfdhcp -6 -xi -t 1 -r 1 -R 10 -l eth0 all
+
+The following examples simulate normal DHCPv4 and DHCPv6 traffic that, after 3 seconds,
+starts pretending not to receive any responses from the server for 10 seconds. The
+DHCPv4 protocol signals this by an increased ``secs`` field, while DHCPv6 uses the
+``Elapsed Time`` option. In real networks, this indicates that clients are not getting
+responses in a timely matter. This can be used to simulate some HA scenarios, as Kea
+uses the ``secs`` field and ``Elapsed Time`` option value as one of the indicators
+that the HA partner is not responding. When enabled with ``-y`` and ``-Y``, the ``secs``
+and ``Elapsed Time`` values increase steadily.
+
+.. code-block:: console
+
+   sudo perfdhcp -xi -t 1 -r 1 -y 10 -Y 3 192.0.2.1
+
+   sudo perfdhcp -6 -xi -t 1 -r 1 -y 10 -Y 3 2001:db8::1
+
+Documentation
+~~~~~~~~~~~~~
+
+Kea comes with an extensive Kea Administrator Reference Manual that covers
+all aspects of running the Kea software - compilation, installation,
+configuration, configuration examples, and much more. Kea also features a
+Kea Messages Manual, which lists all possible messages Kea can print
+with a brief description for each of them. Both documents are
+available in various formats (.txt, .html, .pdf) with the Kea
+distribution. The Kea documentation is available at
+https://kea.readthedocs.io.
+
+Kea source code is documented in the Kea Developer's Guide,
+available at https://reports.kea.isc.org/dev_guide/.
+
+The Kea project website is available at https://kea.isc.org.
+
+Mailing Lists and Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are two public mailing lists available for the Kea project. **kea-users**
+(kea-users at lists.isc.org) is intended for Kea users, while **kea-dev**
+(kea-dev at lists.isc.org) is intended for Kea developers, prospective
+contributors, and other advanced users. Both lists are available at
+https://lists.isc.org. The community provides best-effort support
+on both of those lists.
+
+ISC provides professional support for Kea services. See
+https://www.isc.org/kea/ for details.
+
+History
+~~~~~~~
+
+The ``perfdhcp`` tool was initially coded in October 2011 by John
+DuBois, Francis Dupont, and Marcin Siodelski of ISC. Kea 1.0.0, which
+included ``perfdhcp``, was released in December 2015.
+
+See Also
+~~~~~~~~
+
+:manpage:`kea-dhcp4(8)`, :manpage:`kea-dhcp6(8)`, :manpage:`kea-dhcp-ddns(8)`,
+:manpage:`kea-ctrl-agent(8)`, :manpage:`kea-admin(8)`, :manpage:`kea-netconf(8)`,
+:manpage:`keactrl(8)`, :manpage:`kea-lfc(8)`, Kea Administrator Reference Manual.
diff --git a/doc/sphinx/man/rst_man_sources.mk b/doc/sphinx/man/rst_man_sources.mk
new file mode 100644
index 0000000..933fafe
--- /dev/null
+++ b/doc/sphinx/man/rst_man_sources.mk
@@ -0,0 +1,10 @@
+rst_man_sources += man/kea-admin.8.rst
+rst_man_sources += man/kea-ctrl-agent.8.rst
+rst_man_sources += man/kea-dhcp4.8.rst
+rst_man_sources += man/kea-dhcp6.8.rst
+rst_man_sources += man/kea-dhcp-ddns.8.rst
+rst_man_sources += man/kea-lfc.8.rst
+rst_man_sources += man/kea-netconf.8.rst
+rst_man_sources += man/kea-shell.8.rst
+rst_man_sources += man/keactrl.8.rst
+rst_man_sources += man/perfdhcp.8.rst
diff --git a/doc/sphinx/manpages.rst b/doc/sphinx/manpages.rst
new file mode 100644
index 0000000..a428bfa
--- /dev/null
+++ b/doc/sphinx/manpages.rst
@@ -0,0 +1,28 @@
+..
+   Copyright (C) 2021 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+.. _manpages:
+
+Manual Pages
+============
+
+.. toctree::
+   :maxdepth: 1
+
+   man/kea-dhcp4.8
+   man/kea-dhcp6.8
+   man/kea-ctrl-agent.8
+   man/keactrl.8
+   man/kea-admin.8
+   man/kea-dhcp-ddns.8
+   man/kea-lfc.8
+   man/kea-shell.8
+   man/kea-netconf.8
+   man/perfdhcp.8
diff --git a/doc/sphinx/mes-files.txt b/doc/sphinx/mes-files.txt
new file mode 100644
index 0000000..6d802c9
--- /dev/null
+++ b/doc/sphinx/mes-files.txt
@@ -0,0 +1,28 @@
+src/hooks/dhcp/flex_option/flex_option_messages.mes
+src/hooks/dhcp/bootp/bootp_messages.mes
+src/hooks/dhcp/mysql_cb/mysql_cb_messages.mes
+src/hooks/dhcp/lease_cmds/lease_cmds_messages.mes
+src/hooks/dhcp/high_availability/ha_messages.mes
+src/hooks/dhcp/stat_cmds/stat_cmds_messages.mes
+src/hooks/dhcp/user_chk/user_chk_messages.mes
+src/lib/config/config_messages.mes
+src/lib/hooks/hooks_messages.mes
+src/lib/dhcpsrv/dhcpsrv_messages.mes
+src/lib/dhcpsrv/alloc_engine_messages.mes
+src/lib/dhcpsrv/hosts_messages.mes
+src/lib/http/auth_messages.mes
+src/lib/http/http_messages.mes
+src/lib/dhcp_ddns/dhcp_ddns_messages.mes
+src/lib/database/db_messages.mes
+src/lib/log/log_messages.mes
+src/lib/log/logimpl_messages.mes
+src/lib/log/tests/log_test_messages.mes
+src/lib/process/process_messages.mes
+src/lib/asiodns/asiodns_messages.mes
+src/lib/eval/eval_messages.mes
+src/lib/d2srv/d2_messages.mes
+src/bin/dhcp4/dhcp4_messages.mes
+src/bin/agent/ca_messages.mes
+src/bin/dhcp6/dhcp6_messages.mes
+src/bin/lfc/lfc_messages.mes
+src/bin/netconf/netconf_messages.mes
diff --git a/doc/sphinx/mes2doc.py b/doc/sphinx/mes2doc.py
new file mode 100755
index 0000000..91d13cb
--- /dev/null
+++ b/doc/sphinx/mes2doc.py
@@ -0,0 +1,135 @@
+#!/usr/bin/env python3
+
+# Copyright (C) 2019-2021 Internet Systems Consortium, Inc. ("ISC")
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http:#mozilla.org/MPL/2.0/.
+
+# Produce System Messages Manual
+#
+# This tool reads all the message files given on the command line.
+# It pulls all the messages and description out, sorts them by
+# message ID, and writes them out as a single (formatted) file.
+#
+# Invocation:
+# The code is invoked using the command line:
+#
+# system_messages.py [-o <output-file>] <files>
+#
+# If no output file is specified, output is written to stdout.
+# The produced format is ReStructuredText.
+
+import re
+import argparse
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description='Convert set of *.mes files to .rst documentation format')
+    parser.add_argument('-o', '--output', help='Output file name (default to stdout).')
+    parser.add_argument('files', help='Input .mes files.', nargs='+')
+
+    args = parser.parse_args()
+    return args
+
+
+def read_input_files(files):
+    messages = {}
+    for f in files:
+        with open(f) as fp:
+            print("Processing %s" % f)
+            namespace = None
+            msg_descr = None
+            msg_id = None
+            msg_text = None
+            for line in fp.readlines():
+                line = line.strip()
+
+                if not line or line.startswith('#'):
+                    pass
+
+                elif line.startswith('$'):
+                    pass
+
+                elif line.startswith('%'):
+                    # end previous message
+                    if msg_id is not None:
+                        section = msg_id.split('_')[0]
+                        messages[msg_id] = (section, msg_id, msg_text, msg_descr)
+
+                    # start next message
+                    m = re.search('^%\s?([A-Z0-9_]+)\s+(.*)', line);
+                    msg_id, msg_text = m.groups()
+                    msg_descr = []
+
+                else:
+                    msg_descr.append(line)
+
+    return messages
+
+
+def generate_rst(messages):
+    rst = '''.. _kea-messages:
+
+###################
+Kea Messages Manual
+###################
+
+Kea is an open source implementation of the Dynamic Host Configuration
+Protocol (DHCP) servers, developed and maintained by Internet Systems
+Consortium (ISC).
+
+This is the reference guide for Kea version |release|.
+Links to the most up-to-date version of this document (in PDF, HTML,
+and plain text formats), along with other useful information about
+Kea, can be found in ISC's `Knowledgebase <https://kea.readthedocs.io>`_.
+
+Please note that in the messages below, the percent sign ("%") followed by a number is
+used to indicate a placeholder for data that is provided by the Kea code during its operation.
+
+
+.. toctree::
+   :numbered:
+   :maxdepth: 5
+
+'''
+
+    prev_section = None
+    for _, msg in sorted(messages.items()):
+        section, msg_id, msg_text, msg_descr = msg
+
+        if section != prev_section:
+            prev_section = section
+            rst += section + '\n'
+            rst += '~' * len(section) + '\n\n'
+
+        rst += '**' + msg_id + '**\n\n'
+
+        rst += msg_text + '\n\n'
+
+        rst += ''.join(['  ' + l + '\n' for l in msg_descr])
+        rst += '\n'
+
+
+    return rst
+
+def generate(in_files, out_file):
+    messages = read_input_files(in_files)
+
+    rst = generate_rst(messages)
+
+    if out_file:
+        with open(out_file, 'w') as f:
+            f.write(rst)
+        print('Wrote generated RST content to: %s' % out_file)
+    else:
+        print(rst)
+
+
+def main():
+    args = parse_args()
+    generate(args.files, args.output)
+
+
+if __name__ == '__main__':
+    main()
diff --git a/doc/sphinx/mes_files.mk b/doc/sphinx/mes_files.mk
new file mode 100644
index 0000000..ca612d8
--- /dev/null
+++ b/doc/sphinx/mes_files.mk
@@ -0,0 +1,28 @@
+mes_files += $(top_srcdir)/src/hooks/dhcp/flex_option/flex_option_messages.mes
+mes_files += $(top_srcdir)/src/hooks/dhcp/bootp/bootp_messages.mes
+mes_files += $(top_srcdir)/src/hooks/dhcp/mysql_cb/mysql_cb_messages.mes
+mes_files += $(top_srcdir)/src/hooks/dhcp/lease_cmds/lease_cmds_messages.mes
+mes_files += $(top_srcdir)/src/hooks/dhcp/high_availability/ha_messages.mes
+mes_files += $(top_srcdir)/src/hooks/dhcp/stat_cmds/stat_cmds_messages.mes
+mes_files += $(top_srcdir)/src/hooks/dhcp/user_chk/user_chk_messages.mes
+mes_files += $(top_srcdir)/src/lib/config/config_messages.mes
+mes_files += $(top_srcdir)/src/lib/hooks/hooks_messages.mes
+mes_files += $(top_srcdir)/src/lib/dhcpsrv/dhcpsrv_messages.mes
+mes_files += $(top_srcdir)/src/lib/dhcpsrv/alloc_engine_messages.mes
+mes_files += $(top_srcdir)/src/lib/dhcpsrv/hosts_messages.mes
+mes_files += $(top_srcdir)/src/lib/http/auth_messages.mes
+mes_files += $(top_srcdir)/src/lib/http/http_messages.mes
+mes_files += $(top_srcdir)/src/lib/dhcp_ddns/dhcp_ddns_messages.mes
+mes_files += $(top_srcdir)/src/lib/database/db_messages.mes
+mes_files += $(top_srcdir)/src/lib/log/log_messages.mes
+mes_files += $(top_srcdir)/src/lib/log/logimpl_messages.mes
+mes_files += $(top_srcdir)/src/lib/log/tests/log_test_messages.mes
+mes_files += $(top_srcdir)/src/lib/process/process_messages.mes
+mes_files += $(top_srcdir)/src/lib/asiodns/asiodns_messages.mes
+mes_files += $(top_srcdir)/src/lib/eval/eval_messages.mes
+mes_files += $(top_srcdir)/src/lib/d2srv/d2_messages.mes
+mes_files += $(top_srcdir)/src/bin/dhcp4/dhcp4_messages.mes
+mes_files += $(top_srcdir)/src/bin/agent/ca_messages.mes
+mes_files += $(top_srcdir)/src/bin/dhcp6/dhcp6_messages.mes
+mes_files += $(top_srcdir)/src/bin/lfc/lfc_messages.mes
+mes_files += $(top_srcdir)/src/bin/netconf/netconf_messages.mes
diff --git a/doc/sphinx/static/kea-imageonly-100bw.png b/doc/sphinx/static/kea-imageonly-100bw.png
new file mode 100644
index 0000000..fdbaf40
--- /dev/null
+++ b/doc/sphinx/static/kea-imageonly-100bw.png
diff --git a/doc/sphinx/static/kea-logo-100x70.png b/doc/sphinx/static/kea-logo-100x70.png
new file mode 100644
index 0000000..1de8411
--- /dev/null
+++ b/doc/sphinx/static/kea-logo-100x70.png
diff --git a/doc/sphinx/static/kea-logo-200.png b/doc/sphinx/static/kea-logo-200.png
new file mode 100644
index 0000000..7dbd993
--- /dev/null
+++ b/doc/sphinx/static/kea-logo-200.png
diff --git a/doc/sphinx/static/kea.css b/doc/sphinx/static/kea.css
new file mode 100644
index 0000000..55d7758
--- /dev/null
+++ b/doc/sphinx/static/kea.css
@@ -0,0 +1,26 @@
+/* give more screen width to the content as by default it is too narrow
+   and many tables and boxes are squeezed */
+.wy-nav-content {
+    max-width: 1100px;
+}
+
+/* by default table content is not wrapped and then the tables
+   are pretty wide so removing that
+ */
+.wy-table-responsive table td, .wy-table-responsive table th {
+    white-space: normal;
+}
+
+/* Paint literal text black. */
+.rst-content code.literal {
+    color: black;
+}
+
+/* Have literal text that references other sections underlined.
+ * It helps the reader figure out that it's a clickable link.
+ * This type of referencing can be achieved using text roles.
+ * https://www.sphinx-doc.org/en/master/usage/restructuredtext/roles.html
+ */
+.rst-content code.xref {
+    text-decoration: underline dotted gray;
+}
diff --git a/doc/sphinx/uml/appendRequestedOptions.png b/doc/sphinx/uml/appendRequestedOptions.png
new file mode 100644
index 0000000..8b217f8
--- /dev/null
+++ b/doc/sphinx/uml/appendRequestedOptions.png
diff --git a/doc/sphinx/uml/appendRequestedOptions.svg b/doc/sphinx/uml/appendRequestedOptions.svg
new file mode 100644
index 0000000..93c17ff
--- /dev/null
+++ b/doc/sphinx/uml/appendRequestedOptions.svg
@@ -0,0 +1,41 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="797px" preserveAspectRatio="none" style="width:444px;height:797px;" version="1.1" viewBox="0 0 444 797" width="444px" zoomAndPan="magnify"><defs><filter height="300%" id="fmj8a1z5wugx1" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="420" x="12" y="27.4023">Append requested options algorithm (Kea 1.8.0)</text><rect fill="#FEFECE" filter="url(#fmj8a1z5wugx1)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; 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+@startuml
+
+Title Append requested options algorithm (Kea 1.8.0)
+
+:get configured option list;
+
+:get parameter request list (PRL) from query;
+
+while (for each item from configured option list)
+  :get configured options in dhcp4 space;
+  while (for each persistent option)
+    :push back option code to PRL;
+  endwhile
+endwhile
+
+while (for each code in PRL)
+  if (option is not set in response) then (yes)
+    while (for each item from configured option list)
+      :get configured options in dhcp4 space;
+      if (found) then (first)
+        :add option to response;
+      else (not found or already found)
+      endif
+    endwhile
+  else (no)
+  endif
+endwhile
+->done;
+stop
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/appendRequestedOptions.uml b/doc/sphinx/uml/appendRequestedOptions.uml
new file mode 100644
index 0000000..80a21d9
--- /dev/null
+++ b/doc/sphinx/uml/appendRequestedOptions.uml
@@ -0,0 +1,31 @@
+@startuml
+
+Title Append requested options algorithm (Kea 1.8.0)
+
+:get configured option list;
+
+:get parameter request list (PRL) from query;
+
+while (for each item from configured option list)
+  :get configured options in dhcp4 space;
+  while (for each persistent option)
+    :push back option code to PRL;
+  endwhile
+endwhile
+
+while (for each code in PRL)
+  if (option is not set in response) then (yes)
+    while (for each item from configured option list)
+      :get configured options in dhcp4 space;
+      if (found) then (first)
+        :add option to response;
+      else (not found or already found)
+      endif
+    endwhile
+  else (no)
+  endif
+endwhile
+->done;
+stop
+
+@enduml
diff --git a/doc/sphinx/uml/appendRequestedVendorOptions.png b/doc/sphinx/uml/appendRequestedVendorOptions.png
new file mode 100644
index 0000000..c00fcce
--- /dev/null
+++ b/doc/sphinx/uml/appendRequestedVendorOptions.png
diff --git a/doc/sphinx/uml/appendRequestedVendorOptions.svg b/doc/sphinx/uml/appendRequestedVendorOptions.svg
new file mode 100644
index 0000000..2fe289a
--- /dev/null
+++ b/doc/sphinx/uml/appendRequestedVendorOptions.svg
@@ -0,0 +1,63 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="1590px" preserveAspectRatio="none" style="width:509px;height:1590px;" version="1.1" viewBox="0 0 509 1590" width="509px" zoomAndPan="magnify"><defs><filter height="300%" id="f1fxs94y917cvd" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="485" x="12" y="27.4023">Append vendor requested options algorithm (Kea 1.8.0)</text><rect fill="#FEFECE" filter="url(#f1fxs94y917cvd)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; 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stroke-width: 1.5;"/><line style="stroke: #A80036; stroke-width: 1.5;" x1="433.25" x2="433.25" y1="876.7832" y2="1566.2246"/><line style="stroke: #A80036; stroke-width: 1.5;" x1="433.25" x2="326.25" y1="876.7832" y2="876.7832"/><polygon fill="#A80036" points="336.25,872.7832,326.25,876.7832,336.25,880.7832,332.25,876.7832" style="stroke: #A80036; stroke-width: 1.0;"/><line style="stroke: #A80036; stroke-width: 1.5;" x1="188.25" x2="70.25" y1="876.7832" y2="876.7832"/><line style="stroke: #A80036; stroke-width: 1.5;" x1="70.25" x2="70.25" y1="876.7832" y2="908.7832"/><polygon fill="#A80036" points="66.25,898.7832,70.25,908.7832,74.25,898.7832,70.25,902.7832" style="stroke: #A80036; stroke-width: 1.0;"/><line style="stroke: #A80036; stroke-width: 1.5;" x1="257.25" x2="257.25" y1="844.7832" y2="864.7832"/><polygon fill="#A80036" points="253.25,854.7832,257.25,864.7832,261.25,854.7832,257.25,858.7832" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[1634ff79370ec127c2dd3f2d0c122eb8]
+@startuml
+
+Title Append vendor requested options algorithm (Kea 1.8.0)
+
+:get vendor id from query vivso option;
+:get vendor id from response vivso option;
+if (vendor id) then (no)
+  :return;
+  stop
+else (yes)
+endif
+
+:get configured option list;
+
+:get option request list (ORO) from query DOCSIS vendor option;
+
+while (for each item from configured option list)
+  :get configured options in vendor id space;
+  while (for each persistent option)
+    :push back option code to ORO;
+  endwhile
+endwhile
+
+if (response vivso option) then (no)
+  :create vivso option for vendor id;
+else (yes)
+endif
+
+:added = false;
+while (for each code in ORO)
+  if (sub-option is not set in vivso option) then (yes)
+    while (for each item from configured option list)
+      :get configured options in vendor id space;
+      if (found) then (first)
+        :add sub-option to vivso option;
+        :added = true;
+      else (not found or already found)
+      endif
+    endwhile
+  else (no)
+  endif
+  if (added) then (yes)
+    if (vivso option in response) then (no)
+      :add vivso option in response;
+    else (yes)
+    endif
+  else (no)
+  endif
+endwhile
+->done;
+stop
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/appendRequestedVendorOptions.uml b/doc/sphinx/uml/appendRequestedVendorOptions.uml
new file mode 100644
index 0000000..65d3d54
--- /dev/null
+++ b/doc/sphinx/uml/appendRequestedVendorOptions.uml
@@ -0,0 +1,53 @@
+@startuml
+
+Title Append vendor requested options algorithm (Kea 1.8.0)
+
+:get vendor id from query vivso option;
+:get vendor id from response vivso option;
+if (vendor id) then (no)
+  :return;
+  stop
+else (yes)
+endif
+
+:get configured option list;
+
+:get option request list (ORO) from query DOCSIS vendor option;
+
+while (for each item from configured option list)
+  :get configured options in vendor id space;
+  while (for each persistent option)
+    :push back option code to ORO;
+  endwhile
+endwhile
+
+if (response vivso option) then (no)
+  :create vivso option for vendor id;
+else (yes)
+endif
+
+:added = false;
+while (for each code in ORO)
+  if (sub-option is not set in vivso option) then (yes)
+    while (for each item from configured option list)
+      :get configured options in vendor id space;
+      if (found) then (first)
+        :add sub-option to vivso option;
+        :added = true;
+      else (not found or already found)
+      endif
+    endwhile
+  else (no)
+  endif
+  if (added) then (yes)
+    if (vivso option in response) then (no)
+      :add vivso option in response;
+    else (yes)
+    endif
+  else (no)
+  endif
+endwhile
+->done;
+stop
+
+@enduml
diff --git a/doc/sphinx/uml/assign-lease4.png b/doc/sphinx/uml/assign-lease4.png
new file mode 100644
index 0000000..29e099b
--- /dev/null
+++ b/doc/sphinx/uml/assign-lease4.png
diff --git a/doc/sphinx/uml/assign-lease4.svg b/doc/sphinx/uml/assign-lease4.svg
new file mode 100644
index 0000000..0a51934
--- /dev/null
+++ b/doc/sphinx/uml/assign-lease4.svg
@@ -0,0 +1,113 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="1372px" preserveAspectRatio="none" style="width:1375px;height:1372px;" version="1.1" viewBox="0 0 1375 1372" width="1375px" zoomAndPan="magnify"><defs><filter height="300%" id="f1hqawhmrx3191" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="287" x="535" y="17.4023">DHCPv4 Assign Lease (Kea 1.8.0)</text><!--MD5=[96a966798826de6e056b38ba6b9482ca]
+cluster init_reboot--><rect fill="#FFFFFF" filter="url(#f1hqawhmrx3191)" height="374.86" style="stroke: #000000; stroke-width: 1.5;" width="445" x="493" y="442.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="142" x="644.5" y="457.7344">INIT-REBOOT state</text><!--MD5=[71835f3367ed481a89f53801b2fdf617]
+cluster allocated--><rect fill="#FFFFFF" filter="url(#f1hqawhmrx3191)" height="263.36" style="stroke: #000000; stroke-width: 1.5;" width="158" x="7" y="1092.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="110" x="31" y="1107.5944">Lease allocated</text><!--MD5=[b13a83736ea85c18a1991bca4dbe863b]
+entity by_client_id--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="219" x="517.5" y="547.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="199" x="527.5" y="570.5944">Get existing lease by client id</text><!--MD5=[6b610307314e3774f091112845a2df2b]
+entity by_hw_addr--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="288" x="626" y="660.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="268" x="636" y="683.5944">Get existing lease by hardware address</text><!--MD5=[ef5397f1455a008291e257fb65cb453b]
+entity authoritative--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="134" x="528" y="757.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="114" x="538" y="780.5944">Get authoritative</text><!--MD5=[a54398e3d2c0f7657eea7ade058e1e7f]
+entity ddns--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="110" x="31" y="1198.4192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="90" x="41" y="1221.9544">update DDNS</text><!--MD5=[8edf83f1bb568d804760d31cec2ffb3b]
+entity ack--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="87" x="42.5" y="1295.4192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="67" x="52.5" y="1318.9544">Send ACK</text><!--MD5=[7f6071cca9390999bbf4a53289faea1c]
+entity subnet--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="114" x="1205" y="28.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="94" x="1215" y="51.7344">Check Subnet</text><path d="M1080,33.6992 L1080,59.0098 A0,0 0 0 0 1080,59.0098 L1170,59.0098 A0,0 0 0 0 1170,59.0098 L1170,51.6992 L1205,46.1992 L1170,43.6992 L1170,43.6992 L1160,33.6992 L1080,33.6992 A0,0 0 0 0 1080,33.6992 " fill="#FBFB77" filter="url(#f1hqawhmrx3191)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M1160,33.6992 L1160,43.6992 L1170,43.6992 L1160,33.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="69" x="1086" y="51.2676">entry point</text><!--MD5=[d9ce3005481b6be8203f0e568049ebfd]
+entity server_id--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="106" x="1046" y="125.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="86" x="1056" y="148.7344">Get server id</text><!--MD5=[ee598753b08e093ad1dc6a89dd6a274b]
+entity hint--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="74" x="849" y="222.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="54" x="859" y="245.7344">Get hint</text><!--MD5=[fdc0ebc2726a1e25611a217b1a9cdddd]
+entity ident--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="258" x="565" y="335.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="238" x="575" y="358.7344">Get hardware address and client id</text><!--MD5=[9b403e692b0a4a2d394ce21b0c8a8b18]
+entity hostname--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="144" x="276" y="888.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="124" x="286" y="911.5944">Process hostname</text><!--MD5=[c7571992746652353b375880ae850124]
+entity allocate--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="114" x="204" y="985.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="94" x="214" y="1008.5944">Request lease</text><!--MD5=[18d4eff7c560e0870d2f30d7f8649cf3]
+entity failed--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="144" x="189" y="1101.4192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="124" x="199" y="1124.9544">No lease allocated</text><path d="M368,1106.9192 L368,1115.4192 L333.27,1119.4192 L368,1123.4192 L368,1132.2298 A0,0 0 0 0 368,1132.2298 L450,1132.2298 A0,0 0 0 0 450,1132.2298 L450,1116.9192 L440,1106.9192 L368,1106.9192 A0,0 0 0 0 368,1106.9192 " fill="#FBFB77" filter="url(#f1hqawhmrx3191)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M440,1106.9192 L440,1116.9192 L450,1116.9192 L440,1106.9192 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="61" x="374" y="1124.4876">exit point</text><!--MD5=[6dac4c34c80be6dabf811d62e9db4883]
+entity nak--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="87" x="599.5" y="1198.4192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="67" x="609.5" y="1221.9544">Send NAK</text><path d="M722,1203.9192 L722,1212.4192 L686.59,1216.4192 L722,1220.4192 L722,1229.2298 A0,0 0 0 0 722,1229.2298 L804,1229.2298 A0,0 0 0 0 804,1229.2298 L804,1213.9192 L794,1203.9192 L722,1203.9192 A0,0 0 0 0 722,1203.9192 " fill="#FBFB77" filter="url(#f1hqawhmrx3191)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M794,1203.9192 L794,1213.9192 L804,1213.9192 L794,1203.9192 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="61" x="728" y="1221.4876">exit point</text><!--MD5=[be0cad0b32609f2a377600c2fd818d08]
+entity no_response--><rect fill="#FEFECE" filter="url(#f1hqawhmrx3191)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="106" x="1023" y="985.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="86" x="1033" y="1008.5944">No response</text><path d="M1164,990.5592 L1164,999.0592 L1129.16,1003.0592 L1164,1007.0592 L1164,1015.8698 A0,0 0 0 0 1164,1015.8698 L1246,1015.8698 A0,0 0 0 0 1246,1015.8698 L1246,1000.5592 L1236,990.5592 L1164,990.5592 A0,0 0 0 0 1164,990.5592 " fill="#FBFB77" filter="url(#f1hqawhmrx3191)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M1236,990.5592 L1236,1000.5592 L1246,1000.5592 L1236,990.5592 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="61" x="1170" y="1008.1276">exit point</text><!--MD5=[359b6ca0b36d81a4e33a25f71e3b7c61]
+link subnet to server_id--><path d="M1232.48,64.3992 C1204.44,80.7492 1162.31,105.2992 1132.9,122.4392 " fill="none" id="subnet-&gt;server_id" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1128.3,125.1192,1138.0915,124.0576,1132.6235,122.6079,1134.0733,117.1399,1128.3,125.1192" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[7db9f4f0423b43d622896ef15525c632]
+link subnet to nak--><path d="M1273.1,64.2792 C1284,82.7192 1299,113.3492 1299,142.1992 C1299,142.1992 1299,142.1992 1299,1120.4192 C1299,1186.7792 768.46,1163.0292 705,1182.4192 C694.58,1185.5992 683.88,1190.5892 674.36,1195.7292 " fill="none" id="subnet-&gt;nak" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="669.79,1198.2492,679.6021,1197.3996,674.1668,1195.8319,675.7345,1190.3966,669.79,1198.2492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="63" x="1300" y="626.6276">no subnet</text><!--MD5=[a38dfb09b1bcb8b95a969df0005f111d]
+link server_id to hint--><path d="M1060.43,161.3992 C1022.99,178.0992 966.32,203.3692 927.82,220.5492 " fill="none" id="server_id-&gt;hint" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="923.21,222.5992,933.0589,222.5935,927.7779,220.5659,929.8055,215.2849,923.21,222.5992" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[34fbc802059013c2537c0989625530bb]
+link hint to ident--><path d="M848.75,241.0892 C774.38,241.7392 611.66,247.8692 577,288.1992 C559.81,308.1992 581.08,323.0792 609.99,333.4192 " fill="none" id="hint-&gt;ident" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="615.08,335.1692,607.8731,328.4565,610.3525,333.541,605.268,336.0204,615.08,335.1692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="186" x="578" y="301.7676">use requested address option</text><!--MD5=[34fbc802059013c2537c0989625530bb]
+link hint to ident--><path d="M856.42,258.2992 C821.75,278.3392 764.41,311.4992 727.95,332.5692 " fill="none" id="hint-&gt;ident-1" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="723.61,335.0792,733.4041,334.0418,727.9397,332.5785,729.403,327.1142,723.61,335.0792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="114" x="802" y="301.7676">use client address</text><!--MD5=[34fbc802059013c2537c0989625530bb]
+link hint to ident--><path d="M908.07,258.3492 C922.64,271.7392 937.02,290.4892 925,305.1992 C911.63,321.5592 871.46,332.3692 828.28,339.4492 " fill="none" id="hint-&gt;ident-2" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="823.28,340.2492,832.7964,342.7867,828.218,339.4643,831.5404,334.8859,823.28,340.2492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="45" x="930" y="301.7676">no hint</text><!--MD5=[65f067d78ef63afdf91771d9a656ad03]
+link ident to init_reboot--><path d="M694,371.5692 C694,387.3142 694,411.0567 694,431.1092 C694,433.6158 694,436.0647 694,438.4331 C694,439.6173 694,440.7814 694,441.9225 " fill="none" id="ident-&gt;init_reboot" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="694,441.9225,698,432.9225,694,436.9225,690,432.9225,694,441.9225" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="220" x="695" y="414.7676">requested address and no server id</text><!--MD5=[14830c65b2a034d88d53d1ea466689d7]
+link ident to hostname--><path d="M571.53,371.2492 C471.99,388.6592 348,420.0792 348,468.5592 C348,468.5592 348,468.5592 348,776.0592 C348,813.4892 348,857.0192 348,882.7392 " fill="none" id="ident-&gt;hostname" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="348,887.9492,352,878.9492,348,882.9492,344,878.9492,348,887.9492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[f67bf50fbab8c942c3b4d7a43dc78f8a]
+link init_reboot to by_client_id--><path d="M693.95,470.1292 C692.56,472.0792 661.57,515.5492 642.25,542.6592 " fill="none" id="init_reboot-&gt;by_client_id" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="639.25,546.8692,647.7294,541.8593,642.1508,542.7967,641.2134,537.218,639.25,546.8692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="88" x="673" y="513.6276">has a client id</text><!--MD5=[e73d6babdacfd6f192eca91886274ed0]
+link init_reboot to by_hw_addr--><path d="M694.16,470.0592 C697.44,470.0892 750.21,470.9692 770,500.0592 C802.04,547.1592 787.68,618.8592 777.31,654.8392 " fill="none" id="init_reboot-&gt;by_hw_addr" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="775.82,659.8792,782.2006,652.3767,777.2331,655.0831,774.5268,650.1156,775.82,659.8792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="71" x="790" y="570.1276">no client id</text><!--MD5=[0bee13a6f2540e80d374adb5c9fde696]
+link by_client_id to authoritative--><path d="M612.69,583.0592 C598.68,600.9192 578.27,630.4692 570,660.0592 C561.14,691.7592 573.59,729.1292 583.87,752.2092 " fill="none" id="by_client_id-&gt;authoritative" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="586.03,756.9092,585.9217,747.061,583.9492,752.3628,578.6474,750.3903,586.03,756.9092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="37" x="571" y="683.1276">found</text><!--MD5=[81a28d33e53a361ab0f9b1ac80511604]
+link by_client_id to by_hw_addr--><path d="M622.24,583.2592 C619.47,597.2192 618.2,616.7092 628,630.0592 C636.84,642.0992 648.87,651.0992 662.21,657.8192 " fill="none" id="by_client_id-&gt;by_hw_addr" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="666.79,660.0092,660.4134,652.5033,662.2842,657.8419,656.9456,659.7126,666.79,660.0092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="62" x="629" y="626.6276">not found</text><!--MD5=[996213fdf844dcf095df5ccc9b89cdbf]
+link by_hw_addr to authoritative--><path d="M738.31,696.2592 C708.08,712.6692 662.6,737.3592 631.01,754.5092 " fill="none" id="by_hw_addr-&gt;authoritative" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="626.46,756.9792,636.2784,756.2057,630.8555,754.596,632.4652,749.173,626.46,756.9792" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[cc7ba6fbd1fdcf375abf61565bb8cbda]
+link authoritative to no_response--><path d="M662.09,791.8592 C705.06,803.0892 761.47,819.8992 809,841.0592 C901.17,882.0792 1000.65,948.7092 1047.95,981.9092 " fill="none" id="authoritative-&gt;no_response" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1052.08,984.8292,1047.0166,976.3816,1047.9892,981.9542,1042.4166,982.9269,1052.08,984.8292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="233" x="960" y="911.1276">not authoritative and no owned lease</text><!--MD5=[f287a43fa002547e84e3e2517c1b3af8]
+link authoritative to nak--><path d="M662.08,792.5792 C716.07,810.3592 783,844.5992 783,905.0592 C783,905.0592 783,905.0592 783,1120.4192 C783,1133.0992 719.28,1171.9092 677.82,1195.8192 " fill="none" id="authoritative-&gt;nak" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="673.38,1198.3692,683.178,1197.37,677.7195,1195.8855,679.204,1190.4269,673.38,1198.3692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="203" x="784" y="1008.1276">owned lease with hint mismatch</text><!--MD5=[f287a43fa002547e84e3e2517c1b3af8]
+link authoritative to nak--><path d="M571.78,793.3292 C544.53,815.7792 503,857.7492 503,905.0592 C503,905.0592 503,905.0592 503,1120.4192 C503,1165.8592 554.13,1191.0792 594.59,1203.9092 " fill="none" id="authoritative-&gt;nak-1" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="599.47,1205.4192,592.043,1198.9509,594.6908,1203.9498,589.6919,1206.5976,599.47,1205.4192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="208" x="504" y="1008.1276">authoritative and no owned lease</text><!--MD5=[b7c0267f2f455dcd84cdca29c5404c83]
+link authoritative to hostname--><path d="M527.91,789.4292 C489.09,799.3592 440.63,815.6592 403,841.0592 C386.38,852.2692 371.81,869.7892 361.85,883.6592 " fill="none" id="authoritative-&gt;hostname" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="358.91,887.8392,367.3694,882.7956,361.7945,883.7552,360.8349,878.1803,358.91,887.8392" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="72" x="404" y="854.6276">other cases</text><!--MD5=[986a8f86ec6d7417d34c7fd351c484dc]
+link hostname to allocate--><path d="M332.04,924.4792 C317.45,940.4192 295.83,964.0292 280.28,981.0092 " fill="none" id="hostname-&gt;allocate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="276.86,984.7492,285.886,980.8082,280.2347,981.0599,279.9831,975.4086,276.86,984.7492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[c34dad786bb94ff8f8cc439f61a5c35f]
+link allocate to allocated--><path d="M212.16,1021.1492 C194.16,1028.7392 174.22,1038.7792 158,1051.0592 C150.43,1056.7942 143.1831,1063.7023 136.5469,1070.8789 C133.2288,1074.4672 130.0633,1078.1226 127.0864,1081.732 C125.598,1083.5367 124.1567,1085.3299 122.767,1087.0975 C122.0722,1087.9813 121.3903,1088.8587 120.7219,1089.7279 C120.3876,1090.1625 120.0568,1090.595 119.7294,1091.0253 C119.5657,1091.2405 119.4028,1091.4551 119.2408,1091.6691 C119.1598,1091.7761 119.0791,1091.8829 118.9985,1091.9896 " fill="none" id="allocate-&gt;allocated" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="118.9985,1091.9896,127.6138,1087.2171,122.0113,1087.9992,121.2292,1082.3967,118.9985,1091.9896" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="93" x="159" y="1064.6276">lease allocated</text><!--MD5=[539a3348c1089415ce435c139bd22f41]
+link allocated to ddns--><path d="M100.99,1120.4892 C100.68,1122.4392 93.91,1165.3192 89.58,1192.7692 " fill="none" id="allocated-&gt;ddns" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="88.74,1198.0392,94.1033,1189.7788,89.5249,1193.1012,86.2025,1188.5229,88.74,1198.0392" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[6d51d97a60fea492264b409c209ca1ef]
+link ddns to ack--><path d="M86,1234.8392 C86,1250.3792 86,1273.1992 86,1290.0792 " fill="none" id="ddns-&gt;ack" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="86,1295.1092,90,1286.1092,86,1290.1092,82,1286.1092,86,1295.1092" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[dd12c52c80378d18331ab530a0ed76ab]
+link allocate to failed--><path d="M261,1021.4292 C261,1041.4392 261,1074.3792 261,1096.2292 " fill="none" id="allocate-&gt;failed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="261,1101.2592,265,1092.2592,261,1096.2592,257,1092.2592,261,1101.2592" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="113" x="262" y="1064.6276">no lease allocated</text><!--MD5=[e8032f725f00abe81d7341b4b6fe8340]
+link failed to nak--><path d="M329.74,1137.5092 C406.04,1156.4892 527.27,1186.6392 594.35,1203.3192 " fill="none" id="failed-&gt;nak" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="599.48,1204.5992,591.7189,1198.5358,594.6293,1203.3865,589.7786,1206.297,599.48,1204.5992" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[0f73f9f94dec6643990f2b1b148176bd]
+@startuml
+
+title DHCPv4 Assign Lease (Kea 1.8.0)
+
+agent "Check Subnet" as subnet
+note left : entry point
+
+agent "Get server id" as server_id
+
+agent "Get hint" as hint
+
+agent "Get hardware address and client id" as ident
+
+rectangle "INIT-REBOOT state" as init_reboot {
