21 files changed, 8527 insertions, 0 deletions
diff --git a/src/lib/dhcp_ddns/Makefile.am b/src/lib/dhcp_ddns/Makefile.am
new file mode 100644
index 0000000..7a56064
--- /dev/null
+++ b/src/lib/dhcp_ddns/Makefile.am
@@ -0,0 +1,79 @@
+SUBDIRS = . tests
+
+AM_CPPFLAGS  = -I$(top_builddir)/src/lib -I$(top_srcdir)/src/lib
+AM_CPPFLAGS += $(BOOST_INCLUDES)
+AM_CXXFLAGS  = $(KEA_CXXFLAGS)
+
+# Ensure that the message file is included in the distribution
+EXTRA_DIST = dhcp_ddns_messages.mes libdhcp_ddns.dox
+
+CLEANFILES = *.gcno *.gcda
+
+lib_LTLIBRARIES = libkea-dhcp_ddns.la
+libkea_dhcp_ddns_la_SOURCES  =
+libkea_dhcp_ddns_la_SOURCES += dhcp_ddns_log.cc dhcp_ddns_log.h
+libkea_dhcp_ddns_la_SOURCES += dhcp_ddns_messages.cc dhcp_ddns_messages.h
+libkea_dhcp_ddns_la_SOURCES += ncr_io.cc ncr_io.h
+libkea_dhcp_ddns_la_SOURCES += ncr_msg.cc ncr_msg.h
+libkea_dhcp_ddns_la_SOURCES += ncr_udp.cc ncr_udp.h
+
+libkea_dhcp_ddns_la_CXXFLAGS = $(AM_CXXFLAGS)
+libkea_dhcp_ddns_la_CPPFLAGS = $(AM_CPPFLAGS)
+libkea_dhcp_ddns_la_LDFLAGS  = $(AM_LDFLAGS)
+libkea_dhcp_ddns_la_LDFLAGS += $(CRYPTO_LDFLAGS)
+libkea_dhcp_ddns_la_LDFLAGS += -no-undefined -version-info 29:0:0
+
+libkea_dhcp_ddns_la_LIBADD  =
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/stats/libkea-stats.la
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/dhcp/libkea-dhcp++.la
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/asiolink/libkea-asiolink.la
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/cc/libkea-cc.la
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/dns/libkea-dns++.la
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/cryptolink/libkea-cryptolink.la
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/hooks/libkea-hooks.la
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/log/libkea-log.la
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/util/libkea-util.la
+libkea_dhcp_ddns_la_LIBADD += $(top_builddir)/src/lib/exceptions/libkea-exceptions.la
+libkea_dhcp_ddns_la_LIBADD += $(LOG4CPLUS_LIBS) $(CRYPTO_LIBS) $(BOOST_LIBS)
+
+# If we want to get rid of all generated messages files, we need to use
+# make maintainer-clean. The proper way to introduce custom commands for
+# that operation is to define maintainer-clean-local target. However,
+# make maintainer-clean also removes Makefile, so running configure script
+# is required.  To make it easy to rebuild messages without going through
+# reconfigure, a new target messages-clean has been added.
+maintainer-clean-local:
+	rm -f dhcp_ddns_messages.h dhcp_ddns_messages.cc
+
+# To regenerate messages files, one can do:
+#
+# make messages-clean
+# make messages
+#
+# This is needed only when a .mes file is modified.
+messages-clean: maintainer-clean-local
+
+if GENERATE_MESSAGES
+
+# Define rule to build logging source files from message file
+messages: dhcp_ddns_messages.h dhcp_ddns_messages.cc
+	@echo Message files regenerated
+
+dhcp_ddns_messages.h dhcp_ddns_messages.cc: dhcp_ddns_messages.mes
+	$(top_builddir)/src/lib/log/compiler/kea-msg-compiler $(top_srcdir)/src/lib/dhcp_ddns/dhcp_ddns_messages.mes
+
+else
+
+messages dhcp_ddns_messages.h dhcp_ddns_messages.cc:
+	@echo Messages generation disabled. Configure with --enable-generate-messages to enable it.
+
+endif
+
+# Specify the headers for copying into the installation directory tree.
+libkea_dhcp_ddns_includedir = $(pkgincludedir)/dhcp_ddns
+libkea_dhcp_ddns_include_HEADERS = \
+	dhcp_ddns_log.h \
+	dhcp_ddns_messages.h \
+	ncr_io.h \
+	ncr_msg.h \
+	ncr_udp.h
diff --git a/src/lib/dhcp_ddns/Makefile.in b/src/lib/dhcp_ddns/Makefile.in
new file mode 100644
index 0000000..cefca2e
--- /dev/null
+++ b/src/lib/dhcp_ddns/Makefile.in
@@ -0,0 +1,1033 @@
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+	    || cp -p $$d/$$file "$(distdir)/$$file" \
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+	-rm -f ./$(DEPDIR)/libkea_dhcp_ddns_la-ncr_io.Plo
+	-rm -f ./$(DEPDIR)/libkea_dhcp_ddns_la-ncr_msg.Plo
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+	-rm -f ./$(DEPDIR)/libkea_dhcp_ddns_la-ncr_io.Plo
+	-rm -f ./$(DEPDIR)/libkea_dhcp_ddns_la-ncr_msg.Plo
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+
+.MAKE: $(am__recursive_targets) install-am install-strip
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+.PHONY: $(am__recursive_targets) CTAGS GTAGS TAGS all all-am \
+	am--depfiles check check-am clean clean-generic \
+	clean-libLTLIBRARIES clean-libtool cscopelist-am ctags \
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+	install-libkea_dhcp_ddns_includeHEADERS install-man \
+	install-pdf install-pdf-am install-ps install-ps-am \
+	install-strip installcheck installcheck-am installdirs \
+	installdirs-am maintainer-clean maintainer-clean-generic \
+	maintainer-clean-local mostlyclean mostlyclean-compile \
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+	uninstall-libkea_dhcp_ddns_includeHEADERS
+
+.PRECIOUS: Makefile
+
+
+# If we want to get rid of all generated messages files, we need to use
+# make maintainer-clean. The proper way to introduce custom commands for
+# that operation is to define maintainer-clean-local target. However,
+# make maintainer-clean also removes Makefile, so running configure script
+# is required.  To make it easy to rebuild messages without going through
+# reconfigure, a new target messages-clean has been added.
+maintainer-clean-local:
+	rm -f dhcp_ddns_messages.h dhcp_ddns_messages.cc
+
+# To regenerate messages files, one can do:
+#
+# make messages-clean
+# make messages
+#
+# This is needed only when a .mes file is modified.
+messages-clean: maintainer-clean-local
+
+# Define rule to build logging source files from message file
+@GENERATE_MESSAGES_TRUE@messages: dhcp_ddns_messages.h dhcp_ddns_messages.cc
+@GENERATE_MESSAGES_TRUE@	@echo Message files regenerated
+
+@GENERATE_MESSAGES_TRUE@dhcp_ddns_messages.h dhcp_ddns_messages.cc: dhcp_ddns_messages.mes
+@GENERATE_MESSAGES_TRUE@	$(top_builddir)/src/lib/log/compiler/kea-msg-compiler $(top_srcdir)/src/lib/dhcp_ddns/dhcp_ddns_messages.mes
+
+@GENERATE_MESSAGES_FALSE@messages dhcp_ddns_messages.h dhcp_ddns_messages.cc:
+@GENERATE_MESSAGES_FALSE@	@echo Messages generation disabled. Configure with --enable-generate-messages to enable it.
+
+# Tell versions [3.59,3.63) of GNU make to not export all variables.
+# Otherwise a system limit (for SysV at least) may be exceeded.
+.NOEXPORT:
diff --git a/src/lib/dhcp_ddns/dhcp_ddns_log.cc b/src/lib/dhcp_ddns/dhcp_ddns_log.cc
new file mode 100644
index 0000000..2be7be5
--- /dev/null
+++ b/src/lib/dhcp_ddns/dhcp_ddns_log.cc
@@ -0,0 +1,21 @@
+// Copyright (C) 2013-2015 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/.
+
+/// Defines the logger used by the top-level component of kea-dhcp_ddns.
+
+#include <config.h>
+
+#include <dhcp_ddns/dhcp_ddns_log.h>
+
+namespace isc {
+namespace dhcp_ddns {
+
+/// @brief Defines the logger used within lib dhcp_ddns.
+isc::log::Logger dhcp_ddns_logger("libdhcp-ddns");
+
+} // namespace dhcp_ddns
+} // namespace isc
+
diff --git a/src/lib/dhcp_ddns/dhcp_ddns_log.h b/src/lib/dhcp_ddns/dhcp_ddns_log.h
new file mode 100644
index 0000000..cda7fdf
--- /dev/null
+++ b/src/lib/dhcp_ddns/dhcp_ddns_log.h
@@ -0,0 +1,23 @@
+// Copyright (C) 2013-2015 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/.
+
+#ifndef DHCP_DDNS_LOG_H
+#define DHCP_DDNS_LOG_H
+
+#include <log/logger_support.h>
+#include <log/macros.h>
+#include <dhcp_ddns/dhcp_ddns_messages.h>
+
+namespace isc {
+namespace dhcp_ddns {
+
+/// Define the logger for the "dhcp_ddns" logging.
+extern isc::log::Logger dhcp_ddns_logger;
+
+} // namespace dhcp_ddns
+} // namespace isc
+
+#endif // DHCP_DDNS_LOG_H
diff --git a/src/lib/dhcp_ddns/dhcp_ddns_messages.cc b/src/lib/dhcp_ddns/dhcp_ddns_messages.cc
new file mode 100644
index 0000000..2c440c9
--- /dev/null
+++ b/src/lib/dhcp_ddns/dhcp_ddns_messages.cc
@@ -0,0 +1,51 @@
+// File created from ../../../src/lib/dhcp_ddns/dhcp_ddns_messages.mes
+
+#include <cstddef>
+#include <log/message_types.h>
+#include <log/message_initializer.h>
+
+namespace isc {
+namespace dhcp_ddns {
+
+extern const isc::log::MessageID DHCP_DDNS_INVALID_NCR = "DHCP_DDNS_INVALID_NCR";
+extern const isc::log::MessageID DHCP_DDNS_NCR_FLUSH_IO_ERROR = "DHCP_DDNS_NCR_FLUSH_IO_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_NCR_LISTEN_CLOSE_ERROR = "DHCP_DDNS_NCR_LISTEN_CLOSE_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_NCR_RECV_NEXT_ERROR = "DHCP_DDNS_NCR_RECV_NEXT_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_NCR_SEND_CLOSE_ERROR = "DHCP_DDNS_NCR_SEND_CLOSE_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_NCR_SEND_NEXT_ERROR = "DHCP_DDNS_NCR_SEND_NEXT_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_CLEAR_READY_ERROR = "DHCP_DDNS_NCR_UDP_CLEAR_READY_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_RECV_CANCELED = "DHCP_DDNS_NCR_UDP_RECV_CANCELED";
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_RECV_ERROR = "DHCP_DDNS_NCR_UDP_RECV_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_SEND_CANCELED = "DHCP_DDNS_NCR_UDP_SEND_CANCELED";
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_SEND_ERROR = "DHCP_DDNS_NCR_UDP_SEND_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_UDP_SENDER_WATCH_SOCKET_CLOSE_ERROR = "DHCP_DDNS_UDP_SENDER_WATCH_SOCKET_CLOSE_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_UNCAUGHT_NCR_RECV_HANDLER_ERROR = "DHCP_DDNS_UNCAUGHT_NCR_RECV_HANDLER_ERROR";
+extern const isc::log::MessageID DHCP_DDNS_UNCAUGHT_NCR_SEND_HANDLER_ERROR = "DHCP_DDNS_UNCAUGHT_NCR_SEND_HANDLER_ERROR";
+
+} // namespace dhcp_ddns
+} // namespace isc
+
+namespace {
+
+const char* values[] = {
+    "DHCP_DDNS_INVALID_NCR", "application received an invalid DNS update request: %1",
+    "DHCP_DDNS_NCR_FLUSH_IO_ERROR", "DHCP-DDNS Last send before stopping did not complete successfully: %1",
+    "DHCP_DDNS_NCR_LISTEN_CLOSE_ERROR", "application encountered an error while closing the listener used to receive NameChangeRequests : %1",
+    "DHCP_DDNS_NCR_RECV_NEXT_ERROR", "application could not initiate the next read following a request receive.",
+    "DHCP_DDNS_NCR_SEND_CLOSE_ERROR", "DHCP-DDNS client encountered an error while closing the sender connection used to send NameChangeRequests: %1",
+    "DHCP_DDNS_NCR_SEND_NEXT_ERROR", "DHCP-DDNS client could not initiate the next request send following send completion: %1",
+    "DHCP_DDNS_NCR_UDP_CLEAR_READY_ERROR", "NCR UDP watch socket failed to clear: %1",
+    "DHCP_DDNS_NCR_UDP_RECV_CANCELED", "UDP socket receive was canceled while listening for DNS Update requests",
+    "DHCP_DDNS_NCR_UDP_RECV_ERROR", "UDP socket receive error while listening for DNS Update requests: %1",
+    "DHCP_DDNS_NCR_UDP_SEND_CANCELED", "UDP socket send was canceled while sending a DNS Update request to DHCP_DDNS: %1",
+    "DHCP_DDNS_NCR_UDP_SEND_ERROR", "UDP socket send error while sending a DNS Update request: %1",
+    "DHCP_DDNS_UDP_SENDER_WATCH_SOCKET_CLOSE_ERROR", "watch socket failed to close: %1",
+    "DHCP_DDNS_UNCAUGHT_NCR_RECV_HANDLER_ERROR", "unexpected exception thrown from the application receive completion handler: %1",
+    "DHCP_DDNS_UNCAUGHT_NCR_SEND_HANDLER_ERROR", "unexpected exception thrown from the DHCP-DDNS client send completion handler: %1",
+    NULL
+};
+
+const isc::log::MessageInitializer initializer(values);
+
+} // Anonymous namespace
+
diff --git a/src/lib/dhcp_ddns/dhcp_ddns_messages.h b/src/lib/dhcp_ddns/dhcp_ddns_messages.h
new file mode 100644
index 0000000..cb85946
--- /dev/null
+++ b/src/lib/dhcp_ddns/dhcp_ddns_messages.h
@@ -0,0 +1,29 @@
+// File created from ../../../src/lib/dhcp_ddns/dhcp_ddns_messages.mes
+
+#ifndef DHCP_DDNS_MESSAGES_H
+#define DHCP_DDNS_MESSAGES_H
+
+#include <log/message_types.h>
+
+namespace isc {
+namespace dhcp_ddns {
+
+extern const isc::log::MessageID DHCP_DDNS_INVALID_NCR;
+extern const isc::log::MessageID DHCP_DDNS_NCR_FLUSH_IO_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_NCR_LISTEN_CLOSE_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_NCR_RECV_NEXT_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_NCR_SEND_CLOSE_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_NCR_SEND_NEXT_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_CLEAR_READY_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_RECV_CANCELED;
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_RECV_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_SEND_CANCELED;
+extern const isc::log::MessageID DHCP_DDNS_NCR_UDP_SEND_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_UDP_SENDER_WATCH_SOCKET_CLOSE_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_UNCAUGHT_NCR_RECV_HANDLER_ERROR;
+extern const isc::log::MessageID DHCP_DDNS_UNCAUGHT_NCR_SEND_HANDLER_ERROR;
+
+} // namespace dhcp_ddns
+} // namespace isc
+
+#endif // DHCP_DDNS_MESSAGES_H
diff --git a/src/lib/dhcp_ddns/dhcp_ddns_messages.mes b/src/lib/dhcp_ddns/dhcp_ddns_messages.mes
new file mode 100644
index 0000000..7c15bf9
--- /dev/null
+++ b/src/lib/dhcp_ddns/dhcp_ddns_messages.mes
@@ -0,0 +1,88 @@
+# Copyright (C) 2013-2020 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/.
+
+$NAMESPACE isc::dhcp_ddns
+
+% DHCP_DDNS_INVALID_NCR application received an invalid DNS update request: %1
+This is an error message that indicates that an invalid request to update
+a DNS entry was received by the application.  Either the format or the content
+of the request is incorrect. The request will be ignored.
+
+% DHCP_DDNS_NCR_FLUSH_IO_ERROR DHCP-DDNS Last send before stopping did not complete successfully: %1
+This is an error message that indicates the DHCP-DDNS client was unable to
+complete the last send prior to exiting send mode.  This is a programmatic
+error, highly unlikely to occur, and should not impair the application's ability
+to process requests.
+
+% DHCP_DDNS_NCR_LISTEN_CLOSE_ERROR application encountered an error while closing the listener used to receive NameChangeRequests : %1
+This is an error message that indicates the application was unable to close the
+listener connection used to receive NameChangeRequests.  Closure may occur
+during the course of error recovery or during normal shutdown procedure.  In
+either case the error is unlikely to impair the application's ability to
+process requests but it should be reported for analysis.
+
+% DHCP_DDNS_NCR_RECV_NEXT_ERROR application could not initiate the next read following a request receive.
+This is an error message indicating that NameChangeRequest listener could not
+start another read after receiving a request.  While possible, this is highly
+unlikely and is probably a programmatic error.  The application should recover
+on its own.
+
+% DHCP_DDNS_NCR_SEND_CLOSE_ERROR DHCP-DDNS client encountered an error while closing the sender connection used to send NameChangeRequests: %1
+This is an error message that indicates the DHCP-DDNS client was unable to
+close the connection used to send NameChangeRequests.  Closure may occur during
+the course of error recovery or during normal shutdown procedure.  In either
+case the error is unlikely to impair the client's ability to send requests but
+it should be reported for analysis.
+
+% DHCP_DDNS_NCR_SEND_NEXT_ERROR DHCP-DDNS client could not initiate the next request send following send completion: %1
+This is an error message indicating that NameChangeRequest sender could not
+start another send after completing the send of the previous request.  While
+possible, this is highly unlikely and is probably a programmatic error.  The
+application should recover on its own.
+
+% DHCP_DDNS_NCR_UDP_CLEAR_READY_ERROR NCR UDP watch socket failed to clear: %1
+This is an error message that indicates the application was unable to reset the
+UDP NCR sender ready status after completing a send.  This is programmatic error
+that should be reported.  The application may or may not continue to operate
+correctly.
+
+% DHCP_DDNS_NCR_UDP_RECV_CANCELED UDP socket receive was canceled while listening for DNS Update requests
+This is a debug  message indicating that the listening on a UDP socket
+for DNS update requests has been canceled.  This is a normal part of
+suspending listening operations.
+
+% DHCP_DDNS_NCR_UDP_RECV_ERROR UDP socket receive error while listening for DNS Update requests: %1
+This is an error message indicating that an I/O error occurred while listening
+over a UDP socket for DNS update requests. This could indicate a network
+connectivity or system resource issue.
+
+% DHCP_DDNS_NCR_UDP_SEND_CANCELED UDP socket send was canceled while sending a DNS Update request to DHCP_DDNS: %1
+This is an informational message indicating that sending requests via UDP
+socket to DHCP_DDNS has been interrupted. This is a normal part of suspending
+send operations.
+
+% DHCP_DDNS_NCR_UDP_SEND_ERROR UDP socket send error while sending a DNS Update request: %1
+This is an error message indicating that an IO error occurred while sending a
+DNS update request to DHCP_DDNS over a UDP socket.  This could indicate a
+network connectivity or system resource issue.
+
+% DHCP_DDNS_UDP_SENDER_WATCH_SOCKET_CLOSE_ERROR watch socket failed to close: %1
+This is an error message that indicates the application was unable to close
+the inbound or outbound side of a NCR sender's watch socket. While technically
+possible the error is highly unlikely to occur and should not impair the
+application's ability to process requests.
+
+% DHCP_DDNS_UNCAUGHT_NCR_RECV_HANDLER_ERROR unexpected exception thrown from the application receive completion handler: %1
+This is an error message that indicates that an exception was thrown but not
+caught in the application's request receive completion handler.  This is a
+programmatic error that needs to be reported.  Dependent upon the nature of
+the error the application may or may not continue operating normally.
+
+% DHCP_DDNS_UNCAUGHT_NCR_SEND_HANDLER_ERROR unexpected exception thrown from the DHCP-DDNS client send completion handler: %1
+This is an error message that indicates that an exception was thrown but not
+caught in the application's send completion handler.  This is a programmatic
+error that needs to be reported.  Dependent upon the nature of the error the
+client may or may not continue operating normally.
diff --git a/src/lib/dhcp_ddns/libdhcp_ddns.dox b/src/lib/dhcp_ddns/libdhcp_ddns.dox
new file mode 100644
index 0000000..c285fd8
--- /dev/null
+++ b/src/lib/dhcp_ddns/libdhcp_ddns.dox
@@ -0,0 +1,61 @@
+// Copyright (C) 2013-2020 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/.
+
+/**
+@page libdhcp_ddns libkea-dhcp_ddns - DHCP_DDNS Request I/O Library
+
+@section libdhcp_ddnsIntro Introduction
+
+This is a library of classes (in the isc::dhcp_ddns namespace) for sending
+and receiving requests used by ISC's DHCP-DDNS (aka D2) service to carry
+out DHCP-driven DNS updates.  Each request contains the following information:
+
+    - change-type -  indicates if this is a request to add or remove DNS entries
+    - forward-change - indicates if the forward DNS zone (the one that
+      contains name to address mappings) should be updated
+    - reverse-change - indicates if reverse DNS zone (which contains the
+      address to name mappings) should be updated
+    - fqdn - the fully qualified domain name whose DNS entries should be updated
+    - ip-address - IP address (v4 or v6) leased to the client with the
+      given FQDN
+    - dhcid - DHCID (a form of identification) of the client to whom the IP
+      address is leased
+    - lease-expires-on - timestamp containing the date/time the lease expires
+    - lease-length - duration in seconds for which the lease is valid.
+
+These requests are implemented in this library by the class,
+isc::dhcp_ddns::NameChangeRequest.  This class provides services for
+constructing the requests as well as marshalling them to and from various
+transport formats.  Currently, the only format supported is JSON, however the
+design of the classes in this library is such that supporting additional
+formats will be easy to add.  The JSON "schema" is documented here:
+isc::dhcp_ddns::NameChangeRequest::fromJSON().
+
+For sending and receiving NameChangeRequests, this library supplies an abstract
+pair of classes, isc::dhcp_ddns::NameChangeSender and
+isc::dhcp_ddns::NameChangeListener.  NameChangeSender defines the public
+interface that DHCP_DDNS clients, such as DHCP servers, use for sending
+requests to DHCP_DDNS.   NameChangeListener is used by request consumers,
+primarily the DHCP_DDNS service, for receiving the requests.
+
+By providing abstract interfaces, the implementation isolates the senders and
+listeners from any underlying details of request transportation.  This was done
+to allow support for a variety of transportation mechanisms.  Currently, the
+only transport supported is via UDP Sockets.
+
+The UDP implementation is provided by isc::dhcp_ddns::NameChangeUDPSender
+and isc::dhcp_ddns::NameChangeUDPListener.  The implementation is strictly
+unidirectional: there is no explicit acknowledgment of receipt of a
+request so, as it is UDP, no guarantee of delivery.
+
+@section libdhcp_ddnsMTConsiderations Multi-Threading Consideration for DHCP_DDNS Request I/O Library
+
+By default this library is not thread safe (it uses asynchronous I/O) at
+the exception of the Name Change Request sender class (@c
+isc::dhcp_ddns::NameChangeSender) which is Kea thread safe (i.e. it is
+thread safe when the multi-threading mode is true).
+
+*/
diff --git a/src/lib/dhcp_ddns/ncr_io.cc b/src/lib/dhcp_ddns/ncr_io.cc
new file mode 100644
index 0000000..220fb3b
--- /dev/null
+++ b/src/lib/dhcp_ddns/ncr_io.cc
@@ -0,0 +1,499 @@
+// Copyright (C) 2013-2020 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/.
+
+#include <config.h>
+#include <asiolink/asio_wrapper.h>
+#include <dhcp_ddns/dhcp_ddns_log.h>
+#include <dhcp_ddns/ncr_io.h>
+#include <util/multi_threading_mgr.h>
+
+#include <boost/algorithm/string/predicate.hpp>
+
+#include <mutex>
+
+namespace isc {
+namespace dhcp_ddns {
+
+using namespace isc::util;
+using namespace std;
+
+NameChangeProtocol stringToNcrProtocol(const std::string& protocol_str) {
+    if (boost::iequals(protocol_str, "UDP")) {
+        return (NCR_UDP);
+    }
+
+    if (boost::iequals(protocol_str, "TCP")) {
+        return (NCR_TCP);
+    }
+
+    isc_throw(BadValue,
+              "Invalid NameChangeRequest protocol: " << protocol_str);
+}
+
+std::string ncrProtocolToString(NameChangeProtocol protocol) {
+    switch (protocol) {
+    case NCR_UDP:
+        return ("UDP");
+    case NCR_TCP:
+        return ("TCP");
+    default:
+        break;
+    }
+
+    std::ostringstream stream;
+    stream  << "UNKNOWN(" << protocol << ")";
+    return (stream.str());
+}
+
+
+//************************** NameChangeListener ***************************
+
+NameChangeListener::NameChangeListener(RequestReceiveHandler&
+                                       recv_handler)
+    : listening_(false), io_pending_(false), recv_handler_(recv_handler) {
+};
+
+
+void
+NameChangeListener::startListening(isc::asiolink::IOService& io_service) {
+    if (amListening()) {
+        // This amounts to a programmatic error.
+        isc_throw(NcrListenerError, "NameChangeListener is already listening");
+    }
+
+    // Call implementation dependent open.
+    try {
+        open(io_service);
+    } catch (const isc::Exception& ex) {
+        stopListening();
+        isc_throw(NcrListenerOpenError, "Open failed: " << ex.what());
+    }
+
+    // Set our status to listening.
+    setListening(true);
+
+    // Start the first asynchronous receive.
+    try {
+        receiveNext();
+    } catch (const isc::Exception& ex) {
+        stopListening();
+        isc_throw(NcrListenerReceiveError, "doReceive failed: " << ex.what());
+    }
+}
+
+void
+NameChangeListener::receiveNext() {
+    io_pending_ = true;
+    doReceive();
+}
+
+void
+NameChangeListener::stopListening() {
+    try {
+        // Call implementation dependent close.
+        close();
+    } catch (const isc::Exception &ex) {
+        // Swallow exceptions. If we have some sort of error we'll log
+        // it but we won't propagate the throw.
+        LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_NCR_LISTEN_CLOSE_ERROR)
+                  .arg(ex.what());
+    }
+
+    // Set it false, no matter what.  This allows us to at least try to
+    // re-open via startListening().
+    setListening(false);
+}
+
+void
+NameChangeListener::invokeRecvHandler(const Result result,
+                                      NameChangeRequestPtr& ncr) {
+    // Call the registered application layer handler.
+    // Surround the invocation with a try-catch. The invoked handler is
+    // not supposed to throw, but in the event it does we will at least
+    // report it.
+    try {
+        io_pending_ = false;
+        recv_handler_(result, ncr);
+    } catch (const std::exception& ex) {
+        LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_UNCAUGHT_NCR_RECV_HANDLER_ERROR)
+                  .arg(ex.what());
+    }
+
+    // Start the next IO layer asynchronous receive.
+    // In the event the handler above intervened and decided to stop listening
+    // we need to check that first.
+    if (amListening()) {
+        try {
+            receiveNext();
+        } catch (const isc::Exception& ex) {
+            // It is possible though unlikely, for doReceive to fail without
+            // scheduling the read. While, unlikely, it does mean the callback
+            // will not get called with a failure. A throw here would surface
+            // at the IOService::run (or run variant) invocation.  So we will
+            // close the window by invoking the application handler with
+            // a failed result, and let the application layer sort it out.
+            LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_NCR_RECV_NEXT_ERROR)
+                      .arg(ex.what());
+
+            // Call the registered application layer handler.
+            // Surround the invocation with a try-catch. The invoked handler is
+            // not supposed to throw, but in the event it does we will at least
+            // report it.
+            NameChangeRequestPtr empty;
+            try {
+                io_pending_ = false;
+                recv_handler_(ERROR, empty);
+            } catch (const std::exception& ex) {
+                LOG_ERROR(dhcp_ddns_logger,
+                          DHCP_DDNS_UNCAUGHT_NCR_RECV_HANDLER_ERROR)
+                          .arg(ex.what());
+            }
+        }
+    }
+}
+
+//************************* NameChangeSender ******************************
+
+NameChangeSender::NameChangeSender(RequestSendHandler& send_handler,
+                                   size_t send_queue_max)
+    : sending_(false), send_handler_(send_handler),
+      send_queue_max_(send_queue_max), io_service_(NULL), mutex_(new mutex) {
+
+    // Queue size must be big enough to hold at least 1 entry.
+    setQueueMaxSize(send_queue_max);
+}
+
+void
+NameChangeSender::startSending(isc::asiolink::IOService& io_service) {
+    if (amSending()) {
+        // This amounts to a programmatic error.
+        isc_throw(NcrSenderError, "NameChangeSender is already sending");
+    }
+
+    // Call implementation dependent open.
+    try {
+        if (MultiThreadingMgr::instance().getMode()) {
+            lock_guard<mutex> lock(*mutex_);
+            startSendingInternal(io_service);
+        } else {
+            startSendingInternal(io_service);
+        }
+    } catch (const isc::Exception& ex) {
+        stopSending();
+        isc_throw(NcrSenderOpenError, "Open failed: " << ex.what());
+    }
+}
+
+void
+NameChangeSender::startSendingInternal(isc::asiolink::IOService& io_service) {
+    // Clear send marker.
+    ncr_to_send_.reset();
+
+    // Remember io service we're given.
+    io_service_ = &io_service;
+    open(io_service);
+
+    // Set our status to sending.
+    setSending(true);
+
+    // If there's any queued already.. we'll start sending.
+    sendNext();
+}
+
+void
+NameChangeSender::stopSending() {
+    // Set it send indicator to false, no matter what. This allows us to at
+    // least try to re-open via startSending(). Also, setting it false now,
+    // allows us to break sendNext() chain in invokeSendHandler.
+    setSending(false);
+
+    // If there is an outstanding IO to complete, attempt to process it.
+    if (ioReady() && io_service_ != NULL) {
+        try {
+            runReadyIO();
+        } catch (const std::exception& ex) {
+            // Swallow exceptions. If we have some sort of error we'll log
+            // it but we won't propagate the throw.
