Adding upstream version 3.2.1.upstream/3.2.1upstream

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

66 files changed, 20315 insertions, 0 deletions

diff --git a/lib/README.rst b/lib/README.rst
new file mode 100644
index 0000000..2905676
--- /dev/null
+++ b/lib/README.rst
@@ -0,0 +1,314 @@
+*********************
+Knot Resolver library
+*********************
+
+Requirements
+============
+
+* libknot_ 2.0 (Knot DNS high-performance DNS library.)
+
+For users
+=========
+
+The library as described provides basic services for name resolution, which should cover the usage,
+examples are in the :ref:`resolve API <lib_api_rplan>` documentation.
+
+.. tip:: If you're migrating from ``getaddrinfo()``, see *"synchronous"* API, but the library offers iterative API as well to plug it into your event loop for example.
+
+.. _lib-layers:
+
+For developers
+==============
+
+The resolution process starts with the functions in :ref:`resolve.c <lib_api_rplan>`, they are responsible for:
+
+* reacting to state machine state (i.e. calling consume layers if we have an answer ready)
+* interacting with the library user (i.e. asking caller for I/O, accepting queries)
+* fetching assets needed by layers (i.e. zone cut)
+
+This is the *driver*. The driver is not meant to know *"how"* the query resolves, but rather *"when"* to execute *"what"*.
+
+.. image:: ../doc/resolution.png
+   :align: center
+
+On the other side are *layers*. They are responsible for dissecting the packets and informing the driver about the results. For example, a *produce* layer generates query, a *consume* layer validates answer.
+
+.. tip:: Layers are executed asynchronously by the driver. If you need some asset beforehand, you can signalize the driver using returning state or current query flags. For example, setting a flag ``AWAIT_CUT`` forces driver to fetch zone cut information before the packet is consumed; setting a ``RESOLVED`` flag makes it pop a query after the current set of layers is finished; returning ``FAIL`` state makes it fail current query.
+
+Layers can also change course of resolution, for example by appending additional queries.
+
+.. code-block:: lua
+
+	consume = function (state, req, answer)
+		answer = kres.pkt_t(answer)
+		if answer:qtype() == kres.type.NS then
+			req = kres.request_t(req)
+			local qry = req:push(answer:qname(), kres.type.SOA, kres.class.IN)
+			qry.flags.AWAIT_CUT = true
+		end
+		return state
+	end
+
+This **doesn't** block currently processed query, and the newly created sub-request will start as soon as driver finishes processing current. In some cases you might need to issue sub-request and process it **before** continuing with the current, i.e. validator may need a DNSKEY before it can validate signatures. In this case, layers can yield and resume afterwards.
+
+.. code-block:: lua
+
+	consume = function (state, req, answer)
+		answer = kres.pkt_t(answer)
+		if state == kres.YIELD then
+			print('continuing yielded layer')
+			return kres.DONE
+		else
+			if answer:qtype() == kres.type.NS then
+				req = kres.request_t(req)
+				local qry = req:push(answer:qname(), kres.type.SOA, kres.class.IN)
+				qry.flags.AWAIT_CUT = true
+				print('planned SOA query, yielding')
+				return kres.YIELD
+			end
+			return state
+		end
+	end
+
+The ``YIELD`` state is a bit special. When a layer returns it, it interrupts current walk through the layers. When the layer receives it,
+it means that it yielded before and now it is resumed. This is useful in a situation where you need a sub-request to determine whether current answer is valid or not.
+
+Writing layers
+==============
+
+.. warning::  FIXME: this dev-docs section is outdated!  Better see comments in files instead, for now.
+
+The resolver :ref:`library <lib_index>` leverages the processing API from the libknot to separate packet processing code into layers.
+
+.. note:: This is only crash-course in the library internals, see the resolver :ref:`library <lib_index>` documentation for the complete overview of the services.
+
+The library offers following services:
+
+- :ref:`Cache <lib_api_cache>` - MVCC cache interface for retrieving/storing resource records.
+- :ref:`Resolution plan <lib_api_rplan>` - Query resolution plan, a list of partial queries (with hierarchy) sent in order to satisfy original query. This contains information about the queries, nameserver choice, timing information, answer and its class.
+- :ref:`Nameservers <lib_api_nameservers>` - Reputation database of nameservers, this serves as an aid for nameserver choice.
+
+A processing layer is going to be called by the query resolution driver for each query,
+so you're going to work with :ref:`struct kr_request <lib_api_rplan>` as your per-query context.
+This structure contains pointers to resolution context, resolution plan and also the final answer.
+
+.. code-block:: c
+
+	int consume(kr_layer_t *ctx, knot_pkt_t *pkt)
+	{
+		struct kr_request *req = ctx->req;
+		struct kr_query *qry = req->current_query;
+	}
+
+This is only passive processing of the incoming answer. If you want to change the course of resolution, say satisfy a query from a local cache before the library issues a query to the nameserver, you can use states (see the :ref:`Static hints <mod-hints>` for example).
+
+.. code-block:: c
+
+	int produce(kr_layer_t *ctx, knot_pkt_t *pkt)
+	{
+		struct kr_request *req = ctx->req;
+		struct kr_query *qry = req->current_query;
+		
+		/* Query can be satisfied locally. */
+		if (can_satisfy(qry)) {
+			/* This flag makes the resolver move the query
+			 * to the "resolved" list. */
+			qry->flags.RESOLVED = true;
+			return KR_STATE_DONE;
+		}
+
+		/* Pass-through. */
+		return ctx->state;
+	}
+
+It is possible to not only act during the query resolution, but also to view the complete resolution plan afterwards. This is useful for analysis-type tasks, or *"per answer"* hooks.
+
+.. code-block:: c
+
+	int finish(kr_layer_t *ctx)
+	{
+		struct kr_request *req = ctx->req;
+		struct kr_rplan *rplan = req->rplan;
+
+		/* Print the query sequence with start time. */
+		char qname_str[KNOT_DNAME_MAXLEN];
+		struct kr_query *qry = NULL
+		WALK_LIST(qry, rplan->resolved) {
+			knot_dname_to_str(qname_str, qry->sname, sizeof(qname_str));
+			printf("%s at %u\n", qname_str, qry->timestamp);
+		}
+
+		return ctx->state;
+	}
+
+APIs in Lua
+===========
+
+The APIs in Lua world try to mirror the C APIs using LuaJIT FFI, with several differences and enhancements.
+There is not comprehensive guide on the API yet, but you can have a look at the bindings_ file.
+
+Elementary types and constants
+------------------------------
+
+* States are directly in ``kres`` table, e.g. ``kres.YIELD, kres.CONSUME, kres.PRODUCE, kres.DONE, kres.FAIL``.
+* DNS classes are in ``kres.class`` table, e.g. ``kres.class.IN`` for Internet class.
+* DNS types are in  ``kres.type`` table, e.g. ``kres.type.AAAA`` for AAAA type.
+* DNS rcodes types are in ``kres.rcode`` table, e.g. ``kres.rcode.NOERROR``.
+* Packet sections (QUESTION, ANSWER, AUTHORITY, ADDITIONAL) are in the ``kres.section`` table.
+
+Working with domain names
+-------------------------
+
+The internal API usually works with domain names in label format, you can convert between text and wire freely.
+
+.. code-block:: lua
+
+	local dname = kres.str2dname('business.se')
+	local strname = kres.dname2str(dname)
+
+Working with resource records
+-----------------------------
+
+Resource records are stored as tables.
+
+.. code-block:: lua
+
+	local rr = { owner = kres.str2dname('owner'),
+	             ttl = 0,
+	             class = kres.class.IN,
+	             type = kres.type.CNAME,
+	             rdata = kres.str2dname('someplace') }
+	print(kres.rr2str(rr))
+
+RRSets in packet can be accessed using FFI, you can easily fetch single records.
+
+.. code-block:: lua
+
+	local rrset = { ... }
+	local rr = rrset:get(0) -- Return first RR
+	print(kres.dname2str(rr:owner()))
+	print(rr:ttl())
+	print(kres.rr2str(rr))
+
+Working with packets
+--------------------
+
+Packet is the data structure that you're going to see in layers very often. They consists of a header, and four sections: QUESTION, ANSWER, AUTHORITY, ADDITIONAL. The first section is special, as it contains the query name, type, and class; the rest of the sections contain RRSets.
+
+First you need to convert it to a type known to FFI and check basic properties. Let's start with a snippet of a *consume* layer.
+
+.. code-block:: lua
+
+	consume = function (state, req, pkt)
+		pkt = kres.pkt_t(answer)
+		print('rcode:', pkt:rcode())
+		print('query:', kres.dname2str(pkt:qname()), pkt:qclass(), pkt:qtype())
+		if pkt:rcode() ~= kres.rcode.NOERROR then
+			print('error response')
+		end
+	end
+
+You can enumerate records in the sections.
+
+.. code-block:: lua
+
+	local records = pkt:section(kres.section.ANSWER)
+	for i = 1, #records do
+		local rr = records[i]
+		if rr.type == kres.type.AAAA then
+			print(kres.rr2str(rr))
+		end
+	end
+
+During *produce* or *begin*, you might want to want to write to packet. Keep in mind that you have to write packet sections in sequence,
+e.g. you can't write to ANSWER after writing AUTHORITY, it's like stages where you can't go back.
+
+.. code-block:: lua
+
+		pkt:rcode(kres.rcode.NXDOMAIN)
+		-- Clear answer and write QUESTION
+		pkt:recycle()
+		pkt:question('\7blocked', kres.class.IN, kres.type.SOA)
+		-- Start writing data
+		pkt:begin(kres.section.ANSWER)
+		-- Nothing in answer
+		pkt:begin(kres.section.AUTHORITY)
+		local soa = { owner = '\7blocked', ttl = 900, class = kres.class.IN, type = kres.type.SOA, rdata = '...' }
+		pkt:put(soa.owner, soa.ttl, soa.class, soa.type, soa.rdata)
+
+Working with requests
+---------------------
+
+The request holds information about currently processed query, enabled options, cache, and other extra data.
+You primarily need to retrieve currently processed query.
+
+.. code-block:: lua
+
+	consume = function (state, req, pkt)
+		req = kres.request_t(req)
+		print(req.options)
+		print(req.state)
+
+		-- Print information about current query
+		local current = req:current()
+		print(kres.dname2str(current.owner))
+		print(current.stype, current.sclass, current.id, current.flags)
+	end
+
+In layers that either begin or finalize, you can walk the list of resolved queries.
+
+.. code-block:: lua
+
+	local last = req:resolved()
+	print(last.stype)
+
+As described in the layers, you can not only retrieve information about current query, but also push new ones or pop old ones.
+
+.. code-block:: lua
+
+		-- Push new query
+		local qry = req:push(pkt:qname(), kres.type.SOA, kres.class.IN)
+		qry.flags.AWAIT_CUT = true
+
+		-- Pop the query, this will erase it from resolution plan
+		req:pop(qry)
+
+
+.. _libknot:  https://gitlab.labs.nic.cz/knot/knot-dns/tree/master/src/libknot
+.. _bindings: https://gitlab.labs.nic.cz/knot/knot-resolver/blob/master/daemon/lua/kres.lua
+
+
+Significant Lua API changes
+---------------------------
+
+Incompatible changes since 3.0.0
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In the main ``kres.*`` lua binding, there was only change in struct knot_rrset_t:
+
+- constructor now accepts TTL as additional parameter (defaulting to zero)
+- add_rdata() doesn't accept TTL anymore (and will throw an error if passed)
+
+In case you used knot_* functions and structures bound to lua:
+
+- knot_dname_is_sub(a, b): knot_dname_in_bailiwick(a, b) > 0
+- knot_rdata_rdlen(): knot_rdataset_at().len
+- knot_rdata_data(): knot_rdataset_at().data
+- knot_rdata_array_size(): offsetof(struct knot_data_t, data) + knot_rdataset_at().len
+- struct knot_rdataset: field names were renamed to .count and .rdata
+- some functions got inlined from headers, but you can use their kr_* clones:
+  kr_rrsig_sig_inception(), kr_rrsig_sig_expiration(), kr_rrsig_type_covered().
+  Note that these functions now accept knot_rdata_t* instead of a pair
+  knot_rdataset_t* and size_t - you can use knot_rdataset_at() for that.
+
+- knot_rrset_add_rdata() doesn't take TTL parameter anymore
+- knot_rrset_init_empty() was inlined, but in lua you can use the constructor
+- knot_rrset_ttl() was inlined, but in lua you can use :ttl() method instead
+
+- knot_pkt_qname(), _qtype(), _qclass(), _rr(), _section() were inlined,
+  but in lua you can use methods instead, e.g. myPacket:qname()
+- knot_pkt_free() takes knot_pkt_t* instead of knot_pkt_t**, but from lua
+  you probably didn't want to use that; constructor ensures garbage collection.
+
+
+.. |---| unicode:: U+02014 .. em dash
diff --git a/lib/cache/api.c b/lib/cache/api.c
new file mode 100644
index 0000000..c0591d6
--- /dev/null
+++ b/lib/cache/api.c
@@ -0,0 +1,889 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <limits.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <time.h>
+#include <unistd.h>
+
+#include <libknot/descriptor.h>
+#include <libknot/dname.h>
+#include <libknot/errcode.h>
+#include <libknot/rrtype/rrsig.h>
+
+#include "contrib/cleanup.h"
+#include "contrib/ucw/lib.h"
+#include "lib/cache/api.h"
+#include "lib/cache/cdb_lmdb.h"
+#include "lib/defines.h"
+#include "lib/generic/trie.h"
+#include "lib/resolve.h"
+#include "lib/rplan.h"
+#include "lib/utils.h"
+
+#include "lib/cache/impl.h"
+
+/* TODO:
+ *	- Reconsider when RRSIGs are put in and retrieved from the cache.
+ *	  Currently it's always done, which _might_ be spurious, depending
+ *	  on how kresd will use the returned result.
+ *	  There's also the "problem" that kresd ATM does _not_ ask upstream
+ *	  with DO bit in some cases.
+ */
+
+
+/** Cache version */
+static const uint16_t CACHE_VERSION = 5;
+/** Key size */
+#define KEY_HSIZE (sizeof(uint8_t) + sizeof(uint16_t))
+#define KEY_SIZE (KEY_HSIZE + KNOT_DNAME_MAXLEN)
+
+
+/** @internal Forward declarations of the implementation details
+ * \param optout[out] Set *optout = true; when encountering an opt-out NSEC3 (optional). */
+static ssize_t stash_rrset(struct kr_cache *cache, const struct kr_query *qry,
+		const knot_rrset_t *rr, const knot_rrset_t *rr_sigs, uint32_t timestamp,
+		uint8_t rank, trie_t *nsec_pmap, bool *has_optout);
+/** Preliminary checks before stash_rrset().  Don't call if returns <= 0. */
+static int stash_rrset_precond(const knot_rrset_t *rr, const struct kr_query *qry/*logs*/);
+
+/** @internal Removes all records from cache. */
+static inline int cache_clear(struct kr_cache *cache)
+{
+	cache->stats.delete += 1;
+	return cache_op(cache, clear);
+}
+
+/** @internal Open cache db transaction and check internal data version. */
+static int assert_right_version(struct kr_cache *cache)
+{
+	/* Check cache ABI version. */
+	/* CACHE_KEY_DEF: to avoid collisions with kr_cache_match(). */
+	uint8_t key_str[4] = "VERS";
+	knot_db_val_t key = { .data = key_str, .len = sizeof(key_str) };
+	knot_db_val_t val = { NULL, 0 };
+	int ret = cache_op(cache, read, &key, &val, 1);
+	if (ret == 0 && val.len == sizeof(CACHE_VERSION)
+	    && memcmp(val.data, &CACHE_VERSION, sizeof(CACHE_VERSION)) == 0) {
+		ret = kr_error(EEXIST);
+	} else {
+		int oldret = ret;
+		/* Version doesn't match. Recreate cache and write version key. */
+		ret = cache_op(cache, count);
+		if (ret != 0) { /* Non-empty cache, purge it. */
+			kr_log_info("[     ][cach] incompatible cache database detected, purging\n");
+			if (oldret) {
+				kr_log_verbose("bad ret: %d\n", oldret);
+			} else if (val.len != sizeof(CACHE_VERSION)) {
+				kr_log_verbose("bad length: %d\n", (int)val.len);
+			} else {
+				uint16_t ver;
+				memcpy(&ver, val.data, sizeof(ver));
+				kr_log_verbose("bad version: %d\n", (int)ver);
+			}
+			ret = cache_clear(cache);
+		}
+		/* Either purged or empty. */
+		if (ret == 0) {
+			/* Key/Val is invalidated by cache purge, recreate it */
+			val.data = /*const-cast*/(void *)&CACHE_VERSION;
+			val.len = sizeof(CACHE_VERSION);
+			ret = cache_op(cache, write, &key, &val, 1);
+		}
+	}
+	kr_cache_sync(cache);
+	return ret;
+}
+
+int kr_cache_open(struct kr_cache *cache, const struct kr_cdb_api *api, struct kr_cdb_opts *opts, knot_mm_t *mm)
+{
+	if (!cache) {
+		return kr_error(EINVAL);
+	}
+	/* Open cache */
+	if (!api) {
+		api = kr_cdb_lmdb();
+	}
+	cache->api = api;
+	int ret = cache->api->open(&cache->db, opts, mm);
+	if (ret != 0) {
+		return ret;
+	}
+	memset(&cache->stats, 0, sizeof(cache->stats));
+	cache->ttl_min = KR_CACHE_DEFAULT_TTL_MIN;
+	cache->ttl_max = KR_CACHE_DEFAULT_TTL_MAX;
+	/* Check cache ABI version */
+	kr_cache_make_checkpoint(cache);
+	(void)assert_right_version(cache);
+
+	char *fpath;
+	ret = asprintf(&fpath, "%s/data.mdb", opts->path);
+	if (ret > 0) {
+		kr_cache_emergency_file_to_remove = fpath;
+	} else {
+		assert(false); /* non-critical, but still */
+	}
+	return 0;
+}
+
+const char *kr_cache_emergency_file_to_remove = NULL;
+
+
+#define cache_isvalid(cache) ((cache) && (cache)->api && (cache)->db)
+
+void kr_cache_close(struct kr_cache *cache)
+{
+	if (cache_isvalid(cache)) {
+		cache_op(cache, close);
+		cache->db = NULL;
+	}
+	free(/*const-cast*/(char*)kr_cache_emergency_file_to_remove);
+	kr_cache_emergency_file_to_remove = NULL;
+}
+
+int kr_cache_sync(struct kr_cache *cache)
+{
+	if (!cache_isvalid(cache)) {
+		return kr_error(EINVAL);
+	}
+	if (cache->api->sync) {
+		return cache_op(cache, sync);
+	}
+	return kr_ok();
+}
+
+int kr_cache_insert_rr(struct kr_cache *cache, const knot_rrset_t *rr, const knot_rrset_t *rrsig, uint8_t rank, uint32_t timestamp)
+{
+	int err = stash_rrset_precond(rr, NULL);
+	if (err <= 0) {
+		return kr_ok();
+	}
+	ssize_t written = stash_rrset(cache, NULL, rr, rrsig, timestamp, rank, NULL, NULL);
+		/* Zone's NSEC* parames aren't updated, but that's probably OK
+		 * for kr_cache_insert_rr() */
+	if (written >= 0) {
+		return kr_ok();
+	}
+
+	return (int) written;
+}
+
+int kr_cache_clear(struct kr_cache *cache)
+{
+	if (!cache_isvalid(cache)) {
+		return kr_error(EINVAL);
+	}
+	int ret = cache_clear(cache);
+	if (ret == 0) {
+		kr_cache_make_checkpoint(cache);
+		ret = assert_right_version(cache);
+	}
+	return ret;
+}
+
+/* When going stricter, BEWARE of breaking entry_h_consistent_NSEC() */
+struct entry_h * entry_h_consistent(knot_db_val_t data, uint16_t type)
+{
+	(void) type; /* unused, for now */
+	if (!data.data) return NULL;
+	/* Length checks. */
+	if (data.len < offsetof(struct entry_h, data))
+		return NULL;
+	const struct entry_h *eh = data.data;
+	if (eh->is_packet) {
+		uint16_t pkt_len;
+		if (data.len < offsetof(struct entry_h, data) + sizeof(pkt_len)) {
+			return NULL;
+		}
+		memcpy(&pkt_len, eh->data, sizeof(pkt_len));
+		if (data.len < offsetof(struct entry_h, data) + sizeof(pkt_len)
+				+ pkt_len) {
+			return NULL;
+		}
+	}
+
+	bool ok = true;
+	ok = ok && kr_rank_check(eh->rank);
+	ok = ok && (!kr_rank_test(eh->rank, KR_RANK_BOGUS)
+		    || eh->is_packet);
+	ok = ok && (eh->is_packet || !eh->has_optout);
+
+	return ok ? /*const-cast*/(struct entry_h *)eh : NULL;
+}
+
+int32_t get_new_ttl(const struct entry_h *entry, const struct kr_query *qry,
+                    const knot_dname_t *owner, uint16_t type, uint32_t now)
+{
+	int32_t diff = now - entry->time;
+	if (diff < 0) {
+		/* We may have obtained the record *after* the request started. */
+		diff = 0;
+	}
+	int32_t res = entry->ttl - diff;
+	if (res < 0 && owner && qry && qry->stale_cb) {
+		/* Stale-serving decision, delegated to a callback. */
+		int res_stale = qry->stale_cb(res, owner, type, qry);
+		if (res_stale >= 0)
+			return res_stale;
+	}
+	return res;
+}
+
+int32_t kr_cache_ttl(const struct kr_cache_p *peek, const struct kr_query *qry,
+		     const knot_dname_t *name, uint16_t type)
+{
+	const struct entry_h *eh = peek->raw_data;
+	return get_new_ttl(eh, qry, name, type, qry->timestamp.tv_sec);
+}
+
+/** Check that no label contains a zero character, incl. a log trace.
+ *
+ * We refuse to work with those, as LF and our cache keys might become ambiguous.
+ * Assuming uncompressed name, as usual.
+ * CACHE_KEY_DEF
+ */
+static bool check_dname_for_lf(const knot_dname_t *n, const struct kr_query *qry/*logging*/)
+{
+	const bool ret = knot_dname_size(n) == strlen((const char *)n) + 1;
+	if (!ret) { WITH_VERBOSE(qry) {
+		auto_free char *n_str = kr_dname_text(n);
+		VERBOSE_MSG(qry, "=> skipping zero-containing name %s\n", n_str);
+	} }
+	return ret;
+}
+
+/** Return false on types to be ignored.  Meant both for sname and direct cache requests. */
+static bool check_rrtype(uint16_t type, const struct kr_query *qry/*logging*/)
+{
+	const bool ret = !knot_rrtype_is_metatype(type)
+			&& type != KNOT_RRTYPE_RRSIG;
+	if (!ret) { WITH_VERBOSE(qry) {
+		auto_free char *type_str = kr_rrtype_text(type);
+		VERBOSE_MSG(qry, "=> skipping RR type %s\n", type_str);
+	} }
+	return ret;
+}
+
+/** Like key_exact_type() but omits a couple checks not holding for pkt cache. */
+knot_db_val_t key_exact_type_maypkt(struct key *k, uint16_t type)
+{
+	assert(check_rrtype(type, NULL));
+	switch (type) {
+	case KNOT_RRTYPE_RRSIG: /* no RRSIG query caching, at least for now */
+		assert(false);
+		return (knot_db_val_t){ NULL, 0 };
+	/* xNAME lumped into NS. */
+	case KNOT_RRTYPE_CNAME:
+	case KNOT_RRTYPE_DNAME:
+		type = KNOT_RRTYPE_NS;
+	default:
+		break;
+	}
+
+	int name_len = k->buf[0];
+	k->buf[name_len + 1] = 0; /* make sure different names can never match */
+	k->buf[name_len + 2] = 'E'; /* tag for exact name+type matches */
+	memcpy(k->buf + name_len + 3, &type, 2);
+	k->type = type;
+	/* CACHE_KEY_DEF: key == dname_lf + '\0' + 'E' + RRTYPE */
+	return (knot_db_val_t){ k->buf + 1, name_len + 4 };
+}
+
+
+/** The inside for cache_peek(); implementation separated to ./peek.c */
+int peek_nosync(kr_layer_t *ctx, knot_pkt_t *pkt);
+/** function for .produce phase */
+int cache_peek(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	/* We first check various exit-conditions and then call the _real function. */
+
+	if (!kr_cache_is_open(&req->ctx->cache)
+	    || ctx->state & (KR_STATE_FAIL|KR_STATE_DONE) || qry->flags.NO_CACHE
+	    || (qry->flags.CACHE_TRIED && !qry->stale_cb)
+	    || !check_rrtype(qry->stype, qry) /* LATER: some other behavior for some of these? */
+	    || qry->sclass != KNOT_CLASS_IN) {
+		return ctx->state; /* Already resolved/failed or already tried, etc. */
+	}
+	/* ATM cache only peeks for qry->sname and that would be useless
+	 * to repeat on every iteration, so disable it from now on.