+ agent "Get existing lease by client id" as by_client_id
+
+ agent "Get existing lease by hardware address" as by_hw_addr
+
+ agent "Get authoritative" as authoritative
+}
+
+agent "Process hostname" as hostname
+
+agent "Request lease" as allocate
+
+rectangle "Lease allocated" as allocated {
+ agent "update DDNS" as ddns
+ agent "Send ACK" as ack
+}
+
+agent "No lease allocated" as failed
+note right : exit point
+
+agent "Send NAK" as nak
+note right : exit point
+
+agent "No response" as no_response
+note right : exit point
+
+subnet - -> server_id
+subnet - - -> nak : no subnet
+server_id - -> hint
+hint - -> ident : use requested address option
+hint - -> ident : use client address
+hint - -> ident : no hint
+ident - -> init_reboot : requested address and no server id
+ident - - -> hostname
+init_reboot - -> by_client_id : has a client id
+init_reboot - -> by_hw_addr : no client id
+by_client_id - - -> authoritative : found
+by_client_id - -> by_hw_addr : not found
+by_hw_addr - -> authoritative
+authoritative - - -> no_response : not authoritative and no owned lease
+authoritative - -> nak : owned lease with hint mismatch
+authoritative - -> nak : authoritative and no owned lease
+authoritative - -> hostname : other cases
+hostname - -> allocate
+allocate - -> allocated : lease allocated
+allocated - -> ddns
+ddns - -> ack
+allocate - -> failed : no lease allocated
+failed - -> nak
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/assign-lease4.uml b/doc/sphinx/uml/assign-lease4.uml
new file mode 100644
index 0000000..de19ed7
--- /dev/null
+++ b/doc/sphinx/uml/assign-lease4.uml
@@ -0,0 +1,64 @@
+@startuml
+
+title DHCPv4 Assign Lease (Kea 1.8.0)
+
+agent "Check Subnet" as subnet
+note left : entry point
+
+agent "Get server id" as server_id
+
+agent "Get hint" as hint
+
+agent "Get hardware address and client id" as ident
+
+rectangle "INIT-REBOOT state" as init_reboot {
+ agent "Get existing lease by client id" as by_client_id
+
+ agent "Get existing lease by hardware address" as by_hw_addr
+
+ agent "Get authoritative" as authoritative
+}
+
+agent "Process hostname" as hostname
+
+agent "Request lease" as allocate
+
+rectangle "Lease allocated" as allocated {
+ agent "update DDNS" as ddns
+ agent "Send ACK" as ack
+}
+
+agent "No lease allocated" as failed
+note right : exit point
+
+agent "Send NAK" as nak
+note right : exit point
+
+agent "No response" as no_response
+note right : exit point
+
+subnet --> server_id
+subnet ---> nak : no subnet
+server_id --> hint
+hint --> ident : use requested address option
+hint --> ident : use client address
+hint --> ident : no hint
+ident --> init_reboot : requested address and no server id
+ident ---> hostname
+init_reboot --> by_client_id : has a client id
+init_reboot --> by_hw_addr : no client id
+by_client_id ---> authoritative : found
+by_client_id --> by_hw_addr : not found
+by_hw_addr --> authoritative
+authoritative ---> no_response : not authoritative and no owned lease
+authoritative --> nak : owned lease with hint mismatch
+authoritative --> nak : authoritative and no owned lease
+authoritative --> hostname : other cases
+hostname --> allocate
+allocate --> allocated : lease allocated
+allocated --> ddns
+ddns --> ack
+allocate --> failed : no lease allocated
+failed --> nak
+
+@enduml
diff --git a/doc/sphinx/uml/buildCfgOptionList.png b/doc/sphinx/uml/buildCfgOptionList.png
new file mode 100644
index 0000000..262b10e
--- /dev/null
+++ b/doc/sphinx/uml/buildCfgOptionList.png
diff --git a/doc/sphinx/uml/buildCfgOptionList.svg b/doc/sphinx/uml/buildCfgOptionList.svg
new file mode 100644
index 0000000..c42e8d7
--- /dev/null
+++ b/doc/sphinx/uml/buildCfgOptionList.svg
@@ -0,0 +1,62 @@
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stroke-width: 1.0;"/><!--MD5=[bd4aec0a1192fe47e86baeddbb8cfe25]
+@startuml
+
+title buildCfgOptionList: build configured option list algorithm (Kea 1.8.0)
+
+start
+:Get (empty) configured option list;
+
+if (no subnet) then (yes)
+  :return;
+  stop
+else (no)
+endif
+
+if (current host reservation) then (yes)
+  :push back host configured options;
+else (no)
+endif
+
+if (assigned address) then (yes)
+  :get pool of assigned address;
+  if (pool) then (yes)
+    :push back pool configured options;
+  else (no)
+  endif
+else (no)
+endif
+
+:push back subnet configured options;
+
+:get shared network from subnet;
+if (shared network) then (yes)
+  :push back shared network configured options;
+else (no)
+endif
+
+while (for each query client class)
+ :get client class definition from current configuration;
+ if (found) then (no)
+    if (built-in client class) then (yes)
+    else (no)
+      :log debug "class unconfigured";
+    endif
+  else (yes)
+    :push back client class definition configured options;
+  endif
+endwhile
+
+:push back global configured options;
+:return;
+stop
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/buildCfgOptionList.uml b/doc/sphinx/uml/buildCfgOptionList.uml
new file mode 100644
index 0000000..1df19f8
--- /dev/null
+++ b/doc/sphinx/uml/buildCfgOptionList.uml
@@ -0,0 +1,52 @@
+@startuml
+
+title buildCfgOptionList: build configured option list algorithm (Kea 1.8.0)
+
+start
+:Get (empty) configured option list;
+
+if (no subnet) then (yes)
+  :return;
+  stop
+else (no)
+endif
+
+if (current host reservation) then (yes)
+  :push back host configured options;
+else (no)
+endif
+
+if (assigned address) then (yes)
+  :get pool of assigned address;
+  if (pool) then (yes)
+    :push back pool configured options;
+  else (no)
+  endif
+else (no)
+endif
+
+:push back subnet configured options;
+
+:get shared network from subnet;
+if (shared network) then (yes)
+  :push back shared network configured options;
+else (no)
+endif
+
+while (for each query client class)
+ :get client class definition from current configuration;
+ if (found) then (no)
+    if (built-in client class) then (yes)
+    else (no)
+      :log debug "class unconfigured";
+    endif
+  else (yes)
+    :push back client class definition configured options;
+  endif
+endwhile
+
+:push back global configured options;
+:return;
+stop
+
+@enduml
diff --git a/doc/sphinx/uml/currentHost4.png b/doc/sphinx/uml/currentHost4.png
new file mode 100644
index 0000000..e8aa59e
--- /dev/null
+++ b/doc/sphinx/uml/currentHost4.png
diff --git a/doc/sphinx/uml/currentHost4.svg b/doc/sphinx/uml/currentHost4.svg
new file mode 100644
index 0000000..1db758c
--- /dev/null
+++ b/doc/sphinx/uml/currentHost4.svg
@@ -0,0 +1,147 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="2163px" preserveAspectRatio="none" style="width:969px;height:2163px;" version="1.1" viewBox="0 0 969 2163" width="969px" zoomAndPan="magnify"><defs><filter height="300%" id="fgxgo3z1vpo2" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="277" x="337.25" y="17.4023">currentHost DHCPv4 (Kea 1.8.0)</text><!--MD5=[e3476fda087b0512b1cf4e3a66ca5e59]
+entity entry--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="134" x="314.5" y="28.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="114" x="324.5" y="51.7344">Subnet Selection</text><!--MD5=[f65ad2d20ed779f8ee7fa3e9ca8ab4c3]
+entity setSelected--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="247" x="258" y="125.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="227" x="268" y="148.7344">Set subnet to the selected subnet</text><!--MD5=[c0678c1aaf89874ea821e39d7ef5404f]
+entity clientid_lookup--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="245" x="259" y="222.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="225" x="269" y="245.7344">Has client a lease for its client id?</text><!--MD5=[a51c27fcfb0c2b9388b266a7e30efdf3]
+entity clientid_iterate--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="283" x="7" y="319.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="263" x="17" y="342.7344">Iterate on allowed subnets for client id</text><!--MD5=[96d14c76c72fae1f84c71c464af0f0e6]
+entity found_clientid--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="253" x="22" y="498.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="233" x="32" y="521.7344">Set subnet to the by client id lease</text><!--MD5=[9f5518b92d1482f0724c659635bb4f8f]
+entity hwaddr_lookup--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="211" x="449" y="432.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="191" x="459" y="455.7344">Has client a matching lease?</text><!--MD5=[7366630e5488cbc20c26d829a87e86ca]
+entity hwaddr_iterate--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="352" x="201.5" y="564.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="332" x="211.5" y="587.7344">Iterate on allowed subnets for hardware address</text><!--MD5=[096d593c9a7e1a0b5ae2681804d4217f]
+entity found_hwaddr--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="243" x="229" y="677.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="223" x="239" y="700.7344">Set subnet to the matching lease</text><!--MD5=[f1bd864ca92b3a59ad91e15b6c278a16]
+entity hasAddressReservation--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="211" x="375" y="930.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="191" x="385" y="953.7344">Has an address reservation?</text><!--MD5=[0af8b8cc29117b7db26a4bf8fde82b62]
+entity setAddressReservation--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="300" x="220.5" y="1043.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="280" x="230.5" y="1066.7344">Set subnet to address reservation subnet</text><!--MD5=[42a0a2711e18aa980e3ea9f910af1c90]
+entity pool--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="251" x="355" y="1140.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="231" x="365" y="1163.7344">Is the address in an allowed pool?</text><!--MD5=[ec337e6f6831b541235537d1c5125816]
+entity pool_iterate--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="269" x="141" y="1237.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="249" x="151" y="1260.7344">Iterate on allowed subnets with pool</text><!--MD5=[8426a0f58e3c900bd89aafdc516c0a64]
+entity inAllowedPool--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="254" x="148.5" y="1350.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="234" x="158.5" y="1373.7344">Set subnet to address pool subnet</text><!--MD5=[c7571992746652353b375880ae850124]
+entity allocate--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="158" x="393.5" y="1447.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="138" x="403.5" y="1470.7344">Allocate a new lease</text><!--MD5=[539657d7008b7b9e186112fa27fe2a64]
+entity allocate_iterate--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="201" x="232" y="1560.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="181" x="242" y="1583.7344">Iterate on allowed subnets</text><!--MD5=[98bd7f0fd78ffed8e2b0c08f2369be38]
+entity allocated--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="266" x="270.5" y="1673.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="246" x="280.5" y="1696.7344">Set subnet to allocated lease subnet</text><!--MD5=[a2ab21a8d09e419da8ba4e22e422b87f]
+entity getHRmode--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="252" x="394.5" y="1770.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="232" x="404.5" y="1793.7344">Get subnet host reservation mode</text><!--MD5=[9e66760393f24350dd53d10577644815]
+entity checkHRmode--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="293" x="374" y="1867.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="273" x="384" y="1890.7344">Is subnet host reservation mode global?</text><!--MD5=[9225881c05e5dcc29801826dc3c4a44b]
+entity global--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="205" x="298" y="1980.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="185" x="308" y="2003.7344">Get global host reservation</text><!--MD5=[fb2193611fca68211907294b61bd1772]
+entity bySubnet--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="209" x="538" y="1980.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="189" x="548" y="2003.7344">Get subnet host reservation</text><!--MD5=[c13398c59c328d6fcc544c8c17f5b117]
+entity return--><rect fill="#FEFECE" filter="url(#fgxgo3z1vpo2)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="235" x="403" y="2093.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="215" x="413" y="2116.7344">Return current host reservation</text><!--MD5=[4190d3dcd511d21b11bd238065bcb30b]
+link entry to setSelected--><path d="M381.5,64.6192 C381.5,80.1592 381.5,102.9792 381.5,119.8592 " fill="none" id="entry-&gt;setSelected" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="381.5,124.8892,385.5,115.8892,381.5,119.8892,377.5,115.8892,381.5,124.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[e08d915304835ed62ca4e0728c34eef1]
+link setSelected to clientid_lookup--><path d="M381.5,161.6192 C381.5,177.1592 381.5,199.9792 381.5,216.8592 " fill="none" id="setSelected-&gt;clientid_lookup" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="381.5,221.8892,385.5,212.8892,381.5,216.8892,377.5,212.8892,381.5,221.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[6be1f2e9e03fb1c5265b47f0fe05d4fb]
+link clientid_lookup to hwaddr_lookup--><path d="M450.66,258.2792 C487.31,270.2592 530.95,289.5492 561.5,319.1992 C589.76,346.6192 605.63,365.0792 592.5,402.1992 C589.19,411.5492 583.15,420.3992 576.84,427.8492 " fill="none" id="clientid_lookup-&gt;hwaddr_lookup" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="573.32,431.8292,582.2724,427.7238,576.6267,428.0788,576.2717,422.4331,573.32,431.8292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="116" x="591.5" y="342.2676">no client id option</text><!--MD5=[e88e8ce2e61ddfe0f17d6f35f9f4b567]
+link clientid_lookup to clientid_iterate--><path d="M339.58,258.2892 C298.95,274.8592 237.46,299.9292 195.27,317.1292 " fill="none" id="clientid_lookup-&gt;clientid_iterate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="190.48,319.0792,200.324,319.3879,195.1105,317.1927,197.3056,311.9792,190.48,319.0792" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[574cfa9865ae5a8c4342d01c24825c76]
+link clientid_iterate to clientid_iterate--><path d="M290.1,329.0592 C310.94,330.3392 325,333.0492 325,337.1992 C325,340.9892 313.25,343.5892 295.32,344.9792 " fill="none" id="clientid_iterate-&gt;clientid_iterate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="290.1,345.3392,299.3532,348.7123,295.0882,344.9962,298.8044,340.7312,290.1,345.3392" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="224" x="331" y="342.2676">match-client-id is false or no lease</text><!--MD5=[6bcef6072872efd8a87246b817e1d22e]
+link clientid_iterate to found_clientid--><path d="M148.5,355.4892 C148.5,387.8292 148.5,457.3892 148.5,493.0792 " fill="none" id="clientid_iterate-&gt;found_clientid" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="148.5,498.0992,152.5,489.0992,148.5,493.0992,144.5,489.0992,148.5,498.0992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="84" x="149.5" y="398.7676">found a lease</text><!--MD5=[7615618d548cc7387965d08a49484701]
+link found_clientid to hasAddressReservation--><path d="M148.5,534.3592 C148.5,557.7292 148.5,600.8792 148.5,637.6992 C148.5,637.6992 148.5,637.6992 148.5,869.1992 C148.5,915.6592 273.28,934.4692 369.84,942.0692 " fill="none" id="found_clientid-&gt;hasAddressReservation" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="375,942.4692,366.3353,937.7869,370.0149,942.0836,365.7183,945.7631,375,942.4692" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[a2c6bf2befd5a55c13fb7d14d9b0c240]
+link clientid_iterate to hwaddr_lookup--><path d="M180.8,355.2592 C209.44,369.7192 252.75,389.9992 292.5,402.1992 C341.2,417.1492 396.54,427.9392 443.77,435.3792 " fill="none" id="clientid_iterate-&gt;hwaddr_lookup" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="448.9,436.1792,440.6245,430.8392,443.9598,435.4082,439.3908,438.7436,448.9,436.1792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="294" x="293.5" y="398.7676">not found by client id, try by hardware address</text><!--MD5=[5a497db9eec20d36442cfd8ff0bb8196]
+link hwaddr_lookup to hasAddressReservation--><path d="M660.05,459.9192 C736.51,472.7092 826.5,504.1292 826.5,581.1992 C826.5,581.1992 826.5,581.1992 826.5,869.1992 C826.5,918.2492 692.51,936.4592 591.29,943.2192 " fill="none" id="hwaddr_lookup-&gt;hasAddressReservation" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="586.19,943.5492,595.4238,946.9751,591.1801,943.2347,594.9205,938.9909,586.19,943.5492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="130" x="827.5" y="756.7676">no hardware address</text><!--MD5=[3e65bd8831bbfab836115278d54dbd54]
+link hwaddr_lookup to hwaddr_iterate--><path d="M531,468.4592 C498.37,492.4192 439.49,535.6692 404.91,561.0692 " fill="none" id="hwaddr_lookup-&gt;hwaddr_iterate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="400.82,564.0692,410.4373,561.946,404.8438,561.1013,405.6886,555.5078,400.82,564.0692" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[8827ae6ff5ddcc22e7f77fe98cdf1a45]
+link hwaddr_iterate to hwaddr_iterate--><path d="M553.73,573.1792 C574.76,574.8192 588.5,577.8192 588.5,582.1992 C588.5,586.1992 577.02,589.0592 558.99,590.7692 " fill="none" id="hwaddr_iterate-&gt;hwaddr_iterate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="553.73,591.2192,563.0395,594.4337,558.7116,590.791,562.3544,586.4631,553.73,591.2192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="190" x="594.5" y="587.2676">no lease or client id mismatch</text><!--MD5=[c5ee7e899f7e78ebb49c392f0cd68ce0]
+link hwaddr_iterate to found_hwaddr--><path d="M373.28,600.5392 C368.61,619.7692 361.05,650.8292 355.93,671.8592 " fill="none" id="hwaddr_iterate-&gt;found_hwaddr" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="354.69,676.9792,360.6886,669.1679,355.8623,672.1186,352.9116,667.2923,354.69,676.9792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="84" x="367.5" y="643.7676">found a lease</text><!--MD5=[49806d919f2e8f347acf33d16af6c958]
+link found_hwaddr to hasAddressReservation--><path d="M359.44,713.4492 C382.5,757.9792 443.99,876.6992 469.34,925.6492 " fill="none" id="found_hwaddr-&gt;hasAddressReservation" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="471.67,930.1592,471.0846,920.3278,469.3713,925.7189,463.9802,924.0056,471.67,930.1592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[419c32f3c11394d82c4ebd3db00104c7]
+link hwaddr_iterate to hasAddressReservation--><path d="M433.87,600.2492 C475.7,616.7892 525.5,646.4992 525.5,694.1992 C525.5,694.1992 525.5,694.1992 525.5,869.1992 C525.5,890.4892 512.76,911.2092 500.84,925.9292 " fill="none" id="hwaddr_iterate-&gt;hasAddressReservation" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="497.51,929.9192,506.343,925.5627,500.7095,926.0769,500.1953,920.4435,497.51,929.9192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="62" x="526.5" y="803.7676">not found</text><!--MD5=[1a9e971bc87c9d378000ad9b2e367c91]
+link hasAddressReservation to setAddressReservation--><path d="M463.31,966.5392 C443.86,986.1792 412.17,1018.1492 391.33,1039.1792 " fill="none" id="hasAddressReservation-&gt;setAddressReservation" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="387.57,1042.9792,396.7481,1039.4066,391.0912,1039.4295,391.0684,1033.7726,387.57,1042.9792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="21" x="432.5" y="1009.7676">yes</text><!--MD5=[d42a4bd24fb375c431deb7abe8a74e17]
+link hasAddressReservation to pool--><path d="M497.22,966.4192 C518.88,990.8992 552.33,1037.4392 538.5,1079.1992 C531.33,1100.8692 515.54,1121.4192 502.24,1135.9792 " fill="none" id="hasAddressReservation-&gt;pool" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="498.57,1139.9292,507.6356,1136.0803,501.9821,1136.2744,501.7879,1130.6209,498.57,1139.9292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="225" x="542.5" y="1066.2676">no or not check in the taken branch</text><!--MD5=[791581dff43cc3b6477c496805383c47]
+link setAddressReservation to pool--><path d="M390.42,1079.3992 C409.11,1095.5392 437.07,1119.6992 456.88,1136.7992 " fill="none" id="setAddressReservation-&gt;pool" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="460.73,1140.1192,456.5357,1131.2081,456.9468,1136.85,451.305,1137.2612,460.73,1140.1192" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[7a1241998e61cc09e6a084344a13ee40]
+link pool to pool_iterate--><path d="M443.38,1176.3992 C407.82,1192.8792 354.25,1217.7092 317.23,1234.8592 " fill="none" id="pool-&gt;pool_iterate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="312.35,1237.1192,322.1978,1236.9736,316.8885,1235.0212,318.841,1229.712,312.35,1237.1192" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[1c40abd319323f0f8c3e812984d047be]
+link pool to allocate--><path d="M562.27,1176.2592 C595.56,1187.6592 630.78,1206.4492 650.5,1237.1992 C659.14,1250.6692 654.47,1257.6992 650.5,1273.1992 C636.28,1328.6892 627.14,1343.9092 588.5,1386.1992 C566.39,1410.3992 535.31,1430.7792 510.89,1444.6292 " fill="none" id="pool-&gt;allocate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="506.41,1447.1392,516.2178,1446.2406,510.7747,1444.7001,512.3152,1439.2571,506.41,1447.1392" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="205" x="642.5" y="1316.7676">pool check is not in all branches</text><!--MD5=[f92712dd8e32c9acdf8619de922fc5cb]
+link pool_iterate to pool_iterate--><path d="M410.12,1246.9692 C430.88,1248.2192 445,1250.9592 445,1255.1992 C445,1259.0792 433.2,1261.6992 415.32,1263.0692 " fill="none" id="pool_iterate-&gt;pool_iterate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="410.12,1263.4292,419.3732,1266.8023,415.1082,1263.0862,418.8244,1258.8212,410.12,1263.4292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="193" x="451" y="1260.2676">address not in an allowed pool</text><!--MD5=[89f40702130c31205e20b7afecbe9ed1]
+link pool_iterate to inAllowedPool--><path d="M275.5,1273.5392 C275.5,1292.7692 275.5,1323.8292 275.5,1344.8592 " fill="none" id="pool_iterate-&gt;inAllowedPool" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="275.5,1349.9792,279.5,1340.9792,275.5,1344.9792,271.5,1340.9792,275.5,1349.9792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="168" x="276.5" y="1316.7676">address in an allowed pool</text><!--MD5=[03b0dcad835fe04723134b797eb9a319]
+link pool_iterate to allocate--><path d="M375.89,1273.2492 C408.78,1280.8692 439.69,1290.9192 450.5,1303.1992 C484.66,1341.9792 481.2,1407.7092 476.46,1441.9492 " fill="none" id="pool_iterate-&gt;allocate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="475.7,1447.1692,480.9697,1438.8487,476.4291,1442.2227,473.0552,1437.6821,475.7,1447.1692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="100" x="479.5" y="1373.2676">no allowed pool</text><!--MD5=[27c03cbbcf5b4bbc0f83ff469240ee91]
+link inAllowedPool to allocate--><path d="M311.18,1386.3992 C345.34,1402.8792 396.82,1427.7092 432.4,1444.8592 " fill="none" id="inAllowedPool-&gt;allocate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="437.09,1447.1192,430.7227,1439.6054,432.5869,1444.9463,427.246,1446.8104,437.09,1447.1192" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[c7ed7f8e85efd784aa0446a03842ecad]
+link allocate to allocate_iterate--><path d="M393.3,1481.6592 C375.37,1488.5992 357.97,1498.6492 345.5,1513.1992 C335.73,1524.5992 332.59,1541.3292 331.83,1554.8292 " fill="none" id="allocate-&gt;allocate_iterate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="331.65,1560.0092,335.9813,1551.1639,331.8356,1555.0127,327.9868,1550.867,331.65,1560.0092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="240" x="346.5" y="1526.7676">start from preferred (last used) subnet</text><!--MD5=[b4b32474e67014a0ea8b9d2dcb8b921b]
+link allocate to getHRmode--><path d="M551.57,1482.2592 C567.28,1489.1692 581.88,1499.0592 591.5,1513.1992 C647.03,1594.8392 571.65,1717.1292 536.65,1765.9492 " fill="none" id="allocate-&gt;getHRmode" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="533.6,1770.1692,542.1109,1765.2129,536.5264,1766.1151,535.6242,1760.5306,533.6,1770.1692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="198" x="605.5" y="1639.7676">allocation is not in all branches</text><!--MD5=[5d722979ddb74375b031e6d5bd55f242]
+link allocate_iterate to allocate_iterate--><path d="M433.25,1568.1192 C453.52,1569.2292 468,1572.5892 468,1578.1992 C468,1583.3192 455.9,1586.5692 438.34,1587.9492 " fill="none" id="allocate_iterate-&gt;allocate_iterate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="433.25,1588.2792,442.4936,1591.6787,438.2392,1587.9504,441.9675,1583.696,433.25,1588.2792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="97" x="474" y="1583.2676">no free address</text><!--MD5=[0a74e69bd975a88dffe2300213585d86]
+link allocate_iterate to allocated--><path d="M343.59,1596.5392 C356.05,1616.0092 376.26,1647.6192 389.72,1668.6592 " fill="none" id="allocate_iterate-&gt;allocated" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="392.48,1672.9792,390.9779,1663.2456,389.7762,1668.7733,384.2485,1667.5716,392.48,1672.9792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="129" x="373.5" y="1639.7676">found a free address</text><!--MD5=[1be0f2f74e199399aa4e09476dce36f7]
+link allocated to getHRmode--><path d="M424.69,1709.3992 C444.57,1725.5392 474.31,1749.6992 495.38,1766.7992 " fill="none" id="allocated-&gt;getHRmode" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="499.47,1770.1192,494.9879,1761.3494,495.5824,1766.9749,489.9569,1767.5694,499.47,1770.1192" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[9e14dd0054774aedb71cf602d40d12b7]
+link getHRmode to checkHRmode--><path d="M520.5,1806.6192 C520.5,1822.1592 520.5,1844.9792 520.5,1861.8592 " fill="none" id="getHRmode-&gt;checkHRmode" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="520.5,1866.8892,524.5,1857.8892,520.5,1861.8892,516.5,1857.8892,520.5,1866.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[a84b25cfb30efcca4b707749deb6e97a]
+link checkHRmode to global--><path d="M502.01,1903.2992 C480.76,1922.9592 445.87,1955.2292 423.04,1976.3492 " fill="none" id="checkHRmode-&gt;global" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="419.21,1979.8992,428.5379,1976.7384,422.8857,1976.5096,423.1145,1970.8574,419.21,1979.8992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="21" x="468.5" y="1946.7676">yes</text><!--MD5=[a6bc61640de244f08df3cca17a4f2365]
+link checkHRmode to bySubnet--><path d="M539.3,1903.2992 C560.9,1922.9592 596.37,1955.2292 619.58,1976.3492 " fill="none" id="checkHRmode-&gt;bySubnet" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="623.48,1979.8992,619.5026,1970.8892,619.7771,1976.5394,614.1269,1976.8139,623.48,1979.8992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="16" x="589.5" y="1946.7676">no</text><!--MD5=[b516e9f33f07fd0923019528919312cb]
+link global to return--><path d="M397.59,2016.3892 C396.2,2030.3392 396.61,2049.8292 406.5,2063.1992 C415.42,2075.2592 428,2084.2392 441.56,2090.9292 " fill="none" id="global-&gt;return" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="446.2,2093.1092,439.7564,2085.6607,441.6749,2090.9823,436.3533,2092.9008,446.2,2093.1092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="187" x="407.5" y="2059.7676">return global host reservation</text><!--MD5=[31ce4acb5044d12c75fb908f2994650f]
+link bySubnet to return--><path d="M633.84,2016.2092 C626.18,2030.0592 613.99,2049.4892 599.5,2063.1992 C588.25,2073.8392 574.18,2083.1692 561.05,2090.6492 " fill="none" id="bySubnet-&gt;return" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="556.63,2093.1192,566.4378,2092.2206,560.9947,2090.6801,562.5352,2085.2371,556.63,2093.1192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="191" x="614.5" y="2059.7676">return subnet host reservation</text><text fill="#888888" font-family="sans-serif" font-size="10" lengthAdjust="spacingAndGlyphs" textLength="622" x="164.75" y="2150.3555">Only the initial lookup is always performed: other occasions to change the subnet so the current host are only in some branches</text><!--MD5=[84940467d5c8b64b9d1a8ec6eb53bf6f]
+@startuml
+
+title currentHost DHCPv4 (Kea 1.8.0)
+
+agent "Subnet Selection" as entry
+
+agent "Set subnet to the selected subnet" as setSelected
+
+agent "Has client a lease for its client id?" as clientid_lookup
+
+agent "Iterate on allowed subnets for client id" as clientid_iterate
+
+agent "Set subnet to the by client id lease" as found_clientid
+
+agent "Has client a matching lease?" as hwaddr_lookup
+
+agent "Iterate on allowed subnets for hardware address" as hwaddr_iterate
+
+agent "Set subnet to the matching lease" as found_hwaddr
+
+agent "Has an address reservation?" as hasAddressReservation
+
+agent "Set subnet to address reservation subnet" as setAddressReservation
+
+agent "Is the address in an allowed pool?" as pool
+
+agent "Iterate on allowed subnets with pool" as pool_iterate
+
+agent "Set subnet to address pool subnet" as inAllowedPool
+
+agent "Allocate a new lease" as allocate
+
+agent "Iterate on allowed subnets" as allocate_iterate
+
+agent "Set subnet to allocated lease subnet" as allocated
+
+agent "Get subnet host reservation mode" as getHRmode
+
+agent "Is subnet host reservation mode global?" as checkHRmode
+
+agent "Get global host reservation" as global
+
+agent "Get subnet host reservation" as bySubnet
+
+agent "Return current host reservation" as return
+
+entry - -> setSelected
+setSelected - -> clientid_lookup
+clientid_lookup - - -> hwaddr_lookup : no client id option
+clientid_lookup - -> clientid_iterate
+clientid_iterate -> clientid_iterate : match-client-id is false or no lease
+clientid_iterate - -> found_clientid : found a lease
+found_clientid - - - -> hasAddressReservation
+clientid_iterate - -> hwaddr_lookup : not found by client id, try by hardware address
+hwaddr_lookup - - -> hasAddressReservation : no hardware address
+hwaddr_lookup - -> hwaddr_iterate
+hwaddr_iterate -> hwaddr_iterate : no lease or client id mismatch
+hwaddr_iterate - -> found_hwaddr : found a lease
+found_hwaddr - - - -> hasAddressReservation
+hwaddr_iterate - -> hasAddressReservation : not found
+hasAddressReservation - -> setAddressReservation : yes
+hasAddressReservation - -> pool : no or not check in the taken branch
+setAddressReservation - -> pool
+pool - -> pool_iterate
+pool - - -> allocate : pool check is not in all branches
+pool_iterate -> pool_iterate : address not in an allowed pool
+pool_iterate - -> inAllowedPool : address in an allowed pool
+pool_iterate - - -> allocate : no allowed pool
+inAllowedPool - -> allocate
+allocate - -> allocate_iterate : start from preferred (last used) subnet
+allocate - - -> getHRmode : allocation is not in all branches
+allocate_iterate -> allocate_iterate : no free address
+allocate_iterate - -> allocated : found a free address
+allocated - -> getHRmode
+getHRmode - -> checkHRmode
+checkHRmode - -> global : yes
+checkHRmode - -> bySubnet : no
+global - -> return : return global host reservation
+bySubnet - -> return : return subnet host reservation
+
+footer Only the initial lookup is always performed: other occasions to change the subnet so the current host are only in some branches
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/currentHost4.uml b/doc/sphinx/uml/currentHost4.uml
new file mode 100644
index 0000000..1e9ef4d
--- /dev/null
+++ b/doc/sphinx/uml/currentHost4.uml
@@ -0,0 +1,83 @@
+@startuml
+
+title currentHost DHCPv4 (Kea 1.8.0)
+
+agent "Subnet Selection" as entry
+
+agent "Set subnet to the selected subnet" as setSelected
+
+agent "Has client a lease for its client id?" as clientid_lookup
+
+agent "Iterate on allowed subnets for client id" as clientid_iterate
+
+agent "Set subnet to the by client id lease" as found_clientid
+
+agent "Has client a matching lease?" as hwaddr_lookup
+
+agent "Iterate on allowed subnets for hardware address" as hwaddr_iterate
+
+agent "Set subnet to the matching lease" as found_hwaddr
+
+agent "Has an address reservation?" as hasAddressReservation
+
+agent "Set subnet to address reservation subnet" as setAddressReservation
+
+agent "Is the address in an allowed pool?" as pool
+
+agent "Iterate on allowed subnets with pool" as pool_iterate
+
+agent "Set subnet to address pool subnet" as inAllowedPool
+
+agent "Allocate a new lease" as allocate
+
+agent "Iterate on allowed subnets" as allocate_iterate
+
+agent "Set subnet to allocated lease subnet" as allocated
+
+agent "Get subnet host reservation mode" as getHRmode
+
+agent "Is subnet host reservation mode global?" as checkHRmode
+
+agent "Get global host reservation" as global
+
+agent "Get subnet host reservation" as bySubnet
+
+agent "Return current host reservation" as return
+
+entry --> setSelected
+setSelected --> clientid_lookup
+clientid_lookup ---> hwaddr_lookup : no client id option
+clientid_lookup --> clientid_iterate
+clientid_iterate -> clientid_iterate : match-client-id is false or no lease
+clientid_iterate --> found_clientid : found a lease
+found_clientid ----> hasAddressReservation
+clientid_iterate --> hwaddr_lookup : not found by client id, try by hardware address
+hwaddr_lookup ---> hasAddressReservation : no hardware address
+hwaddr_lookup --> hwaddr_iterate
+hwaddr_iterate -> hwaddr_iterate : no lease or client id mismatch
+hwaddr_iterate --> found_hwaddr : found a lease
+found_hwaddr ----> hasAddressReservation
+hwaddr_iterate --> hasAddressReservation : not found
+hasAddressReservation --> setAddressReservation : yes
+hasAddressReservation --> pool : no or not check in the taken branch
+setAddressReservation --> pool
+pool --> pool_iterate
+pool ---> allocate : pool check is not in all branches
+pool_iterate -> pool_iterate : address not in an allowed pool
+pool_iterate --> inAllowedPool : address in an allowed pool
+pool_iterate ---> allocate : no allowed pool
+inAllowedPool --> allocate
+allocate --> allocate_iterate : start from preferred (last used) subnet
+allocate ---> getHRmode : allocation is not in all branches
+allocate_iterate -> allocate_iterate : no free address
+allocate_iterate --> allocated : found a free address
+allocated --> getHRmode
+getHRmode --> checkHRmode
+checkHRmode --> global : yes
+checkHRmode --> bySubnet : no
+global --> return : return global host reservation
+bySubnet --> return : return subnet host reservation
+
+footer Only the initial lookup is always performed: other occasions to change the subnet so the current host are only in some branches
+
+@enduml
\ No newline at end of file
diff --git a/doc/sphinx/uml/lease-states.png b/doc/sphinx/uml/lease-states.png
new file mode 100644
index 0000000..76fc762
--- /dev/null
+++ b/doc/sphinx/uml/lease-states.png
diff --git a/doc/sphinx/uml/lease-states.svg b/doc/sphinx/uml/lease-states.svg
new file mode 100644
index 0000000..ae70b45
--- /dev/null
+++ b/doc/sphinx/uml/lease-states.svg
@@ -0,0 +1,67 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="699px" preserveAspectRatio="none" style="width:631px;height:699px;" version="1.1" viewBox="0 0 631 699" width="631px" zoomAndPan="magnify"><defs><filter height="300%" id="f14qs590hur024" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="203" x="205" y="17.4023">lease states (Kea 1.8.0)</text><!--MD5=[4278daa906671312366ccb0dccb3e92f]
+entity free--><rect fill="#FEFECE" filter="url(#f14qs590hur024)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="50" x="268" y="35.3392"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="30" x="278" y="58.8744">Free</text><path d="M55,40.8392 L55,66.1498 A0,0 0 0 0 55,66.1498 L233,66.1498 A0,0 0 0 0 233,66.1498 L233,58.8392 L267.71,53.3392 L233,50.8392 L233,50.8392 L223,40.8392 L55,40.8392 A0,0 0 0 0 55,40.8392 " fill="#FBFB77" filter="url(#f14qs590hur024)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M223,40.8392 L223,50.8392 L233,50.8392 L223,40.8392 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="157" x="61" y="58.4076">not in the lease database</text><!--MD5=[4c0421e83b31106584008715812a1ea8]
+entity assigned--><rect fill="#FEFECE" filter="url(#f14qs590hur024)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="83" x="256.5" y="210.3392"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="63" x="266.5" y="233.8744">Assigned</text><!--MD5=[046a8c2cc2caa2564a440430281543c8]
+entity assigned_expired--><rect fill="#FEFECE" filter="url(#f14qs590hur024)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="140" x="357" y="323.3392"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="120" x="367" y="346.8744">Assigned expired</text><!--MD5=[be39be446611673079158bd75084bb29]
+entity declined--><rect fill="#FEFECE" filter="url(#f14qs590hur024)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="79" x="130.5" y="436.3392"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="59" x="140.5" y="459.8744">Declined</text><!--MD5=[b74f0280ed02bec002eedfc3903cd610]
+entity declined_expired--><rect fill="#FEFECE" filter="url(#f14qs590hur024)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="136" x="38" y="549.3392"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="116" x="48" y="572.8744">Declined expired</text><!--MD5=[309798e71ae1dfa592ce5bb406cc7544]