+            LOG_ERROR(dhcp_ddns_logger,
+                  DHCP_DDNS_NCR_FLUSH_IO_ERROR).arg(ex.what());
+        }
+    }
+
+    try {
+        // Call implementation dependent close.
+        close();
+    } catch (const isc::Exception &ex) {
+        // Swallow exceptions. If we have some sort of error we'll log
+        // it but we won't propagate the throw.
+        LOG_ERROR(dhcp_ddns_logger,
+                  DHCP_DDNS_NCR_SEND_CLOSE_ERROR).arg(ex.what());
+    }
+
+    io_service_ = NULL;
+}
+
+void
+NameChangeSender::sendRequest(NameChangeRequestPtr& ncr) {
+    if (!amSending()) {
+        isc_throw(NcrSenderError, "sender is not ready to send");
+    }
+
+    if (!ncr) {
+        isc_throw(NcrSenderError, "request to send is empty");
+    }
+
+    if (MultiThreadingMgr::instance().getMode()) {
+        lock_guard<mutex> lock(*mutex_);
+        sendRequestInternal(ncr);
+    } else {
+        sendRequestInternal(ncr);
+    }
+}
+
+void
+NameChangeSender::sendRequestInternal(NameChangeRequestPtr& ncr) {
+    if (send_queue_.size() >= send_queue_max_) {
+        isc_throw(NcrSenderQueueFull,
+                  "send queue has reached maximum capacity: "
+                  << send_queue_max_);
+    }
+
+    // Put it on the queue.
+    send_queue_.push_back(ncr);
+
+    // Call sendNext to schedule the next one to go.
+    sendNext();
+}
+
+void
+NameChangeSender::sendNext() {
+    if (ncr_to_send_) {
+        // @todo Not sure if there is any risk of getting stuck here but
+        // an interval timer to defend would be good.
+        // In reality, the derivation should ensure they timeout themselves
+        return;
+    }
+
+    // If queue isn't empty, then get one from the front. Note we leave
+    // it on the front of the queue until we successfully send it.
+    if (!send_queue_.empty()) {
+        ncr_to_send_ = send_queue_.front();
+
+       // @todo start defense timer
+       // If a send were to hang and we timed it out, then timeout
+       // handler need to cycle thru open/close ?
+
+       // Call implementation dependent send.
+       doSend(ncr_to_send_);
+    }
+}
+
+void
+NameChangeSender::invokeSendHandler(const NameChangeSender::Result result) {
+    if (MultiThreadingMgr::instance().getMode()) {
+        lock_guard<mutex> lock(*mutex_);
+        invokeSendHandlerInternal(result);
+    } else {
+        invokeSendHandlerInternal(result);
+    }
+}
+
+void
+NameChangeSender::invokeSendHandlerInternal(const NameChangeSender::Result result) {
+    // @todo reset defense timer
+    if (result == SUCCESS) {
+        // It shipped so pull it off the queue.
+        send_queue_.pop_front();
+    }
+
+    // Invoke the completion handler passing in the result and a pointer
+    // the request involved.
+    // Surround the invocation with a try-catch. The invoked handler is
+    // not supposed to throw, but in the event it does we will at least
+    // report it.
+    try {
+        send_handler_(result, ncr_to_send_);
+    } catch (const std::exception& ex) {
+        LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_UNCAUGHT_NCR_SEND_HANDLER_ERROR)
+                  .arg(ex.what());
+    }
+
+    // Clear the pending ncr pointer.
+    ncr_to_send_.reset();
+
+    // Set up the next send
+    try {
+        if (amSending()) {
+            sendNext();
+        }
+    } catch (const isc::Exception& ex) {
+        // It is possible though unlikely, for sendNext to fail without
+        // scheduling the send. While, unlikely, it does mean the callback
+        // will not get called with a failure. A throw here would surface
+        // at the IOService::run (or run variant) invocation.  So we will
+        // close the window by invoking the application handler with
+        // a failed result, and let the application layer sort it out.
+        LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_NCR_SEND_NEXT_ERROR)
+                  .arg(ex.what());
+
+        // Invoke the completion handler passing in failed result.
+        // Surround the invocation with a try-catch. The invoked handler is
+        // not supposed to throw, but in the event it does we will at least
+        // report it.
+        try {
+            send_handler_(ERROR, ncr_to_send_);
+        } catch (const std::exception& ex) {
+            LOG_ERROR(dhcp_ddns_logger,
+                      DHCP_DDNS_UNCAUGHT_NCR_SEND_HANDLER_ERROR).arg(ex.what());
+        }
+    }
+}
+
+void
+NameChangeSender::skipNext() {
+    if (MultiThreadingMgr::instance().getMode()) {
+        lock_guard<mutex> lock(*mutex_);
+        skipNextInternal();
+    } else {
+        skipNextInternal();
+    }
+}
+
+void
+NameChangeSender::skipNextInternal() {
+    if (!send_queue_.empty()) {
+        // Discards the request at the front of the queue.
+        send_queue_.pop_front();
+    }
+}
+
+void
+NameChangeSender::clearSendQueue() {
+    if (amSending()) {
+        isc_throw(NcrSenderError, "Cannot clear queue while sending");
+    }
+
+    if (MultiThreadingMgr::instance().getMode()) {
+        lock_guard<mutex> lock(*mutex_);
+        send_queue_.clear();
+    } else {
+        send_queue_.clear();
+    }
+}
+
+void
+NameChangeSender::setQueueMaxSize(const size_t new_max) {
+    if (new_max == 0) {
+        isc_throw(NcrSenderError, "NameChangeSender:"
+                  " queue size must be greater than zero");
+    }
+
+    send_queue_max_ = new_max;
+}
+
+size_t
+NameChangeSender::getQueueSize() const {
+    if (MultiThreadingMgr::instance().getMode()) {
+        lock_guard<mutex> lock(*mutex_);
+        return (getQueueSizeInternal());
+    } else {
+        return (getQueueSizeInternal());
+    }
+}
+
+size_t
+NameChangeSender::getQueueSizeInternal() const {
+    return (send_queue_.size());
+}
+
+const NameChangeRequestPtr&
+NameChangeSender::peekAt(const size_t index) const {
+    if (MultiThreadingMgr::instance().getMode()) {
+        lock_guard<mutex> lock(*mutex_);
+        return (peekAtInternal(index));
+    } else {
+        return (peekAtInternal(index));
+    }
+}
+
+const NameChangeRequestPtr&
+NameChangeSender::peekAtInternal(const size_t index) const {
+    auto size = getQueueSizeInternal();
+    if (index >= size) {
+        isc_throw(NcrSenderError,
+                  "NameChangeSender::peekAt peek beyond end of queue attempted"
+                  << " index: " << index << " queue size: " << size);
+    }
+
+    return (send_queue_.at(index));
+}
+
+bool
+NameChangeSender::isSendInProgress() const {
+    if (MultiThreadingMgr::instance().getMode()) {
+        lock_guard<mutex> lock(*mutex_);
+        return ((ncr_to_send_) ? true : false);
+    } else {
+        return ((ncr_to_send_) ? true : false);
+    }
+}
+
+void
+NameChangeSender::assumeQueue(NameChangeSender& source_sender) {
+    if (source_sender.amSending()) {
+        isc_throw(NcrSenderError, "Cannot assume queue:"
+                  " source sender is actively sending");
+    }
+
+    if (amSending()) {
+        isc_throw(NcrSenderError, "Cannot assume queue:"
+                  " target sender is actively sending");
+    }
+
+    if (getQueueMaxSize() < source_sender.getQueueSize()) {
+        isc_throw(NcrSenderError, "Cannot assume queue:"
+                  " source queue count exceeds target queue max");
+    }
+
+    if (MultiThreadingMgr::instance().getMode()) {
+        lock_guard<mutex> lock(*mutex_);
+        assumeQueueInternal(source_sender);
+    } else {
+        assumeQueueInternal(source_sender);
+    }
+}
+
+void
+NameChangeSender::assumeQueueInternal(NameChangeSender& source_sender) {
+    if (!send_queue_.empty()) {
+        isc_throw(NcrSenderError, "Cannot assume queue:"
+                  " target queue is not empty");
+    }
+
+    send_queue_.swap(source_sender.getSendQueue());
+}
+
+int
+NameChangeSender::getSelectFd() {
+    isc_throw(NotImplemented, "NameChangeSender::getSelectFd is not supported");
+}
+
+void
+NameChangeSender::runReadyIO() {
+    if (!io_service_) {
+        isc_throw(NcrSenderError, "NameChangeSender::runReadyIO"
+                  " sender io service is null");
+    }
+
+    // We shouldn't be here if IO isn't ready to execute.
+    // By running poll we're guaranteed not to hang.
+    /// @todo Trac# 3325 requests that asiolink::IOService provide a
+    /// wrapper for poll().
+    io_service_->get_io_service().poll_one();
+}
+
+}  // namespace dhcp_ddns
+}  // namespace isc
diff --git a/src/lib/dhcp_ddns/ncr_io.h b/src/lib/dhcp_ddns/ncr_io.h
new file mode 100644
index 0000000..664057d
--- /dev/null
+++ b/src/lib/dhcp_ddns/ncr_io.h
@@ -0,0 +1,853 @@
+// Copyright (C) 2013-2020 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/.
+
+#ifndef NCR_IO_H
+#define NCR_IO_H
+
+/// @file ncr_io.h
+/// @brief This file defines abstract classes for exchanging NameChangeRequests.
+///
+/// These classes are used for sending and receiving requests to update DNS
+/// information for FQDNs embodied as NameChangeRequests (aka NCRs). Ultimately,
+/// NCRs must move through the following three layers in order to implement
+/// DHCP-DDNS:
+///
+///    * Application layer - the business layer which needs to
+///    transport NameChangeRequests, and is unaware of the means by which
+///    they are transported.
+///
+///    * NameChangeRequest layer - This is the layer which acts as the
+///    intermediary between the Application layer and the IO layer.  It must
+///    be able to move NameChangeRequests to the IO layer as raw data and move
+///    raw data from the IO layer in the Application layer as
+///    NameChangeRequests.
+///
+///    * IO layer - the low-level layer that is directly responsible for
+///    sending and receiving data asynchronously and is supplied through
+///    other libraries.  This layer is largely unaware of the nature of the
+///    data being transmitted.  In other words, it doesn't know beans about
+///    NCRs.
+///
+/// The abstract classes defined here implement the latter, middle layer,
+/// the NameChangeRequest layer.  There are two types of participants in this
+/// middle ground:
+///
+///    * listeners - Receive NCRs from one or more sources. The DHCP-DDNS
+///   application, (aka D2), is a listener. Listeners are embodied by the
+///   class, NameChangeListener.
+///
+///    * senders - sends NCRs to a given target.  DHCP servers are senders.
+///   Senders are embodied by the class, NameChangeSender.
+///
+/// These two classes present a public interface for asynchronous
+/// communications that is independent of the IO layer mechanisms.  While the
+/// type and details of the IO mechanism are not relevant to either class, it
+/// is presumed to use isc::asiolink library for asynchronous event processing.
+
+#include <asiolink/io_address.h>
+#include <asiolink/io_service.h>
+#include <dhcp_ddns/ncr_msg.h>
+#include <exceptions/exceptions.h>
+
+#include <boost/scoped_ptr.hpp>
+
+#include <deque>
+#include <mutex>
+
+namespace isc {
+namespace dhcp_ddns {
+
+/// @brief Defines the list of socket protocols supported.
+/// Currently only UDP is implemented.
+/// @todo TCP is intended to be implemented prior 1.0 release.
+/// @todo Give some thought to an ANY protocol which might try
+/// first as UDP then as TCP, etc.
+enum NameChangeProtocol {
+  NCR_UDP,
+  NCR_TCP
+};
+
+/// @brief Function which converts text labels to @ref NameChangeProtocol enums.
+///
+/// @param protocol_str text to convert to an enum.
+/// Valid string values: "UDP", "TCP"
+///
+/// @return NameChangeProtocol value which maps to the given string.
+///
+/// @throw isc::BadValue if given a string value which does not map to an
+/// enum value.
+extern NameChangeProtocol stringToNcrProtocol(const std::string& protocol_str);
+
+/// @brief Function which converts @ref NameChangeProtocol enums to text labels.
+///
+/// @param protocol enum value to convert to label
+///
+/// @return std:string containing the text label if the value is valid, or
+/// "UNKNOWN" if not.
+extern std::string ncrProtocolToString(NameChangeProtocol protocol);
+
+/// @brief Exception thrown if an NcrListenerError encounters a general error.
+class NcrListenerError : public isc::Exception {
+public:
+    NcrListenerError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+/// @brief Exception thrown if an error occurs during IO source open.
+class NcrListenerOpenError : public isc::Exception {
+public:
+    NcrListenerOpenError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+/// @brief Exception thrown if an error occurs initiating an IO receive.
+class NcrListenerReceiveError : public isc::Exception {
+public:
+    NcrListenerReceiveError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+
+/// @brief Abstract interface for receiving NameChangeRequests.
+///
+/// NameChangeListener provides the means to:
+/// -  Supply a callback to invoke upon receipt of an NCR or a listening
+/// error
+/// -  Start listening using a given IOService instance to process events
+/// -  Stop listening
+///
+/// It implements the high level logic flow to listen until a request arrives,
+/// invoke the implementation's handler and return to listening for the next
+/// request.
+///
+/// It provides virtual methods that allow derivations supply implementations
+/// to open the appropriate IO source, perform a listen, and close the IO
+/// source.
+///
+/// The overall design is based on a callback chain. The listener's caller (the
+/// application) supplies an "application" layer callback through which it will
+/// receive inbound NameChangeRequests.  The listener derivation will supply
+/// its own callback to the IO layer to process receive events from its IO
+/// source.  This is referred to as the NameChangeRequest completion handler.
+/// It is through this handler that the NameChangeRequest layer gains access
+/// to the low level IO read service results.  It is expected to assemble
+/// NameChangeRequests from the inbound data and forward them to the
+/// application layer by invoking the application layer callback registered
+/// with the listener.
+///
+/// The application layer callback is structured around a nested class,
+/// RequestReceiveHandler.  It consists of single, abstract operator() which
+/// accepts a result code and a pointer to a NameChangeRequest as parameters.
+/// In order to receive inbound NCRs, a caller implements a derivation of the
+/// RequestReceiveHandler and supplies an instance of this derivation to the
+/// NameChangeListener constructor. This "registers" the handler with the
+/// listener.
+///
+/// To begin listening, the caller invokes the listener's startListener()
+/// method, passing in an IOService instance.  This in turn will pass the
+/// IOService into the virtual method, open().  The open method is where the
+/// listener derivation performs the steps necessary to prepare its IO source
+/// for reception (e.g. opening a socket, connecting to a database).
+///
+/// Assuming the open is successful, startListener will call receiveNext, to
+/// initiate an asynchronous receive.  This method calls the virtual method,
+/// doReceive().  The listener derivation uses doReceive to instigate an IO
+/// layer asynchronous receive passing in its IO layer callback to
+/// handle receive events from the IO source.
+///
+/// As stated earlier, the derivation's NameChangeRequest completion handler
+/// MUST invoke the application layer handler registered with the listener.
+/// This is done by passing in either a success status and a populated
+/// NameChangeRequest or an error status and an empty request into the
+/// listener's invokeRecvHandler method. This is the mechanism by which the
+/// listener's caller is handed inbound NCRs.
+class NameChangeListener {
+public:
+
+    /// @brief Defines the outcome of an asynchronous NCR receive
+    enum Result {
+        SUCCESS,
+        TIME_OUT,
+        STOPPED,
+        ERROR
+    };
+
+    /// @brief Abstract class for defining application layer receive callbacks.
+    ///
+    /// Applications which will receive NameChangeRequests must provide a
+    /// derivation of this class to the listener constructor in order to
+    /// receive NameChangeRequests.
+    class RequestReceiveHandler {
+    public:
+
+        /// @brief Function operator implementing a NCR receive callback.
+        ///
+        /// This method allows the application to receive the inbound
+        /// NameChangeRequests. It is intended to function as a hand off of
+        /// information and should probably not be time-consuming.
+        ///
+        /// @param result contains that receive outcome status.
+        /// @param ncr is a pointer to the newly received NameChangeRequest if
+        /// result is NameChangeListener::SUCCESS.  It is indeterminate other
+        /// wise.
+        ///
+        /// @throw This method MUST NOT throw.
+        virtual void operator ()(const Result result,
+                                 NameChangeRequestPtr& ncr) = 0;
+
+        virtual ~RequestReceiveHandler() {
+        }
+    };
+
+    /// @brief Constructor
+    ///
+    /// @param recv_handler is a pointer the application layer handler to be
+    /// invoked each time a NCR is received or a receive error occurs.
+    NameChangeListener(RequestReceiveHandler& recv_handler);
+
+    /// @brief Destructor
+    virtual ~NameChangeListener() {
+    };
+
+    /// @brief Prepares the IO for reception and initiates the first receive.
+    ///
+    /// Calls the derivation's open implementation to initialize the IO layer
+    /// source for receiving inbound requests.  If successful, it starts the
+    /// first asynchronous read by receiveNext.
+    ///
+    /// @param io_service is the IOService that will handle IO event processing.
+    ///
+    /// @throw NcrListenError if the listener is already "listening" or
+    /// in the event the open or doReceive methods fail.
+    void startListening(isc::asiolink::IOService& io_service);
+
+    /// @brief Closes the IO source and stops listen logic.
+    ///
+    /// Calls the derivation's implementation of close and marks the state
+    /// as not listening.
+    void stopListening();
+
+protected:
+    /// @brief Initiates an asynchronous receive
+    ///
+    /// Sets context information to indicate that IO is in progress and invokes
+    /// the derivation's asynchronous receive method, doReceive.  Note doReceive
+    /// should not be called outside this method to ensure context information
+    /// integrity.
+    ///
+    /// @throw Derivation's doReceive method may throw isc::Exception upon
+    /// error.
+    void receiveNext();
+
+    /// @brief Calls the NCR receive handler registered with the listener.
+    ///
+    /// This is the hook by which the listener's caller's NCR receive handler
+    /// is called.  This method MUST be invoked by the derivation's
+    /// implementation of doReceive.
+    ///
+    /// NOTE:
+    /// The handler invoked by this method MUST NOT THROW. The handler is
+    /// at application level and should trap and handle any errors at
+    /// that level, rather than throw exceptions.  If an error has occurred
+    /// prior to invoking the handler, it will be expressed in terms a failed
+    /// result being passed to the handler, not a throw.  Therefore any
+    /// exceptions at the handler level are application issues and should be
+    /// dealt with at that level.
+    ///
+    /// This method does wrap the handler invocation within a try-catch
+    /// block as a fail-safe.  The exception will be logged but the
+    /// receive logic will continue.  What this implies is that continued
+    /// operation may or may not succeed as the application has violated
+    /// the interface contract.
+    ///
+    /// @param result contains that receive outcome status.
+    /// @param ncr is a pointer to the newly received NameChangeRequest if
+    /// result is NameChangeListener::SUCCESS.  It is indeterminate other
+    /// wise.
+    void invokeRecvHandler(const Result result, NameChangeRequestPtr& ncr);
+
+    /// @brief Abstract method which opens the IO source for reception.
+    ///
+    /// The derivation uses this method to perform the steps needed to
+    /// prepare the IO source to receive requests.
+    ///
+    /// @param io_service is the IOService that process IO events.
+    ///
+    /// @throw If the implementation encounters an error it MUST
+    /// throw it as an isc::Exception or derivative.
+    virtual void open(isc::asiolink::IOService& io_service) = 0;
+
+    /// @brief Abstract method which closes the IO source.
+    ///
+    /// The derivation uses this method to perform the steps needed to
+    /// "close" the IO source.
+    ///
+    /// @throw If the implementation encounters an error it  MUST
+    /// throw it as an isc::Exception or derivative.
+    virtual void close() = 0;
+
+    /// @brief Initiates an IO layer asynchronous read.
+    ///
+    /// The derivation uses this method to perform the steps needed to
+    /// initiate an asynchronous read of the IO source with the
+    /// derivation's IO layer handler as the IO completion callback.
+    ///
+    /// @throw If the implementation encounters an error it  MUST
+    /// throw it as an isc::Exception or derivative.
+    virtual void doReceive() = 0;
+
+public:
+
+    /// @brief Returns true if the listener is listening, false otherwise.
+    ///
+    /// A true value indicates that the IO source has been opened successfully,
+    /// and that receive loop logic is active.  This implies that closing the
+    /// IO source will interrupt that operation, resulting in a callback
+    /// invocation.
+    ///
+    /// @return The listening mode.
+    bool amListening() const {
+        return (listening_);
+    }
+
+    /// @brief Returns true if the listener has an IO call in progress.
+    ///
+    /// A true value indicates that the listener has an asynchronous IO in
+    /// progress which will complete at some point in the future. Completion
+    /// of the call will invoke the registered callback.  It is important to
+    /// understand that the listener and its related objects should not be
+    /// deleted while there is an IO call pending.  This can result in the
+    /// IO service attempting to invoke methods on objects that are no longer
+    /// valid.
+    ///
+    /// @return The IO pending flag.
+    bool isIoPending() const {
+        return (io_pending_);
+    }
+
+private:
+    /// @brief Sets the listening indicator to the given value.
+    ///
+    /// Note, this method is private as it is used the base class is solely
+    /// responsible for managing the state.
+    ///
+    /// @param value is the new value to assign to the indicator.
+    void setListening(bool value) {
+        listening_ = value;
+    }
+
+    /// @brief Indicates if the listener is in listening mode.
+    bool listening_;
+
+    /// @brief Indicates that listener has an async IO pending completion.
+    bool io_pending_;
+
+    /// @brief Application level NCR receive completion handler.
+    RequestReceiveHandler& recv_handler_;
+};
+
+/// @brief Defines a smart pointer to an instance of a listener.
+typedef boost::shared_ptr<NameChangeListener> NameChangeListenerPtr;
+
+
+/// @brief Thrown when a NameChangeSender encounters an error.
+class NcrSenderError : public isc::Exception {
+public:
+    NcrSenderError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+/// @brief Exception thrown if an error occurs during IO source open.
+class NcrSenderOpenError : public isc::Exception {
+public:
+    NcrSenderOpenError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+/// @brief Exception thrown if an error occurs initiating an IO send.
+class NcrSenderQueueFull : public isc::Exception {
+public:
+    NcrSenderQueueFull(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+/// @brief Exception thrown if an error occurs initiating an IO send.
+class NcrSenderSendError : public isc::Exception {
+public:
+    NcrSenderSendError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+
+/// @brief Abstract interface for sending NameChangeRequests.
+///
+/// NameChangeSender provides the means to:
+/// - Supply a callback to invoke upon completing the delivery of an NCR or a
+/// send error
+/// - Start sending using a given IOService instance to process events
+/// - Queue NCRs for delivery
+/// - Stop sending
+///
+/// It implements the high level logic flow to queue requests for delivery,
+/// and ship them one at a time, waiting for the send to complete prior to
+/// sending the next request in the queue.  If a send fails, the request
+/// will remain at the front of queue and the send will be retried
+/// endlessly unless the caller dequeues the request.  Note, it is presumed that
+/// a send failure is some form of IO error such as loss of connectivity and
+/// not a message content error.  It should not be possible to queue an invalid
+/// message.
+///
+/// It should be noted that once a request is placed onto the send queue it
+/// will remain there until one of three things occur:
+///     * It is successfully delivered
+///     * @c NameChangeSender::skipNext() is called
+///     * @c NameChangeSender::clearSendQueue() is called
+///
+/// The queue contents are preserved across start and stop listening
+/// transitions. This is to provide for error recovery without losing
+/// undelivered requests.
+
+/// It provides virtual methods so derivations may supply implementations to
+/// open the appropriate IO sink, perform a send, and close the IO sink.
+///
+/// The overall design is based on a callback chain.  The sender's caller (the
+/// application) supplies an "application" layer callback through which it will
+/// be given send completion notifications. The sender derivation will employ
+/// its own callback at the IO layer to process send events from its IO sink.
+/// This callback is expected to forward the outcome of each asynchronous send
+/// to the application layer by invoking the application layer callback
+/// registered with the sender.
+///
+/// The application layer callback is structured around a nested class,
+/// RequestSendHandler.  It consists of single, abstract operator() which
+/// accepts a result code and a pointer to a NameChangeRequest as parameters.
+/// In order to receive send completion notifications, a caller implements a
+/// derivation of the RequestSendHandler and supplies an instance of this
+/// derivation to the NameChangeSender constructor. This "registers" the
+/// handler with the sender.
+///
+/// To begin sending, the caller invokes the listener's startSending()
+/// method, passing in an IOService instance.  This in turn will pass the
+/// IOService into the virtual method, open().  The open method is where the
+/// sender derivation performs the steps necessary to prepare its IO sink for
+/// output (e.g. opening a socket, connecting to a database).  At this point,
+/// the sender is ready to send messages.
+///
+/// In order to send a request, the application layer invokes the sender
+/// method, sendRequest(), passing in the NameChangeRequest to send.  This
+/// method places the request onto the back of the send queue, and then invokes
+/// the sender method, sendNext().
+///
+/// If there is already a send in progress when sendNext() is called, the method
+/// will return immediately rather than initiate the next send.  This is to
+/// ensure that sends are processed sequentially.
+///
+/// If there is not a send in progress and the send queue is not empty,
+/// the sendNext method will pass the NCR at the front of the send queue into
+/// the virtual doSend() method.
+///
+/// The sender derivation uses this doSend() method to instigate an IO layer
+/// asynchronous send with its IO layer callback to handle send events from its
+/// IO sink.
+///
+/// As stated earlier, the derivation's IO layer callback MUST invoke the
+/// application layer handler registered with the sender.  This is done by
+/// passing in  a status indicating the outcome of the send into the sender's
+/// invokeSendHandler method. This is the mechanism by which the sender's
+/// caller is handed outbound notifications.
+
+/// After invoking the application layer handler, the invokeSendHandler method
+/// will call the sendNext() method to initiate the next send.  This ensures
+/// that requests continue to dequeue and ship.
+///
+class NameChangeSender {
+public:
+
+    /// @brief Defines the type used for the request send queue.
+    typedef std::deque<NameChangeRequestPtr> SendQueue;
+
+    /// @brief Defines a default maximum number of entries in the send queue.
+    static const size_t MAX_QUEUE_DEFAULT = 1024;
+
+    /// @brief Defines the outcome of an asynchronous NCR send.
+    enum Result {
+        SUCCESS,
+        TIME_OUT,
+        STOPPED,
+        ERROR
+    };
+
+    /// @brief Abstract class for defining application layer send callbacks.
+    ///
+    /// Applications which will send NameChangeRequests must provide a
+    /// derivation of this class to the sender constructor in order to
+    /// receive send outcome notifications.
+    class RequestSendHandler {
+    public:
+
+        /// @brief Function operator implementing a NCR send callback.
+        ///
+        /// This method allows the application to receive the outcome of
+        /// each send.  It is intended to function as a hand off of information
+        /// and should probably not be time-consuming.
+        ///
+        /// @param result contains that send outcome status.
+        /// @param ncr is a pointer to the NameChangeRequest that was
+        /// delivered (or attempted).
+        ///
+        /// @throw This method MUST NOT throw.
+        virtual void operator ()(const Result result,
+                                 NameChangeRequestPtr& ncr) = 0;
+
+        virtual ~RequestSendHandler() {
+        }
+    };
+
+    /// @brief Constructor
+    ///
+    /// @param send_handler is a pointer the application layer handler to be
+    /// invoked each time a NCR send attempt completes.
+    /// @param send_queue_max is the maximum number of entries allowed in the
+    /// send queue.  Once the maximum number is reached, all calls to
+    /// sendRequest will fail with an exception.
+    NameChangeSender(RequestSendHandler& send_handler,
+                     size_t send_queue_max = MAX_QUEUE_DEFAULT);
+
+    /// @brief Destructor
+    virtual ~NameChangeSender() {
+    }
+
+    /// @brief Prepares the IO for transmission.
+    ///
+    /// Calls the derivation's open implementation to initialize the IO layer
+    /// sink for sending outbound requests.
+    ///
+    /// @param io_service is the IOService that will handle IO event processing.
+    ///
+    /// @throw NcrSenderError if the sender is already "sending" or
+    /// NcrSenderOpenError if the open fails.
+    void startSending(isc::asiolink::IOService & io_service);
+
+    /// @brief Closes the IO sink and stops send logic.
+    ///
+    /// Calls the derivation's implementation of close and marks the state
+    /// as not sending.
+    void stopSending();
+
+    /// @brief Queues the given request to be sent.
+    ///
+    /// The given request is placed at the back of the send queue and then
+    /// sendNext is invoked.
+    ///
+    /// @param ncr is the NameChangeRequest to send.
+    ///
+    /// @throw NcrSenderError if the sender is not in sending state or
+    /// the request is empty; NcrSenderQueueFull if the send queue has reached
+    /// capacity.
+    void sendRequest(NameChangeRequestPtr& ncr);
+
+    /// @brief Move all queued requests from a given sender into the send queue
+    ///
+    /// Moves all of the entries in the given sender's queue and places them
+    /// into send queue.  This provides a mechanism of reassigning queued
+    /// messages from one sender to another. This is useful for dealing with
+    /// dynamic configuration changes.
+    ///
+    /// @param source_sender from whom the queued messages will be taken
+    ///
+    /// @throw NcrSenderError if either sender is in send mode, if the number of
+    /// messages in the source sender's queue is larger than this sender's
+    /// maximum queue size, or if this sender's queue is not empty.
+    void assumeQueue(NameChangeSender& source_sender);
+
+    /// @brief Returns a file descriptor suitable for use with select
+    ///
+    /// The value returned is an open file descriptor which can be used with
+    /// select() system call to monitor the sender for IO events.  This allows
+    /// NameChangeSenders to be used in applications which use select, rather
+    /// than IOService to wait for IO events to occur.
+    ///
+    /// @warning Attempting other use of this value may lead to unpredictable
+    /// behavior in the sender.
+    ///
+    /// @return Returns an "open" file descriptor
+    ///
+    /// @throw NcrSenderError if the sender is not in send mode,
+    virtual int getSelectFd() = 0;
+
+    /// @brief Returns whether or not the sender has IO ready to process.
+    ///
+    /// @return true if the sender has at IO ready, false otherwise.
+    virtual bool ioReady() = 0;
+
+private:
+
+    /// @brief Prepares the IO for transmission in a thread safe context.
+    ///
+    /// @param io_service is the IOService that will handle IO event processing.
+    void startSendingInternal(isc::asiolink::IOService & io_service);
+
+    /// @brief Queues the given request to be sent in a thread safe context.