+	 * LATER(optim.): assist with more precise QNAME minimization. */
+	qry->flags.CACHE_TRIED = true;
+
+	if (qry->stype == KNOT_RRTYPE_NSEC) {
+		VERBOSE_MSG(qry, "=> skipping stype NSEC\n");
+		return ctx->state;
+	}
+	if (!check_dname_for_lf(qry->sname, qry)) {
+		return ctx->state;
+	}
+
+	int ret = peek_nosync(ctx, pkt);
+	kr_cache_sync(&req->ctx->cache);
+	return ret;
+}
+
+
+
+/** It's simply inside of cycle taken out to decrease indentation.  \return error code. */
+static int stash_rrarray_entry(ranked_rr_array_t *arr, int arr_i,
+			const struct kr_query *qry, struct kr_cache *cache,
+			int *unauth_cnt, trie_t *nsec_pmap, bool *has_optout);
+/** Stash a single nsec_p.  \return 0 (errors are ignored). */
+static int stash_nsec_p(const knot_dname_t *dname, const char *nsec_p_v,
+			struct kr_request *req);
+
+/** The whole .consume phase for the cache module. */
+int cache_stash(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	struct kr_cache *cache = &req->ctx->cache;
+
+	/* Note: we cache even in KR_STATE_FAIL.  For example,
+	 * BOGUS answer can go to +cd cache even without +cd request. */
+	if (!kr_cache_is_open(cache) || !qry
+	    || qry->flags.CACHED || !check_rrtype(knot_pkt_qtype(pkt), qry)
+	    || qry->sclass != KNOT_CLASS_IN) {
+		return ctx->state;
+	}
+	/* Do not cache truncated answers, at least for now.  LATER */
+	if (knot_wire_get_tc(pkt->wire)) {
+		return ctx->state;
+	}
+	/* Stash individual records. */
+	ranked_rr_array_t *selected[] = kr_request_selected(req);
+	int unauth_cnt = 0;
+	trie_t *nsec_pmap = trie_create(&req->pool);
+	if (!nsec_pmap) {
+		assert(!ENOMEM);
+		goto finally;
+	}
+	bool has_optout = false;
+		/* ^^ DNSSEC_OPTOUT is not fired in cases like `com. A`,
+		 * but currently we don't stash separate NSEC3 proving that. */
+	for (int psec = KNOT_ANSWER; psec <= KNOT_ADDITIONAL; ++psec) {
+		ranked_rr_array_t *arr = selected[psec];
+		/* uncached entries are located at the end */
+		for (ssize_t i = arr->len - 1; i >= 0; --i) {
+			ranked_rr_array_entry_t *entry = arr->at[i];
+			if (entry->qry_uid != qry->uid) {
+				continue;
+				/* TODO: probably safe to break but maybe not worth it */
+			}
+			int ret = stash_rrarray_entry(arr, i, qry, cache, &unauth_cnt,
+							nsec_pmap, &has_optout);
+			if (ret) {
+				VERBOSE_MSG(qry, "=> stashing RRs errored out\n");
+				goto finally;
+			}
+			/* LATER(optim.): maybe filter out some type-rank combinations
+			 * that won't be useful as separate RRsets. */
+		}
+	}
+
+	trie_it_t *it;
+	for (it = trie_it_begin(nsec_pmap); !trie_it_finished(it); trie_it_next(it)) {
+		stash_nsec_p((const knot_dname_t *)trie_it_key(it, NULL),
+				(const char *)*trie_it_val(it), req);
+	}
+	trie_it_free(it);
+	/* LATER(optim.): typically we also have corresponding NS record in the list,
+	 * so we might save a cache operation. */
+
+	stash_pkt(pkt, qry, req, has_optout);
+
+finally:
+	if (unauth_cnt) {
+		VERBOSE_MSG(qry, "=> stashed also %d nonauth RRsets\n", unauth_cnt);
+	};
+	kr_cache_sync(cache);
+	return ctx->state; /* we ignore cache-stashing errors */
+}
+
+/** Preliminary checks before stash_rrset().  Don't call if returns <= 0. */
+static int stash_rrset_precond(const knot_rrset_t *rr, const struct kr_query *qry/*logs*/)
+{
+	if (!rr || rr->rclass != KNOT_CLASS_IN) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+	if (!check_rrtype(rr->type, qry)) {
+		return kr_ok();
+	}
+	if (!check_dname_for_lf(rr->owner, qry)) {
+		return kr_ok();
+	}
+	return 1/*proceed*/;
+}
+
+static ssize_t stash_rrset(struct kr_cache *cache, const struct kr_query *qry,
+		const knot_rrset_t *rr, const knot_rrset_t *rr_sigs, uint32_t timestamp,
+		uint8_t rank, trie_t *nsec_pmap, bool *has_optout)
+{
+	assert(stash_rrset_precond(rr, qry) > 0);
+	if (!cache) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+
+	const int wild_labels = rr_sigs == NULL ? 0 :
+	       knot_dname_labels(rr->owner, NULL) - knot_rrsig_labels(rr_sigs->rrs.rdata);
+	if (wild_labels < 0) {
+		return kr_ok();
+	}
+	const knot_dname_t *encloser = rr->owner; /**< the closest encloser name */
+	for (int i = 0; i < wild_labels; ++i) {
+		encloser = knot_wire_next_label(encloser, NULL);
+	}
+	int ret = 0;
+
+	/* Construct the key under which RRs will be stored,
+	 * and add corresponding nsec_pmap item (if necessary). */
+	struct key k_storage, *k = &k_storage;
+	knot_db_val_t key;
+	switch (rr->type) {
+	case KNOT_RRTYPE_NSEC3:
+		/* Skip "suspicious" or opt-out NSEC3 sets. */
+		if (rr->rrs.count != 1) return kr_ok();
+		if (KNOT_NSEC3_FLAG_OPT_OUT & knot_nsec3_flags(rr->rrs.rdata)) {
+			if (has_optout) *has_optout = true;
+			return kr_ok();
+		}
+		/* fall through */
+	case KNOT_RRTYPE_NSEC:
+		if (!kr_rank_test(rank, KR_RANK_SECURE)) {
+			/* Skip any NSEC*s that aren't validated. */
+			return kr_ok();
+		}
+		if (!rr_sigs || !rr_sigs->rrs.count || !rr_sigs->rrs.rdata) {
+			assert(!EINVAL);
+			return kr_error(EINVAL);
+		}
+		const knot_dname_t *signer = knot_rrsig_signer_name(rr_sigs->rrs.rdata);
+		const int signer_size = knot_dname_size(signer);
+		k->zlf_len = signer_size - 1;
+
+		void **npp = nsec_pmap == NULL ? NULL
+			: trie_get_ins(nsec_pmap, (const char *)signer, signer_size);
+		assert(!nsec_pmap || (npp && ENOMEM));
+		if (rr->type == KNOT_RRTYPE_NSEC) {
+			key = key_NSEC1(k, encloser, wild_labels);
+			break;
+		}
+
+		assert(rr->type == KNOT_RRTYPE_NSEC3);
+		const knot_rdata_t * const rdata = rr->rrs.rdata;
+		if (rdata->len <= 4) return kr_error(EILSEQ); /*< data from outside; less trust */
+		const int np_dlen = nsec_p_rdlen(rdata->data);
+		if (np_dlen > rdata->len) return kr_error(EILSEQ);
+		key = key_NSEC3(k, encloser, nsec_p_mkHash(rdata->data));
+		if (npp && !*npp) {
+			*npp = mm_alloc(&qry->request->pool, np_dlen);
+			if (!*npp) {
+				assert(!ENOMEM);
+				break;
+			}
+			memcpy(*npp, rdata->data, np_dlen);
+		}
+		break;
+	default:
+		ret = kr_dname_lf(k->buf, encloser, wild_labels);
+		if (ret) {
+			assert(!ret);
+			return kr_error(ret);
+		}
+		key = key_exact_type(k, rr->type);
+	}
+
+	/* Compute materialized sizes of the new data. */
+	const knot_rdataset_t *rds_sigs = rr_sigs ? &rr_sigs->rrs : NULL;
+	const int rr_ssize = rdataset_dematerialize_size(&rr->rrs);
+	assert(rr_ssize == to_even(rr_ssize));
+	knot_db_val_t val_new_entry = {
+		.data = NULL,
+		.len = offsetof(struct entry_h, data) + rr_ssize
+			+ rdataset_dematerialize_size(rds_sigs),
+	};
+
+	/* Prepare raw memory for the new entry. */
+	ret = entry_h_splice(&val_new_entry, rank, key, k->type, rr->type,
+				rr->owner, qry, cache, timestamp);
+	if (ret) return kr_ok(); /* some aren't really errors */
+	assert(val_new_entry.data);
+
+	const uint32_t ttl = rr->ttl;
+	/* FIXME: consider TTLs and expirations of RRSIGs as well, just in case. */
+
+	/* Write the entry itself. */
+	struct entry_h *eh = val_new_entry.data;
+	memset(eh, 0, offsetof(struct entry_h, data));
+	eh->time = timestamp;
+	eh->ttl  = MAX(MIN(ttl, cache->ttl_max), cache->ttl_min);
+	eh->rank = rank;
+	if (rdataset_dematerialize(&rr->rrs, eh->data)
+	    || rdataset_dematerialize(rds_sigs, eh->data + rr_ssize)) {
+		/* minimize the damage from incomplete write; TODO: better */
+		eh->time = 0;
+		eh->ttl = 0;
+		eh->rank = 0;
+		assert(false);
+	}
+	assert(entry_h_consistent(val_new_entry, rr->type));
+
+	#if 0 /* Occasionally useful when debugging some kinds of changes. */
+	{
+	kr_cache_sync(cache);
+	knot_db_val_t val = { NULL, 0 };
+	ret = cache_op(cache, read, &key, &val, 1);
+	if (ret != kr_error(ENOENT)) { // ENOENT might happen in some edge case, I guess
+		assert(!ret);
+		entry_list_t el;
+		entry_list_parse(val, el);
+	}
+	}
+	#endif
+
+	/* Update metrics */
+	cache->stats.insert += 1;
+
+	/* Verbose-log some not-too-common cases. */
+	WITH_VERBOSE(qry) { if (kr_rank_test(rank, KR_RANK_AUTH)
+				|| rr->type == KNOT_RRTYPE_NS) {
+		auto_free char *type_str = kr_rrtype_text(rr->type),
+			*encl_str = kr_dname_text(encloser);
+		VERBOSE_MSG(qry, "=> stashed %s%s %s, rank 0%.2o, "
+			"%d B total, incl. %d RRSIGs\n",
+			(wild_labels ? "*." : ""), encl_str, type_str, rank,
+			(int)val_new_entry.len, (rr_sigs ? rr_sigs->rrs.count : 0)
+			);
+	} }
+
+	return (ssize_t) val_new_entry.len;
+}
+
+static int stash_rrarray_entry(ranked_rr_array_t *arr, int arr_i,
+			const struct kr_query *qry, struct kr_cache *cache,
+			int *unauth_cnt, trie_t *nsec_pmap, bool *has_optout)
+{
+	ranked_rr_array_entry_t *entry = arr->at[arr_i];
+	if (entry->cached) {
+		return kr_ok();
+	}
+	const knot_rrset_t *rr = entry->rr;
+	if (rr->type == KNOT_RRTYPE_RRSIG) {
+		return kr_ok(); /* reduce verbose logging from the following call */
+	}
+	int ret = stash_rrset_precond(rr, qry);
+	if (ret <= 0) {
+		return ret;
+	}
+
+	/* Try to find corresponding signatures, always.  LATER(optim.): speed. */
+	ranked_rr_array_entry_t *entry_rrsigs = NULL;
+	const knot_rrset_t *rr_sigs = NULL;
+	for (ssize_t j = arr->len - 1; j >= 0; --j) {
+		/* TODO: ATM we assume that some properties are the same
+		 * for all RRSIGs in the set (esp. label count). */
+		ranked_rr_array_entry_t *e = arr->at[j];
+		bool ok = e->qry_uid == qry->uid && !e->cached
+			&& e->rr->type == KNOT_RRTYPE_RRSIG
+			&& knot_rrsig_type_covered(e->rr->rrs.rdata) == rr->type
+			&& knot_dname_is_equal(rr->owner, e->rr->owner);
+		if (!ok) continue;
+		entry_rrsigs = e;
+		rr_sigs = e->rr;
+		break;
+	}
+
+	ssize_t written = stash_rrset(cache, qry, rr, rr_sigs, qry->timestamp.tv_sec,
+					entry->rank, nsec_pmap, has_optout);
+	if (written < 0) {
+		kr_log_error("[%05u.%02u][cach] stash failed, ret = %d\n", qry->request->uid,
+			     qry->uid, ret);
+		return (int) written;
+	}
+
+	if (written > 0) {
+		/* Mark entry as cached for the rest of the query processing */
+		entry->cached = true;
+		if (entry_rrsigs) {
+			entry_rrsigs->cached = true;
+		}
+		if (!kr_rank_test(entry->rank, KR_RANK_AUTH) && rr->type != KNOT_RRTYPE_NS) {
+			*unauth_cnt += 1;
+		}
+	}
+
+	return kr_ok();
+}
+
+static int stash_nsec_p(const knot_dname_t *dname, const char *nsec_p_v,
+			struct kr_request *req)
+{
+	const struct kr_query *qry = req->current_query;
+	struct kr_cache *cache = &req->ctx->cache;
+	uint32_t valid_until = qry->timestamp.tv_sec + cache->ttl_max;
+		/* LATER(optim.): be more precise here ^^ and reduce calls. */
+	static const int32_t ttl_margin = 3600;
+	const uint8_t *nsec_p = (const uint8_t *)nsec_p_v;
+	int data_stride = sizeof(valid_until) + nsec_p_rdlen(nsec_p);
+
+	unsigned int log_hash = 0xFeeeFeee; /* this type is simpler for printf args */
+	auto_free char *log_dname = NULL;
+	WITH_VERBOSE(qry) {
+		log_hash = nsec_p_v ? nsec_p_mkHash((const uint8_t *)nsec_p_v) : 0;
+		log_dname = kr_dname_text(dname);
+	}
+	/* Find what's in the cache. */
+	struct key k_storage, *k = &k_storage;
+	int ret = kr_dname_lf(k->buf, dname, false);
+	if (ret) return kr_error(ret);
+	knot_db_val_t key = key_exact_type(k, KNOT_RRTYPE_NS);
+	knot_db_val_t val_orig = { NULL, 0 };
+	ret = cache_op(cache, read, &key, &val_orig, 1);
+	if (ret && ret != -ABS(ENOENT)) {
+		VERBOSE_MSG(qry, "=> EL read failed (ret: %d)\n", ret);
+		return kr_ok();
+	}
+	/* Prepare new entry_list_t so we can just write at el[0]. */
+	entry_list_t el;
+	int log_refresh_by = 0;
+	if (ret == -ABS(ENOENT)) {
+		memset(el, 0, sizeof(el));
+	} else {
+		ret = entry_list_parse(val_orig, el);
+		if (ret) {
+			VERBOSE_MSG(qry, "=> EL parse failed (ret: %d)\n", ret);
+			return kr_error(0);
+		}
+		/* Find the index to replace. */
+		int i_replace = ENTRY_APEX_NSECS_CNT - 1;
+		for (int i = 0; i < ENTRY_APEX_NSECS_CNT; ++i) {
+			if (el[i].len != data_stride) continue;
+			if (nsec_p && memcmp(nsec_p, (uint8_t *)el[i].data + sizeof(uint32_t),
+						data_stride - sizeof(uint32_t)) != 0) {
+				continue;
+			}
+			/* Save a cache operation if TTL extended only a little. */
+			uint32_t valid_orig;
+			memcpy(&valid_orig, el[i].data, sizeof(valid_orig));
+			const int32_t ttl_extended_by = valid_until - valid_orig;
+			if (ttl_extended_by < ttl_margin) {
+				VERBOSE_MSG(qry,
+					"=> nsec_p stash for %s skipped (extra TTL: %d, hash: %x)\n",
+					log_dname, ttl_extended_by, log_hash);
+				return kr_ok();
+			}
+			i_replace = i;
+			log_refresh_by = ttl_extended_by;
+			break;
+		}
+		/* Shift the other indices: move the first `i_replace` blocks
+		 * by one position. */
+		if (i_replace) {
+			memmove(&el[1], &el[0], sizeof(el[0]) * i_replace);
+		}
+	}
+	/* Prepare old data into a buffer.  See entry_h_splice() for why.  LATER(optim.) */
+	el[0].len = data_stride;
+	el[0].data = NULL;
+	knot_db_val_t val;
+	val.len = entry_list_serial_size(el),
+	val.data = mm_alloc(&req->pool, val.len),
+	entry_list_memcpy(val.data, el);
+	/* Prepare the new data chunk */
+	memcpy(el[0].data, &valid_until, sizeof(valid_until));
+	if (nsec_p) {
+		memcpy((uint8_t *)el[0].data + sizeof(valid_until), nsec_p,
+			data_stride - sizeof(valid_until));
+	}
+	/* Write it all to the cache */
+	ret = cache_op(cache, write, &key, &val, 1);
+	if (ret || !val.data) {
+		VERBOSE_MSG(qry, "=> EL write failed (ret: %d)\n", ret);
+		return kr_ok();
+	}
+	if (log_refresh_by) {
+		VERBOSE_MSG(qry, "=> nsec_p stashed for %s (refresh by %d, hash: %x)\n",
+				log_dname, log_refresh_by, log_hash);
+	} else {
+		VERBOSE_MSG(qry, "=> nsec_p stashed for %s (new, hash: %x)\n",
+				log_dname, log_hash);
+	}
+	return kr_ok();
+}
+
+
+static int peek_exact_real(struct kr_cache *cache, const knot_dname_t *name, uint16_t type,
+			struct kr_cache_p *peek)
+{
+	if (!check_rrtype(type, NULL) || !check_dname_for_lf(name, NULL)) {
+		return kr_error(ENOTSUP);
+	}
+	struct key k_storage, *k = &k_storage;
+
+	int ret = kr_dname_lf(k->buf, name, false);
+	if (ret) return kr_error(ret);
+
+	knot_db_val_t key = key_exact_type(k, type);
+	knot_db_val_t val = { NULL, 0 };
+	ret = cache_op(cache, read, &key, &val, 1);
+	if (!ret) ret = entry_h_seek(&val, type);
+	if (ret) return kr_error(ret);
+
+	const struct entry_h *eh = entry_h_consistent(val, type);
+	if (!eh || eh->is_packet) {
+		// TODO: no packets, but better get rid of whole kr_cache_peek_exact().
+		return kr_error(ENOENT);
+	}
+	*peek = (struct kr_cache_p){
+		.time = eh->time,
+		.ttl  = eh->ttl,
+		.rank = eh->rank,
+		.raw_data = val.data,
+		.raw_bound = knot_db_val_bound(val),
+	};
+	return kr_ok();
+}
+int kr_cache_peek_exact(struct kr_cache *cache, const knot_dname_t *name, uint16_t type,
+			struct kr_cache_p *peek)
+{	/* Just wrap with extra verbose logging. */
+	const int ret = peek_exact_real(cache, name, type, peek);
+	if (false && VERBOSE_STATUS) { /* too noisy for usual --verbose */
+		auto_free char *type_str = kr_rrtype_text(type),
+			*name_str = kr_dname_text(name);
+		const char *result_str = (ret == kr_ok() ? "hit" :
+				(ret == kr_error(ENOENT) ? "miss" : "error"));
+		VERBOSE_MSG(NULL, "_peek_exact: %s %s %s (ret: %d)",
+				type_str, name_str, result_str, ret);
+	}
+	return ret;
+}
+
+int kr_cache_remove(struct kr_cache *cache, const knot_dname_t *name, uint16_t type)
+{
+	if (!cache_isvalid(cache)) {
+		return kr_error(EINVAL);
+	}
+	if (!cache->api->remove) {
+		return kr_error(ENOSYS);
+	}
+	struct key k_storage, *k = &k_storage;
+	int ret = kr_dname_lf(k->buf, name, false);
+	if (ret) return kr_error(ret);
+
+	knot_db_val_t key = key_exact_type(k, type);
+	return cache_op(cache, remove, &key, 1);
+}
+
+int kr_cache_match(struct kr_cache *cache, const knot_dname_t *name,
+		   bool exact_name, knot_db_val_t keyval[][2], int maxcount)
+{
+	if (!cache_isvalid(cache)) {
+		return kr_error(EINVAL);
+	}
+	if (!cache->api->match) {
+		return kr_error(ENOSYS);
+	}
+
+	struct key k_storage, *k = &k_storage;
+
+	int ret = kr_dname_lf(k->buf, name, false);
+	if (ret) return kr_error(ret);
+
+	// use a mock type
+	knot_db_val_t key = key_exact_type(k, KNOT_RRTYPE_A);
+	/* CACHE_KEY_DEF */
+	key.len -= sizeof(uint16_t); /* the type */
+	if (!exact_name) {
+		key.len -= 2; /* '\0' 'E' */
+		if (name[0] == '\0') ++key.len; /* the root name is special ATM */
+	}
+	return cache_op(cache, match, &key, keyval, maxcount);
+}
+
+int kr_unpack_cache_key(knot_db_val_t key, knot_dname_t *buf, uint16_t *type)
+{
+	if (key.data == NULL || buf == NULL || type == NULL) {
+		return kr_error(EINVAL);
+	}
+
+	int len = -1;
+	const char *tag, *key_data = key.data;
+	for (tag = key_data + 1; tag < key_data + key.len; ++tag) {
+		/* CACHE_KEY_DEF */
+		if (tag[-1] == '\0' && (tag == key_data + 1 || tag[-2] == '\0')) {
+			if (tag[0] != 'E') return kr_error(EINVAL);
+			len = tag - 1 - key_data;
+			break;
+		}
+	}
+
+	if (len == -1 || len > KNOT_DNAME_MAXLEN) {
+		return kr_error(EINVAL);
+	}
+
+	int ret = knot_dname_lf2wire(buf, len, key.data);
+	if (ret < 0) {
+		return kr_error(ret);
+	}
+
+	/* CACHE_KEY_DEF: jump over "\0 E/1" */
+	memcpy(type, tag + 1, sizeof(uint16_t));
+
+	return kr_ok();
+}
+
+
+int kr_cache_remove_subtree(struct kr_cache *cache, const knot_dname_t *name,
+			    bool exact_name, int maxcount)
+{
+	if (!cache_isvalid(cache)) {
+		return kr_error(EINVAL);
+	}
+
+	knot_db_val_t keyval[maxcount][2], keys[maxcount];
+	int ret = kr_cache_match(cache, name, exact_name, keyval, maxcount);
+	if (ret <= 0) { /* ENOENT -> nothing to remove */
+		return (ret == KNOT_ENOENT) ? 0 : ret;
+	}
+	const int count = ret;
+	/* Duplicate the key strings, as deletion may invalidate the pointers. */
+	int i;
+	for (i = 0; i < count; ++i) {
+		keys[i].len = keyval[i][0].len;
+		keys[i].data = malloc(keys[i].len);
+		if (!keys[i].data) {
+			ret = kr_error(ENOMEM);
+			goto cleanup;
+		}
+		memcpy(keys[i].data, keyval[i][0].data, keys[i].len);
+	}
+	ret = cache->api->remove(cache->db, keys, count);
+cleanup:
+	kr_cache_sync(cache); /* Sync even after just kr_cache_match(). */
+	/* Free keys */
+	while (--i >= 0) {
+		free(keys[i].data);
+	}
+	return ret;
+}
+
diff --git a/lib/cache/api.h b/lib/cache/api.h
new file mode 100644
index 0000000..61bf796
--- /dev/null
+++ b/lib/cache/api.h
@@ -0,0 +1,201 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <libknot/consts.h>
+#include <libknot/rrset.h>
+#include <sys/time.h>
+#include "lib/cache/cdb_api.h"
+#include "lib/defines.h"
+#include "contrib/ucw/config.h" /*uint*/
+
+/** When knot_pkt is passed from cache without ->wire, this is the ->size. */
+static const size_t PKT_SIZE_NOWIRE = -1;
+
+
+#include "lib/module.h"
+/* Prototypes for the 'cache' module implementation. */
+int cache_peek(kr_layer_t *ctx, knot_pkt_t *pkt);
+int cache_stash(kr_layer_t *ctx, knot_pkt_t *pkt);
+
+
+/**
+ * Cache structure, keeps API, instance and metadata.
+ */
+struct kr_cache
+{
+	knot_db_t *db;		      /**< Storage instance */
+	const struct kr_cdb_api *api; /**< Storage engine */
+	struct {
+		uint32_t hit;         /**< Number of cache hits */
+		uint32_t miss;        /**< Number of cache misses */
+		uint32_t insert;      /**< Number of insertions */
+		uint32_t delete;      /**< Number of deletions */
+	} stats;
+
+	uint32_t ttl_min, ttl_max; /**< TTL limits */
+
+	/* A pair of stamps for detection of real-time shifts during runtime. */
+	struct timeval checkpoint_walltime; /**< Wall time on the last check-point. */
+	uint64_t checkpoint_monotime; /**< Monotonic milliseconds on the last check-point. */
+};
+
+/**
+ * Open/create cache with provided storage options.
+ * @param cache cache structure to be initialized
+ * @param api   storage engine API
+ * @param opts  storage-specific options (may be NULL for default)
+ * @param mm    memory context.
+ * @return 0 or an error code
+ */
+KR_EXPORT
+int kr_cache_open(struct kr_cache *cache, const struct kr_cdb_api *api, struct kr_cdb_opts *opts, knot_mm_t *mm);
+
+/**
+ * Path to cache file to remove on critical out-of-space error. (do NOT modify it)
+ */
+KR_EXPORT extern
+const char *kr_cache_emergency_file_to_remove;
+
+/**
+ * Close persistent cache.
+ * @note This doesn't clear the data, just closes the connection to the database.
+ * @param cache structure
+ */
+KR_EXPORT
+void kr_cache_close(struct kr_cache *cache);
+
+/** Run after a row of operations to release transaction/lock if needed. */
+KR_EXPORT
+int kr_cache_sync(struct kr_cache *cache);
+
+/**
+ * Return true if cache is open and enabled.
+ */
+static inline bool kr_cache_is_open(struct kr_cache *cache)
+{
+	return cache->db != NULL;
+}
+
+/** (Re)set the time pair to the current values. */
+static inline void kr_cache_make_checkpoint(struct kr_cache *cache)
+{
+	cache->checkpoint_monotime = kr_now();
+	gettimeofday(&cache->checkpoint_walltime, NULL);
+}
+
+/**
+ * Insert RRSet into cache, replacing any existing data.