+entity reclaimed--><rect fill="#FEFECE" filter="url(#f14qs590hur024)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="151" x="272.5" y="646.3392"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="131" x="282.5" y="669.8744">Expired-Reclaimed</text><!--MD5=[219c0a330ff1ab87a7e7f51a72cedfde]
+link free to assigned--><path d="M276.19,71.5392 C260.17,90.0792 239.64,120.7892 248,149.3392 C254.2,170.4992 268.1,191.3692 279.68,206.1892 " fill="none" id="free-&gt;assigned" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="282.87,210.1992,280.3967,200.666,279.757,206.2865,274.1364,205.6468,282.87,210.1992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="73" x="249" y="145.9076">assignment</text><!--MD5=[d0e432b1584877a475e5f2fe76611e15]
+reverse link free to assigned--><path d="M305.4,76.1392 C313.32,91.3492 322.85,112.4192 327,132.3392 C332.77,160.0292 319.25,191.2292 308.78,210.0792 " fill="none" id="free&lt;-assigned" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="303.01,71.6192,303.6712,81.4459,305.3429,76.0416,310.7471,77.7133,303.01,71.6192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="83" x="330" y="145.9076">release query</text><!--MD5=[7534ad65a31e40f6f58c860fbe4b1334]
+link assigned to assigned_expired--><path d="M339.85,243.3892 C357.83,250.9992 378.09,261.8492 393,276.3392 C405.06,288.0492 413.79,304.9692 419.38,318.4692 " fill="none" id="assigned-&gt;assigned_expired" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="421.3,323.2692,421.6714,313.4274,419.443,318.6268,414.2436,316.3985,421.3,323.2692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="115" x="407" y="289.9076">after valid lifetime</text><!--MD5=[fde569cd6ac85f95e2a638ce16dc5096]
+reverse link assigned to assigned_expired--><path d="M312.18,250.8492 C321.59,264.0992 334.8,280.8792 349,293.3392 C362.19,304.9092 378.61,315.2892 392.97,323.3192 " fill="none" id="assigned&lt;-assigned_expired" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="309.13,246.4992,311.0324,256.1626,312.005,250.59,317.5776,251.5626,309.13,246.4992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="34" x="350" y="289.9076">reuse</text><!--MD5=[21716a85bcf00f22f38541e3e291568a]
+link assigned to assigned--><path d="M339.71,219.4792 C358.36,218.6392 374.5,221.5892 374.5,228.3392 C374.5,234.4592 361.25,237.4592 344.88,237.3392 " fill="none" id="assigned-&gt;assigned" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="339.71,237.1992,348.6042,241.4292,344.7083,237.3277,348.8098,233.4319,339.71,237.1992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="76" x="380.5" y="233.4076">renew query</text><!--MD5=[8bb46c3b4dde016c313b8e321f1d7e1a]
+link assigned to declined--><path d="M269.68,246.4392 C245,262.9292 210.38,290.2192 192,323.3392 C173.05,357.4892 169.59,403.8692 169.39,430.9992 " fill="none" id="assigned-&gt;declined" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="169.39,436.1592,173.39,427.1592,169.39,431.1592,165.39,427.1592,169.39,436.1592" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="84" x="193" y="346.4076">decline query</text><!--MD5=[8dc60d8855cbb8c3dba4463bc36210b7]
+link declined to declined_expired--><path d="M157.58,472.3892 C151.4,481.1592 144,492.1192 138,502.3392 C130.01,515.9592 122.06,531.8392 116.09,544.3692 " fill="none" id="declined-&gt;declined_expired" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="113.82,549.1692,121.2851,542.7449,115.9586,544.6497,114.0538,539.3231,113.82,549.1692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="138" x="139" y="515.9076">after probation period</text><!--MD5=[6d44915acfde63a8254178afd3aa27e3]
+reverse link assigned to declined_expired--><path d="M251.59,248.4092 C236.48,255.8492 220.22,265.2692 207,276.3392 C159.82,315.8392 153.14,333.6292 127,389.3392 C101.63,443.4092 102.58,516.5492 104.58,549.2792 " fill="none" id="assigned&lt;-declined_expired" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="256.23,246.1592,246.386,246.468,251.7269,248.3322,249.8627,253.673,256.23,246.1592" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="34" x="128" y="402.9076">reuse</text><!--MD5=[bdcfcd9c1cacddd2a3f75c7ff5da35a5]
+link assigned_expired to reclaimed--><path d="M422.75,359.5992 C409.44,413.6992 368.51,579.9992 353.55,640.7892 " fill="none" id="assigned_expired-&gt;reclaimed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="352.27,645.9992,358.3119,638.2213,353.4692,641.1452,350.5454,636.3025,352.27,645.9992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="46" x="388" y="515.9076">reclaim</text><!--MD5=[1c9e2837121ab398f7070aba53df7029]
+link declined_expired to free--><path d="M75.18,549.2492 C45.8,530.4392 6,497.2292 6,455.3392 C6,139.8392 6,139.8392 6,139.8392 C6,27.1992 143.26,107.3192 250,71.3392 C254.16,69.9392 258.5,68.3592 262.75,66.7492 " fill="none" id="declined_expired-&gt;free" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="267.69,64.8392,257.8532,64.3528,263.0262,66.6418,260.7373,71.8148,267.69,64.8392" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="46" x="7" y="289.9076">remove</text><!--MD5=[b52d5a7ca53f64269da3993e04180d07]
+reverse link assigned to reclaimed--><path d="M299.31,251.7292 C301.08,283.8392 304,344.8492 304,396.8392 C304,396.8392 304,396.8392 304,568.3392 C304,597.7892 321.62,628.0092 334.56,646.2292 " fill="none" id="assigned&lt;-reclaimed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="299.02,246.4492,295.5152,255.6534,299.2918,251.4418,303.5033,255.2185,299.02,246.4492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="34" x="305" y="459.4076">reuse</text><!--MD5=[d78006695828b24d5c043b2b2f6223cc]
+reverse link free to reclaimed--><path d="M323.27,57.1392 C395.5,64.6392 572,88.2592 572,139.8392 C572,139.8392 572,139.8392 572,568.3392 C572,634.3392 488.55,655.1692 423.52,661.3692 " fill="none" id="free&lt;-reclaimed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="318.25,56.6192,326.8045,61.4998,323.2249,57.1196,327.6051,53.5399,318.25,56.6192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="46" x="573" y="346.4076">remove</text><!--MD5=[7a97b2a903c7311ebfa1bcbf72f0a383]
+link declined_expired to reclaimed--><!--MD5=[ad1f216ff27ad402bdd959662ff0ee60]
+@startuml
+
+title lease states (Kea 1.8.0)
+
+agent "Free" as free
+note left : not in the lease database
+
+agent "Assigned" as assigned
+
+agent "Assigned expired" as assigned_expired
+
+agent "Declined" as declined
+
+agent "Declined expired" as declined_expired
+
+agent "Expired-Reclaimed" as reclaimed
+
+free - - -> assigned : assignment
+
+assigned -> assigned_expired : after valid lifetime
+assigned -> assigned : renew query
+assigned - - -> declined : decline query
+assigned -up-> free : release query
+
+declined - -> declined_expired : after probation period
+
+assigned_expired -up-> assigned : reuse
+declined_expired -up-> assigned : reuse
+
+assigned_expired - - -> reclaimed : reclaim
+declined_expired - - -> free : remove
+
+reclaimed -up-> assigned : reuse
+reclaimed -up- -> free : remove
+
+declined_expired -[hidden]-> reclaimed
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/lease-states.uml b/doc/sphinx/uml/lease-states.uml
new file mode 100644
index 0000000..66de2bb
--- /dev/null
+++ b/doc/sphinx/uml/lease-states.uml
@@ -0,0 +1,38 @@
+@startuml
+
+title lease states (Kea 1.8.0)
+
+agent "Free" as free
+note left : not in the lease database
+
+agent "Assigned" as assigned
+
+agent "Assigned expired" as assigned_expired
+
+agent "Declined" as declined
+
+agent "Declined expired" as declined_expired
+
+agent "Expired-Reclaimed" as reclaimed
+
+free ---> assigned : assignment
+
+assigned -> assigned_expired : after valid lifetime
+assigned -> assigned : renew query
+assigned ---> declined : decline query
+assigned -up-> free : release query
+
+declined --> declined_expired : after probation period
+
+assigned_expired -up-> assigned : reuse
+declined_expired -up-> assigned : reuse
+
+assigned_expired ---> reclaimed : reclaim
+declined_expired ---> free : remove
+
+reclaimed -up-> assigned : reuse
+reclaimed -up--> free : remove
+
+declined_expired -[hidden]-> reclaimed
+
+@enduml
diff --git a/doc/sphinx/uml/main-loop.png b/doc/sphinx/uml/main-loop.png
new file mode 100644
index 0000000..8734007
--- /dev/null
+++ b/doc/sphinx/uml/main-loop.png
diff --git a/doc/sphinx/uml/main-loop.svg b/doc/sphinx/uml/main-loop.svg
new file mode 100644
index 0000000..9ad33e1
--- /dev/null
+++ b/doc/sphinx/uml/main-loop.svg
@@ -0,0 +1,99 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="974px" preserveAspectRatio="none" style="width:674px;height:974px;" version="1.1" viewBox="0 0 674 974" width="674px" zoomAndPan="magnify"><defs><filter height="300%" id="f1hatkcuz2d0l4" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="300" x="178" y="17.4023">DHCP server main loop (Kea 1.8.0)</text><!--MD5=[f7a7ee0c51b4e04c55c1f405505b5a33]
+cluster Main Loop--><rect fill="#FFFFFF" filter="url(#f1hatkcuz2d0l4)" height="911.86" style="stroke: #000000; stroke-width: 1.5;" width="650" x="7" y="28.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="75" x="294.5" y="43.7344">Main Loop</text><!--MD5=[5612987a0f9796801dd6d08eccf6974b]
+cluster run_one--><rect fill="#FFFFFF" filter="url(#f1hatkcuz2d0l4)" height="467.86" style="stroke: #000000; stroke-width: 1.5;" width="572" x="49" y="170.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="79" x="295.5" y="185.7344">Event Loop</text><!--MD5=[983d0794f401e349a629364dfc448d7d]
+entity run--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="149" x="145.5" y="63.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="129" x="155.5" y="86.7344">Wait for next event</text><!--MD5=[463fa6ce3d00da797e8ff80a4d9c8378]
+entity shutdown--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="135" x="28.5" y="888.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="115" x="38.5" y="911.5944">Check Shutdown</text><!--MD5=[f73c77a11c1a01c10ee045ae76f5a064]
+entity timeout--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="77" x="306.5" y="578.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="57" x="316.5" y="601.5944">Timeout</text><!--MD5=[53133b9ef51e4e7f3d2c6bacee8894bf]
+entity signal--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="62" x="311" y="277.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="42" x="321" y="300.5944">Signal</text><!--MD5=[7492a645d94b1ba942c71cddc305dc30]
+entity handleSignal--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="114" x="97" y="277.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="94" x="107" y="300.5944">Handle Signal</text><!--MD5=[82e30069e7a5a9e7454e349f4f7c28bc]
+entity external_socket--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="126" x="97" y="378.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="106" x="107" y="401.5944">External Socket</text><!--MD5=[ba069a43eac8d7db5b41bef0d2c2bb79]
+entity handleExternalSocket--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="178" x="395" y="378.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="158" x="405" y="401.5944">Handle External Socket</text><!--MD5=[a096c1983bcf686c95ea726f28f7a0ed]
+entity query--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="103" x="371.5" y="479.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="83" x="381.5" y="502.5944">DHCP Query</text><!--MD5=[15a052d0312126cb226db0f9a615136d]
+entity processQuery--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="117" x="97.5" y="479.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="97" x="107.5" y="502.5944">Process Query</text><!--MD5=[3ec86a5ecee919912764a4f49fada726]
+entity poll--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="94" x="60" y="711.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="74" x="70" y="734.5944">I/O Service</text><!--MD5=[55a3d76f9f066a914db2e6a0219879c4]
+entity ready--><rect fill="#FEFECE" filter="url(#f1hatkcuz2d0l4)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="173" x="275.5" y="711.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="153" x="285.5" y="734.5944">Execute ready handler</text><!--MD5=[5e1c1922f34751d45a9d92a38b9ac144]
+link run to run_one--><path d="M265,99.3792 C265,114.9742 265,138.0042 265,157.8405 C265,160.32 265,162.7496 265,165.1086 C265,166.2881 265,167.4499 265,168.5915 C265,168.8768 265,169.161 265,169.4438 C265,169.5852 265,169.7263 265,169.867 " fill="none" id="run-&gt;run_one" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="265,169.867,269,160.867,265,164.867,261,160.867,265,169.867" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="90" x="236" y="142.7676">get next event</text><!--MD5=[0596cb5bc7e39429b5a70ee803d7702a]
+link run_one to signal--><path d="M265,198.1292 C265,205.6592 265,286.0592 265,286.0592 C265,286.0592 305.68,286.0592 305.68,286.0592 " fill="none" id="run_one-&gt;signal" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="310.68,286.0592,301.68,282.0592,305.68,286.0592,301.68,290.0592,310.68,286.0592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[71bca8b2b5579f3e01e5a5e6d05e252f]
+link signal to handleSignal--><path d="M310.96,295.0592 C310.96,295.0592 216.31,295.0592 216.31,295.0592 " fill="none" id="signal-&gt;handleSignal" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="211.31,295.0592,220.31,299.0592,216.31,295.0592,220.31,291.0592,211.31,295.0592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[59b958d73309821d887c593216a24bf9]
+link handleSignal to poll--><path d="M96.78,295.0592 C86.25,295.0592 78.5,295.0592 78.5,295.0592 C78.5,295.0592 78.5,705.9592 78.5,705.9592 " fill="none" id="handleSignal-&gt;poll" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="78.5,710.9592,82.5,701.9592,78.5,705.9592,74.5,701.9592,78.5,710.9592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[85a6501bbdb71fe843a154c65df0b326]
+link signal to external_socket--><path d="M310.78,304.0592 C273.76,304.0592 217,304.0592 217,304.0592 C217,304.0592 217,372.8792 217,372.8792 " fill="none" id="signal-&gt;external_socket" style="stroke: #A80036; stroke-width: 1.0; stroke-dasharray: 7.0,7.0;"/><polygon fill="#A80036" points="217,377.8792,221,368.8792,217,372.8792,213,368.8792,217,377.8792" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[3cd4ee53a51a0c2827ab7b17e0cc3c3c]
+link external_socket to handleExternalSocket--><path d="M223.24,390.0592 C223.24,390.0592 389.87,390.0592 389.87,390.0592 " fill="none" id="external_socket-&gt;handleExternalSocket" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="394.87,390.0592,385.87,386.0592,389.87,390.0592,385.87,394.0592,394.87,390.0592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[9e360989e7d922bcf27daccb5299f564]
+link handleExternalSocket to poll--><path d="M394.76,402.0592 C335.73,402.0592 269.17,402.0592 269.17,402.0592 C269.17,402.0592 269.17,723.0592 269.17,723.0592 C269.17,723.0592 159.34,723.0592 159.34,723.0592 " fill="none" id="handleExternalSocket-&gt;poll" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="154.34,723.0592,163.34,727.0592,159.34,723.0592,163.34,719.0592,154.34,723.0592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[281658fee0b0d1e8e512917c18413af8]
+link external_socket to query--><path d="M218.75,414.3792 C218.75,441.9792 218.75,491.0592 218.75,491.0592 C218.75,491.0592 366.46,491.0592 366.46,491.0592 " fill="none" id="external_socket-&gt;query" style="stroke: #A80036; stroke-width: 1.0; stroke-dasharray: 7.0,7.0;"/><polygon fill="#A80036" points="371.46,491.0592,362.46,487.0592,366.46,491.0592,362.46,495.0592,371.46,491.0592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[0da47bb881eae3b3085d664f44c330f1]
+link query to processQuery--><path d="M371.2,503.0592 C371.2,503.0592 219.62,503.0592 219.62,503.0592 " fill="none" id="query-&gt;processQuery" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="214.62,503.0592,223.62,507.0592,219.62,503.0592,223.62,499.0592,214.62,503.0592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[5ae6948e7f9ea24c9961deb19f615012]
+link processQuery to poll--><path d="M116.33,515.2592 C116.33,515.2592 116.33,705.9392 116.33,705.9392 " fill="none" id="processQuery-&gt;poll" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="116.33,710.9392,120.33,701.9392,116.33,705.9392,112.33,701.9392,116.33,710.9392" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[351006a45bcbe20db47f41960f495fbd]
+link query to timeout--><path d="M377.5,515.2192 C377.5,515.2192 377.5,573.0192 377.5,573.0192 " fill="none" id="query-&gt;timeout" style="stroke: #A80036; stroke-width: 1.0; stroke-dasharray: 7.0,7.0;"/><polygon fill="#A80036" points="377.5,578.0192,381.5,569.0192,377.5,573.0192,373.5,569.0192,377.5,578.0192" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[8da1f0cfac91639d3cdbe4344b95ba5e]
+link timeout to poll--><path d="M306.02,596.0592 C245.34,596.0592 135.17,596.0592 135.17,596.0592 C135.17,596.0592 135.17,705.8492 135.17,705.8492 " fill="none" id="timeout-&gt;poll" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="135.17,710.8492,139.17,701.8492,135.17,705.8492,131.17,701.8492,135.17,710.8492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="100" x="277" y="675.6276">timeout expired</text><!--MD5=[7fc4943622e5fd2b8bdecbc7965863a3]
+link poll to ready--><path d="M154.07,735.0592 C154.07,735.0592 270.48,735.0592 270.48,735.0592 " fill="none" id="poll-&gt;ready" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="275.48,735.0592,266.48,731.0592,270.48,735.0592,266.48,739.0592,275.48,735.0592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[82806226eee1d65d24007de8ef94d3ba]
+link poll to shutdown--><path d="M107,747.3392 C107,747.3392 107,882.8792 107,882.8792 " fill="none" id="poll-&gt;shutdown" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="107,887.8792,111,878.8792,107,882.8792,103,878.8792,107,887.8792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="105" x="102" y="823.6276">no ready handler</text><!--MD5=[9e95aa1826d8662af772234e20e4c11a]
+link ready to ready--><path d="M285,711.0292 C285,691.4792 285,663.0592 285,663.0592 C285,663.0592 272.33,663.0592 272.33,663.0592 C272.33,663.0592 272.33,818.0592 272.33,818.0592 C272.33,818.0592 362,818.0592 362,818.0592 C362,818.0592 362,752.0692 362,752.0692 " fill="none" id="ready-&gt;ready" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="362,747.0692,358,756.0692,362,752.0692,366,756.0692,362,747.0692" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[e3e9af49381d3719c9282a3c352c133e]
+reverse link run to shutdown--><path d="M243.5,104.5792 C243.5,104.5792 243.5,906.0592 243.5,906.0592 C243.5,906.0592 202.48,906.0592 163.71,906.0592 " fill="none" id="run&lt;-shutdown" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="243.5,99.5792,239.5,108.5792,243.5,104.5792,247.5,108.5792,243.5,99.5792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#888888" font-family="sans-serif" font-size="10" lengthAdjust="spacingAndGlyphs" textLength="139" x="258.5" y="960.7272">dashed arrow means priority</text><!--MD5=[8fa551d0c9d64d50247cb50d8338b7c4]
+@startuml
+
+title DHCP server main loop (Kea 1.8.0)
+
+skinparam linetype ortho
+
+rectangle "Main Loop" {
+ agent "Wait for next event" as run
+
+ rectangle "Event Loop" as run_one {
+  together {
+   agent "Signal" as signal
+
+   agent "Handle Signal" as handleSignal
+  }
+
+  together {
+   agent "External Socket" as external_socket
+
+   agent "Handle External Socket" as handleExternalSocket
+  }
+
+  together {
+   agent "DHCP Query" as query
+
+   agent "Process Query" as processQuery
+  }
+
+   agent "Timeout" as timeout
+ }
+
+ together {
+  agent "I/O Service" as poll
+
+  agent "Execute ready handler" as ready
+ }
+
+ agent "Check Shutdown" as shutdown
+}
+
+run - -> run_one : get next event
+run_one - -> signal
+signal -right-> handleSignal : got signal
+handleSignal - -> poll
+signal -[dashed]-> external_socket
+external_socket -right-> handleExternalSocket : external socket ready
+handleExternalSocket - -> poll
+external_socket -[dashed]-> query
+query -right-> processQuery : DHCP socket ready
+processQuery - -> poll
+query -[dashed]-> timeout
+timeout - -> poll : timeout expired
+poll -> ready : handler ready
+poll - - -> shutdown : no ready handler
+ready -> ready : execute ready handler
+shutdown -u-> run
+
+footer dashed arrow means priority
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/main-loop.uml b/doc/sphinx/uml/main-loop.uml
new file mode 100644
index 0000000..9e29c9f
--- /dev/null
+++ b/doc/sphinx/uml/main-loop.uml
@@ -0,0 +1,60 @@
+@startuml
+
+title DHCP server main loop (Kea 1.8.0)
+
+skinparam linetype ortho
+
+rectangle "Main Loop" {
+ agent "Wait for next event" as run
+
+ rectangle "Event Loop" as run_one {
+  together {
+   agent "Signal" as signal
+
+   agent "Handle Signal" as handleSignal
+  }
+
+  together {
+   agent "External Socket" as external_socket
+
+   agent "Handle External Socket" as handleExternalSocket
+  }
+
+  together {
+   agent "DHCP Query" as query
+
+   agent "Process Query" as processQuery
+  }
+
+   agent "Timeout" as timeout
+ }
+
+ together {
+  agent "I/O Service" as poll
+
+  agent "Execute ready handler" as ready
+ }
+
+ agent "Check Shutdown" as shutdown
+}
+
+run --> run_one : get next event
+run_one --> signal
+signal -right-> handleSignal : got signal
+handleSignal --> poll
+signal -[dashed]-> external_socket
+external_socket -right-> handleExternalSocket : external socket ready
+handleExternalSocket --> poll
+external_socket -[dashed]-> query
+query -right-> processQuery : DHCP socket ready
+processQuery --> poll
+query -[dashed]-> timeout
+timeout --> poll : timeout expired
+poll -> ready : handler ready
+poll ---> shutdown : no ready handler
+ready -> ready : execute ready handler
+shutdown -u-> run
+
+footer dashed arrow means priority
+
+@enduml
\ No newline at end of file
diff --git a/doc/sphinx/uml/packet4.png b/doc/sphinx/uml/packet4.png
new file mode 100644
index 0000000..6fef4e2
--- /dev/null
+++ b/doc/sphinx/uml/packet4.png
diff --git a/doc/sphinx/uml/packet4.svg b/doc/sphinx/uml/packet4.svg
new file mode 100644
index 0000000..2e37ed9
--- /dev/null
+++ b/doc/sphinx/uml/packet4.svg
@@ -0,0 +1,160 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="1814px" preserveAspectRatio="none" style="width:1862px;height:1814px;" version="1.1" viewBox="0 0 1862 1814" width="1862px" zoomAndPan="magnify"><defs><filter height="300%" id="f1u1c8b25aigi3" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="332" x="756" y="17.4023">DHCPv4 packet processing (Kea 1.8.0)</text><!--MD5=[91c043391605f0bbc36c648123f05f04]
+cluster process--><rect fill="#FFFFFF" filter="url(#f1u1c8b25aigi3)" height="103" style="stroke: #000000; stroke-width: 1.5;" width="849" x="715" y="924.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="257" x="1011" y="939.7344">Process Query on its Message Type</text><!--MD5=[a6437f938727ef6368484703a6d5a51f]
+entity processDiscover--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="134" x="1088" y="967.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="114" x="1098" y="990.7344">Process Discover</text><!--MD5=[776f46e8e787ed3ff8f7399fa81d4ef1]
+entity processRequest--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="131" x="758.5" y="967.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="111" x="768.5" y="990.7344">Process Request</text><!--MD5=[fc7d6e37f840cd9a10a681e81df6f28b]
+entity processRelease--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="128" x="925" y="967.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="108" x="935" y="990.7344">Process Release</text><!--MD5=[8d825f552c438f1d41e38a94f08e3f47]
+entity processDecline--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="126" x="1257" y="967.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="106" x="1267" y="990.7344">Process Decline</text><!--MD5=[3b341f45531d1fcf2cf88cb83e9fdef4]
+entity processInform--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="122" x="1418" y="967.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="102" x="1428" y="990.7344">Process Inform</text><!--MD5=[aa62c1eea3f70b4dbb2d8a2ad04d8b75]
+entity receivePacket--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="114" x="1560" y="28.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="94" x="1570" y="51.7344">Receive query</text><path d="M1471,33.6992 L1471,59.0098 A0,0 0 0 0 1471,59.0098 L1525,59.0098 A0,0 0 0 0 1525,59.0098 L1525,51.6992 L1559.77,46.1992 L1525,43.6992 L1525,43.6992 L1515,33.6992 L1471,33.6992 A0,0 0 0 0 1471,33.6992 " fill="#FBFB77" filter="url(#f1u1c8b25aigi3)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M1515,33.6992 L1515,43.6992 L1525,43.6992 L1515,33.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="33" x="1477" y="51.2676">input</text><!--MD5=[37dd4220ca2f2608029cfa1ef00c2d62]
+entity isServiceEnabled--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="127" x="1553.5" y="125.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="107" x="1563.5" y="148.7344">Service Enabled</text><!--MD5=[f1e4a9c8bda8d25100748cfdff400bf1]
+entity buffer4_receive--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="179" x="1000.5" y="238.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="159" x="1010.5" y="261.7344">Callout buffer4_receive</text><path d="M1214.5,243.6992 L1214.5,252.1992 L1179.66,256.1992 L1214.5,260.1992 L1214.5,269.0098 A0,0 0 0 0 1214.5,269.0098 L1267.5,269.0098 A0,0 0 0 0 1267.5,269.0098 L1267.5,253.6992 L1257.5,243.6992 L1214.5,243.6992 A0,0 0 0 0 1214.5,243.6992 " fill="#FBFB77" filter="url(#f1u1c8b25aigi3)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M1257.5,243.6992 L1257.5,253.6992 L1267.5,253.6992 L1257.5,243.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="32" x="1220.5" y="261.2676">hook</text><!--MD5=[ce6c3f645c8aec4915456c978c48f6f1]
+entity unpack--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="114" x="640" y="351.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="94" x="650" y="374.7344">Unpack query</text><!--MD5=[f8582116def27e35cdbbbf5463e43073]
+entity classify--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="115" x="639.5" y="448.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="95" x="649.5" y="471.7344">Classify query</text><!--MD5=[92aee3b8b080bbd52e01e7cb395370c4]
+entity pkt4_receive--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="159" x="454.5" y="545.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="139" x="464.5" y="568.7344">Callout pkt4_receive</text><path d="M648.5,550.6992 L648.5,559.1992 L613.59,563.1992 L648.5,567.1992 L648.5,576.0098 A0,0 0 0 0 648.5,576.0098 L701.5,576.0098 A0,0 0 0 0 701.5,576.0098 L701.5,560.6992 L691.5,550.6992 L648.5,550.6992 A0,0 0 0 0 648.5,550.6992 " fill="#FBFB77" filter="url(#f1u1c8b25aigi3)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M691.5,550.6992 L691.5,560.6992 L701.5,560.6992 L691.5,550.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="32" x="654.5" y="568.2676">hook</text><!--MD5=[7aeeef4718a003ce2e7ad9bcbdf71ad9]
+entity drop_class--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="141" x="243.5" y="658.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="121" x="253.5" y="681.7344">Check DROP class</text><!--MD5=[a52533196b9ad0f42d77bd2c5acf5304]
+entity same_client--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="333" x="147.5" y="755.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="313" x="157.5" y="778.7344">Avoid same client race in multi-threaded mode</text><path d="M587.5,760.6992 L587.5,769.1992 L480.63,773.1992 L587.5,777.1992 L587.5,786.0098 A0,0 0 0 0 587.5,786.0098 L790.5,786.0098 A0,0 0 0 0 790.5,786.0098 L790.5,770.6992 L780.5,760.6992 L587.5,760.6992 A0,0 0 0 0 587.5,760.6992 " fill="#FBFB77" filter="url(#f1u1c8b25aigi3)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M780.5,760.6992 L780.5,770.6992 L790.5,770.6992 L780.5,760.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="182" x="593.5" y="778.2676">postpone processing or drop</text><!--MD5=[a8af8e48f2cc558a0fee70431885f908]
+entity leases4_committed--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="197" x="1045.5" y="1098.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="177" x="1055.5" y="1121.7344">Callout leases4_committed</text><path d="M1277.5,1103.6992 L1277.5,1112.1992 L1242.75,1116.1992 L1277.5,1120.1992 L1277.5,1129.0098 A0,0 0 0 0 1277.5,1129.0098 L1330.5,1129.0098 A0,0 0 0 0 1330.5,1129.0098 L1330.5,1113.6992 L1320.5,1103.6992 L1277.5,1103.6992 A0,0 0 0 0 1277.5,1103.6992 " fill="#FBFB77" filter="url(#f1u1c8b25aigi3)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M1320.5,1103.6992 L1320.5,1113.6992 L1330.5,1113.6992 L1320.5,1103.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="32" x="1283.5" y="1121.2676">hook</text><!--MD5=[8e18f13991ca58e5a79e0b81ed56b9db]
+entity park--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="50" x="1119" y="1211.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="30" x="1129" y="1234.7344">Park</text><!--MD5=[145fde1089ff11319f35031b66a8b2bf]
+entity pkt4_send--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="144" x="943" y="1324.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="124" x="953" y="1347.7344">Callout pkt4_send</text><!--MD5=[62d5b04920c444814fafa1dbf06b35cd]
+entity send--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="121" x="1052.5" y="1647.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="101" x="1062.5" y="1670.7344">Send response</text><!--MD5=[5f600c2348a98514851ba709bbd3f597]
+entity pack--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="118" x="1077" y="1437.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="98" x="1087" y="1460.7344">Pack response</text><!--MD5=[d6829aa81ee0cd45a2e878b8b13197d5]
+entity buffer4_send--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="164" x="1037" y="1534.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="144" x="1047" y="1557.7344">Callout buffer4_send</text><path d="M954.5,1652.6992 L954.5,1678.0098 A0,0 0 0 0 954.5,1678.0098 L1017.5,1678.0098 A0,0 0 0 0 1017.5,1678.0098 L1017.5,1670.6992 L1052.35,1665.1992 L1017.5,1662.6992 L1017.5,1662.6992 L1007.5,1652.6992 L954.5,1652.6992 A0,0 0 0 0 954.5,1652.6992 " fill="#FBFB77" filter="url(#f1u1c8b25aigi3)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M1007.5,1652.6992 L1007.5,1662.6992 L1017.5,1662.6992 L1007.5,1652.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="42" x="960.5" y="1670.2676">output</text><!--MD5=[c92710f32fe9c293a125fb7e80204a05]
+entity drop--><rect fill="#FEFECE" filter="url(#f1u1c8b25aigi3)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="103" x="912.5" y="1744.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="83" x="922.5" y="1767.7344">Drop packet</text><path d="M826.5,1749.6992 L826.5,1775.0098 A0,0 0 0 0 826.5,1775.0098 L877.5,1775.0098 A0,0 0 0 0 877.5,1775.0098 L877.5,1767.6992 L912.49,1762.1992 L877.5,1759.6992 L877.5,1759.6992 L867.5,1749.6992 L826.5,1749.6992 A0,0 0 0 0 826.5,1749.6992 " fill="#FBFB77" filter="url(#f1u1c8b25aigi3)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M867.5,1749.6992 L867.5,1759.6992 L877.5,1759.6992 L867.5,1749.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="30" x="832.5" y="1767.2676">error</text><!--MD5=[9670815d90e482d849702fdd57183fae]
+link receivePacket to isServiceEnabled--><path d="M1617,64.6192 C1617,80.1592 1617,102.9792 1617,119.8592 " fill="none" id="receivePacket-&gt;isServiceEnabled" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1617,124.8892,1621,115.8892,1617,119.8892,1613,115.8892,1617,124.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[8b6c78e5054b687dbc9e19308d3a0129]
+link isServiceEnabled to buffer4_receive--><path d="M1553.43,157.5892 C1459.11,177.4592 1281.88,214.7792 1176.04,237.0792 " fill="none" id="isServiceEnabled-&gt;buffer4_receive" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1171.05,238.1292,1180.681,240.1893,1175.9427,237.0992,1179.0329,232.3609,1171.05,238.1292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="112" x="1386" y="204.7676">service is enabled</text><!--MD5=[228411fb88ef1bcdfe7f19b853e215d2]
+link isServiceEnabled to drop--><path d="M1655.3,161.3592 C1689.09,179.3992 1733,211.2992 1733,255.1992 C1733,255.1992 1733,255.1992 1733,1666.1992 C1733,1737.9692 1198.66,1756.0992 1020.81,1760.1492 " fill="none" id="isServiceEnabled-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1015.65,1760.2592,1024.7391,1764.0525,1020.6487,1760.145,1024.5562,1756.0546,1015.65,1760.2592" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="116" x="1734" y="896.7676">service is disabled</text><!--MD5=[939988dada0403ed6d1a4e6924dd7701]
+link buffer4_receive to unpack--><path d="M1029.46,274.2992 C956.18,294.9992 833.42,329.6692 759.35,350.5892 " fill="none" id="buffer4_receive-&gt;unpack" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="754.1,352.0692,763.8515,353.4505,758.9087,350.6994,761.6598,345.7566,754.1,352.0692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="67" x="918" y="317.7676">CONTINUE</text><!--MD5=[02f70f5bfef59fd4c02228f0fd276994]
+link buffer4_receive to classify--><path d="M1066.12,274.4492 C1047.04,287.8992 1019.38,306.6792 994,321.1992 C907.16,370.8892 800.63,419.7792 741.66,445.8492 " fill="none" id="buffer4_receive-&gt;classify" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="736.8,447.9892,746.6488,448.032,741.3778,445.9784,743.4314,440.7075,736.8,447.9892" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="26" x="940" y="374.2676">SKIP</text><!--MD5=[41e6595d93b5d76e06ef1219c230b624]
+link buffer4_receive to drop--><path d="M1179.77,272.9392 C1336.38,300.6992 1643,356.5292 1643,368.1992 C1643,368.1992 1643,368.1992 1643,1666.1992 C1643,1728.8292 1184.07,1752.6892 1020.81,1759.1992 " fill="none" id="buffer4_receive-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1015.59,1759.3992,1024.7431,1763.0353,1020.586,1759.1988,1024.4224,1755.0417,1015.59,1759.3992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="35" x="1644" y="990.2676">DROP</text><!--MD5=[1ecae68ae42d9a73e40e9217f03f9ce7]
+link unpack to classify--><path d="M697,387.6192 C697,403.1592 697,425.9792 697,442.8592 " fill="none" id="unpack-&gt;classify" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="697,447.8892,701,438.8892,697,442.8892,693,438.8892,697,447.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[27fcba0ca5551c2a3eff6088113b3400]
+link unpack to drop--><path d="M639.86,372.0692 C474.31,378.2592 6,401.3992 6,465.1992 C6,465.1992 6,465.1992 6,1666.1992 C6,1765.3592 797.05,1728.7492 895,1744.1992 C898.94,1744.8192 902.99,1745.5592 907.05,1746.3692 " fill="none" id="unpack-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="912.2,1747.4292,904.201,1741.6833,907.3044,1746.4129,902.5748,1749.5163,912.2,1747.4292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="50" x="7" y="1064.7676">on error</text><!--MD5=[6d44324a94e4b11142830ec71aa81556]
+link classify to pkt4_receive--><path d="M667.48,484.3992 C639.44,500.7492 597.31,525.2992 567.9,542.4392 " fill="none" id="classify-&gt;pkt4_receive" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="563.3,545.1192,573.0915,544.0576,567.6235,542.6079,569.0733,537.1399,563.3,545.1192" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[0057d53684278b0199141f1c920049f3]
+link pkt4_receive to drop_class--><path d="M499.2,581.2692 C481.2,590.1392 458.89,601.1892 439,611.1992 C409.58,626.0092 376.4,643.0092 351.62,655.7692 " fill="none" id="pkt4_receive-&gt;drop_class" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="347.1,658.0992,356.9329,657.5388,351.5461,655.8118,353.2731,650.425,347.1,658.0992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="67" x="440" y="624.7676">CONTINUE</text><!--MD5=[23d76d484a8ade2f68bc32d339275e55]
+link pkt4_receive to drop--><path d="M534,581.4992 C534,603.3392 534,642.0492 534,675.1992 C534,675.1992 534,675.1992 534,1666.1992 C534,1687.5792 558.43,1677.3692 579,1683.1992 C716.63,1722.1692 755.29,1713.5292 895,1744.1992 C899.07,1745.0892 903.27,1746.0492 907.49,1747.0292 " fill="none" id="pkt4_receive-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="912.45,1748.1992,904.6015,1742.2493,907.5822,1747.0572,902.7743,1750.0379,912.45,1748.1992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="35" x="535" y="1177.7676">DROP</text><!--MD5=[2ba86aae9fb469d61f9b8011ebc0bd96]
+link drop_class to same_client--><path d="M314,694.6192 C314,710.1592 314,732.9792 314,749.8592 " fill="none" id="drop_class-&gt;same_client" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="314,754.8892,318,745.8892,314,749.8892,310,745.8892,314,754.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[4eef49efa4e6a39b9cad1f9dd4db75c9]
+link drop_class to drop--><path d="M243.48,679.2592 C179.13,685.3592 94,705.9492 94,772.1992 C94,772.1992 94,772.1992 94,1666.1992 C94,1720.9492 161.68,1676.3392 216,1683.1992 C337.59,1698.5492 367.98,1702.7792 490,1714.1992 C669.71,1731.0192 716.75,1715.8392 895,1744.1992 C898.94,1744.8292 902.99,1745.5692 907.05,1746.3792 " fill="none" id="drop_class-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="912.2,1747.4492,904.1976,1741.708,907.3038,1746.4357,902.576,1749.5419,912.2,1747.4492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="126" x="95" y="1234.2676">query in DROP class</text><!--MD5=[bb9b361438ecdeec2ed5ec34799fad2e]