+    ///
+    /// @param ncr is the NameChangeRequest to send.
+    ///
+    /// @throw NcrSenderQueueFull if the send queue has reached capacity.
+    void sendRequestInternal(NameChangeRequestPtr& ncr);
+
+    /// @brief Move all queued requests from a given sender into the send queue
+    /// in a thread safe context.
+    ///
+    /// @param source_sender from whom the queued messages will be taken
+    ///
+    /// @throw NcrSenderError if this sender's queue is not empty.
+    void assumeQueueInternal(NameChangeSender& source_sender);
+
+    /// @brief Calls the NCR send completion handler registered with the
+    /// sender in a thread safe context.
+    ///
+    /// @param result contains that send outcome status.
+    void invokeSendHandlerInternal(const NameChangeSender::Result result);
+
+    /// @brief Removes the request at the front of the send queue in a thread
+    /// safe context.
+    void skipNextInternal();
+
+    /// @brief Returns the number of entries currently in the send queue in a
+    /// thread safe context.
+    ///
+    /// @return the queue size.
+    size_t getQueueSizeInternal() const;
+
+    /// @brief Returns the entry at a given position in the queue in a thread
+    /// safe context.
+    ///
+    /// @return Pointer reference to the queue entry.
+    ///
+    /// @throw NcrSenderError if the given index is beyond the
+    /// end of the queue.
+    const NameChangeRequestPtr& peekAtInternal(const size_t index) const;
+
+protected:
+
+    /// @brief Dequeues and sends the next request on the send queue in a thread
+    /// safe context.
+    ///
+    /// If there is already a send in progress just return. If there is not
+    /// a send in progress and the send queue is not empty the grab the next
+    /// message on the front of the queue and call doSend().
+    void sendNext();
+
+    /// @brief Calls the NCR send completion handler registered with the
+    /// sender.
+    ///
+    /// This is the hook by which the sender's caller's NCR send completion
+    /// handler is called.  This method MUST be invoked by the derivation's
+    /// implementation of doSend.  Note that if the send was a success, the
+    /// entry at the front of the queue is removed from the queue.
+    /// If not we leave it there so we can retry it.  After we invoke the
+    /// handler we clear the pending ncr value and queue up the next send.
+    ///
+    /// NOTE:
+    /// The handler invoked by this method MUST NOT THROW. The handler is
+    /// application level logic and should trap and handle any errors at
+    /// that level, rather than throw exceptions.  If IO errors have occurred
+    /// prior to invoking the handler, they are expressed in terms a failed
+    /// result being passed to the handler.  Therefore any exceptions at the
+    /// handler level are application issues and should be dealt with at that
+    /// level.
+    ///
+    /// This method does wrap the handler invocation within a try-catch
+    /// block as a fail-safe.  The exception will be logged but the
+    /// send logic will continue.  What this implies is that continued
+    /// operation may or may not succeed as the application has violated
+    /// the interface contract.
+    ///
+    /// @param result contains that send outcome status.
+    void invokeSendHandler(const NameChangeSender::Result result);
+
+    /// @brief Abstract method which opens the IO sink for transmission.
+    ///
+    /// The derivation uses this method to perform the steps needed to
+    /// prepare the IO sink to send requests.
+    ///
+    /// @param io_service is the IOService that process IO events.
+    ///
+    /// @throw If the implementation encounters an error it MUST
+    /// throw it as an isc::Exception or derivative.
+    virtual void open(isc::asiolink::IOService& io_service) = 0;
+
+    /// @brief Abstract method which closes the IO sink.
+    ///
+    /// The derivation uses this method to perform the steps needed to
+    /// "close" the IO sink.
+    ///
+    /// @throw If the implementation encounters an error it MUST
+    /// throw it as an isc::Exception or derivative.
+    virtual void close() = 0;
+
+    /// @brief Initiates an IO layer asynchronous send
+    ///
+    /// The derivation uses this method to perform the steps needed to
+    /// initiate an asynchronous send through the IO sink of the given NCR.
+    ///
+    /// @param ncr is a pointer to the NameChangeRequest to send.
+    /// derivation's IO layer handler as the IO completion callback.
+    ///
+    /// @throw If the implementation encounters an error it MUST
+    /// throw it as an isc::Exception or derivative.
+    virtual void doSend(NameChangeRequestPtr& ncr) = 0;
+
+public:
+
+    /// @brief Removes the request at the front of the send queue
+    ///
+    /// This method can be used to avoid further retries of a failed
+    /// send. It is provided primarily as a just-in-case measure. Since
+    /// a failed send results in the same request being retried continuously
+    /// this method makes it possible to remove that entry, causing the
+    /// subsequent entry in the queue to be attempted on the next send.
+    /// It is presumed that sends will only fail due to some sort of
+    /// communications issue. In the unlikely event that a request is
+    /// somehow tainted and causes an send failure based on its content,
+    /// this method provides a means to remove the message.
+    void skipNext();
+
+    /// @brief Flushes all entries in the send queue
+    ///
+    /// This method can be used to discard all of the NCRs currently in the
+    /// the send queue.  Note it may not be called while the sender is in
+    /// the sending state.
+    ///
+    /// @throw NcrSenderError if called and sender is in sending state.
+    void clearSendQueue();
+
+    /// @brief Returns true if the sender is in send mode, false otherwise.
+    ///
+    /// A true value indicates that the IO sink has been opened successfully,
+    /// and that send loop logic is active.
+    ///
+    /// @return The send mode.
+    bool amSending() const {
+        return (sending_);
+    }
+
+    /// @brief Returns true when a send is in progress.
+    ///
+    /// A true value indicates that a request is actively in the process of
+    /// being delivered.
+    ///
+    /// @return The send in progress flag.
+    bool isSendInProgress() const;
+
+    /// @brief Returns the maximum number of entries allowed in the send queue.
+    ///
+    /// @return The queue maximum size.
+    size_t getQueueMaxSize() const  {
+        return (send_queue_max_);
+    }
+
+    /// @brief Sets the maximum queue size to the given value.
+    ///
+    /// Sets the maximum number of entries allowed in the queue to the
+    /// the given value.
+    ///
+    /// @param new_max the new value to use as the maximum
+    ///
+    /// @throw NcrSenderError if the value is less than one.
+    void setQueueMaxSize(const size_t new_max);
+
+    /// @brief Returns the number of entries currently in the send queue.
+    ///
+    /// @return The queue size.
+    size_t getQueueSize() const;
+
+    /// @brief Returns the entry at a given position in the queue.
+    ///
+    /// Note that the entry is not removed from the queue.
+    ///
+    /// @param index the index of the entry in the queue to fetch.
+    /// Valid values are 0 (front of the queue) to (queue size - 1).
+    ///
+    /// @return Pointer reference to the queue entry.
+    ///
+    /// @throw NcrSenderError if the given index is beyond the
+    /// end of the queue.
+    const NameChangeRequestPtr& peekAt(const size_t index) const;
+
+    /// @brief Processes sender IO events
+    ///
+    /// Executes at most one ready handler on the sender's IO service. If
+    /// no handlers are ready it returns immediately.
+    ///
+    /// @warning - Running all ready handlers, in theory, could process all
+    /// messages currently queued.
+    ///
+    /// NameChangeSender daisy chains requests together in its completion
+    /// by one message completion's handler initiating the next message's send.
+    /// When using UDP, a send immediately marks its event handler as ready
+    /// to run.  If this occurs inside a call to ioservice::poll() or run(),
+    /// that event will also be run.  If that handler calls UDP send then
+    /// that send's handler will be marked ready and executed and so on.  If
+    /// there were 1000 messages in the queue then all them would be sent from
+    /// within the context of one call to runReadyIO().
+    /// By running only one handler at time, we ensure that NCR IO activity
+    /// doesn't starve other processing.  It is unclear how much of a real
+    /// threat this poses but for now it is best to err on the side of caution.
+    virtual void runReadyIO();
+
+protected:
+
+    /// @brief Returns a reference to the send queue.
+    ///
+    /// @return The send queue.
+    SendQueue& getSendQueue() {
+        return (send_queue_);
+    }
+
+private:
+
+    /// @brief Sets the sending indicator to the given value.
+    ///
+    /// Note, this method is private as it is used the base class is solely
+    /// responsible for managing the state.
+    ///
+    /// @param value is the new value to assign to the indicator.
+    void setSending(bool value) {
+        sending_ = value;
+    }
+
+    /// @brief Boolean indicator which tracks sending status.
+    bool sending_;
+
+    /// @brief A pointer to registered send completion handler.
+    RequestSendHandler& send_handler_;
+
+    /// @brief Maximum number of entries permitted in the send queue.
+    size_t send_queue_max_;
+
+    /// @brief Queue of the requests waiting to be sent.
+    SendQueue send_queue_;
+
+    /// @brief Pointer to the request which is in the process of being sent.
+    NameChangeRequestPtr ncr_to_send_;
+
+    /// @brief Pointer to the IOService currently being used by the sender.
+    /// @note We need to remember the io_service but we receive it by
+    /// reference.  Use a raw pointer to store it.  This value should never be
+    /// exposed and is only valid while in send mode.
+    asiolink::IOService* io_service_;
+
+    /// @brief The mutex used to protect internal state.
+    const boost::scoped_ptr<std::mutex> mutex_;
+};
+
+/// @brief Defines a smart pointer to an instance of a sender.
+typedef boost::shared_ptr<NameChangeSender> NameChangeSenderPtr;
+
+}  // namespace dhcp_ddns
+}  // namespace isc
+
+#endif
diff --git a/src/lib/dhcp_ddns/ncr_msg.cc b/src/lib/dhcp_ddns/ncr_msg.cc
new file mode 100644
index 0000000..cc595b4
--- /dev/null
+++ b/src/lib/dhcp_ddns/ncr_msg.cc
@@ -0,0 +1,696 @@
+// Copyright (C) 2013-2021 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/.
+
+#include <config.h>
+
+#include <dhcp_ddns/ncr_msg.h>
+#include <asiolink/io_address.h>
+#include <asiolink/io_error.h>
+#include <cryptolink/cryptolink.h>
+#include <cryptolink/crypto_hash.h>
+#include <util/encode/hex.h>
+
+#include <boost/algorithm/string/predicate.hpp>
+
+#include <sstream>
+#include <limits>
+
+
+namespace isc {
+namespace dhcp_ddns {
+
+
+NameChangeFormat stringToNcrFormat(const std::string& fmt_str) {
+    if (boost::iequals(fmt_str, "JSON")) {
+        return FMT_JSON;
+    }
+
+    isc_throw(BadValue, "Invalid NameChangeRequest format: " << fmt_str);
+}
+
+
+std::string ncrFormatToString(NameChangeFormat format) {
+    if (format == FMT_JSON) {
+        return ("JSON");
+    }
+
+    std::ostringstream stream;
+    stream  << "UNKNOWN(" << format << ")";
+    return (stream.str());
+}
+
+/********************************* D2Dhcid ************************************/
+
+namespace {
+
+///
+/// @name Constants which define DHCID identifier-type
+//@{
+/// DHCID created from client's HW address.
+const uint8_t DHCID_ID_HWADDR   = 0x0;
+/// DHCID created from client identifier.
+const uint8_t DHCID_ID_CLIENTID = 0x1;
+/// DHCID created from DUID.
+const uint8_t DHCID_ID_DUID     = 0x2;
+
+}
+
+D2Dhcid::D2Dhcid() {
+}
+
+D2Dhcid::D2Dhcid(const std::string& data) {
+    fromStr(data);
+}
+
+D2Dhcid::D2Dhcid(const isc::dhcp::HWAddrPtr& hwaddr,
+                 const std::vector<uint8_t>& wire_fqdn) {
+    fromHWAddr(hwaddr, wire_fqdn);
+}
+
+D2Dhcid::D2Dhcid(const std::vector<uint8_t>& clientid_data,
+                 const std::vector<uint8_t>& wire_fqdn) {
+    fromClientId(clientid_data, wire_fqdn);
+}
+
+D2Dhcid::D2Dhcid(const isc::dhcp::DUID& duid,
+                 const std::vector<uint8_t>& wire_fqdn) {
+    fromDUID(duid, wire_fqdn);
+}
+
+
+void
+D2Dhcid::fromStr(const std::string& data) {
+    bytes_.clear();
+    try {
+        isc::util::encode::decodeHex(data, bytes_);
+    } catch (const isc::Exception& ex) {
+        isc_throw(NcrMessageError, "Invalid data in Dhcid: " << ex.what());
+    }
+}
+
+std::string
+D2Dhcid::toStr() const {
+    return (isc::util::encode::encodeHex(bytes_));
+}
+
+void
+D2Dhcid::fromClientId(const std::vector<uint8_t>& clientid_data,
+                      const std::vector<uint8_t>& wire_fqdn) {
+    // IPv4 Client ID containing a DUID looks like this in RFC4361
+    //  Type  IAID                DUID
+    // +-----+----+----+----+----+----+----+---
+    // | 255 | i1 | i2 | i3 | i4 | d1 | d2 |...
+    // +-----+----+----+----+----+----+----+---
+    if (!clientid_data.empty() && clientid_data[0] == 255) {
+        if (clientid_data.size() <= 5) {
+            isc_throw(isc::dhcp_ddns::DhcidRdataComputeError,
+                      "unable to compute DHCID from client identifier, embedded DUID "
+                      "length of: " << clientid_data.size() << ", is too short");
+        }
+        // RFC3315 states that the DUID is a type code of 2 octets followed
+        // by no more then 128 octets. So add the 5 from above and make sure
+        // the length is not too long.
+        if (clientid_data.size() > 135) {
+            isc_throw(isc::dhcp_ddns::DhcidRdataComputeError,
+                      "unable to compute DHCID from client identifier, embedded DUID "
+                      "length of: " << clientid_data.size() << ", is too long");
+        }
+        std::vector<uint8_t>::const_iterator start = clientid_data.begin() + 5;
+        std::vector<uint8_t>::const_iterator end = clientid_data.end();
+        std::vector<uint8_t> duid(start, end);
+        createDigest(DHCID_ID_DUID, duid, wire_fqdn);
+    } else {
+        createDigest(DHCID_ID_CLIENTID, clientid_data, wire_fqdn);
+    }
+}
+
+void
+D2Dhcid::fromHWAddr(const isc::dhcp::HWAddrPtr& hwaddr,
+                    const std::vector<uint8_t>& wire_fqdn) {
+    if (!hwaddr) {
+        isc_throw(isc::dhcp_ddns::DhcidRdataComputeError,
+                  "unable to compute DHCID from the HW address, "
+                  "NULL pointer has been specified");
+    } else if (hwaddr->hwaddr_.empty()) {
+        isc_throw(isc::dhcp_ddns::DhcidRdataComputeError,
+                  "unable to compute DHCID from the HW address, "
+                  "HW address is empty");
+    }
+    std::vector<uint8_t> hwaddr_data;
+    hwaddr_data.push_back(hwaddr->htype_);
+    hwaddr_data.insert(hwaddr_data.end(), hwaddr->hwaddr_.begin(),
+                       hwaddr->hwaddr_.end());
+    createDigest(DHCID_ID_HWADDR, hwaddr_data, wire_fqdn);
+}
+
+
+void
+D2Dhcid::fromDUID(const isc::dhcp::DUID& duid,
+                  const std::vector<uint8_t>& wire_fqdn) {
+
+    createDigest(DHCID_ID_DUID, duid.getDuid(), wire_fqdn);
+}
+
+void
+D2Dhcid::createDigest(const uint8_t identifier_type,
+                      const std::vector<uint8_t>& identifier_data,
+                      const std::vector<uint8_t>& wire_fqdn) {
+    // We get FQDN in the wire format, so we don't know if it is
+    // valid. It is caller's responsibility to make sure it is in
+    // the valid format. Here we just make sure it is not empty.
+    if (wire_fqdn.empty()) {
+        isc_throw(isc::dhcp_ddns::DhcidRdataComputeError,
+                  "empty FQDN used to create DHCID");
+    }
+
+    // It is a responsibility of the classes which encapsulate client
+    // identifiers, e.g. DUID, to validate the client identifier data.
+    // But let's be on the safe side and at least check that it is not
+    // empty.
+    if (identifier_data.empty()) {
+        isc_throw(isc::dhcp_ddns::DhcidRdataComputeError,
+                  "empty DUID used to create DHCID");
+    }
+
+    // A data buffer will be used to compute the digest.
+    std::vector<uint8_t> data = identifier_data;
+
+    // Append FQDN in the wire format.
+    data.insert(data.end(), wire_fqdn.begin(), wire_fqdn.end());
+
+    // Use the DUID and FQDN to compute the digest (see RFC4701, section 3).
+
+    isc::util::OutputBuffer hash(0);
+    try {
+        // We have checked already that the DUID and FQDN aren't empty
+        // so it is safe to assume that the data buffer is not empty.
+        cryptolink::digest(&data[0], data.size(), cryptolink::SHA256, hash);
+    } catch (const std::exception& ex) {
+        isc_throw(isc::dhcp_ddns::DhcidRdataComputeError,
+                  "error while generating DHCID from DUID: "
+                  << ex.what());
+    }
+
+    // The DHCID RDATA has the following structure:
+    //
+    //    < identifier-type > < digest-type > < digest >
+    //
+    // where identifier type
+
+    // Let's allocate the space for the identifier-type (2 bytes) and
+    // digest-type (1 byte). This is 3 bytes all together.
+    bytes_.resize(3 + hash.getLength());
+    // Leave first byte 0 and set the second byte. Those two bytes
+    // form the identifier-type.
+    bytes_[1] = identifier_type;
+    // Third byte is always equal to 1, which specifies SHA-256 digest type.
+    bytes_[2] = 1;
+    // Now let's append the digest.
+    std::memcpy(&bytes_[3], hash.getData(), hash.getLength());
+}
+
+std::ostream&
+operator<<(std::ostream& os, const D2Dhcid& dhcid) {
+    os << dhcid.toStr();
+    return (os);
+}
+
+
+
+/**************************** NameChangeRequest ******************************/
+
+NameChangeRequest::NameChangeRequest()
+    : change_type_(CHG_ADD), forward_change_(false),
+    reverse_change_(false), fqdn_(""), ip_io_address_("0.0.0.0"),
+    dhcid_(), lease_expires_on_(), lease_length_(0), conflict_resolution_(true),
+    status_(ST_NEW) {
+}
+
+NameChangeRequest::NameChangeRequest(const NameChangeType change_type,
+            const bool forward_change, const bool reverse_change,
+            const std::string& fqdn, const std::string& ip_address,
+            const D2Dhcid& dhcid,
+            const uint64_t lease_expires_on,
+            const uint32_t lease_length,
+            const bool conflict_resolution)
+    : change_type_(change_type), forward_change_(forward_change),
+    reverse_change_(reverse_change), fqdn_(fqdn), ip_io_address_("0.0.0.0"),
+    dhcid_(dhcid), lease_expires_on_(lease_expires_on),
+    lease_length_(lease_length), conflict_resolution_(conflict_resolution),
+    status_(ST_NEW) {
+
+    // User setter to validate fqdn.
+    setFqdn(fqdn);
+
+    // User setter to validate address.
+    setIpAddress(ip_address);
+
+    // Validate the contents. This will throw a NcrMessageError if anything
+    // is invalid.
+    validateContent();
+}
+
+NameChangeRequestPtr
+NameChangeRequest::fromFormat(const NameChangeFormat format,
+                              isc::util::InputBuffer& buffer) {
+    // Based on the format requested, pull the marshalled request from
+    // InputBuffer and pass it into the appropriate format-specific factory.
+    NameChangeRequestPtr ncr;
+    switch (format) {
+    case FMT_JSON: {
+        try {
+            // Get the length of the JSON text.
+            size_t len = buffer.readUint16();
+
+            // Read the text from the buffer into a vector.
+            std::vector<uint8_t> vec;
+            buffer.readVector(vec, len);
+
+            // Turn the vector into a string.
+            std::string string_data(vec.begin(), vec.end());
+
+            // Pass the string of JSON text into JSON factory to create the
+            // NameChangeRequest instance.  Note the factory may throw
+            // NcrMessageError.
+            ncr = NameChangeRequest::fromJSON(string_data);
+        } catch (const isc::util::InvalidBufferPosition& ex) {
+            // Read error accessing data in InputBuffer.
+            isc_throw(NcrMessageError, "fromFormat: buffer read error: "
+                      << ex.what());
+        }
+
+        break;
+        }
+    default:
+        // Programmatic error, shouldn't happen.
+        isc_throw(NcrMessageError, "fromFormat - invalid format");
+        break;
+    }
+
+    return (ncr);
+}
+
+void
+NameChangeRequest::toFormat(const NameChangeFormat format,
+                            isc::util::OutputBuffer& buffer) const {
+    // Based on the format requested, invoke the appropriate format handler
+    // which will marshal this request's contents into the OutputBuffer.
+    switch (format) {
+    case FMT_JSON: {
+        // Invoke toJSON to create a JSON text of this request's contents.
+        std::string json = toJSON();
+        uint16_t length = json.size();
+
+        // Write the length of the JSON text to the OutputBuffer first, then
+        // write the JSON text itself.
+        buffer.writeUint16(length);
+        buffer.writeData(json.c_str(), length);
+        break;
+        }
+    default:
+        // Programmatic error, shouldn't happen.
+        isc_throw(NcrMessageError, "toFormat - invalid format");
+        break;
+    }
+}
+
+NameChangeRequestPtr
+NameChangeRequest::fromJSON(const std::string& json) {
+    // This method leverages the existing JSON parsing provided by isc::data
+    // library.  Should this prove to be a performance issue, it may be that
+    // lighter weight solution would be appropriate.
+
+    // Turn the string of JSON text into an Element set.
+    isc::data::ElementPtr elements;
+    try {
+        elements = isc::data::Element::fromJSON(json);
+    } catch (const isc::data::JSONError& ex) {
+        isc_throw(NcrMessageError,
+                  "Malformed NameChangeRequest JSON: " << ex.what());
+    }
+
+    // Get a map of the Elements, keyed by element name.
+    ElementMap element_map = elements->mapValue();
+    isc::data::ConstElementPtr element;
+
+    // Use default constructor to create a "blank" NameChangeRequest.
+    NameChangeRequestPtr ncr(new NameChangeRequest());
+
+    // For each member of NameChangeRequest, find its element in the map and
+    // call the appropriate Element-based setter.  These setters may throw
+    // NcrMessageError if the given Element is the wrong type or its data
+    // content is lexically invalid.   If the element is NOT found in the
+    // map, getElement will throw NcrMessageError indicating the missing
+    // member.
+    element = ncr->getElement("change-type", element_map);
+    ncr->setChangeType(element);
+
+    element = ncr->getElement("forward-change", element_map);
+    ncr->setForwardChange(element);
+
+    element = ncr->getElement("reverse-change", element_map);
+    ncr->setReverseChange(element);
+
+    element = ncr->getElement("fqdn", element_map);
+    ncr->setFqdn(element);
+
+    element = ncr->getElement("ip-address", element_map);
+    ncr->setIpAddress(element);
+
+    element = ncr->getElement("dhcid", element_map);
+    ncr->setDhcid(element);
+
+    element = ncr->getElement("lease-expires-on", element_map);
+    ncr->setLeaseExpiresOn(element);
+
+    element = ncr->getElement("lease-length", element_map);
+    ncr->setLeaseLength(element);
+
+    // For backward compatibility  use-conflict-resolution is optional
+    // and defaults to true.
+    auto found = element_map.find("use-conflict-resolution");
+    if (found != element_map.end()) {
+        ncr->setConflictResolution(found->second);
+    } else {
+        ncr->setConflictResolution(true);
+    }
+
+    // All members were in the Element set and were correct lexically. Now
+    // validate the overall content semantically.  This will throw an
+    // NcrMessageError if anything is amiss.
+    ncr->validateContent();
+
+    // Everything is valid, return the new instance.
+    return (ncr);
+}
+
+std::string
+NameChangeRequest::toJSON() const  {
+    // Create a JSON string of this request's contents.  Note that this method
+    // does NOT use the isc::data library as generating the output is straight
+    // forward.
+    std::ostringstream stream;
+
+    stream << "{\"change-type\":" << getChangeType() << ","
+        << "\"forward-change\":"
+        << (isForwardChange() ? "true" : "false") << ","
+        << "\"reverse-change\":"
+        << (isReverseChange() ? "true" : "false") << ","
+        << "\"fqdn\":\"" << getFqdn() << "\","
+        << "\"ip-address\":\"" << getIpAddress() << "\","
+        << "\"dhcid\":\"" << getDhcid().toStr() << "\","
+        << "\"lease-expires-on\":\""  << getLeaseExpiresOnStr() << "\","
+        << "\"lease-length\":" << getLeaseLength() << ","
+        << "\"use-conflict-resolution\":"
+        << (useConflictResolution() ? "true" : "false") << "}";
+
+    return (stream.str());
+}
+
+
+void
+NameChangeRequest::validateContent() {
+    //@todo This is an initial implementation which provides a minimal amount
+    // of validation.  FQDN and DHCID members are all currently
+    // strings, these may be replaced with richer classes.
+    if (fqdn_ == "") {
+        isc_throw(NcrMessageError, "FQDN cannot be blank");
+    }
+
+    // Validate the DHCID.
+    if (dhcid_.getBytes().size()  == 0) {
+        isc_throw(NcrMessageError, "DHCID cannot be blank");
+    }
+
+    // Ensure the request specifies at least one direction to update.
+    if (!forward_change_ && !reverse_change_) {
+        isc_throw(NcrMessageError,
+                  "Invalid Request, forward and reverse flags are both false");
+    }
+}
+
+isc::data::ConstElementPtr
+NameChangeRequest::getElement(const std::string& name,
+                              const ElementMap& element_map) const {
+    // Look for "name" in the element map.
+    ElementMap::const_iterator it = element_map.find(name);
+    if (it == element_map.end()) {
+        // Didn't find the element, so throw.
+        isc_throw(NcrMessageError,
+                  "NameChangeRequest value missing for: " << name );
+    }
+
+    // Found the element, return it.
+    return (it->second);
+}
+
+void
+NameChangeRequest::setChangeType(const NameChangeType value) {
+    change_type_ = value;
+}
+
+
+void
+NameChangeRequest::setChangeType(isc::data::ConstElementPtr element) {
+    long raw_value = -1;
+    try {
+        // Get the element's integer value.
+        raw_value = element->intValue();
+    } catch (const isc::data::TypeError& ex) {
+        // We expect a integer Element type, don't have one.
+        isc_throw(NcrMessageError,
+                  "Wrong data type for change_type: " << ex.what());
+    }
+
+    if ((raw_value != CHG_ADD) && (raw_value != CHG_REMOVE)) {
+        // Value is not a valid change type.
+        isc_throw(NcrMessageError,
+                  "Invalid data value for change_type: " << raw_value);
+    }
+
+    // Good to go, make the assignment.
+    setChangeType(static_cast<NameChangeType>(raw_value));
+}
+
+void
+NameChangeRequest::setForwardChange(const bool value) {
+    forward_change_ = value;
+}
+
+void
+NameChangeRequest::setForwardChange(isc::data::ConstElementPtr element) {
+    bool value;
+    try {
+        // Get the element's boolean value.
+        value = element->boolValue();
+    } catch (const isc::data::TypeError& ex) {
+        // We expect a boolean Element type, don't have one.
+        isc_throw(NcrMessageError,
+                  "Wrong data type for forward-change: " << ex.what());
+    }
+
+    // Good to go, make the assignment.
+    setForwardChange(value);
+}
+
+void
+NameChangeRequest::setReverseChange(const bool value) {
+    reverse_change_ = value;
+}
+
+void
+NameChangeRequest::setReverseChange(isc::data::ConstElementPtr element) {
+    bool value;
+    try {
+        // Get the element's boolean value.
+        value = element->boolValue();
+    } catch (const isc::data::TypeError& ex) {
+        // We expect a boolean Element type, don't have one.
+        isc_throw(NcrMessageError,
+                  "Wrong data type for reverse_change: " << ex.what());
+    }
+
+    // Good to go, make the assignment.
+    setReverseChange(value);
+}
+
+
+void
+NameChangeRequest::setFqdn(isc::data::ConstElementPtr element) {
+    setFqdn(element->stringValue());
+}
+
+void
+NameChangeRequest::setFqdn(const std::string& value) {
+    try {
+        dns::Name tmp(value);
+        fqdn_ = tmp.toText();
+    } catch (const std::exception& ex) {
+        isc_throw(NcrMessageError,
+                  "Invalid FQDN value: " << value << ", reason: "
+                  << ex.what());
+    }
+}
+
+void
+NameChangeRequest::setIpAddress(const std::string& value) {
+    // Validate IP Address.
+    try {
+        ip_io_address_ = isc::asiolink::IOAddress(value);
+    } catch (const isc::asiolink::IOError&) {
+        isc_throw(NcrMessageError,
+                  "Invalid ip address string for ip_address: " << value);
+    }
+}
+
+void
+NameChangeRequest::setIpAddress(isc::data::ConstElementPtr element) {
+    setIpAddress(element->stringValue());
+}
+
+
+void
+NameChangeRequest::setDhcid(const std::string& value) {
+    dhcid_.fromStr(value);
+}
+
+void
+NameChangeRequest::setDhcid(isc::data::ConstElementPtr element) {
+    setDhcid(element->stringValue());
+}
+
+std::string
+NameChangeRequest::getLeaseExpiresOnStr() const {
+    return (isc::util::timeToText64(lease_expires_on_));
+}
+
+void
+NameChangeRequest::setLeaseExpiresOn(const std::string&  value) {
+    try {
+        lease_expires_on_ = isc::util::timeFromText64(value);
+    } catch (...) {
+        // We were given an invalid string, so throw.
+        isc_throw(NcrMessageError,
+            "Invalid date-time string: [" << value << "]");
+    }
+
+}
+
+void NameChangeRequest::setLeaseExpiresOn(isc::data::ConstElementPtr element) {
+    // Pull out the string value and pass it into the string setter.
+    setLeaseExpiresOn(element->stringValue());
+}
+
+void
+NameChangeRequest::setLeaseLength(const uint32_t value) {
+    lease_length_ = value;
+}
+
+void
+NameChangeRequest::setLeaseLength(isc::data::ConstElementPtr element) {
+    long value = -1;
+    try {
+        // Get the element's integer value.
+        value = element->intValue();
+    } catch (const isc::data::TypeError& ex) {
+        // We expect a integer Element type, don't have one.
+        isc_throw(NcrMessageError,
+                  "Wrong data type for lease_length: " << ex.what());
+    }
+
+    // Make sure we the range is correct and value is positive.