+ * @param cache cache structure
+ * @param rr inserted RRSet
+ * @param rrsig RRSIG for inserted RRSet (optional)
+ * @param rank rank of the data
+ * @param timestamp current time
+ * @return 0 or an errcode
+ */
+KR_EXPORT
+int kr_cache_insert_rr(struct kr_cache *cache, const knot_rrset_t *rr, const knot_rrset_t *rrsig, uint8_t rank, uint32_t timestamp);
+
+/**
+ * Clear all items from the cache.
+ * @param cache cache structure
+ * @return 0 or an errcode
+ */
+KR_EXPORT
+int kr_cache_clear(struct kr_cache *cache);
+
+
+/* ** This interface is temporary. ** */
+
+struct kr_cache_p {
+	uint32_t time;	/**< The time of inception. */
+	uint32_t ttl;	/**< TTL at inception moment.  Assuming it fits into int32_t ATM. */
+	uint8_t  rank;	/**< See enum kr_rank */
+	struct {
+		/* internal: pointer to eh struct */
+		void *raw_data, *raw_bound;
+	};
+};
+KR_EXPORT
+int kr_cache_peek_exact(struct kr_cache *cache, const knot_dname_t *name, uint16_t type,
+			struct kr_cache_p *peek);
+/* Parameters (qry, name, type) are used for timestamp and stale-serving decisions. */
+KR_EXPORT
+int32_t kr_cache_ttl(const struct kr_cache_p *peek, const struct kr_query *qry,
+		     const knot_dname_t *name, uint16_t type);
+
+KR_EXPORT
+int kr_cache_materialize(knot_rdataset_t *dst, const struct kr_cache_p *ref,
+			 knot_mm_t *pool);
+
+
+/**
+ * Remove an entry from cache.
+ * @param cache cache structure
+ * @param name dname
+ * @param type rr type
+ * @return number of deleted records, or negative error code
+ * @note only "exact hits" are considered ATM, and
+ * 	some other information may be removed alongside.
+ */
+KR_EXPORT
+int kr_cache_remove(struct kr_cache *cache, const knot_dname_t *name, uint16_t type);
+
+/**
+ * Get keys matching a dname lf prefix
+ * @param cache cache structure
+ * @param name dname
+ * @param exact_name whether to only consider exact name matches
+ * @param keyval matched key-value pairs
+ * @param maxcount limit on the number of returned key-value pairs
+ * @return result count or an errcode
+ * @note the cache keys are matched by prefix, i.e. it very much depends
+ * 	on their structure; CACHE_KEY_DEF.
+ */
+KR_EXPORT
+int kr_cache_match(struct kr_cache *cache, const knot_dname_t *name,
+		   bool exact_name, knot_db_val_t keyval[][2], int maxcount);
+
+/**
+ * Remove a subtree in cache.  It's like _match but removing them instead of returning.
+ * @return number of deleted entries or an errcode
+ */
+KR_EXPORT
+int kr_cache_remove_subtree(struct kr_cache *cache, const knot_dname_t *name,
+			    bool exact_name, int maxcount);
+
+/**
+ * Find the closest cached zone apex for a name (in cache).
+ * @param is_DS start searching one name higher
+ * @return the number of labels to remove from the name, or negative error code
+ * @note timestamp is found by a syscall, and stale-serving is not considered
+ */
+KR_EXPORT
+int kr_cache_closest_apex(struct kr_cache *cache, const knot_dname_t *name, bool is_DS,
+			  knot_dname_t **apex);
+
+/**
+ * Unpack dname and type from db key
+ * @param key db key representation
+ * @param buf output buffer of domain name in dname format
+ * @param type output for type
+ * @return length of dname or an errcode
+ * @note only "exact hits" are considered ATM, moreover xNAME records
+ * 	are "hidden" as NS. (see comments in struct entry_h)
+ */
+KR_EXPORT
+int kr_unpack_cache_key(knot_db_val_t key, knot_dname_t *buf, uint16_t *type);
diff --git a/lib/cache/cdb_api.h b/lib/cache/cdb_api.h
new file mode 100644
index 0000000..814a5f5
--- /dev/null
+++ b/lib/cache/cdb_api.h
@@ -0,0 +1,68 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include <libknot/db/db.h>
+
+/* Cache options. */
+struct kr_cdb_opts {
+	const char *path; /*!< Cache URI path. */
+	size_t maxsize;   /*!< Suggested cache size in bytes. */
+};
+
+/*! Cache database API.
+  * This is a simplified version of generic DB API from libknot,
+  * that is tailored to caching purposes.
+  */
+struct kr_cdb_api {
+	const char *name;
+
+	/* Context operations */
+
+	int (*open)(knot_db_t **db, struct kr_cdb_opts *opts, knot_mm_t *mm);
+	void (*close)(knot_db_t *db);
+	int (*count)(knot_db_t *db);
+	int (*clear)(knot_db_t *db);
+
+	/** Run after a row of operations to release transaction/lock if needed. */
+	int (*sync)(knot_db_t *db);
+
+	/* Data access */
+
+	int (*read)(knot_db_t *db, const knot_db_val_t *key, knot_db_val_t *val,
+			int maxcount);
+	int (*write)(knot_db_t *db, const knot_db_val_t *key, knot_db_val_t *val,
+			int maxcount);
+
+	/** Remove maxcount keys.
+	 * \returns the number of succesfully removed keys or the first error code
+	 * It returns on first error, but ENOENT is not considered an error. */
+	int (*remove)(knot_db_t *db, knot_db_val_t keys[], int maxcount);
+
+	/* Specialised operations */
+
+	/** Find key-value pairs that are prefixed by the given key, limited by maxcount.
+	 * \return the number of pairs or negative error. */
+	int (*match)(knot_db_t *db, knot_db_val_t *key, knot_db_val_t keyval[][2], int maxcount);
+	/** Not implemented ATM. */
+	int (*prune)(knot_db_t *db, int maxcount);
+
+	/** Less-or-equal search (lexicographic ordering).
+	 * On successful return, key->data and val->data point to DB-owned data.
+	 * return: 0 for equality, > 0 for less, < 0 kr_error */
+	int (*read_leq)(knot_db_t *db, knot_db_val_t *key, knot_db_val_t *val);
+};
diff --git a/lib/cache/cdb_lmdb.c b/lib/cache/cdb_lmdb.c
new file mode 100644
index 0000000..621d2e8
--- /dev/null
+++ b/lib/cache/cdb_lmdb.c
@@ -0,0 +1,710 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+#include <assert.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <lmdb.h>
+
+#include "contrib/cleanup.h"
+#include "lib/cache/cdb_lmdb.h"
+#include "lib/cache/api.h"
+#include "lib/utils.h"
+
+
+/* Defines */
+#define LMDB_DIR_MODE   0770
+#define LMDB_FILE_MODE  0660
+
+struct lmdb_env
+{
+	size_t mapsize;
+	MDB_dbi dbi;
+	MDB_env *env;
+
+	/** Cached transactions
+	 *
+	 * - only one of (ro,rw) may be active at once
+	 * - non-NULL .ro may be active or reset
+	 * - non-NULL .rw is always active
+	 */
+	struct {
+		bool ro_active, ro_curs_active;
+		MDB_txn *ro, *rw;
+		MDB_cursor *ro_curs;
+	} txn;
+};
+
+/** @brief Convert LMDB error code. */
+static int lmdb_error(int error)
+{
+	/* _BAD_TXN may happen with overfull DB,
+	 * even during mdb_get with a single fork :-/ */
+	if (error == MDB_BAD_TXN) {
+		kr_log_info("[cache] MDB_BAD_TXN, probably overfull\n");
+		error = ENOSPC;
+	}
+	switch (error) {
+	case MDB_SUCCESS:
+		return kr_ok();
+	case MDB_NOTFOUND:
+		return kr_error(ENOENT);
+	case ENOSPC:
+	case MDB_MAP_FULL:
+	case MDB_TXN_FULL:
+		return kr_error(ENOSPC);
+	default:
+		kr_log_error("[cache] LMDB error: %s\n", mdb_strerror(error));
+		return kr_error(error);
+	}
+}
+
+/** Conversion between knot and lmdb structs for values. */
+static inline knot_db_val_t val_mdb2knot(MDB_val v)
+{
+	return (knot_db_val_t){ .len = v.mv_size, .data = v.mv_data };
+}
+static inline MDB_val val_knot2mdb(knot_db_val_t v)
+{
+	return (MDB_val){ .mv_size = v.len, .mv_data = v.data };
+}
+
+
+/*! \brief Set the environment map size.
+ * \note This also sets the maximum database size, see \fn mdb_env_set_mapsize
+ */
+static int set_mapsize(MDB_env *env, size_t map_size)
+{
+	long page_size = sysconf(_SC_PAGESIZE);
+	if (page_size <= 0) {
+		return KNOT_ERROR;
+	}
+
+	/* Round to page size. */
+	map_size = (map_size / page_size) * page_size;
+	int ret = mdb_env_set_mapsize(env, map_size);
+	if (ret != MDB_SUCCESS) {
+		return lmdb_error(ret);
+	}
+
+	return 0;
+}
+
+#define FLAG_RENEW (2*MDB_RDONLY)
+/** mdb_txn_begin or _renew + handle MDB_MAP_RESIZED.
+ *
+ * The retrying logic for MDB_MAP_RESIZED is so ugly that it has its own function.
+ * \note this assumes no transactions are active
+ * \return MDB_ errcode, not usual kr_error(...)
+ */
+static int txn_get_noresize(struct lmdb_env *env, unsigned int flag, MDB_txn **txn)
+{
+	assert(!env->txn.rw && (!env->txn.ro || !env->txn.ro_active));
+	int ret;
+	if (flag == FLAG_RENEW) {
+		ret = mdb_txn_renew(*txn);
+	} else {
+		ret = mdb_txn_begin(env->env, NULL, flag, txn);
+	}
+	if (ret != MDB_MAP_RESIZED) {
+		return ret;
+	}
+	//:unlikely
+	/* Another process increased the size; let's try to recover. */
+	kr_log_info("[cache] detected size increased by another process\n");
+	ret = mdb_env_set_mapsize(env->env, 0);
+	if (ret != MDB_SUCCESS) {
+		return ret;
+	}
+	if (flag == FLAG_RENEW) {
+		ret = mdb_txn_renew(*txn);
+	} else {
+		ret = mdb_txn_begin(env->env, NULL, flag, txn);
+	}
+	return ret;
+}
+
+/** Obtain a transaction.  (they're cached in env->txn) */
+static int txn_get(struct lmdb_env *env, MDB_txn **txn, bool rdonly)
+{
+	assert(env && txn);
+	if (env->txn.rw) {
+		/* Reuse the *open* RW txn even if only reading is requested.
+		 * We leave the management of this to the cdb_sync command.
+		 * The user may e.g. want to do some reads between the writes. */
+		*txn = env->txn.rw;
+		return kr_ok();
+	}
+
+	if (!rdonly) {
+		/* avoid two active transactions */
+		if (env->txn.ro && env->txn.ro_active) {
+			mdb_txn_reset(env->txn.ro);
+			env->txn.ro_active = false;
+			env->txn.ro_curs_active = false;
+		}
+		int ret = txn_get_noresize(env, 0/*RW*/, &env->txn.rw);
+		if (ret == MDB_SUCCESS) {
+			*txn = env->txn.rw;
+			assert(*txn);
+		}
+		return lmdb_error(ret);
+	}
+
+	/* Get an active RO txn and return it. */
+	int ret = MDB_SUCCESS;
+	if (!env->txn.ro) { //:unlikely
+		ret = txn_get_noresize(env, MDB_RDONLY, &env->txn.ro);
+	} else if (!env->txn.ro_active) {
+		ret = txn_get_noresize(env, FLAG_RENEW, &env->txn.ro);
+	}
+	if (ret != MDB_SUCCESS) {
+		return lmdb_error(ret);
+	}
+	env->txn.ro_active = true;
+	*txn = env->txn.ro;
+	assert(*txn);
+	return kr_ok();
+}
+
+static int cdb_sync(knot_db_t *db)
+{
+	struct lmdb_env *env = db;
+	int ret = kr_ok();
+	if (env->txn.rw) {
+		ret = lmdb_error(mdb_txn_commit(env->txn.rw));
+		env->txn.rw = NULL; /* the transaction got freed even in case of errors */
+	} else if (env->txn.ro && env->txn.ro_active) {
+		mdb_txn_reset(env->txn.ro);
+		env->txn.ro_active = false;
+		env->txn.ro_curs_active = false;
+	}
+	return ret;
+}
+
+/** Obtain a read-only cursor (and a read-only transaction). */
+static int txn_curs_get(struct lmdb_env *env, MDB_cursor **curs)
+{
+	assert(env && curs);
+	if (env->txn.ro_curs_active) {
+		goto success;
+	}
+	/* Only in a read-only txn; TODO: it's a bit messy/coupled */
+	if (env->txn.rw) {
+		int ret = cdb_sync(env);
+		if (ret) return ret;
+	}
+	MDB_txn *txn = NULL;
+	int ret = txn_get(env, &txn, true);
+	if (ret) return ret;
+
+	if (env->txn.ro_curs) {
+		ret = mdb_cursor_renew(txn, env->txn.ro_curs);
+	} else {
+		ret = mdb_cursor_open(txn, env->dbi, &env->txn.ro_curs);
+	}
+	if (ret) return ret;
+	env->txn.ro_curs_active = true;
+success:
+	assert(env->txn.ro_curs_active && env->txn.ro && env->txn.ro_active
+		&& !env->txn.rw);
+	*curs = env->txn.ro_curs;
+	assert(*curs);
+	return kr_ok();
+}
+
+static void free_txn_ro(struct lmdb_env *env)
+{
+	if (env->txn.ro) {
+		mdb_txn_abort(env->txn.ro);
+		env->txn.ro = NULL;
+	}
+	if (env->txn.ro_curs) {
+		mdb_cursor_close(env->txn.ro_curs);
+		env->txn.ro_curs = NULL;
+	}
+}
+
+/*! \brief Close the database. */
+static void cdb_close_env(struct lmdb_env *env)
+{
+	assert(env && env->env);
+
+	/* Get rid of any transactions. */
+	cdb_sync(env);
+	free_txn_ro(env);
+
+	mdb_env_sync(env->env, 1);
+	mdb_dbi_close(env->env, env->dbi);
+	mdb_env_close(env->env);
+	memset(env, 0, sizeof(*env));
+}
+
+/*! \brief Open database environment. */
+static int cdb_open_env(struct lmdb_env *env, unsigned flags, const char *path, size_t mapsize)
+{
+	int ret = mkdir(path, LMDB_DIR_MODE);
+	if (ret == -1 && errno != EEXIST) {
+		return kr_error(errno);
+	}
+
+	MDB_env *mdb_env = NULL;
+	ret = mdb_env_create(&mdb_env);
+	if (ret != MDB_SUCCESS) {
+		return lmdb_error(ret);
+	}
+
+	ret = set_mapsize(mdb_env, mapsize);
+	if (ret != 0) {
+		mdb_env_close(mdb_env);
+		return ret;
+	}
+
+	ret = mdb_env_open(mdb_env, path, flags, LMDB_FILE_MODE);
+	if (ret != MDB_SUCCESS) {
+		mdb_env_close(mdb_env);
+		return lmdb_error(ret);
+	}
+
+	/* Keep the environment pointer. */
+	env->env = mdb_env;
+	env->mapsize = mapsize;
+	return 0;
+}
+
+static int cdb_open(struct lmdb_env *env, const char *path, size_t mapsize)
+{
+	/* Cache doesn't require durability, we can be
+	 * loose with the requirements as a tradeoff for speed. */
+	const unsigned flags = MDB_WRITEMAP | MDB_MAPASYNC | MDB_NOTLS;
+	int ret = cdb_open_env(env, flags, path, mapsize);
+	if (ret != 0) {
+		return ret;
+	}
+
+	/* Open the database. */
+	MDB_txn *txn = NULL;
+	ret = mdb_txn_begin(env->env, NULL, 0, &txn);
+	if (ret != MDB_SUCCESS) {
+		mdb_env_close(env->env);
+		return lmdb_error(ret);
+	}
+
+	ret = mdb_dbi_open(txn, NULL, 0, &env->dbi);
+	if (ret != MDB_SUCCESS) {
+		mdb_txn_abort(txn);
+		mdb_env_close(env->env);
+		return lmdb_error(ret);
+	}
+
+	ret = mdb_txn_commit(txn);
+	if (ret != MDB_SUCCESS) {
+		mdb_env_close(env->env);
+		return lmdb_error(ret);
+	}
+
+	return 0;
+}
+
+static int cdb_init(knot_db_t **db, struct kr_cdb_opts *opts, knot_mm_t *pool)
+{
+	if (!db || !opts) {
+		return kr_error(EINVAL);
+	}
+
+	struct lmdb_env *env = malloc(sizeof(*env));
+	if (!env) {
+		return kr_error(ENOMEM);
+	}
+	memset(env, 0, sizeof(struct lmdb_env));
+
+	/* Clear stale lockfiles. */
+	auto_free char *lockfile = kr_strcatdup(2, opts->path, "/.cachelock");
+	if (lockfile) {
+		if (unlink(lockfile) == 0) {
+			kr_log_info("[cache] cleared stale lockfile '%s'\n", lockfile);
+		} else if (errno != ENOENT) {
+			kr_log_info("[cache] failed to clear stale lockfile '%s': %s\n", lockfile,
+				    strerror(errno));
+		}
+	}
+
+	/* Open the database. */
+	int ret = cdb_open(env, opts->path, opts->maxsize);
+	if (ret != 0) {
+		free(env);
+		return ret;
+	}
+
+	*db = env;
+	return 0;
+}
+
+static void cdb_deinit(knot_db_t *db)
+{
+	struct lmdb_env *env = db;
+	cdb_close_env(env);
+	free(env);
+}
+
+static int cdb_count(knot_db_t *db)
+{
+	struct lmdb_env *env = db;
+	MDB_txn *txn = NULL;
+	int ret = txn_get(env, &txn, true);
+	if (ret != 0) {
+		return ret;
+	}
+
+	MDB_stat stat;
+	ret = mdb_stat(txn, env->dbi, &stat);
+
+	return (ret == MDB_SUCCESS) ? stat.ms_entries : lmdb_error(ret);
+}
+
+static int cdb_clear(knot_db_t *db)
+{
+	struct lmdb_env *env = db;
+	/* First try mdb_drop() to clear the DB; this may fail with ENOSPC. */
+	/* If we didn't do this, explicit cache.clear() ran on an instance
+	 * would lead to the instance detaching from the cache of others,
+	 * until they reopened cache explicitly or cleared it for some reason.
+	 */
+	{
+		MDB_txn *txn = NULL;
+		int ret = txn_get(env, &txn, false);
+		if (ret == kr_ok()) {
+			ret = lmdb_error(mdb_drop(txn, env->dbi, 0));
+			if (ret == kr_ok()) {
+				ret = cdb_sync(db);
+			}
+			if (ret == kr_ok()) {
+				return ret;
+			}
+		}
+		kr_log_info("[cache] clearing error, falling back\n");
+	}
+
+	/* We are about to switch to a different file, so end all txns, to be sure. */
+	(void) cdb_sync(db);
+	free_txn_ro(db);
+
+	/* Since there is no guarantee that there will be free
+	 * pages to hold whole dirtied db for transaction-safe clear,
+	 * we simply remove the database files and reopen.
+	 * We can afford this since other readers will continue to read
+	 * from removed file, but will reopen when encountering next
+	 * error. */
+	mdb_filehandle_t fd = -1;
+	int ret = mdb_env_get_fd(env->env, &fd);
+	if (ret != MDB_SUCCESS) {
+		return lmdb_error(ret);
+	}
+	const char *path = NULL;
+	ret = mdb_env_get_path(env->env, &path);
+	if (ret != MDB_SUCCESS) {
+		return lmdb_error(ret);
+	}
+
+	auto_free char *mdb_datafile = kr_strcatdup(2, path, "/data.mdb");
+	auto_free char *mdb_lockfile = kr_strcatdup(2, path, "/lock.mdb");
+	auto_free char *lockfile = kr_strcatdup(2, path, "/.cachelock");
+	if (!mdb_datafile || !mdb_lockfile || !lockfile) {
+		return kr_error(ENOMEM);
+	}
+	/* Find if we get a lock on lockfile. */
+	ret = open(lockfile, O_CREAT|O_EXCL|O_RDONLY, S_IRUSR);
+	if (ret == -1) {
+		kr_log_error("[cache] clearing failed to get ./.cachelock; retry later\n");
+		/* As we're out of space (almost certainly - mdb_drop didn't work),
+		 * we will retry on the next failing write operation. */
+		return kr_error(errno);
+	}
+	close(ret);
+	/* We acquired lockfile.  Now find whether *.mdb are what we have open now. */
+	struct stat old_stat, new_stat;
+	if (fstat(fd, &new_stat) || stat(mdb_datafile, &old_stat)) {
+		ret = errno;
+		unlink(lockfile);
+		return kr_error(ret);
+	}
+	/* Remove underlying files only if current open environment
+	 * points to file on the disk. Otherwise just reopen as someone
+	 * else has already removed the files.
+	 */
+	if (old_stat.st_dev == new_stat.st_dev && old_stat.st_ino == new_stat.st_ino) {
+		kr_log_verbose("[cache] clear: identical files, unlinking\n");
+		// coverity[toctou]
+		unlink(mdb_datafile);
+		unlink(mdb_lockfile);
+	} else
+		kr_log_verbose("[cache] clear: not identical files, reopening\n");
+	/* Keep copy as it points to current handle internals. */
+	auto_free char *path_copy = strdup(path);
+	size_t mapsize = env->mapsize;
+	cdb_close_env(env);
+	ret = cdb_open(env, path_copy, mapsize);
+	/* Environment updated, release lockfile. */
+	unlink(lockfile);
+	return ret;
+}
+
+static int cdb_readv(knot_db_t *db, const knot_db_val_t *key, knot_db_val_t *val,
+		     int maxcount)
+{
+	struct lmdb_env *env = db;
+	MDB_txn *txn = NULL;
+	int ret = txn_get(env, &txn, true);
+	if (ret) {
+		return ret;
+	}
+
+	for (int i = 0; i < maxcount; ++i) {
+		/* Convert key structs */
+		MDB_val _key = val_knot2mdb(key[i]);
+		MDB_val _val = val_knot2mdb(val[i]);
+		ret = mdb_get(txn, env->dbi, &_key, &_val);
+		if (ret != MDB_SUCCESS) {
+			ret = lmdb_error(ret);
+			if (ret == kr_error(ENOSPC)) {
+				/* we're likely to be forced to cache clear anyway */
+				ret = kr_error(ENOENT);
+			}
+			return ret;
+		}
+		/* Update the result. */
+		val[i] = val_mdb2knot(_val);
+	}
+	return kr_ok();
+}
+
+static int cdb_write(struct lmdb_env *env, MDB_txn **txn, const knot_db_val_t *key,
+			knot_db_val_t *val, unsigned flags)
+{
+	/* Convert key structs and write */
+	MDB_val _key = val_knot2mdb(*key);
+	MDB_val _val = val_knot2mdb(*val);
+	int ret = mdb_put(*txn, env->dbi, &_key, &_val, flags);
+
+	/* Try to recover from doing too much writing in a single transaction. */
+	if (ret == MDB_TXN_FULL) {
+		ret = cdb_sync(env);
+		if (ret) {
+			ret = txn_get(env, txn, false);
+		}
+		if (ret) {
+			ret = mdb_put(*txn, env->dbi, &_key, &_val, flags);
+		}
+	}
+	if (ret != MDB_SUCCESS) {
+		return lmdb_error(ret);
+	}
+
+	/* Update the result. */
+	val->data = _val.mv_data;
+	val->len = _val.mv_size;
+	return kr_ok();
+}
+
+static int cdb_writev(knot_db_t *db, const knot_db_val_t *key, knot_db_val_t *val,
+			int maxcount)
+{
+	struct lmdb_env *env = db;
+	MDB_txn *txn = NULL;
+	int ret = txn_get(env, &txn, false);
+
+	for (int i = 0; ret == kr_ok() && i < maxcount; ++i) {
+		/* This is LMDB specific optimisation,
+		 * if caller specifies value with NULL data and non-zero length,
+		 * LMDB will preallocate the entry for caller and leave write
+		 * transaction open, caller is responsible for syncing thus committing transaction.