+link same_client to process--><path d="M347.12,791.2092 C395.425,816.0092 488.31,863.6992 569.655,905.4642 C610.3275,926.3467 648.115,945.748 676.0025,960.0661 C689.9463,967.2252 701.415,973.1134 709.5319,977.2807 C711.5611,978.3225 713.3808,979.2568 714.9774,980.0764 " fill="none" id="same_client-&gt;process" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="714.9774,980.0764,708.7978,972.4075,710.5293,977.7928,705.144,979.5244,714.9774,980.0764" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[2de62570b816e5df0f82700c4b296cc3]
+link same_client to drop--><path d="M299.7,791.2592 C288.57,806.3092 275,829.3392 275,852.1992 C275,852.1992 275,852.1992 275,1173.6992 C275,1222.3992 247.11,1229.1792 239,1277.1992 C237.74,1284.6492 238.76,1286.6492 239,1294.1992 C239.67,1315.1192 242,1320.2692 242,1341.1992 C242,1341.1992 242,1341.1992 242,1666.1992 C242,1713.3692 777.64,1725.3292 895,1744.1992 C898.94,1744.8292 902.99,1745.5792 907.05,1746.3992 " fill="none" id="same_client-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="912.19,1747.4692,904.2071,1741.7009,907.2973,1746.4392,902.559,1749.5293,912.19,1747.4692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="267" x="240" y="1290.7676">queries from the same client possible race</text><!--MD5=[3640933a3eded42de606c73d1c2efb26]
+link process to drop--><path d="M714.7345,990.1215 C714.4884,990.2441 714.2376,990.3695 713.9823,990.4976 C712.9607,991.0103 711.8653,991.5676 710.703,992.1686 C708.3783,993.3708 705.7858,994.7482 702.9805,996.2952 C691.7591,1002.483 677.1319,1011.383 662.6163,1022.6242 C633.585,1045.1067 605,1076.9542 605,1115.1992 C605,1115.1992 605,1115.1992 605,1286.6992 C605,1382.9192 605,1406.9792 605,1503.1992 C605,1503.1992 605,1503.1992 605,1666.1992 C605,1670.0592 805.92,1721.3092 907.14,1746.8892 " fill="none" id="process-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="912.18,1748.1592,904.4231,1742.0904,907.3301,1746.9432,902.4774,1749.8502,912.18,1748.1592" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="148" x="606" y="1403.7676">unknown message type</text><!--MD5=[952846e6e065ca3396c39be4d5d60980]
+link processDiscover to leases4_committed--><path d="M1153.54,1003.3292 C1151.58,1026.3592 1148.08,1067.3592 1145.91,1092.8192 " fill="none" id="processDiscover-&gt;leases4_committed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1145.47,1097.9992,1150.2261,1089.3749,1145.8982,1093.0176,1142.2555,1088.6897,1145.47,1097.9992" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[7f61b5f2e024f0ea6329d761794804a2]
+link processDiscover to drop--><path d="M1178.66,1003.2492 C1195.43,1015.0392 1218.66,1030.7692 1240,1043.1992 C1301.84,1079.1992 1384,1043.6492 1384,1115.1992 C1384,1115.1992 1384,1115.1992 1384,1343.1992 C1384,1405.5792 1346.5,1559.4192 1323,1617.1992 C1310.64,1647.5792 1313.41,1660.2292 1290,1683.1992 C1252.31,1720.1992 1104.17,1743.9392 1021.16,1754.6292 " fill="none" id="processDiscover-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1015.79,1755.3092,1025.2217,1758.1453,1020.7503,1754.6802,1024.2153,1750.2088,1015.79,1755.3092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="50" x="1380" y="1403.7676">on error</text><!--MD5=[f46ab6743faf3720230dd3ca9adf25a5]
+link processRequest to leases4_committed--><path d="M845.36,1003.3592 C861.72,1015.8092 885.26,1032.3292 908,1043.1992 C957.4,1066.8292 1016.32,1084.8192 1062.92,1096.8992 " fill="none" id="processRequest-&gt;leases4_committed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1067.97,1098.1992,1060.2468,1092.0875,1063.1269,1096.9563,1058.2582,1099.8364,1067.97,1098.1992" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[46780bcbdce00599e22cc2808afc4298]
+link processRequest to drop--><path d="M814.47,1003.5592 C802.08,1027.7992 782,1073.5092 782,1115.1992 C782,1115.1992 782,1115.1992 782,1343.1992 C782,1504.6592 842.57,1536.4892 910,1683.1992 C916.56,1697.4792 918.33,1701.0892 927,1714.1992 C932.7,1722.8192 939.57,1731.8492 945.83,1739.6592 " fill="none" id="processRequest-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="949.23,1743.8592,946.6802,1734.3461,946.0857,1739.9717,940.4601,1739.3771,949.23,1743.8592" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="50" x="786" y="1403.7676">on error</text><!--MD5=[dd5280f7a4fbe519a789693377d2c3dc]
+link processRelease to leases4_committed--><path d="M1009.58,1003.3292 C1037.95,1026.9392 1089.01,1069.4292 1119.37,1094.6992 " fill="none" id="processRelease-&gt;leases4_committed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1123.33,1097.9992,1118.9735,1089.1663,1119.4877,1094.7997,1113.8543,1095.3139,1123.33,1097.9992" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[9c1ccee308c843163ae9c7fab5373c87]
+link processRelease to drop--><path d="M958.18,1003.1992 C924.12,1024.5192 874,1064.4892 874,1115.1992 C874,1115.1992 874,1115.1992 874,1343.1992 C874,1496.1392 893.83,1533.8992 927,1683.1992 C930.11,1697.2092 930.28,1701.0392 936,1714.1992 C939.7,1722.7092 944.65,1731.5692 949.37,1739.2792 " fill="none" id="processRelease-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="952.26,1743.9092,950.8732,1734.1585,949.6062,1739.6716,944.093,1738.4046,952.26,1743.9092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="50" x="876" y="1403.7676">on error</text><!--MD5=[762f153a4fd6a7efd08d553c7afbf530]
+link processDecline to leases4_committed--><path d="M1296.63,1003.3292 C1264.28,1027.0392 1205.97,1069.7792 1171.54,1095.0092 " fill="none" id="processDecline-&gt;leases4_committed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1167.47,1097.9992,1177.0921,1095.8981,1171.5007,1095.0405,1172.3582,1089.4491,1167.47,1097.9992" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[6d9fbe084438a9903d341665e19467c6]
+link processDecline to drop--><path d="M1344.72,1003.4392 C1388.71,1034.5392 1476,1098.3692 1476,1115.1992 C1476,1115.1992 1476,1115.1992 1476,1666.1992 C1476,1712.0592 1154.4,1744.8992 1020.96,1756.5492 " fill="none" id="processDecline-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1015.91,1756.9892,1025.2195,1760.2037,1020.8916,1756.561,1024.5344,1752.2331,1015.91,1756.9892" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="50" x="1477" y="1403.7676">on error</text><!--MD5=[403b2bcd25ba6f5a11641c975fae6de0]
+link processInform to leases4_committed--><path d="M1459.75,1003.3292 C1444.69,1015.9292 1422.73,1032.6492 1401,1043.1992 C1350.13,1067.9092 1289.34,1085.4192 1239.66,1096.9892 " fill="none" id="processInform-&gt;leases4_committed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1234.58,1098.1592,1244.2506,1100.0248,1239.451,1097.0307,1242.445,1092.2312,1234.58,1098.1592" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[c5223c78dfc731d8a0b6dd3ad2587a32]
+link processInform to drop--><path d="M1501,1003.2392 C1527.36,1025.7692 1568,1068.1292 1568,1115.1992 C1568,1115.1992 1568,1115.1992 1568,1666.1992 C1568,1721.2392 1171.5,1749.4592 1021.01,1758.1792 " fill="none" id="processInform-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1015.76,1758.4792,1024.9741,1761.9578,1020.7518,1758.1932,1024.5164,1753.9709,1015.76,1758.4792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="50" x="1569" y="1403.7676">on error</text><!--MD5=[887612e1a41deb0055e6b261cad7b207]
+link leases4_committed to pkt4_send--><path d="M1113.34,1134.3192 C1087.4,1150.5592 1051.56,1177.4592 1033,1211.1992 C1014.26,1245.2592 1012.51,1291.6692 1013.42,1318.8292 " fill="none" id="leases4_committed-&gt;pkt4_send" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1013.63,1323.9992,1017.2398,1314.8358,1013.4153,1319.0038,1009.2472,1315.1793,1013.63,1323.9992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="67" x="1034" y="1234.2676">CONTINUE</text><!--MD5=[03d4f1b76350f6f230f27d5a69f4e552]
+link leases4_committed to drop--><path d="M1215.67,1134.3092 C1261.73,1150.0592 1313,1178.6992 1313,1228.1992 C1313,1228.1992 1313,1228.1992 1313,1399.6992 C1313,1528.5792 1332.51,1582.5492 1252,1683.1992 C1223.32,1719.0492 1096.3,1742.6492 1020.86,1753.7692 " fill="none" id="leases4_committed-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1015.52,1754.5492,1025.0071,1757.1941,1020.4666,1753.8201,1023.8405,1749.2796,1015.52,1754.5492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="35" x="1315" y="1460.2676">DROP</text><!--MD5=[e6b479318b22374427e5a12769813441]
+link leases4_committed to park--><path d="M1144,1134.5392 C1144,1153.7692 1144,1184.8292 1144,1205.8592 " fill="none" id="leases4_committed-&gt;park" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1144,1210.9792,1148,1201.9792,1144,1205.9792,1140,1201.9792,1144,1210.9792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="32" x="1145" y="1177.7676">PARK</text><!--MD5=[6b0b05ab5b5e01054aa0e3030e86c15b]
+link park to pkt4_send--><path d="M1124.13,1247.2992 C1101.18,1267.0392 1063.46,1299.4992 1038.93,1320.6092 " fill="none" id="park-&gt;pkt4_send" style="stroke: #A80036; stroke-width: 1.0; stroke-dasharray: 7.0,7.0;"/><polygon fill="#A80036" points="1035.11,1323.8992,1044.5412,1321.0616,1038.9002,1320.6382,1039.3236,1314.9972,1035.11,1323.8992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="44" x="1088" y="1290.7676">unpark</text><!--MD5=[e1e7c40ae99ae9db4be329f6b3cb143f]
+link pkt4_send to pack--><path d="M1033.64,1360.2992 C1055.07,1379.9592 1090.25,1412.2292 1113.27,1433.3492 " fill="none" id="pkt4_send-&gt;pack" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1117.14,1436.8992,1113.218,1427.8649,1113.4578,1433.5167,1107.806,1433.7565,1117.14,1436.8992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="67" x="1083" y="1403.7676">CONTINUE</text><!--MD5=[729fab78839d14d65a522c939ef9b552]
+link pkt4_send to buffer4_send--><path d="M1013.6,1360.3192 C1012.24,1386.3092 1012.69,1436.5492 1032,1473.1992 C1044.57,1497.0592 1067.55,1517.1692 1086.73,1530.9992 " fill="none" id="pkt4_send-&gt;buffer4_send" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1091.02,1534.0292,1085.9763,1525.5698,1086.936,1531.1447,1081.3611,1532.1043,1091.02,1534.0292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="26" x="1033" y="1460.2676">SKIP</text><!--MD5=[7a343c005ca5222349b93a374f6aa4be]
+link pkt4_send to drop--><path d="M1008.96,1360.3792 C993.2,1406.2292 951.09,1535.5692 937,1647.1992 C935,1663.0692 934.35,1667.4192 937,1683.1992 C940.27,1702.6292 947.81,1723.6792 954.1,1739.0092 " fill="none" id="pkt4_send-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="956.17,1743.9792,956.39,1734.1328,954.2419,1739.3659,949.0087,1737.2179,956.17,1743.9792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="35" x="959" y="1557.2676">DROP</text><!--MD5=[e1b3754cee4214144faeedd0f77d1671]
+link pack to buffer4_send--><path d="M1132.88,1473.6192 C1130.1,1489.1592 1126.02,1511.9792 1123,1528.8592 " fill="none" id="pack-&gt;buffer4_send" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1122.1,1533.8892,1127.61,1525.7259,1122.973,1528.966,1119.7329,1524.3291,1122.1,1533.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[0fe92c55fb860475c26b6ea914a50894]
+link buffer4_send to send--><path d="M1118.06,1570.5392 C1117.02,1589.7692 1115.34,1620.8292 1114.21,1641.8592 " fill="none" id="buffer4_send-&gt;send" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1113.93,1646.9792,1118.412,1638.2093,1114.201,1641.9866,1110.4237,1637.7756,1113.93,1646.9792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="67" x="1117" y="1613.7676">CONTINUE</text><!--MD5=[887aa11356841167329c21249679272f]
+link buffer4_send to drop--><path d="M1161.34,1570.3192 C1173.8,1577.5792 1185.96,1587.3992 1193,1600.1992 C1201.95,1616.4792 1222.86,1639.9692 1191,1683.1992 C1151.85,1736.3392 1074.24,1753.5792 1020.76,1758.9992 " fill="none" id="buffer4_send-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1015.66,1759.4892,1025.0054,1762.5977,1020.6364,1759.0044,1024.2297,1754.6354,1015.66,1759.4892" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="35" x="1208" y="1670.2676">DROP</text><!--MD5=[6b25e4fe160ab604f67b02c1ded86970]
+link send to drop--><text fill="#888888" font-family="sans-serif" font-size="10" lengthAdjust="spacingAndGlyphs" textLength="225" x="809.5" y="1801.3555">dashed arrow means asynchronous processing</text><!--MD5=[3241bf81dfc1d82f66e0faca3c9d8456]
+@startuml
+
+title DHCPv4 packet processing (Kea 1.8.0)
+
+agent "Receive query" as receivePacket
+note left : input
+
+agent "Service Enabled" as isServiceEnabled
+
+agent "Callout buffer4_receive" as buffer4_receive
+note right : hook
+
+agent "Unpack query" as unpack
+
+agent "Classify query" as classify
+
+agent "Callout pkt4_receive" as pkt4_receive
+note right : hook
+
+agent "Check DROP class" as drop_class
+
+agent "Avoid same client race in multi-threaded mode" as same_client
+note right : postpone processing or drop
+
+rectangle "Process Query on its Message Type" as process {
+ agent "Process Discover" as processDiscover
+ agent "Process Request" as processRequest
+ agent "Process Release" as processRelease
+ agent "Process Decline" as processDecline
+ agent "Process Inform" as processInform
+}
+
+agent "Callout leases4_committed" as leases4_committed
+note right : hook
+
+agent "Park" as park
+
+agent "Callout pkt4_send" as pkt4_send
+
+agent "Send response" as send
+
+agent "Pack response" as pack
+
+agent "Callout buffer4_send" as buffer4_send
+
+agent "Send response" as send
+note left : output
+
+agent "Drop packet" as drop
+note left : error
+
+receivePacket - -> isServiceEnabled
+isServiceEnabled - -> buffer4_receive : service is enabled
+isServiceEnabled - - - -> drop : service is disabled
+buffer4_receive - -> unpack : CONTINUE
+buffer4_receive - -> classify : SKIP
+buffer4_receive - - - -> drop : DROP
+unpack - -> classify
+unpack - - -> drop : on error
+classify - -> pkt4_receive
+pkt4_receive - -> drop_class : CONTINUE
+pkt4_receive - - -> drop : DROP
+drop_class - -> same_client
+drop_class - - -> drop : query in DROP class
+same_client - - -> process
+same_client - - -> drop : queries from the same client possible race
+process - - -> drop : unknown message type
+processDiscover - -> leases4_committed
+processDiscover - - -> drop : on error
+processRequest - -> leases4_committed
+processRequest - - -> drop : on error
+processRelease - -> leases4_committed
+processRelease - - -> drop : on error
+processDecline - -> leases4_committed
+processDecline - - -> drop : on error
+processInform - -> leases4_committed
+processInform - - -> drop : on error
+leases4_committed - -> pkt4_send : CONTINUE
+leases4_committed - - -> drop : DROP
+leases4_committed - -> park : PARK
+park -[dashed]-> pkt4_send : unpark
+pkt4_send - -> pack : CONTINUE
+pkt4_send - -> buffer4_send : SKIP
+pkt4_send - - -> drop : DROP
+pack - -> buffer4_send
+buffer4_send - -> send : CONTINUE
+buffer4_send - - -> drop : DROP
+send -[hidden]-> drop
+
+footer dashed arrow means asynchronous processing
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
diff --git a/doc/sphinx/uml/packet4.uml b/doc/sphinx/uml/packet4.uml
new file mode 100644
index 0000000..15263c7
--- /dev/null
+++ b/doc/sphinx/uml/packet4.uml
@@ -0,0 +1,92 @@
+@startuml
+
+title DHCPv4 packet processing (Kea 1.8.0)
+
+agent "Receive query" as receivePacket
+note left : input
+
+agent "Service Enabled" as isServiceEnabled
+
+agent "Callout buffer4_receive" as buffer4_receive
+note right : hook
+
+agent "Unpack query" as unpack
+
+agent "Classify query" as classify
+
+agent "Callout pkt4_receive" as pkt4_receive
+note right : hook
+
+agent "Check DROP class" as drop_class
+
+agent "Avoid same client race in multi-threaded mode" as same_client
+note right : postpone processing or drop
+
+rectangle "Process Query on its Message Type" as process {
+ agent "Process Discover" as processDiscover
+ agent "Process Request" as processRequest
+ agent "Process Release" as processRelease
+ agent "Process Decline" as processDecline
+ agent "Process Inform" as processInform
+}
+
+agent "Callout leases4_committed" as leases4_committed
+note right : hook
+
+agent "Park" as park
+
+agent "Callout pkt4_send" as pkt4_send
+
+agent "Send response" as send
+
+agent "Pack response" as pack
+
+agent "Callout buffer4_send" as buffer4_send
+
+agent "Send response" as send
+note left : output
+
+agent "Drop packet" as drop
+note left : error
+
+receivePacket --> isServiceEnabled
+isServiceEnabled --> buffer4_receive : service is enabled
+isServiceEnabled ----> drop : service is disabled
+buffer4_receive --> unpack : CONTINUE
+buffer4_receive --> classify : SKIP
+buffer4_receive ----> drop : DROP
+unpack --> classify
+unpack ---> drop : on error
+classify --> pkt4_receive
+pkt4_receive --> drop_class : CONTINUE
+pkt4_receive ---> drop : DROP
+drop_class --> same_client
+drop_class ---> drop : query in DROP class
+same_client ---> process
+same_client ---> drop : queries from the same client possible race
+process ---> drop : unknown message type
+processDiscover --> leases4_committed
+processDiscover ---> drop : on error
+processRequest --> leases4_committed
+processRequest ---> drop : on error
+processRelease --> leases4_committed
+processRelease ---> drop : on error
+processDecline --> leases4_committed
+processDecline ---> drop : on error
+processInform --> leases4_committed
+processInform ---> drop : on error
+leases4_committed --> pkt4_send : CONTINUE
+leases4_committed ---> drop : DROP
+leases4_committed --> park : PARK
+park -[dashed]-> pkt4_send : unpark
+pkt4_send --> pack : CONTINUE
+pkt4_send --> buffer4_send : SKIP
+pkt4_send ---> drop : DROP
+pack --> buffer4_send
+buffer4_send --> send : CONTINUE
+buffer4_send ---> drop : DROP
+send -[hidden]-> drop
+
+footer dashed arrow means asynchronous processing
+
+@enduml
diff --git a/doc/sphinx/uml/request4-lease.png b/doc/sphinx/uml/request4-lease.png
new file mode 100644
index 0000000..23b95cd
--- /dev/null
+++ b/doc/sphinx/uml/request4-lease.png
diff --git a/doc/sphinx/uml/request4-lease.svg b/doc/sphinx/uml/request4-lease.svg
new file mode 100644
index 0000000..28b47de
--- /dev/null
+++ b/doc/sphinx/uml/request4-lease.svg
@@ -0,0 +1,203 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="2399px" preserveAspectRatio="none" style="width:2294px;height:2399px;" version="1.1" viewBox="0 0 2294 2399" width="2294px" zoomAndPan="magnify"><defs><filter height="300%" id="f5oag86dlpmno" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="399" x="938.5" y="17.4023">Allocate a lease for DHCPREQUEST (Kea 1.8.0)</text><!--MD5=[eaee9025590d004dcfc2daa117adb8bb]
+cluster check_hint--><rect fill="#FFFFFF" filter="url(#f5oag86dlpmno)" height="378.72" style="stroke: #000000; stroke-width: 1.5;" width="939" x="950" y="248.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="180" x="1329.5" y="263.7344">Check requested address</text><!--MD5=[c6fdc214782d2c6b530af6f84e869950]
+cluster get_existing--><rect fill="#FFFFFF" filter="url(#f5oag86dlpmno)" height="164.86" style="stroke: #000000; stroke-width: 1.5;" width="245" x="1604" y="347.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="229" x="1612" y="362.5944">Get lease for requested address</text><!--MD5=[57e960cb4db100c9a2ccd6f4d6705f05]
+cluster check_done--><rect fill="#FFFFFF" filter="url(#f5oag86dlpmno)" height="164.86" style="stroke: #000000; stroke-width: 1.5;" width="161" x="470" y="691.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="130" x="485.5" y="707.4544">Check client lease</text><!--MD5=[a6e23b86b5ec2c7080f88f7cf966373c]
+cluster new_lease--><rect fill="#FFFFFF" filter="url(#f5oag86dlpmno)" height="1385.08" style="stroke: #000000; stroke-width: 1.5;" width="1138" x="7" y="905.7792"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="147" x="502.5" y="921.3144">Allocate a new lease</text><!--MD5=[c0a0058b985d9500e1903c17b16df914]
+cluster allocateOrReuseLease4--><rect fill="#FFFFFF" filter="url(#f5oag86dlpmno)" height="685.36" style="stroke: #000000; stroke-width: 1.5;" width="300" x="71" y="1466.4992"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="164" x="139" y="1482.0344">Allocate or reuse lease</text><!--MD5=[23478a531f37cd80899cad04cd2b7f18]
+cluster allocateUnreservedLease4--><rect fill="#FFFFFF" filter="url(#f5oag86dlpmno)" height="588.22" style="stroke: #000000; stroke-width: 1.5;" width="514" x="411" y="1044.6392"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="184" x="576" y="1060.1744">Allocate unreserved lease</text><!--MD5=[f07ece90dffecaa599052c39e01a94c5]
+entity getReservedLease--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="246" x="1136" y="451.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="226" x="1146" y="475.4544">Check lease for reserved address</text><!--MD5=[8636dd2beae72b933abf12250cfd1025]
+entity out_of_pool--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="208" x="1020" y="566.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="188" x="1030" y="590.4544">Check out-of-pool address</text><!--MD5=[ec14e8cae259e632e03b8f7e5f2fa627]
+entity existing--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="174" x="1651" y="451.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="154" x="1661" y="475.4544">Check requested lease</text><!--MD5=[0edbe06a49914a247f1c11b045d92815]
+entity client_lease--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="108" x="494" y="796.7792"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="88" x="504" y="820.3144">Check renew</text><!--MD5=[66e1e431ca0dbea91ea05cb758558585]
+entity create--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="148" x="973" y="1703.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="128" x="983" y="1727.3944">Create a new lease</text><!--MD5=[a85809bef6165a661ce702016b2b24bf]
+entity old_lease--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="128" x="747" y="2230.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="108" x="757" y="2254.3944">Delete old lease</text><!--MD5=[3e4eb9e968ddf7eb79447dabaa827d00]
+entity candidate--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="153" x="188.5" y="1572.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="133" x="198.5" y="1596.3944">Get candidate lease</text><!--MD5=[3dd4b79f11e480f9e62df46d2d0a412b]
+entity reuseExpiredLease4--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="157" x="118.5" y="1703.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="137" x="128.5" y="1727.3944">Reuse expired lease</text><!--MD5=[7989e4485f5064553517c02d5ce8346d]
+entity reclaimExpiredLease--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="169" x="111.5" y="1800.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="149" x="121.5" y="1824.3944">Reclaim expired lease</text><!--MD5=[8b161cca1eea0fa2f14429822e5193fc]
+entity updateLease4Information--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="192" x="96" y="1897.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="172" x="106" y="1921.3944">update lease information</text><!--MD5=[20b997f41be7d019adfd03f05289a85b]
+entity lease4_select--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="163" x="95.5" y="1994.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="143" x="105.5" y="2018.3944">Callout lease4_select</text><path d="M293.5,2000.3592 L293.5,2008.8592 L258.55,2012.8592 L293.5,2016.8592 L293.5,2025.6698 A0,0 0 0 0 293.5,2025.6698 L346.5,2025.6698 A0,0 0 0 0 346.5,2025.6698 L346.5,2010.3592 L336.5,2000.3592 L293.5,2000.3592 A0,0 0 0 0 293.5,2000.3592 " fill="#FBFB77" filter="url(#f5oag86dlpmno)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M336.5,2000.3592 L336.5,2010.3592 L346.5,2010.3592 L336.5,2000.3592 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="32" x="299.5" y="2017.9276">hook</text><!--MD5=[d0c6f6a5b1ca3e5ac503933fbe44aaa9]
+entity updateLease4--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="108" x="210" y="2091.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="88" x="220" y="2115.3944">Update lease</text><!--MD5=[8ae068fcc4f60e406016be9ba14134ac]
+entity iterate--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="194" x="450" y="1133.4992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="174" x="460" y="1157.0344">Iterate pools and subnets</text><!--MD5=[cb628e8ea2f367fa2f488bc44b336c46]
+entity pick--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="105" x="509.5" y="1246.4992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="85" x="519.5" y="1270.0344">Pick address</text><!--MD5=[3307242102673314e57f67fe596f1a7c]
+entity pick_reserved--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="200" x="640" y="1359.4992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="180" x="650" y="1383.0344">Check reserved addressed</text><!--MD5=[ac311a8dd9b9ea9d39416a955479a4fe]
+entity mt_in_use--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="288" x="506" y="1475.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="268" x="516" y="1499.3944">Check already in use by another thread</text><!--MD5=[3fa202f6559a381d70247672876b819e]
+entity pick_lease--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="101" x="476.5" y="1572.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="81" x="486.5" y="1596.3944">Check lease</text><!--MD5=[1213eaa42773f0ba0384c538d3efa224]
+entity findClientLease--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="130" x="1383" y="28.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="110" x="1393" y="51.7344">Find client lease</text><path d="M1548,33.6992 L1548,42.1992 L1513.14,46.1992 L1548,50.1992 L1548,59.0098 A0,0 0 0 0 1548,59.0098 L1638,59.0098 A0,0 0 0 0 1638,59.0098 L1638,43.6992 L1628,33.6992 L1548,33.6992 A0,0 0 0 0 1548,33.6992 " fill="#FBFB77" filter="url(#f5oag86dlpmno)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M1628,33.6992 L1628,43.6992 L1638,43.6992 L1628,33.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="69" x="1554" y="51.2676">entry point</text><!--MD5=[0f69bb3143e68c3e4ebf8b928e2a1af4]
+entity addressReserved--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="216" x="1615" y="141.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="196" x="1625" y="164.7344">Check requested reservation</text><!--MD5=[f1bd864ca92b3a59ad91e15b6c278a16]
+entity hasAddressReservation--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="124" x="1112" y="141.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="104" x="1122" y="164.7344">Get reservation</text><!--MD5=[29cbf9a69668994ea4ff4bb0b8dea6d6]
+entity update_hint--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="200" x="1380" y="141.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="180" x="1390" y="164.7344">Update requested address</text><!--MD5=[999fe650e2a9819ebed27de3d290658a]
+entity no_lease--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="127" x="1444.5" y="2230.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="107" x="1454.5" y="2254.3944">Return no lease</text><path d="M1607,2236.3592 L1607,2244.8592 L1571.71,2248.8592 L1607,2252.8592 L1607,2261.6698 A0,0 0 0 0 1607,2261.6698 L1689,2261.6698 A0,0 0 0 0 1689,2261.6698 L1689,2246.3592 L1679,2236.3592 L1607,2236.3592 A0,0 0 0 0 1607,2236.3592 " fill="#FBFB77" filter="url(#f5oag86dlpmno)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M1679,2236.3592 L1679,2246.3592 L1689,2246.3592 L1679,2236.3592 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="61" x="1613" y="2253.9276">exit point</text><!--MD5=[45b45980895812fee5a3bd80c1953e7a]
+entity renew--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="168" x="971" y="796.7792"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="148" x="981" y="820.3144">Return renewed lease</text><path d="M1174,802.2792 L1174,810.7792 L1139.06,814.7792 L1174,818.7792 L1174,827.5898 A0,0 0 0 0 1174,827.5898 L1256,827.5898 A0,0 0 0 0 1256,827.5898 L1256,812.2792 L1246,802.2792 L1174,802.2792 A0,0 0 0 0 1174,802.2792 " fill="#FBFB77" filter="url(#f5oag86dlpmno)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M1246,802.2792 L1246,812.2792 L1256,812.2792 L1246,802.2792 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="61" x="1180" y="819.8476">exit point</text><!--MD5=[c13398c59c328d6fcc544c8c17f5b117]
+entity return--><rect fill="#FEFECE" filter="url(#f5oag86dlpmno)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="105" x="758.5" y="2345.8592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="85" x="768.5" y="2369.3944">Return lease</text><path d="M899,2351.3592 L899,2359.8592 L863.66,2363.8592 L899,2367.8592 L899,2376.6698 A0,0 0 0 0 899,2376.6698 L981,2376.6698 A0,0 0 0 0 981,2376.6698 L981,2361.3592 L971,2351.3592 L899,2351.3592 A0,0 0 0 0 899,2351.3592 " fill="#FBFB77" filter="url(#f5oag86dlpmno)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M971,2351.3592 L971,2361.3592 L981,2361.3592 L971,2351.3592 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="61" x="905" y="2368.9276">exit point</text><!--MD5=[58c45ac03f61bca16a2604d1f9090edc]
+link findClientLease to addressReserved--><path d="M1490.37,64.2992 C1540.43,84.5092 1623.49,118.0392 1675.64,139.0792 " fill="none" id="findClientLease-&gt;addressReserved" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1680.59,141.0792,1673.7456,133.9973,1675.9546,139.205,1670.7468,141.414,1680.59,141.0792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="178" x="1602" y="107.7676">has requested address (hint)</text><!--MD5=[3ed98210a29f20764b03cb44cfd671eb]
+link findClientLease to hasAddressReservation--><path d="M1405.79,64.2992 C1355.91,84.5092 1273.15,118.0392 1221.19,139.0792 " fill="none" id="findClientLease-&gt;hasAddressReservation" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1216.26,141.0792,1226.1032,141.414,1220.8954,139.205,1223.1044,133.9973,1216.26,141.0792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="172" x="1328" y="107.7676">no requested address (hint)</text><!--MD5=[0f8169b991248aaf1e86d3e126ee7fc7]
+link addressReserved to check_hint--><path d="M1706.14,177.5692 C1690.855,193.3142 1667.81,217.0567 1648.3475,237.1092 C1645.9147,239.6158 1643.5379,242.0647 1641.2391,244.4331 C1640.0898,245.6173 1638.96,246.7814 1637.8525,247.9225 " fill="none" id="addressReserved-&gt;check_hint" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1637.8525,247.9225,1646.991,244.2501,1641.3348,244.3346,1641.2503,238.6783,1637.8525,247.9225" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="162" x="1675" y="220.7676">no conflicting reservation</text><!--MD5=[afeb447a9f6636bece5d73dd5d09cefa]
+link addressReserved to no_lease--><path d="M1831.12,176.2492 C1928.35,193.8192 2056,226.1192 2056,274.5592 C2056,274.5592 2056,274.5592 2056,2110.8592 C2056,2245.5392 1894.72,2159.4592 1764,2191.8592 C1729.14,2200.4992 1639.9,2219.7792 1576.62,2233.2992 " fill="none" id="addressReserved-&gt;no_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1571.73,2234.3392,1581.3655,2236.3781,1576.6205,2233.2984,1579.7002,2228.5534,1571.73,2234.3392" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="225" x="2057" y="1213.0676">reservation owned by another client</text><!--MD5=[961d5a31619e7d456669487d013a1899]
+link hasAddressReservation to update_hint--><path d="M1236.29,159.1992 C1276.08,159.1992 1328.68,159.1992 1374.83,159.1992 " fill="none" id="hasAddressReservation-&gt;update_hint" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1379.85,159.1992,1370.85,155.1992,1374.85,159.1992,1370.85,163.1992,1379.85,159.1992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="107" x="1254.5" y="152.7676">has a reservation</text><!--MD5=[05586e2e35799af932c772159165fde5]
+link update_hint to check_hint--><path d="M1480.56,177.2992 C1481.87,191.3892 1485.77,211.1092 1497,224.1992 C1501.4688,229.4105 1506.5789,234.1017 1512.105,238.322 C1514.868,240.4322 1517.735,242.4246 1520.6778,244.3054 C1522.1492,245.2458 1523.6395,246.1583 1525.1453,247.0437 C1525.5217,247.2651 1525.8991,247.4847 1526.2774,247.7027 C1526.4666,247.8117 1526.656,247.9202 1526.8456,248.0284 " fill="none" id="update_hint-&gt;check_hint" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1526.8456,248.0284,1521.0095,240.0949,1522.5024,245.5512,1517.046,247.044,1526.8456,248.0284" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="157" x="1498" y="220.7676">request reserved address</text><!--MD5=[f5740591afdec92972eb12364704fbda]
+link hasAddressReservation to check_done--><path d="M1111.78,160.2292 C968.42,161.9792 627,176.4492 627,274.5592 C627,274.5592 627,274.5592 627,585.9192 C627,614.8842 626.03,647.4017 625.045,672.958 C624.7987,679.347 624.5516,685.301 624.3184,690.6556 C624.3038,690.9903 624.2893,691.3226 624.2748,691.6526 " fill="none" id="hasAddressReservation-&gt;check_done" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="624.2748,691.6526,628.6651,682.8364,624.4938,686.6574,620.6728,682.486,624.2748,691.6526" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="90" x="628" y="418.4876">no reservation</text><!--MD5=[05b1cca34cf1798b13fb9b06f5ca5f3a]
+link check_hint to get_existing--><path d="M1612,276.1292 C1612,277.5792 1612,301.1692 1612,324.7542 C1612,330.6505 1612,336.5464 1612,342.096 C1612,343.4834 1612,344.8492 1612,346.1879 C1612,346.3552 1612,346.5221 1612,346.6886 " fill="none" id="check_hint-&gt;get_existing" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1612,346.6886,1616,337.6886,1612,341.6886,1608,337.6886,1612,346.6886" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[a6e7bc949cef76964a3dcada3d94e736]
+link get_existing to existing--><path d="M1612.09,374.9892 C1614.74,376.9592 1674.43,421.4892 1710.66,448.5192 " fill="none" id="get_existing-&gt;existing" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1714.95,451.7292,1710.1157,443.1485,1710.938,448.7452,1705.3413,449.5676,1714.95,451.7292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="124" x="1676" y="418.4876">has requested lease</text><!--MD5=[86bae6c5db5c6e2b2f64eec8702a172a]
+link existing to no_lease--><path d="M1738,488.1492 C1738,510.3092 1738,549.9792 1738,583.9192 C1738,583.9192 1738,583.9192 1738,2110.8592 C1738,2169.0192 1692.68,2170.6192 1643,2200.8592 C1622.7,2213.2092 1598.7,2222.8992 1576.6,2230.1892 " fill="none" id="existing-&gt;no_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1571.62,2231.7992,1581.415,2232.8276,1576.3761,2230.2567,1578.947,2225.2178,1571.62,2231.7992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="263" x="1739" y="1382.5676">not expired lease owned by another client</text><!--MD5=[d1913c1ad5468c4f26e27e58c8f67311]
+link get_existing to out_of_pool--><path d="M1603.5702,375.107 C1603.282,375.1139 1602.9868,375.1209 1602.6847,375.1282 C1602.0805,375.1427 1601.4485,375.158 1600.7892,375.1741 C1599.4706,375.2063 1598.043,375.2417 1596.5101,375.2804 C1593.4444,375.3579 1589.9579,375.4487 1586.0818,375.5535 C1570.5772,375.973 1548.8378,376.6183 1522.855,377.543 C1470.8894,379.3923 1401.95,382.3592 1331.9675,386.8717 C1192.0025,395.8967 1047.865,411.1042 1027,435.9192 C1000.68,467.2192 1006.56,492.5092 1027,527.9192 C1036.33,544.0792 1052.3,555.9992 1068.62,564.5792 " fill="none" id="get_existing-&gt;out_of_pool" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1073.22,566.9092,1066.998,559.2747,1068.7594,564.6503,1063.3837,566.4117,1073.22,566.9092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="90" x="1028" y="474.9876">no reservation</text><!--MD5=[d1913c1ad5468c4f26e27e58c8f67311]
+link get_existing to out_of_pool--><path d="M1603.8377,376.8955 C1603.4057,377.006 1602.9584,377.1212 1602.4962,377.2411 C1600.6472,377.7206 1598.5597,378.2751 1596.2617,378.9056 C1587.0697,381.4277 1574.5094,385.1648 1560.3738,390.173 C1532.1025,400.1892 1497.53,415.2892 1471,435.9192 C1430.23,467.6192 1443.85,500.6192 1400,527.9192 C1350.34,558.8392 1286.82,573.0892 1233.23,579.4992 " fill="none" id="get_existing-&gt;out_of_pool-1" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1228.08,580.0892,1237.4862,583.0087,1233.0457,579.5042,1236.5502,575.0636,1228.08,580.0892" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="162" x="1472" y="474.9876">has requested reservation</text><!--MD5=[a80af0ff9802cb26b63fe0e5cdeeb896]
+link get_existing to getReservedLease--><path d="M1603.7999,374.8934 C1603.5697,374.893 1603.3349,374.8927 1603.0956,374.8923 C1602.6171,374.8916 1602.1205,374.891 1601.6064,374.8904 C1599.5497,374.8882 1597.2106,374.8875 1594.61,374.8892 C1584.2075,374.8962 1569.6199,374.9436 1552.1798,375.1011 C1517.2997,375.4161 1471.0094,376.1717 1423.9688,377.9267 C1329.8875,381.4367 1232.805,388.9442 1218,404.9192 C1205.95,417.9192 1217.84,434.9092 1231.87,448.1092 " fill="none" id="get_existing-&gt;getReservedLease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1235.86,451.7292,1231.8826,442.7192,1232.1571,448.3694,1226.5069,448.6439,1235.86,451.7292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="223" x="1219" y="418.4876">has reservation for another address</text><!--MD5=[460f9433d097e6134b488e2edc059749]