+    if (value > std::numeric_limits<uint32_t>::max()) {
+        isc_throw(NcrMessageError, "lease_length value " << value <<
+                "is too large for unsigned 32-bit integer.");
+    }
+    if (value < 0) {
+        isc_throw(NcrMessageError, "lease_length value " << value <<
+             "is negative.  It must greater than or equal to zero ");
+    }
+
+    // Good to go, make the assignment.
+    setLeaseLength(static_cast<uint32_t>(value));
+}
+
+void
+NameChangeRequest::setConflictResolution(const bool value) {
+    conflict_resolution_ = value;
+}
+
+void
+NameChangeRequest::setConflictResolution(isc::data::ConstElementPtr element) {
+    bool value;
+    try {
+        // Get the element's boolean value.
+        value = element->boolValue();
+    } catch (const isc::data::TypeError& ex) {
+        // We expect a boolean Element type, don't have one.
+        isc_throw(NcrMessageError,
+                  "Wrong data type for use-conflict-resolution: " << ex.what());
+    }
+
+    // Good to go, make the assignment.
+    setConflictResolution(value);
+}
+
+void
+NameChangeRequest::setStatus(const NameChangeStatus value) {
+    status_ = value;
+}
+
+std::string
+NameChangeRequest::toText() const {
+    std::ostringstream stream;
+
+    stream << "Type: " << static_cast<int>(change_type_) << " (";
+    switch (change_type_) {
+    case CHG_ADD:
+        stream << "CHG_ADD)\n";
+        break;
+    case CHG_REMOVE:
+        stream << "CHG_REMOVE)\n";
+        break;
+    default:
+        // Shouldn't be possible.
+        stream << "Invalid Value\n";
+    }
+
+    stream << "Forward Change: " << (forward_change_ ? "yes" : "no")
+           << std::endl
+           << "Reverse Change: " << (reverse_change_ ? "yes" : "no")
+           << std::endl
+           << "FQDN: [" << fqdn_ << "]" << std::endl
+           << "IP Address: [" << ip_io_address_ << "]" << std::endl
+           << "DHCID: [" << dhcid_.toStr() << "]" << std::endl
+           << "Lease Expires On: " << getLeaseExpiresOnStr() << std::endl
+           << "Lease Length: " << lease_length_ << std::endl
+           << "Conflict Resolution: " << (conflict_resolution_ ? "yes" : "no")
+           << std::endl;
+
+    return (stream.str());
+}
+
+bool
+NameChangeRequest::operator == (const NameChangeRequest& other) {
+    return ((change_type_ == other.change_type_) &&
+            (forward_change_ == other.forward_change_) &&
+            (reverse_change_ == other.reverse_change_) &&
+            (fqdn_ == other.fqdn_) &&
+            (ip_io_address_ == other.ip_io_address_) &&
+            (dhcid_ == other.dhcid_) &&
+            (lease_expires_on_ == other.lease_expires_on_) &&
+            (lease_length_ == other.lease_length_) &&
+            (conflict_resolution_ == other.conflict_resolution_));
+}
+
+bool
+NameChangeRequest::operator != (const NameChangeRequest& other) {
+    return (!(*this == other));
+}
+
+
+}; // end of isc::dhcp namespace
+}; // end of isc namespace
diff --git a/src/lib/dhcp_ddns/ncr_msg.h b/src/lib/dhcp_ddns/ncr_msg.h
new file mode 100644
index 0000000..e3a708f
--- /dev/null
+++ b/src/lib/dhcp_ddns/ncr_msg.h
@@ -0,0 +1,761 @@
+// Copyright (C) 2013-2021 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/.
+
+#ifndef NCR_MSG_H
+#define NCR_MSG_H
+
+/// @file ncr_msg.h
+/// @brief This file provides the classes needed to embody, compose, and
+/// decompose DNS update requests that are sent by DHCP-DDNS clients to
+/// DHCP-DDNS. These requests are referred to as NameChangeRequests.
+
+#include <cc/data.h>
+#include <dhcp/duid.h>
+#include <dhcp/hwaddr.h>
+#include <dns/name.h>
+#include <exceptions/exceptions.h>
+#include <util/buffer.h>
+#include <util/time_utilities.h>
+
+#include <time.h>
+#include <string>
+
+namespace isc {
+namespace dhcp_ddns {
+
+/// @brief Exception thrown when NameChangeRequest marshalling error occurs.
+class NcrMessageError : public isc::Exception {
+public:
+    NcrMessageError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+/// @brief Exception thrown when there is an error occurred during computation
+/// of the DHCID.
+class DhcidRdataComputeError : public isc::Exception {
+public:
+    DhcidRdataComputeError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+
+/// @brief Defines the types of DNS updates that can be requested.
+enum NameChangeType {
+  CHG_ADD,
+  CHG_REMOVE
+};
+
+/// @brief Defines the runtime processing status values for requests.
+enum NameChangeStatus  {
+  ST_NEW,
+  ST_PENDING,
+  ST_COMPLETED,
+  ST_FAILED
+};
+
+/// @brief Defines the list of data wire formats supported.
+enum NameChangeFormat {
+  FMT_JSON
+};
+
+/// @brief Function which converts labels to  NameChangeFormat enum values.
+///
+/// @param fmt_str text to convert to an enum.
+/// Valid string values: "JSON"
+///
+/// @return NameChangeFormat value which maps to the given string.
+///
+/// @throw isc::BadValue if given a string value which does not map to an
+/// enum value.
+extern NameChangeFormat stringToNcrFormat(const std::string& fmt_str);
+
+/// @brief Function which converts NameChangeFormat enums to text labels.
+///
+/// @param format enum value to convert to label
+///
+/// @return std:string containing the text label if the value is valid, or
+/// "UNKNOWN" if not.
+extern std::string ncrFormatToString(NameChangeFormat format);
+
+/// @brief Container class for handling the DHCID value within a
+/// NameChangeRequest. It provides conversion to and from string for JSON
+/// formatting, but stores the data internally as unsigned bytes.
+class D2Dhcid {
+public:
+    /// @brief Default constructor
+    D2Dhcid();
+
+    /// @brief Constructor - Creates a new instance, populated by converting
+    /// a given string of digits into an array of unsigned bytes.
+    ///
+    /// @param data is a string of hexadecimal digits. The format is simply
+    /// a contiguous stream of digits, with no delimiters. For example a string
+    /// containing "14A3" converts to a byte array containing:  0x14, 0xA3.
+    ///
+    /// @throw NcrMessageError if the input data contains non-digits
+    /// or there is an odd number of digits.
+    D2Dhcid(const std::string& data);
+
+    /// @brief Constructor, creates an instance of the @c D2Dhcid from the
+    /// HW address.
+    ///
+    /// @param hwaddr A pointer to the object encapsulating HW address.
+    /// @param wire_fqdn A on-wire canonical representation of the FQDN.
+    D2Dhcid(const isc::dhcp::HWAddrPtr& hwaddr,
+            const std::vector<uint8_t>& wire_fqdn);
+
+    /// @brief Constructor, creates an instance of the @c D2Dhcid from the
+    /// client identifier carried in the Client Identifier option.
+    ///
+    /// @param clientid_data Holds the raw bytes representing client identifier.
+    /// @param wire_fqdn A on-wire canonical representation of the FQDN.
+    D2Dhcid(const std::vector<uint8_t>& clientid_data,
+            const std::vector<uint8_t>& wire_fqdn);
+
+    /// @brief Constructor, creates an instance of the @c D2Dhcid from the
+    /// @c isc::dhcp::DUID.
+    ///
+    /// @param duid An object representing DUID.
+    /// @param wire_fqdn A on-wire canonical representation of the FQDN.
+    D2Dhcid(const isc::dhcp::DUID& duid,
+            const std::vector<uint8_t>& wire_fqdn);
+
+    /// @brief Returns the DHCID value as a string of hexadecimal digits.
+    ///
+    /// @return a string containing a contiguous stream of digits.
+    std::string toStr() const;
+
+    /// @brief Sets the DHCID value based on the given string.
+    ///
+    /// @param data is a string of hexadecimal digits. The format is simply
+    /// a contiguous stream of digits, with no delimiters. For example a string
+    /// containing "14A3" converts to a byte array containing:  0x14, 0xA3.
+    ///
+    /// @throw NcrMessageError if the input data contains non-digits
+    /// or there is an odd number of digits.
+    void fromStr(const std::string& data);
+
+    /// @brief Sets the DHCID value based on the Client Identifier.
+    ///
+    /// @param clientid_data Holds the raw bytes representing client identifier.
+    /// @param wire_fqdn A on-wire canonical representation of the FQDN.
+    void fromClientId(const std::vector<uint8_t>& clientid_data,
+                      const std::vector<uint8_t>& wire_fqdn);
+
+    /// @brief Sets the DHCID value based on the DUID and FQDN.
+    ///
+    /// This function requires that the FQDN conforms to the section 3.5
+    /// of the RFC4701, which says that the FQDN must be in lowercase.
+    /// This function doesn't validate if it really converted.
+    ///
+    /// @param duid A @c isc::dhcp::DUID object encapsulating DUID.
+    /// @param wire_fqdn A on-wire canonical representation of the FQDN.
+    void fromDUID(const isc::dhcp::DUID& duid,
+                  const std::vector<uint8_t>& wire_fqdn);
+
+    /// @brief Sets the DHCID value based on the HW address and FQDN.
+    ///
+    /// @param hwaddr A pointer to the object encapsulating HW address.
+    /// @param wire_fqdn A on-wire canonical representation of the FQDN.
+    void fromHWAddr(const isc::dhcp::HWAddrPtr& hwaddr,
+                    const std::vector<uint8_t>& wire_fqdn);
+
+    /// @brief Returns a reference to the DHCID byte vector.
+    ///
+    /// @return a reference to the vector.
+    const std::vector<uint8_t>& getBytes() const {
+        return (bytes_);
+    }
+
+    /// @brief Compares two D2Dhcids for equality
+    bool operator==(const D2Dhcid& other) const {
+        return (this->bytes_ == other.bytes_);
+    }
+
+    /// @brief Compares two D2Dhcids for inequality
+    bool operator!=(const D2Dhcid& other) const {
+        return (this->bytes_ != other.bytes_);
+    }
+
+    /// @brief Compares two D2Dhcids lexically
+    bool operator<(const D2Dhcid& other) const {
+        return (this->bytes_ < other.bytes_);
+    }
+
+private:
+
+    /// @brief Creates the DHCID using specified identifier.
+    ///
+    /// This function creates the DHCID RDATA as specified in RFC4701,
+    /// section 3.5.
+    ///
+    /// @param identifier_type is a less significant byte of the identifier-type
+    /// defined in RFC4701.
+    /// @param identifier_data A buffer holding client identifier raw data -
+    /// e.g. DUID, data carried in the Client Identifier option or client's
+    /// HW address.
+    /// @param A on-wire canonical representation of the FQDN.
+    void createDigest(const uint8_t identifier_type,
+                      const std::vector<uint8_t>& identifier_data,
+                      const std::vector<uint8_t>& wire_fqdn);
+
+    /// @brief Storage for the DHCID value in unsigned bytes.
+    std::vector<uint8_t> bytes_;
+};
+
+std::ostream&
+operator<<(std::ostream& os, const D2Dhcid& dhcid);
+
+class NameChangeRequest;
+/// @brief Defines a pointer to a NameChangeRequest.
+typedef boost::shared_ptr<NameChangeRequest> NameChangeRequestPtr;
+
+/// @brief Defines a map of Elements, keyed by their string name.
+typedef std::map<std::string, isc::data::ConstElementPtr> ElementMap;
+
+/// @brief  Represents a DHCP-DDNS client request.
+/// This class is used by DHCP-DDNS clients (e.g. DHCP4, DHCP6) to
+/// request DNS updates.  Each message contains a single DNS change (either an
+/// add/update or a remove) for a single FQDN.  It provides marshalling services
+/// for moving instances to and from the wire.  Currently, the only format
+/// supported is JSON detailed here isc::dhcp_ddns::NameChangeRequest::fromJSON
+/// The class provides an interface such that other formats can be readily
+/// supported.
+class NameChangeRequest {
+public:
+    /// @brief Default Constructor.
+    ///
+    /// @todo Currently, fromWire makes use of the ability to create an empty
+    /// NameChangeRequest and then builds it bit by bit.  This means that it
+    /// is technically possible to create one and attempt to use in ways
+    /// other than intended and its invalid content may or may not be handled
+    /// gracefully by consuming code.  It might be wise to revisit this
+    /// structuring such that we do not use a default constructor and only
+    /// allow valid instantiations.
+    NameChangeRequest();
+
+    /// @brief Constructor.  Full constructor, which provides parameters for
+    /// all of the class members, except status.
+    ///
+    /// @param change_type the type of change (Add or Update)
+    /// @param forward_change indicates if this change should be sent to forward
+    /// DNS servers.
+    /// @param reverse_change indicates if this change should be sent to reverse
+    /// DNS servers.
+    /// @param fqdn the domain name whose pointer record(s) should be
+    /// updated.
+    /// @param ip_address the ip address leased to the given FQDN.
+    /// @param dhcid the lease client's unique DHCID.
+    /// @param lease_expires_on a timestamp containing the date/time the lease
+    /// expires.
+    /// @param lease_length the amount of time in seconds for which the
+    /// lease is valid (TTL).
+    /// @param conflict_resolution indicates whether or not conflict resolution
+    /// (per RFC 4703) is enabled.
+    NameChangeRequest(const NameChangeType change_type,
+                      const bool forward_change, const bool reverse_change,
+                      const std::string& fqdn, const std::string& ip_address,
+                      const D2Dhcid& dhcid,
+                      const uint64_t lease_expires_on,
+                      const uint32_t lease_length,
+                      const bool conflict_resolution = true);
+
+    /// @brief Static method for creating a NameChangeRequest from a
+    /// buffer containing a marshalled request in a given format.
+    ///
+    /// When the format is:
+    ///
+    /// JSON: The buffer is expected to contain a two byte unsigned integer
+    /// which specified the length of the JSON text; followed by the JSON
+    /// text itself.  This method attempts to extract "length" characters
+    /// from the buffer. This data is used to create a character string that
+    /// is than treated as JSON which is then parsed into the data needed
+    /// to create a request instance.
+    ///
+    /// (NOTE currently only JSON is supported.)
+    ///
+    /// @param format indicates the data format to use
+    /// @param buffer is the input buffer containing the marshalled request
+    ///
+    /// @return a pointer to the new NameChangeRequest
+    ///
+    /// @throw NcrMessageError if an error occurs creating new
+    /// request.
+    static NameChangeRequestPtr fromFormat(const NameChangeFormat format,
+                                           isc::util::InputBuffer& buffer);
+
+    /// @brief Instance method for marshalling the contents of the request
+    /// into the given buffer in the given format.
+    ///
+    /// When the format is:
+    ///
+    /// JSON: Upon completion, the buffer will contain a two byte unsigned
+    /// integer which specifies the length of the JSON text; followed by the
+    /// JSON text itself. The JSON text contains the names and values for all
+    /// the request data needed to reassemble the request on the receiving
+    /// end. The JSON text in the buffer is NOT null-terminated.  The format
+    /// is identical that described under
+    /// isc::dhcp_ddns::NameChangeRequest::fromJSON
+    ///
+    /// (NOTE currently only JSON is supported.)
+    ///
+    /// @param format indicates the data format to use
+    /// @param buffer is the output buffer to which the request should be
+    /// marshalled.
+    void toFormat(const NameChangeFormat format,
+                  isc::util::OutputBuffer& buffer) const;
+
+    /// @brief Static method for creating a NameChangeRequest from a
+    /// string containing a JSON rendition of a request.
+    ///
+    /// The JSON expected is described below.  Note that a request must be
+    /// enclosed within curly brackets "{..}" and that whitespace is optional
+    /// (it is used in the following examples for clarity).
+    ///
+    /// @code
+    ///     {
+    ///      "change-type" : <integer>,
+    ///      "forward-change" : <boolean>,
+    ///      "reverse-change" : <boolean>,
+    ///      "fqdn" : "<fqdn>",
+    ///      "ip-address" : "<address>",
+    ///      "dhcid" : "<hex_string>",
+    ///      "lease-expires-on" : "<yyyymmddHHMMSS>",
+    ///      "lease-length" : <secs>,
+    ///      "use-conflict-resolution": <boolean>
+    ///     }
+    /// @endcode
+    ///
+    /// - change-type - indicates whether this request is to add or update
+    ///   DNS entries or to remove them.  The value is an integer and is
+    ///   0 for add/update and 1 for remove.
+    /// - forward-change - indicates whether the forward (name to
+    ///   address) DNS zone should be updated.  The value is a string
+    ///   representing a boolean.  It is "true" if the zone should be updated
+    ///   and "false" if not. (Unlike the keyword, the boolean value is
+    ///   case-insensitive.)
+    /// - reverse-change - indicates whether the reverse (address to
+    ///   name) DNS zone should be updated.  The value is a string
+    ///   representing a boolean.  It is "true" if the zone should be updated
+    ///   and "false" if not. (Unlike the keyword, the boolean value is
+    ///   case-insensitive.)
+    /// - fqdn - fully qualified domain name such as "myhost.example.com.".
+    ///   (Note that a trailing dot will be appended if not supplied.)
+    /// - ip-address - the IPv4 or IPv6 address of the client.  The value
+    ///   is a string representing the IP address (e.g. "192.168.0.1" or
+    ///   "2001:db8:1::2").
+    /// - dhcid - identification of the DHCP client to whom the IP address has
+    ///   been leased.  The value is a string containing an even number of
+    ///   hexadecimal digits without delimiters such as "2C010203040A7F8E3D"
+    ///   (case insensitive).
+    /// - lease-expires-on - the date and time on which the lease expires.
+    ///   The value is a string of the form "yyyymmddHHMMSS" where:
+    ///     - yyyy - four digit year
+    ///     - mm - month of year (1-12),
+    ///     - dd - day of the month (1-31),
+    ///     - HH - hour of the day (0-23)
+    ///     - MM - minutes of the hour (0-59)
+    ///     - SS - seconds of the minute (0-59)
+    /// - lease-length - the length of the lease in seconds.  This is an
+    ///   integer and may range between 1 and 4294967295 (2^32 - 1) inclusive.
+    /// - use-conflict-resolution - when true, follow RFC 4703 which uses
+    ///   DHCID records to prohibit multiple clients from updating an FQDN
+    ///
+    /// Examples:
+    ///
+    /// Removal of an IPv4 address from the forward DNS zone only:
+    ///
+    /// @code
+    ///  {
+    ///     "change-type" : 1,
+    ///     "forward-change" : true,
+    ///     "reverse-change" : false,
+    ///     "fqdn" : "myhost.example.com.",
+    ///     "ip-address" : "192.168.2.1" ,
+    ///     "dhcid" : "010203040A7F8E3D" ,
+    ///     "lease-expires-on" : "20130121132405",
+    ///     "lease-length" : 1300,
+    ///     "use-conflict-resolution": true
+    ///  }
+    /// @endcode
+    ///
+    /// Addition of an IPv6 address to both forward and reverse DNS zones:
+    ///
+    /// @code
+    ///  {
+    ///     "change-type" : 0,
+    ///     "forward-change" : true,
+    ///     "reverse-change" : true,
+    ///     "fqdn" : "someother.example.com.",
+    ///     "ip-address" : "2001::db8:1::2",
+    ///     "dhcid" : "010203040A7F8E3D" , "
+    ///     "lease-expires-on" : "20130121132405",
+    ///     "lease-length" : 27400,
+    ///     "use-conflict-resolution": true
+    ///   }
+    /// @endcode
+    ///
+    /// @param json is a string containing the JSON text
+    ///
+    /// @return a pointer to the new NameChangeRequest
+    ///
+    /// @throw NcrMessageError if an error occurs creating new request.
+    static NameChangeRequestPtr fromJSON(const std::string& json);
+
+    /// @brief Instance method for marshalling the contents of the request
+    /// into a string of JSON text.
+    ///
+    /// @return a string containing the JSON rendition of the request
+    std::string toJSON() const;
+
+    /// @brief Validates the content of a populated request.  This method is
+    /// used by both the full constructor and from-wire marshalling to ensure
+    /// that the request is content valid.  Currently it enforces the
+    /// following rules:
+    ///
+    ///  - FQDN must not be blank.
+    ///  - The IP address must be a valid address.
+    ///  - The DHCID must not be blank.
+    ///  - The lease expiration date must be a valid date/time.
+    ///  - That at least one of the two direction flags, forward change and
+    ///    reverse change is true.
+    ///
+    /// @todo This is an initial implementation which provides a minimal amount
+    /// of validation.  FQDN, DHCID, and IP Address members are all currently
+    /// strings, these may be replaced with richer classes.
+    ///
+    /// @throw NcrMessageError if the request content violates any
+    /// of the validation rules.
+    void validateContent();
+
+    /// @brief Fetches the request change type.
+    ///
+    /// @return the change type
+    NameChangeType getChangeType() const {
+        return (change_type_);
+    }
+
+    /// @brief Sets the change type to the given value.
+    ///
+    /// @param value is the NameChangeType value to assign to the request.
+    void setChangeType(const NameChangeType value);
+
+    /// @brief Sets the change type to the value of the given Element.
+    ///
+    /// @param element is an integer Element containing the change type value.
+    ///
+    /// @throw NcrMessageError if the element is not an integer
+    /// Element or contains an invalid value.
+    void setChangeType(isc::data::ConstElementPtr element);
+
+    /// @brief Checks forward change flag.
+    ///
+    /// @return a true if the forward change flag is true.
+    bool isForwardChange() const {
+        return (forward_change_);
+    }
+
+    /// @brief Sets the forward change flag to the given value.
+    ///
+    /// @param value contains the new value to assign to the forward change
+    /// flag
+    void setForwardChange(const bool value);
+
+    /// @brief Sets the forward change flag to the value of the given Element.
+    ///
+    /// @param element is a boolean Element containing the forward change flag
+    /// value.
+    ///
+    /// @throw NcrMessageError if the element is not a boolean
+    /// Element
+    void setForwardChange(isc::data::ConstElementPtr element);
+
+    /// @brief Checks reverse change flag.
+    ///
+    /// @return a true if the reverse change flag is true.
+    bool isReverseChange() const {
+        return (reverse_change_);
+    }
+
+    /// @brief Sets the reverse change flag to the given value.
+    ///
+    /// @param value contains the new value to assign to the reverse change
+    /// flag
+    void setReverseChange(const bool value);
+
+    /// @brief Sets the reverse change flag to the value of the given Element.
+    ///
+    /// @param element is a boolean Element containing the reverse change flag
+    /// value.
+    ///
+    /// @throw NcrMessageError if the element is not a boolean
+    /// Element
+    void setReverseChange(isc::data::ConstElementPtr element);
+
+    /// @brief Fetches the request FQDN
+    ///
+    /// @return a string containing the FQDN
+    const std::string getFqdn() const {
+        return (fqdn_);
+    }
+
+    /// @brief Sets the FQDN to the given value.
+    ///
+    /// @param value contains the new value to assign to the FQDN
+    void setFqdn(const std::string& value);
+
+    /// @brief Sets the FQDN to the value of the given Element.
+    ///
+    /// @param element is a string Element containing the FQDN
+    ///
+    /// @throw NcrMessageError if the element is not a string
+    /// Element
+    void setFqdn(isc::data::ConstElementPtr element);
+
+    /// @brief Fetches the request IP address string.
+    ///
+    /// @return a string containing the IP address
+    std::string getIpAddress() const {
+        return (ip_io_address_.toText());
+    }
+
+    /// @brief Fetches the request IP address as an IOAddress.
+    ///
+    /// @return a asiolink::IOAddress containing the IP address
+    const asiolink::IOAddress& getIpIoAddress() const {
+        return (ip_io_address_);
+    }
+
+    /// @brief Returns true if the lease address is a IPv4 lease.
+    ///
+    /// @return boolean true if the lease address family is AF_INET.
+    bool isV4 () const {
+        return (ip_io_address_.isV4());
+    }
+
+    /// @brief Returns true if the lease address is a IPv6 lease.
+    ///
+    /// @return boolean true if the lease address family is AF_INET6.
+    bool isV6 () const {
+        return (ip_io_address_.isV6());
+    }
+
+    /// @brief Sets the IP address to the given value.
+    ///
+    /// @param value contains the new value to assign to the IP address
+    void setIpAddress(const std::string& value);
+
+    /// @brief Sets the IP address to the value of the given Element.
+    ///
+    /// @param element is a string Element containing the IP address
+    ///
+    /// @throw NcrMessageError if the element is not a string
+    /// Element
+    void setIpAddress(isc::data::ConstElementPtr element);
+
+    /// @brief Fetches the request DHCID
+    ///
+    /// @return a reference to the request's D2Dhcid
+    const D2Dhcid& getDhcid() const {
+        return (dhcid_);
+    }
+
+    /// @brief Sets the DHCID based on the given string value.
+    ///
+    /// @param value is a string of hexadecimal digits. The format is simply
+    /// a contiguous stream of digits, with no delimiters. For example a string
+    /// containing "14A3" converts to a byte array containing:  0x14, 0xA3.
+    ///
+    /// @throw NcrMessageError if the input data contains non-digits
+    /// or there is an odd number of digits.
+    void setDhcid(const std::string& value);
+
+    /// @brief Sets the DHCID based on the value of the given Element.
+    ///
+    /// @param element is a string Element containing the string of hexadecimal
+    /// digits. (See setDhcid(std::string&) above.)
+    ///
+    /// @throw NcrMessageError if the input data contains non-digits
+    /// or there is an odd number of digits.
+    void setDhcid(isc::data::ConstElementPtr element);
+
+    /// @brief Fetches the request ID.
+    ///
+    /// @todo Currently this is the DHCID, in the future we may add a unique ID per
+    /// request to allow for correlating messages and events between the DHCP servers
+    /// and the D2 server.  If we do that we shall also need to add or update other
+    /// functions to: set the request ID, add it to the JSON strings, etc.  The
+    /// primary purpose of this function is to provide a consistent way to identify
+    /// requests for logging purposes.
+    ///
+    /// @return a string with the request's request ID (currently DHCID)
+    std::string getRequestId() const {
+        return (dhcid_.toStr());
+    }
+
+    /// @brief Fetches the request lease expiration
+    ///
+    /// @return the lease expiration as the number of seconds since
+    /// the (00:00:00 January 1, 1970)
+    uint64_t getLeaseExpiresOn() const {
+        return (lease_expires_on_);
+    }
+
+    /// @brief Fetches the request lease expiration as string.
+    ///
+    /// The format of the string returned is:
+    ///
+    ///    YYYYMMDDHHmmSS
+    ///
+    /// Example: 18:54:54 June 26, 2013 would be: 20130626185455
+    /// NOTE This is always UTC time.
+    ///
+    /// @return a ISO date-time string of the lease expiration.
+    std::string getLeaseExpiresOnStr() const;
+
+    /// @brief Sets the lease expiration based on the given string.
+    ///
+    /// @param value is an date-time string from which to set the
+    /// lease expiration. The format of the input is:
+    ///
+    ///    YYYYMMDDHHmmSS
+    ///
+    /// Example: 18:54:54 June 26, 2013 would be: 20130626185455
+    /// NOTE This is always UTC time.
+    ///
+    /// @throw NcrMessageError if the ISO string is invalid.
+    void setLeaseExpiresOn(const std::string& value);
+
+    /// @brief Sets the lease expiration based on the given Element.
+    ///
+    /// @param element is string Element containing a date-time string.
+    ///
+    /// @throw NcrMessageError if the element is not a string
+    /// Element, or if the element value is an invalid date-time string.
+    void setLeaseExpiresOn(isc::data::ConstElementPtr element);
+
+    /// @brief Fetches the request lease length.
+    ///
+    /// @return an integer containing the lease length
+    uint32_t getLeaseLength() const {
+        return (lease_length_);
+    }
+
+    /// @brief Sets the lease length to the given value.
+    ///
+    /// @param value contains the new value to assign to the lease length
+    void setLeaseLength(const uint32_t value);
+
+    /// @brief Sets the lease length to the value of the given Element.
+    ///
+    /// @param element is a integer Element containing the lease length
+    ///
+    /// @throw NcrMessageError if the element is not a string
+    /// Element
+    void setLeaseLength(isc::data::ConstElementPtr element);
+
+    /// @brief Checks if conflict resolution is enabled
+    ///
+    /// @return a true if the conflict resolution is enabled.
+    bool useConflictResolution() const {
+        return (conflict_resolution_);
+    }
+
+    /// @brief Sets the conflict resolution flag to the given value.
+    ///
+    /// @param value contains the new value to assign to the conflict
+    /// resolution flag
+    void setConflictResolution(const bool value);
+
+    /// @brief Sets the conflict resolution flag to the value of the given Element.
+    ///
+    /// @param element is a boolean Element containing the conflict resolution flag
+    /// value.
+    ///
+    /// @throw NcrMessageError if the element is not a boolean
+    /// Element
+    void setConflictResolution(isc::data::ConstElementPtr element);
+
+    /// @brief Fetches the request status.
+    ///
+    /// @return the request status as a NameChangeStatus
+    NameChangeStatus getStatus() const {
+        return (status_);
+    }
+
+    /// @brief Sets the request status to the given value.
+    ///
+    /// @param value contains the new value to assign to request status
+    void setStatus(const NameChangeStatus value);
+
+    /// @brief Given a name, finds and returns an element from a map of
+    /// elements.
+    ///
+    /// @param name is the name of the desired element
+    /// @param element_map is the map of elements to search
+    ///
+    /// @return a pointer to the element if located
+    /// @throw NcrMessageError if the element cannot be found within
+    /// the map
+    isc::data::ConstElementPtr getElement(const std::string& name,
+                                          const ElementMap& element_map) const;
+
+    /// @brief Returns a text rendition of the contents of the request.
+    /// This method is primarily for logging purposes.
+    ///
+    /// @return a string containing the text.
+    std::string toText() const;
+
+    bool operator == (const NameChangeRequest& b);
+    bool operator != (const NameChangeRequest& b);
+
+private:
+    /// @brief Denotes the type of this change as either an Add or a Remove.
+    NameChangeType change_type_;
+
+    /// @brief Indicates if this change should sent to forward DNS servers.
+    bool forward_change_;
+
+    /// @brief Indicates if this change should sent to reverse DNS servers.
+    bool reverse_change_;
+
+    /// @brief The domain name whose DNS entry(ies) are to be updated.
+    /// @todo Currently, this is a std::string but may be replaced with
+    /// dns::Name which provides additional validation and domain name
+    /// manipulation.