+		 */
+		unsigned mdb_flags = 0;
+		if (val[i].len > 0 && val[i].data == NULL) {
+			mdb_flags |= MDB_RESERVE;
+		}
+		ret = cdb_write(env, &txn, &key[i], &val[i], mdb_flags);
+	}
+
+	return ret;
+}
+
+static int cdb_remove(knot_db_t *db, knot_db_val_t keys[], int maxcount)
+{
+	struct lmdb_env *env = db;
+	MDB_txn *txn = NULL;
+	int ret = txn_get(env, &txn, false);
+	int deleted = 0;
+
+	for (int i = 0; ret == kr_ok() && i < maxcount; ++i) {
+		MDB_val _key = val_knot2mdb(keys[i]);
+		MDB_val val = { 0, NULL };
+		ret = lmdb_error(mdb_del(txn, env->dbi, &_key, &val));
+		if (ret == kr_ok())
+			deleted++;
+		else if (ret == KNOT_ENOENT)
+			ret = kr_ok();  /* skip over non-existing entries */
+	}
+
+	return ret < 0 ? ret : deleted;
+}
+
+static int cdb_match(knot_db_t *db, knot_db_val_t *key, knot_db_val_t keyval[][2], int maxcount)
+{
+	struct lmdb_env *env = db;
+	MDB_txn *txn = NULL;
+	int ret = txn_get(env, &txn, true);
+	if (ret != 0) {
+		return ret;
+	}
+
+	/* LATER(optim.): use txn_curs_get() instead, to save resources. */
+	MDB_cursor *cur = NULL;
+	ret = mdb_cursor_open(txn, env->dbi, &cur);
+	if (ret != 0) {
+		return lmdb_error(ret);
+	}
+
+	MDB_val cur_key = val_knot2mdb(*key);
+	MDB_val cur_val = { 0, NULL };
+	ret = mdb_cursor_get(cur, &cur_key, &cur_val, MDB_SET_RANGE);
+	if (ret != MDB_SUCCESS) {
+		mdb_cursor_close(cur);
+		return lmdb_error(ret);
+	}
+
+	int results = 0;
+	while (ret == MDB_SUCCESS) {
+		/* Retrieve current key and compare with prefix */
+		if (cur_key.mv_size < key->len || memcmp(cur_key.mv_data, key->data, key->len) != 0) {
+			break;
+		}
+		/* Add to result set */
+		if (results < maxcount) {
+			keyval[results][0] = val_mdb2knot(cur_key);
+			keyval[results][1] = val_mdb2knot(cur_val);
+			++results;
+		} else {
+			break;
+		}
+		ret = mdb_cursor_get(cur, &cur_key, &cur_val, MDB_NEXT);
+	}
+
+	mdb_cursor_close(cur);
+	return results;
+}
+
+
+static int cdb_prune(knot_db_t *db, int limit)
+{
+	return -1;
+#if 0
+	/* Sync in-flight transactions */
+	cdb_sync(db);
+
+	/* Prune old records */
+	struct lmdb_env *env = db;
+	MDB_txn *txn = NULL;
+	int ret = txn_get(env, &txn, false);
+	if (ret != 0) {
+		return ret;
+	}
+
+	MDB_cursor *cur = NULL;
+	ret = mdb_cursor_open(txn, env->dbi, &cur);
+	if (ret != 0) {
+		return lmdb_error(ret);
+	}
+
+	MDB_val cur_key, cur_val;
+	ret = mdb_cursor_get(cur, &cur_key, &cur_val, MDB_FIRST);
+	if (ret != 0) {
+		mdb_cursor_close(cur);
+		return lmdb_error(ret);
+	}
+
+	int results = 0;
+	struct timeval now;
+	gettimeofday(&now, NULL);
+	while (ret == 0 && results < limit) {
+		/* Ignore special namespaces. */
+		if (cur_key.mv_size < 2 || ((const char *)cur_key.mv_data)[0] == 'V') {
+			ret = mdb_cursor_get(cur, &cur_key, &cur_val, MDB_NEXT);
+			continue;
+		}
+		/* Check entry age. */
+		struct kr_cache_entry *entry = cur_val.mv_data;
+		if (entry->timestamp > now.tv_sec ||
+			(now.tv_sec - entry->timestamp) < entry->ttl) {
+			ret = mdb_cursor_get(cur, &cur_key, &cur_val, MDB_NEXT);
+			continue;
+		}
+		/* Remove entry */
+		mdb_cursor_del(cur, 0);
+		++results;
+		ret = mdb_cursor_get(cur, &cur_key, &cur_val, MDB_NEXT);
+	}
+	mdb_cursor_close(cur);
+	return ret < 0 ? ret : results;
+#endif
+}
+
+static int cdb_read_leq(knot_db_t *env, knot_db_val_t *key, knot_db_val_t *val)
+{
+	assert(env && key && key->data && val);
+	MDB_cursor *curs = NULL;
+	int ret = txn_curs_get(env, &curs);
+	if (ret) return ret;
+
+	MDB_val key2_m = val_knot2mdb(*key);
+	MDB_val val2_m = { 0, NULL };
+	ret = mdb_cursor_get(curs, &key2_m, &val2_m, MDB_SET_RANGE);
+	if (ret) return lmdb_error(ret);
+	/* test for equality //:unlikely */
+	if (key2_m.mv_size == key->len
+	    && memcmp(key2_m.mv_data, key->data, key->len) == 0) {
+		ret = 0; /* equality */
+		goto success;
+	}
+	/* we must be greater than key; do one step to smaller */
+	ret = mdb_cursor_get(curs, &key2_m, &val2_m, MDB_PREV);
+	if (ret) return lmdb_error(ret);
+	ret = 1;
+success:
+	/* finalize the output */
+	*key = val_mdb2knot(key2_m);
+	*val = val_mdb2knot(val2_m);
+	return ret;
+}
+
+
+const struct kr_cdb_api *kr_cdb_lmdb(void)
+{
+	static const struct kr_cdb_api api = {
+		"lmdb",
+		cdb_init, cdb_deinit, cdb_count, cdb_clear, cdb_sync,
+		cdb_readv, cdb_writev, cdb_remove,
+		cdb_match, cdb_prune,
+		cdb_read_leq
+	};
+
+	return &api;
+}
diff --git a/lib/cache/cdb_lmdb.h b/lib/cache/cdb_lmdb.h
new file mode 100644
index 0000000..bc2c7d6
--- /dev/null
+++ b/lib/cache/cdb_lmdb.h
@@ -0,0 +1,23 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include "lib/cache/cdb_api.h"
+#include "lib/defines.h"
+
+KR_EXPORT KR_CONST
+const struct kr_cdb_api *kr_cdb_lmdb(void);
diff --git a/lib/cache/entry_list.c b/lib/cache/entry_list.c
new file mode 100644
index 0000000..6a5001c
--- /dev/null
+++ b/lib/cache/entry_list.c
@@ -0,0 +1,293 @@
+/*  Copyright (C) 2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ * Implementation of chaining in struct entry_h.  Prototypes in ./impl.h
+ */
+
+#include "lib/cache/impl.h"
+#include "lib/utils.h"
+
+
+static int entry_h_len(knot_db_val_t val);
+
+
+void entry_list_memcpy(struct entry_apex *ea, entry_list_t list)
+{
+	assert(ea);
+	memset(ea, 0, offsetof(struct entry_apex, data));
+	ea->has_ns	= list[EL_NS	].len;
+	ea->has_cname	= list[EL_CNAME	].len;
+	ea->has_dname	= list[EL_DNAME	].len;
+	for (int i = 0; i < ENTRY_APEX_NSECS_CNT; ++i) {
+		ea->nsecs[i] =   list[i].len == 0 ? 0 :
+				(list[i].len == 4 ? 1 : 3);
+	}
+	uint8_t *it = ea->data;
+	for (int i = 0; i < EL_LENGTH; ++i) {
+		if (list[i].data) {
+			memcpy(it, list[i].data, list[i].len);
+			/* LATER(optim.): coalesce consecutive writes? */
+		} else {
+			list[i].data = it;
+		}
+		it += to_even(list[i].len);
+	}
+}
+
+int entry_list_parse(const knot_db_val_t val, entry_list_t list)
+{
+	const bool ok = val.data && val.len && list;
+	if (!ok) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+	/* Parse the apex itself (nsec parameters). */
+	const struct entry_apex *ea = entry_apex_consistent(val);
+	if (!ea) {
+		return kr_error(EILSEQ);
+	}
+	const uint8_t *it = ea->data,
+		*it_bound = knot_db_val_bound(val);
+	for (int i = 0; i < ENTRY_APEX_NSECS_CNT; ++i) {
+		if (it > it_bound) {
+			return kr_error(EILSEQ);
+		}
+		list[i].data = (void *)it;
+		switch (ea->nsecs[i]) {
+		case 0:
+			list[i].len = 0;
+			break;
+		case 1:
+			list[i].len = sizeof(uint32_t); /* just timestamp */
+			break;
+		case 3: { /* timestamp + NSEC3PARAM wire */
+			if (it + sizeof(uint32_t) + 4 > it_bound) {
+				return kr_error(EILSEQ);
+			}
+			list[i].len = sizeof(uint32_t)
+				+ nsec_p_rdlen(it + sizeof(uint32_t));
+			break;
+			}
+		default:
+			return kr_error(EILSEQ);
+		};
+		it += to_even(list[i].len);
+	}
+	/* Parse every entry_h. */
+	for (int i = ENTRY_APEX_NSECS_CNT; i < EL_LENGTH; ++i) {
+		list[i].data = (void *)it;
+		bool has_type;
+		switch (i) {
+		case EL_NS:	has_type = ea->has_ns;		break;
+		case EL_CNAME:	has_type = ea->has_cname;	break;
+		case EL_DNAME:	has_type = ea->has_dname;	break;
+		default: assert(false); return kr_error(EINVAL); /* something very bad */
+		}
+		if (!has_type) {
+			list[i].len = 0;
+			continue;
+		}
+		if (it >= it_bound) {
+			assert(!EILSEQ);
+			return kr_error(EILSEQ);
+		}
+		const int len = entry_h_len(
+			(knot_db_val_t){ .data = (void *)it, .len = it_bound - it });
+		if (len < 0) {
+			assert(false);
+			return kr_error(len);
+		}
+		list[i].len = len;
+		it += to_even(len);
+	}
+	assert(it == it_bound);
+	return kr_ok();
+}
+
+/** Given a valid entry header, find its length (i.e. offset of the next entry).
+ * \param val The beginning of the data and the bound (read only).
+ */
+static int entry_h_len(const knot_db_val_t val)
+{
+	const bool ok = val.data && ((ssize_t)val.len) > 0;
+	if (!ok) return kr_error(EINVAL);
+	const struct entry_h *eh = val.data;
+	const uint8_t *d = eh->data; /* iterates over the data in entry */
+	const uint8_t *data_bound = knot_db_val_bound(val);
+	if (d >= data_bound) return kr_error(EILSEQ);
+	if (!eh->is_packet) { /* Positive RRset + its RRsig set (may be empty). */
+		int sets = 2;
+		while (sets-- > 0) {
+			d += rdataset_dematerialized_size(d);
+			if (d > data_bound) {
+				assert(!EILSEQ);
+				return kr_error(EILSEQ);
+			}
+		}
+	} else { /* A "packet" (opaque ATM). */
+		uint16_t len;
+		if (d + sizeof(len) > data_bound) return kr_error(EILSEQ);
+		memcpy(&len, d, sizeof(len));
+		d += 2 + to_even(len);
+	}
+	if (d > data_bound) {
+		assert(!EILSEQ);
+		return kr_error(EILSEQ);
+	}
+	return d - (uint8_t *)val.data;
+}
+
+struct entry_apex * entry_apex_consistent(knot_db_val_t val)
+{
+	//XXX: check lengths, etc.
+	return val.data;
+}
+
+/* See the header file. */
+int entry_h_seek(knot_db_val_t *val, uint16_t type)
+{
+	int i = -1;
+	switch (type) {
+	case KNOT_RRTYPE_NS:	i = EL_NS;	break;
+	case KNOT_RRTYPE_CNAME:	i = EL_CNAME;	break;
+	case KNOT_RRTYPE_DNAME:	i = EL_DNAME;	break;
+	default:		return kr_ok();
+	}
+
+	entry_list_t el;
+	int ret = entry_list_parse(*val, el);
+	if (ret) return ret;
+	*val = el[i];
+	return val->len ? kr_ok() : kr_error(ENOENT);
+}
+
+static int cache_write_or_clear(struct kr_cache *cache, const knot_db_val_t *key,
+				knot_db_val_t *val, const struct kr_query *qry)
+{
+	int ret = cache_op(cache, write, key, val, 1);
+	if (!ret) return kr_ok();
+	/* Clear cache if overfull.  It's nontrivial to do better with LMDB.
+	 * LATER: some garbage-collection mechanism. */
+	if (ret == kr_error(ENOSPC)) {
+		ret = kr_cache_clear(cache);
+		const char *msg = "[cache] clearing because overfull, ret = %d\n";
+		if (ret) {
+			kr_log_error(msg, ret);
+		} else {
+			kr_log_info(msg, ret);
+			ret = kr_error(ENOSPC);
+		}
+		return ret;
+	}
+	VERBOSE_MSG(qry, "=> failed backend write, ret = %d\n", ret);
+	return kr_error(ret ? ret : ENOSPC);
+}
+
+
+/* See the header file. */
+int entry_h_splice(
+	knot_db_val_t *val_new_entry, uint8_t rank,
+	const knot_db_val_t key, const uint16_t ktype, const uint16_t type,
+	const knot_dname_t *owner/*log only*/,
+	const struct kr_query *qry, struct kr_cache *cache, uint32_t timestamp)
+{
+	//TODO: another review, perhaps incuding the API
+	const bool ok = val_new_entry && val_new_entry->len > 0;
+	if (!ok) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+
+	int i_type;
+	switch (type) {
+	case KNOT_RRTYPE_NS:	i_type = EL_NS;		break;
+	case KNOT_RRTYPE_CNAME:	i_type = EL_CNAME;	break;
+	case KNOT_RRTYPE_DNAME:	i_type = EL_DNAME;	break;
+	default:		i_type = 0;
+	}
+
+	/* Get eh_orig (original entry), and also el list if multi-entry case. */
+	const struct entry_h *eh_orig = NULL;
+	entry_list_t el;
+	int ret = -1;
+	if (!kr_rank_test(rank, KR_RANK_SECURE) || ktype == KNOT_RRTYPE_NS) {
+		knot_db_val_t val;
+		ret = cache_op(cache, read, &key, &val, 1);
+		if (i_type) {
+			if (!ret) ret = entry_list_parse(val, el);
+			if (ret) memset(el, 0, sizeof(el));
+			val = el[i_type];
+		}
+		/* val is on the entry, in either case (or error) */
+		if (!ret) {
+			eh_orig = entry_h_consistent(val, type);
+		}
+	} else {
+		/* We want to fully overwrite the entry, so don't even read it. */
+		memset(el, 0, sizeof(el));
+	}
+
+	if (!kr_rank_test(rank, KR_RANK_SECURE) && eh_orig) {
+		/* If equal rank was accepted, spoofing a *single* answer would be
+		 * enough to e.g. override NS record in AUTHORITY section.
+		 * This way they would have to hit the first answer
+		 * (whenever TTL nears expiration).
+		 * Stale-serving is NOT considered, but TTL 1 would be considered
+		 * as expiring anyway, ... */
+		int32_t old_ttl = get_new_ttl(eh_orig, qry, NULL, 0, timestamp);
+		if (old_ttl > 0 && !is_expiring(eh_orig->ttl, old_ttl)
+		    && rank <= eh_orig->rank) {
+			WITH_VERBOSE(qry) {
+				auto_free char *type_str = kr_rrtype_text(type),
+					*owner_str = kr_dname_text(owner);
+				VERBOSE_MSG(qry, "=> not overwriting %s %s\n",
+						type_str, owner_str);
+			}
+			return kr_error(EEXIST);
+		}
+	}
+
+	if (!i_type) {
+		/* The non-list types are trivial now. */
+		return cache_write_or_clear(cache, &key, val_new_entry, qry);
+	}
+	/* Now we're in trouble.  In some cases, parts of data to be written
+	 * is an lmdb entry that may be invalidated by our write request.
+	 * (lmdb does even in-place updates!) Therefore we copy all into a buffer.
+	 * (We don't bother deallocating from the mempool.)
+	 * LATER(optim.): do this only when neccessary, or perhaps another approach.
+	 * This is also complicated by the fact that the val_new_entry part
+	 * is to be written *afterwards* by the caller.
+	 */
+	el[i_type] = (knot_db_val_t){
+		.len = val_new_entry->len,
+		.data = NULL, /* perhaps unclear in the entry_h_splice() API */
+	};
+	knot_db_val_t val = {
+		.len = entry_list_serial_size(el),
+		.data = NULL,
+	};
+	void *buf = mm_alloc(&qry->request->pool, val.len);
+	entry_list_memcpy(buf, el);
+	ret = cache_write_or_clear(cache, &key, &val, qry);
+	if (ret) return kr_error(ret);
+	memcpy(val.data, buf, val.len); /* we also copy the "empty" space, but well... */
+	val_new_entry->data = (uint8_t *)val.data
+			    + ((uint8_t *)el[i_type].data - (uint8_t *)buf);
+	return kr_ok();
+}
+
diff --git a/lib/cache/entry_pkt.c b/lib/cache/entry_pkt.c
new file mode 100644
index 0000000..00e73d4
--- /dev/null
+++ b/lib/cache/entry_pkt.c
@@ -0,0 +1,224 @@
+/*  Copyright (C) 2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ * Implementation of packet-caching.  Prototypes in ./impl.h
+ *
+ * The packet is stashed in entry_h::data as uint16_t length + full packet wire format.
+ */
+
+#include "lib/utils.h"
+#include "lib/layer/iterate.h" /* kr_response_classify */
+#include "lib/cache/impl.h"
+
+
+/** Compute TTL for a packet.  Generally it's minimum TTL, with extra conditions. */
+static uint32_t packet_ttl(const knot_pkt_t *pkt, bool is_negative)
+{
+	bool has_ttl = false;
+	uint32_t ttl = UINT32_MAX;
+	/* Find minimum entry TTL in the packet or SOA minimum TTL. */
+	for (knot_section_t i = KNOT_ANSWER; i <= KNOT_ADDITIONAL; ++i) {
+		const knot_pktsection_t *sec = knot_pkt_section(pkt, i);
+		for (unsigned k = 0; k < sec->count; ++k) {
+			const knot_rrset_t *rr = knot_pkt_rr(sec, k);
+			if (is_negative) {
+				/* Use SOA minimum TTL for negative answers. */
+				if (rr->type == KNOT_RRTYPE_SOA) {
+					return MIN(rr->ttl, knot_soa_minimum(rr->rrs.rdata));
+				} else {
+					continue; /* Use SOA only for negative answers. */
+				}
+			}
+			if (knot_rrtype_is_metatype(rr->type)) {
+				continue; /* Skip metatypes. */
+			}
+			ttl = MIN(ttl, rr->ttl);
+		}
+	}
+	/* If no valid TTL present, go with zero (will get clamped to minimum). */
+	return has_ttl ? ttl : 0;
+}
+
+
+void stash_pkt(const knot_pkt_t *pkt, const struct kr_query *qry,
+		const struct kr_request *req, const bool has_optout)
+{
+	/* In some cases, stash also the packet. */
+	const bool is_negative = kr_response_classify(pkt)
+				& (PKT_NODATA|PKT_NXDOMAIN);
+	const struct kr_qflags * const qf = &qry->flags;
+	const bool want_negative = qf->DNSSEC_INSECURE || !qf->DNSSEC_WANT || has_optout;
+	const bool want_pkt = qf->DNSSEC_BOGUS /*< useful for +cd answers */
+				|| (is_negative && want_negative);
+
+	if (!want_pkt || !knot_wire_get_aa(pkt->wire)
+	    || pkt->parsed != pkt->size /*< malformed packet; still can't detect KNOT_EFEWDATA */
+	   ) {
+		return;
+	}
+
+	/* Compute rank.  If cd bit is set or we got answer via non-validated
+	 * forwarding, make the rank bad; otherwise it depends on flags.
+	 * TODO: probably make validator attempt validation even with +cd. */
+	uint8_t rank = KR_RANK_AUTH;
+	const bool risky_vldr = is_negative && qf->FORWARD && qf->CNAME;
+		/* ^^ CNAME'ed NXDOMAIN answer in forwarding mode can contain
+		 * unvalidated records; original commit: d6e22f476. */
+	if (knot_wire_get_cd(req->qsource.packet->wire) || qf->STUB || risky_vldr) {
+		kr_rank_set(&rank, KR_RANK_OMIT);
+	} else {
+		if (qf->DNSSEC_BOGUS) {
+			kr_rank_set(&rank, KR_RANK_BOGUS);
+		} else if (qf->DNSSEC_INSECURE) {
+			kr_rank_set(&rank, KR_RANK_INSECURE);
+		} else if (!qf->DNSSEC_WANT) {
+			/* no TAs at all, leave _RANK_AUTH */
+		} else if (has_optout) {
+			/* All bad cases should be filtered above,
+			 * at least the same way as pktcache in kresd 1.5.x. */
+			kr_rank_set(&rank, KR_RANK_SECURE);
+		} else assert(false);
+	}
+
+	const uint16_t pkt_type = knot_pkt_qtype(pkt);
+	const knot_dname_t *owner = knot_pkt_qname(pkt); /* qname can't be compressed */
+
+	// LATER: nothing exists under NXDOMAIN.  Implement that (optionally)?
+#if 0
+	if (knot_wire_get_rcode(pkt->wire) == KNOT_RCODE_NXDOMAIN
+	 /* && !qf->DNSSEC_INSECURE */ ) {
+		pkt_type = KNOT_RRTYPE_NS;
+	}
+#endif
+
+	/* Construct the key under which the pkt will be stored. */
+	struct key k_storage, *k = &k_storage;
+	knot_db_val_t key;
+	int ret = kr_dname_lf(k->buf, owner, false);
+	if (ret) {
+		/* A server might (incorrectly) reply with QDCOUNT=0. */
+		assert(owner == NULL);
+		return;
+	}
+	key = key_exact_type_maypkt(k, pkt_type);
+
+	/* For now we stash the full packet byte-exactly as it came from upstream. */
+	const uint16_t pkt_size = pkt->size;
+	knot_db_val_t val_new_entry = {
+		.data = NULL,
+		.len = offsetof(struct entry_h, data) + sizeof(pkt_size) + pkt->size,
+	};
+	/* Prepare raw memory for the new entry and fill it. */
+	struct kr_cache *cache = &req->ctx->cache;
+	ret = entry_h_splice(&val_new_entry, rank, key, k->type, pkt_type,
+				owner, qry, cache, qry->timestamp.tv_sec);
+	if (ret) return; /* some aren't really errors */
+	assert(val_new_entry.data);
+	struct entry_h *eh = val_new_entry.data;
+	memset(eh, 0, offsetof(struct entry_h, data));
+	eh->time = qry->timestamp.tv_sec;
+	eh->ttl  = MAX(MIN(packet_ttl(pkt, is_negative), cache->ttl_max), cache->ttl_min);
+	eh->rank = rank;
+	eh->is_packet = true;
+	eh->has_optout = qf->DNSSEC_OPTOUT;
+	memcpy(eh->data, &pkt_size, sizeof(pkt_size));
+	memcpy(eh->data + sizeof(pkt_size), pkt->wire, pkt_size);
+
+	WITH_VERBOSE(qry) {
+		auto_free char *type_str = kr_rrtype_text(pkt_type),
+			*owner_str = kr_dname_text(owner);
+		VERBOSE_MSG(qry, "=> stashed packet: rank 0%.2o, TTL %d, "
+				"%s %s (%d B)\n",
+				eh->rank, eh->ttl,
+				type_str, owner_str, (int)val_new_entry.len);
+	}
+}
+
+
+int answer_from_pkt(kr_layer_t *ctx, knot_pkt_t *pkt, uint16_t type,
+		const struct entry_h *eh, const void *eh_bound, uint32_t new_ttl)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+
+	uint16_t pkt_len;
+	memcpy(&pkt_len, eh->data, sizeof(pkt_len));
+	if (pkt_len > pkt->max_size) {
+		return kr_error(ENOENT);
+	}
+
+	/* Copy answer and reparse it, but keep the original message id. */
+	uint16_t msgid = knot_wire_get_id(pkt->wire);
+	knot_pkt_clear(pkt);
+	memcpy(pkt->wire, eh->data + 2, pkt_len);
+	pkt->size = pkt_len;
+	int ret = knot_pkt_parse(pkt, 0);
+	if (ret == KNOT_EFEWDATA || ret == KNOT_EMALF) {
+		return kr_error(ENOENT);
+		/* LATER(opt): try harder to avoid stashing such packets */
+	}
+	if (ret != KNOT_EOK) {
+		assert(!ret);
+		return kr_error(ret);
+	}
+	knot_wire_set_id(pkt->wire, msgid);
+
+	/* Add rank into the additional field. */
+	for (size_t i = 0; i < pkt->rrset_count; ++i) {
+		assert(!pkt->rr[i].additional);
+		uint8_t *rr_rank = mm_alloc(&pkt->mm, sizeof(*rr_rank));
+		if (!rr_rank) {
+			return kr_error(ENOMEM);
+		}
+		*rr_rank = eh->rank;
+		pkt->rr[i].additional = rr_rank;
+	}
+
+	/* Adjust TTL in each record. */
+	const uint32_t drift = eh->ttl - new_ttl;
+	for (knot_section_t i = KNOT_ANSWER; i <= KNOT_ADDITIONAL; ++i) {
+		const knot_pktsection_t *sec = knot_pkt_section(pkt, i);
+		for (unsigned k = 0; k < sec->count; ++k) {
+			knot_rrset_t *rrs = // vv FIXME??
+				/*const-cast*/(knot_rrset_t *)knot_pkt_rr(sec, k);
+			/* We need to be careful: due to enforcing minimum TTL
+			 * on packet, some records may be below that value.