+link getReservedLease to no_lease--><path d="M1298.31,487.9392 C1370.31,519.1292 1516,582.4492 1516,583.9192 C1516,583.9192 1516,583.9192 1516,1321.9992 C1516,1356.7992 1520.59,1368.8792 1543,1395.4992 C1560.18,1415.9092 1578.19,1404.7792 1595,1425.4992 C1614.84,1449.9592 1617,1461.3692 1617,1492.8592 C1617,1492.8592 1617,1492.8592 1617,2110.8592 C1617,2161.3292 1571.14,2203.9592 1538.92,2227.6992 " fill="none" id="getReservedLease-&gt;no_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1534.66,2230.7792,1544.2952,2228.7389,1538.7092,2227.846,1539.6021,2222.2601,1534.66,2230.7792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="150" x="1544" y="1382.5676">no active reserved lease</text><!--MD5=[e9bc3bd5a379396c200e43b0baf79c85]
+link getReservedLease to out_of_pool--><path d="M1238.5,488.0792 C1214.41,508.2392 1174.48,541.6692 1148.71,563.2392 " fill="none" id="getReservedLease-&gt;out_of_pool" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1144.7,566.5992,1154.1757,563.9139,1148.5423,563.3997,1149.0565,557.7663,1144.7,566.5992" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[e17e653abfe61c21e03d310137f9f5d3]
+link out_of_pool to check_done--><path d="M1094.93,603.0392 C1061.57,621.9092 1004.65,651.7292 952,667.9192 C882.41,689.3242 801.6225,701.8592 737.5188,709.0692 C705.4669,712.6742 677.5859,714.948 657.3611,716.3336 C647.2487,717.0264 639.0503,717.4972 633.2015,717.8013 C632.4705,717.8393 631.7761,717.8748 631.1193,717.9077 " fill="none" id="out_of_pool-&gt;check_done" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="631.1193,717.9077,640.3082,721.4522,636.113,717.6574,639.9078,713.4622,631.1193,717.9077" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="280" x="997" y="664.4876">owned reservation for the requested address</text><!--MD5=[e17e653abfe61c21e03d310137f9f5d3]
+link out_of_pool to check_done--><path d="M1019.57,594.3492 C910.87,604.4092 748.83,623.3992 693,650.9192 C674.24,660.1642 657.23,676.2567 644.6763,690.3942 C641.5378,693.9286 638.6779,697.3408 636.1388,700.4932 C634.8692,702.0695 633.6798,703.5808 632.576,705.0099 C632.3,705.3672 632.0294,705.7194 631.7642,706.0662 C631.6316,706.2395 631.5003,706.4116 631.3705,706.5822 C631.3055,706.6675 631.2409,706.7525 631.1767,706.8371 " fill="none" id="out_of_pool-&gt;check_done-1" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="631.1767,706.8371,639.8049,702.088,634.2002,702.8549,633.4333,697.2503,631.1767,706.8371" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="249" x="694" y="664.4876">requested address is in allowed an pool</text><!--MD5=[7bd3c3d867479d62123546af0a0eba34]
+link out_of_pool to no_lease--><path d="M1203.74,602.9892 C1232.91,612.7492 1264.1,627.8392 1286,650.9192 C1307.77,673.8692 1309,686.6492 1309,718.2792 C1309,718.2792 1309,718.2792 1306,1434.9992 C1306,1673.5792 1398,1725.2792 1398,1963.8592 C1398,1963.8592 1398,1963.8592 1398,2110.8592 C1398,2161.5092 1444.28,2204.0892 1476.8,2227.7592 " fill="none" id="out_of_pool-&gt;no_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1481.09,2230.8292,1476.0801,2222.3498,1477.0175,2227.9284,1471.4388,2228.8658,1481.09,2230.8292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="283" x="1310" y="1439.0676">address not reserved and not in allowed pool</text><!--MD5=[285a75cccafb8a8e1e8a8d054b6bd861]
+link check_done to client_lease--><path d="M622.95,719.8492 C621.39,721.7992 586.7,765.2692 565.07,792.3792 " fill="none" id="check_done-&gt;client_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="561.72,796.5892,570.4617,792.0524,564.84,792.6821,564.2103,787.0604,561.72,796.5892" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="108" x="600" y="763.3476">has a client lease</text><!--MD5=[69a418bc3ca1e1b953129b8feacd7c7c]
+link client_lease to renew--><path d="M602.26,814.7792 C689.18,814.7792 860.52,814.7792 965.69,814.7792 " fill="none" id="client_lease-&gt;renew" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="970.96,814.7792,961.96,810.7792,965.96,814.7792,961.96,818.7792,970.96,814.7792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="332" x="620.5" y="808.3476">requested address was already assigned to the client</text><!--MD5=[82bd19346130f27c4982b22ea05f0ccb]
+link client_lease to new_lease--><path d="M547.85,832.9492 C547.715,848.8792 547.5075,873.1567 547.3313,893.7055 C547.3092,896.2741 547.2877,898.7844 547.2668,901.2129 C547.2564,902.4271 547.2461,903.6209 547.2361,904.7913 C547.2336,905.0839 547.2311,905.375 547.2286,905.6646 " fill="none" id="client_lease-&gt;new_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="547.2286,905.6646,551.3058,896.6993,547.2715,900.6648,543.3061,896.6306,547.2286,905.6646" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[f19fad7ef643a710f1fa744c146e27e1]
+link new_lease to allocateOrReuseLease4--><path d="M546.94,933.6392 C542.11,933.4192 233,919.8692 233,1070.9992 C233,1070.9992 233,1070.9992 233,1378.4992 C233,1403.8242 237.36,1431.9242 241.7888,1453.9317 C242.3423,1456.6827 242.897,1459.3384 243.4444,1461.8816 C243.7181,1463.1532 243.9899,1464.3967 244.2589,1465.6099 C244.2925,1465.7616 244.3261,1465.9127 244.3596,1466.0634 " fill="none" id="new_lease-&gt;allocateOrReuseLease4" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="244.3596,1466.0634,246.3094,1456.4095,243.2737,1461.1828,238.5004,1458.147,244.3596,1466.0634" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="152" x="234" y="1213.0676">has a requested address</text><!--MD5=[1e19bcf55215d199025544543592d337]
+link new_lease to allocateUnreservedLease4--><path d="M547,933.7392 C547,935.7842 547,969.0667 547,1002.3417 C547,1010.6605 547,1018.9788 547,1026.8084 C547,1030.7232 547,1034.5158 547,1038.1252 C547,1039.93 547,1041.6889 547,1043.3944 C547,1043.6076 547,1043.8199 547,1044.0314 " fill="none" id="new_lease-&gt;allocateUnreservedLease4" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="547,1044.0314,551,1035.0314,547,1039.0314,543,1035.0314,547,1044.0314" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="135" x="548" y="977.2076">no requested address</text><!--MD5=[2c84e3b0a8d19577f3d2d8902e61dda6]
+link allocateOrReuseLease4 to candidate--><path d="M251.01,1494.9292 C251.3,1496.8792 257.62,1539.7592 261.66,1567.2092 " fill="none" id="allocateOrReuseLease4-&gt;candidate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="262.44,1572.4792,265.0848,1562.9921,261.7109,1567.5327,257.1703,1564.1587,262.44,1572.4792" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[a5e8e7e456414e548f2004cb6dbe84b6]
+link candidate to reuseExpiredLease4--><path d="M255.97,1608.9892 C243.73,1632.2192 221.85,1673.7092 208.46,1699.1092 " fill="none" id="candidate-&gt;reuseExpiredLease4" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="206.07,1703.6592,213.799,1697.5549,208.397,1699.2337,206.7181,1693.8317,206.07,1703.6592" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="148" x="230" y="1670.4276">expired candidate lease</text><!--MD5=[d2a65277aca220a8b88ff33e161a522b]
+link candidate to no_lease--><path d="M300.41,1608.9492 C331,1622.7292 376.81,1641.0592 419,1648.8592 C438.61,1652.4892 1119.78,1646.7992 1137,1656.8592 C1165.37,1673.4392 1174,1687.9992 1174,1720.8592 C1174,1720.8592 1174,1720.8592 1174,2110.8592 C1174,2167.7192 1341.77,2212.7992 1439.5,2234.2292 " fill="none" id="candidate-&gt;no_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1444.39,2235.2992,1436.4557,2229.4642,1439.5061,2234.2282,1434.7421,2237.2785,1444.39,2235.2992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="169" x="1175" y="1920.9276">conflicting candidate lease</text><!--MD5=[7d0ea550df801bc4f2e5d77c4007fd73]
+link candidate to create--><path d="M302.78,1608.8892 C333.47,1621.9592 378.19,1639.3492 419,1648.8592 C452.51,1656.6692 461.8,1653.0992 496,1656.8592 C663.96,1675.3392 860.53,1698.5492 967.59,1711.3292 " fill="none" id="candidate-&gt;create" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="972.62,1711.9292,964.1641,1706.8797,967.656,1711.3301,963.2056,1714.822,972.62,1711.9292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="117" x="634" y="1670.4276">no candidate lease</text><!--MD5=[41d477ba3ffb73c8ff7e1f8771a2bc5c]
+link reuseExpiredLease4 to reclaimExpiredLease--><path d="M196.82,1740.2792 C196.65,1755.8192 196.41,1778.6392 196.24,1795.5192 " fill="none" id="reuseExpiredLease4-&gt;reclaimExpiredLease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="196.18,1800.5492,200.2572,1791.5839,196.223,1795.5494,192.2575,1791.5152,196.18,1800.5492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[6426546e78ac0ba7440fd3d40f44ede2]
+link reclaimExpiredLease to updateLease4Information--><path d="M195.27,1837.2792 C194.61,1852.8192 193.65,1875.6392 192.94,1892.5192 " fill="none" id="reclaimExpiredLease-&gt;updateLease4Information" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="192.73,1897.5492,197.0865,1888.7163,192.9298,1892.5532,189.0929,1888.3965,192.73,1897.5492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[a62828ac2ba9e6deab1d38c41c6a28c7]
+link updateLease4Information to lease4_select--><path d="M189.25,1934.2792 C186.8,1949.8192 183.19,1972.6392 180.53,1989.5192 " fill="none" id="updateLease4Information-&gt;lease4_select" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="179.73,1994.5492,185.097,1986.2912,180.5172,1989.6116,177.1968,1985.0317,179.73,1994.5492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[8451cb76573000a7f0f17878defd5d68]
+link lease4_select to no_lease--><path d="M256.64,2030.8892 C422.11,2065.8992 815.39,2147.1692 1148,2200.8592 C1249.02,2217.1692 1366.7,2231.6892 1439.28,2240.1392 " fill="none" id="lease4_select-&gt;no_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1444.43,2240.7392,1435.9456,2235.7377,1439.4627,2240.1683,1435.0321,2243.6853,1444.43,2240.7392" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="26" x="1090" y="2114.9276">SKIP</text><!--MD5=[6d30d4fb129fbbb4308e51704d598b83]
+link lease4_select to updateLease4--><path d="M187.75,2031.0092 C194.04,2040.4992 202.41,2052.2792 211,2061.8592 C219.4,2071.2392 229.56,2080.6292 238.73,2088.5292 " fill="none" id="lease4_select-&gt;updateLease4" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="242.59,2091.8092,238.3406,2082.9243,238.7867,2088.5635,233.1474,2089.0096,242.59,2091.8092" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[f38e7914af006d3091e34eae716cf611]
+link updateLease4 to old_lease--><path d="M271.13,2128.1092 C280.01,2147.2092 297.1,2177.2192 322,2191.8592 C391.49,2232.7292 624.21,2243.7792 741.78,2246.7592 " fill="none" id="updateLease4-&gt;old_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="746.95,2246.8892,738.0438,2242.6846,741.9513,2246.775,737.8609,2250.6825,746.95,2246.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[9b569e4e69bfc07b8f4591db492d7934]
+link allocateUnreservedLease4 to iterate--><path d="M547,1072.5592 C547,1074.0692 547,1105.5792 547,1128.0692 " fill="none" id="allocateUnreservedLease4-&gt;iterate" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="547,1133.2792,551,1124.2792,547,1128.2792,543,1124.2792,547,1133.2792" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[913c99c1aa5de4d885de0fade3210176]
+link iterate to pick--><path d="M549.34,1169.8392 C551.94,1189.0692 556.14,1220.1292 558.98,1241.1592 " fill="none" id="iterate-&gt;pick" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="559.67,1246.2792,562.4258,1236.8238,558.9989,1241.3245,554.4982,1237.8975,559.67,1246.2792" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[98fd2d33f60f8d171595f3ad38490357]
+link pick to pick_reserved--><path d="M614.74,1276.6292 C662.69,1287.2492 727.13,1302.9992 735,1312.4992 C744.41,1323.8692 745.43,1340.5992 744.21,1354.0992 " fill="none" id="pick-&gt;pick_reserved" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="743.62,1359.2892,748.6002,1350.7923,744.1784,1354.3205,740.6502,1349.8988,743.62,1359.2892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[40bbb0c51a3c4e170e8c88288f4abbc7]
+reverse link iterate to pick_reserved--><path d="M587.85,1171.9592 C635.04,1196.9992 710.25,1245.3892 742,1312.4992 C748.94,1327.1692 747.31,1345.9192 744.63,1359.3292 " fill="none" id="iterate&lt;-pick_reserved" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="583.37,1169.6092,589.4641,1177.3463,587.7924,1171.9421,593.1966,1170.2704,583.37,1169.6092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="214" x="723" y="1269.5676">address reserved to another client</text><!--MD5=[d452465c31c3e200782285fc87364de7]
+link pick_reserved to mt_in_use--><path d="M726.33,1395.8692 C710.31,1416.2192 683.78,1449.9292 666.6,1471.7692 " fill="none" id="pick_reserved-&gt;mt_in_use" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="663.5,1475.6992,672.2152,1471.1118,666.5973,1471.7741,665.935,1466.1561,663.5,1475.6992" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[0d2cb4b21f131724b772926f54d8c5a6]
+reverse link iterate to mt_in_use--><path d="M525.22,1173.1292 C491.49,1207.6292 434.06,1278.2892 470,1329.4992 C492.53,1361.6092 521.64,1335.9392 553,1359.4992 C595.57,1391.4892 627.49,1447.3892 641.76,1475.5692 " fill="none" id="iterate&lt;-mt_in_use" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="528.81,1169.5092,519.6392,1173.1004,525.296,1173.0661,525.3302,1178.7229,528.81,1169.5092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="255" x="471" y="1326.0676">address already in use by another thread</text><!--MD5=[bc2a6c320076cde845cfe5f7d4f3068f]
+link mt_in_use to pick_lease--><path d="M627.73,1512.0592 C606.74,1528.2692 575.3,1552.5592 553.13,1569.6792 " fill="none" id="mt_in_use-&gt;pick_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="549.11,1572.7792,558.6776,1570.4423,553.0667,1569.7224,553.7867,1564.1115,549.11,1572.7792" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[2a521ba838ca3ea39c3c98b97230fab1]
+reverse link iterate to pick_lease--><path d="M513.37,1172.6092 C502.3,1180.1892 490.42,1189.4392 481,1199.4992 C464.23,1217.4192 458.7,1222.8892 452,1246.4992 C435.76,1303.7492 469.06,1455.4492 488,1511.8592 C495.37,1533.8192 507.86,1557.3892 516.72,1572.7992 " fill="none" id="iterate&lt;-pick_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="517.73,1169.6792,508.0294,1171.3818,513.5808,1172.4692,512.4934,1178.0206,517.73,1169.6792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="73" x="461" y="1382.5676">active lease</text><!--MD5=[63357d070723cd23e47a694c7dc5adee]
+link pick_lease to reuseExpiredLease4--><path d="M486.46,1608.9192 C461.21,1620.5292 428.75,1637.3192 403,1656.8592 C394.74,1663.1292 395.96,1668.6192 387,1673.8592 C377.25,1679.5592 326.42,1692.0092 279.78,1702.6592 " fill="none" id="pick_lease-&gt;reuseExpiredLease4" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="274.7,1703.8192,284.3588,1705.7447,279.5779,1702.721,282.6016,1697.9401,274.7,1703.8192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="83" x="404" y="1670.4276">expired lease</text><!--MD5=[cf9da26e069a0df2c62fe2799950086c]
+link pick_lease to create--><path d="M577.81,1604.4592 C670.26,1627.3992 866.3,1676.0292 973.39,1702.5992 " fill="none" id="pick_lease-&gt;create" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="978.42,1703.8492,970.6421,1697.8074,973.5659,1702.65,968.7233,1705.5738,978.42,1703.8492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="52" x="849" y="1670.4276">no lease</text><!--MD5=[64e111b9225aa9d21cd5edaf123c77e3]
+link create to old_lease--><path d="M1027.36,1740.0192 C1009.53,1757.5992 986,1786.6992 986,1817.8592 C986,1817.8592 986,1817.8592 986,2110.8592 C986,2170.8492 921.44,2208.5092 870.75,2228.8292 " fill="none" id="create-&gt;old_lease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="865.89,2230.7392,875.7293,2231.1732,870.5441,2228.9118,872.8055,2223.7267,865.89,2230.7392" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[f504166a5b4bb527b5be2231a925b659]
+link old_lease to return--><path d="M811,2267.0192 C811,2286.5992 811,2318.6892 811,2340.2892 " fill="none" id="old_lease-&gt;return" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="811,2345.5392,815,2336.5392,811,2340.5392,807,2336.5392,811,2345.5392" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[1b4d46ef90f054326099bee1d7a95d46]
+@startuml
+
+title Allocate a lease for DHCPREQUEST (Kea 1.8.0)
+
+agent "Find client lease" as findClientLease
+note right : entry point
+
+agent "Check requested reservation" as addressReserved
+
+agent "Get reservation" as hasAddressReservation
+
+agent "Update requested address" as update_hint
+
+rectangle "Check requested address" as check_hint {
+ rectangle "Get lease for requested address" as get_existing {
+  agent "Check requested lease" as existing
+ }
+
+ agent "Check lease for reserved address" as getReservedLease
+
+ agent "Check out-of-pool address" as out_of_pool
+}
+
+rectangle "Check client lease" as check_done {
+ agent "Check renew" as client_lease
+}
+
+rectangle "Allocate a new lease" as new_lease {
+ together {
+  rectangle "Allocate or reuse lease" as allocateOrReuseLease4 {
+   agent "Get candidate lease" as candidate
+
+   agent "Reuse expired lease" as reuseExpiredLease4
+
+   agent "Reclaim expired lease" as reclaimExpiredLease
+
+   agent "update lease information" as updateLease4Information
+
+   agent "Callout lease4_select" as lease4_select
+   note right : hook
+
+   agent "Update lease" as updateLease4
+  }
+
+  rectangle "Allocate unreserved lease" as allocateUnreservedLease4 {
+   agent "Iterate pools and subnets" as iterate
+
+   agent "Pick address" as pick
+
+   agent "Check reserved addressed" as pick_reserved
+
+   agent "Check already in use by another thread" as mt_in_use
+
+   agent "Check lease" as pick_lease
+  }
+ }
+
+ agent "Create a new lease" as create
+
+ agent "Delete old lease" as old_lease
+}
+
+agent "Return no lease" as no_lease
+note right : exit point
+
+agent "Return renewed lease" as renew
+note right : exit point
+
+agent "Return lease" as return
+note right : exit point
+
+findClientLease - -> addressReserved : has requested address (hint)
+findClientLease - -> hasAddressReservation : no requested address (hint)
+addressReserved - -> check_hint : no conflicting reservation
+addressReserved - -> no_lease : reservation owned by another client
+hasAddressReservation -> update_hint : has a reservation
+update_hint - -> check_hint : request reserved address
+hasAddressReservation - -> check_done : no reservation
+check_hint - -> get_existing
+get_existing - -> existing : has requested lease
+existing - - -> no_lease : not expired lease owned by another client
+get_existing - -> out_of_pool : no reservation
+get_existing - -> out_of_pool : has requested reservation
+get_existing - -> getReservedLease : has reservation for another address
+getReservedLease - - -> no_lease : no active reserved lease
+getReservedLease - -> out_of_pool
+out_of_pool - -> check_done : owned reservation for the requested address
+out_of_pool - -> check_done : requested address is in allowed an pool
+out_of_pool - -> no_lease : address not reserved and not in allowed pool
+check_done - -> client_lease : has a client lease
+client_lease -> renew : requested address was already assigned to the client
+client_lease - -> new_lease
+new_lease - -> allocateOrReuseLease4 : has a requested address
+new_lease - -> allocateUnreservedLease4 : no requested address
+allocateOrReuseLease4 - -> candidate
+candidate - -> reuseExpiredLease4 : expired candidate lease
+candidate - -> no_lease : conflicting candidate lease
+candidate - -> create : no candidate lease
+reuseExpiredLease4 - -> reclaimExpiredLease
+reclaimExpiredLease - -> updateLease4Information
+updateLease4Information - -> lease4_select
+lease4_select - - -> no_lease : SKIP
+lease4_select - -> updateLease4
+updateLease4 - -> old_lease
+allocateUnreservedLease4 - -> iterate
+iterate - -> pick
+pick - -> pick_reserved
+pick_reserved -up-> iterate : address reserved to another client
+pick_reserved - -> mt_in_use
+mt_in_use -up-> iterate : address already in use by another thread
+mt_in_use - -> pick_lease
+pick_lease -up-> iterate : active lease
+pick_lease - -> reuseExpiredLease4 : expired lease
+pick_lease - -> create : no lease
+create - -> old_lease
+old_lease - -> return
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/request4-lease.uml b/doc/sphinx/uml/request4-lease.uml
new file mode 100644
index 0000000..54f0c81
--- /dev/null
+++ b/doc/sphinx/uml/request4-lease.uml
@@ -0,0 +1,118 @@
+@startuml
+
+title Allocate a lease for DHCPREQUEST (Kea 1.8.0)
+
+agent "Find client lease" as findClientLease
+note right : entry point
+
+agent "Check requested reservation" as addressReserved
+
+agent "Get reservation" as hasAddressReservation
+
+agent "Update requested address" as update_hint
+
+rectangle "Check requested address" as check_hint {
+ rectangle "Get lease for requested address" as get_existing {
+  agent "Check requested lease" as existing
+ }
+
+ agent "Check lease for reserved address" as getReservedLease
+
+ agent "Check out-of-pool address" as out_of_pool
+}
+
+rectangle "Check client lease" as check_done {
+ agent "Check renew" as client_lease
+}
+
+rectangle "Allocate a new lease" as new_lease {
+ together {
+  rectangle "Allocate or reuse lease" as allocateOrReuseLease4 {
+   agent "Get candidate lease" as candidate
+
+   agent "Reuse expired lease" as reuseExpiredLease4
+
+   agent "Reclaim expired lease" as reclaimExpiredLease
+
+   agent "update lease information" as updateLease4Information
+
+   agent "Callout lease4_select" as lease4_select
+   note right : hook
+
+   agent "Update lease" as updateLease4
+  }
+
+  rectangle "Allocate unreserved lease" as allocateUnreservedLease4 {
+   agent "Iterate pools and subnets" as iterate
+
+   agent "Pick address" as pick
+
+   agent "Check reserved addressed" as pick_reserved
+
+   agent "Check already in use by another thread" as mt_in_use
+
+   agent "Check lease" as pick_lease
+  }
+ }
+
+ agent "Create a new lease" as create
+
+ agent "Delete old lease" as old_lease
+}
+
+agent "Return no lease" as no_lease
+note right : exit point
+
+agent "Return renewed lease" as renew
+note right : exit point
+
+agent "Return lease" as return
+note right : exit point
+
+findClientLease --> addressReserved : has requested address (hint)
+findClientLease --> hasAddressReservation : no requested address (hint)
+addressReserved --> check_hint : no conflicting reservation
+addressReserved --> no_lease : reservation owned by another client
+hasAddressReservation -> update_hint : has a reservation
+update_hint --> check_hint : request reserved address
+hasAddressReservation --> check_done : no reservation
+check_hint --> get_existing
+get_existing --> existing : has requested lease
+existing ---> no_lease : not expired lease owned by another client
+get_existing --> out_of_pool : no reservation
+get_existing --> out_of_pool : has requested reservation
+get_existing --> getReservedLease : has reservation for another address
+getReservedLease ---> no_lease : no active reserved lease
+getReservedLease --> out_of_pool
+out_of_pool --> check_done : owned reservation for the requested address
+out_of_pool --> check_done : requested address is in allowed an pool
+out_of_pool --> no_lease : address not reserved and not in allowed pool
+check_done --> client_lease : has a client lease
+client_lease -> renew : requested address was already assigned to the client
+client_lease --> new_lease
+new_lease --> allocateOrReuseLease4 : has a requested address
+new_lease --> allocateUnreservedLease4 : no requested address
+allocateOrReuseLease4 --> candidate
+candidate --> reuseExpiredLease4 : expired candidate lease
+candidate --> no_lease : conflicting candidate lease
+candidate --> create : no candidate lease
+reuseExpiredLease4 --> reclaimExpiredLease
+reclaimExpiredLease --> updateLease4Information
+updateLease4Information --> lease4_select
+lease4_select ---> no_lease : SKIP
+lease4_select --> updateLease4
+updateLease4 --> old_lease
+allocateUnreservedLease4 --> iterate
+iterate --> pick
+pick --> pick_reserved
+pick_reserved -up-> iterate : address reserved to another client
+pick_reserved --> mt_in_use
+mt_in_use -up-> iterate : address already in use by another thread
+mt_in_use --> pick_lease
+pick_lease -up-> iterate : active lease
+pick_lease --> reuseExpiredLease4 : expired lease
+pick_lease --> create : no lease
+create --> old_lease
+old_lease --> return
+
+@enduml
diff --git a/doc/sphinx/uml/request4.png b/doc/sphinx/uml/request4.png
new file mode 100644
index 0000000..6818c2c
--- /dev/null
+++ b/doc/sphinx/uml/request4.png
diff --git a/doc/sphinx/uml/request4.svg b/doc/sphinx/uml/request4.svg
new file mode 100644
index 0000000..527f2ef
--- /dev/null
+++ b/doc/sphinx/uml/request4.svg
@@ -0,0 +1,107 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="1782px" preserveAspectRatio="none" style="width:740px;height:1782px;" version="1.1" viewBox="0 0 740 1782" width="740px" zoomAndPan="magnify"><defs><filter height="300%" id="f1ilk3q3nd6gdc" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="326" x="198" y="17.4023">DHCPREQUEST processing (Kea 1.8.0)</text><!--MD5=[638108c05bc1ef8eca3fbd57a1e57fe7]
+cluster ack--><rect fill="#FFFFFF" filter="url(#f1ilk3q3nd6gdc)" height="762.86" style="stroke: #000000; stroke-width: 1.5;" width="304" x="419" y="717.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="154" x="494" y="732.7344">A lease was assigned</text><!--MD5=[bf2e5648ffce4090541457b458b3eec7]
+entity setReservedClasses--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="163" x="449.5" y="806.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="143" x="459.5" y="829.5944">Add reserved classes</text><!--MD5=[b4c6d216ba631a143bfc1836b312cb78]
+entity requiredClassify--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="187" x="447.5" y="903.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="167" x="457.5" y="926.5944">Classify required classes</text><!--MD5=[f89e27cff326c32e9ba835d84fbfe859]
+entity buildCfgOptionList--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="206" x="455" y="1000.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="186" x="465" y="1023.5944">Build configured option list</text><!--MD5=[66aecdc5adcec4353637f7b7b5526ad2]
+entity appendRequestedOptions--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="203" x="464.5" y="1113.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="183" x="474.5" y="1136.5944">Append requested options</text><!--MD5=[c1e338234dc43680cac932baec853545]
+entity appendRequestedVendorOptions--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="255" x="443.5" y="1226.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="235" x="453.5" y="1249.5944">Append requested vendor options</text><!--MD5=[c9adb4adbcc3777a62f0437095b92421]
+entity appendBasicOptions--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="169" x="485.5" y="1323.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="149" x="495.5" y="1346.5944">Append basic options</text><!--MD5=[f001f897bdcc87f34b1f31db09c9e4bc]
+entity setFixedFields--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="121" x="508.5" y="1420.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="101" x="518.5" y="1443.5944">Set fixed fields</text><!--MD5=[e3476fda087b0512b1cf4e3a66ca5e59]
+entity entry--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="95" x="78.5" y="28.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="75" x="88.5" y="51.7344">Entry point</text><!--MD5=[a7ec37c34d1a4a150f9193e171f7b981]
+entity selectSubnet--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="111" x="70.5" y="125.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="91" x="80.5" y="148.7344">Select subnet</text><path d="M217,130.6992 L217,139.1992 L181.52,143.1992 L217,147.1992 L217,156.0098 A0,0 0 0 0 217,156.0098 L307,156.0098 A0,0 0 0 0 307,156.0098 L307,140.6992 L297,130.6992 L217,130.6992 A0,0 0 0 0 217,130.6992 " fill="#FBFB77" filter="url(#f1ilk3q3nd6gdc)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M297,130.6992 L297,140.6992 L307,140.6992 L297,130.6992 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="69" x="223" y="148.2676">hook point</text><!--MD5=[bd2ef8d619eb080c7e3a318a85d9bc74]
+entity findReservation--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="165" x="187.5" y="222.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="145" x="197.5" y="245.7344">Find host reservation</text><!--MD5=[2cdbe39ce7f7beceaf096677903e27aa]
+entity known--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="280" x="174" y="319.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="260" x="184" y="342.7344">Add either KNOWN or UNKNOWN class</text><!--MD5=[63b5186a9d9ded916d56a4c496be57e4]
+entity classify2--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="148" x="248" y="416.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="128" x="258" y="439.7344">Classify (2nd pass)</text><!--MD5=[40832264567e158d4eae9eb68a571da4]
+entity processClientName--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="155" x="248.5" y="513.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="135" x="258.5" y="536.7344">Process client name</text><!--MD5=[2a562006d844a2c20ab5026a88816353]
+entity assignLease--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="117" x="269.5" y="610.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="97" x="279.5" y="633.7344">Assign a lease</text><!--MD5=[8274bfb416b6365278739ca5c48d26ea]
+entity common--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="162" x="487" y="1535.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="142" x="497" y="1558.5944">Adjust interface data</text><!--MD5=[ca1312f187078c0b4317d510df91f0fb]
+entity appendServerID--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="138" x="499" y="1632.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="118" x="509" y="1655.5944">Append server ID</text><path d="M308,1637.5592 L308,1662.8698 A0,0 0 0 0 308,1662.8698 L464,1662.8698 A0,0 0 0 0 464,1662.8698 L464,1655.5592 L498.67,1650.0592 L464,1647.5592 L464,1647.5592 L454,1637.5592 L308,1637.5592 A0,0 0 0 0 308,1637.5592 " fill="#FBFB77" filter="url(#f1ilk3q3nd6gdc)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M454,1637.5592 L454,1647.5592 L464,1647.5592 L454,1637.5592 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="135" x="314" y="1655.1276">on success exit point</text><!--MD5=[c92710f32fe9c293a125fb7e80204a05]
+entity drop--><rect fill="#FEFECE" filter="url(#f1ilk3q3nd6gdc)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="155" x="177.5" y="1729.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="135" x="187.5" y="1752.5944">Return no response</text><path d="M6,1734.5592 L6,1759.8698 A0,0 0 0 0 6,1759.8698 L142,1759.8698 A0,0 0 0 0 142,1759.8698 L142,1752.5592 L177.47,1747.0592 L142,1744.5592 L142,1744.5592 L132,1734.5592 L6,1734.5592 A0,0 0 0 0 6,1734.5592 " fill="#FBFB77" filter="url(#f1ilk3q3nd6gdc)" style="stroke: #A80036; stroke-width: 1.0;"/><path d="M132,1734.5592 L132,1744.5592 L142,1744.5592 L132,1734.5592 " fill="#FBFB77" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="115" x="12" y="1752.1276">on error exit point</text><!--MD5=[f1b2710c384eb85faf81d18e639f63a6]
+link entry to selectSubnet--><path d="M126,64.6192 C126,80.1592 126,102.9792 126,119.8592 " fill="none" id="entry-&gt;selectSubnet" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="126,124.8892,130,115.8892,126,119.8892,122,115.8892,126,124.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[b2566f3d1f41175aa140f0cd50933407]
+link selectSubnet to findReservation--><path d="M152.08,161.3992 C176.75,177.6792 213.76,202.0992 239.73,219.2292 " fill="none" id="selectSubnet-&gt;findReservation" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="244.12,222.1192,238.8174,213.8197,239.9488,219.3622,234.4062,220.4936,244.12,222.1192" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[1a93233187986d890dbf5eee85d4aa4a]
+link selectSubnet to drop--><path d="M120.11,161.4792 C114.21,180.3392 106,211.5592 106,239.1992 C106,239.1992 106,239.1992 106,1651.0592 C106,1689.5192 141.74,1713.0992 178.21,1727.1392 " fill="none" id="selectSubnet-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="183.12,1728.9792,176.0975,1722.0738,178.4384,1727.2236,173.2885,1729.5644,183.12,1728.9792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="94" x="107" y="926.1276">hook set DROP</text><!--MD5=[ec2fdd3e226382e0a9d3911ff6fdaa1e]
+link findReservation to known--><path d="M278.07,258.6192 C285.33,274.2892 296.02,297.3792 303.85,314.2892 " fill="none" id="findReservation-&gt;known" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="305.98,318.8892,305.8344,309.0414,303.882,314.3507,298.5728,312.3982,305.98,318.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[9b534dc7ab92ef37bc4e582dc201fb22]
+link known to classify2--><path d="M315.47,355.6192 C316.78,371.1592 318.7,393.9792 320.12,410.8592 " fill="none" id="known-&gt;classify2" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="320.54,415.8892,323.781,406.5889,320.126,410.9064,315.8085,407.2514,320.54,415.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[96b9d5e38c2d93af2aa0f6088adcad57]
+link classify2 to processClientName--><path d="M322.73,452.6192 C323.39,468.1592 324.35,490.9792 325.06,507.8592 " fill="none" id="classify2-&gt;processClientName" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="325.27,512.8892,328.9071,503.7365,325.0702,507.8932,320.9135,504.0563,325.27,512.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[ad449cd118a7a2b2ce8548c9076b781b]
+link processClientName to assignLease--><path d="M326.37,549.6192 C326.69,565.1592 327.17,587.9792 327.53,604.8592 " fill="none" id="processClientName-&gt;assignLease" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="327.64,609.8892,331.4592,600.811,327.54,604.8902,323.4608,600.971,327.64,609.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[dbcae5b7ba85be5e06360ecde09c32a7]
+link assignLease to ack--><path d="M350.16,646.3192 C370.48,662.0192 401.2825,685.8217 427.3263,705.9467 C430.5817,708.4623 433.7628,710.9205 436.8398,713.2982 C438.3783,714.4871 439.8908,715.6558 441.3735,716.8015 " fill="none" id="assignLease-&gt;ack" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="441.3735,716.8015,436.6977,708.1333,437.4171,713.7443,431.8061,714.4636,441.3735,716.8015" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="62" x="407" y="689.7676">DHCPACK</text><!--MD5=[2f984fc865edd3cdda8891855a184a01]
+link assignLease to common--><path d="M328.48,646.2492 C329.08,668.5892 330,709.0092 330,743.5592 C330,743.5592 330,743.5592 330,1439.0592 C330,1508.3792 413.41,1535.2292 481.47,1545.5992 " fill="none" id="assignLease-&gt;common" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="486.76,1546.3692,478.4373,1541.103,481.8131,1545.6422,477.274,1549.018,486.76,1546.3692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="63" x="331" y="1079.6276">DHCPNAK</text><!--MD5=[1a01e4a77361624092d23c61082f06c9]
+link assignLease to drop--><path d="M308.05,646.4192 C286.44,667.0992 255,703.9892 255,743.5592 C255,743.5592 255,743.5592 255,1651.0592 C255,1675.9292 255,1704.4692 255,1723.7292 " fill="none" id="assignLease-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="255,1728.8992,259,1719.8992,255,1723.8992,251,1719.8992,255,1728.8992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="50" x="256" y="1192.6276">on error</text><!--MD5=[45361b0d0807638813b657d9c2aeacea]
+link ack to setReservedClasses--><path d="M476.04,745.1192 C477.12,746.6492 499.89,778.9392 515.78,801.4792 " fill="none" id="ack-&gt;setReservedClasses" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="518.86,805.8392,516.9576,796.1758,515.985,801.7484,510.4124,800.7758,518.86,805.8392" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[59a85614cff14ca40e3cee07aa3bbe30]
+link setReservedClasses to requiredClassify--><path d="M532.83,842.4792 C534.47,858.0192 536.87,880.8392 538.65,897.7192 " fill="none" id="setReservedClasses-&gt;requiredClassify" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="539.18,902.7492,542.206,893.3768,538.6514,897.7772,534.2509,894.2226,539.18,902.7492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[2efe0b9050a6d4600ee0e20f04479830]
+link requiredClassify to buildCfgOptionList--><path d="M544.12,939.4792 C546.9,955.0192 550.98,977.8392 554,994.7192 " fill="none" id="requiredClassify-&gt;buildCfgOptionList" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="554.9,999.7492,557.2671,990.1891,554.027,994.826,549.39,991.5859,554.9,999.7492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[7441c48dbaadb9becd02fb7c753a194c]
+link buildCfgOptionList to appendRequestedOptions--><path d="M559.25,1036.3992 C560.64,1055.6292 562.87,1086.6892 564.39,1107.7192 " fill="none" id="buildCfgOptionList-&gt;appendRequestedOptions" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="564.76,1112.8392,568.1067,1103.5764,564.4027,1107.852,560.1272,1104.148,564.76,1112.8392" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[47343daf35e3c3d46fb0ba57547a88fa]
+link appendRequestedOptions to appendRequestedVendorOptions--><path d="M566.78,1149.3992 C567.65,1168.6292 569.05,1199.6892 569.99,1220.7192 " fill="none" id="appendRequestedOptions-&gt;appendRequestedVendorOptions" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="570.22,1225.8392,573.8048,1216.6659,569.9917,1220.8444,565.8132,1217.0313,570.22,1225.8392" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[58b55c53e5f94649550176181093f5f5]