+    std::string fqdn_;
+
+    /// @brief The ip address leased to the FQDN as an IOAddress.
+    ///
+    /// The lease address is used in many places, sometimes as a string
+    /// and sometimes as an IOAddress.  To avoid converting back and forth
+    /// continually over the life span of an NCR, we do it once when the
+    /// ip address is actually set.
+    asiolink::IOAddress ip_io_address_;
+
+    /// @brief The lease client's unique DHCID.
+    /// @todo Currently, this is uses D2Dhcid it but may be replaced with
+    /// dns::DHCID which provides additional validation.
+    D2Dhcid dhcid_;
+
+    /// @brief The date-time the lease expires.
+    uint64_t lease_expires_on_;
+
+    /// @brief The amount of time in seconds for which the lease is valid (TTL).
+    uint32_t lease_length_;
+
+    /// @brief Indicates if conflict resolution is enabled.
+    bool conflict_resolution_;
+
+    /// @brief The processing status of the request.  Used internally.
+    NameChangeStatus status_;
+};
+
+
+}; // end of isc::dhcp_ddns namespace
+}; // end of isc namespace
+
+#endif
diff --git a/src/lib/dhcp_ddns/ncr_udp.cc b/src/lib/dhcp_ddns/ncr_udp.cc
new file mode 100644
index 0000000..ae37793
--- /dev/null
+++ b/src/lib/dhcp_ddns/ncr_udp.cc
@@ -0,0 +1,386 @@
+// Copyright (C) 2013-2022 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/.
+
+#include <config.h>
+
+#include <dhcp_ddns/dhcp_ddns_log.h>
+#include <dhcp_ddns/ncr_udp.h>
+#include <stats/stats_mgr.h>
+
+#include <functional>
+
+namespace ph = std::placeholders;
+
+namespace isc {
+namespace dhcp_ddns {
+
+//*************************** UDPCallback ***********************
+UDPCallback::UDPCallback (RawBufferPtr& buffer, const size_t buf_size,
+                          UDPEndpointPtr& data_source,
+                          const UDPCompletionHandler& handler)
+    : handler_(handler), data_(new Data(buffer, buf_size, data_source)) {
+    if (!handler) {
+        isc_throw(NcrUDPError, "UDPCallback - handler can't be null");
+    }
+
+    if (!buffer) {
+        isc_throw(NcrUDPError, "UDPCallback - buffer can't be null");
+    }
+}
+
+void
+UDPCallback::operator ()(const boost::system::error_code error_code,
+                         const size_t bytes_transferred) {
+
+    // Save the result state and number of bytes transferred.
+    setErrorCode(error_code);
+    setBytesTransferred(bytes_transferred);
+
+    // Invoke the NameChangeRequest layer completion handler.
+    // First argument is a boolean indicating success or failure.
+    // The second is a pointer to "this" callback object. By passing
+    // ourself in, we make all of the service related data available
+    // to the completion handler.
+    handler_(!error_code, this);
+}
+
+void
+UDPCallback::putData(const uint8_t* src, size_t len) {
+    if (!src) {
+        isc_throw(NcrUDPError, "UDPCallback putData, data source is NULL");
+    }
+
+    if (len > data_->buf_size_) {
+        isc_throw(NcrUDPError, "UDPCallback putData, data length too large");
+    }
+
+    memcpy (data_->buffer_.get(), src, len);
+    data_->put_len_ = len;
+}
+
+
+//*************************** NameChangeUDPListener ***********************
+NameChangeUDPListener::
+NameChangeUDPListener(const isc::asiolink::IOAddress& ip_address,
+                      const uint32_t port, const NameChangeFormat format,
+                      RequestReceiveHandler& ncr_recv_handler,
+                      const bool reuse_address)
+    : NameChangeListener(ncr_recv_handler), ip_address_(ip_address),
+      port_(port), format_(format), reuse_address_(reuse_address) {
+    // Instantiate the receive callback.  This gets passed into each receive.
+    // Note that the callback constructor is passed an instance method
+    // pointer to our completion handler method, receiveCompletionHandler.
+    RawBufferPtr buffer(new uint8_t[RECV_BUF_MAX]);
+    UDPEndpointPtr data_source(new asiolink::UDPEndpoint());
+    recv_callback_.reset(new UDPCallback(buffer, RECV_BUF_MAX, data_source,
+        std::bind(&NameChangeUDPListener::receiveCompletionHandler,
+                  this, ph::_1, ph::_2)));
+}
+
+NameChangeUDPListener::~NameChangeUDPListener() {
+    // Clean up.
+    stopListening();
+}
+
+void
+NameChangeUDPListener::open(isc::asiolink::IOService& io_service) {
+    // create our endpoint and bind the low level socket to it.
+    isc::asiolink::UDPEndpoint endpoint(ip_address_, port_);
+
+    // Create the low level socket.
+    try {
+        asio_socket_.reset(new boost::asio::ip::udp::
+                           socket(io_service.get_io_service(),
+                                  (ip_address_.isV4() ? boost::asio::ip::udp::v4() :
+                                   boost::asio::ip::udp::v6())));
+
+        // Set the socket option to reuse addresses if it is enabled.
+        if (reuse_address_) {
+            asio_socket_->set_option(boost::asio::socket_base::reuse_address(true));
+        }
+
+        // Bind the low level socket to our endpoint.
+        asio_socket_->bind(endpoint.getASIOEndpoint());
+    } catch (const boost::system::system_error& ex) {
+        asio_socket_.reset();
+        isc_throw (NcrUDPError, ex.code().message());
+    }
+
+    // Create the asiolink socket from the low level socket.
+    socket_.reset(new NameChangeUDPSocket(*asio_socket_));
+}
+
+
+void
+NameChangeUDPListener::doReceive() {
+    // Call the socket's asynchronous receiving, passing ourself in as callback.
+    RawBufferPtr recv_buffer = recv_callback_->getBuffer();
+    socket_->asyncReceive(recv_buffer.get(), recv_callback_->getBufferSize(),
+                          0, recv_callback_->getDataSource().get(),
+                          *recv_callback_);
+}
+
+void
+NameChangeUDPListener::close() {
+    // Whether we think we are listening or not, make sure we aren't.
+    // Since we are managing our own socket, we need to close it ourselves.
+    // NOTE that if there is a pending receive, it will be canceled, which
+    // WILL generate an invocation of the callback with error code of
+    // "operation aborted".
+    if (asio_socket_) {
+        if (asio_socket_->is_open()) {
+            try {
+                asio_socket_->close();
+            } catch (const boost::system::system_error& ex) {
+                // It is really unlikely that this will occur.
+                // If we do reopen later it will be with a new socket
+                // instance. Repackage exception as one that is conformant
+                // with the interface.
+                isc_throw (NcrUDPError, ex.code().message());
+            }
+        }
+
+        asio_socket_.reset();
+    }
+
+    socket_.reset();
+}
+
+void
+NameChangeUDPListener::receiveCompletionHandler(const bool successful,
+                                                const UDPCallback *callback) {
+    NameChangeRequestPtr ncr;
+    Result result = SUCCESS;
+
+    if (successful) {
+        // Make an InputBuffer from our internal array
+        isc::util::InputBuffer input_buffer(callback->getData(),
+                                            callback->getBytesTransferred());
+
+        try {
+            ncr = NameChangeRequest::fromFormat(format_, input_buffer);
+            isc::stats::StatsMgr::instance().addValue("ncr-received",
+                                                      static_cast<int64_t>(1));
+        } catch (const NcrMessageError& ex) {
+            // log it and go back to listening
+            LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_INVALID_NCR).arg(ex.what());
+            isc::stats::StatsMgr::instance().addValue("ncr-invalid",
+                                                      static_cast<int64_t>(1));
+
+            // Queue up the next receive.
+            // NOTE: We must call the base class, NEVER doReceive
+            receiveNext();
+            return;
+        }
+    } else {
+        boost::system::error_code error_code = callback->getErrorCode();
+        if (error_code.value() == boost::asio::error::operation_aborted) {
+            // A shutdown cancels all outstanding reads.  For this reason,
+            // it can be an expected event, so log it as a debug message.
+            LOG_DEBUG(dhcp_ddns_logger, isc::log::DBGLVL_TRACE_BASIC,
+                      DHCP_DDNS_NCR_UDP_RECV_CANCELED);
+            result = STOPPED;
+        } else {
+            LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_NCR_UDP_RECV_ERROR)
+                      .arg(error_code.message());
+            isc::stats::StatsMgr::instance().addValue("ncr-error",
+                                                      static_cast<int64_t>(1));
+            result = ERROR;
+        }
+    }
+
+    // Call the application's registered request receive handler.
+    invokeRecvHandler(result, ncr);
+}
+
+
+//*************************** NameChangeUDPSender ***********************
+
+NameChangeUDPSender::
+NameChangeUDPSender(const isc::asiolink::IOAddress& ip_address,
+                    const uint32_t port,
+                    const isc::asiolink::IOAddress& server_address,
+                    const uint32_t server_port, const NameChangeFormat format,
+                    RequestSendHandler& ncr_send_handler,
+                    const size_t send_que_max, const bool reuse_address)
+    : NameChangeSender(ncr_send_handler, send_que_max),
+      ip_address_(ip_address), port_(port), server_address_(server_address),
+      server_port_(server_port), format_(format),
+      reuse_address_(reuse_address) {
+    // Instantiate the send callback.  This gets passed into each send.
+    // Note that the callback constructor is passed the an instance method
+    // pointer to our completion handler, sendCompletionHandler.
+    RawBufferPtr buffer(new uint8_t[SEND_BUF_MAX]);
+    UDPEndpointPtr data_source(new asiolink::UDPEndpoint());
+    send_callback_.reset(new UDPCallback(buffer, SEND_BUF_MAX, data_source,
+        std::bind(&NameChangeUDPSender::sendCompletionHandler,
+                  this, ph::_1, ph::_2)));
+}
+
+NameChangeUDPSender::~NameChangeUDPSender() {
+    // Clean up.
+    stopSending();
+}
+
+void
+NameChangeUDPSender::open(isc::asiolink::IOService& io_service) {
+    // create our endpoint and bind the low level socket to it.
+    isc::asiolink::UDPEndpoint endpoint(ip_address_, port_);
+
+    // Create the low level socket.
+    try {
+        asio_socket_.reset(new boost::asio::ip::udp::
+                           socket(io_service.get_io_service(),
+                                  (ip_address_.isV4() ? boost::asio::ip::udp::v4() :
+                                   boost::asio::ip::udp::v6())));
+
+        // Set the socket option to reuse addresses if it is enabled.
+        if (reuse_address_) {
+            asio_socket_->set_option(boost::asio::socket_base::reuse_address(true));
+        }
+
+        // Bind the low level socket to our endpoint.
+        asio_socket_->bind(endpoint.getASIOEndpoint());
+    } catch (const boost::system::system_error& ex) {
+        isc_throw (NcrUDPError, ex.code().message());
+    }
+
+    // Create the asiolink socket from the low level socket.
+    socket_.reset(new NameChangeUDPSocket(*asio_socket_));
+
+    // Create the server endpoint
+    server_endpoint_.reset(new isc::asiolink::
+                           UDPEndpoint(server_address_, server_port_));
+
+    send_callback_->setDataSource(server_endpoint_);
+
+    closeWatchSocket();
+    watch_socket_.reset(new util::WatchSocket());
+}
+
+void
+NameChangeUDPSender::close() {
+    // Whether we think we are sending or not, make sure we aren't.
+    // Since we are managing our own socket, we need to close it ourselves.
+    // NOTE that if there is a pending send, it will be canceled, which
+    // WILL generate an invocation of the callback with error code of
+    // "operation aborted".
+    if (asio_socket_) {
+        if (asio_socket_->is_open()) {
+            try {
+                asio_socket_->close();
+            } catch (const boost::system::system_error& ex) {
+                // It is really unlikely that this will occur.
+                // If we do reopen later it will be with a new socket
+                // instance. Repackage exception as one that is conformant
+                // with the interface.
+                isc_throw (NcrUDPError, ex.code().message());
+            }
+        }
+
+        asio_socket_.reset();
+    }
+
+    socket_.reset();
+
+    closeWatchSocket();
+    watch_socket_.reset();
+}
+
+void
+NameChangeUDPSender::doSend(NameChangeRequestPtr& ncr) {
+    // Now use the NCR to write JSON to an output buffer.
+    isc::util::OutputBuffer ncr_buffer(SEND_BUF_MAX);
+    ncr->toFormat(format_, ncr_buffer);
+
+    // Copy the wire-ized request to callback.  This way we know after
+    // send completes what we sent (or attempted to send).
+    send_callback_->putData(static_cast<const uint8_t*>(ncr_buffer.getData()),
+                            ncr_buffer.getLength());
+
+    // Call the socket's asynchronous send, passing our callback
+    socket_->asyncSend(send_callback_->getData(), send_callback_->getPutLen(),
+                       send_callback_->getDataSource().get(), *send_callback_);
+
+    // Set IO ready marker so sender activity is visible to select() or poll().
+    // Note, if this call throws it will manifest itself as a throw from
+    // from sendRequest() which the application calls directly and is documented
+    // as throwing exceptions; or caught inside invokeSendHandler() which
+    // will invoke the application's send_handler with an error status.
+    watch_socket_->markReady();
+}
+
+void
+NameChangeUDPSender::sendCompletionHandler(const bool successful,
+                                           const UDPCallback *send_callback) {
+    // Clear the IO ready marker.
+    try {
+        watch_socket_->clearReady();
+    } catch (const std::exception& ex) {
+        // This can only happen if the WatchSocket's select_fd has been
+        // compromised which is a programmatic error. We'll log the error
+        // here, then continue on and process the IO result we were given.
+        // WatchSocket issue will resurface on the next send as a closed
+        // fd in markReady().  This allows application's handler to deal
+        // with watch errors more uniformly.
+        LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_NCR_UDP_CLEAR_READY_ERROR)
+                 .arg(ex.what());
+    }
+
+    Result result;
+    if (successful) {
+        result = SUCCESS;
+    } else {
+        // On a failure, log the error and set the result to ERROR.
+        boost::system::error_code error_code = send_callback->getErrorCode();
+        if (error_code.value() == boost::asio::error::operation_aborted) {
+            LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_NCR_UDP_SEND_CANCELED)
+                      .arg(error_code.message());
+            result = STOPPED;
+        } else {
+            LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_NCR_UDP_SEND_ERROR)
+                      .arg(error_code.message());
+            result = ERROR;
+        }
+    }
+
+    // Call the application's registered request send handler.
+    invokeSendHandler(result);
+}
+
+int
+NameChangeUDPSender::getSelectFd() {
+    if (!amSending()) {
+        isc_throw(NotImplemented, "NameChangeUDPSender::getSelectFd"
+                                  " not in send mode");
+    }
+
+    return(watch_socket_->getSelectFd());
+}
+
+bool
+NameChangeUDPSender::ioReady() {
+    if (watch_socket_) {
+        return (watch_socket_->isReady());
+    }
+
+    return (false);
+}
+
+void
+NameChangeUDPSender::closeWatchSocket() {
+    if (watch_socket_) {
+        std::string error_string;
+        watch_socket_->closeSocket(error_string);
+        if (!error_string.empty()) {
+            LOG_ERROR(dhcp_ddns_logger, DHCP_DDNS_UDP_SENDER_WATCH_SOCKET_CLOSE_ERROR)
+                .arg(error_string);
+        }
+    }
+}
+
+} // end of isc::dhcp_ddns namespace
+} // end of isc namespace
diff --git a/src/lib/dhcp_ddns/ncr_udp.h b/src/lib/dhcp_ddns/ncr_udp.h
new file mode 100644
index 0000000..01284af
--- /dev/null
+++ b/src/lib/dhcp_ddns/ncr_udp.h
@@ -0,0 +1,588 @@
+// Copyright (C) 2013-2020 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/.
+
+#ifndef NCR_UDP_LISTENER_H
+#define NCR_UDP_LISTENER_H
+
+/// @file ncr_udp.h
+/// @brief This file provides UDP socket based implementation for sending and
+/// receiving NameChangeRequests
+///
+/// These classes are derived from the abstract classes, NameChangeListener
+/// and NameChangeSender (see ncr_io.h).
+///
+/// The following discussion will refer to three layers of communications:
+///
+///    * Application layer - This is the business layer which needs to
+///    transport NameChangeRequests, and is unaware of the means by which
+///    they are transported.
+///
+///    * IO layer - This is the low-level layer that is directly responsible
+///    for sending and receiving data asynchronously and is supplied through
+///    other libraries.  This layer is largely unaware of the nature of the
+///    data being transmitted.  In other words, it doesn't know beans about
+///    NCRs.
+///
+///    * NameChangeRequest layer - This is the layer which acts as the
+///    intermediary between the Application layer and the IO layer.  It must
+///    be able to move NameChangeRequests to the IO layer as raw data and move
+///    raw data from the IO layer in the Application layer as
+///    NameChangeRequests.
+///
+/// This file defines NameChangeUDPListener class for receiving NCRs, and
+/// NameChangeUDPSender for sending NCRs.
+///
+/// Both the listener and sender implementations utilize the same underlying
+/// construct to move NCRs to and from a UDP socket. This construct consists
+/// of a set of classes centered around isc::asiolink::UDPSocket.  UDPSocket
+/// is a templated class that supports asio asynchronous event processing; and
+/// which accepts as its parameter, the name of a callback class.
+///
+/// The asynchronous services provided by UDPSocket typically accept a buffer
+/// for transferring data (either in or out depending on the service direction)
+/// and an object which supplies a callback to invoke upon completion of the
+/// service.
+///
+/// The callback class must provide an operator() with the following signature:
+/// @code
+///    void operator ()(const boost::system::error_code error_code,
+///                     const size_t bytes_transferred);
+/// @endcode
+///
+/// Upon completion of the service, the callback instance's operator() is
+/// invoked by the asio layer.  It is given both a outcome result and the
+/// number of bytes either read or written, to or from the buffer supplied
+/// to the service.
+///
+/// Typically, an asiolink based implementation would simply implement the
+/// callback operator directly.  However, the nature of the asiolink library
+/// is such that the callback object may be copied several times during course
+/// of a service invocation.  This implies that any class being used as a
+/// callback class must be copyable.  This is not always desirable.  In order
+/// to separate the callback class from the NameChangeRequest, the construct
+/// defines the UDPCallback class for use as a copyable, callback object.
+///
+/// The UDPCallback class provides the asiolink layer callback operator(),
+/// which is invoked by the asiolink layer upon service completion.  It
+/// contains:
+///    * a pointer to the transfer buffer
+///    * the capacity of the transfer buffer
+///    * a IO layer outcome result
+///    * the number of bytes transferred
+///    * a method pointer to a NameChangeRequest layer completion handler
+///
+/// This last item, is critical. It points to an instance method that
+/// will be invoked by the UDPCallback operator.  This provides access to
+/// the outcome of the service call to the NameChangeRequest layer without
+/// that layer being used as the actual callback object.
+///
+/// The completion handler method signature is codified in the typedef,
+/// UDPCompletionHandler, and must be as follows:
+///
+/// @code
+///     void(const bool, const UDPCallback*)
+/// @endcode
+///
+/// Note that is accepts two parameters.  The first is a boolean indicator
+/// which indicates if the service call completed successfully or not.  The
+/// second is a pointer to the callback object invoked by the IOService upon
+/// completion of the service.  The callback instance will contain all of the
+/// pertinent information about the invocation and outcome of the service.
+///
+/// Using the contents of the callback, it is the responsibility of the
+/// UDPCompletionHandler to interpret the results of the service invocation and
+/// pass the interpretation to the application layer via either
+/// NameChangeListener::invokeRecvHandler in the case of the UDP listener, or
+/// NameChangeSender::invokeSendHandler in the case of UDP sender.
+///
+
+#include <asiolink/asio_wrapper.h>
+#include <asiolink/io_address.h>
+#include <asiolink/io_service.h>
+#include <asiolink/udp_endpoint.h>
+#include <asiolink/udp_socket.h>
+#include <dhcp_ddns/ncr_io.h>
+#include <util/buffer.h>
+#include <util/watch_socket.h>
+
+#include <boost/shared_array.hpp>
+
+
+/// responsibility of the completion handler to perform the steps necessary
+/// to interpret the raw data provided by the service outcome.   The
+/// UDPCallback operator implementation is mostly a pass through.
+///
+namespace isc {
+namespace dhcp_ddns {
+
+/// @brief Thrown when a UDP level exception occurs.
+class NcrUDPError : public isc::Exception {
+public:
+    NcrUDPError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+class UDPCallback;
+/// @brief Defines a function pointer for NameChangeRequest completion handlers.
+typedef std::function<void(const bool, const UDPCallback*)>
+          UDPCompletionHandler;
+
+/// @brief Defines a dynamically allocated shared array.
+typedef boost::shared_array<uint8_t> RawBufferPtr;
+
+typedef boost::shared_ptr<asiolink::UDPEndpoint> UDPEndpointPtr;
+
+/// @brief Implements the callback class passed into UDPSocket calls.
+///
+/// It serves as the link between the asiolink::UDPSocket asynchronous services
+/// and the NameChangeRequest layer. The class provides the asiolink layer
+/// callback operator(), which is invoked by the asiolink layer upon service
+/// completion.  It contains all of the data pertinent to both the invocation
+/// and completion of a service, as well as a pointer to NameChangeRequest
+/// layer completion handler to invoke.
+///
+class UDPCallback {
+
+public:
+    /// @brief Container class which stores service invocation related data.
+    ///
+    /// Because the callback object may be copied numerous times during the
+    /// course of service invocation, it does not directly contain data values.
+    /// Rather it will retain a shared pointer to an instance of this structure
+    /// thus ensuring that all copies of the callback object, ultimately refer
+    /// to the same data values.
+    struct Data {
+
+        /// @brief Constructor
+        ///
+        /// @param buffer is a pointer to the data transfer buffer. This is
+        /// the buffer data will be written to on a read, or read from on a
+        /// send.
+        /// @param buf_size is the capacity of the buffer
+        /// @param data_source storage for UDP endpoint which supplied the data
+        Data(RawBufferPtr& buffer, const size_t buf_size,
+             UDPEndpointPtr& data_source)
+            : buffer_(buffer), buf_size_(buf_size), data_source_(data_source),
+              put_len_(0), error_code_(), bytes_transferred_(0) {
+        };
+
+        /// @brief A pointer to the data transfer buffer.
+        RawBufferPtr buffer_;
+
+        /// @brief Storage capacity of the buffer.
+        size_t buf_size_;
+
+        /// @brief The UDP endpoint that is the origin of the data transferred.
+        UDPEndpointPtr data_source_;
+
+        /// @brief Stores this size of the data within the buffer when written
+        /// there manually. (See UDPCallback::putData()) .
+        size_t put_len_;
+
+        /// @brief Stores the IO layer result code of the completed IO service.
+        boost::system::error_code error_code_;
+
+        /// @brief Stores the number of bytes transferred by completed IO
+        /// service.
+        /// For a read it is the number of bytes written into the
+        /// buffer.  For a write it is the number of bytes read from the
+        /// buffer.
+        size_t bytes_transferred_;
+
+    };
+
+    /// @brief Used as the callback object for UDPSocket services.
+    ///
+    /// @param buffer is a pointer to the data transfer buffer. This is
+    /// the buffer data will be written to on a read, or read from on a
+    /// send.
+    /// @param buf_size is the capacity of the buffer
+    /// @param data_source storage for UDP endpoint which supplied the data
+    /// @param handler is a method pointer to the completion handler that
+    /// is to be called by the operator() implementation.
+    ///
+    /// @throw NcrUDPError if either the handler or buffer pointers
+    /// are invalid.
+    UDPCallback (RawBufferPtr& buffer, const size_t buf_size,
+                 UDPEndpointPtr& data_source,
+                 const UDPCompletionHandler& handler);
+
+    /// @brief Operator that will be invoked by the asiolink layer.
+    ///
+    /// @param error_code is the IO layer result code of the
+    /// completed IO service.
+    /// @param bytes_transferred is the number of bytes transferred by
+    /// completed IO.
+    /// For a read it is the number of bytes written into the
+    /// buffer.  For a write it is the number of bytes read from the
+    /// buffer.
+    void operator ()(const boost::system::error_code error_code,
+                     const size_t bytes_transferred);
+
+    /// @brief Returns the number of bytes transferred by the completed IO
+    /// service.
+    ///
+    /// For a read it is the number of bytes written into the
+    /// buffer.  For a write it is the number of bytes read from the
+    /// buffer.
+    size_t getBytesTransferred() const {
+        return (data_->bytes_transferred_);
+    }
+
+    /// @brief Sets the number of bytes transferred.
+    ///
+    /// @param value is the new value to assign to bytes transferred.
+    void setBytesTransferred(const size_t value) {
+        data_->bytes_transferred_ = value;
+    }
+
+    /// @brief Returns the completed IO layer service outcome status.
+    boost::system::error_code getErrorCode() const {
+        return (data_->error_code_);
+    }
+
+    /// @brief Sets the completed IO layer service outcome status.
+    ///
+    /// @param value is the new value to assign to outcome status.
+    void setErrorCode(const boost::system::error_code value) {
+        data_->error_code_  = value;
+    }
+
+    /// @brief Returns the data transfer buffer.
+    RawBufferPtr getBuffer() const {
+        return (data_->buffer_);
+    }
+
+    /// @brief Returns the data transfer buffer capacity.
+    size_t getBufferSize() const {
+        return (data_->buf_size_);
+    }
+
+    /// @brief Returns a pointer the data transfer buffer content.
+    const uint8_t* getData() const {
+        return (data_->buffer_.get());
+    }
+
+    /// @brief Copies data into the data transfer buffer.
+    ///
+    /// Copies the given number of bytes from the given source buffer
+    /// into the data transfer buffer, and updates the value of put length.
+    /// This method may be used when performing sends to make a copy of
+    /// the "raw data" that was shipped (or attempted) accessible to the
+    /// upstream callback.
+    ///
+    /// @param src is a pointer to the data source from which to copy
+    /// @param len is the number of bytes to copy
+    ///
+    /// @throw NcrUDPError if the number of bytes to copy exceeds
+    /// the buffer capacity or if the source pointer is invalid.
+    void putData(const uint8_t* src, size_t len);
+
+    /// @brief Returns the number of bytes manually written into the
+    /// transfer buffer.
+    size_t getPutLen() const {
+        return (data_->put_len_);
+    }
+
+    /// @brief Sets the data source to the given endpoint.
+    ///
+    /// @param endpoint is the new value to assign to data source.
+    void setDataSource(UDPEndpointPtr& endpoint) {
+        data_->data_source_ = endpoint;
+    }
+
+    /// @brief Returns the UDP endpoint that provided the transferred data.
+    const UDPEndpointPtr& getDataSource() {
+        return (data_->data_source_);
+    }
+
+  private:
+    /// @brief NameChangeRequest layer completion handler to invoke.
+    UDPCompletionHandler handler_;
+
+    /// @brief Shared pointer to the service data container.
+    boost::shared_ptr<Data> data_;
+};
+
+/// @brief Convenience type for UDP socket based listener
+typedef isc::asiolink::UDPSocket<UDPCallback> NameChangeUDPSocket;
+
+/// @brief Provides the ability to receive NameChangeRequests via  UDP socket
+///
+/// This class is a derivation of the NameChangeListener which is capable of
+/// receiving NameChangeRequests through a UDP socket.  The caller need only
+/// supply network addressing and a RequestReceiveHandler instance to receive
+/// NameChangeRequests asynchronously.
+class NameChangeUDPListener : public NameChangeListener {
+public:
+    /// @brief Defines the maximum size packet that can be received.
+    static const size_t RECV_BUF_MAX = isc::asiolink::
+                                       UDPSocket<UDPCallback>::MIN_SIZE;
+
+    /// @brief Constructor
+    ///
+    /// @param ip_address is the network address on which to listen
+    /// @param port is the UDP port on which to listen
+    /// @param format is the wire format of the inbound requests. Currently
+    /// only JSON is supported
+    /// @param ncr_recv_handler the receive handler object to notify when
+    /// a receive completes.
+    /// @param reuse_address enables IP address sharing when true
+    /// It defaults to false.
+    ///
+    /// @throw base class throws NcrListenerError if handler is invalid.
+    NameChangeUDPListener(const isc::asiolink::IOAddress& ip_address,
+                          const uint32_t port,
+                          const NameChangeFormat format,
+                          RequestReceiveHandler& ncr_recv_handler,
+                          const bool reuse_address = false);
+
+    /// @brief Destructor.
+    virtual ~NameChangeUDPListener();
+
+    /// @brief Opens a UDP socket using the given IOService.
+    ///
+    /// Creates a NameChangeUDPSocket bound to the listener's ip address
+    /// and port, that is monitored by the given IOService instance.
+    ///
+    /// @param io_service the IOService which will monitor the socket.
+    ///
+    /// @throw NcrUDPError if the open fails.
+    virtual void open(isc::asiolink::IOService& io_service);
+
+    /// @brief Closes the UDPSocket.
+    ///
+    /// It first invokes the socket's cancel method which should stop any
+    /// pending read and remove the socket callback from the IOService. It
+    /// then calls the socket's close method to actually close the socket.
+    ///
+    /// @throw NcrUDPError if the open fails.
+    virtual void close();
+
+    /// @brief Initiates an asynchronous read on the socket.
+    ///
+    /// Invokes the asyncReceive() method on the socket passing in the
+    /// recv_callback_ member's transfer buffer as the receive buffer, and
+    /// recv_callback_ itself as the callback object.
+    ///
+    /// @throw NcrUDPError if the open fails.
+    void doReceive();
+
+    /// @brief Implements the NameChangeRequest level receive completion
+    /// handler.
+    ///
+    /// This method is invoked by the UPDCallback operator() implementation,
+    /// passing in the boolean success indicator and pointer to itself.
+    ///
+    /// If the indicator denotes success, then the method will attempt to
+    /// to construct a NameChangeRequest from the received data.  If the
+    /// construction was successful, it will send the new NCR to the
+    /// application layer by calling invokeRecvHandler() with a success
+    /// status and a pointer to the new NCR.
+    ///
+    /// If the buffer contains invalid data such that construction fails,
+    /// the method will log the failure and then call doReceive() to start a
+    /// initiate the next receive.
+    ///
+    /// If the indicator denotes failure the method will log the failure and
+    /// notify the application layer by calling invokeRecvHandler() with
+    /// an error status and an empty pointer.
+    ///
+    /// @param successful boolean indicator that should be true if the
+    /// socket receive completed without error, false otherwise.