+			 * We keep those records at TTL 0. */
+			if (rrs->ttl >= drift) {
+				rrs->ttl -= drift;
+			} else {
+				rrs->ttl = 0;
+			}
+		}
+	}
+
+	/* Finishing touches. TODO: perhaps factor out */
+	struct kr_qflags * const qf = &qry->flags;
+	qf->EXPIRING = is_expiring(eh->ttl, new_ttl);
+	qf->CACHED = true;
+	qf->NO_MINIMIZE = true;
+	qf->DNSSEC_INSECURE = kr_rank_test(eh->rank, KR_RANK_INSECURE);
+	qf->DNSSEC_BOGUS = kr_rank_test(eh->rank, KR_RANK_BOGUS);
+	if (qf->DNSSEC_INSECURE || qf->DNSSEC_BOGUS) {
+		qf->DNSSEC_WANT = false;
+	}
+	qf->DNSSEC_OPTOUT = eh->has_optout;
+	VERBOSE_MSG(qry, "=> satisfied by exact packet: rank 0%.2o, new TTL %d\n",
+			eh->rank, new_ttl);
+	return kr_ok();
+}
+
diff --git a/lib/cache/entry_rr.c b/lib/cache/entry_rr.c
new file mode 100644
index 0000000..94dd0e8
--- /dev/null
+++ b/lib/cache/entry_rr.c
@@ -0,0 +1,146 @@
+/*  Copyright (C) 2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ * Implementation of RRset (de)materialization, i.e. (de)serialization to storage
+ * format used in cache (some repeated fields are omitted).  Prototypes in ./impl.h
+ */
+
+#include "lib/cache/impl.h"
+
+int rdataset_dematerialize(const knot_rdataset_t *rds, uint8_t * restrict data)
+{
+	/* FIXME: either give up on even alignment and thus direct usability
+	 * of rdatasets as they are in lmdb, or align inside cdb_* functions
+	 * (request sizes one byte longer and shift iff on an odd address). */
+	//if ((size_t)data & 1) VERBOSE_MSG(NULL, "dematerialize: odd address\n");
+	//const uint8_t *data0 = data;
+	if (!data) {
+		assert(data);
+		return kr_error(EINVAL);
+	}
+	const uint16_t rr_count = rds ? rds->count : 0;
+	memcpy(data, &rr_count, sizeof(rr_count));
+	data += sizeof(rr_count);
+	if (rr_count) {
+		size_t size = knot_rdataset_size(rds);
+		memcpy(data, rds->rdata, size);
+		data += size;
+	}
+	//VERBOSE_MSG(NULL, "dematerialized to %d B\n", (int)(data - data0));
+	(void)data;
+	return kr_ok();
+}
+
+/** Materialize a knot_rdataset_t from cache with given TTL.
+ * Return the number of bytes consumed or an error code.
+ */
+static int rdataset_materialize(knot_rdataset_t * restrict rds, const uint8_t * const data,
+				const uint8_t *data_bound, knot_mm_t *pool)
+{
+	assert(rds && data && data_bound && data_bound > data && !rds->rdata
+		/*&& !((size_t)data & 1)*/);
+	assert(pool); /* not required, but that's our current usage; guard leaks */
+	const uint8_t *d = data; /* iterates over the cache data */
+	{
+		uint16_t rr_count;
+		memcpy(&rr_count, d, sizeof(rr_count));
+		d += sizeof(rr_count);
+		rds->count = rr_count;
+		if (!rr_count) { /* avoid mm_alloc(pool, 0); etc. */
+			return d - data;
+		}
+	}
+	/* First sum up the sizes for wire format length. */
+	const knot_rdataset_t rds_tmp = {
+		.count = rds->count,
+		.rdata = (knot_rdata_t *)d,
+	};
+	size_t rds_size = knot_rdataset_size(&rds_tmp); /* TODO: we might overrun here already,
+							but we need to trust cache anyway...*/
+	if (d + rds_size > data_bound) {
+		VERBOSE_MSG(NULL, "materialize: EILSEQ!\n");
+		return kr_error(EILSEQ);
+	}
+	rds->rdata = mm_alloc(pool, rds_size);
+	if (!rds->rdata) {
+		return kr_error(ENOMEM);
+	}
+	memcpy(rds->rdata, d, rds_size);
+	d += rds_size;
+	//VERBOSE_MSG(NULL, "materialized from %d B\n", (int)(d - data));
+	return d - data;
+}
+
+int kr_cache_materialize(knot_rdataset_t *dst, const struct kr_cache_p *ref,
+			 knot_mm_t *pool)
+{
+	struct entry_h *eh = ref->raw_data;
+	return rdataset_materialize(dst, eh->data, ref->raw_bound, pool);
+}
+
+
+int entry2answer(struct answer *ans, int id,
+		const struct entry_h *eh, const uint8_t *eh_bound,
+		const knot_dname_t *owner, uint16_t type, uint32_t new_ttl)
+{
+	/* We assume it's zeroed.  Do basic sanity check. */
+	if (ans->rrsets[id].set.rr || ans->rrsets[id].sig_rds.rdata
+	    || (type == KNOT_RRTYPE_NSEC  &&  ans->nsec_p.raw)
+	    || (type == KNOT_RRTYPE_NSEC3 && !ans->nsec_p.raw)
+	   )
+	{
+		assert(false);
+		return kr_error(EINVAL);
+	}
+	/* Materialize the base RRset. */
+	knot_rrset_t *rr = ans->rrsets[id].set.rr
+		= knot_rrset_new(owner, type, KNOT_CLASS_IN, new_ttl, ans->mm);
+	if (!rr) {
+		assert(!ENOMEM);
+		return kr_error(ENOMEM);
+	}
+	int ret = rdataset_materialize(&rr->rrs, eh->data, eh_bound, ans->mm);
+	if (ret < 0) goto fail;
+	size_t data_off = ret;
+	ans->rrsets[id].set.rank = eh->rank;
+	ans->rrsets[id].set.expiring = is_expiring(eh->ttl, new_ttl);
+	/* Materialize the RRSIG RRset for the answer in (pseudo-)packet. */
+	bool want_rrsigs = true; /* LATER(optim.): might be omitted in some cases. */
+	if (want_rrsigs) {
+		ret = rdataset_materialize(&ans->rrsets[id].sig_rds, eh->data + data_off,
+					   eh_bound, ans->mm);
+		if (ret < 0) goto fail;
+		/* Sanity check: we consumed exactly all data. */
+		int unused_bytes = eh_bound - (uint8_t *)eh->data - data_off - ret;
+		if (unused_bytes) {
+			kr_log_error("[cach] entry2answer ERROR: unused bytes: %d\n",
+					unused_bytes);
+			assert(!EILSEQ);
+			ret = kr_error(EILSEQ);
+			goto fail; /* to be on the safe side */
+		}
+	}
+	return kr_ok();
+fail:
+	assert(/*false*/!ret);
+	/* Cleanup the item that we might've (partially) written to. */
+	knot_rrset_free(ans->rrsets[id].set.rr, ans->mm);
+	knot_rdataset_clear(&ans->rrsets[id].sig_rds, ans->mm);
+	memset(&ans->rrsets[id], 0, sizeof(ans->rrsets[id]));
+	return kr_error(ret);
+}
+
diff --git a/lib/cache/impl.h b/lib/cache/impl.h
new file mode 100644
index 0000000..a08f355
--- /dev/null
+++ b/lib/cache/impl.h
@@ -0,0 +1,412 @@
+/*  Copyright (C) 2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ * Header internal for cache implementation(s).
+ * Only LMDB works for now.
+ */
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include <libdnssec/error.h>
+#include <libdnssec/nsec.h>
+#include <libknot/consts.h>
+#include <libknot/db/db.h>
+#include <libknot/dname.h>
+
+#include "contrib/cleanup.h"
+#include "contrib/murmurhash3/murmurhash3.h" /* hash() for nsec_p_hash() */
+#include "lib/cache/cdb_api.h"
+#include "lib/resolve.h"
+
+/* Cache entry values - binary layout.
+ *
+ * It depends on type which is recognizable by the key.
+ * Code depending on the contents of the key is marked by CACHE_KEY_DEF.
+ *
+ * 'E' entry (exact hit):
+ *	- ktype == NS: struct entry_apex - multiple types inside (NS and xNAME);
+ *	- ktype != NS: struct entry_h
+ *	    * is_packet: uint16_t length, the rest is opaque and handled by ./entry_pkt.c
+ *	    * otherwise RRset + its RRSIG set (possibly empty).
+ * '1' or '3' entry (NSEC or NSEC3)
+ *	- struct entry_h, contents is the same as for exact hit
+ *	- flags don't make sense there
+ */
+
+struct entry_h {
+	uint32_t time;	/**< The time of inception. */
+	uint32_t ttl;	/**< TTL at inception moment.  Assuming it fits into int32_t ATM. */
+	uint8_t  rank : 6;	/**< See enum kr_rank */
+	bool is_packet : 1;	/**< Negative-answer packet for insecure/bogus name. */
+	bool has_optout : 1;	/**< Only for packets; persisted DNSSEC_OPTOUT. */
+	uint8_t _pad;		/**< We need even alignment for data now. */
+	uint8_t data[];
+};
+struct entry_apex;
+
+/** Check basic consistency of entry_h for 'E' entries, not looking into ->data.
+ * (for is_packet the length of data is checked)
+ */
+struct entry_h * entry_h_consistent(knot_db_val_t data, uint16_t type);
+
+struct entry_apex * entry_apex_consistent(knot_db_val_t val);
+
+/** Consistency check, ATM common for NSEC and NSEC3. */
+static inline struct entry_h * entry_h_consistent_NSEC(knot_db_val_t data)
+{
+	/* ATM it's enough to just extend the checks for exact entries. */
+	const struct entry_h *eh = entry_h_consistent(data, KNOT_RRTYPE_NSEC);
+	bool ok = eh != NULL;
+	ok = ok && !eh->is_packet && !eh->has_optout;
+	return ok ? /*const-cast*/(struct entry_h *)eh : NULL;
+}
+
+
+/* nsec_p* - NSEC* chain parameters */
+
+static inline int nsec_p_rdlen(const uint8_t *rdata)
+{
+	//TODO: do we really need the zero case?
+	return rdata ? 5 + rdata[4] : 0; /* rfc5155 4.2 and 3.2. */
+}
+static const int NSEC_P_MAXLEN = sizeof(uint32_t) + 5 + 255; // TODO: remove??
+
+/** Hash of NSEC3 parameters, used as a tag to separate different chains for same zone. */
+typedef uint32_t nsec_p_hash_t;
+static inline nsec_p_hash_t nsec_p_mkHash(const uint8_t *nsec_p)
+{
+	assert(nsec_p && !(KNOT_NSEC3_FLAG_OPT_OUT & nsec_p[1]));
+	return hash((const char *)nsec_p, nsec_p_rdlen(nsec_p));
+}
+
+/** NSEC* parameters for the chain. */
+struct nsec_p {
+	const uint8_t *raw; /**< Pointer to raw NSEC3 parameters; NULL for NSEC. */
+	nsec_p_hash_t hash; /**< Hash of `raw`, used for cache keys. */
+	dnssec_nsec3_params_t libknot; /**< Format for libknot; owns malloced memory! */
+};
+
+
+
+/** LATER(optim.): this is overshot, but struct key usage should be cheap ATM. */
+#define KR_CACHE_KEY_MAXLEN (KNOT_DNAME_MAXLEN + 100) /* CACHE_KEY_DEF */
+
+struct key {
+	const knot_dname_t *zname; /**< current zone name (points within qry->sname) */
+	uint8_t zlf_len; /**< length of current zone's lookup format */
+
+	/** Corresponding key type; e.g. NS for CNAME.
+	 * Note: NSEC type is ambiguous (exact and range key). */
+	uint16_t type;
+	/** The key data start at buf+1, and buf[0] contains some length.
+	 * For details see key_exact* and key_NSEC* functions. */
+	uint8_t buf[KR_CACHE_KEY_MAXLEN];
+	/* LATER(opt.): ^^ probably change the anchoring, so that kr_dname_lf()
+	 * doesn't need to move data after knot_dname_lf(). */
+};
+
+static inline size_t key_nwz_off(const struct key *k)
+{
+	/* CACHE_KEY_DEF: zone name lf + 0 ('1' or '3').
+	 * NSEC '1' case continues just with the name within zone. */
+	return k->zlf_len + 2;
+}
+static inline size_t key_nsec3_hash_off(const struct key *k)
+{
+	/* CACHE_KEY_DEF NSEC3: tag (nsec_p_hash_t) + 20 bytes NSEC3 name hash) */
+	return key_nwz_off(k) + sizeof(nsec_p_hash_t);
+}
+/** Hash is always SHA1; I see no plans to standardize anything else.
+ * https://www.iana.org/assignments/dnssec-nsec3-parameters/dnssec-nsec3-parameters.xhtml#dnssec-nsec3-parameters-3
+ */
+static const int NSEC3_HASH_LEN = 20,
+		 NSEC3_HASH_TXT_LEN = 32;
+
+/** Finish constructing string key for for exact search.
+ * It's assumed that kr_dname_lf(k->buf, owner, *) had been ran.
+ */
+knot_db_val_t key_exact_type_maypkt(struct key *k, uint16_t type);
+
+/** Like key_exact_type_maypkt but with extra checks if used for RRs only. */
+static inline knot_db_val_t key_exact_type(struct key *k, uint16_t type)
+{
+	switch (type) {
+	/* Sanity check: forbidden types represented in other way(s). */
+	case KNOT_RRTYPE_NSEC:
+	case KNOT_RRTYPE_NSEC3:
+		assert(false);
+		return (knot_db_val_t){ NULL, 0 };
+	}
+	return key_exact_type_maypkt(k, type);
+}
+
+
+/* entry_h chaining; implementation in ./entry_list.c */
+
+enum { ENTRY_APEX_NSECS_CNT = 2 };
+
+/** Header of 'E' entry with ktype == NS.  Inside is private to ./entry_list.c
+ *
+ * We store xNAME at NS type to lower the number of searches in closest_NS().
+ * CNAME is only considered for equal name, of course.
+ * We also store NSEC* parameters at NS type.
+ */
+struct entry_apex {
+	/* ENTRY_H_FLAGS */
+	bool has_ns : 1;
+	bool has_cname : 1;
+	bool has_dname : 1;
+
+	uint8_t pad_; /**< Weird: 1 byte + 2 bytes + x bytes; let's do 2+2+x. */
+	int8_t nsecs[ENTRY_APEX_NSECS_CNT]; /**< values:  0: none, 1: NSEC, 3: NSEC3 */
+	uint8_t data[];
+	/* XXX: if not first, stamp of last being the first?
+	 * Purpose: save cache operations if rolled the algo/params long ago. */
+};
+
+/** Indices for decompressed entry_list_t. */
+enum EL {
+	EL_NS = ENTRY_APEX_NSECS_CNT,
+	EL_CNAME,
+	EL_DNAME,
+	EL_LENGTH
+};
+/** Decompressed entry_apex.  It's an array of unparsed entry_h references.
+ * Note: arrays are passed "by reference" to functions (in C99). */
+typedef knot_db_val_t entry_list_t[EL_LENGTH];
+
+static inline uint16_t EL2RRTYPE(enum EL i)
+{
+	switch (i) {
+	case EL_NS:	return KNOT_RRTYPE_NS;
+	case EL_CNAME:	return KNOT_RRTYPE_CNAME;
+	case EL_DNAME:	return KNOT_RRTYPE_DNAME;
+	default:	assert(false);  return 0;
+	}
+}
+
+/** There may be multiple entries within, so rewind `val` to the one we want.
+ *
+ * ATM there are multiple types only for the NS ktype - it also accommodates xNAMEs.
+ * \note `val->len` represents the bound of the whole list, not of a single entry.
+ * \note in case of ENOENT, `val` is still rewound to the beginning of the next entry.
+ * \return error code
+ * TODO: maybe get rid of this API?
+ */
+int entry_h_seek(knot_db_val_t *val, uint16_t type);
+
+/** Prepare space to insert an entry.
+ *
+ * Some checks are performed (rank, TTL), the current entry in cache is copied
+ * with a hole ready for the new entry (old one of the same type is cut out).
+ *
+ * \param val_new_entry The only changing parameter; ->len is read, ->data written.
+ * \return error code
+ */
+int entry_h_splice(
+	knot_db_val_t *val_new_entry, uint8_t rank,
+	const knot_db_val_t key, const uint16_t ktype, const uint16_t type,
+	const knot_dname_t *owner/*log only*/,
+	const struct kr_query *qry, struct kr_cache *cache, uint32_t timestamp);
+
+/** Parse an entry_apex into individual items.  @return error code. */
+int entry_list_parse(const knot_db_val_t val, entry_list_t list);
+
+static inline size_t to_even(size_t n)
+{
+	return n + (n & 1);
+}
+
+static inline int entry_list_serial_size(const entry_list_t list)
+{
+	int size = offsetof(struct entry_apex, data);
+	for (int i = 0; i < EL_LENGTH; ++i) {
+		size += to_even(list[i].len);
+	}
+	return size;
+}
+
+/** Fill contents of an entry_apex.
+ *
+ * @note NULL pointers are overwritten - caller may like to fill the space later.
+ */
+void entry_list_memcpy(struct entry_apex *ea, entry_list_t list);
+
+
+
+/* Packet caching; implementation in ./entry_pkt.c */
+
+/** Stash the packet into cache (if suitable, etc.)
+ * \param has_optout whether the packet contains an opt-out NSEC3 */
+void stash_pkt(const knot_pkt_t *pkt, const struct kr_query *qry,
+		const struct kr_request *req, bool has_optout);
+
+/** Try answering from packet cache, given an entry_h.
+ *
+ * This assumes the TTL is OK and entry_h_consistent, but it may still return error.
+ * On success it handles all the rest, incl. qry->flags.
+ */
+int answer_from_pkt(kr_layer_t *ctx, knot_pkt_t *pkt, uint16_t type,
+		const struct entry_h *eh, const void *eh_bound, uint32_t new_ttl);
+
+
+/** Record is expiring if it has less than 1% TTL (or less than 5s) */
+static inline bool is_expiring(uint32_t orig_ttl, uint32_t new_ttl)
+{
+	int64_t nttl = new_ttl; /* avoid potential over/under-flow */
+	return 100 * (nttl - 5) < orig_ttl;
+}
+
+/** Returns signed result so you can inspect how much stale the RR is.
+ *
+ * @param owner name for stale-serving decisions.  You may pass NULL to disable stale.
+ * @note: NSEC* uses zone name ATM; for NSEC3 the owner may not even be knowable.
+ * @param type for stale-serving.
+ */
+int32_t get_new_ttl(const struct entry_h *entry, const struct kr_query *qry,
+                    const knot_dname_t *owner, uint16_t type, uint32_t now);
+
+
+/* RRset (de)materialization; implementation in ./entry_rr.c */
+
+/** Size of the RR count field */
+#define KR_CACHE_RR_COUNT_SIZE sizeof(uint16_t)
+
+/** Compute size of serialized rdataset.  NULL is accepted as empty set. */
+static inline int rdataset_dematerialize_size(const knot_rdataset_t *rds)
+{
+	return KR_CACHE_RR_COUNT_SIZE + (rds == NULL ? 0 : knot_rdataset_size(rds));
+}
+
+static inline int rdataset_dematerialized_size(const uint8_t *data)
+{
+	knot_rdataset_t rds;
+	memcpy(&rds.count, data, sizeof(rds.count));
+	rds.rdata = (knot_rdata_t *)(data + sizeof(rds.count));
+	return sizeof(rds.count) + knot_rdataset_size(&rds);
+}
+
+/** Serialize an rdataset. */
+int rdataset_dematerialize(const knot_rdataset_t *rds, uint8_t * restrict data);
+
+
+/** Partially constructed answer when gathering RRsets from cache. */
+struct answer {
+	int rcode;		/**< PKT_NODATA, etc. */
+	struct nsec_p nsec_p;	/**< Don't mix different NSEC* parameters in one answer. */
+	knot_mm_t *mm;		/**< Allocator for rrsets */
+	struct answer_rrset {
+		ranked_rr_array_entry_t set;	/**< set+rank for the main data */
+		knot_rdataset_t sig_rds;	/**< RRSIG data, if any */
+	} rrsets[1+1+3]; /**< see AR_ANSWER and friends; only required records are filled */
+};
+enum {
+	AR_ANSWER = 0, /**< Positive answer record.  It might be wildcard-expanded. */
+	AR_SOA,  /**< SOA record. */
+	AR_NSEC, /**< NSEC* covering or matching the SNAME (next closer name in NSEC3 case). */
+	AR_WILD, /**< NSEC* covering or matching the source of synthesis. */
+	AR_CPE,  /**< NSEC3 matching the closest provable encloser. */
+};
+
+/** Materialize RRset + RRSIGs into ans->rrsets[id].
+ * LATER(optim.): it's slightly wasteful that we allocate knot_rrset_t for the packet
+ *
+ * \return error code.  They are all bad conditions and "guarded" by assert.
+ */
+int entry2answer(struct answer *ans, int id,
+		const struct entry_h *eh, const uint8_t *eh_bound,
+		const knot_dname_t *owner, uint16_t type, uint32_t new_ttl);
+
+
+/* Preparing knot_pkt_t for cache answer from RRs; implementation in ./knot_pkt.c */
+
+/** Prepare answer packet to be filled by RRs (without RR data in wire). */
+int pkt_renew(knot_pkt_t *pkt, const knot_dname_t *name, uint16_t type);
+
+/** Append RRset + its RRSIGs into the current section (*shallow* copy), with given rank.
+ * \note it works with empty set as well (skipped)
+ * \note pkt->wire is not updated in any way
+ * \note KNOT_CLASS_IN is assumed
+ */
+int pkt_append(knot_pkt_t *pkt, const struct answer_rrset *rrset, uint8_t rank);
+
+
+
+/* NSEC (1) stuff.  Implementation in ./nsec1.c */
+
+/** Construct a string key for for NSEC (1) predecessor-search.
+ * \param add_wildcard Act as if the name was extended by "*."
+ * \note k->zlf_len is assumed to have been correctly set */
+knot_db_val_t key_NSEC1(struct key *k, const knot_dname_t *name, bool add_wildcard);
+
+/** Closest encloser check for NSEC (1).
+ * To understand the interface, see the call point.
+ * \param k	space to store key + input: zname and zlf_len
+ * \return 0: success;  >0: try other (NSEC3);  <0: exit cache immediately. */
+int nsec1_encloser(struct key *k, struct answer *ans,
+		   const int sname_labels, int *clencl_labels,
+		   knot_db_val_t *cover_low_kwz, knot_db_val_t *cover_hi_kwz,
+		   const struct kr_query *qry, struct kr_cache *cache);
+
+/** Source of synthesis (SS) check for NSEC (1).
+ * To understand the interface, see the call point.
+ * \return 0: continue; <0: exit cache immediately;
+ * 	AR_SOA: skip to adding SOA (SS was covered or matched for NODATA). */
+int nsec1_src_synth(struct key *k, struct answer *ans, const knot_dname_t *clencl_name,
+		    knot_db_val_t cover_low_kwz, knot_db_val_t cover_hi_kwz,
+		    const struct kr_query *qry, struct kr_cache *cache);
+
+
+/* NSEC3 stuff.  Implementation in ./nsec3.c */
+
+/** Construct a string key for for NSEC3 predecessor-search, from an NSEC3 name.
+ * \note k->zlf_len is assumed to have been correctly set */
+knot_db_val_t key_NSEC3(struct key *k, const knot_dname_t *nsec3_name,
+			const nsec_p_hash_t nsec_p_hash);
+
+/** TODO.  See nsec1_encloser(...) */
+int nsec3_encloser(struct key *k, struct answer *ans,
+		   const int sname_labels, int *clencl_labels,
+		   const struct kr_query *qry, struct kr_cache *cache);
+
+/** TODO.  See nsec1_src_synth(...) */
+int nsec3_src_synth(struct key *k, struct answer *ans, const knot_dname_t *clencl_name,
+		    const struct kr_query *qry, struct kr_cache *cache);
+
+
+
+#define VERBOSE_MSG(qry, ...) QRVERBOSE((qry), "cach",  ## __VA_ARGS__)
+
+/** Shorthand for operations on cache backend */
+#define cache_op(cache, op, ...) (cache)->api->op((cache)->db, ## __VA_ARGS__)
+
+
+static inline uint16_t get_uint16(const void *address)
+{
+	uint16_t tmp;
+	memcpy(&tmp, address, sizeof(tmp));
+	return tmp;
+}
+
+/** Useful pattern, especially as void-pointer arithmetic isn't standard-compliant. */
+static inline uint8_t * knot_db_val_bound(knot_db_val_t val)
+{
+	return (uint8_t *)val.data + val.len;
+}
+
diff --git a/lib/cache/knot_pkt.c b/lib/cache/knot_pkt.c
new file mode 100644
index 0000000..56836a6
--- /dev/null
+++ b/lib/cache/knot_pkt.c
@@ -0,0 +1,106 @@
+/*  Copyright (C) 2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ * Implementation of preparing knot_pkt_t for filling with RRs.
+ * Prototypes in ./impl.h
+ */
+
+#include "lib/cache/impl.h"
+
+int pkt_renew(knot_pkt_t *pkt, const knot_dname_t *name, uint16_t type)
+{
+	/* Update packet question if needed. */
+	if (!knot_dname_is_equal(knot_pkt_qname(pkt), name)
+	    || knot_pkt_qtype(pkt) != type || knot_pkt_qclass(pkt) != KNOT_CLASS_IN) {
+		int ret = kr_pkt_recycle(pkt);
+		if (ret) return kr_error(ret);
+		ret = knot_pkt_put_question(pkt, name, KNOT_CLASS_IN, type);
+		if (ret) return kr_error(ret);
+	}
+
+	pkt->parsed = pkt->size = PKT_SIZE_NOWIRE;
+	knot_wire_set_qr(pkt->wire);
+	knot_wire_set_aa(pkt->wire);
+	return kr_ok();
+}
+
+/** Reserve space for additional `count` RRsets.