+link appendRequestedVendorOptions to appendBasicOptions--><path d="M570.82,1262.4792 C570.65,1278.0192 570.41,1300.8392 570.24,1317.7192 " fill="none" id="appendRequestedVendorOptions-&gt;appendBasicOptions" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="570.18,1322.7492,574.2572,1313.7839,570.223,1317.7494,566.2575,1313.7152,570.18,1322.7492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[7264f1f21cb707b81d802a97c78240a4]
+link appendBasicOptions to setFixedFields--><path d="M569.82,1359.4792 C569.65,1375.0192 569.41,1397.8392 569.24,1414.7192 " fill="none" id="appendBasicOptions-&gt;setFixedFields" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="569.18,1419.7492,573.2572,1410.7839,569.223,1414.7494,565.2575,1410.7152,569.18,1419.7492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[6bbcaa41c57dc9195ee921caca416269]
+link setFixedFields to common--><path d="M568.85,1456.2192 C568.67,1475.7992 568.39,1507.8892 568.2,1529.4892 " fill="none" id="setFixedFields-&gt;common" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="568.15,1534.7392,572.227,1525.7738,568.1929,1529.7394,564.2273,1525.7053,568.15,1534.7392" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[132fd8477c39c92905ed9637c759fac2]
+link common to appendServerID--><path d="M568,1571.4792 C568,1587.0192 568,1609.8392 568,1626.7192 " fill="none" id="common-&gt;appendServerID" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="568,1631.7492,572,1622.7492,568,1626.7492,564,1622.7492,568,1631.7492" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[c3fa6a6e0f86213585b749ab16a0c5af]
+link appendServerID to drop--><!--MD5=[4750f740a763649f6d3712e660b5e97b]
+@startuml
+
+title DHCPREQUEST processing (Kea 1.8.0)
+
+agent "Entry point" as entry
+
+agent "Select subnet" as selectSubnet
+note right : hook point
+
+agent "Find host reservation" as findReservation
+
+agent "Add either KNOWN or UNKNOWN class" as known
+
+agent "Classify (2nd pass)" as classify2
+
+agent "Process client name" as processClientName
+
+agent "Assign a lease" as assignLease
+
+rectangle "A lease was assigned" as ack {
+ agent "Add reserved classes" as setReservedClasses
+ agent "Classify required classes" as requiredClassify
+ agent "Build configured option list" as buildCfgOptionList
+ agent "Append requested options" as appendRequestedOptions
+ agent "Append requested vendor options" as appendRequestedVendorOptions
+ agent "Append basic options" as appendBasicOptions
+ agent "Set fixed fields" as setFixedFields
+}
+
+agent "Adjust interface data" as common
+
+agent "Append server ID" as appendServerID
+note left : on success exit point
+
+agent "Return no response" as drop
+note left : on error exit point
+
+entry - -> selectSubnet
+selectSubnet - -> findReservation
+selectSubnet - - -> drop : hook set DROP
+findReservation - -> known
+known - -> classify2
+classify2 - -> processClientName
+processClientName - -> assignLease
+assignLease - -> ack : DHCPACK
+assignLease - -> common : DHCPNAK
+assignLease - - -> drop : on error
+ack - -> setReservedClasses
+setReservedClasses - -> requiredClassify
+requiredClassify - -> buildCfgOptionList
+buildCfgOptionList - -> appendRequestedOptions
+appendRequestedOptions - -> appendRequestedVendorOptions
+appendRequestedVendorOptions - -> appendBasicOptions
+appendBasicOptions - -> setFixedFields
+setFixedFields - -> common
+common - -> appendServerID
+appendServerID -[hidden]-> drop
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/request4.uml b/doc/sphinx/uml/request4.uml
new file mode 100644
index 0000000..a5878b9
--- /dev/null
+++ b/doc/sphinx/uml/request4.uml
@@ -0,0 +1,59 @@
+@startuml
+
+title DHCPREQUEST processing (Kea 1.8.0)
+
+agent "Entry point" as entry
+
+agent "Select subnet" as selectSubnet
+note right : hook point
+
+agent "Find host reservation" as findReservation
+
+agent "Add either KNOWN or UNKNOWN class" as known
+
+agent "Classify (2nd pass)" as classify2
+
+agent "Process client name" as processClientName
+
+agent "Assign a lease" as assignLease
+
+rectangle "A lease was assigned" as ack {
+ agent "Add reserved classes" as setReservedClasses
+ agent "Classify required classes" as requiredClassify
+ agent "Build configured option list" as buildCfgOptionList
+ agent "Append requested options" as appendRequestedOptions
+ agent "Append requested vendor options" as appendRequestedVendorOptions
+ agent "Append basic options" as appendBasicOptions
+ agent "Set fixed fields" as setFixedFields
+}
+
+agent "Adjust interface data" as common
+
+agent "Append server ID" as appendServerID
+note left : on success exit point
+
+agent "Return no response" as drop
+note left : on error exit point
+
+entry --> selectSubnet
+selectSubnet --> findReservation
+selectSubnet ---> drop : hook set DROP
+findReservation --> known
+known --> classify2
+classify2 --> processClientName
+processClientName --> assignLease
+assignLease --> ack : DHCPACK
+assignLease --> common : DHCPNAK
+assignLease ---> drop : on error
+ack --> setReservedClasses
+setReservedClasses --> requiredClassify
+requiredClassify --> buildCfgOptionList
+buildCfgOptionList --> appendRequestedOptions
+appendRequestedOptions --> appendRequestedVendorOptions
+appendRequestedVendorOptions --> appendBasicOptions
+appendBasicOptions --> setFixedFields
+setFixedFields --> common
+common --> appendServerID
+appendServerID -[hidden]-> drop
+
+@enduml
\ No newline at end of file
diff --git a/doc/sphinx/uml/requestLease4.png b/doc/sphinx/uml/requestLease4.png
new file mode 100644
index 0000000..52ff01f
--- /dev/null
+++ b/doc/sphinx/uml/requestLease4.png
diff --git a/doc/sphinx/uml/requestLease4.svg b/doc/sphinx/uml/requestLease4.svg
new file mode 100644
index 0000000..800e77d
--- /dev/null
+++ b/doc/sphinx/uml/requestLease4.svg
@@ -0,0 +1,310 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="2560px" preserveAspectRatio="none" style="width:1579px;height:2560px;" version="1.1" viewBox="0 0 1579 2560" width="1579px" zoomAndPan="magnify"><defs><filter height="300%" id="f1aicqcofdeklm" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="316" x="630.5" y="27.4023">requestLease4 algorithm (Kea 1.8.0)</text><ellipse cx="631.3125" cy="41.1992" fill="#000000" filter="url(#f1aicqcofdeklm)" rx="10" ry="10" style="stroke: none; stroke-width: 1.0;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="148" x="557.3125" y="71.1992"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="128" x="567.3125" y="92.8008">get lease for the client</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="584.8125,125.332,677.8125,125.332,689.8125,137.332,677.8125,149.332,584.8125,149.332,572.8125,137.332,584.8125,125.332" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="93" x="584.8125" y="141.4893">reserved address</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="554.8125" y="135.0117">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="689.8125" y="135.0117">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="229,159.332,329,159.332,341,171.332,329,183.332,229,183.332,217,171.332,229,159.332" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="100" x="229" y="175.4893">requested address</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="203" y="169.0117">no</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="341" y="169.0117">yes</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="250" x="11" y="193.332"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="230" x="21" y="214.9336">requested address = reserved address</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="368.5" y="241.8096"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="378.5" y="263.4111">return no lease</text><ellipse cx="422" cy="321.9424" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="422" cy="321.9424" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="293,193.332,551,193.332,563,205.332,551,217.332,293,217.332,281,205.332,293,193.332" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="426" y="227.9668">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="258" x="293" y="209.4893">requested address is reserved for another client</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="563" y="203.0117">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="279,363.4199,291,375.4199,279,387.4199,267,375.4199,279,363.4199" style="stroke: #A80036; stroke-width: 1.5;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="225.5" y="519.375"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="235.5" y="540.9766">return no lease</text><ellipse cx="279" cy="599.5078" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="279" cy="599.5078" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="186.5,470.8975,371.5,470.8975,383.5,482.8975,371.5,494.8975,186.5,494.8975,174.5,482.8975,186.5,470.8975" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="283" y="505.5322">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="185" x="186.5" y="487.0547">active and owned by another client</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="383.5" y="480.5771">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="204.5,422.4199,353.5,422.4199,365.5,434.4199,353.5,446.4199,204.5,446.4199,192.5,434.4199,204.5,422.4199" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="283" y="457.0547">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="149" x="204.5" y="438.5771">lease for requested address</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="365.5" y="432.0996">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="279,665.4629,291,677.4629,279,689.4629,267,677.4629,279,665.4629" style="stroke: #A80036; stroke-width: 1.5;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="225.5" y="869.8955"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="235.5" y="891.4971">return no lease</text><ellipse cx="279" cy="950.0283" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="279" cy="950.0283" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="263.5,821.418,294.5,821.418,306.5,833.418,294.5,845.418,263.5,845.418,251.5,833.418,263.5,821.418" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="283" y="856.0527">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="31" x="263.5" y="837.5752">active</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="306.5" y="831.0977">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="204.5,772.9404,353.5,772.9404,365.5,784.9404,353.5,796.9404,204.5,796.9404,192.5,784.9404,204.5,772.9404" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="283" y="807.5752">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="149" x="204.5" y="789.0977">lease for requested address</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="365.5" y="782.6201">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="279,1015.9834,291,1027.9834,279,1039.9834,267,1027.9834,279,1015.9834" style="stroke: #A80036; stroke-width: 1.5;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="225.5" y="1123.4609"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="235.5" y="1145.0625">return no lease</text><ellipse cx="279" cy="1197.6045" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="279" cy="1197.6045" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="187.5,1074.9834,370.5,1074.9834,382.5,1086.9834,370.5,1098.9834,187.5,1098.9834,175.5,1086.9834,187.5,1074.9834" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="283" y="1109.6182">no</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="183" x="187.5" y="1091.1406">requested address in allowed pool</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="382.5" y="1084.6631">yes</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="170.5,724.4629,387.5,724.4629,399.5,736.4629,387.5,748.4629,170.5,748.4629,158.5,736.4629,170.5,724.4629" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="283" y="759.0977">no</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="217" x="170.5" y="740.6201">requested address == reserved address</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="399.5" y="734.1426">yes</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="279,1259.082,291,1271.082,279,1283.082,267,1271.082,279,1259.082" style="stroke: #A80036; stroke-width: 1.5;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="933.625,159.332,1033.625,159.332,1045.625,171.332,1033.625,183.332,933.625,183.332,921.625,171.332,933.625,159.332" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="100" x="933.625" y="175.4893">requested address</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="903.625" y="169.0117">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="1045.625" y="169.0117">no</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="702.5" y="241.8096"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="712.5" y="263.4111">return no lease</text><ellipse cx="756" cy="321.9424" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="756" cy="321.9424" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="627,193.332,885,193.332,897,205.332,885,217.332,627,217.332,615,205.332,627,193.332" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="760" y="227.9668">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="258" x="627" y="209.4893">requested address is reserved for another client</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="897" y="203.0117">no</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="702.5" y="489.375"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="712.5" y="510.9766">return no lease</text><ellipse cx="756" cy="569.5078" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="756" cy="569.5078" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="663.5,440.8975,848.5,440.8975,860.5,452.8975,848.5,464.8975,663.5,464.8975,651.5,452.8975,663.5,440.8975" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="760" y="475.5322">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="185" x="663.5" y="457.0547">active and owned by another client</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="860.5" y="450.5771">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="681.5,392.4199,830.5,392.4199,842.5,404.4199,830.5,416.4199,681.5,416.4199,669.5,404.4199,681.5,392.4199" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="760" y="427.0547">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="149" x="681.5" y="408.5771">lease for requested address</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="842.5" y="402.0996">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="756,635.4629,768,647.4629,756,659.4629,744,647.4629,756,635.4629" style="stroke: #A80036; stroke-width: 1.5;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="702.5" y="742.9404"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="712.5" y="764.542">return no lease</text><ellipse cx="756" cy="823.0732" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="756" cy="823.0732" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="664.5,694.4629,847.5,694.4629,859.5,706.4629,847.5,718.4629,664.5,718.4629,652.5,706.4629,664.5,694.4629" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="760" y="729.0977">no</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="183" x="664.5" y="710.6201">requested address in allowed pool</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="859.5" y="704.1426">yes</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="156" x="1133.25" y="289.8096"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="136" x="1143.25" y="311.4111">pick candidate address</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="1160.75,449.8975,1261.75,449.8975,1273.75,461.8975,1261.75,473.8975,1160.75,473.8975,1148.75,461.8975,1160.75,449.8975" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="101" x="1160.75" y="466.0547">lease for candidate</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="1134.75" y="459.5771">no</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="1273.75" y="459.5771">yes</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="182" x="993" y="483.8975"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="162" x="1003" y="505.499">create and return new lease</text><ellipse cx="1084" cy="564.0303" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="1084" cy="564.0303" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="145" x="1266" y="532.375"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="125" x="1276" y="553.9766">reclaim expired lease</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="164" x="1256.5" y="601.5078"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="144" x="1266.5" y="623.1094">update lease information</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="138" x="1269.5" y="670.6406"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="118" x="1279.5" y="692.2422">callout lease4_select</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="1302,739.7734,1375,739.7734,1387,751.7734,1375,763.7734,1302,763.7734,1290,751.7734,1302,739.7734" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="73" x="1302" y="755.9307">callout return</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="22" x="1268" y="749.4531">SKIP</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="57" x="1387" y="749.4531">CONTINUE</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="1215" y="773.7734"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="1225" y="795.375">return no lease</text><ellipse cx="1268.5" cy="853.9063" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="1268.5" cy="853.9063" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="95" x="1361" y="773.7734"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="75" x="1371" y="795.375">update lease</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="133" x="1342" y="842.9063"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="113" x="1352" y="864.5078">return reused lease</text><ellipse cx="1408.5" cy="923.0391" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="1408.5" cy="923.0391" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="1318,483.8975,1359,483.8975,1371,495.8975,1359,507.8975,1318,507.8975,1306,495.8975,1318,483.8975" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="1342.5" y="518.5322">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="41" x="1318" y="500.0547">expired</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="1371" y="493.5771">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="1115.25,401.4199,1307.25,401.4199,1319.25,413.4199,1307.25,425.4199,1115.25,425.4199,1103.25,413.4199,1115.25,401.4199" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="1215.25" y="436.0547">no</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="192" x="1115.25" y="417.5771">candidate is used by another thread</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="1319.25" y="411.0996">yes</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="1211.25,1000.9941,1223.25,1012.9941,1211.25,1024.9941,1199.25,1012.9941,1211.25,1000.9941" style="stroke: #A80036; stroke-width: 1.5;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="1106.25,352.9424,1316.25,352.9424,1328.25,364.9424,1316.25,376.9424,1106.25,376.9424,1094.25,364.9424,1106.25,352.9424" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="1215.25" y="387.5771">no</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="210" x="1106.25" y="369.0996">candidate is reserved for another client</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="1328.25" y="362.6221">yes</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="1211.25,1049.4717,1223.25,1061.4717,1211.25,1073.4717,1199.25,1061.4717,1211.25,1049.4717" style="stroke: #A80036; stroke-width: 1.5;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="1129.75,241.8096,1292.75,241.8096,1304.75,253.8096,1292.75,265.8096,1129.75,265.8096,1117.75,253.8096,1129.75,241.8096" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="163" x="1129.75" y="257.9668">iterate over pools and subnets</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="132" x="1145.25" y="1132.4717"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="112" x="1155.25" y="1154.0732">maximum attempts</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="1157.75" y="1195.6152"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="1167.75" y="1217.2168">return no lease</text><ellipse cx="1211.25" cy="1271.2705" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="1211.25" cy="1271.2705" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="1090.75,193.332,1331.75,193.332,1343.75,205.332,1331.75,217.332,1090.75,217.332,1078.75,205.332,1090.75,193.332" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="1215.25" y="227.9668">no</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="241" x="1090.75" y="209.4893">client lease and lease address in allowed pool</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="1343.75" y="203.0117">yes</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="983.625,1311.082,995.625,1323.082,983.625,1335.082,971.625,1323.082,983.625,1311.082" style="stroke: #A80036; stroke-width: 1.5;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="631.3125,1341.082,643.3125,1353.082,631.3125,1365.082,619.3125,1353.082,631.3125,1341.082" style="stroke: #A80036; stroke-width: 1.5;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="164" x="549.3125" y="1530.5146"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="144" x="559.3125" y="1552.1162">update lease information</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="145" x="558.8125" y="1633.125"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="125" x="568.8125" y="1654.7266">reclaim expired lease</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="585.8125,1584.6475,676.8125,1584.6475,688.8125,1596.6475,676.8125,1608.6475,585.8125,1608.6475,573.8125,1596.6475,585.8125,1584.6475" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="635.3125" y="1619.2822">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="91" x="585.8125" y="1600.8047">old lease expired</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="688.8125" y="1594.3271">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="631.3125,1687.2578,643.3125,1699.2578,631.3125,1711.2578,619.3125,1699.2578,631.3125,1687.2578" style="stroke: #A80036; stroke-width: 1.5;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="140" x="561.3125" y="1731.2578"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="120" x="571.3125" y="1752.8594">callout lease4_renew</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="594.8125,1785.3906,667.8125,1785.3906,679.8125,1797.3906,667.8125,1809.3906,594.8125,1809.3906,582.8125,1797.3906,594.8125,1785.3906" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="73" x="594.8125" y="1801.5479">callout return</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="22" x="560.8125" y="1795.0703">SKIP</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="57" x="679.8125" y="1795.0703">CONTINUE</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="145" x="468.3125" y="1819.3906"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="125" x="478.3125" y="1840.9922">return old client lease</text><ellipse cx="540.8125" cy="1884.5234" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="540.8125" cy="1884.5234" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="95" x="674.3125" y="1819.3906"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="75" x="684.3125" y="1840.9922">update lease</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="177" x="633.3125" y="1873.5234"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="157" x="643.3125" y="1895.125">return renewed client lease</text><ellipse cx="721.8125" cy="1938.6563" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="721.8125" cy="1938.6563" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="470.8125,1482.0371,791.8125,1482.0371,803.8125,1494.0371,791.8125,1506.0371,470.8125,1506.0371,458.8125,1494.0371,470.8125,1482.0371" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="635.3125" y="1516.6719">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="321" x="470.8125" y="1498.1943">has reserved address or client lease address in allowed pool</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="803.8125" y="1491.7168">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="449.3125,1433.5596,813.3125,1433.5596,825.3125,1445.5596,813.3125,1457.5596,449.3125,1457.5596,437.3125,1445.5596,449.3125,1433.5596" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="635.3125" y="1468.1943">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="364" x="449.3125" y="1449.7168">no requested address or requested address == client lease address</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="825.3125" y="1443.2393">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="631.3125,1991.6563,643.3125,2003.6563,631.3125,2015.6563,619.3125,2003.6563,631.3125,1991.6563" style="stroke: #A80036; stroke-width: 1.5;"/><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="601.8125,1385.082,660.8125,1385.082,672.8125,1397.082,660.8125,1409.082,601.8125,1409.082,589.8125,1397.082,601.8125,1385.082" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="635.3125" y="1419.7168">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="59" x="601.8125" y="1401.2393">client lease</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="672.8125" y="1394.7617">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="631.3125,2035.6563,643.3125,2047.6563,631.3125,2059.6563,619.3125,2047.6563,631.3125,2035.6563" style="stroke: #A80036; stroke-width: 1.5;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="206" x="528.3125" y="2079.6563"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="186" x="538.3125" y="2101.2578">get lease for requested address</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="589.3125,2133.7891,673.3125,2133.7891,685.3125,2145.7891,673.3125,2157.7891,589.3125,2157.7891,577.3125,2145.7891,589.3125,2133.7891" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="84" x="589.3125" y="2149.9463">requested lease</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="559.3125" y="2143.4688">yes</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="685.3125" y="2143.4688">no</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="425.3125,2167.7891,466.3125,2167.7891,478.3125,2179.7891,466.3125,2191.7891,425.3125,2191.7891,413.3125,2179.7891,425.3125,2167.7891" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="41" x="425.3125" y="2183.9463">expired</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="14" x="399.3125" y="2177.4688">no</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="18" x="478.3125" y="2177.4688">yes</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="288.8125" y="2201.7891"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="298.8125" y="2223.3906">return no lease</text><ellipse cx="342.3125" cy="2281.9219" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="342.3125" cy="2281.9219" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; stroke-width: 1.0;"/><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="145" x="476.8125" y="2201.7891"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="125" x="486.8125" y="2223.3906">reclaim expired lease</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="164" x="467.3125" y="2270.9219"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="144" x="477.3125" y="2292.5234">update lease information</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="138" x="480.3125" y="2325.0547"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="118" x="490.3125" y="2346.6563">callout lease4_select</text><polygon fill="#FEFECE" filter="url(#f1aicqcofdeklm)" points="512.8125,2379.1875,585.8125,2379.1875,597.8125,2391.1875,585.8125,2403.1875,512.8125,2403.1875,500.8125,2391.1875,512.8125,2379.1875" style="stroke: #A80036; stroke-width: 1.5;"/><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="73" x="512.8125" y="2395.3447">callout return</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="22" x="478.8125" y="2388.8672">SKIP</text><text fill="#000000" font-family="sans-serif" font-size="11" lengthAdjust="spacingAndGlyphs" textLength="57" x="597.8125" y="2388.8672">CONTINUE</text><rect fill="#FEFECE" filter="url(#f1aicqcofdeklm)" height="34.1328" rx="12.5" ry="12.5" style="stroke: #A80036; stroke-width: 1.5;" width="107" x="425.8125" y="2413.1875"/><text fill="#000000" font-family="sans-serif" font-size="12" lengthAdjust="spacingAndGlyphs" textLength="87" x="435.8125" y="2434.7891">return no lease</text><ellipse cx="479.3125" cy="2478.3203" fill="#FFFFFF" filter="url(#f1aicqcofdeklm)" rx="11" ry="11" style="stroke: #000000; stroke-width: 1.0;"/><ellipse cx="479.3125" cy="2478.3203" fill="#000000" rx="6" ry="6" style="stroke: #7F7F7F; 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stroke-width: 1.0;"/><!--MD5=[afafd38710d9a052946de087a4cad58a]
+@startuml
+
+title requestLease4 algorithm (Kea 1.8.0)
+
+start
+:get lease for the client;
+
+if (reserved address) then (yes)
+  if (requested address) then (no)
+    :requested address = reserved address;
+  else (yes)
+    if (requested address is reserved for another client) then (yes)
+      :return no lease;
+      stop
+    else (no)
+    endif
+  endif
+  if (lease for requested address) then (yes)
+    if (active and owned by another client) then (yes)
+      :return no lease;
+      stop
+    else (no)
+    endif
+  else (no)
+  endif
+  if (requested address == reserved address) then (no)
+    if (lease for requested address) then (yes)
+      if (active) then (yes)
+        :return no lease;
+        stop
+      else (no)
+      endif
+    else (no)
+    endif
+    if (requested address in allowed pool) then (no)
+      :return no lease;
+      stop
+    else (yes)
+    endif
+  else (yes)
+  endif
+
+else (no)
+
+  if (requested address) then (yes)
+    if (requested address is reserved for another client) then (yes)
+      :return no lease;
+      stop
+    else (no)
+    endif
+    if (lease for requested address) then (yes)
+      if (active and owned by another client) then (yes)
+        :return no lease;
+        stop
+      else (no)
+      endif
+    else (no)
+    endif
+    if (requested address in allowed pool) then (no)
+      :return no lease;
+      stop
+    else (yes)
+    endif
+  else (no)
+    if (client lease and lease address in allowed pool) then (no)
+      while (iterate over pools and subnets)
+        :pick candidate address;
+        if (candidate is reserved for another client) then (no)
+          if (candidate is used by another thread) then (no)
+            if (lease for candidate) then (no)
+              :create and return new lease;
+              stop
+            else (yes)
+              if (expired) then (yes)
+                :reclaim expired lease;
+                :update lease information;
+                :callout lease4_select;
+                if (callout return) then (SKIP)
+                  :return no lease;
+                  stop
+                else (CONTINUE)
+                  :update lease;
+                  :return reused lease;
+                  stop
+                endif
+              else (no)
+              endif
+            endif
+          else (yes)
+          endif
+        else (yes)
+        endif
+      endwhile
+      :maximum attempts;
+      :return no lease;
+      stop
+    else (yes)
+    endif
+  endif
+endif
+
+' after check
+if (client lease) then (yes)
+  if (no requested address or requested address == client lease address) then (yes)
+    if (has reserved address or client lease address in allowed pool) then (yes)
+      :update lease information;
+      if (old lease expired) then (yes)
+        :reclaim expired lease;
+      else (no)
+      endif
+      :callout lease4_renew;
+      if (callout return) then (SKIP)
+        :return old client lease;
+        stop
+      else (CONTINUE)
+        :update lease;
+        :return renewed client lease;
+        stop
+      endif
+    else (no)
+    endif
+  else (no)
+  endif
+else (no)
+endif
+
+:get lease for requested address;
+if (requested lease) then (yes)
+  if (expired) then (no)
+    :return no lease;
+    stop
+  else (yes)
+    :reclaim expired lease;
+    :update lease information;
+    :callout lease4_select;
+    if (callout return) then (SKIP)
+      :return no lease;
+      stop
+    else (CONTINUE)
+      :update lease;
+      :return reused lease;
+      stop
+    endif
+  endif
+else (no)
+ :create and return new lease;
+ stop
+endif
+
+@enduml
+
+@startuml
+
+title requestLease4 algorithm (Kea 1.8.0)
+
+start
+:get lease for the client;
+
+if (reserved address) then (yes)
+  if (requested address) then (no)
+    :requested address = reserved address;
+  else (yes)
+    if (requested address is reserved for another client) then (yes)
+      :return no lease;
+      stop
+    else (no)
+    endif
+  endif
+  if (lease for requested address) then (yes)
+    if (active and owned by another client) then (yes)
+      :return no lease;
+      stop
+    else (no)
+    endif
+  else (no)
+  endif
+  if (requested address == reserved address) then (no)
+    if (lease for requested address) then (yes)
+      if (active) then (yes)
+        :return no lease;
+        stop
+      else (no)
+      endif
+    else (no)
+    endif
+    if (requested address in allowed pool) then (no)
+      :return no lease;
+      stop
+    else (yes)
+    endif
+  else (yes)
+  endif
+
+else (no)
+
+  if (requested address) then (yes)
+    if (requested address is reserved for another client) then (yes)
+      :return no lease;
+      stop
+    else (no)
+    endif
+    if (lease for requested address) then (yes)
+      if (active and owned by another client) then (yes)
+        :return no lease;
+        stop
+      else (no)
+      endif
+    else (no)
+    endif
+    if (requested address in allowed pool) then (no)
+      :return no lease;
+      stop
+    else (yes)
+    endif
+  else (no)
+    if (client lease and lease address in allowed pool) then (no)
+      while (iterate over pools and subnets)
+        :pick candidate address;
+        if (candidate is reserved for another client) then (no)
+          if (candidate is used by another thread) then (no)
+            if (lease for candidate) then (no)
+              :create and return new lease;
+              stop
+            else (yes)
+              if (expired) then (yes)
+                :reclaim expired lease;
+                :update lease information;
+                :callout lease4_select;
+                if (callout return) then (SKIP)
+                  :return no lease;
+                  stop
+                else (CONTINUE)
+                  :update lease;
+                  :return reused lease;
+                  stop
+                endif
+              else (no)
+              endif
+            endif
+          else (yes)
+          endif
+        else (yes)
+        endif
+      endwhile
+      :maximum attempts;
+      :return no lease;
+      stop
+    else (yes)
+    endif
+  endif
+endif
+
+if (client lease) then (yes)
+  if (no requested address or requested address == client lease address) then (yes)
+    if (has reserved address or client lease address in allowed pool) then (yes)
+      :update lease information;
+      if (old lease expired) then (yes)
+        :reclaim expired lease;
+      else (no)
+      endif
+      :callout lease4_renew;
+      if (callout return) then (SKIP)
+        :return old client lease;
+        stop
+      else (CONTINUE)
+        :update lease;
+        :return renewed client lease;
+        stop
+      endif
+    else (no)
+    endif
+  else (no)
+  endif
+else (no)
+endif
+
+:get lease for requested address;
+if (requested lease) then (yes)
+  if (expired) then (no)
+    :return no lease;
+    stop
+  else (yes)
+    :reclaim expired lease;
+    :update lease information;
+    :callout lease4_select;
+    if (callout return) then (SKIP)
+      :return no lease;
+      stop
+    else (CONTINUE)
+      :update lease;
+      :return reused lease;
+      stop
+    endif
+  endif
+else (no)
+ :create and return new lease;
+ stop
+endif
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/requestLease4.uml b/doc/sphinx/uml/requestLease4.uml
new file mode 100644
index 0000000..4cb55b5
--- /dev/null
+++ b/doc/sphinx/uml/requestLease4.uml
@@ -0,0 +1,150 @@
+@startuml
+
+title requestLease4 algorithm (Kea 1.8.0)
+
+start
+:get lease for the client;
+
+if (reserved address) then (yes)
+  if (requested address) then (no)
+    :requested address = reserved address;
+  else (yes)
+    if (requested address is reserved for another client) then (yes)
+      :return no lease;
+      stop
+    else (no)
+    endif
+  endif
+  if (lease for requested address) then (yes)
+    if (active and owned by another client) then (yes)
+      :return no lease;
+      stop