+    /// @param recv_callback pointer to the callback instance which handled
+    /// the socket receive completion.
+    void receiveCompletionHandler(const bool successful,
+                                  const UDPCallback* recv_callback);
+private:
+    /// @brief IP address on which to listen for requests.
+    isc::asiolink::IOAddress ip_address_;
+
+    /// @brief Port number on which to listen for requests.
+    uint32_t port_;
+
+    /// @brief Wire format of the inbound requests.
+    NameChangeFormat format_;
+
+    /// @brief Low level socket underneath the listening socket
+    boost::shared_ptr<boost::asio::ip::udp::socket> asio_socket_;
+
+    /// @brief NameChangeUDPSocket listening socket
+    boost::shared_ptr<NameChangeUDPSocket> socket_;
+
+    /// @brief Pointer to the receive callback
+    boost::shared_ptr<UDPCallback> recv_callback_;
+
+    /// @brief Flag which enables the reuse address socket option if true.
+    bool reuse_address_;
+
+    ///
+    /// @name Copy and constructor assignment operator
+    ///
+    /// The copy constructor and assignment operator are private to avoid
+    /// potential issues with multiple listeners attempting to share sockets
+    /// and callbacks.
+private:
+    NameChangeUDPListener(const NameChangeUDPListener& source);
+    NameChangeUDPListener& operator=(const NameChangeUDPListener& source);
+    //@}
+};
+
+
+/// @brief Provides the ability to send NameChangeRequests via  UDP socket
+///
+/// This class is a derivation of the NameChangeSender which is capable of
+/// sending NameChangeRequests through a UDP socket.  The caller need only
+/// supply network addressing and a RequestSendHandler instance to send
+/// NameChangeRequests asynchronously.
+class NameChangeUDPSender : public NameChangeSender {
+public:
+
+    /// @brief Defines the maximum size packet that can be sent.
+    static const size_t SEND_BUF_MAX =  NameChangeUDPListener::RECV_BUF_MAX;
+
+    /// @brief Constructor
+    ///
+    /// @param ip_address the IP address from which to send
+    /// @param port the port from which to send
+    /// @param server_address the IP address of the target listener
+    /// @param server_port is the IP port  of the target listener
+    /// @param format is the wire format of the outbound requests.
+    /// @param ncr_send_handler the send handler object to notify when
+    /// when a send completes.
+    /// @param send_que_max sets the maximum number of entries allowed in
+    /// the send queue.
+    /// It defaults to NameChangeSender::MAX_QUEUE_DEFAULT
+    /// @param reuse_address enables IP address sharing when true
+    /// It defaults to false.
+    ///
+    NameChangeUDPSender(const isc::asiolink::IOAddress& ip_address,
+        const uint32_t port, const isc::asiolink::IOAddress& server_address,
+        const uint32_t server_port, const NameChangeFormat format,
+        RequestSendHandler& ncr_send_handler,
+        const size_t send_que_max = NameChangeSender::MAX_QUEUE_DEFAULT,
+        const bool reuse_address = false);
+
+    /// @brief Destructor
+    virtual ~NameChangeUDPSender();
+
+
+    /// @brief Opens a UDP socket using the given IOService.
+    ///
+    /// Creates a NameChangeUDPSocket bound to the sender's IP address
+    /// and port, that is monitored by the given IOService instance.
+    ///
+    /// @param io_service the IOService which will monitor the socket.
+    ///
+    /// @throw NcrUDPError if the open fails.
+    virtual void open(isc::asiolink::IOService& io_service);
+
+
+    /// @brief Closes the UDPSocket.
+    ///
+    /// It first invokes the socket's cancel method which should stop any
+    /// pending send and remove the socket callback from the IOService. It
+    /// then calls the socket's close method to actually close the socket.
+    ///
+    /// @throw NcrUDPError if the open fails.
+    virtual void close();
+
+    /// @brief Sends a given request asynchronously over the socket
+    ///
+    /// The given NameChangeRequest is converted to wire format and copied
+    /// into the send callback's transfer buffer.  Then the socket's
+    /// asyncSend() method is called, passing in send_callback_ member's
+    /// transfer buffer as the send buffer and the send_callback_ itself
+    /// as the callback object.
+    /// @param ncr NameChangeRequest to send.
+    virtual void doSend(NameChangeRequestPtr& ncr);
+
+    /// @brief Implements the NameChangeRequest level send completion handler.
+    ///
+    /// This method is invoked by the UDPCallback operator() implementation,
+    /// passing in the boolean success indicator and pointer to itself.
+    ///
+    /// If the indicator denotes success, then the method will notify the
+    /// application layer by calling invokeSendHandler() with a success
+    /// status.
+    ///
+    /// If the indicator denotes failure the method will log the failure and
+    /// notify the application layer by calling invokeRecvHandler() with
+    /// an error status.
+    ///
+    /// @param successful boolean indicator that should be true if the
+    /// socket send completed without error, false otherwise.
+    /// @param send_callback pointer to the callback instance which handled
+    /// the socket receive completion.
+    void sendCompletionHandler(const bool successful,
+                               const UDPCallback* send_callback);
+
+    /// @brief Returns a file descriptor suitable for use with select
+    ///
+    /// The value returned is an open file descriptor which can be used with
+    /// select() system call to monitor the sender for IO events.  This allows
+    /// NameChangeUDPSenders to be used in applications which use select,
+    /// rather than IOService to wait for IO events to occur.
+    ///
+    /// @warning Attempting other use of this value may lead to unpredictable
+    /// behavior in the sender.
+    ///
+    /// @return Returns an "open" file descriptor
+    ///
+    /// @throw NcrSenderError if the sender is not in send mode,
+    virtual int getSelectFd();
+
+    /// @brief Returns whether or not the sender has IO ready to process.
+    ///
+    /// @return true if the sender has at IO ready, false otherwise.
+    virtual bool ioReady();
+
+private:
+
+    /// @brief Closes watch socket if the socket is open.
+    ///
+    /// This method closes watch socket if its instance exists and if the
+    /// socket is open. An error message is logged when this operation fails.
+    void closeWatchSocket();
+
+    /// @brief IP address from which to send.
+    isc::asiolink::IOAddress ip_address_;
+
+    /// @brief Port from which to send.
+    uint32_t port_;
+
+    /// @brief IP address of the target listener.
+    isc::asiolink::IOAddress server_address_;
+
+    /// @brief Port of the target listener.
+    uint32_t server_port_;
+
+    /// @brief Wire format of the outbound requests.
+    NameChangeFormat format_;
+
+    /// @brief Low level socket underneath the sending socket.
+    boost::shared_ptr<boost::asio::ip::udp::socket> asio_socket_;
+
+    /// @brief NameChangeUDPSocket sending socket.
+    boost::shared_ptr<NameChangeUDPSocket> socket_;
+
+    /// @brief Endpoint of the target listener.
+    boost::shared_ptr<isc::asiolink::UDPEndpoint> server_endpoint_;
+
+    /// @brief Pointer to the send callback
+    boost::shared_ptr<UDPCallback> send_callback_;
+
+    /// @brief Flag which enables the reuse address socket option if true.
+    bool reuse_address_;
+
+    /// @brief Pointer to WatchSocket instance supplying the "select-fd".
+    util::WatchSocketPtr watch_socket_;
+};
+
+} // namespace isc::dhcp_ddns
+} // namespace isc
+
+#endif
diff --git a/src/lib/dhcp_ddns/tests/Makefile.am b/src/lib/dhcp_ddns/tests/Makefile.am
new file mode 100644
index 0000000..e1f27d1
--- /dev/null
+++ b/src/lib/dhcp_ddns/tests/Makefile.am
@@ -0,0 +1,49 @@
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+
+AM_CPPFLAGS = -I$(top_builddir)/src/lib -I$(top_srcdir)/src/lib
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+
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+
+TESTS =
+if HAVE_GTEST
+TESTS += libdhcp_ddns_unittests
+
+libdhcp_ddns_unittests_SOURCES  = run_unittests.cc
+libdhcp_ddns_unittests_SOURCES += ncr_unittests.cc
+libdhcp_ddns_unittests_SOURCES += ncr_udp_unittests.cc
+libdhcp_ddns_unittests_SOURCES += test_utils.cc test_utils.h
+
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+
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+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/stats/libkea-stats.la
+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/dhcp/libkea-dhcp++.la
+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/asiolink/libkea-asiolink.la
+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/cc/libkea-cc.la
+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/dns/libkea-dns++.la
+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/cryptolink/libkea-cryptolink.la
+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/hooks/libkea-hooks.la
+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/log/libkea-log.la
+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/util/libkea-util.la
+libdhcp_ddns_unittests_LDADD += $(top_builddir)/src/lib/exceptions/libkea-exceptions.la
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new file mode 100644
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diff --git a/src/lib/dhcp_ddns/tests/ncr_udp_unittests.cc b/src/lib/dhcp_ddns/tests/ncr_udp_unittests.cc
new file mode 100644
index 0000000..b63ed8c
--- /dev/null
+++ b/src/lib/dhcp_ddns/tests/ncr_udp_unittests.cc
@@ -0,0 +1,1428 @@
+// Copyright (C) 2013-2021 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/.
+
+#include <config.h>
+
+#include <gtest/gtest.h>
+
+#include <asiolink/interval_timer.h>
+#include <dhcp_ddns/ncr_io.h>
+#include <dhcp_ddns/ncr_udp.h>
+#include <util/multi_threading_mgr.h>
+#include <util/time_utilities.h>
+#include <test_utils.h>
+
+#include <boost/asio/ip/udp.hpp>
+
+#include <functional>
+#include <algorithm>
+
+#include <sys/select.h>
+
+using namespace std;
+using namespace isc;
+using namespace isc::util;
+using namespace isc::dhcp_ddns;
+
+namespace {
+
+/// @brief Defines a list of valid JSON NameChangeRequest test messages.
+const char *valid_msgs[] =
+{
+    // Valid Add.
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Valid Remove.
+     "{"
+     " \"change-type\" : 1 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": false"
+     "}",
+     // Valid Add with IPv6 address
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"fe80::2acf:e9ff:fe12:e56f\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\" : true"
+     "}"
+};
+
+const char* TEST_ADDRESS = "127.0.0.1";
+const uint32_t LISTENER_PORT = 5301;
+const uint32_t SENDER_PORT = LISTENER_PORT+1;
+const long TEST_TIMEOUT = 5 * 1000;
+
+/// @brief A NOP derivation for constructor test purposes.
+class SimpleListenHandler : public NameChangeListener::RequestReceiveHandler {
+public:
+    virtual void operator ()(const NameChangeListener::Result,
+                             NameChangeRequestPtr&) {
+    }
+};
+
+/// @brief Tests the NameChangeUDPListener constructors.
+/// This test verifies that:
+/// 1. Given valid parameters, the listener constructor works
+TEST(NameChangeUDPListenerBasicTest, constructionTests) {
+    // Verify the default constructor works.
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    uint32_t port = LISTENER_PORT;
+    isc::asiolink::IOService io_service;
+    SimpleListenHandler ncr_handler;
+    // Verify that valid constructor works.
+    EXPECT_NO_THROW(NameChangeUDPListener(ip_address, port, FMT_JSON,
+                                          ncr_handler));
+}
+
+/// @brief Tests NameChangeUDPListener starting and stopping listening .
+/// This test verifies that the listener will:
+/// 1. Enter listening state
+/// 2. If in the listening state, does not allow calls to start listening
+/// 3. Exist the listening state
+/// 4. Return to the listening state after stopping
+TEST(NameChangeUDPListenerBasicTest, basicListenTests) {
+    // Verify the default constructor works.
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    uint32_t port = LISTENER_PORT;
+    isc::asiolink::IOService io_service;
+    SimpleListenHandler ncr_handler;
+
+    NameChangeListenerPtr listener;
+    ASSERT_NO_THROW(listener.reset(
+        new NameChangeUDPListener(ip_address, port, FMT_JSON, ncr_handler)));
+
+    // Verify that we can start listening.
+    EXPECT_NO_THROW(listener->startListening(io_service));
+
+    // Verify that we are in listening mode.
+    EXPECT_TRUE(listener->amListening());
+    // Verify that a read is in progress.
+    EXPECT_TRUE(listener->isIoPending());
+
+    // Verify that attempting to listen when we already are is an error.
+    EXPECT_THROW(listener->startListening(io_service), NcrListenerError);
+
+    // Verify that we can stop listening.
+    EXPECT_NO_THROW(listener->stopListening());
+    EXPECT_FALSE(listener->amListening());
+
+    // Verify that IO pending is still true, as IO cancel event has not yet
+    // occurred.
+    EXPECT_TRUE(listener->isIoPending());
+
+    // Verify that IO pending is false, after cancel event occurs.
+    EXPECT_NO_THROW(io_service.run_one());
+    EXPECT_FALSE(listener->isIoPending());
+
+    // Verify that attempting to stop listening when we are not is ok.
+    EXPECT_NO_THROW(listener->stopListening());
+
+    // Verify that we can re-enter listening.
+    EXPECT_NO_THROW(listener->startListening(io_service));
+    EXPECT_TRUE(listener->amListening());
+}
+
+/// @brief Compares two NameChangeRequests for equality.
+bool checkSendVsReceived(NameChangeRequestPtr sent_ncr,
+                         NameChangeRequestPtr received_ncr) {
+    return ((sent_ncr && received_ncr) &&
+        (*sent_ncr == *received_ncr));
+}
+
+/// @brief Text fixture for testing NameChangeUDPListener
+class NameChangeUDPListenerTest : public virtual ::testing::Test,
+                                  NameChangeListener::RequestReceiveHandler {
+public:
+    isc::asiolink::IOService io_service_;
+    NameChangeListener::Result result_;
+    NameChangeRequestPtr sent_ncr_;
+    NameChangeRequestPtr received_ncr_;
+    NameChangeListenerPtr listener_;
+    isc::asiolink::IntervalTimer test_timer_;
+
+    /// @brief Constructor
+    //
+    // Instantiates the listener member and the test timer. The timer is used
+    // to ensure a test doesn't go awry and hang forever.
+    NameChangeUDPListenerTest()
+        : io_service_(), result_(NameChangeListener::SUCCESS),
+          test_timer_(io_service_) {
+        isc::asiolink::IOAddress addr(TEST_ADDRESS);
+        listener_.reset(new NameChangeUDPListener(addr, LISTENER_PORT,
+                                              FMT_JSON, *this, true));
+
+        // Set the test timeout to break any running tasks if they hang.
+        test_timer_.setup(std::bind(&NameChangeUDPListenerTest::
+                                    testTimeoutHandler, this),
+                          TEST_TIMEOUT);
+    }
+
+    virtual ~NameChangeUDPListenerTest(){
+    }
+
+
+    /// @brief Converts JSON string into an NCR and sends it to the listener.
+    ///
+    void sendNcr(const std::string& msg) {
+        // Build an NCR  from json string. This verifies that the
+        // test string is valid.
+        ASSERT_NO_THROW(sent_ncr_ = NameChangeRequest::fromJSON(msg));
+
+        // Now use the NCR to write JSON to an output buffer.
+        isc::util::OutputBuffer ncr_buffer(1024);
+        ASSERT_NO_THROW(sent_ncr_->toFormat(FMT_JSON, ncr_buffer));
+
+        // Create a UDP socket through which our "sender" will send the NCR.
+        boost::asio::ip::udp::socket
+            udp_socket(io_service_.get_io_service(), boost::asio::ip::udp::v4());
+
+        // Create an endpoint pointed at the listener.
+        boost::asio::ip::udp::endpoint
+            listener_endpoint(boost::asio::ip::address::from_string(TEST_ADDRESS),
+                              LISTENER_PORT);
+
+        // A response message is now ready to send. Send it!
+        // Note this uses a synchronous send so it ships immediately.
+        // If listener isn't in listening mode, it will get missed.
+        udp_socket.send_to(boost::asio::buffer(ncr_buffer.getData(),
+                                     ncr_buffer.getLength()),
+                            listener_endpoint);
+    }
+
+    /// @brief RequestReceiveHandler operator implementation for receiving NCRs.
+    ///
+    /// The fixture acts as the "application" layer.  It derives from
+    /// RequestReceiveHandler and as such implements operator() in order to
+    /// receive NCRs.
+    virtual void operator ()(const NameChangeListener::Result result,
+                             NameChangeRequestPtr& ncr) {
+        // save the result and the NCR we received
+        result_ = result;
+        received_ncr_ = ncr;
+    }
+
+    /// @brief Handler invoked when test timeout is hit
+    ///
+    /// This callback stops all running (hanging) tasks on IO service.
+    void testTimeoutHandler() {
+        io_service_.stop();
+        FAIL() << "Test timeout hit.";
+    }
+};
+
+/// @brief  Tests NameChangeUDPListener ability to receive NCRs.
+/// This test verifies that a listener can enter listening mode and
+/// receive NCRs in wire format on its UDP socket; reconstruct the
+/// NCRs and delivery them to the "application" layer.
+TEST_F(NameChangeUDPListenerTest, basicReceiveTests) {
+    // Verify we can enter listening mode.
+    ASSERT_FALSE(listener_->amListening());
+    ASSERT_NO_THROW(listener_->startListening(io_service_));
+    ASSERT_TRUE(listener_->amListening());
+    ASSERT_TRUE(listener_->isIoPending());
+
+    // Iterate over a series of requests, sending and receiving one
+    /// at time.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+    for (int i = 0; i < num_msgs; i++) {
+        // We are not verifying ability to send, so if we can't test is over.
+        ASSERT_NO_THROW(sendNcr(valid_msgs[i]));
+
+        // Execute no more then one event, which should be receive complete.
+        EXPECT_NO_THROW(io_service_.run_one());
+
+        // Verify the "application" status value for a successful complete.
+        EXPECT_EQ(NameChangeListener::SUCCESS, result_);
+
+        // Verify the received request matches the sent request.
+        EXPECT_TRUE(checkSendVsReceived(sent_ncr_, received_ncr_));
+    }
+
+    // Verify we can gracefully stop listening.
+    EXPECT_NO_THROW(listener_->stopListening());
+    EXPECT_FALSE(listener_->amListening());
+
+    // Verify that IO pending is false, after cancel event occurs.
+    EXPECT_NO_THROW(io_service_.run_one());
+    EXPECT_FALSE(listener_->isIoPending());
+}
+
+/// @brief A NOP derivation for constructor test purposes.
+class SimpleSendHandler : public NameChangeSender::RequestSendHandler {
+public:
+    SimpleSendHandler() : pass_count_(0), error_count_(0) {
+    }
+
+    virtual void operator ()(const NameChangeSender::Result result,
+                             NameChangeRequestPtr&) {
+        if (result == NameChangeSender::SUCCESS) {
+            ++pass_count_;
+        } else {
+            ++error_count_;
+        }
+    }
+
+    int pass_count_;
+    int error_count_;
+};
+
+/// @brief Text fixture for testing NameChangeUDPListener
+class NameChangeUDPSenderBasicTest : public virtual ::testing::Test {
+public:
+    NameChangeUDPSenderBasicTest() {
+        // Disable multi-threading
+        MultiThreadingMgr::instance().setMode(false);
+    }
+
+    ~NameChangeUDPSenderBasicTest() {
+        // Disable multi-threading
+        MultiThreadingMgr::instance().setMode(false);
+    }
+};
+
+/// @brief Tests the NameChangeUDPSender constructors.
+/// This test verifies that:
+/// 1. Constructing with a max queue size of 0 is not allowed
+/// 2. Given valid parameters, the sender constructor works
+/// 3. Default construction provides default max queue size
+/// 4. Construction with a custom max queue size works
+TEST_F(NameChangeUDPSenderBasicTest, constructionTests) {
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    uint32_t port = SENDER_PORT;
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Verify that constructing with an queue size of zero is not allowed.
+    EXPECT_THROW(NameChangeUDPSender(ip_address, port,
+        ip_address, port, FMT_JSON, ncr_handler, 0), NcrSenderError);
+
+    NameChangeSenderPtr sender;
+    // Verify that valid constructor works.
+    EXPECT_NO_THROW(sender.reset(
+                    new NameChangeUDPSender(ip_address, port, ip_address, port,
+                                            FMT_JSON, ncr_handler)));
+
+    // Verify that send queue default max is correct.
+    size_t expected = NameChangeSender::MAX_QUEUE_DEFAULT;
+    EXPECT_EQ(expected, sender->getQueueMaxSize());
+
+    // Verify that constructor with a valid custom queue size works.
+    EXPECT_NO_THROW(sender.reset(
+                    new NameChangeUDPSender(ip_address, port, ip_address, port,
+                                            FMT_JSON, ncr_handler, 100)));
+
+    EXPECT_EQ(100, sender->getQueueMaxSize());
+}
+
+/// @brief Tests the NameChangeUDPSender constructors.
+/// This test verifies that:
+/// 1. Constructing with a max queue size of 0 is not allowed
+/// 2. Given valid parameters, the sender constructor works
+/// 3. Default construction provides default max queue size
+/// 4. Construction with a custom max queue size works
+TEST_F(NameChangeUDPSenderBasicTest, constructionTestsMultiThreading) {
+    // Enable multi-threading
+    MultiThreadingMgr::instance().setMode(true);
+
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    uint32_t port = SENDER_PORT;
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Verify that constructing with an queue size of zero is not allowed.
+    EXPECT_THROW(NameChangeUDPSender(ip_address, port,
+        ip_address, port, FMT_JSON, ncr_handler, 0), NcrSenderError);
+
+    NameChangeSenderPtr sender;
+    // Verify that valid constructor works.
+    EXPECT_NO_THROW(sender.reset(
+                    new NameChangeUDPSender(ip_address, port, ip_address, port,
+                                            FMT_JSON, ncr_handler)));
+
+    // Verify that send queue default max is correct.
+    size_t expected = NameChangeSender::MAX_QUEUE_DEFAULT;
+    EXPECT_EQ(expected, sender->getQueueMaxSize());
+
+    // Verify that constructor with a valid custom queue size works.
+    EXPECT_NO_THROW(sender.reset(
+                    new NameChangeUDPSender(ip_address, port, ip_address, port,
+                                            FMT_JSON, ncr_handler, 100)));
+
+    EXPECT_EQ(100, sender->getQueueMaxSize());
+}
+
+/// @brief Tests NameChangeUDPSender basic send functionality
+TEST_F(NameChangeUDPSenderBasicTest, basicSendTests) {
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Tests are based on a list of messages, get the count now.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Create the sender, setting the queue max equal to the number of
+    // messages we will have in the list.
+    NameChangeUDPSender sender(ip_address, SENDER_PORT, ip_address,
+                               LISTENER_PORT, FMT_JSON, ncr_handler,
+                               num_msgs, true);
+
+    // Verify that we can start sending.
+    EXPECT_NO_THROW(sender.startSending(io_service));
+    EXPECT_TRUE(sender.amSending());
+
+    // Verify that attempting to send when we already are is an error.
+    EXPECT_THROW(sender.startSending(io_service), NcrSenderError);
+
+    // Verify that we can stop sending.
+    EXPECT_NO_THROW(sender.stopSending());
+    EXPECT_FALSE(sender.amSending());
+
+    // Verify that attempting to stop sending when we are not is ok.
+    EXPECT_NO_THROW(sender.stopSending());
+
+    // Verify that we can re-enter sending after stopping.
+    EXPECT_NO_THROW(sender.startSending(io_service));
+    EXPECT_TRUE(sender.amSending());
+
+    // Fetch the sender's select-fd.
+    int select_fd = sender.getSelectFd();
+
+    // Verify select_fd is valid and currently shows no ready to read.
+    ASSERT_NE(util::WatchSocket::SOCKET_NOT_VALID, select_fd);
+
+    // Make sure select_fd does evaluates to not ready via select and
+    // that ioReady() method agrees.
+    ASSERT_EQ(0, selectCheck(select_fd));
+    ASSERT_FALSE(sender.ioReady());
+
+    // Iterate over a series of messages, sending each one. Since we
+    // do not invoke IOService::run, then the messages should accumulate
+    // in the queue.
+    NameChangeRequestPtr ncr;
+    NameChangeRequestPtr ncr2;
+    for (int i = 0; i < num_msgs; i++) {
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        EXPECT_NO_THROW(sender.sendRequest(ncr));
+        // Verify that the queue count increments in step with each send.
+        EXPECT_EQ(i+1, sender.getQueueSize());
+
+        // Verify that peekAt(i) returns the NCR we just added.
+        ASSERT_NO_THROW(ncr2 = sender.peekAt(i));
+        ASSERT_TRUE(ncr2);
+        EXPECT_TRUE(*ncr == *ncr2);
+    }
+
+    // Verify that attempting to peek beyond the end of the queue, throws.
+    ASSERT_THROW(sender.peekAt(sender.getQueueSize()+1), NcrSenderError);
+
+    // Verify that attempting to send an additional message results in a
+    // queue full exception.
+    EXPECT_THROW(sender.sendRequest(ncr), NcrSenderQueueFull);
+
+    // Loop for the number of valid messages. So long as there is at least
+    // on NCR in the queue, select-fd indicate ready to read. Invoke
+    // IOService::run_one. This should complete the send of exactly one
+    // message and the queue count should decrement accordingly.
+    for (int i = num_msgs; i > 0; i--) {
+        // Make sure select_fd does evaluates to ready via select and
+        // that ioReady() method agrees.
+        ASSERT_TRUE(selectCheck(select_fd) > 0);
+        ASSERT_TRUE(sender.ioReady());
+
+        // Execute at one ready handler.
+        ASSERT_NO_THROW(sender.runReadyIO());
+
+        // Verify that the queue count decrements in step with each run.
+        EXPECT_EQ(i-1, sender.getQueueSize());
+    }
+
+    // Make sure select_fd does evaluates to not ready via select and
+    // that ioReady() method agrees.
+    ASSERT_EQ(0, selectCheck(select_fd));
+    ASSERT_FALSE(sender.ioReady());
+
+    // Verify that the queue is empty.
+    EXPECT_EQ(0, sender.getQueueSize());
+
+    // Verify that we can add back to the queue
+    EXPECT_NO_THROW(sender.sendRequest(ncr));
+    EXPECT_EQ(1, sender.getQueueSize());
+
+    // Verify that we can remove the current entry at the front of the queue.
+    EXPECT_NO_THROW(sender.skipNext());
+    EXPECT_EQ(0, sender.getQueueSize());
+
+    // Verify that flushing the queue is not allowed in sending state.
+    EXPECT_THROW(sender.clearSendQueue(), NcrSenderError);
+
+    // Put num_msgs messages on the queue.
+    for (int i = 0; i < num_msgs; i++) {
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        EXPECT_NO_THROW(sender.sendRequest(ncr));
+    }
+
+    // Make sure we have number of messages expected.
+    EXPECT_EQ(num_msgs, sender.getQueueSize());
+
+    // Verify that we can gracefully stop sending.
+    EXPECT_NO_THROW(sender.stopSending());
+    EXPECT_FALSE(sender.amSending());
+
+    // Verify that the queue is preserved after leaving sending state.
+    EXPECT_EQ(num_msgs - 1, sender.getQueueSize());
+
+    // Verify that flushing the queue works when not sending.
+    EXPECT_NO_THROW(sender.clearSendQueue());
+    EXPECT_EQ(0, sender.getQueueSize());
+}
+
+/// @brief Tests NameChangeUDPSender basic send functionality
+TEST_F(NameChangeUDPSenderBasicTest, basicSendTestsMultiThreading) {
+    // Enable multi-threading
+    MultiThreadingMgr::instance().setMode(true);
+
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Tests are based on a list of messages, get the count now.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Create the sender, setting the queue max equal to the number of
+    // messages we will have in the list.
+    NameChangeUDPSender sender(ip_address, SENDER_PORT, ip_address,
+                               LISTENER_PORT, FMT_JSON, ncr_handler,
+                               num_msgs, true);
+
+    // Verify that we can start sending.
+    EXPECT_NO_THROW(sender.startSending(io_service));
+    EXPECT_TRUE(sender.amSending());
+
+    // Verify that attempting to send when we already are is an error.
+    EXPECT_THROW(sender.startSending(io_service), NcrSenderError);
+
+    // Verify that we can stop sending.
+    EXPECT_NO_THROW(sender.stopSending());
+    EXPECT_FALSE(sender.amSending());
+
+    // Verify that attempting to stop sending when we are not is ok.
+    EXPECT_NO_THROW(sender.stopSending());
+
+    // Verify that we can re-enter sending after stopping.
+    EXPECT_NO_THROW(sender.startSending(io_service));
+    EXPECT_TRUE(sender.amSending());
+
+    // Fetch the sender's select-fd.
+    int select_fd = sender.getSelectFd();
+
+    // Verify select_fd is valid and currently shows no ready to read.
+    ASSERT_NE(util::WatchSocket::SOCKET_NOT_VALID, select_fd);
+
+    // Make sure select_fd does evaluates to not ready via select and
+    // that ioReady() method agrees.
+    ASSERT_EQ(0, selectCheck(select_fd));
+    ASSERT_FALSE(sender.ioReady());
+
+    // Iterate over a series of messages, sending each one. Since we
+    // do not invoke IOService::run, then the messages should accumulate
+    // in the queue.
+    NameChangeRequestPtr ncr;
+    NameChangeRequestPtr ncr2;
+    for (int i = 0; i < num_msgs; i++) {
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        EXPECT_NO_THROW(sender.sendRequest(ncr));
+        // Verify that the queue count increments in step with each send.
+        EXPECT_EQ(i+1, sender.getQueueSize());
+
+        // Verify that peekAt(i) returns the NCR we just added.
+        ASSERT_NO_THROW(ncr2 = sender.peekAt(i));
+        ASSERT_TRUE(ncr2);
+        EXPECT_TRUE(*ncr == *ncr2);
+    }
+
+    // Verify that attempting to peek beyond the end of the queue, throws.
+    ASSERT_THROW(sender.peekAt(sender.getQueueSize()+1), NcrSenderError);
+
+    // Verify that attempting to send an additional message results in a
+    // queue full exception.
+    EXPECT_THROW(sender.sendRequest(ncr), NcrSenderQueueFull);
+
+    // Loop for the number of valid messages. So long as there is at least
+    // on NCR in the queue, select-fd indicate ready to read. Invoke
+    // IOService::run_one. This should complete the send of exactly one
+    // message and the queue count should decrement accordingly.
+    for (int i = num_msgs; i > 0; i--) {
+        // Make sure select_fd does evaluates to ready via select and
+        // that ioReady() method agrees.