+ * \note pkt->rr_info gets correct length but is always zeroed
+ */
+static int pkt_alloc_space(knot_pkt_t *pkt, int count)
+{
+	size_t allocd_orig = pkt->rrset_allocd;
+	if (pkt->rrset_count + count <= allocd_orig) {
+		return kr_ok();
+	}
+	/* A simple growth strategy, amortized O(count). */
+	pkt->rrset_allocd = MAX(
+			pkt->rrset_count + count,
+			pkt->rrset_count + allocd_orig);
+
+	pkt->rr = mm_realloc(&pkt->mm, pkt->rr,
+				sizeof(pkt->rr[0]) * pkt->rrset_allocd,
+				sizeof(pkt->rr[0]) * allocd_orig);
+	if (!pkt->rr) {
+		return kr_error(ENOMEM);
+	}
+	/* Allocate pkt->rr_info to be certain, but just leave it zeroed. */
+	mm_free(&pkt->mm, pkt->rr_info);
+	pkt->rr_info = mm_alloc(&pkt->mm, sizeof(pkt->rr_info[0]) * pkt->rrset_allocd);
+	if (!pkt->rr_info) {
+		return kr_error(ENOMEM);
+	}
+	memset(pkt->rr_info, 0, sizeof(pkt->rr_info[0]) * pkt->rrset_allocd);
+	return kr_ok();
+}
+
+int pkt_append(knot_pkt_t *pkt, const struct answer_rrset *rrset, uint8_t rank)
+{
+	/* allocate space, to be sure */
+	int rrset_cnt = (rrset->set.rr->rrs.count > 0) + (rrset->sig_rds.count > 0);
+	int ret = pkt_alloc_space(pkt, rrset_cnt);
+	if (ret) return kr_error(ret);
+	/* write both sets */
+	const knot_rdataset_t *rdss[2] = { &rrset->set.rr->rrs, &rrset->sig_rds };
+	for (int i = 0; i < rrset_cnt; ++i) {
+		assert(rdss[i]->count);
+		/* allocate rank */
+		uint8_t *rr_rank = mm_alloc(&pkt->mm, sizeof(*rr_rank));
+		if (!rr_rank) return kr_error(ENOMEM);
+		*rr_rank = (i == 0) ? rank : (KR_RANK_OMIT | KR_RANK_AUTH);
+			/* rank for RRSIGs isn't really useful: ^^ */
+		if (i == 0) {
+			pkt->rr[pkt->rrset_count] = *rrset->set.rr;
+			pkt->rr[pkt->rrset_count].additional = rr_rank;
+		} else {
+		/* append the RR array */
+			pkt->rr[pkt->rrset_count] = (knot_rrset_t){
+				.owner = knot_dname_copy(rrset->set.rr->owner, &pkt->mm),
+					/* ^^ well, another copy isn't really needed */
+				.ttl = rrset->set.rr->ttl,
+				.type = KNOT_RRTYPE_RRSIG,
+				.rclass = KNOT_CLASS_IN,
+				.rrs = *rdss[i],
+				.additional = rr_rank,
+			};
+		}
+		++pkt->rrset_count;
+		++(pkt->sections[pkt->current].count);
+	}
+	return kr_ok();
+}
+
diff --git a/lib/cache/nsec1.c b/lib/cache/nsec1.c
new file mode 100644
index 0000000..74b3d34
--- /dev/null
+++ b/lib/cache/nsec1.c
@@ -0,0 +1,511 @@
+/*  Copyright (C) 2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ * Implementation of NSEC (1) handling.  Prototypes in ./impl.h
+ */
+
+#include "lib/cache/impl.h"
+#include "lib/dnssec/nsec.h"
+#include "lib/layer/iterate.h"
+
+
+/** Reconstruct a name into a buffer (assuming length at least KNOT_DNAME_MAXLEN).
+ * \return kr_ok() or error code (<0). */
+static int dname_wire_reconstruct(knot_dname_t *buf, const struct key *k,
+		 knot_db_val_t kwz)
+{
+	/* Reconstruct from key: first the ending, then zone name. */
+	int ret = knot_dname_lf2wire(buf, kwz.len, kwz.data);
+	if (ret < 0) {
+		VERBOSE_MSG(NULL, "=> NSEC: LF2wire ret = %d\n", ret);
+		assert(false);
+		return ret;
+	}
+		/* The last written byte is the zero label for root -> overwrite. */
+	knot_dname_t *zone_start = buf + ret - 1;
+	assert(*zone_start == '\0');
+	ret = knot_dname_to_wire(zone_start, k->zname, KNOT_DNAME_MAXLEN - kwz.len);
+	if (ret != k->zlf_len + 1) {
+		assert(false);
+		return ret < 0 ? ret : kr_error(EILSEQ);
+	}
+	return kr_ok();
+}
+
+
+knot_db_val_t key_NSEC1(struct key *k, const knot_dname_t *name, bool add_wildcard)
+{
+	/* we basically need dname_lf with two bytes added
+	 * on a correct place within the name (the cut) */
+	int ret;
+	const bool ok = k && name
+		&& !(ret = kr_dname_lf(k->buf, name, add_wildcard));
+	if (!ok) {
+		assert(false);
+		return (knot_db_val_t){ NULL, 0 };
+	}
+
+	uint8_t *begin = k->buf + 1 + k->zlf_len; /* one byte after zone's zero */
+	uint8_t *end = k->buf + 1 + k->buf[0]; /* we don't use the final zero in key,
+						* but move it anyway */
+	if (end < begin) {
+		assert(false);
+		return (knot_db_val_t){ NULL, 0 };
+	}
+	int key_len;
+	if (end > begin) {
+		memmove(begin + 2, begin, end - begin);
+		key_len = k->buf[0] + 1;
+	} else {
+		key_len = k->buf[0] + 2;
+	}
+	/* CACHE_KEY_DEF: key == zone's dname_lf + '\0' + '1' + dname_lf
+	 * of the name within the zone without the final 0.  Iff the latter is empty,
+	 * there's no zero to cut and thus the key_len difference.
+	 */
+	begin[0] = 0;
+	begin[1] = '1'; /* tag for NSEC1 */
+	k->type = KNOT_RRTYPE_NSEC;
+
+	/*
+	VERBOSE_MSG(NULL, "<> key_NSEC1; name: ");
+	kr_dname_print(name, add_wildcard ? "*." : "" , " ");
+	kr_log_verbose("(zone name LF length: %d; total key length: %d)\n",
+			k->zlf_len, key_len);
+	*/
+
+	return (knot_db_val_t){ k->buf + 1, key_len };
+}
+
+
+/** Assuming that k1 < k4, find where k2 is.  (Considers DNS wrap-around.)
+ *
+ * \return Intuition: position of k2 among kX.
+ *	0: k2 < k1;  1: k1 == k2;  2: k1 is a prefix of k2 < k4;
+ *	3: k1 < k2 < k4 (and not 2);  4: k2 == k4;  5: k2 > k4
+ * \note k1.data may be NULL, meaning assumption that k1 < k2 and not a prefix
+ *       (i.e. return code will be > 2)
+ */
+static int kwz_between(knot_db_val_t k1, knot_db_val_t k2, knot_db_val_t k4)
+{
+	assert(k2.data && k4.data);
+	/* CACHE_KEY_DEF; we need to beware of one key being a prefix of another */
+	int ret_maybe; /**< result, assuming we confirm k2 < k4 */
+	if (k1.data) {
+		const int cmp12 = memcmp(k1.data, k2.data, MIN(k1.len, k2.len));
+		if (cmp12 == 0 && k1.len == k2.len) /* iff k1 == k2 */
+			return 1;
+		if (cmp12 > 0 || (cmp12 == 0 && k1.len > k2.len)) /* iff k1 > k2 */
+			return 0;
+		ret_maybe = cmp12 == 0 ? 2 : 3;
+	} else {
+		ret_maybe = 3;
+	}
+	if (k4.len == 0) { /* wrap-around */
+		return k2.len > 0 ? ret_maybe : 4;
+	} else {
+		const int cmp24 = memcmp(k2.data, k4.data, MIN(k2.len, k4.len));
+		if (cmp24 == 0 && k2.len == k4.len) /* iff k2 == k4 */
+			return 4;
+		if (cmp24 > 0 || (cmp24 == 0 && k2.len > k4.len)) /* iff k2 > k4 */
+			return 5;
+		return ret_maybe;
+	}
+}
+
+
+/** NSEC1 range search.
+ *
+ * \param key Pass output of key_NSEC1(k, ...)
+ * \param value[out] The raw data of the NSEC cache record (optional; consistency checked).
+ * \param exact_match[out] Whether the key was matched exactly or just covered (optional).
+ * \param kwz_low[out] Output the low end of covering NSEC, pointing within DB (optional).
+ * \param kwz_high[in,out] Storage for the high end of covering NSEC (optional).
+ * 		It's only set if !exact_match.
+ * \param new_ttl[out] New TTL of the NSEC (optional).
+ * \return Error message or NULL.
+ * \note The function itself does *no* bitmap checks, e.g. RFC 6840 sec. 4.
+ */
+static const char * find_leq_NSEC1(struct kr_cache *cache, const struct kr_query *qry,
+			const knot_db_val_t key, const struct key *k, knot_db_val_t *value,
+			bool *exact_match, knot_db_val_t *kwz_low, knot_db_val_t *kwz_high,
+			uint32_t *new_ttl)
+{
+	/* Do the cache operation. */
+	const size_t nwz_off = key_nwz_off(k);
+	if (!key.data || key.len < nwz_off) {
+		assert(false);
+		return "range search ERROR";
+	}
+	knot_db_val_t key_nsec = key;
+	knot_db_val_t val = { NULL, 0 };
+	int ret = cache_op(cache, read_leq, &key_nsec, &val);
+	if (ret < 0) {
+		if (ret == kr_error(ENOENT)) {
+			return "range search miss";
+		} else {
+			assert(false);
+			return "range search ERROR";
+		}
+	}
+	if (value) {
+		*value = val;
+	}
+	/* Check consistency, TTL, rank. */
+	const bool is_exact = (ret == 0);
+	if (exact_match) {
+		*exact_match = is_exact;
+	}
+	const struct entry_h *eh = entry_h_consistent_NSEC(val);
+	if (!eh) {
+		/* This might be just finding something else than NSEC1 entry,
+		 * in case we searched before the very first one in the zone. */
+		return "range search found inconsistent entry";
+	}
+	/* Passing just zone name instead of owner, as we don't
+	 * have it reconstructed at this point. */
+	int32_t new_ttl_ = get_new_ttl(eh, qry, k->zname, KNOT_RRTYPE_NSEC,
+					qry->timestamp.tv_sec);
+	if (new_ttl_ < 0 || !kr_rank_test(eh->rank, KR_RANK_SECURE)) {
+		return "range search found stale or insecure entry";
+		/* TODO: remove the stale record *and* retry,
+		 * in case we haven't run off.  Perhaps start by in_zone check. */
+	}
+	if (new_ttl) {
+		*new_ttl = new_ttl_;
+	}
+	if (kwz_low) {
+		*kwz_low = (knot_db_val_t){
+			.data = (uint8_t *)key_nsec.data + nwz_off,
+			.len = key_nsec.len - nwz_off,
+		};	/* CACHE_KEY_DEF */
+	}
+	if (is_exact) {
+		/* Nothing else to do. */
+		return NULL;
+	}
+	/* The NSEC starts strictly before our target name;
+	 * now check that it still belongs into that zone. */
+	const bool nsec_in_zone = key_nsec.len >= nwz_off
+		/* CACHE_KEY_DEF */
+		&& memcmp(key.data, key_nsec.data, nwz_off) == 0;
+	if (!nsec_in_zone) {
+		return "range search miss (!nsec_in_zone)";
+	}
+	/* We know it starts before sname, so let's check the other end.
+	 * 1. construct the key for the next name - kwz_hi. */
+	/* it's *full* name ATM */
+	const knot_rdata_t *next = (const knot_rdata_t *)
+				(eh->data + KR_CACHE_RR_COUNT_SIZE);
+	if (KR_CACHE_RR_COUNT_SIZE != 2 || get_uint16(eh->data) == 0) {
+		assert(false);
+		return "ERROR";
+		/* TODO: more checks? */
+	}
+	/*
+	WITH_VERBOSE {
+		VERBOSE_MSG(qry, "=> NSEC: next name: ");
+		kr_dname_print(next, "", "\n");
+	}
+	*/
+	knot_dname_t ch_buf[KNOT_DNAME_MAXLEN];
+	knot_dname_t *chs = kwz_high ? kwz_high->data : ch_buf;
+	if (!chs) {
+		assert(false);
+		return "EINVAL";
+	}
+	{
+		/* Lower-case chs; see also RFC 6840 5.1.
+		 * LATER(optim.): we do lots of copying etc. */
+		knot_dname_t lower_buf[KNOT_DNAME_MAXLEN];
+		ret = knot_dname_to_wire(lower_buf, next->data,
+					 MIN(next->len, KNOT_DNAME_MAXLEN));
+		if (ret < 0) { /* _ESPACE */
+			return "range search found record with incorrect contents";
+		}
+		knot_dname_to_lower(lower_buf);
+		ret = kr_dname_lf(chs, lower_buf, false);
+	}
+	if (ret) {
+		assert(false);
+		return "ERROR";
+	}
+	knot_db_val_t kwz_hi = { /* skip the zone name */
+		.data = chs + 1 + k->zlf_len,
+		.len = chs[0] - k->zlf_len,
+	};
+	assert((ssize_t)(kwz_hi.len) >= 0);
+	/* 2. do the actual range check. */
+	const knot_db_val_t kwz_sname = {
+		.data = (void *)/*const-cast*/(k->buf + 1 + nwz_off),
+		.len = k->buf[0] - k->zlf_len,
+	};
+	assert((ssize_t)(kwz_sname.len) >= 0);
+	bool covers = /* we know for sure that the low end is before kwz_sname */
+		3 == kwz_between((knot_db_val_t){ NULL, 0 }, kwz_sname, kwz_hi);
+	if (!covers) {
+		return "range search miss (!covers)";
+	}
+	if (kwz_high) {
+		*kwz_high = kwz_hi;
+	}
+	return NULL;
+}
+
+
+int nsec1_encloser(struct key *k, struct answer *ans,
+		   const int sname_labels, int *clencl_labels,
+		   knot_db_val_t *cover_low_kwz, knot_db_val_t *cover_hi_kwz,
+		   const struct kr_query *qry, struct kr_cache *cache)
+{
+	static const int ESKIP = ABS(ENOENT);
+	/* Basic sanity check. */
+	const bool ok = k && ans && clencl_labels && cover_low_kwz && cover_hi_kwz
+			&& qry && cache;
+	if (!ok) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+	
+	/* Find a previous-or-equal name+NSEC in cache covering the QNAME,
+	 * checking TTL etc. */
+	knot_db_val_t key = key_NSEC1(k, qry->sname, false);
+	knot_db_val_t val = { NULL, 0 };
+	bool exact_match;
+	uint32_t new_ttl;
+	const char *err = find_leq_NSEC1(cache, qry, key, k, &val,
+			&exact_match, cover_low_kwz, cover_hi_kwz, &new_ttl);
+	if (err) {
+		VERBOSE_MSG(qry, "=> NSEC sname: %s\n", err);
+		return ESKIP;
+	}
+
+	/* Get owner name of the record. */
+	const knot_dname_t *owner;
+	knot_dname_t owner_buf[KNOT_DNAME_MAXLEN];
+	if (exact_match) {
+		owner = qry->sname;
+	} else {
+		int ret = dname_wire_reconstruct(owner_buf, k, *cover_low_kwz);
+		if (unlikely(ret)) return ESKIP;
+		owner = owner_buf;
+	}
+	/* Basic checks OK -> materialize data. */
+	{
+		const struct entry_h *nsec_eh = val.data;
+		int ret = entry2answer(ans, AR_NSEC, nsec_eh, knot_db_val_bound(val),
+					owner, KNOT_RRTYPE_NSEC, new_ttl);
+		if (ret) return kr_error(ret);
+	}
+
+	/* Final checks, split for matching vs. covering our sname. */
+	const knot_rrset_t *nsec_rr = ans->rrsets[AR_NSEC].set.rr;
+	const uint8_t *bm = knot_nsec_bitmap(nsec_rr->rrs.rdata);
+	uint16_t bm_size = knot_nsec_bitmap_len(nsec_rr->rrs.rdata);
+	assert(bm);
+
+	if (exact_match) {
+		if (kr_nsec_bitmap_nodata_check(bm, bm_size, qry->stype, nsec_rr->owner) != 0) {
+			VERBOSE_MSG(qry,
+				"=> NSEC sname: match but failed type check\n");
+			return ESKIP;
+		}
+		/* NODATA proven; just need to add SOA+RRSIG later */
+		VERBOSE_MSG(qry, "=> NSEC sname: match proved NODATA, new TTL %d\n",
+				new_ttl);
+		ans->rcode = PKT_NODATA;
+		return kr_ok();
+	} /* else */
+
+	/* Inexact match.  First check if sname is delegated by that NSEC. */
+	const int nsec_matched = knot_dname_matched_labels(nsec_rr->owner, qry->sname);
+	const bool is_sub = nsec_matched == knot_dname_labels(nsec_rr->owner, NULL);
+	if (is_sub && kr_nsec_children_in_zone_check(bm, bm_size) != 0) {
+		VERBOSE_MSG(qry, "=> NSEC sname: covered but delegated (or error)\n");
+		return ESKIP;
+	}
+	/* NXDOMAIN proven *except* for wildcards. */
+	WITH_VERBOSE(qry) {
+		auto_free char *owner_str = kr_dname_text(nsec_rr->owner),
+			  *next_str = kr_dname_text(knot_nsec_next(nsec_rr->rrs.rdata));
+		VERBOSE_MSG(qry, "=> NSEC sname: covered by: %s -> %s, new TTL %d\n",
+				owner_str, next_str, new_ttl);
+	}
+
+	/* Find label count of the closest encloser.
+	 * Both endpoints in an NSEC do exist (though possibly in a child zone)
+	 * and any prefixes of those names as well (empty non-terminals),
+	 * but nothing else exists inside this "triangle".
+	 *
+	 * Note that we have to lower-case the next name for comparison,
+	 * even though we have canonicalized NSEC already; see RFC 6840 5.1.
+	 * LATER(optim.): it might be faster to use the LFs we already have.
+	 */
+	knot_dname_t next[KNOT_DNAME_MAXLEN];
+	int ret = knot_dname_to_wire(next, knot_nsec_next(nsec_rr->rrs.rdata), sizeof(next));
+	if (ret < 0) {
+		assert(!ret);
+		return kr_error(ret);
+	}
+	knot_dname_to_lower(next);
+	*clencl_labels = MAX(
+		nsec_matched,
+		knot_dname_matched_labels(qry->sname, next)
+		);
+
+	/* Empty non-terminals don't need to have
+	 * a matching NSEC record. */
+	if (sname_labels == *clencl_labels) {
+		ans->rcode = PKT_NODATA;
+		VERBOSE_MSG(qry,
+			"=> NSEC sname: empty non-terminal by the same RR\n");
+	} else {
+		ans->rcode = PKT_NXDOMAIN;
+	}
+	return kr_ok();
+}
+
+/** Verify non-existence after kwz_between() call. */
+static bool nonexistence_ok(int cmp, const knot_rrset_t *rrs)
+{
+	if (cmp == 3) {
+		return true;
+	}
+	if (cmp != 2) {
+		return false;
+	}
+	const uint8_t *bm = knot_nsec_bitmap(rrs->rrs.rdata);
+	uint16_t bm_size = knot_nsec_bitmap_len(rrs->rrs.rdata);
+	return kr_nsec_children_in_zone_check(bm, bm_size) != 0;
+}
+
+int nsec1_src_synth(struct key *k, struct answer *ans, const knot_dname_t *clencl_name,
+		    knot_db_val_t cover_low_kwz, knot_db_val_t cover_hi_kwz,
+		    const struct kr_query *qry, struct kr_cache *cache)
+{
+	/* Construct key for the source of synthesis. */
+	knot_db_val_t key = key_NSEC1(k, clencl_name, true);
+	const size_t nwz_off = key_nwz_off(k);
+	if (!key.data || key.len < nwz_off) {
+		assert(false);
+		return kr_error(1);
+	}
+	/* Check if our sname-covering NSEC also covers/matches SS. */
+	knot_db_val_t kwz = {
+		.data = (uint8_t *)key.data + nwz_off,
+		.len = key.len - nwz_off,
+	};
+	assert((ssize_t)(kwz.len) >= 0);
+	const int cmp = kwz_between(cover_low_kwz, kwz, cover_hi_kwz);
+	if (nonexistence_ok(cmp, ans->rrsets[AR_NSEC].set.rr)) {
+		VERBOSE_MSG(qry, "=> NSEC wildcard: covered by the same RR\n");
+		return AR_SOA;
+	}
+	const knot_rrset_t *nsec_rr = NULL; /**< the wildcard proof NSEC */
+	bool exact_match; /**< whether it matches the source of synthesis */
+	if (cmp == 1) {
+		exact_match = true;
+		nsec_rr = ans->rrsets[AR_NSEC].set.rr;
+	} else {
+		/* Try to find the NSEC for SS. */
+		knot_db_val_t val = { NULL, 0 };
+		knot_db_val_t wild_low_kwz = { NULL, 0 };
+		uint32_t new_ttl;
+		const char *err = find_leq_NSEC1(cache, qry, key, k, &val,
+				&exact_match, &wild_low_kwz, NULL, &new_ttl);
+		if (err) {
+			VERBOSE_MSG(qry, "=> NSEC wildcard: %s\n", err);
+			return kr_ok();
+		}
+		/* Materialize the record into answer (speculatively). */
+		knot_dname_t owner[KNOT_DNAME_MAXLEN];
+		int ret = dname_wire_reconstruct(owner, k, wild_low_kwz);
+		if (ret) return kr_error(ret);
+		const struct entry_h *nsec_eh = val.data;
+		ret = entry2answer(ans, AR_WILD, nsec_eh, knot_db_val_bound(val),
+				   owner, KNOT_RRTYPE_NSEC, new_ttl);
+		if (ret) return kr_error(ret);
+		nsec_rr = ans->rrsets[AR_WILD].set.rr;
+	}
+
+	assert(nsec_rr);
+	const uint32_t new_ttl_log =
+		kr_verbose_status ? nsec_rr->ttl : -1;
+	const uint8_t *bm = knot_nsec_bitmap(nsec_rr->rrs.rdata);
+	uint16_t bm_size = knot_nsec_bitmap_len(nsec_rr->rrs.rdata);
+	int ret;
+	struct answer_rrset * const arw = &ans->rrsets[AR_WILD];
+	if (!bm) {
+		assert(false);
+		ret = kr_error(1);
+		goto clean_wild;
+	}
+	if (!exact_match) {
+		/* Finish verification that the source of synthesis doesn't exist. */
+		const int nsec_matched =
+			knot_dname_matched_labels(nsec_rr->owner, clencl_name);
+			/* we don't need to use the full source of synthesis ^ */
+		const bool is_sub =
+			nsec_matched == knot_dname_labels(nsec_rr->owner, NULL);
+		if (is_sub && kr_nsec_children_in_zone_check(bm, bm_size) != 0) {
+			VERBOSE_MSG(qry,
+				"=> NSEC wildcard: covered but delegated (or error)\n");
+			ret = kr_ok();
+			goto clean_wild;
+		}
+		/* We have a record proving wildcard non-existence. */
+		WITH_VERBOSE(qry) {
+			auto_free char *owner_str = kr_dname_text(nsec_rr->owner),
+				*next_str = kr_dname_text(knot_nsec_next(nsec_rr->rrs.rdata));
+			VERBOSE_MSG(qry, "=> NSEC wildcard: covered by: %s -> %s, new TTL %d\n",
+					owner_str, next_str, new_ttl_log);
+		}
+		return AR_SOA;
+	}
+
+	/* The wildcard exists.  Find if it's NODATA - check type bitmap. */
+	if (kr_nsec_bitmap_nodata_check(bm, bm_size, qry->stype, nsec_rr->owner) == 0) {
+		/* NODATA proven; just need to add SOA+RRSIG later */
+		WITH_VERBOSE(qry) {
+			const char *msg_start = "=> NSEC wildcard: match proved NODATA";
+			if (arw->set.rr) {
+				auto_free char *owner_str = kr_dname_text(nsec_rr->owner);
+				VERBOSE_MSG(qry, "%s: %s, new TTL %d\n",
+						msg_start, owner_str, new_ttl_log);
+			} else {
+				/* don't repeat the RR if it's the same */
+				VERBOSE_MSG(qry, "%s, by the same RR\n", msg_start);
+			}
+		}
+		ans->rcode = PKT_NODATA;
+		return AR_SOA;
+
+	} /* else */
+	/* The data probably exists -> don't add this NSEC
+	 * and (later) try to find the real wildcard data */
+	VERBOSE_MSG(qry, "=> NSEC wildcard: should exist (or error)\n");
+	ans->rcode = PKT_NOERROR;
+	ret = kr_ok();
+clean_wild:
+	if (arw->set.rr) { /* we may have matched AR_NSEC */
+		knot_rrset_free(arw->set.rr, ans->mm);
+		arw->set.rr = NULL;
+		knot_rdataset_clear(&arw->sig_rds, ans->mm);
+	}
+	return ret;
+}
+
diff --git a/lib/cache/nsec3.c b/lib/cache/nsec3.c
new file mode 100644
index 0000000..d2ae72a
--- /dev/null
+++ b/lib/cache/nsec3.c
@@ -0,0 +1,501 @@
+/*  Copyright (C) 2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ * Implementation of NSEC3 handling.  Prototypes in ./impl.h
+ */
+
+#include "lib/cache/impl.h"
+
+#include "contrib/base32hex.h"
+#include "lib/dnssec/nsec.h"
+#include "lib/layer/iterate.h"
+
+#include <libknot/rrtype/nsec3.h>
+
+static const knot_db_val_t VAL_EMPTY = { NULL, 0 };
+
+/** Common part: write all but the NSEC3 hash. */
+static knot_db_val_t key_NSEC3_common(struct key *k, const knot_dname_t *zname,
+					const nsec_p_hash_t nsec_p_hash)
+{
+	int ret;
+	const bool ok = k && zname
+		&& !(ret = kr_dname_lf(k->buf, zname, false));
+	if (!ok) {
+		assert(false);
+		return VAL_EMPTY;
+	}
+
+	/* CACHE_KEY_DEF: key == zone's dname_lf + '\0' + '3' + nsec_p hash (4B)
+	 * 			+ NSEC3 hash (20B == NSEC3_HASH_LEN binary!)