+    else (no)
+    endif
+  else (no)
+  endif
+  if (requested address == reserved address) then (no)
+    if (lease for requested address) then (yes)
+      if (active) then (yes)
+        :return no lease;
+        stop
+      else (no)
+      endif
+    else (no)
+    endif
+    if (requested address in allowed pool) then (no)
+      :return no lease;
+      stop
+    else (yes)
+    endif
+  else (yes)
+  endif
+
+else (no)
+
+  if (requested address) then (yes)
+    if (requested address is reserved for another client) then (yes)
+      :return no lease;
+      stop
+    else (no)
+    endif
+    if (lease for requested address) then (yes)
+      if (active and owned by another client) then (yes)
+        :return no lease;
+        stop
+      else (no)
+      endif
+    else (no)
+    endif
+    if (requested address in allowed pool) then (no)
+      :return no lease;
+      stop
+    else (yes)
+    endif
+  else (no)
+    if (client lease and lease address in allowed pool) then (no)
+      while (iterate over pools and subnets)
+        :pick candidate address;
+        if (candidate is reserved for another client) then (no)
+          if (candidate is used by another thread) then (no)
+            if (lease for candidate) then (no)
+              :create and return new lease;
+              stop
+            else (yes)
+              if (expired) then (yes)
+                :reclaim expired lease;
+                :update lease information;
+                :callout lease4_select;
+                if (callout return) then (SKIP)
+                  :return no lease;
+                  stop
+                else (CONTINUE)
+                  :update lease;
+                  :return reused lease;
+                  stop
+                endif
+              else (no)
+              endif
+            endif
+          else (yes)
+          endif
+        else (yes)
+        endif
+      endwhile
+      :maximum attempts;
+      :return no lease;
+      stop
+    else (yes)
+    endif
+  endif
+endif
+
+' after check
+if (client lease) then (yes)
+  if (no requested address or requested address == client lease address) then (yes)
+    if (has reserved address or client lease address in allowed pool) then (yes)
+      :update lease information;
+      if (old lease expired) then (yes)
+        :reclaim expired lease;
+      else (no)
+      endif
+      :callout lease4_renew;
+      if (callout return) then (SKIP)
+        :return old client lease;
+        stop
+      else (CONTINUE)
+        :update lease;
+        :return renewed client lease;
+        stop
+      endif
+    else (no)
+    endif
+  else (no)
+  endif
+else (no)
+endif
+
+:get lease for requested address;
+if (requested lease) then (yes)
+  if (expired) then (no)
+    :return no lease;
+    stop
+  else (yes)
+    :reclaim expired lease;
+    :update lease information;
+    :callout lease4_select;
+    if (callout return) then (SKIP)
+      :return no lease;
+      stop
+    else (CONTINUE)
+      :update lease;
+      :return reused lease;
+      stop
+    endif
+  endif
+else (no)
+ :create and return new lease;
+ stop
+endif
+
+@enduml
diff --git a/doc/sphinx/uml/select4.png b/doc/sphinx/uml/select4.png
new file mode 100644
index 0000000..a89f54c
--- /dev/null
+++ b/doc/sphinx/uml/select4.png
diff --git a/doc/sphinx/uml/select4.svg b/doc/sphinx/uml/select4.svg
new file mode 100644
index 0000000..a2b5ed6
--- /dev/null
+++ b/doc/sphinx/uml/select4.svg
@@ -0,0 +1,157 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="2210px" preserveAspectRatio="none" style="width:1468px;height:2210px;" version="1.1" viewBox="0 0 1468 2210" width="1468px" zoomAndPan="magnify"><defs><filter height="300%" id="f5nw3f4rb2pkr" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacingAndGlyphs" textLength="317" x="566.5" y="17.4023">DHCPv4 subnet selection (Kea 1.8.0)</text><!--MD5=[73860abe08ab23c9b8e49eb23f18ae46]
+cluster relayed--><rect fill="#FFFFFF" filter="url(#f5nw3f4rb2pkr)" height="374.86" style="stroke: #000000; stroke-width: 1.5;" width="445" x="7" y="329.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="56" x="201.5" y="344.7344">Relayed</text><!--MD5=[234613e222536af9475ae40e3492b0e6]
+cluster set_address--><rect fill="#FFFFFF" filter="url(#f5nw3f4rb2pkr)" height="164.86" style="stroke: #000000; stroke-width: 1.5;" width="803" x="227" y="769.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="164" x="546.5" y="784.5944">Set address for lookup</text><!--MD5=[a59c1d05a8f6fb54290705d41e67acbe]
+cluster interface--><rect fill="#FFFFFF" filter="url(#f5nw3f4rb2pkr)" height="488" style="stroke: #000000; stroke-width: 1.5;" width="395" x="945" y="990.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="164" x="1060.5" y="1006.4544">Try incoming interface</text><!--MD5=[8f3f5adf9176dbd9c419c05d483ab0c6]
+cluster address--><rect fill="#FFFFFF" filter="url(#f5nw3f4rb2pkr)" height="294" style="stroke: #000000; stroke-width: 1.5;" width="190" x="745" y="1527.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" font-weight="bold" lengthAdjust="spacingAndGlyphs" textLength="85" x="797.5" y="1543.4544">Try address</text><!--MD5=[aeb2f621969028d4547d386ac1a1ba6d]
+entity relay_subnet--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="226" x="172" y="418.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="206" x="182" y="441.5944">Relay address matches subnet</text><!--MD5=[bf459b32eaaf498e62edf6d622ac5891]
+entity relay_network--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="286" x="142" y="531.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="266" x="152" y="554.5944">Relay address matches shared network</text><!--MD5=[076bfff500cab59e856b606fdf63ed5a]
+entity relay_class--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="140" x="112" y="644.0592"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="120" x="122" y="667.5944">Check client class</text><!--MD5=[467e96f12fdeb7da53b220e72b6eb1fc]
+entity relay_address--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="136" x="251" y="873.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="116" x="261" y="897.4544">Set relay address</text><!--MD5=[a0e4201c97a623c3dfa593fb75aad03b]
+entity client_address--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="140" x="553" y="873.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="120" x="563" y="897.4544">Set client address</text><!--MD5=[a2d7389029b0dd04029e629f1661a883]
+entity source_address--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="149" x="856.5" y="873.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="129" x="866.5" y="897.4544">Set source address</text><!--MD5=[8eaa1e77cbee43fcac8de4e493864e04]
+entity interface_subnet--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="192" x="997" y="1025.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="172" x="1007" y="1049.4544">Interface matches subnet</text><!--MD5=[44eac5a65cc5cd7e6cc1fc4b89b09f4d]
+entity interface_network--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="252" x="1072" y="1138.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="232" x="1082" y="1162.4544">Interface matches shared network</text><!--MD5=[8e51806cb27b2b60db022c6084a961c9]
+entity interface_class--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="140" x="1022" y="1251.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="120" x="1032" y="1275.4544">Check client class</text><!--MD5=[953883d00ea10db133fca33539954fed]
+entity interface_address--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="163" x="961.5" y="1426.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="143" x="971.5" y="1450.4544">Set interface address</text><!--MD5=[132ec46735878e55c0250b14c07769ad]
+entity inRange--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="158" x="761" y="1562.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="138" x="771" y="1586.4544">Check subnet prefix</text><!--MD5=[a34f95003b379bc2f5b7f1af307bcb98]
+entity address_class--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="140" x="779" y="1769.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="120" x="789" y="1793.4544">Check client class</text><!--MD5=[e3476fda087b0512b1cf4e3a66ca5e59]
+entity entry--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="95" x="350.5" y="28.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="75" x="360.5" y="51.7344">Entry point</text><!--MD5=[a23c6b9dab1f8744947aaee2891e743e]
+entity rai_link_select--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="141" x="327.5" y="125.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="121" x="337.5" y="148.7344">Try RAI link select</text><!--MD5=[6d8910fd8533ab76ffd986c0d960248c]
+entity subnet_select--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="207" x="294.5" y="222.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="187" x="304.5" y="245.7344">Try subnet selection option</text><!--MD5=[6348f6d706001cc5dc6ed638bec44faf]
+entity found--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="127" x="708.5" y="1946.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="107" x="718.5" y="1970.4544">Found a subnet</text><!--MD5=[7dc9e356e22f2f113ceeb6da807ce9ff]
+entity not_found--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="137" x="870.5" y="1946.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="117" x="880.5" y="1970.4544">Found no subnet</text><!--MD5=[4a9142d0fee9ff77eb50a001ac7877e7]
+entity subnet4_select--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="175" x="767.5" y="2043.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="155" x="777.5" y="2067.4544">Callout subnet4_select</text><!--MD5=[d0fdc5cb89e99cab1ccfec009231794d]
+entity success--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="129" x="584.5" y="2156.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="109" x="594.5" y="2180.4544">Return a subnet</text><!--MD5=[d0255a03afa46a62fe0c456dae837167]
+entity no_subnet--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="139" x="785.5" y="2156.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="119" x="795.5" y="2180.4544">Return no subnet</text><!--MD5=[c92710f32fe9c293a125fb7e80204a05]
+entity drop--><rect fill="#FEFECE" filter="url(#f5nw3f4rb2pkr)" height="36.4883" style="stroke: #A80036; stroke-width: 1.5;" width="97" x="986.5" y="2156.9192"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacingAndGlyphs" textLength="77" x="996.5" y="2180.4544">Drop query</text><!--MD5=[732ffb0ffbc5cdc82abf95e46b9c6dc7]
+link entry to rai_link_select--><path d="M398,64.6192 C398,80.1592 398,102.9792 398,119.8592 " fill="none" id="entry-&gt;rai_link_select" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="398,124.8892,402,115.8892,398,119.8892,394,115.8892,398,124.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[f0b6d7b08c058a6efc1e3a3886382c22]
+link rai_link_select to subnet_select--><path d="M398,161.6192 C398,177.1592 398,199.9792 398,216.8592 " fill="none" id="rai_link_select-&gt;subnet_select" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="398,221.8892,402,212.8892,398,216.8892,394,212.8892,398,221.8892" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[2989df9457f995d9ec76378f9e46e3a6]
+link subnet_select to relayed--><path d="M389.65,258.5692 C382.075,274.3142 370.655,298.0567 361.01,318.1092 C359.8044,320.6158 358.6265,323.0647 357.4873,325.4331 C356.9177,326.6173 356.3578,327.7814 355.8089,328.9225 " fill="none" id="subnet_select-&gt;relayed" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="355.8089,328.9225,363.3147,322.5458,357.9762,324.4167,356.1053,319.0781,355.8089,328.9225" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="45" x="374" y="301.7676">relayed</text><!--MD5=[19a01d6111b1c934e32249a327a2afa6]
+link subnet_select to set_address--><path d="M433.44,258.3692 C466.58,277.1792 511,310.7592 511,355.5592 C511,355.5592 511,355.5592 511,663.0592 C511,711.2292 468.365,744.0467 425.0638,764.9542 C422.3574,766.2609 419.6485,767.5211 416.9472,768.7356 " fill="none" id="subnet_select-&gt;set_address" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="416.9472,768.7356,426.796,768.6933,421.5075,766.6853,423.5155,761.3968,416.9472,768.7356" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="70" x="512" y="497.6276">not relayed</text><!--MD5=[289599dfcd7d1f32272e42cc3c26c895]
+link relayed to relay_subnet--><path d="M342.96,357.1192 C341.81,358.6492 317.61,391.2092 300.84,413.7592 " fill="none" id="relayed-&gt;relay_subnet" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="297.8,417.8392,306.3807,413.0049,300.784,413.8273,299.9616,408.2305,297.8,417.8392" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[65c9b407d2d4ddf1b89c397faeac317e]
+link relay_subnet to relay_network--><path d="M285,454.3992 C285,473.6292 285,504.6892 285,525.7192 " fill="none" id="relay_subnet-&gt;relay_network" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="285,530.8392,289,521.8392,285,525.8392,281,521.8392,285,530.8392" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="59" x="286" y="497.6276">no match</text><!--MD5=[918f6d4a891df42092f9be64f359f985]
+link relay_subnet to relay_class--><path d="M199.58,454.0892 C156.79,467.3892 108.74,490.6992 83,531.0592 C56.99,571.8592 109.58,615.9992 147.59,640.9192 " fill="none" id="relay_subnet-&gt;relay_class" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="152.15,643.8592,146.7424,635.6277,147.9441,641.1554,142.4164,642.3571,152.15,643.8592" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="39" x="84" y="554.1276">match</text><!--MD5=[ec56da742308e5dcfe86ad0421278606]
+link relay_network to set_address--><path d="M288.52,567.3092 C294.12,594.7992 305.4675,650.4892 315.5475,699.9592 C320.5875,724.6942 325.3106,747.8742 328.84,765.1967 C329.0606,766.2794 329.2765,767.3392 329.4876,768.375 " fill="none" id="relay_network-&gt;set_address" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="329.4876,768.375,331.6103,758.7576,328.4893,763.4756,323.7713,760.3547,329.4876,768.375" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="59" x="319" y="667.1276">no match</text><!--MD5=[a30462b61ddf59585f12c8e1078496e0]
+link relay_network to relay_class--><path d="M268.91,567.3992 C250.69,587.0392 221.02,619.0092 201.5,640.0392 " fill="none" id="relay_network-&gt;relay_class" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="197.98,643.8392,207.0376,639.9713,201.3844,640.1773,201.1785,634.5242,197.98,643.8392" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="39" x="241" y="610.6276">match</text><!--MD5=[44feab40ce9c0df31465bdb13adac7ed]
+link relay_class to found--><path d="M177.97,680.0792 C172.39,705.1692 163,753.6292 163,795.4192 C163,795.4192 163,795.4192 163,1878.4192 C163,1932.4492 543.78,1954.4892 703.15,1961.3492 " fill="none" id="relay_class-&gt;found" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="708.26,1961.5692,699.4395,1957.1875,703.2646,1961.3551,699.097,1965.1802,708.26,1961.5692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="70" x="164" y="1362.4876">compatible</text><!--MD5=[d5e1893c7bc3c7589901f4b78d6439f0]
+link relay_class to set_address--><path d="M185.6,680.2592 C190.22,698.4992 199.91,727.0992 218,745.0592 C222.9438,749.9667 228.4423,754.4291 234.2844,758.4815 C237.2054,760.5077 240.2123,762.4314 243.2786,764.2571 C244.8117,765.1699 246.3597,766.0582 247.9193,766.9226 C248.6991,767.3547 249.4818,767.7809 250.2669,768.2012 C250.6595,768.4113 251.0527,768.6199 251.4464,768.8271 " fill="none" id="relay_class-&gt;set_address" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="251.4464,768.8271,245.3441,761.0965,247.0215,766.499,241.6191,768.1764,251.4464,768.8271" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="95" x="219" y="741.6276">not compatible</text><!--MD5=[3f679d64a1cccee12b0e824b1733c0ed]
+link set_address to relay_address--><path d="M334.99,796.9892 C334.66,798.9192 327.44,841.3492 322.81,868.5092 " fill="none" id="set_address-&gt;relay_address" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="321.93,873.7292,327.3899,865.5323,322.7728,868.8008,319.5043,864.1837,321.93,873.7292" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="135" x="330" y="840.4876">try the relay address</text><!--MD5=[9d0435cdb5bba0d446c223c46240db6f]
+link relay_address to client_address--><path d="M387.22,891.9192 C434.95,891.9192 498.7,891.9192 547.88,891.9192 " fill="none" id="relay_address-&gt;client_address" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="552.9,891.9192,543.9,887.9192,547.9,891.9192,543.9,895.9192,552.9,891.9192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="129" x="405.5" y="885.4876">has no relay address</text><!--MD5=[4192df04ddbb3f1e00a57ee174f51cdb]
+link client_address to source_address--><path d="M693.28,891.9192 C740.3,891.9192 802.28,891.9192 851.17,891.9192 " fill="none" id="client_address-&gt;source_address" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="856.46,891.9192,847.46,887.9192,851.46,891.9192,847.46,895.9192,856.46,891.9192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="127" x="711.25" y="885.4876">has no client address</text><!--MD5=[1cd4e848379fc555ffa76a6d3111f3fb]
+link source_address to interface_subnet--><path d="M949.58,910.1292 C979.61,937.9292 1038.68,992.6192 1070.85,1022.4092 " fill="none" id="source_address-&gt;interface_subnet" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1074.63,1025.9092,1070.7255,1016.8674,1070.9543,1022.5196,1065.3021,1022.7484,1074.63,1025.9092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="123" x="1017" y="971.4876">no suitable address</text><!--MD5=[a29ca77fdc41863d51ecafa8e32dcb85]
+link relay_address to inRange--><path d="M319,910.0192 C319,937.8592 319,994.7392 319,1042.9192 C319,1042.9192 319,1042.9192 319,1445.9192 C319,1534.9892 608.22,1565.7192 755.69,1575.5992 " fill="none" id="relay_address-&gt;inRange" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="760.87,1575.9392,752.1525,1571.356,755.8808,1575.6104,751.6264,1579.3387,760.87,1575.9392" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="120" x="320" y="1274.9876">has a relay address</text><!--MD5=[bf38c5431748c4414750c7275409615d]
+link client_address to inRange--><path d="M598.14,910.0992 C565.15,935.1492 511,985.0692 511,1042.9192 C511,1042.9192 511,1042.9192 511,1445.9192 C511,1498.7592 658.41,1540.8992 755.88,1562.9892 " fill="none" id="client_address-&gt;inRange" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="760.78,1564.0892,752.8657,1558.2272,755.8997,1563.0015,751.1254,1566.0356,760.78,1564.0892" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="125" x="512" y="1274.9876">has a client address</text><!--MD5=[306377b471c1f30003804df3ba3e4280]
+link source_address to inRange--><path d="M856.74,909.9992 C791.87,929.8492 708,969.6692 708,1042.9192 C708,1042.9192 708,1042.9192 708,1445.9192 C708,1498.6392 760.49,1538.1592 799.27,1560.1592 " fill="none" id="source_address-&gt;inRange" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="803.93,1562.7492,798.0248,1554.8671,799.5653,1560.3101,794.1222,1561.8506,803.93,1562.7492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="219" x="709" y="1274.9876">has source address and use unicast</text><!--MD5=[4c5f9760336ab58778079bb174cbf5f0]
+link interface_subnet to not_found--><path d="M1183.41,1061.9192 C1267.54,1080.3992 1380,1113.1092 1380,1155.9192 C1380,1155.9192 1380,1155.9192 1380,1878.4192 C1380,1952.2692 1138.67,1963.6392 1013.06,1964.5692 " fill="none" id="interface_subnet-&gt;not_found" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1007.91,1964.5992,1016.9327,1968.5477,1012.9099,1964.5706,1016.887,1960.5479,1007.91,1964.5992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="75" x="1381" y="1508.4876">no interface</text><!--MD5=[f6d146b568a537518d52dd0109d2cafd]
+link interface_subnet to interface_class--><path d="M1071.84,1062.1092 C1052.58,1079.2392 1025.46,1107.4692 1014,1138.9192 C998.88,1180.3992 1037.07,1223.3392 1065.19,1248.0092 " fill="none" id="interface_subnet-&gt;interface_class" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1069.26,1251.5192,1065.0657,1242.6081,1065.4768,1248.25,1059.835,1248.6612,1069.26,1251.5192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="39" x="1015" y="1161.9876">match</text><!--MD5=[8c73b6f253b7f8003f1aeec9d3e2c401]
+link interface_subnet to interface_network--><path d="M1109.41,1062.2592 C1127.98,1081.8992 1158.22,1113.8692 1178.12,1134.8992 " fill="none" id="interface_subnet-&gt;interface_network" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1181.71,1138.6992,1178.417,1129.4172,1178.2685,1135.0721,1172.6136,1134.9236,1181.71,1138.6992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="59" x="1152" y="1105.4876">no match</text><!--MD5=[8a490629b42afa0a067bde343f0409be]
+link interface_network to interface_class--><path d="M1181.44,1175.2592 C1162.69,1194.8992 1132.15,1226.8692 1112.07,1247.8992 " fill="none" id="interface_network-&gt;interface_class" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1108.45,1251.6992,1117.5542,1247.9424,1111.899,1248.0792,1111.7622,1242.424,1108.45,1251.6992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="39" x="1152" y="1218.4876">march</text><!--MD5=[e1288d340d0c431aabe10a4c239c74f7]
+link interface_network to not_found--><path d="M1216.94,1175.1492 C1237.06,1195.4392 1266,1231.1792 1266,1268.9192 C1266,1268.9192 1266,1268.9192 1266,1878.4192 C1266,1930.4492 1109.1,1951.4192 1012.67,1959.3992 " fill="none" id="interface_network-&gt;not_found" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1007.55,1959.8192,1016.8511,1963.058,1012.5327,1959.404,1016.1867,1955.0856,1007.55,1959.8192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="59" x="1267" y="1585.9876">no match</text><!--MD5=[9d13a96273b9c1dbfb8a7fbd997b0088]
+link interface_class to found--><path d="M1111.94,1288.2092 C1127.1,1302.7092 1146.84,1324.8592 1156,1348.9192 C1203,1472.3792 1160.06,1514.0492 1168,1645.9192 C1169,1662.6092 1171,1666.6992 1171,1683.4192 C1171,1683.4192 1171,1683.4192 1171,1878.4192 C1171,1879.4592 954.79,1925.2992 840.68,1949.4192 " fill="none" id="interface_class-&gt;found" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="835.66,1950.4792,845.2955,1952.5181,840.5505,1949.4384,843.6302,1944.6934,835.66,1950.4792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="70" x="1169" y="1642.4876">compatible</text><!--MD5=[d4a81a9eb6ae9754c2f91708a00f90ba]
+link interface_class to interface_address--><path d="M1081.97,1287.9492 C1073.39,1303.3492 1061.43,1326.9092 1055,1348.9192 C1047.93,1373.1292 1045.02,1402.0192 1043.83,1421.5292 " fill="none" id="interface_class-&gt;interface_address" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1043.54,1426.7692,1048.0484,1418.0128,1043.8261,1421.7774,1040.0615,1417.5551,1043.54,1426.7692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="95" x="1056" y="1362.4876">not compatible</text><!--MD5=[18f0036984a219b8e279d39e6955cbb3]
+link interface_address to inRange--><path d="M961.24,1454.9892 C910.72,1462.4692 852.64,1475.1192 837,1494.9192 C823.19,1512.3892 826.7,1538.7792 831.91,1557.5092 " fill="none" id="interface_address-&gt;inRange" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="833.41,1562.5792,834.6953,1552.8146,831.993,1557.7842,827.0233,1555.0818,833.41,1562.5792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="153" x="838" y="1508.4876">has an interface address</text><!--MD5=[1be935c2e674a39bb491f742257146af]
+link interface_address to not_found--><path d="M1037.7,1463.0692 C1030.36,1488.3792 1018,1537.3192 1018,1579.9192 C1018,1579.9192 1018,1579.9192 1018,1878.4192 C1018,1906.2692 995.11,1928.9092 973.97,1943.8892 " fill="none" id="interface_address-&gt;not_found" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="969.77,1946.7792,979.4482,1944.9538,973.8835,1943.9369,974.9005,1938.3722,969.77,1946.7792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="128" x="1019" y="1736.4876">no interface address</text><!--MD5=[65c872516cd5acbef394f498ee60e6f6]
+link inRange to address_class--><path d="M840.75,1599.0492 C842.38,1636.0492 846.21,1723.4492 848.02,1764.6692 " fill="none" id="inRange-&gt;address_class" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="848.24,1769.6992,851.8498,1760.5358,848.0253,1764.7038,843.8572,1760.8793,848.24,1769.6992" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="39" x="845" y="1689.4876">match</text><!--MD5=[c6a81dd9b5c38fb7a31992aeb43efba5]
+link inRange to not_found--><path d="M768.39,1598.9792 C726.98,1613.5792 683,1639.4392 683,1683.4192 C683,1683.4192 683,1683.4192 683,1878.4192 C683,1897.7892 789.82,1927.8092 865.46,1946.6392 " fill="none" id="inRange-&gt;not_found" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="870.4,1947.8692,862.6221,1941.8274,865.5459,1946.67,860.7033,1949.5938,870.4,1947.8692" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="59" x="684" y="1792.9876">no match</text><!--MD5=[6bbdb059bb8431be14feb2edf9179bcc]
+link address_class to found--><path d="M815.7,1805.9392 C765.48,1832.3692 674.36,1883.6192 657,1915.9192 C644.07,1939.9792 671.86,1951.9792 703.35,1957.9692 " fill="none" id="address_class-&gt;found" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="708.43,1958.8792,700.2794,1953.3504,703.5088,1957.9948,698.8644,1961.2243,708.43,1958.8792" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="70" x="708" y="1882.4876">compatible</text><!--MD5=[6fa859304e08ed6b1a2f69b396a973f6]
+link address_class to not_found--><path d="M856.62,1805.9192 C865.47,1825.4292 880.68,1858.2892 895,1885.9192 C904.99,1905.1792 917.16,1926.6292 926.17,1942.1492 " fill="none" id="address_class-&gt;not_found" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="928.86,1946.7592,927.7843,1936.9693,926.3424,1942.4393,920.8724,1940.9974,928.86,1946.7592" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="95" x="896" y="1882.4876">not compatible</text><!--MD5=[920af236d2bfe8ac015294b6ec32c751]
+link found to subnet4_select--><path d="M787.22,1983.3392 C801.03,1999.1492 821.43,2022.4892 836.24,2039.4392 " fill="none" id="found-&gt;subnet4_select" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="839.87,2043.6092,836.9563,2034.2012,836.5785,2039.8454,830.9343,2039.4676,839.87,2043.6092" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[be5a985c5094547d1aa8a3dfda06631d]
+link not_found to subnet4_select--><path d="M923.59,1983.3392 C909.62,1999.1492 888.98,2022.4892 873.99,2039.4392 " fill="none" id="not_found-&gt;subnet4_select" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="870.31,2043.6092,879.2712,2039.523,873.6247,2039.8659,873.2818,2034.2194,870.31,2043.6092" style="stroke: #A80036; stroke-width: 1.0;"/><!--MD5=[085d72d70044aeb14e8d963046e88b11]
+link found to not_found--><!--MD5=[d0da1e00427a0ca7837196c7dddb3af4]
+link subnet4_select to success--><path d="M767.05,2070.2692 C735.7,2076.7092 702,2088.4992 677,2109.9192 C664.53,2120.5992 657.42,2137.8792 653.49,2151.7992 " fill="none" id="subnet4_select-&gt;success" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="652.18,2156.7492,658.3343,2149.0599,653.4497,2151.9131,650.5965,2147.0285,652.18,2156.7492" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="164" x="678" y="2123.4876">CONTINUE and subnet set</text><!--MD5=[48d8edc0219dd4d7c3847b4159c280ef]
+link subnet4_select to no_subnet--><path d="M853.62,2080.3192 C852.99,2089.1692 852.31,2100.1092 852,2109.9192 C851.56,2123.8292 852.26,2139.4292 853.1,2151.7492 " fill="none" id="subnet4_select-&gt;no_subnet" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="853.47,2156.8092,856.8167,2147.5464,853.1127,2151.822,848.8372,2148.118,853.47,2156.8092" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="138" x="853" y="2123.4876">SKIP or subnet not set</text><!--MD5=[f590b573e48b5dfdcd1774729941f83a]
+link subnet4_select to drop--><path d="M938.2,2080.0192 C958.54,2086.9392 979.25,2096.5792 996,2109.9192 C1009.78,2120.8892 1019.89,2138.1592 1026.36,2151.9892 " fill="none" id="subnet4_select-&gt;drop" style="stroke: #A80036; stroke-width: 1.0;"/><polygon fill="#A80036" points="1028.58,2156.9192,1028.5229,2147.0705,1026.5228,2152.362,1021.2313,2150.362,1028.58,2156.9192" style="stroke: #A80036; stroke-width: 1.0;"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacingAndGlyphs" textLength="35" x="1012" y="2123.4876">DROP</text><!--MD5=[ac540f98c992b562d25c0989cf3dd0fa]
+@startuml
+
+title DHCPv4 subnet selection (Kea 1.8.0)
+
+agent "Entry point" as entry
+
+agent "Try RAI link select" as rai_link_select
+
+agent "Try subnet selection option" as subnet_select
+
+rectangle "Relayed" as relayed {
+ agent "Relay address matches subnet" as relay_subnet
+ agent "Relay address matches shared network" as relay_network
+ agent "Check client class" as relay_class
+}
+
+rectangle "Set address for lookup" as set_address {
+ agent "Set relay address" as relay_address
+ agent "Set client address" as client_address
+ agent "Set source address" as source_address
+}
+
+rectangle "Try incoming interface" as interface {
+ agent "Interface matches subnet" as interface_subnet
+ agent "Interface matches shared network" as interface_network
+ agent "Check client class" as interface_class
+ agent "Set interface address" as interface_address
+}
+
+rectangle "Try address" as address {
+ agent "Check subnet prefix" as inRange
+ agent "Check client class" as address_class
+}
+
+agent "Found a subnet" as found
+
+agent "Found no subnet" as not_found
+
+agent "Callout subnet4_select" as subnet4_select
+
+agent "Return a subnet" as success
+
+agent "Return no subnet" as no_subnet
+
+agent "Drop query" as drop
+
+entry - -> rai_link_select
+rai_link_select - -> subnet_select
+subnet_select - -> relayed : relayed
+subnet_select - -> set_address : not relayed
+relayed - -> relay_subnet
+relay_subnet - -> relay_network : no match
+relay_subnet - -> relay_class : match
+relay_network - -> set_address : no match
+relay_network - -> relay_class : match
+relay_class - - -> found : compatible
+relay_class - -> set_address : not compatible
+set_address - -> relay_address : try the relay address
+relay_address -r-> client_address : has no relay address
+client_address -r-> source_address : has no client address
+source_address - -> interface_subnet : no suitable address
+relay_address - -> inRange : has a relay address
+client_address - -> inRange : has a client address
+source_address - -> inRange : has source address and use unicast
+interface_subnet - - -> not_found : no interface
+interface_subnet - -> interface_class : match
+interface_subnet - -> interface_network : no match
+interface_network - -> interface_class : march
+interface_network - - -> not_found : no match
+interface_class - - -> found : compatible
+interface_class - - -> interface_address : not compatible
+interface_address - -> inRange : has an interface address
+interface_address - - -> not_found : no interface address
+inRange - - -> address_class : match
+inRange - - -> not_found : no match
+address_class - - -> found : compatible
+address_class - - -> not_found : not compatible
+found - -> subnet4_select
+not_found - -> subnet4_select
+found -[hidden]> not_found
+subnet4_select - -> success : CONTINUE and subnet set
+subnet4_select - -> no_subnet : SKIP or subnet not set
+subnet4_select - -> drop : DROP
+
+@enduml
+
+PlantUML version 1.2020.15(Sun Jun 28 13:39:45 CEST 2020)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/select4.uml b/doc/sphinx/uml/select4.uml
new file mode 100644
index 0000000..ed8b65c
--- /dev/null
+++ b/doc/sphinx/uml/select4.uml
@@ -0,0 +1,85 @@
+@startuml
+
+title DHCPv4 subnet selection (Kea 1.8.0)
+
+agent "Entry point" as entry
+
+agent "Try RAI link select" as rai_link_select
+
+agent "Try subnet selection option" as subnet_select
+
+rectangle "Relayed" as relayed {
+ agent "Relay address matches subnet" as relay_subnet
+ agent "Relay address matches shared network" as relay_network
+ agent "Check client class" as relay_class
+}
+
+rectangle "Set address for lookup" as set_address {
+ agent "Set relay address" as relay_address
+ agent "Set client address" as client_address
+ agent "Set source address" as source_address
+}
+
+rectangle "Try incoming interface" as interface {
+ agent "Interface matches subnet" as interface_subnet
+ agent "Interface matches shared network" as interface_network
+ agent "Check client class" as interface_class
+ agent "Set interface address" as interface_address
+}
+
+rectangle "Try address" as address {
+ agent "Check subnet prefix" as inRange
+ agent "Check client class" as address_class
+}
+
+agent "Found a subnet" as found
+
+agent "Found no subnet" as not_found
+
+agent "Callout subnet4_select" as subnet4_select
+
+agent "Return a subnet" as success
+
+agent "Return no subnet" as no_subnet
+
+agent "Drop query" as drop
+
+entry --> rai_link_select
+rai_link_select --> subnet_select
+subnet_select --> relayed : relayed
+subnet_select --> set_address : not relayed
+relayed --> relay_subnet
+relay_subnet --> relay_network : no match
+relay_subnet --> relay_class : match
+relay_network --> set_address : no match
+relay_network --> relay_class : match
+relay_class ---> found : compatible
+relay_class --> set_address : not compatible
+set_address --> relay_address : try the relay address
+relay_address -r-> client_address : has no relay address
+client_address -r-> source_address : has no client address
+source_address --> interface_subnet : no suitable address
+relay_address --> inRange : has a relay address
+client_address --> inRange : has a client address
+source_address --> inRange : has source address and use unicast
+interface_subnet ---> not_found : no interface
+interface_subnet --> interface_class : match
+interface_subnet --> interface_network : no match
+interface_network --> interface_class : march
+interface_network ---> not_found : no match
+interface_class ---> found : compatible
+interface_class ---> interface_address : not compatible
+interface_address --> inRange : has an interface address
+interface_address ---> not_found : no interface address
+inRange ---> address_class : match
+inRange ---> not_found : no match
+address_class ---> found : compatible
+address_class ---> not_found : not compatible
+found --> subnet4_select
+not_found --> subnet4_select
+found -[hidden]> not_found
+subnet4_select --> success : CONTINUE and subnet set
+subnet4_select --> no_subnet : SKIP or subnet not set
+subnet4_select --> drop : DROP
+
+@enduml
diff --git a/doc/sphinx/uml/tkey.png b/doc/sphinx/uml/tkey.png
new file mode 100644
index 0000000..c10ec7c
--- /dev/null
+++ b/doc/sphinx/uml/tkey.png
diff --git a/doc/sphinx/uml/tkey.svg b/doc/sphinx/uml/tkey.svg
new file mode 100644
index 0000000..6bfb43f
--- /dev/null
+++ b/doc/sphinx/uml/tkey.svg
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="197px" preserveAspectRatio="none" style="width:308px;height:197px;background:#FFFFFF;" version="1.1" viewBox="0 0 308 197" width="308px" zoomAndPan="magnify"><defs><filter height="300%" id="fz1ehskz14z05" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacing" textLength="283" x="9" y="29.4023">TKEY Exchange (GSS-TSIG hook)</text><line style="stroke:#A80036;stroke-width:1.0;stroke-dasharray:5.0,5.0;" x1="70.5" x2="70.5" y1="75.6875" y2="154.3086"/><line style="stroke:#A80036;stroke-width:1.0;stroke-dasharray:5.0,5.0;" x1="240.5" x2="240.5" y1="75.6875" y2="154.3086"/><rect fill="#FEFECE" filter="url(#fz1ehskz14z05)" height="30.4883" style="stroke:#A80036;stroke-width:1.5;" width="108" x="14.5" y="40.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacing" textLength="94" x="21.5" y="60.7344">Kea D2 server</text><rect fill="#FEFECE" filter="url(#fz1ehskz14z05)" height="30.4883" style="stroke:#A80036;stroke-width:1.5;" width="108" x="14.5" y="153.3086"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacing" textLength="94" x="21.5" y="173.8438">Kea D2 server</text><rect fill="#FEFECE" filter="url(#fz1ehskz14z05)" height="30.4883" style="stroke:#A80036;stroke-width:1.5;" width="88" x="194.5" y="40.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacing" textLength="74" x="201.5" y="60.7344">DNS server</text><rect fill="#FEFECE" filter="url(#fz1ehskz14z05)" height="30.4883" style="stroke:#A80036;stroke-width:1.5;" width="88" x="194.5" y="153.3086"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacing" textLength="74" x="201.5" y="173.8438">DNS server</text><polygon fill="#A80036" points="228.5,102.998,238.5,106.998,228.5,110.998,232.5,106.998" style="stroke:#A80036;stroke-width:1.0;"/><line style="stroke:#A80036;stroke-width:1.0;" x1="70.5" x2="234.5" y1="106.998" y2="106.998"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacing" textLength="82" x="77.5" y="102.2559">TKEY request</text><polygon fill="#A80036" points="81.5,132.3086,71.5,136.3086,81.5,140.3086,77.5,136.3086" style="stroke:#A80036;stroke-width:1.0;"/><line style="stroke:#A80036;stroke-width:1.0;" x1="75.5" x2="239.5" y1="136.3086" y2="136.3086"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacing" textLength="146" x="87.5" y="131.5664">TKEY response (signed)</text><!--MD5=[7d4889a5feeb1588c9f7e0e768327f46]
+@startuml