+        ASSERT_TRUE(selectCheck(select_fd) > 0);
+        ASSERT_TRUE(sender.ioReady());
+
+        // Execute at one ready handler.
+        ASSERT_NO_THROW(sender.runReadyIO());
+
+        // Verify that the queue count decrements in step with each run.
+        EXPECT_EQ(i-1, sender.getQueueSize());
+    }
+
+    // Make sure select_fd does evaluates to not ready via select and
+    // that ioReady() method agrees.
+    ASSERT_EQ(0, selectCheck(select_fd));
+    ASSERT_FALSE(sender.ioReady());
+
+    // Verify that the queue is empty.
+    EXPECT_EQ(0, sender.getQueueSize());
+
+    // Verify that we can add back to the queue
+    EXPECT_NO_THROW(sender.sendRequest(ncr));
+    EXPECT_EQ(1, sender.getQueueSize());
+
+    // Verify that we can remove the current entry at the front of the queue.
+    EXPECT_NO_THROW(sender.skipNext());
+    EXPECT_EQ(0, sender.getQueueSize());
+
+    // Verify that flushing the queue is not allowed in sending state.
+    EXPECT_THROW(sender.clearSendQueue(), NcrSenderError);
+
+    // Put num_msgs messages on the queue.
+    for (int i = 0; i < num_msgs; i++) {
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        EXPECT_NO_THROW(sender.sendRequest(ncr));
+    }
+
+    // Make sure we have number of messages expected.
+    EXPECT_EQ(num_msgs, sender.getQueueSize());
+
+    // Verify that we can gracefully stop sending.
+    EXPECT_NO_THROW(sender.stopSending());
+    EXPECT_FALSE(sender.amSending());
+
+    // Verify that the queue is preserved after leaving sending state.
+    EXPECT_EQ(num_msgs - 1, sender.getQueueSize());
+
+    // Verify that flushing the queue works when not sending.
+    EXPECT_NO_THROW(sender.clearSendQueue());
+    EXPECT_EQ(0, sender.getQueueSize());
+}
+
+/// @brief Tests that sending gets kick-started if the queue isn't empty
+/// when startSending is called.
+TEST_F(NameChangeUDPSenderBasicTest, autoStart) {
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Tests are based on a list of messages, get the count now.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Create the sender, setting the queue max equal to the number of
+    // messages we will have in the list.
+    NameChangeUDPSender sender(ip_address, SENDER_PORT, ip_address,
+                               LISTENER_PORT, FMT_JSON, ncr_handler,
+                               num_msgs, true);
+
+    // Verify that we can start sending.
+    EXPECT_NO_THROW(sender.startSending(io_service));
+    EXPECT_TRUE(sender.amSending());
+
+    // Queue up messages.
+    NameChangeRequestPtr ncr;
+    for (int i = 0; i < num_msgs; i++) {
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        EXPECT_NO_THROW(sender.sendRequest(ncr));
+    }
+    // Make sure queue count is what we expect.
+    EXPECT_EQ(num_msgs, sender.getQueueSize());
+
+    // Stop sending.
+    ASSERT_NO_THROW(sender.stopSending());
+    ASSERT_FALSE(sender.amSending());
+
+    // We should have completed the first message only.
+    EXPECT_EQ(--num_msgs, sender.getQueueSize());
+
+    // Restart sending.
+    EXPECT_NO_THROW(sender.startSending(io_service));
+
+    // We should be able to loop through remaining messages and send them.
+    for (int i = num_msgs; i > 0; i--) {
+        // ioReady() should evaluate to true.
+        ASSERT_TRUE(sender.ioReady());
+
+        // Execute at one ready handler.
+        ASSERT_NO_THROW(sender.runReadyIO());
+    }
+
+    // Verify that the queue is empty.
+    EXPECT_EQ(0, sender.getQueueSize());
+}
+
+/// @brief Tests that sending gets kick-started if the queue isn't empty
+/// when startSending is called.
+TEST_F(NameChangeUDPSenderBasicTest, autoStartMultiThreading) {
+    // Enable multi-threading
+    MultiThreadingMgr::instance().setMode(true);
+
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Tests are based on a list of messages, get the count now.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Create the sender, setting the queue max equal to the number of
+    // messages we will have in the list.
+    NameChangeUDPSender sender(ip_address, SENDER_PORT, ip_address,
+                               LISTENER_PORT, FMT_JSON, ncr_handler,
+                               num_msgs, true);
+
+    // Verify that we can start sending.
+    EXPECT_NO_THROW(sender.startSending(io_service));
+    EXPECT_TRUE(sender.amSending());
+
+    // Queue up messages.
+    NameChangeRequestPtr ncr;
+    for (int i = 0; i < num_msgs; i++) {
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        EXPECT_NO_THROW(sender.sendRequest(ncr));
+    }
+    // Make sure queue count is what we expect.
+    EXPECT_EQ(num_msgs, sender.getQueueSize());
+
+    // Stop sending.
+    ASSERT_NO_THROW(sender.stopSending());
+    ASSERT_FALSE(sender.amSending());
+
+    // We should have completed the first message only.
+    EXPECT_EQ(--num_msgs, sender.getQueueSize());
+
+    // Restart sending.
+    EXPECT_NO_THROW(sender.startSending(io_service));
+
+    // We should be able to loop through remaining messages and send them.
+    for (int i = num_msgs; i > 0; i--) {
+        // ioReady() should evaluate to true.
+        ASSERT_TRUE(sender.ioReady());
+
+        // Execute at one ready handler.
+        ASSERT_NO_THROW(sender.runReadyIO());
+    }
+
+    // Verify that the queue is empty.
+    EXPECT_EQ(0, sender.getQueueSize());
+}
+
+/// @brief Tests NameChangeUDPSender basic send  with INADDR_ANY and port 0.
+TEST_F(NameChangeUDPSenderBasicTest, anyAddressSend) {
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOAddress any_address("0.0.0.0");
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Tests are based on a list of messages, get the count now.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Create the sender, setting the queue max equal to the number of
+    // messages we will have in the list.
+    NameChangeUDPSender sender(any_address, 0, ip_address, LISTENER_PORT,
+                               FMT_JSON, ncr_handler, num_msgs);
+
+    // Enter send mode.
+    ASSERT_NO_THROW(sender.startSending(io_service));
+    EXPECT_TRUE(sender.amSending());
+
+    // Create and queue up a message.
+    NameChangeRequestPtr ncr;
+    ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[0]));
+    EXPECT_NO_THROW(sender.sendRequest(ncr));
+    EXPECT_EQ(1, sender.getQueueSize());
+
+    // Verify we have a ready IO, then execute at one ready handler.
+    ASSERT_TRUE(sender.ioReady());
+    ASSERT_NO_THROW(sender.runReadyIO());
+
+    // Verify that sender shows no IO ready.
+    // and that the queue is empty.
+    ASSERT_FALSE(sender.ioReady());
+    EXPECT_EQ(0, sender.getQueueSize());
+}
+
+/// @brief Tests NameChangeUDPSender basic send  with INADDR_ANY and port 0.
+TEST_F(NameChangeUDPSenderBasicTest, anyAddressSendMultiThreading) {
+    // Enable multi-threading
+    MultiThreadingMgr::instance().setMode(true);
+
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOAddress any_address("0.0.0.0");
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Tests are based on a list of messages, get the count now.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Create the sender, setting the queue max equal to the number of
+    // messages we will have in the list.
+    NameChangeUDPSender sender(any_address, 0, ip_address, LISTENER_PORT,
+                               FMT_JSON, ncr_handler, num_msgs);
+
+    // Enter send mode.
+    ASSERT_NO_THROW(sender.startSending(io_service));
+    EXPECT_TRUE(sender.amSending());
+
+    // Create and queue up a message.
+    NameChangeRequestPtr ncr;
+    ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[0]));
+    EXPECT_NO_THROW(sender.sendRequest(ncr));
+    EXPECT_EQ(1, sender.getQueueSize());
+
+    // Verify we have a ready IO, then execute at one ready handler.
+    ASSERT_TRUE(sender.ioReady());
+    ASSERT_NO_THROW(sender.runReadyIO());
+
+    // Verify that sender shows no IO ready.
+    // and that the queue is empty.
+    ASSERT_FALSE(sender.ioReady());
+    EXPECT_EQ(0, sender.getQueueSize());
+}
+
+/// @brief Test the NameChangeSender::assumeQueue method.
+TEST_F(NameChangeUDPSenderBasicTest, assumeQueue) {
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    uint32_t port = SENDER_PORT;
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+    NameChangeRequestPtr ncr;
+
+    // Tests are based on a list of messages, get the count now.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Create two senders with queue max equal to the number of
+    // messages we will have in the list.
+    NameChangeUDPSender sender1(ip_address, port, ip_address, port,
+                               FMT_JSON, ncr_handler, num_msgs);
+
+    NameChangeUDPSender sender2(ip_address, port+1, ip_address, port,
+                                FMT_JSON, ncr_handler, num_msgs);
+
+    // Place sender1 into send mode and queue up messages.
+    ASSERT_NO_THROW(sender1.startSending(io_service));
+    for (int i = 0; i < num_msgs; i++) {
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        ASSERT_NO_THROW(sender1.sendRequest(ncr));
+    }
+
+    // Make sure sender1's queue count is as expected.
+    ASSERT_EQ(num_msgs, sender1.getQueueSize());
+
+    // Verify sender1 is sending, sender2 is not.
+    ASSERT_TRUE(sender1.amSending());
+    ASSERT_FALSE(sender2.amSending());
+
+    // Transfer from sender1 to sender2 should fail because
+    // sender1 is in send mode.
+    ASSERT_THROW(sender2.assumeQueue(sender1), NcrSenderError);
+
+    // Take sender1 out of send mode.
+    ASSERT_NO_THROW(sender1.stopSending());
+    ASSERT_FALSE(sender1.amSending());
+    // Stopping should have completed the first message.
+    --num_msgs;
+    EXPECT_EQ(num_msgs, sender1.getQueueSize());
+
+    // Transfer should succeed. Verify sender1 has none,
+    // and sender2 has num_msgs queued.
+    EXPECT_NO_THROW(sender2.assumeQueue(sender1));
+    EXPECT_EQ(0, sender1.getQueueSize());
+    EXPECT_EQ(num_msgs, sender2.getQueueSize());
+
+    // Reduce sender1's max queue size.
+    ASSERT_NO_THROW(sender1.setQueueMaxSize(num_msgs - 1));
+
+    // Transfer should fail as sender1's queue is not large enough.
+    ASSERT_THROW(sender1.assumeQueue(sender2), NcrSenderError);
+
+    // Place sender1 into send mode and queue up a message.
+    ASSERT_NO_THROW(sender1.startSending(io_service));
+    ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[0]));
+    ASSERT_NO_THROW(sender1.sendRequest(ncr));
+
+    // Take sender1 out of send mode.
+    ASSERT_NO_THROW(sender1.stopSending());
+
+    // Try to transfer from sender1 to sender2. This should fail
+    // as sender2's queue is not empty.
+    ASSERT_THROW(sender2.assumeQueue(sender1), NcrSenderError);
+}
+
+/// @brief Test the NameChangeSender::assumeQueue method.
+TEST_F(NameChangeUDPSenderBasicTest, assumeQueueMultiThreading) {
+    // Enable multi-threading
+    MultiThreadingMgr::instance().setMode(true);
+
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    uint32_t port = SENDER_PORT;
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+    NameChangeRequestPtr ncr;
+
+    // Tests are based on a list of messages, get the count now.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Create two senders with queue max equal to the number of
+    // messages we will have in the list.
+    NameChangeUDPSender sender1(ip_address, port, ip_address, port,
+                               FMT_JSON, ncr_handler, num_msgs);
+
+    NameChangeUDPSender sender2(ip_address, port+1, ip_address, port,
+                                FMT_JSON, ncr_handler, num_msgs);
+
+    // Place sender1 into send mode and queue up messages.
+    ASSERT_NO_THROW(sender1.startSending(io_service));
+    for (int i = 0; i < num_msgs; i++) {
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        ASSERT_NO_THROW(sender1.sendRequest(ncr));
+    }
+
+    // Make sure sender1's queue count is as expected.
+    ASSERT_EQ(num_msgs, sender1.getQueueSize());
+
+    // Verify sender1 is sending, sender2 is not.
+    ASSERT_TRUE(sender1.amSending());
+    ASSERT_FALSE(sender2.amSending());
+
+    // Transfer from sender1 to sender2 should fail because
+    // sender1 is in send mode.
+    ASSERT_THROW(sender2.assumeQueue(sender1), NcrSenderError);
+
+    // Take sender1 out of send mode.
+    ASSERT_NO_THROW(sender1.stopSending());
+    ASSERT_FALSE(sender1.amSending());
+    // Stopping should have completed the first message.
+    --num_msgs;
+    EXPECT_EQ(num_msgs, sender1.getQueueSize());
+
+    // Transfer should succeed. Verify sender1 has none,
+    // and sender2 has num_msgs queued.
+    EXPECT_NO_THROW(sender2.assumeQueue(sender1));
+    EXPECT_EQ(0, sender1.getQueueSize());
+    EXPECT_EQ(num_msgs, sender2.getQueueSize());
+
+    // Reduce sender1's max queue size.
+    ASSERT_NO_THROW(sender1.setQueueMaxSize(num_msgs - 1));
+
+    // Transfer should fail as sender1's queue is not large enough.
+    ASSERT_THROW(sender1.assumeQueue(sender2), NcrSenderError);
+
+    // Place sender1 into send mode and queue up a message.
+    ASSERT_NO_THROW(sender1.startSending(io_service));
+    ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[0]));
+    ASSERT_NO_THROW(sender1.sendRequest(ncr));
+
+    // Take sender1 out of send mode.
+    ASSERT_NO_THROW(sender1.stopSending());
+
+    // Try to transfer from sender1 to sender2. This should fail
+    // as sender2's queue is not empty.
+    ASSERT_THROW(sender2.assumeQueue(sender1), NcrSenderError);
+}
+
+/// @brief Text fixture that allows testing a listener and sender together
+/// It derives from both the receive and send handler classes and contains
+/// and instance of UDP listener and UDP sender.
+class NameChangeUDPTest : public virtual ::testing::Test,
+                          NameChangeListener::RequestReceiveHandler,
+                          NameChangeSender::RequestSendHandler {
+public:
+    isc::asiolink::IOService io_service_;
+    NameChangeListener::Result recv_result_;
+    NameChangeSender::Result send_result_;
+    NameChangeListenerPtr listener_;
+    NameChangeSenderPtr   sender_;
+    isc::asiolink::IntervalTimer test_timer_;
+
+    std::vector<NameChangeRequestPtr> sent_ncrs_;
+    std::vector<NameChangeRequestPtr> received_ncrs_;
+
+    NameChangeUDPTest()
+        : io_service_(), recv_result_(NameChangeListener::SUCCESS),
+          send_result_(NameChangeSender::SUCCESS), test_timer_(io_service_) {
+        isc::asiolink::IOAddress addr(TEST_ADDRESS);
+        // Create our listener instance. Note that reuse_address is true.
+        listener_.reset(
+            new NameChangeUDPListener(addr, LISTENER_PORT, FMT_JSON,
+                                      *this, true));
+
+        // Create our sender instance. Note that reuse_address is true.
+         sender_.reset(
+             new NameChangeUDPSender(addr, SENDER_PORT, addr, LISTENER_PORT,
+                                     FMT_JSON, *this, 100, true));
+
+        // Set the test timeout to break any running tasks if they hang.
+        test_timer_.setup(std::bind(&NameChangeUDPTest::testTimeoutHandler,
+                                    this),
+                          TEST_TIMEOUT);
+        // Disable multi-threading
+        MultiThreadingMgr::instance().setMode(false);
+    }
+
+    ~NameChangeUDPTest() {
+        // Disable multi-threading
+        MultiThreadingMgr::instance().setMode(false);
+    }
+
+    void reset_results() {
+        sent_ncrs_.clear();
+        received_ncrs_.clear();
+    }
+
+    /// @brief Implements the receive completion handler.
+    virtual void operator ()(const NameChangeListener::Result result,
+                             NameChangeRequestPtr& ncr) {
+        // save the result and the NCR received.
+        recv_result_ = result;
+        received_ncrs_.push_back(ncr);
+    }
+
+    /// @brief Implements the send completion handler.
+    virtual void operator ()(const NameChangeSender::Result result,
+                             NameChangeRequestPtr& ncr) {
+        // save the result and the NCR sent.
+        send_result_ = result;
+        sent_ncrs_.push_back(ncr);
+    }
+
+    /// @brief Handler invoked when test timeout is hit
+    ///
+    /// This callback stops all running (hanging) tasks on IO service.
+    void testTimeoutHandler() {
+        io_service_.stop();
+        FAIL() << "Test timeout hit.";
+    }
+
+    /// @brief checks the received NCR content, ignoring the order if necessary.
+    ///
+    /// The UDP does not provide any guarantees regarding order. While in most cases
+    /// the NCRs are received in the order they're sent, that's not guaranteed. As such,
+    /// the test does the normal ordered check, which will pass in most cases. However,
+    /// we have documented Jenkins history that it sometimes fail. In those cases, we
+    /// need to go through a full check assuming the packets were received not in order.
+    /// If that fails, the test will print detailed information about the failure.
+    ///
+    /// This function returns a status, but it's not really necessary to check it as
+    /// it calls gtest macros to indicate failures.
+    ///
+    /// @param num_msgs number of received and sent messages
+    /// @param sent vector of sent NCRs
+    /// @param rcvd vector of received NCRs
+    /// @return true if all packets were received, false otherwise
+    bool checkUnordered(size_t num_msgs, const std::vector<NameChangeRequestPtr>& sent,
+                      const std::vector<NameChangeRequestPtr>& rcvd) {
+        // Verify that what we sent matches what we received.
+        // WRONG ASSUMPTION HERE: UDP does not guarantee ordered delivery.
+        bool ok = true;
+        for (int i = 0; i < num_msgs; i++) {
+            if (!checkSendVsReceived(sent[i], rcvd[i])) {
+                // Ok, the data was not received in order.
+                ok = false;
+                break;
+            }
+        }
+        if (!ok) {
+            std::cout << "UDP data received not in order! Checking un ordered delivery"
+                      << std::endl;
+            // We need to double iterate through the messages to check every one
+            // against one another.
+            for (int i = 0; i < num_msgs; i++) {
+                ok = false;
+                for (int j = 0; j < num_msgs; j++) {
+                    if (checkSendVsReceived(sent[i], rcvd[j])) {
+                        std::cout << "Found UDP packet " << i << ", received as " << j << "th"
+                                  << std::endl;
+                        ok = true;
+                    }
+                }
+                EXPECT_TRUE(ok) << "failed to find UDP packet " << i << " among total of "
+                                << num_msgs << " messages received";
+            }
+        }
+        return (ok);
+    }
+};
+
+/// @brief Uses a sender and listener to test UDP-based NCR delivery
+/// Conducts a "round-trip" test using a sender to transmit a set of valid
+/// NCRs to a listener.  The test verifies that what was sent matches what
+/// was received both in quantity and in content.
+TEST_F(NameChangeUDPTest, roundTripTest) {
+    // Place the listener into listening state.
+    ASSERT_NO_THROW(listener_->startListening(io_service_));
+    EXPECT_TRUE(listener_->amListening());
+
+    // Get the number of messages in the list of test messages.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Place the sender into sending state.
+    ASSERT_NO_THROW(sender_->startSending(io_service_));
+    EXPECT_TRUE(sender_->amSending());
+
+    for (int i = 0; i < num_msgs; i++) {
+        NameChangeRequestPtr ncr;
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        sender_->sendRequest(ncr);
+        EXPECT_EQ(i+1, sender_->getQueueSize());
+    }
+
+    // Execute callbacks until we have sent and received all of messages.
+    while (sender_->getQueueSize() > 0 || (received_ncrs_.size() < num_msgs)) {
+        EXPECT_NO_THROW(io_service_.run_one());
+    }
+
+    // Send queue should be empty.
+    EXPECT_EQ(0, sender_->getQueueSize());
+
+    // We should have the same number of sends and receives as we do messages.
+    ASSERT_EQ(num_msgs, sent_ncrs_.size());
+    ASSERT_EQ(num_msgs, received_ncrs_.size());
+
+    // Check if the payload was received, ignoring the order if necessary.
+    checkUnordered(num_msgs, sent_ncrs_, received_ncrs_);
+
+    // Verify that we can gracefully stop listening.
+    EXPECT_NO_THROW(listener_->stopListening());
+    EXPECT_FALSE(listener_->amListening());
+
+    // Verify that IO pending is false, after cancel event occurs.
+    EXPECT_NO_THROW(io_service_.run_one());
+    EXPECT_FALSE(listener_->isIoPending());
+
+    // Verify that we can gracefully stop sending.
+    EXPECT_NO_THROW(sender_->stopSending());
+    EXPECT_FALSE(sender_->amSending());
+}
+
+/// @brief Uses a sender and listener to test UDP-based NCR delivery
+/// Conducts a "round-trip" test using a sender to transmit a set of valid
+/// NCRs to a listener.  The test verifies that what was sent matches what
+/// was received both in quantity and in content.
+TEST_F(NameChangeUDPTest, roundTripTestMultiThreading) {
+    // Enable multi-threading
+    MultiThreadingMgr::instance().setMode(true);
+
+    // Place the listener into listening state.
+    ASSERT_NO_THROW(listener_->startListening(io_service_));
+    EXPECT_TRUE(listener_->amListening());
+
+    // Get the number of messages in the list of test messages.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+
+    // Place the sender into sending state.
+    ASSERT_NO_THROW(sender_->startSending(io_service_));
+    EXPECT_TRUE(sender_->amSending());
+
+    for (int i = 0; i < num_msgs; i++) {
+        NameChangeRequestPtr ncr;
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        sender_->sendRequest(ncr);
+        EXPECT_EQ(i+1, sender_->getQueueSize());
+    }
+
+    // Execute callbacks until we have sent and received all of messages.
+    while (sender_->getQueueSize() > 0 || (received_ncrs_.size() < num_msgs)) {
+        EXPECT_NO_THROW(io_service_.run_one());
+    }
+
+    // Send queue should be empty.
+    EXPECT_EQ(0, sender_->getQueueSize());
+
+    // We should have the same number of sends and receives as we do messages.
+    ASSERT_EQ(num_msgs, sent_ncrs_.size());
+    ASSERT_EQ(num_msgs, received_ncrs_.size());
+
+    // Verify that what we sent matches what we received. Ignore the order
+    // if necessary.
+    checkUnordered(num_msgs, sent_ncrs_, received_ncrs_);
+
+    // Verify that we can gracefully stop listening.
+    EXPECT_NO_THROW(listener_->stopListening());
+    EXPECT_FALSE(listener_->amListening());
+
+    // Verify that IO pending is false, after cancel event occurs.
+    EXPECT_NO_THROW(io_service_.run_one());
+    EXPECT_FALSE(listener_->isIoPending());
+
+    // Verify that we can gracefully stop sending.
+    EXPECT_NO_THROW(sender_->stopSending());
+    EXPECT_FALSE(sender_->amSending());
+}
+
+// Tests error handling of a failure to mark the watch socket ready, when
+// sendRequest() is called.
+TEST_F(NameChangeUDPSenderBasicTest, watchClosedBeforeSendRequest) {
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Create the sender and put into send mode.
+    NameChangeUDPSender sender(ip_address, 0, ip_address, LISTENER_PORT,
+                               FMT_JSON, ncr_handler, 100, true);
+    ASSERT_NO_THROW(sender.startSending(io_service));
+    ASSERT_TRUE(sender.amSending());
+
+    // Create an NCR.
+    NameChangeRequestPtr ncr;
+    ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[0]));
+
+    // Tamper with the watch socket by closing the select-fd.
+    close(sender.getSelectFd());
+
+    // Send should fail as we interfered by closing the select-fd.
+    ASSERT_THROW(sender.sendRequest(ncr), util::WatchSocketError);
+
+    // Verify we didn't invoke the handler.
+    EXPECT_EQ(0, ncr_handler.pass_count_);
+    EXPECT_EQ(0, ncr_handler.error_count_);
+
+    // Request remains in the queue. Technically it was sent but its
+    // completion handler won't get called.
+    EXPECT_EQ(1, sender.getQueueSize());
+}
+
+// Tests error handling of a failure to mark the watch socket ready, when
+// sendRequest() is called.
+TEST_F(NameChangeUDPSenderBasicTest, watchClosedBeforeSendRequestMultiThreading) {
+    // Enable multi-threading
+    MultiThreadingMgr::instance().setMode(true);
+
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Create the sender and put into send mode.
+    NameChangeUDPSender sender(ip_address, 0, ip_address, LISTENER_PORT,
+                               FMT_JSON, ncr_handler, 100, true);
+    ASSERT_NO_THROW(sender.startSending(io_service));
+    ASSERT_TRUE(sender.amSending());
+
+    // Create an NCR.
+    NameChangeRequestPtr ncr;
+    ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[0]));
+
+    // Tamper with the watch socket by closing the select-fd.
+    close(sender.getSelectFd());
+
+    // Send should fail as we interfered by closing the select-fd.
+    ASSERT_THROW(sender.sendRequest(ncr), util::WatchSocketError);
+
+    // Verify we didn't invoke the handler.
+    EXPECT_EQ(0, ncr_handler.pass_count_);
+    EXPECT_EQ(0, ncr_handler.error_count_);
+
+    // Request remains in the queue. Technically it was sent but its
+    // completion handler won't get called.
+    EXPECT_EQ(1, sender.getQueueSize());
+}
+
+// Tests error handling of a failure to mark the watch socket ready, when
+// sendNext() is called during completion handling.
+TEST_F(NameChangeUDPSenderBasicTest, watchClosedAfterSendRequest) {
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Create the sender and put into send mode.
+    NameChangeUDPSender sender(ip_address, 0, ip_address, LISTENER_PORT,
+                               FMT_JSON, ncr_handler, 100, true);
+    ASSERT_NO_THROW(sender.startSending(io_service));
+    ASSERT_TRUE(sender.amSending());
+
+    // Build and queue up 2 messages.  No handlers will get called yet.
+    for (int i = 0; i < 2; i++) {
+        NameChangeRequestPtr ncr;
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        sender.sendRequest(ncr);
+        EXPECT_EQ(i+1, sender.getQueueSize());
+    }
+
+    // Tamper with the watch socket by closing the select-fd.
+    close (sender.getSelectFd());
+
+    // Run one handler. This should execute the send completion handler
+    // after sending the first message.  Doing completion handling, we will
+    // attempt to queue the second message which should fail.
+    ASSERT_NO_THROW(sender.runReadyIO());
+
+    // Verify handler got called twice. First request should have be sent
+    // without error, second call should have failed to send due to watch
+    // socket markReady failure.
+    EXPECT_EQ(1, ncr_handler.pass_count_);
+    EXPECT_EQ(1, ncr_handler.error_count_);
+
+    // The second request should still be in the queue.
+    EXPECT_EQ(1, sender.getQueueSize());
+}
+
+// Tests error handling of a failure to mark the watch socket ready, when
+// sendNext() is called during completion handling.
+TEST_F(NameChangeUDPSenderBasicTest, watchClosedAfterSendRequestMultiThreading) {
+    // Enable multi-threading
+    MultiThreadingMgr::instance().setMode(true);
+
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Create the sender and put into send mode.
+    NameChangeUDPSender sender(ip_address, 0, ip_address, LISTENER_PORT,
+                               FMT_JSON, ncr_handler, 100, true);
+    ASSERT_NO_THROW(sender.startSending(io_service));
+    ASSERT_TRUE(sender.amSending());
+
+    // Build and queue up 2 messages.  No handlers will get called yet.
+    for (int i = 0; i < 2; i++) {
+        NameChangeRequestPtr ncr;
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        sender.sendRequest(ncr);
+        EXPECT_EQ(i+1, sender.getQueueSize());
+    }
+
+    // Tamper with the watch socket by closing the select-fd.
+    close (sender.getSelectFd());
+
+    // Run one handler. This should execute the send completion handler
+    // after sending the first message.  Doing completion handling, we will
+    // attempt to queue the second message which should fail.
+    ASSERT_NO_THROW(sender.runReadyIO());
+
+    // Verify handler got called twice. First request should have be sent
+    // without error, second call should have failed to send due to watch
+    // socket markReady failure.
+    EXPECT_EQ(1, ncr_handler.pass_count_);
+    EXPECT_EQ(1, ncr_handler.error_count_);
+
+    // The second request should still be in the queue.
+    EXPECT_EQ(1, sender.getQueueSize());
+}
+
+
+// Tests error handling of a failure to clear the watch socket during
+// completion handling.
+TEST_F(NameChangeUDPSenderBasicTest, watchSocketBadRead) {
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Create the sender and put into send mode.
+    NameChangeUDPSender sender(ip_address, 0, ip_address, LISTENER_PORT,
+                               FMT_JSON, ncr_handler, 100, true);
+    ASSERT_NO_THROW(sender.startSending(io_service));
+    ASSERT_TRUE(sender.amSending());
+
+    // Build and queue up 2 messages.  No handlers will get called yet.
+    for (int i = 0; i < 2; i++) {
+        NameChangeRequestPtr ncr;
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        sender.sendRequest(ncr);
+        EXPECT_EQ(i+1, sender.getQueueSize());
+    }
+
+    // Fetch the sender's select-fd.
+    int select_fd = sender.getSelectFd();
+
+    // Verify that select_fd appears ready.
+    ASSERT_TRUE(selectCheck(select_fd) > 0);
+
+    // Interfere by reading part of the marker from the select-fd.
+    uint32_t buf = 0;
+    ASSERT_EQ((read (select_fd, &buf, 1)), 1);
+    ASSERT_NE(util::WatchSocket::MARKER, buf);
+
+    // Run one handler. This should execute the send completion handler
+    // after sending the message.  Doing completion handling clearing the
+    // watch socket should fail, which will close the socket, but not
+    // result in a throw.
+    ASSERT_NO_THROW(sender.runReadyIO());
+
+    // Verify handler got called twice. First request should have be sent
+    // without error, second call should have failed to send due to watch
+    // socket markReady failure.
+    EXPECT_EQ(1, ncr_handler.pass_count_);
+    EXPECT_EQ(1, ncr_handler.error_count_);
+
+    // The second request should still be in the queue.
+    EXPECT_EQ(1, sender.getQueueSize());
+}
+
+// Tests error handling of a failure to clear the watch socket during
+// completion handling.