+	 * LATER(optim.) nsec_p hash: perhaps 2B would give a sufficient probability
+	 * of avoiding collisions.
+	 */
+	uint8_t *begin = k->buf + 1 + k->zlf_len; /* one byte after zone's zero */
+	begin[0] = 0;
+	begin[1] = '3'; /* tag for NSEC3 */
+	k->type = KNOT_RRTYPE_NSEC3;
+	memcpy(begin + 2, &nsec_p_hash, sizeof(nsec_p_hash));
+	return (knot_db_val_t){
+		.data = k->buf + 1,
+		.len = begin + 2 + sizeof(nsec_p_hash) - (k->buf + 1),
+	};
+}
+
+knot_db_val_t key_NSEC3(struct key *k, const knot_dname_t *nsec3_name,
+			const nsec_p_hash_t nsec_p_hash)
+{
+	knot_db_val_t val = key_NSEC3_common(k, nsec3_name /*only zname required*/,
+						nsec_p_hash);
+	if (!val.data) return val;
+	int len = base32hex_decode(nsec3_name + 1, nsec3_name[0],
+			knot_db_val_bound(val), KR_CACHE_KEY_MAXLEN - val.len);
+	if (len != NSEC3_HASH_LEN) {
+		return VAL_EMPTY;
+	}
+	val.len += len;
+	return val;
+}
+
+/** Construct a string key for for NSEC3 predecessor-search, from an non-NSEC3 name.
+ * \note k->zlf_len and k->zname are assumed to have been correctly set */
+static knot_db_val_t key_NSEC3_name(struct key *k, const knot_dname_t *name,
+		const bool add_wildcard, const struct nsec_p *nsec_p)
+{
+	bool ok = k && name && nsec_p && nsec_p->raw;
+	if (!ok) return VAL_EMPTY;
+	knot_db_val_t val = key_NSEC3_common(k, k->zname, nsec_p->hash);
+	if (!val.data) return val;
+
+	/* Make `name` point to correctly wildcarded owner name. */
+	uint8_t buf[KNOT_DNAME_MAXLEN];
+	int name_len;
+	if (add_wildcard) {
+		buf[0] = '\1';
+		buf[1] = '*';
+		name_len = knot_dname_to_wire(buf + 2, name, sizeof(buf) - 2);
+		if (name_len < 0) return VAL_EMPTY; /* wants wildcard but doesn't fit */
+		name = buf;
+		name_len += 2;
+	} else {
+		name_len = knot_dname_size(name);
+	}
+	/* Append the NSEC3 hash. */
+	const dnssec_binary_t dname = {
+		.size = name_len,
+		.data = (uint8_t *)/*const-cast*/name,
+	};
+
+	#if 0 // LATER(optim.): this requires a patched libdnssec - tries to realloc()
+	dnssec_binary_t hash = {
+		.size = KR_CACHE_KEY_MAXLEN - val.len,
+		.data = val.data + val.len,
+	};
+	int ret = dnssec_nsec3_hash(&dname, &nsec_p->libknot, &hash);
+	if (ret != DNSSEC_EOK) return VAL_EMPTY;
+	assert(hash.size == NSEC3_HASH_LEN);
+
+	#else
+	dnssec_binary_t hash = { .size = 0, .data = NULL };
+	int ret = dnssec_nsec3_hash(&dname, &nsec_p->libknot, &hash);
+	if (ret != DNSSEC_EOK) return VAL_EMPTY;
+	if (hash.size != NSEC3_HASH_LEN || !hash.data) {
+		assert(false);
+		return VAL_EMPTY;
+	}
+	memcpy(knot_db_val_bound(val), hash.data, NSEC3_HASH_LEN);
+	free(hash.data);
+	#endif
+
+	val.len += hash.size;
+	return val;
+}
+
+/** Return h1 < h2, semantically on NSEC3 hashes. */
+static inline bool nsec3_hash_ordered(const uint8_t *h1, const uint8_t *h2)
+{
+	return memcmp(h1, h2, NSEC3_HASH_LEN) < 0;
+}
+
+/** NSEC3 range search.
+ *
+ * \param key Pass output of key_NSEC3(k, ...)
+ * \param nsec_p Restrict to this NSEC3 parameter-set.
+ * \param value[out] The raw data of the NSEC3 cache record (optional; consistency checked).
+ * \param exact_match[out] Whether the key was matched exactly or just covered (optional).
+ * \param hash_low[out] Output the low end hash of covering NSEC3, pointing within DB (optional).
+ * \param new_ttl[out] New TTL of the NSEC3 (optional).
+ * \return Error message or NULL.
+ * \note The function itself does *no* bitmap checks, e.g. RFC 6840 sec. 4.
+ */
+static const char * find_leq_NSEC3(struct kr_cache *cache, const struct kr_query *qry,
+		const knot_db_val_t key, const struct key *k, const struct nsec_p *nsec_p,
+		knot_db_val_t *value, bool *exact_match, const uint8_t **hash_low,
+		uint32_t *new_ttl)
+{
+	/* Do the cache operation. */
+	const size_t hash_off = key_nsec3_hash_off(k);
+	if (!key.data || key.len < hash_off) {
+		assert(false);
+		return "range search ERROR";
+	}
+	knot_db_val_t key_found = key;
+	knot_db_val_t val = { NULL, 0 };
+	int ret = cache_op(cache, read_leq, &key_found, &val);
+		/* ^^ LATER(optim.): incrementing key and doing less-than search
+		 * would probably be slightly more efficient with LMDB,
+		 * but the code complexity would grow considerably. */
+	if (ret < 0) {
+		if (ret == kr_error(ENOENT)) {
+			return "range search miss";
+		} else {
+			assert(false);
+			return "range search ERROR";
+		}
+	}
+	if (value) {
+		*value = val;
+	}
+	/* Check consistency, TTL, rank. */
+	const bool is_exact = (ret == 0);
+	if (exact_match) {
+		*exact_match = is_exact;
+	}
+	const struct entry_h *eh = entry_h_consistent_NSEC(val);
+	if (!eh) {
+		/* This might be just finding something else than NSEC3 entry,
+		 * in case we searched before the very first one in the zone. */
+		return "range search found inconsistent entry";
+	}
+	/* Passing just zone name instead of owner. */
+	int32_t new_ttl_ = get_new_ttl(eh, qry, k->zname, KNOT_RRTYPE_NSEC3,
+					qry->timestamp.tv_sec);
+	if (new_ttl_ < 0 || !kr_rank_test(eh->rank, KR_RANK_SECURE)) {
+		return "range search found stale or insecure entry";
+		/* TODO: remove the stale record *and* retry,
+		 * in case we haven't run off.  Perhaps start by in_zone check. */
+	}
+	if (new_ttl) {
+		*new_ttl = new_ttl_;
+	}
+	if (hash_low) {
+		*hash_low = (uint8_t *)key_found.data + hash_off;
+	}
+	if (is_exact) {
+		/* Nothing else to do. */
+		return NULL;
+	}
+	/* The NSEC3 starts strictly before our target name;
+	 * now check that it still belongs into that zone and chain. */
+	const uint8_t *nsec_p_raw = eh->data + KR_CACHE_RR_COUNT_SIZE
+					+ 2 /* RDLENGTH from rfc1034 */;
+	const int nsec_p_len = nsec_p_rdlen(nsec_p_raw);
+	const bool same_chain = key_found.len == hash_off + NSEC3_HASH_LEN
+		/* CACHE_KEY_DEF */
+		&& memcmp(key.data, key_found.data, hash_off) == 0
+		/* exact comparison of NSEC3 parameters */
+		&& nsec_p_len == nsec_p_rdlen(nsec_p->raw)
+		&& memcmp(nsec_p_raw, nsec_p->raw, nsec_p_len) == 0;
+	if (!same_chain) {
+		return "range search miss (!same_chain)";
+	}
+	/* We know it starts before sname, so let's check the other end.
+	 * A. find the next hash and check its length. */
+	if (KR_CACHE_RR_COUNT_SIZE != 2 || get_uint16(eh->data) == 0) {
+		assert(false);
+		return "ERROR";
+		/* TODO: more checks?  Also, `next` computation is kinda messy. */
+	}
+	const uint8_t *hash_next = nsec_p_raw + nsec_p_len
+				 + sizeof(uint8_t) /* hash length from rfc5155 */;
+	if (hash_next[-1] != NSEC3_HASH_LEN) {
+		return "unexpected next hash length";
+	}
+	/* B. do the actual range check. */
+	const uint8_t * const hash_searched = (uint8_t *)key.data + hash_off;
+	bool covers = /* we know for sure that the low end is before the searched name */
+		nsec3_hash_ordered(hash_searched, hash_next)
+		/* and the wrap-around case */
+		|| nsec3_hash_ordered(hash_next, (const uint8_t *)key_found.data + hash_off);
+	if (!covers) {
+		return "range search miss (!covers)";
+	}
+	return NULL;
+}
+
+/** Extract textual representation of NSEC3 hash from a cache key.
+ * \param text must have length at least NSEC3_HASH_TXT_LEN+1 (will get 0-terminated). */
+static void key_NSEC3_hash2text(const knot_db_val_t key, char *text)
+{
+	assert(key.data && key.len > NSEC3_HASH_LEN);
+	const uint8_t *hash_raw = knot_db_val_bound(key) - NSEC3_HASH_LEN;
+			/* CACHE_KEY_DEF ^^ */
+	int len = base32hex_encode(hash_raw, NSEC3_HASH_LEN, (uint8_t *)text,
+				   NSEC3_HASH_TXT_LEN);
+	assert(len == NSEC3_HASH_TXT_LEN); (void)len;
+	text[NSEC3_HASH_TXT_LEN] = '\0';
+}
+
+/** Reconstruct a name into a buffer (assuming length at least KNOT_DNAME_MAXLEN).
+ * \return kr_ok() or error code (<0). */
+static int dname_wire_reconstruct(knot_dname_t *buf, const knot_dname_t *zname,
+				  const uint8_t *hash_raw)
+{
+	int len = base32hex_encode(hash_raw, NSEC3_HASH_LEN, buf + 1, NSEC3_HASH_TXT_LEN);
+	if (len != NSEC3_HASH_TXT_LEN) {
+		assert(false);
+		return kr_error(EINVAL);
+	}
+	buf[0] = len;
+	int ret = knot_dname_to_wire(buf + 1 + len, zname, KNOT_DNAME_MAXLEN - 1 - len);
+	return ret < 0 ? kr_error(ret) : kr_ok();
+}
+
+static void nsec3_hash2text(const knot_dname_t *owner, char *text)
+{
+	assert(owner[0] == NSEC3_HASH_TXT_LEN);
+	memcpy(text, owner + 1, MIN(owner[0], NSEC3_HASH_TXT_LEN));
+	text[NSEC3_HASH_TXT_LEN] = '\0';
+}
+
+int nsec3_encloser(struct key *k, struct answer *ans,
+		   const int sname_labels, int *clencl_labels,
+		   const struct kr_query *qry, struct kr_cache *cache)
+{
+	static const int ESKIP = ABS(ENOENT);
+	/* Basic sanity check. */
+	const bool ok = k && k->zname && ans && clencl_labels
+			&& qry && cache;
+	if (!ok) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+
+	/*** Find the closest encloser - cycle: name starting at sname,
+	 * proceeding while longer than zname, shortening by one label on step.
+	 * We need a pair where a name doesn't exist *and* its parent does. */
+		/* LATER(optim.): perhaps iterate in the other order - that
+		 * should help significantly against deep queries where we have
+		 * a shallow proof in the cache.  We can also optimize by using
+		 * only exact search unless we had a match in the previous iteration. */
+	const int zname_labels = knot_dname_labels(k->zname, NULL);
+	int last_nxproven_labels = -1;
+	const knot_dname_t *name = qry->sname;
+	for (int name_labels = sname_labels; name_labels >= zname_labels;
+					--name_labels, name += 1 + name[0]) {
+		/* Find a previous-or-equal NSEC3 in cache covering the name,
+		 * checking TTL etc. */
+		const knot_db_val_t key = key_NSEC3_name(k, name, false, &ans->nsec_p);
+		if (!key.data) continue;
+		WITH_VERBOSE(qry) {
+			char hash_txt[NSEC3_HASH_TXT_LEN + 1];
+			key_NSEC3_hash2text(key, hash_txt);
+			VERBOSE_MSG(qry, "=> NSEC3 depth %d: hash %s\n",
+					name_labels - zname_labels, hash_txt);
+		}
+		knot_db_val_t val = { NULL, 0 };
+		bool exact_match;
+		uint32_t new_ttl;
+		const uint8_t *hash_low;
+		const char *err = find_leq_NSEC3(cache, qry, key, k, &ans->nsec_p, &val,
+						 &exact_match, &hash_low, &new_ttl);
+		if (err) {
+			WITH_VERBOSE(qry) {
+				auto_free char *name_str = kr_dname_text(name);
+				VERBOSE_MSG(qry, "=> NSEC3 encloser error for %s: %s\n",
+						name_str, err);
+			}
+			continue;
+		}
+		if (exact_match && name_labels != sname_labels
+				&& name_labels + 1 != last_nxproven_labels) {
+			/* This name exists (checked rank and TTL), and it's
+			 * neither of the two interesting cases, so we do not
+			 * keep searching for non-existence above this name. */
+			VERBOSE_MSG(qry,
+				"=> NSEC3 encloser: only found existence of an ancestor\n");
+			return ESKIP;
+		}
+		/* Optimization: avoid the rest of the last iteration if pointless. */
+		if (!exact_match && name_labels == zname_labels
+		    && last_nxproven_labels != name_labels + 1) {
+			break;
+		}
+
+		/* Basic checks OK -> materialize data, cleaning any previous
+		 * records on that answer index (unsuccessful attempts). */
+		knot_dname_t owner[KNOT_DNAME_MAXLEN];
+		{
+			int ret = dname_wire_reconstruct(owner, k->zname, hash_low);
+			if (unlikely(ret)) continue;
+		}
+		const int ans_id = (exact_match && name_labels + 1 == last_nxproven_labels)
+				 ? AR_CPE : AR_NSEC;
+		{
+			const struct entry_h *nsec_eh = val.data;
+			memset(&ans->rrsets[ans_id], 0, sizeof(ans->rrsets[ans_id]));
+			int ret = entry2answer(ans, ans_id, nsec_eh, knot_db_val_bound(val),
+						owner, KNOT_RRTYPE_NSEC3, new_ttl);
+			if (ret) return kr_error(ret);
+		}
+
+		if (!exact_match) {
+			/* Non-existence proven, but we don't know if `name`
+			 * is the next closer name.
+			 * Note: we don't need to check for the sname being
+			 * delegated away by this record, as with NSEC3 only
+			 * *exact* match on an ancestor could do that. */
+			last_nxproven_labels = name_labels;
+			WITH_VERBOSE(qry) {
+				char hash_low_txt[NSEC3_HASH_TXT_LEN + 1];
+				nsec3_hash2text(owner, hash_low_txt);
+				VERBOSE_MSG(qry,
+					"=> NSEC3 depth %d: covered by %s -> TODO, new TTL %d\n",
+					name_labels - zname_labels, hash_low_txt, new_ttl);
+			}
+			continue;
+		}
+
+		/* Exactly matched NSEC3: two cases, one after another. */
+		const knot_rrset_t *nsec_rr = ans->rrsets[ans_id].set.rr;
+		const uint8_t *bm = knot_nsec3_bitmap(nsec_rr->rrs.rdata);
+		uint16_t bm_size = knot_nsec3_bitmap_len(nsec_rr->rrs.rdata);
+		assert(bm);
+		if (name_labels == sname_labels) {
+			if (kr_nsec_bitmap_nodata_check(bm, bm_size, qry->stype,
+							nsec_rr->owner) != 0) {
+				VERBOSE_MSG(qry,
+					"=> NSEC3 sname: match but failed type check\n");
+				return ESKIP;
+			}
+			/* NODATA proven; just need to add SOA+RRSIG later */
+			VERBOSE_MSG(qry,
+				"=> NSEC3 sname: match proved NODATA, new TTL %d\n",
+				new_ttl);
+			ans->rcode = PKT_NODATA;
+			return kr_ok();
+
+		} /* else */
+
+		assert(name_labels + 1 == last_nxproven_labels);
+		if (kr_nsec_children_in_zone_check(bm, bm_size) != 0) {
+			VERBOSE_MSG(qry,
+				"=> NSEC3 encloser: found but delegated (or error)\n");
+			return ESKIP;
+		}
+		/* NXDOMAIN proven *except* for wildcards. */
+		WITH_VERBOSE(qry) {
+			auto_free char *name_str = kr_dname_text(name);
+			VERBOSE_MSG(qry,
+				"=> NSEC3 encloser: confirmed as %s, new TTL %d\n",
+				name_str, new_ttl);
+		}
+		*clencl_labels = name_labels;
+		ans->rcode = PKT_NXDOMAIN;
+		/* Avoid repeated NSEC3 - remove either if the hashes match.
+		 * This is very unlikely in larger zones: 1/size (per attempt).
+		 * Well, deduplication would happen anyway when the answer
+		 * from cache is read by kresd (internally). */
+		if (unlikely(0 == memcmp(ans->rrsets[AR_NSEC].set.rr->owner + 1,
+					 ans->rrsets[AR_CPE ].set.rr->owner + 1,
+					 NSEC3_HASH_LEN))) {
+			memset(&ans->rrsets[AR_CPE], 0, sizeof(ans->rrsets[AR_CPE]));
+			/* LATER(optim.): perhaps check this earlier and avoid some work? */
+		}
+		return kr_ok();
+	}
+
+	/* We've ran out of options. */
+	if (last_nxproven_labels > 0) {
+		/* We didn't manage to prove existence of the closest encloser,
+		 * meaning the only chance left is a *positive* wildcard record. */
+		*clencl_labels = last_nxproven_labels - 1;
+		ans->rcode = PKT_NXDOMAIN;
+		/* FIXME: review */
+	}
+	return ESKIP;
+}
+
+int nsec3_src_synth(struct key *k, struct answer *ans, const knot_dname_t *clencl_name,
+		    const struct kr_query *qry, struct kr_cache *cache)
+{
+	/* Find a previous-or-equal NSEC3 in cache covering or matching
+	 * the source of synthesis, checking TTL etc. */
+	const knot_db_val_t key = key_NSEC3_name(k, clencl_name, true, &ans->nsec_p);
+	if (!key.data) return kr_error(1);
+	WITH_VERBOSE(qry) {
+		char hash_txt[NSEC3_HASH_TXT_LEN + 1];
+		key_NSEC3_hash2text(key, hash_txt);
+		VERBOSE_MSG(qry, "=> NSEC3 wildcard: hash %s\n", hash_txt);
+	}
+	knot_db_val_t val = { NULL, 0 };
+	bool exact_match;
+	uint32_t new_ttl;
+	const uint8_t *hash_low;
+	const char *err = find_leq_NSEC3(cache, qry, key, k, &ans->nsec_p, &val,
+					 &exact_match, &hash_low, &new_ttl);
+	if (err) {
+		VERBOSE_MSG(qry, "=> NSEC3 wildcard: %s\n", err);
+		return kr_ok();
+	}
+
+	/* LATER(optim.): avoid duplicities in answer. */
+
+	/* Basic checks OK -> materialize the data (speculatively). */
+	knot_dname_t owner[KNOT_DNAME_MAXLEN];
+	{
+		int ret = dname_wire_reconstruct(owner, k->zname, hash_low);
+		if (unlikely(ret)) return kr_ok();
+		const struct entry_h *nsec_eh = val.data;
+		ret = entry2answer(ans, AR_WILD, nsec_eh, knot_db_val_bound(val),
+				   owner, KNOT_RRTYPE_NSEC3, new_ttl);
+		if (ret) return kr_error(ret);
+	}
+	const knot_rrset_t *nsec_rr = ans->rrsets[AR_WILD].set.rr;
+
+	if (!exact_match) {
+		/* The record proves wildcard non-existence. */
+		WITH_VERBOSE(qry) {
+			char hash_low_txt[NSEC3_HASH_TXT_LEN + 1];
+			nsec3_hash2text(owner, hash_low_txt);
+			VERBOSE_MSG(qry,
+				"=> NSEC3 wildcard: covered by %s -> TODO, new TTL %d\n",
+				hash_low_txt, new_ttl);
+		}
+		return AR_SOA;
+	}
+
+	/* The wildcard exists.  Find if it's NODATA - check type bitmap. */
+	const uint8_t *bm = knot_nsec3_bitmap(nsec_rr->rrs.rdata);
+	uint16_t bm_size = knot_nsec3_bitmap_len(nsec_rr->rrs.rdata);
+	assert(bm);
+	if (kr_nsec_bitmap_nodata_check(bm, bm_size, qry->stype, nsec_rr->owner) == 0) {
+		/* NODATA proven; just need to add SOA+RRSIG later */
+		VERBOSE_MSG(qry, "=> NSEC3 wildcard: match proved NODATA, new TTL %d\n",
+				 new_ttl);
+		ans->rcode = PKT_NODATA;
+		return AR_SOA;
+
+	} /* else */
+	/* The data probably exists -> don't add this NSEC3
+	 * and (later) try to find the real wildcard data */
+	VERBOSE_MSG(qry, "=> NSEC3 wildcard: should exist (or error)\n");
+	ans->rcode = PKT_NOERROR;
+	memset(&ans->rrsets[AR_WILD], 0, sizeof(ans->rrsets[AR_WILD]));
+	return kr_ok();
+}
+
diff --git a/lib/cache/peek.c b/lib/cache/peek.c
new file mode 100644
index 0000000..1af1627
--- /dev/null
+++ b/lib/cache/peek.c
@@ -0,0 +1,724 @@
+/*  Copyright (C) 2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "lib/cache/impl.h"
+
+#include "lib/dnssec/ta.h"
+#include "lib/layer/iterate.h"
+
+/* The whole file only exports peek_nosync().
+ * Forwards for larger chunks of code: */
+
+static int found_exact_hit(kr_layer_t *ctx, knot_pkt_t *pkt, knot_db_val_t val,
+			   uint8_t lowest_rank);
+static int closest_NS(struct kr_cache *cache, struct key *k, entry_list_t el,
+			struct kr_query *qry, bool only_NS, bool is_DS);
+static int answer_simple_hit(kr_layer_t *ctx, knot_pkt_t *pkt, uint16_t type,
+		const struct entry_h *eh, const void *eh_bound, uint32_t new_ttl);
+static int try_wild(struct key *k, struct answer *ans, const knot_dname_t *clencl_name,
+		    uint16_t type, uint8_t lowest_rank,
+		    const struct kr_query *qry, struct kr_cache *cache);
+
+static int peek_encloser(
+	struct key *k, struct answer *ans, int sname_labels,
+	uint8_t lowest_rank, const struct kr_query *qry, struct kr_cache *cache);
+
+
+static int nsec_p_init(struct nsec_p *nsec_p, knot_db_val_t nsec_p_entry, bool with_knot)
+{
+	const size_t stamp_len = sizeof(uint32_t);
+	if (nsec_p_entry.len <= stamp_len) { /* plain NSEC if equal */
+		nsec_p->raw = NULL;
+		nsec_p->hash = 0;
+		return kr_ok();
+	}
+	nsec_p->raw = (uint8_t *)nsec_p_entry.data + stamp_len;
+	nsec_p->hash = nsec_p_mkHash(nsec_p->raw);
+	if (!with_knot) return kr_ok();
+	/* Convert NSEC3 params to another format. */
+	const dnssec_binary_t rdata = {
+		.size = nsec_p_rdlen(nsec_p->raw),
+		.data = (uint8_t *)/*const-cast*/nsec_p->raw,
+	};
+	int ret = dnssec_nsec3_params_from_rdata(&nsec_p->libknot, &rdata);
+	return ret == DNSSEC_EOK ? kr_ok() : kr_error(ret);
+}
+
+static void nsec_p_cleanup(struct nsec_p *nsec_p)
+{
+	dnssec_binary_free(&nsec_p->libknot.salt);
+	/* We don't really need to clear it, but it's not large. (`salt` zeroed above) */
+	memset(nsec_p, 0, sizeof(*nsec_p));
+}
+
+/** Compute new TTL for nsec_p entry, using SOA serial arith.
+ * \param new_ttl (optionally) write the new TTL (even if negative)
+ * \return error code, e.g. kr_error(ESTALE) */
+static int nsec_p_ttl(knot_db_val_t entry, const uint32_t timestamp, int32_t *new_ttl)
+{
+	if (!entry.data) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+	uint32_t stamp;
+	if (!entry.len) {
+		return kr_error(ENOENT);
+	}
+	if (entry.len < sizeof(stamp)) {
+		assert(!EILSEQ);
+		return kr_error(EILSEQ);
+	}
+	memcpy(&stamp, entry.data, sizeof(stamp));
+	int32_t newttl = stamp - timestamp;
+	if (new_ttl) *new_ttl = newttl;
+	return newttl < 0 ? kr_error(ESTALE) : kr_ok();
+}
+
+static uint8_t get_lowest_rank(const struct kr_request *req, const struct kr_query *qry)
+{
+	/* TODO: move rank handling into the iterator (DNSSEC_* flags)? */
+	const bool allow_unverified =
+		knot_wire_get_cd(req->qsource.packet->wire) || qry->flags.STUB;
+		/* in stub mode we don't trust RRs anyway ^^ */
+	if (qry->flags.NONAUTH) {
+		return KR_RANK_INITIAL;
+		/* Note: there's little sense in validation status for non-auth records.
+		 * In case of using NONAUTH to get NS IPs, knowing that you ask correct
+		 * IP doesn't matter much for security; it matters whether you can
+		 * validate the answers from the NS.