+

+title TKEY Exchange (GSS-TSIG hook)

+

+participant "Kea D2 server" as Kea

+participant "DNS server" as DNS

+

+Kea -> DNS: TKEY request

+DNS -> Kea: TKEY response (signed)

+

+@enduml

+
+PlantUML version 1.2021.9(Sun Jul 25 12:13:56 CEST 2021)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/tkey.uml b/doc/sphinx/uml/tkey.uml
new file mode 100644
index 0000000..4cc33e5
--- /dev/null
+++ b/doc/sphinx/uml/tkey.uml
@@ -0,0 +1,11 @@
+@startuml
+
+title TKEY Exchange (GSS-TSIG hook)
+
+participant "Kea D2 server" as Kea
+participant "DNS server" as DNS
+
+Kea -> DNS: TKEY request
+DNS -> Kea: TKEY response (signed)
+
+@enduml
diff --git a/doc/sphinx/uml/update.png b/doc/sphinx/uml/update.png
new file mode 100644
index 0000000..9b0520e
--- /dev/null
+++ b/doc/sphinx/uml/update.png
diff --git a/doc/sphinx/uml/update.svg b/doc/sphinx/uml/update.svg
new file mode 100644
index 0000000..7fb4947
--- /dev/null
+++ b/doc/sphinx/uml/update.svg
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" contentScriptType="application/ecmascript" contentStyleType="text/css" height="197px" preserveAspectRatio="none" style="width:367px;height:197px;background:#FFFFFF;" version="1.1" viewBox="0 0 367 197" width="367px" zoomAndPan="magnify"><defs><filter height="300%" id="f1k5dkaewnu0nj" width="300%" x="-1" y="-1"><feGaussianBlur result="blurOut" stdDeviation="2.0"/><feColorMatrix in="blurOut" result="blurOut2" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .4 0"/><feOffset dx="4.0" dy="4.0" in="blurOut2" result="blurOut3"/><feBlend in="SourceGraphic" in2="blurOut3" mode="normal"/></filter></defs><g><text fill="#000000" font-family="sans-serif" font-size="18" lengthAdjust="spacing" textLength="342" x="9" y="29.4023">DNS Update Exchange (GSS-TSIG hook)</text><line style="stroke:#A80036;stroke-width:1.0;stroke-dasharray:5.0,5.0;" x1="78.5" x2="78.5" y1="75.6875" y2="154.3086"/><line style="stroke:#A80036;stroke-width:1.0;stroke-dasharray:5.0,5.0;" x1="291.5" x2="291.5" y1="75.6875" y2="154.3086"/><rect fill="#FEFECE" filter="url(#f1k5dkaewnu0nj)" height="30.4883" style="stroke:#A80036;stroke-width:1.5;" width="108" x="22.5" y="40.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacing" textLength="94" x="29.5" y="60.7344">Kea D2 server</text><rect fill="#FEFECE" filter="url(#f1k5dkaewnu0nj)" height="30.4883" style="stroke:#A80036;stroke-width:1.5;" width="108" x="22.5" y="153.3086"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacing" textLength="94" x="29.5" y="173.8438">Kea D2 server</text><rect fill="#FEFECE" filter="url(#f1k5dkaewnu0nj)" height="30.4883" style="stroke:#A80036;stroke-width:1.5;" width="88" x="245.5" y="40.1992"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacing" textLength="74" x="252.5" y="60.7344">DNS server</text><rect fill="#FEFECE" filter="url(#f1k5dkaewnu0nj)" height="30.4883" style="stroke:#A80036;stroke-width:1.5;" width="88" x="245.5" y="153.3086"/><text fill="#000000" font-family="sans-serif" font-size="14" lengthAdjust="spacing" textLength="74" x="252.5" y="173.8438">DNS server</text><polygon fill="#A80036" points="279.5,102.998,289.5,106.998,279.5,110.998,283.5,106.998" style="stroke:#A80036;stroke-width:1.0;"/><line style="stroke:#A80036;stroke-width:1.0;" x1="78.5" x2="285.5" y1="106.998" y2="106.998"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacing" textLength="179" x="85.5" y="102.2559">DNS update request (signed)</text><polygon fill="#A80036" points="89.5,132.3086,79.5,136.3086,89.5,140.3086,85.5,136.3086" style="stroke:#A80036;stroke-width:1.0;"/><line style="stroke:#A80036;stroke-width:1.0;" x1="83.5" x2="290.5" y1="136.3086" y2="136.3086"/><text fill="#000000" font-family="sans-serif" font-size="13" lengthAdjust="spacing" textLength="189" x="95.5" y="131.5664">DNS update response (signed)</text><!--MD5=[1878df8bb6338e54fcd61a1faf1a5cc0]
+@startuml

+

+title DNS Update Exchange (GSS-TSIG hook)

+

+participant "Kea D2 server" as Kea

+participant "DNS server" as DNS

+

+Kea -> DNS: DNS update request (signed)

+DNS -> Kea: DNS update response (signed)

+

+@enduml

+
+PlantUML version 1.2021.9(Sun Jul 25 12:13:56 CEST 2021)
+(GPL source distribution)
+Java Runtime: OpenJDK Runtime Environment
+JVM: OpenJDK 64-Bit Server VM
+Default Encoding: UTF-8
+Language: en
+Country: US
+--></g></svg>
\ No newline at end of file
diff --git a/doc/sphinx/uml/update.uml b/doc/sphinx/uml/update.uml
new file mode 100644
index 0000000..9738f30
--- /dev/null
+++ b/doc/sphinx/uml/update.uml
@@ -0,0 +1,11 @@
+@startuml
+
+title DNS Update Exchange (GSS-TSIG hook)
+
+participant "Kea D2 server" as Kea
+participant "DNS server" as DNS
+
+Kea -> DNS: DNS update request (signed)
+DNS -> Kea: DNS update response (signed)
+
+@enduml
diff --git a/doc/sphinx/umls.rst b/doc/sphinx/umls.rst
new file mode 100644
index 0000000..1054310
--- /dev/null
+++ b/doc/sphinx/umls.rst
@@ -0,0 +1,146 @@
+..
+   Copyright (C) 2020-2022 Internet Systems Consortium, Inc. ("ISC")
+
+   This Source Code Form is subject to the terms of the Mozilla Public
+   License, v. 2.0. If a copy of the MPL was not distributed with this
+   file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+   See the COPYRIGHT file distributed with this work for additional
+   information regarding copyright ownership.
+
+.. _umls:
+
+Kea Flow Diagrams
+=================
+
+These flow diagrams describe Kea's DHCPv4 server implementation, and they may be useful for system administrators. To design a configuration that results in clients getting the intended addresses and options, it is important to understand the sequence of request-processing steps. For example, Kea iterates looking for a suitable address, and conditionally accepts the first available address, so the order in which addresses are evaluated matters.
+
+It is also useful to understand Kea's processing logic because there are configuration choices which can make the process far more efficient. Kea is very flexible, so it can be applied to very different use cases and in different environments. In an environment where throughput and efficiency are a priority, the administrator can choose to limit some of the processing steps. For example, it is possible to limit the number of different client identifiers Kea evaluates in looking for a host reservation, or even to skip the step of checking for host reservations.
+
+These diagrams are focused on those aspects of Kea processing that will be most useful to operators. The diagrams illustrate DHCPv4 request processing, but most of the logic applies equally to DHCPv6. Following the title of each diagram is a Kea version number. Kea behavior has evolved over time, and the diagrams document the behavior as of the Kea version indicated. These diagrams are provided in the Kea source tree in UML (source), PNG, and SVG formats.
+
+Main Loop
+^^^^^^^^^
+
+The main loop is common to both DHCPv4 and DHPCv6 servers.
+
+.. figure:: uml/main-loop.*
+
+    The DHCP server main loop
+
+.. _uml_packet4:
+
+DHCPv4 Packet Processing
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+DHCPv4 packet processing evaluates the type DHCP message: Discover, Request, Release, Decline, or Inform. This diagram shows the general, high-level flow for processing an inbound client DHCP packet from receipt to the server's response.
+
+.. figure:: uml/packet4.*
+
+    DHCPv4 packet processing
+
+.. _uml_request4:
+
+DHCPREQUEST Processing
+^^^^^^^^^^^^^^^^^^^^^^
+
+The following diagrams focus on DHCPREQUEST processing. This chart gives an overview of the process, from subnet selection to checking for host reservations to evaluating client classes. Finally, before acknowledging the lease, the options are evaluated and added to the message.
+
+.. figure:: uml/request4.*
+
+    DHCPREQUEST processing
+
+.. _uml_select4:
+
+DHCPv4 Subnet Selection
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Subnet selection is the process of choosing a subnet that is topologically appropriate for the client. When the selected subnet is a member of a shared network, the whole shared network is selected. During subnet selection the client class may be checked more than once while iterating through subnets, to determine whether it is permitted in the selected subnet.
+
+.. figure:: uml/select4.*
+
+    DHCPv4 subnet selection
+
+.. _uml_assign-lease4:
+
+DHCPv4 Special Case of Double-Booting
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+After subnet selection and before lease allocation, the DHCPv4 server handles the special case of clients restarting with an image provided by PXE boot or bootp. The Lease Request box is expanded below.
+
+.. figure:: uml/assign-lease4.*
+
+    DHCPv4 lease assignment
+
+.. _uml_request4-lease:
+
+DHCPv4 Lease Allocation
+^^^^^^^^^^^^^^^^^^^^^^^
+
+The first diagram below illustrates the details of processing the client request, showing the renewal of an existing lease, the assignment of a reserved lease, and the allocation of an unreserved lease.
+
+.. figure:: uml/request4-lease.*
+
+    DHCPREQUEST lease allocation
+
+The second diagram shows the algorithm used to validate a requested lease or select a new address to offer. The right-hand side of the diagram shows how a new address is selected, when a new lease is required and the client has neither a requested address nor a reservation. When a new lease is required and Kea iterates over pools and subnets, it starts with the subnet selected above in the subnet selection process.
+
+.. figure:: uml/requestLease4.*
+
+    The requestLease4 algorithm
+
+.. note::
+
+    Declined addresses are included in the statistic for assigned addresses,
+    so the :math:`assigned + free = total` equation is true.
+
+.. _uml_lease-states:
+
+Lease States
+^^^^^^^^^^^^
+
+This diagram illustrates the different lease states, including the ``free`` one, where no lease object exists.
+
+.. figure:: uml/lease-states.*
+
+    Lease states
+
+.. _uml_currentHost4:
+
+Checking for Host Reservations
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The allocation engine checks for host reservations after selecting a subnet; this diagram shows the details of that operation. Subnet selection is based on network topology. Host reservations are primarily for assigning options, and options are evaluated after subnet selection. However, if client classes are added in the host reservation, those are also evaluated against the selected subnet in a further check (added in Kea 1.7.10). Kea includes several options to skip checking for host reservations, which can make this process much more efficient if reservations are not being used.
+
+.. note::
+
+    To find a free lease, the allocation engine begins by evaluating the most recently used subnet.
+    The current subnet depends on the history of prior queries.
+
+.. figure:: uml/currentHost4.*
+
+    Host reservation evaluation
+
+.. _uml_CfgOptionList:
+
+Building the Options List
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Before sending a response, options are added:
+ - evaluate required client classes
+ - build the configured option list
+ - append requested options
+ - append requested vendor options
+ - append basic options
+
+.. figure:: uml/buildCfgOptionList.*
+
+    The buildCfgOptionList (build configured option list) algorithm
+
+.. figure:: uml/appendRequestedOptions.*
+
+    The appendRequestedOptions (append requested options) algorithm
+
+.. figure:: uml/appendRequestedVendorOptions.*
+
+    The appendRequestedVendorOptions (append vendor requested options) algorithm