+TEST_F(NameChangeUDPSenderBasicTest, watchSocketBadReadMultiThreading) {
+    // Enable multi-threading
+    MultiThreadingMgr::instance().setMode(true);
+
+    isc::asiolink::IOAddress ip_address(TEST_ADDRESS);
+    isc::asiolink::IOService io_service;
+    SimpleSendHandler ncr_handler;
+
+    // Create the sender and put into send mode.
+    NameChangeUDPSender sender(ip_address, 0, ip_address, LISTENER_PORT,
+                               FMT_JSON, ncr_handler, 100, true);
+    ASSERT_NO_THROW(sender.startSending(io_service));
+    ASSERT_TRUE(sender.amSending());
+
+    // Build and queue up 2 messages.  No handlers will get called yet.
+    for (int i = 0; i < 2; i++) {
+        NameChangeRequestPtr ncr;
+        ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(valid_msgs[i]));
+        sender.sendRequest(ncr);
+        EXPECT_EQ(i+1, sender.getQueueSize());
+    }
+
+    // Fetch the sender's select-fd.
+    int select_fd = sender.getSelectFd();
+
+    // Verify that select_fd appears ready.
+    ASSERT_TRUE(selectCheck(select_fd) > 0);
+
+    // Interfere by reading part of the marker from the select-fd.
+    uint32_t buf = 0;
+    ASSERT_EQ((read (select_fd, &buf, 1)), 1);
+    ASSERT_NE(util::WatchSocket::MARKER, buf);
+
+    // Run one handler. This should execute the send completion handler
+    // after sending the message.  Doing completion handling clearing the
+    // watch socket should fail, which will close the socket, but not
+    // result in a throw.
+    ASSERT_NO_THROW(sender.runReadyIO());
+
+    // Verify handler got called twice. First request should have be sent
+    // without error, second call should have failed to send due to watch
+    // socket markReady failure.
+    EXPECT_EQ(1, ncr_handler.pass_count_);
+    EXPECT_EQ(1, ncr_handler.error_count_);
+
+    // The second request should still be in the queue.
+    EXPECT_EQ(1, sender.getQueueSize());
+}
+
+} // end of anonymous namespace
diff --git a/src/lib/dhcp_ddns/tests/ncr_unittests.cc b/src/lib/dhcp_ddns/tests/ncr_unittests.cc
new file mode 100644
index 0000000..6ac2d09
--- /dev/null
+++ b/src/lib/dhcp_ddns/tests/ncr_unittests.cc
@@ -0,0 +1,742 @@
+// Copyright (C) 2013-2021 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/.
+
+#include <config.h>
+
+#include <dhcp_ddns/ncr_io.h>
+#include <dhcp/duid.h>
+#include <dhcp/hwaddr.h>
+#include <util/time_utilities.h>
+
+#include <testutils/gtest_utils.h>
+#include <gtest/gtest.h>
+#include <algorithm>
+
+using namespace std;
+using namespace isc;
+using namespace isc::dhcp_ddns;
+using namespace isc::dhcp;
+
+namespace {
+
+/// @brief Defines a list of valid JSON NameChangeRequest renditions.
+/// They are used as input to test conversion from JSON.
+const char *valid_msgs[] =
+{
+    // Valid Add.
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Valid Remove.
+     "{"
+     " \"change-type\" : 1 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+     // Valid Add with IPv6 address
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"fe80::2acf:e9ff:fe12:e56f\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Missing use-conflict-resolution
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300 "
+     "}"
+};
+
+/// @brief Defines a list of invalid JSON NameChangeRequest renditions.
+/// They are used as input to test conversion from JSON.
+const char *invalid_msgs[] =
+{
+    // Invalid change type.
+     "{"
+     " \"change-type\" : 7 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Invalid forward change.
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : \"bogus\" , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Invalid reverse change.
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : 500 , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Forward and reverse change both false.
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : false , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Blank FQDN
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Malformed FQDN
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \".bad_name\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Bad IP address
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"xxxxxx\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300 "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Blank DHCID
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Odd number of digits in DHCID
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Text in DHCID
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"THIS IS BOGUS!!!\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Invalid lease expiration string
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"Wed Jun 26 13:46:46 EDT 2013\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Non-integer for lease length.
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : \"BOGUS\", "
+     " \"use-conflict-resolution\": true"
+     "}",
+    // Invalid use-conflict-resolution
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300, "
+     " \"use-conflict-resolution\": 777"
+     "}"
+};
+
+/// @brief Tests the NameChangeRequest constructors.
+/// This test verifies that:
+/// 1. Default constructor works.
+/// 2. "Full" constructor, when given valid parameter values, works.
+/// 3. "Full" constructor, given a blank FQDN fails
+/// 4. "Full" constructor, given an invalid IP Address FQDN fails
+/// 5. "Full" constructor, given a blank DHCID fails
+/// 6. "Full" constructor, given false for both forward and reverse fails
+TEST(NameChangeRequestTest, constructionTests) {
+    // Verify the default constructor works.
+    NameChangeRequestPtr ncr;
+    EXPECT_NO_THROW(ncr.reset(new NameChangeRequest()));
+    EXPECT_TRUE(ncr);
+
+    // Verify that full constructor works.
+    uint64_t expiry = isc::util::detail::gettimeWrapper();
+    D2Dhcid dhcid("010203040A7F8E3D");
+
+    EXPECT_NO_THROW(ncr.reset(new NameChangeRequest(
+                    CHG_ADD, true, true, "walah.walah.com",
+                    "192.168.1.101", dhcid, expiry, 1300)));
+    EXPECT_TRUE(ncr);
+    ncr.reset();
+
+    // Verify blank FQDN is detected.
+    EXPECT_THROW(NameChangeRequest(CHG_ADD, true, true, "",
+                 "192.168.1.101", dhcid, expiry, 1300), NcrMessageError);
+
+    // Verify that an invalid IP address is detected.
+    EXPECT_THROW(NameChangeRequest(CHG_ADD, true, true, "valid.fqdn",
+                 "xxx.168.1.101", dhcid, expiry, 1300), NcrMessageError);
+
+    // Verify that a blank DHCID is detected.
+    D2Dhcid blank_dhcid;
+    EXPECT_THROW(NameChangeRequest(CHG_ADD, true, true, "walah.walah.com",
+                 "192.168.1.101", blank_dhcid, expiry, 1300), NcrMessageError);
+
+    // Verify that one or both of direction flags must be true.
+    EXPECT_THROW(NameChangeRequest(CHG_ADD, false, false, "valid.fqdn",
+                "192.168.1.101", dhcid, expiry, 1300), NcrMessageError);
+
+}
+
+/// @brief Tests the basic workings of D2Dhcid to and from string conversions.
+/// It verifies that:
+/// 1. DHCID input strings must contain an even number of characters
+/// 2. DHCID input strings must contain only hexadecimal character digits
+/// 3. A valid DHCID string converts correctly.
+/// 4. Converting a D2Dhcid to a string works correctly.
+/// 5. Equality, inequality, and less-than-equal operators work.
+TEST(NameChangeRequestTest, dhcidTest) {
+    D2Dhcid dhcid;
+
+    // Odd number of digits should be rejected.
+    std::string test_str = "010203040A7F8E3";
+    EXPECT_THROW(dhcid.fromStr(test_str), NcrMessageError);
+
+    // Non digit content should be rejected.
+    test_str = "0102BOGUSA7F8E3D";
+    EXPECT_THROW(dhcid.fromStr(test_str), NcrMessageError);
+
+    // Verify that valid input converts into a proper byte array.
+    test_str = "010203040A7F8E3D";
+    ASSERT_NO_THROW(dhcid.fromStr(test_str));
+
+    // Create a test vector of expected byte contents.
+    const uint8_t bytes[] = { 0x1, 0x2, 0x3, 0x4, 0xA, 0x7F, 0x8E, 0x3D };
+    std::vector<uint8_t> expected_bytes(bytes, bytes + sizeof(bytes));
+
+    // Fetch the byte vector from the dhcid and verify if equals the expected
+    // content.
+    const std::vector<uint8_t>& converted_bytes = dhcid.getBytes();
+    EXPECT_EQ(expected_bytes.size(), converted_bytes.size());
+    EXPECT_TRUE (std::equal(expected_bytes.begin(),
+                            expected_bytes.begin()+expected_bytes.size(),
+                            converted_bytes.begin()));
+
+    // Convert the new dhcid back to string and verify it matches the original
+    // DHCID input string.
+    std::string next_str = dhcid.toStr();
+    EXPECT_EQ(test_str, next_str);
+
+    // Test equality, inequality, and less-than-equal operators
+    test_str="AABBCCDD";
+    EXPECT_NO_THROW(dhcid.fromStr(test_str));
+
+    D2Dhcid other_dhcid;
+    EXPECT_NO_THROW(other_dhcid.fromStr(test_str));
+
+    EXPECT_TRUE(dhcid == other_dhcid);
+    EXPECT_FALSE(dhcid != other_dhcid);
+
+    EXPECT_NO_THROW(other_dhcid.fromStr("BBCCDDEE"));
+    EXPECT_TRUE(dhcid < other_dhcid);
+
+}
+
+/// @brief Test fixture class for testing DHCID creation.
+class DhcidTest : public ::testing::Test {
+public:
+    /// @brief Constructor
+    DhcidTest() {
+        const uint8_t fqdn_data[] = {
+            6, 109, 121, 104, 111, 115, 116,     // myhost.
+            7, 101, 120, 97, 109, 112, 108, 101, // example.
+            3, 99, 111, 109, 0                   // com.
+        };
+        wire_fqdn_.assign(fqdn_data, fqdn_data + sizeof(fqdn_data));
+    }
+
+    /// @brief Destructor
+    virtual ~DhcidTest() {
+    }
+
+    std::vector<uint8_t> wire_fqdn_;
+};
+
+/// Tests that DHCID is correctly created from a DUID and FQDN. The final format
+/// of the DHCID is as follows:
+/// <identifier-type> <digest-type-code> <digest>
+/// where:
+/// - identifier-type (2 octets) is 0x0002.
+/// - digest-type-code (1 octet) indicates SHA-256 hashing and is equal 0x1.
+/// - digest = SHA-256(<DUID> <FQDN>)
+/// Note: FQDN is given in the on-wire canonical format.
+TEST_F(DhcidTest, fromDUID) {
+    D2Dhcid dhcid;
+
+    // Create DUID.
+    uint8_t duid_data[] = { 0, 1, 2, 3, 4, 5, 6 };
+    DUID duid(duid_data, sizeof(duid_data));
+
+    // Create DHCID.
+    ASSERT_NO_THROW(dhcid.fromDUID(duid, wire_fqdn_));
+
+    // The reference DHCID (represented as string of hexadecimal digits)
+    // has been calculated using one of the online calculators.
+    std::string dhcid_ref = "0002012191B7B21AF97E0E656DF887C5E2D"
+        "EF30E7758A207EDF4CCB2DE8CA37066021C";
+
+    // Make sure that the DHCID is valid.
+    EXPECT_EQ(dhcid_ref, dhcid.toStr());
+}
+
+// Test that DHCID is correctly created when the DUID has minimal length (1).
+TEST_F(DhcidTest, fromMinDUID) {
+    D2Dhcid dhcid;
+
+    // Create DUID.
+    uint8_t duid_data[] = { 1 };
+    DUID duid(duid_data, sizeof(duid_data));
+
+    // Create DHCID.
+    ASSERT_NO_THROW(dhcid.fromDUID(duid, wire_fqdn_));
+
+    // The reference DHCID (represented as string of hexadecimal digits)
+    // has been calculated using one of the online calculators.
+    std::string dhcid_ref = "000201F89004F73E60CAEDFF514E11CB91D"
+        "1F45C8F0A55D4BC4C688484A819F8EA4074";
+
+    // Make sure that the DHCID is valid.
+    EXPECT_EQ(dhcid_ref, dhcid.toStr());
+}
+
+// Test that DHCID is correctly created when the DUID has maximal length (128).
+TEST_F(DhcidTest, fromMaxDUID) {
+    D2Dhcid dhcid;
+
+    // Create DUID.
+    std::vector<uint8_t> duid_data(128, 1);
+    DUID duid(&duid_data[0], duid_data.size());
+
+    // Create DHCID.
+    ASSERT_NO_THROW(dhcid.fromDUID(duid, wire_fqdn_));
+
+    // The reference DHCID (represented as string of hexadecimal digits)
+    // has been calculated using one of the online calculators.
+    std::string dhcid_ref = "00020137D8FBDC0585B44DFA03FAD2E36C6"
+        "159737D545A12EFB40B0D88D110A5748234";
+
+    // Make sure that the DHCID is valid.
+    EXPECT_EQ(dhcid_ref, dhcid.toStr());
+}
+
+// This test verifies that DHCID is properly computed from a buffer holding
+// client identifier data.
+TEST_F(DhcidTest, fromClientId) {
+    D2Dhcid dhcid;
+
+    // Create a buffer holding client id..
+    uint8_t clientid_data[] = { 0, 1, 2, 3, 4, 5, 6 };
+    std::vector<uint8_t> clientid(clientid_data,
+                                  clientid_data + sizeof(clientid_data));
+
+    // Create DHCID.
+    ASSERT_NO_THROW(dhcid.fromClientId(clientid, wire_fqdn_));
+
+    // The reference DHCID (represented as string of hexadecimal digits)
+    // has been calculated using one of the online calculators.
+    std::string dhcid_ref = "0001012191B7B21AF97E0E656DF887C5E2D"
+        "EF30E7758A207EDF4CCB2DE8CA37066021C";
+
+    // Make sure that the DHCID is valid.
+    EXPECT_EQ(dhcid_ref, dhcid.toStr());
+
+    // Make sure that the empty FQDN is not accepted.
+    std::vector<uint8_t> empty_wire_fqdn;
+    EXPECT_THROW(dhcid.fromClientId(clientid, empty_wire_fqdn),
+                 isc::dhcp_ddns::DhcidRdataComputeError);
+
+    // Make sure that the empty client identifier is not accepted.
+    clientid.clear();
+    EXPECT_THROW(dhcid.fromClientId(clientid, wire_fqdn_),
+                 isc::dhcp_ddns::DhcidRdataComputeError);
+
+
+}
+
+// This test verifies that DHCID is properly computed from a buffer holding
+// client identifier data that contains a DUID.
+TEST_F(DhcidTest, fromClientIdDUID) {
+    D2Dhcid dhcid;
+
+    // Create a buffer holding client id..
+    uint8_t clientid_data[] = { 0xff, 0x5d, 0xe2, 0x6c, 0x15, 0x00, 0x02,
+        0x00, 0x00, 0xab, 0x11, 0x9a, 0x57, 0x20, 0x95, 0x71, 0x61, 0xbd, 0xd0 };
+    std::vector<uint8_t> clientid(clientid_data,
+                                  clientid_data + sizeof(clientid_data));
+
+    // Create DHCID.
+    ASSERT_NO_THROW(dhcid.fromClientId(clientid, wire_fqdn_));
+
+    // The reference DHCID (represented as string of hexadecimal digits)
+    std::string dhcid_ref = "000201A250D060B9352AE68E5014B78D25"
+        "1C30EFB0D5F64E48303B2BC56E6938F129E7";
+
+    // Make sure that the DHCID is valid.
+    EXPECT_EQ(dhcid_ref, dhcid.toStr());
+
+    // Make sure that a too long client identifier is not accepted.
+    clientid.resize(136);
+    EXPECT_THROW_MSG(dhcid.fromClientId(clientid, wire_fqdn_),
+                     isc::dhcp_ddns::DhcidRdataComputeError,
+                     "unable to compute DHCID from client identifier,"
+                     " embedded DUID length of: 136, is too long");
+
+    // Make sure that a too short client identifier is not accepted.
+    clientid.resize(5);
+    EXPECT_THROW_MSG(dhcid.fromClientId(clientid, wire_fqdn_),
+                     isc::dhcp_ddns::DhcidRdataComputeError,
+                     "unable to compute DHCID from client identifier,"
+                     " embedded DUID length of: 5, is too short");
+
+    // Make sure an empty client identifier is not accepted.
+    clientid.clear();
+    EXPECT_THROW_MSG(dhcid.fromClientId(clientid, wire_fqdn_),
+                     isc::dhcp_ddns::DhcidRdataComputeError,
+                     "empty DUID used to create DHCID");
+}
+
+// This test verifies that DHCID is properly computed from a HW address.
+TEST_F(DhcidTest, fromHWAddr) {
+    D2Dhcid dhcid;
+
+    // Create a buffer holding client id..
+    uint8_t hwaddr_data[] = { 0, 1, 2, 3, 4, 5, 6 };
+    HWAddrPtr hwaddr(new HWAddr(hwaddr_data, sizeof(hwaddr_data),
+                                HTYPE_ETHER));
+
+    // Create DHCID.
+    ASSERT_NO_THROW(dhcid.fromHWAddr(hwaddr, wire_fqdn_));
+
+    // The reference DHCID (represented as string of hexadecimal digits)
+    // has been calculated using one of the online calculators.
+    std::string dhcid_ref = "0000012247F6DC4423C3E8627434A9D686860"
+        "9D88948F78018B215EDCAA30C0C135035";
+
+    // Make sure that the DHCID is valid.
+    EXPECT_EQ(dhcid_ref, dhcid.toStr());
+
+    // Make sure that the empty FQDN is not accepted.
+    std::vector<uint8_t> empty_wire_fqdn;
+    EXPECT_THROW(dhcid.fromHWAddr(hwaddr, empty_wire_fqdn),
+                 isc::dhcp_ddns::DhcidRdataComputeError);
+
+    // Make sure that the NULL HW address is not accepted.
+    hwaddr.reset();
+    EXPECT_THROW(dhcid.fromHWAddr(hwaddr, wire_fqdn_),
+                 isc::dhcp_ddns::DhcidRdataComputeError);
+}
+
+// test operator<< on D2Dhcid
+TEST(NameChangeRequestTest, leftShiftOperation) {
+    const D2Dhcid dhcid("010203040A7F8E3D");
+
+    ostringstream oss;
+    oss << dhcid;
+    EXPECT_EQ(dhcid.toStr(), oss.str());
+}
+
+/// @brief Verifies the fundamentals of converting from and to JSON.
+/// It verifies that:
+/// 1. A NameChangeRequest can be created from a valid JSON string.
+/// 2. A valid JSON string can be created from a NameChangeRequest
+TEST(NameChangeRequestTest, basicJsonTest) {
+    // Define valid JSON rendition of a request.
+    std::string msg_str = "{"
+                            "\"change-type\":1,"
+                            "\"forward-change\":true,"
+                            "\"reverse-change\":false,"
+                            "\"fqdn\":\"walah.walah.com.\","
+                            "\"ip-address\":\"192.168.2.1\","
+                            "\"dhcid\":\"010203040A7F8E3D\","
+                            "\"lease-expires-on\":\"20130121132405\","
+                            "\"lease-length\":1300,"
+                            "\"use-conflict-resolution\":true"
+                          "}";
+
+    // Verify that a NameChangeRequests can be instantiated from the
+    // a valid JSON rendition.
+    NameChangeRequestPtr ncr;
+    ASSERT_NO_THROW_LOG(ncr  = NameChangeRequest::fromJSON(msg_str));
+    ASSERT_TRUE(ncr);
+
+    // Verify that the JSON string created by the new request equals the
+    // original input string.
+    std::string json_str = ncr->toJSON();
+    EXPECT_EQ(msg_str, json_str);
+
+    // Verify that the request ID matches the string from the DHCID.
+    std::string dhcid_str = "010203040A7F8E3D";
+    EXPECT_EQ(dhcid_str, ncr->getRequestId());
+}
+
+/// @brief Tests a variety of invalid JSON message strings.
+/// This test iterates over a list of JSON messages, each containing a single
+/// content error. The list of messages is defined by the global array,
+/// invalid_messages. Currently that list contains the following invalid
+/// conditions:
+///  1. Invalid change type
+///  2. Invalid forward change
+///  3. Invalid reverse change
+///  4. Forward and reverse change both false
+///  5. Invalid forward change
+///  6. Blank FQDN
+///  7. Bad IP address
+///  8. Blank DHCID
+///  9. Odd number of digits in DHCID
+/// 10. Text in DHCID
+/// 11. Invalid lease expiration string
+/// 12. Non-integer for lease length.
+/// If more permutations arise they can easily be added to the list.
+TEST(NameChangeRequestTest, invalidMsgChecks) {
+    // Iterate over the list of JSON strings, attempting to create a
+    // NameChangeRequest. The attempt should throw a NcrMessageError.
+    int num_msgs = sizeof(invalid_msgs)/sizeof(char*);
+    for (int i = 0; i < num_msgs; i++) {
+        EXPECT_THROW(NameChangeRequest::fromJSON(invalid_msgs[i]),
+                     NcrMessageError) << "Invalid message not caught idx: "
+                     << i << std::endl << " text:[" << invalid_msgs[i] << "]"
+                     << std::endl;
+    }
+}
+
+/// @brief Tests a variety of valid JSON message strings.
+/// This test iterates over a list of JSON messages, each containing a single
+/// valid request rendition. The list of messages is defined by the global
+/// array, valid_messages. Currently that list contains the following valid
+/// messages:
+///  1. Valid, IPv4 Add
+///  2. Valid, IPv4 Remove
+///  3. Valid, IPv6 Add
+/// If more permutations arise they can easily be added to the list.
+TEST(NameChangeRequestTest, validMsgChecks) {
+    // Iterate over the list of JSON strings, attempting to create a
+    // NameChangeRequest. The attempt should succeed.
+    int num_msgs = sizeof(valid_msgs)/sizeof(char*);
+    for (int i = 0; i < num_msgs; i++) {
+        EXPECT_NO_THROW(NameChangeRequest::fromJSON(valid_msgs[i]))
+                        << "Valid message failed,  message idx: " << i
+                        << std::endl << " text:[" << valid_msgs[i] << "]"
+                        << std::endl;
+    }
+}
+
+/// @brief Tests converting to and from JSON via isc::util buffer classes.
+/// This test verifies that:
+/// 1. A NameChangeRequest can be rendered in JSON written to an OutputBuffer
+/// 2. A InputBuffer containing a valid JSON request rendition can be used
+/// to create a NameChangeRequest.
+TEST(NameChangeRequestTest, toFromBufferTest) {
+    // Define a string containing a valid JSON NameChangeRequest rendition.
+    std::string msg_str = "{"
+                            "\"change-type\":1,"
+                            "\"forward-change\":true,"
+                            "\"reverse-change\":false,"
+                            "\"fqdn\":\"walah.walah.com.\","
+                            "\"ip-address\":\"192.168.2.1\","
+                            "\"dhcid\":\"010203040A7F8E3D\","
+                            "\"lease-expires-on\":\"20130121132405\","
+                            "\"lease-length\":1300,"
+                            "\"use-conflict-resolution\":true"
+                          "}";
+
+    // Create a request from JSON directly.
+    NameChangeRequestPtr ncr;
+    ASSERT_NO_THROW(ncr = NameChangeRequest::fromJSON(msg_str));
+
+    // Verify that we output the request as JSON text to a buffer
+    // without error.
+    isc::util::OutputBuffer output_buffer(1024);
+    ASSERT_NO_THROW(ncr->toFormat(FMT_JSON, output_buffer));
+
+    // Make an InputBuffer from the OutputBuffer.
+    isc::util::InputBuffer input_buffer(output_buffer.getData(),
+                                        output_buffer.getLength());
+
+    // Verify that we can create a new request from the InputBuffer.
+    NameChangeRequestPtr ncr2;
+    ASSERT_NO_THROW(ncr2 =
+                    NameChangeRequest::fromFormat(FMT_JSON, input_buffer));
+
+    // Convert the new request to JSON directly.
+    std::string final_str = ncr2->toJSON();
+
+    // Verify that the final string matches the original.
+    ASSERT_EQ(final_str, msg_str);
+}
+
+/// @brief Tests ip address modification and validation
+TEST(NameChangeRequestTest, ipAddresses) {
+    NameChangeRequest ncr;
+
+    // Verify that a valid IPv4 address works.
+    ASSERT_NO_THROW(ncr.setIpAddress("192.168.1.1"));
+    const asiolink::IOAddress& io_addr4 = ncr.getIpIoAddress();
+    EXPECT_EQ(ncr.getIpAddress(), io_addr4.toText());
+    EXPECT_TRUE(ncr.isV4());
+    EXPECT_FALSE(ncr.isV6());
+
+    // Verify that a valid IPv6 address works.
+    ASSERT_NO_THROW(ncr.setIpAddress("2001:1::f3"));
+    const asiolink::IOAddress& io_addr6 = ncr.getIpIoAddress();
+    EXPECT_EQ(ncr.getIpAddress(), io_addr6.toText());
+    EXPECT_FALSE(ncr.isV4());
+    EXPECT_TRUE(ncr.isV6());
+
+    // Verify that an invalid address fails.
+    ASSERT_THROW(ncr.setIpAddress("x001:1::f3"),NcrMessageError);
+}
+
+/// @brief Tests conversion of NameChangeFormat between enum and strings.
+TEST(NameChangeFormatTest, formatEnumConversion){
+    ASSERT_EQ(stringToNcrFormat("JSON"), dhcp_ddns::FMT_JSON);
+    ASSERT_EQ(stringToNcrFormat("jSoN"), dhcp_ddns::FMT_JSON);
+    ASSERT_THROW(stringToNcrFormat("bogus"), isc::BadValue);
+
+    ASSERT_EQ(ncrFormatToString(dhcp_ddns::FMT_JSON), "JSON");
+}
+
+/// @brief Tests conversion of NameChangeProtocol between enum and strings.
+TEST(NameChangeProtocolTest, protocolEnumConversion){
+    ASSERT_EQ(stringToNcrProtocol("UDP"), dhcp_ddns::NCR_UDP);
+    ASSERT_EQ(stringToNcrProtocol("udP"), dhcp_ddns::NCR_UDP);
+    ASSERT_EQ(stringToNcrProtocol("TCP"), dhcp_ddns::NCR_TCP);
+    ASSERT_EQ(stringToNcrProtocol("Tcp"), dhcp_ddns::NCR_TCP);
+    ASSERT_THROW(stringToNcrProtocol("bogus"), isc::BadValue);
+
+    ASSERT_EQ(ncrProtocolToString(dhcp_ddns::NCR_UDP), "UDP");
+    ASSERT_EQ(ncrProtocolToString(dhcp_ddns::NCR_TCP), "TCP");
+}
+
+TEST(NameChangeRequestTest, useConflictResolutionParsing) {
+    std::string base_json =
+     "{"
+     " \"change-type\" : 0 , "
+     " \"forward-change\" : true , "
+     " \"reverse-change\" : false , "
+     " \"fqdn\" : \"walah.walah.com\" , "
+     " \"ip-address\" : \"192.168.2.1\" , "
+     " \"dhcid\" : \"010203040A7F8E3D\" , "
+     " \"lease-expires-on\" : \"20130121132405\" , "
+     " \"lease-length\" : 1300 ";
+
+    std::string its_true(base_json + ",\"use-conflict-resolution\": true}");
+    NameChangeRequestPtr ncr;
+    ASSERT_NO_THROW_LOG(ncr = NameChangeRequest::fromJSON(its_true));
+    ASSERT_TRUE(ncr);
+    EXPECT_TRUE(ncr->useConflictResolution());
+
+    std::string its_false(base_json + ",\"use-conflict-resolution\": false}");
+    ASSERT_NO_THROW_LOG(ncr = NameChangeRequest::fromJSON(its_false));
+    ASSERT_TRUE(ncr);
+    EXPECT_FALSE(ncr->useConflictResolution());
+
+    std::string its_missing(base_json + "}");
+    ASSERT_NO_THROW_LOG(ncr = NameChangeRequest::fromJSON(its_true));
+    ASSERT_TRUE(ncr);
+    EXPECT_TRUE(ncr->useConflictResolution());
+}
+
+} // end of anonymous namespace
+
diff --git a/src/lib/dhcp_ddns/tests/run_unittests.cc b/src/lib/dhcp_ddns/tests/run_unittests.cc
new file mode 100644
index 0000000..e1c0801
--- /dev/null
+++ b/src/lib/dhcp_ddns/tests/run_unittests.cc
@@ -0,0 +1,21 @@
+// Copyright (C) 2011-2015 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/.
+
+#include <config.h>
+
+#include <log/logger_support.h>
+
+#include <gtest/gtest.h>
+
+int
+main(int argc, char* argv[]) {
+    ::testing::InitGoogleTest(&argc, argv);
+    isc::log::initLogger();
+
+    int result = RUN_ALL_TESTS();
+
+    return (result);
+}
diff --git a/src/lib/dhcp_ddns/tests/test_utils.cc b/src/lib/dhcp_ddns/tests/test_utils.cc
new file mode 100644
index 0000000..0671307
--- /dev/null
+++ b/src/lib/dhcp_ddns/tests/test_utils.cc
@@ -0,0 +1,37 @@
+// Copyright (C) 2014-2015 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/.
+
+#include <config.h>
+
+#include <gtest/gtest.h>
+
+#include <sys/select.h>
+#include <sys/ioctl.h>
+
+using namespace std;
+
+namespace isc {
+namespace dhcp_ddns {
+
+int selectCheck(int fd_to_check) {
+    fd_set read_fds;
+    int maxfd = 0;
+
+    FD_ZERO(&read_fds);
+
+    // Add this socket to listening set
+    FD_SET(fd_to_check,  &read_fds);
+    maxfd = fd_to_check;
+
+    struct timeval select_timeout;
+    select_timeout.tv_sec = 0;
+    select_timeout.tv_usec = 0;
+
+    return (select(maxfd + 1, &read_fds, NULL, NULL, &select_timeout));
+}
+
+}; // namespace isc::d2
+}; // namespace isc
diff --git a/src/lib/dhcp_ddns/tests/test_utils.h b/src/lib/dhcp_ddns/tests/test_utils.h
new file mode 100644
index 0000000..256350e
--- /dev/null
+++ b/src/lib/dhcp_ddns/tests/test_utils.h
@@ -0,0 +1,29 @@
+// Copyright (C) 2014-2015 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/.
+
+#ifndef TEST_UTILS_H
+#define TEST_UTILS_H
+
+/// @file test_utils.h Common dhcp_ddns testing elements
+
+#include <gtest/gtest.h>
+
+
+namespace isc {
+namespace dhcp_ddns {
+
+/// @brief Returns the result of select() given an fd to check for read status.
+///
+/// @param fd_to_check The file descriptor to test
+///
+/// @return Returns less than one on an error, 0 if the fd is not ready to
+/// read, > 0 if it is ready to read. 
+int selectCheck(int fd_to_check);
+
+}; // namespace isc::dhcp_ddns;
+}; // namespace isc;
+
+#endif