+		 */
+	} else if (!allow_unverified) {
+		/* Records not present under any TA don't have their security
+		 * verified at all, so we also accept low ranks in that case. */
+		const bool ta_covers = kr_ta_covers_qry(req->ctx, qry->sname, qry->stype);
+		/* ^ TODO: performance?  TODO: stype - call sites */
+		if (ta_covers) {
+			return KR_RANK_INSECURE | KR_RANK_AUTH;
+		} /* else falltrhough */
+	}
+	return KR_RANK_INITIAL | KR_RANK_AUTH;
+}
+
+
+/** Almost whole .produce phase for the cache module.
+ * \note we don't transition to KR_STATE_FAIL even in case of "unexpected errors".
+ */
+int peek_nosync(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	struct kr_cache *cache = &req->ctx->cache;
+
+	struct key k_storage, *k = &k_storage;
+	int ret = kr_dname_lf(k->buf, qry->sname, false);
+	if (unlikely(ret)) {
+		assert(false);
+		return ctx->state;
+	}
+
+	const uint8_t lowest_rank = get_lowest_rank(req, qry);
+
+	/**** 1. find the name or the closest (available) zone, not considering wildcards
+	 **** 1a. exact name+type match (can be negative answer in insecure zones) */
+	{
+		knot_db_val_t key = key_exact_type_maypkt(k, qry->stype);
+		knot_db_val_t val = { NULL, 0 };
+		ret = cache_op(cache, read, &key, &val, 1);
+		if (!ret) {
+			/* found an entry: test conditions, materialize into pkt, etc. */
+			ret = found_exact_hit(ctx, pkt, val, lowest_rank);
+		}
+	}
+	if (ret && ret != -abs(ENOENT)) {
+		VERBOSE_MSG(qry, "=> exact hit error: %d %s\n", ret, kr_strerror(ret));
+		assert(false);
+		return ctx->state;
+	} else if (!ret) {
+		return KR_STATE_DONE;
+	}
+
+	/**** 1b. otherwise, find the longest prefix zone/xNAME (with OK time+rank). [...] */
+	k->zname = qry->sname;
+	ret = kr_dname_lf(k->buf, k->zname, false); /* LATER(optim.): probably remove */
+	if (unlikely(ret)) {
+		assert(false);
+		return ctx->state;
+	}
+	entry_list_t el;
+	ret = closest_NS(cache, k, el, qry, false, qry->stype == KNOT_RRTYPE_DS);
+	if (ret) {
+		assert(ret == kr_error(ENOENT));
+		if (ret != kr_error(ENOENT) || !el[0].len) {
+			return ctx->state;
+		}
+	}
+	switch (k->type) {
+	case KNOT_RRTYPE_CNAME: {
+		const knot_db_val_t v = el[EL_CNAME];
+		assert(v.data && v.len);
+		const int32_t new_ttl = get_new_ttl(v.data, qry, qry->sname,
+						KNOT_RRTYPE_CNAME, qry->timestamp.tv_sec);
+		ret = answer_simple_hit(ctx, pkt, KNOT_RRTYPE_CNAME, v.data,
+					knot_db_val_bound(v), new_ttl);
+		/* TODO: ^^ cumbersome code; we also recompute the TTL */
+		return ret == kr_ok() ? KR_STATE_DONE : ctx->state;
+		}
+	case KNOT_RRTYPE_DNAME:
+		VERBOSE_MSG(qry, "=> DNAME not supported yet\n"); // LATER
+		return ctx->state;
+	}
+
+	/* We have to try proving from NSEC*. */
+	auto_free char *log_zname = NULL;
+	WITH_VERBOSE(qry) {
+		log_zname = kr_dname_text(k->zname);
+		if (!el[0].len) {
+			VERBOSE_MSG(qry, "=> no NSEC* cached for zone: %s\n", log_zname);
+		}
+	}
+
+#if 0
+	if (!eh) { /* fall back to root hints? */
+		ret = kr_zonecut_set_sbelt(req->ctx, &qry->zone_cut);
+		if (ret) return ctx->state;
+		assert(!qry->zone_cut.parent);
+
+		//VERBOSE_MSG(qry, "=> using root hints\n");
+		//qry->flags.AWAIT_CUT = false;
+		return ctx->state;
+	}
+
+	/* Now `eh` points to the closest NS record that we've found,
+	 * and that's the only place to start - we may either find
+	 * a negative proof or we may query upstream from that point. */
+	kr_zonecut_set(&qry->zone_cut, k->zname);
+	ret = kr_make_query(qry, pkt); // TODO: probably not yet - qname minimization
+	if (ret) return ctx->state;
+#endif
+
+	/** Structure for collecting multiple NSEC* + RRSIG records,
+	 * in preparation for the answer, and for tracking the progress. */
+	struct answer ans;
+	memset(&ans, 0, sizeof(ans));
+	ans.mm = &pkt->mm;
+	const int sname_labels = knot_dname_labels(qry->sname, NULL);
+
+	/* Try the NSEC* parameters in order, until success.
+	 * Let's not mix different parameters for NSEC* RRs in a single proof. */
+	for (int i = 0; ;) {
+		int32_t log_new_ttl = -123456789; /* visually recognizable value */
+		ret = nsec_p_ttl(el[i], qry->timestamp.tv_sec, &log_new_ttl);
+		if (!ret || VERBOSE_STATUS) {
+			nsec_p_init(&ans.nsec_p, el[i], !ret);
+		}
+		if (ret) {
+			VERBOSE_MSG(qry, "=> skipping zone: %s, %s, hash %x;"
+				"new TTL %d, ret %d\n",
+				log_zname, (ans.nsec_p.raw ? "NSEC3" : "NSEC"),
+				(unsigned)ans.nsec_p.hash, (int)log_new_ttl, ret);
+			/* no need for nsec_p_cleanup() in this case */
+			goto cont;
+		}
+		VERBOSE_MSG(qry, "=> trying zone: %s, %s, hash %x\n",
+				log_zname, (ans.nsec_p.raw ? "NSEC3" : "NSEC"),
+				(unsigned)ans.nsec_p.hash);
+		/**** 2. and 3. inside */
+		ret = peek_encloser(k, &ans, sname_labels,
+					lowest_rank, qry, cache);
+		nsec_p_cleanup(&ans.nsec_p);
+		if (!ret) break;
+		if (ret < 0) return ctx->state;
+	cont:
+		/* Otherwise we try another nsec_p, if available. */
+		if (++i == ENTRY_APEX_NSECS_CNT) return ctx->state;
+		/* clear possible partial answers in `ans` (no need to deallocate) */
+		ans.rcode = 0;
+		memset(&ans.rrsets, 0, sizeof(ans.rrsets));
+	}
+
+	/**** 4. add SOA iff needed */
+	if (ans.rcode != PKT_NOERROR) {
+		/* Assuming k->buf still starts with zone's prefix,
+		 * look up the SOA in cache. */
+		k->buf[0] = k->zlf_len;
+		knot_db_val_t key = key_exact_type(k, KNOT_RRTYPE_SOA);
+		knot_db_val_t val = { NULL, 0 };
+		ret = cache_op(cache, read, &key, &val, 1);
+		const struct entry_h *eh;
+		if (ret || !(eh = entry_h_consistent(val, KNOT_RRTYPE_SOA))) {
+			assert(ret); /* only want to catch `eh` failures */
+			VERBOSE_MSG(qry, "=> SOA missed\n");
+			return ctx->state;
+		}
+		/* Check if the record is OK. */
+		int32_t new_ttl = get_new_ttl(eh, qry, k->zname, KNOT_RRTYPE_SOA,
+						qry->timestamp.tv_sec);
+		if (new_ttl < 0 || eh->rank < lowest_rank || eh->is_packet) {
+			VERBOSE_MSG(qry, "=> SOA unfit %s: rank 0%.2o, new TTL %d\n",
+					(eh->is_packet ? "packet" : "RR"),
+					eh->rank, new_ttl);
+			return ctx->state;
+		}
+		/* Add the SOA into the answer. */
+		ret = entry2answer(&ans, AR_SOA, eh, knot_db_val_bound(val),
+				   k->zname, KNOT_RRTYPE_SOA, new_ttl);
+		if (ret) return ctx->state;
+	}
+
+	/* Find our target RCODE. */
+	int real_rcode;
+	switch (ans.rcode) {
+	case PKT_NODATA:
+	case PKT_NOERROR: /* positive wildcarded response */
+		real_rcode = KNOT_RCODE_NOERROR;
+		break;
+	case PKT_NXDOMAIN:
+		real_rcode = KNOT_RCODE_NXDOMAIN;
+		break;
+	default:
+		assert(false);
+	case 0: /* i.e. nothing was found */
+		/* LATER(optim.): zone cut? */
+		VERBOSE_MSG(qry, "=> cache miss\n");
+		return ctx->state;
+	}
+
+	if (pkt_renew(pkt, qry->sname, qry->stype)
+	    || knot_pkt_begin(pkt, KNOT_ANSWER)
+	   ) {
+		assert(false);
+		return ctx->state;
+	}
+	knot_wire_set_rcode(pkt->wire, real_rcode);
+
+	bool expiring = false; // TODO
+	VERBOSE_MSG(qry, "=> writing RRsets: ");
+	for (int i = 0; i < sizeof(ans.rrsets) / sizeof(ans.rrsets[0]); ++i) {
+		if (i == 1) knot_pkt_begin(pkt, KNOT_AUTHORITY);
+		if (!ans.rrsets[i].set.rr) continue;
+		expiring = expiring || ans.rrsets[i].set.expiring;
+		ret = pkt_append(pkt, &ans.rrsets[i], ans.rrsets[i].set.rank);
+		if (ret) {
+			assert(false);
+			return ctx->state;
+		}
+		kr_log_verbose(kr_rank_test(ans.rrsets[i].set.rank, KR_RANK_SECURE)
+				? "+" : "-");
+	}
+	kr_log_verbose("\n");
+
+	/* Finishing touches. */
+	struct kr_qflags * const qf = &qry->flags;
+	qf->EXPIRING = expiring;
+	qf->CACHED = true;
+	qf->NO_MINIMIZE = true;
+
+	return KR_STATE_DONE;
+}
+
+/**
+ * This is where the high-level "business logic" of aggressive cache is.
+ * \return 0: success (may need SOA);  >0: try other nsec_p;  <0: exit cache immediately.
+ */
+static int peek_encloser(
+	struct key *k, struct answer *ans, const int sname_labels,
+	uint8_t lowest_rank, const struct kr_query *qry, struct kr_cache *cache)
+{
+	/** Start of NSEC* covering the sname;
+	 * it's part of key - the one within zone (read only) */
+	knot_db_val_t cover_low_kwz = { NULL, 0 };
+	knot_dname_t cover_hi_storage[KNOT_DNAME_MAXLEN];
+	/** End of NSEC* covering the sname. */
+	knot_db_val_t cover_hi_kwz = {
+		.data = cover_hi_storage,
+		.len = sizeof(cover_hi_storage),
+	};
+
+	/**** 2. Find a closest (provable) encloser (of sname). */
+	int clencl_labels = -1;
+	bool clencl_is_tentative = false;
+	if (!ans->nsec_p.raw) { /* NSEC */
+		int ret = nsec1_encloser(k, ans, sname_labels, &clencl_labels,
+					 &cover_low_kwz, &cover_hi_kwz, qry, cache);
+		if (ret) return ret;
+	} else {
+		int ret = nsec3_encloser(k, ans, sname_labels, &clencl_labels,
+					 qry, cache);
+		clencl_is_tentative = ret == ABS(ENOENT) && clencl_labels >= 0;
+		/* ^^ Last chance: *positive* wildcard record under this clencl. */
+		if (ret && !clencl_is_tentative) return ret;
+	}
+
+	/* We should have either a match or a cover at this point. */
+	if (ans->rcode != PKT_NODATA && ans->rcode != PKT_NXDOMAIN) {
+		assert(false);
+		return kr_error(EINVAL);
+	}
+	const bool ncloser_covered = ans->rcode == PKT_NXDOMAIN;
+
+	/** Name of the closest (provable) encloser. */
+	const knot_dname_t *clencl_name = qry->sname;
+	for (int l = sname_labels; l > clencl_labels; --l)
+		clencl_name = knot_wire_next_label(clencl_name, NULL);
+
+	/**** 3. source of synthesis checks, in case the next closer name was covered.
+	 **** 3a. We want to query for NSEC* of source of synthesis (SS) or its
+	 * predecessor, providing us with a proof of its existence or non-existence. */
+	if (ncloser_covered && !ans->nsec_p.raw) {
+		int ret = nsec1_src_synth(k, ans, clencl_name,
+					  cover_low_kwz, cover_hi_kwz, qry, cache);
+		if (ret == AR_SOA) return 0;
+		assert(ret <= 0);
+		if (ret) return ret;
+
+	} else if (ncloser_covered && ans->nsec_p.raw && !clencl_is_tentative) {
+		int ret = nsec3_src_synth(k, ans, clencl_name, qry, cache);
+		if (ret == AR_SOA) return 0;
+		assert(ret <= 0);
+		if (ret) return ret;
+
+	} /* else (!ncloser_covered) so no wildcard checks needed,
+	   * as we proved that sname exists. */
+
+	/**** 3b. find wildcarded answer, if next closer name was covered
+	 * and we don't have a full proof yet.  (common for NSEC*) */
+	if (!ncloser_covered)
+		return kr_ok(); /* decrease indentation */
+	/* Construct key for exact qry->stype + source of synthesis. */
+	int ret = kr_dname_lf(k->buf, clencl_name, true);
+	if (ret) {
+		assert(!ret);
+		return kr_error(ret);
+	}
+	const uint16_t types[] = { qry->stype, KNOT_RRTYPE_CNAME };
+	for (int i = 0; i < (2 - (qry->stype == KNOT_RRTYPE_CNAME)); ++i) {
+		ret = try_wild(k, ans, clencl_name, types[i],
+				lowest_rank, qry, cache);
+		if (ret == kr_ok()) {
+			return kr_ok();
+		} else if (ret != -ABS(ENOENT) && ret != -ABS(ESTALE)) {
+			assert(false);
+			return kr_error(ret);
+		}
+		/* else continue */
+	}
+	/* Neither attempt succeeded, but the NSEC* proofs were found,
+	 * so skip trying other parameters, as it seems very unlikely
+	 * to turn out differently than by the same wildcard search. */
+	return -ABS(ENOENT);
+}
+
+
+static int answer_simple_hit(kr_layer_t *ctx, knot_pkt_t *pkt, uint16_t type,
+		const struct entry_h *eh, const void *eh_bound, uint32_t new_ttl)
+#define CHECK_RET(ret) do { \
+	if ((ret) < 0) { assert(false); return kr_error((ret)); } \
+} while (false)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+
+	/* All OK, so start constructing the (pseudo-)packet. */
+	int ret = pkt_renew(pkt, qry->sname, qry->stype);
+	CHECK_RET(ret);
+
+	/* Materialize the sets for the answer in (pseudo-)packet. */
+	struct answer ans;
+	memset(&ans, 0, sizeof(ans));
+	ans.mm = &pkt->mm;
+	ret = entry2answer(&ans, AR_ANSWER, eh, eh_bound,
+			   qry->sname, type, new_ttl);
+	CHECK_RET(ret);
+	/* Put links to the materialized data into the pkt. */
+	ret = pkt_append(pkt, &ans.rrsets[AR_ANSWER], eh->rank);
+	CHECK_RET(ret);
+
+	/* Finishing touches. */
+	struct kr_qflags * const qf = &qry->flags;
+	qf->EXPIRING = is_expiring(eh->ttl, new_ttl);
+	qf->CACHED = true;
+	qf->NO_MINIMIZE = true;
+	qf->DNSSEC_INSECURE = kr_rank_test(eh->rank, KR_RANK_INSECURE);
+	if (qf->DNSSEC_INSECURE) {
+		qf->DNSSEC_WANT = false;
+	}
+	VERBOSE_MSG(qry, "=> satisfied by exact %s: rank 0%.2o, new TTL %d\n",
+			(type == KNOT_RRTYPE_CNAME ? "CNAME" : "RRset"),
+			eh->rank, new_ttl);
+	return kr_ok();
+}
+#undef CHECK_RET
+
+
+/** TODO: description; see the single call site for now. */
+static int found_exact_hit(kr_layer_t *ctx, knot_pkt_t *pkt, knot_db_val_t val,
+			   uint8_t lowest_rank)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+
+	int ret = entry_h_seek(&val, qry->stype);
+	if (ret) return ret;
+	const struct entry_h *eh = entry_h_consistent(val, qry->stype);
+	if (!eh) {
+		assert(false);
+		return kr_error(ENOENT);
+		// LATER: recovery in case of error, perhaps via removing the entry?
+		// LATER(optim): pehaps optimize the zone cut search
+	}
+
+	int32_t new_ttl = get_new_ttl(eh, qry, qry->sname, qry->stype,
+					qry->timestamp.tv_sec);
+	if (new_ttl < 0 || eh->rank < lowest_rank) {
+		/* Positive record with stale TTL or bad rank.
+		 * LATER(optim.): It's unlikely that we find a negative one,
+		 * so we might theoretically skip all the cache code. */
+
+		VERBOSE_MSG(qry, "=> skipping exact %s: rank 0%.2o (min. 0%.2o), new TTL %d\n",
+				eh->is_packet ? "packet" : "RR", eh->rank, lowest_rank, new_ttl);
+		return kr_error(ENOENT);
+	}
+
+	const uint8_t *eh_bound = knot_db_val_bound(val);
+	if (eh->is_packet) {
+		/* Note: we answer here immediately, even if it's (theoretically)
+		 * possible that we could generate a higher-security negative proof.
+		 * Rank is high-enough so we take it to save time searching. */
+		return answer_from_pkt  (ctx, pkt, qry->stype, eh, eh_bound, new_ttl);
+	} else {
+		return answer_simple_hit(ctx, pkt, qry->stype, eh, eh_bound, new_ttl);
+	}
+}
+
+
+/** Try to satisfy via wildcard (positively).  See the single call site. */
+static int try_wild(struct key *k, struct answer *ans, const knot_dname_t *clencl_name,
+		    const uint16_t type, const uint8_t lowest_rank,
+		    const struct kr_query *qry, struct kr_cache *cache)
+{
+	knot_db_val_t key = key_exact_type(k, type);
+	/* Find the record. */
+	knot_db_val_t val = { NULL, 0 };
+	int ret = cache_op(cache, read, &key, &val, 1);
+	if (!ret) {
+		ret = entry_h_seek(&val, type);
+	}
+	if (ret) {
+		if (ret != -ABS(ENOENT)) {
+			VERBOSE_MSG(qry, "=> wildcard: hit error %d %s\n",
+					ret, strerror(abs(ret)));
+			assert(false);
+		}
+		WITH_VERBOSE(qry) {
+			auto_free char *clencl_str = kr_dname_text(clencl_name),
+				*type_str = kr_rrtype_text(type);
+			VERBOSE_MSG(qry, "=> wildcard: not found: *.%s %s\n",
+					clencl_str, type_str);
+		}
+		return ret;
+	}
+	/* Check if the record is OK. */
+	const struct entry_h *eh = entry_h_consistent(val, type);
+	if (!eh) {
+		assert(false);
+		return kr_error(ret);
+		// LATER: recovery in case of error, perhaps via removing the entry?
+	}
+	int32_t new_ttl = get_new_ttl(eh, qry, qry->sname, type, qry->timestamp.tv_sec);
+		/* ^^ here we use the *expanded* wildcard name */
+	if (new_ttl < 0 || eh->rank < lowest_rank || eh->is_packet) {
+		/* Wildcard record with stale TTL, bad rank or packet.  */
+		VERBOSE_MSG(qry, "=> wildcard: skipping %s, rank 0%.2o, new TTL %d\n",
+				eh->is_packet ? "packet" : "RR", eh->rank, new_ttl);
+		return -ABS(ESTALE);
+	}
+	/* Add the RR into the answer. */
+	ret = entry2answer(ans, AR_ANSWER, eh, knot_db_val_bound(val),
+			   qry->sname, type, new_ttl);
+	VERBOSE_MSG(qry, "=> wildcard: answer expanded, ret = %d, new TTL %d\n",
+			ret, (int)new_ttl);
+	if (ret) return kr_error(ret);
+	ans->rcode = PKT_NOERROR;
+	return kr_ok();
+}
+
+int kr_cache_closest_apex(struct kr_cache *cache, const knot_dname_t *name, bool is_DS,
+			  knot_dname_t ** apex)
+{
+	if (!cache || !cache->db || !name || !apex || *apex) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+	struct key k_storage, *k = &k_storage;
+	int ret = kr_dname_lf(k->buf, name, false);
+	if (ret)
+		return kr_error(ret);
+	entry_list_t el_;
+	k->zname = name;
+	ret = closest_NS(cache, k, el_, NULL, true, is_DS);
+	if (ret && ret != -abs(ENOENT))
+		return ret;
+	*apex = knot_dname_copy(k->zname, NULL);
+	if (!*apex)
+		return kr_error(ENOMEM);
+	return kr_ok();
+}
+
+/** \internal for closest_NS.  Check suitability of a single entry, setting k->type if OK.
+ * \return error code, negative iff whole list should be skipped.
+ */
+static int check_NS_entry(struct key *k, knot_db_val_t entry, int i,
+			  bool exact_match, bool is_DS,
+			  const struct kr_query *qry, uint32_t timestamp);
+
+/**
+ * Find the longest prefix zone/xNAME (with OK time+rank), starting at k->*.
+ *
+ * The found type is returned via k->type; the values are returned in el.
+ * \note we use k->type = KNOT_RRTYPE_NS also for the nsec_p result.
+ * \param qry can be NULL (-> gettimeofday(), but you lose the stale-serve hook)
+ * \param only_NS don't consider xNAMEs
+ * \return error code
+ */
+static int closest_NS(struct kr_cache *cache, struct key *k, entry_list_t el,
+			struct kr_query *qry, const bool only_NS, const bool is_DS)
+{
+	/* get the current timestamp */
+	uint32_t timestamp;
+	if (qry) {
+		timestamp = qry->timestamp.tv_sec;
+	} else {
+		struct timeval tv;
+		if (gettimeofday(&tv, NULL)) return kr_error(errno);
+		timestamp = tv.tv_sec;
+	}
+
+	int zlf_len = k->buf[0];
+
+	// LATER(optim): if stype is NS, we check the same value again
+	bool exact_match = true;
+	bool need_zero = true;
+	/* Inspect the NS/xNAME entries, shortening by a label on each iteration. */
+	do {
+		k->buf[0] = zlf_len;
+		knot_db_val_t key = key_exact_type(k, KNOT_RRTYPE_NS);
+		knot_db_val_t val;
+		int ret = cache_op(cache, read, &key, &val, 1);
+		if (ret == -abs(ENOENT)) goto next_label;
+		if (ret) {
+			assert(!ret);
+			if (need_zero) memset(el, 0, sizeof(entry_list_t));
+			return kr_error(ret);
+		}
+
+		/* Check consistency, find any type;
+		 * using `goto` for shortening by another label. */
+		ret = entry_list_parse(val, el);
+		if (ret) {
+			assert(!ret); // do something about it?
+			goto next_label;
+		}
+		need_zero = false;
+		/* More types are possible; try in order.
+		 * For non-fatal failures just "continue;" to try the next type. */
+		const int el_count = only_NS ? EL_NS + 1 : EL_LENGTH;
+		for (int i = 0; i < el_count; ++i) {
+			ret = check_NS_entry(k, el[i], i, exact_match, is_DS,
+						qry, timestamp);
+			if (ret < 0) goto next_label; else
+			if (!ret) {
+				/* We found our match. */
+				k->zlf_len = zlf_len;
+				return kr_ok();
+			}
+		}
+
+	next_label:
+		/* remove one more label */
+		exact_match = false;
+		if (k->zname[0] == 0) {
+			/* We miss root NS in cache, but let's at least assume it exists. */
+			k->type = KNOT_RRTYPE_NS;
+			k->zlf_len = zlf_len;
+			assert(zlf_len == 0);
+			if (need_zero) memset(el, 0, sizeof(entry_list_t));
+			return kr_error(ENOENT);
+		}
+		zlf_len -= (k->zname[0] + 1);
+		k->zname += (k->zname[0] + 1);
+		k->buf[zlf_len + 1] = 0;
+	} while (true);
+}
+
+static int check_NS_entry(struct key *k, const knot_db_val_t entry, const int i,
+			  const bool exact_match, const bool is_DS,
+			  const struct kr_query *qry, uint32_t timestamp)
+{
+	const int ESKIP = ABS(ENOENT);
+	if (!entry.len
+		/* On a zone cut we want DS from the parent zone. */
+		|| (i <= EL_NS && exact_match && is_DS)
+		/* CNAME is interesting only if we
+		 * directly hit the name that was asked.
+		 * Note that we want it even in the DS case. */
+		|| (i == EL_CNAME && !exact_match)
+		/* DNAME is interesting only if we did NOT
+		 * directly hit the name that was asked. */
+		|| (i == EL_DNAME && exact_match)
+	   ) {
+		return ESKIP;
+	}
+
+	uint16_t type;
+	if (i < ENTRY_APEX_NSECS_CNT) {
+		type = KNOT_RRTYPE_NS;
+		int32_t log_new_ttl = -123456789; /* visually recognizable value */
+		const int err = nsec_p_ttl(entry, timestamp, &log_new_ttl);
+		if (err) {
+			VERBOSE_MSG(qry,
+				"=> skipping unfit nsec_p: new TTL %d, error %d\n",
+				(int)log_new_ttl, err);
+			return ESKIP;
+		}
+	} else {
+		type = EL2RRTYPE(i);
+		/* Find the entry for the type, check positivity, TTL */
+		const struct entry_h *eh = entry_h_consistent(entry, type);
+		if (!eh) {
+			VERBOSE_MSG(qry, "=> EH not consistent\n");
+			assert(false);
+			return kr_error(EILSEQ);
+		}
+		const int32_t log_new_ttl = get_new_ttl(eh, qry, k->zname, type, timestamp);
+		const uint8_t rank_min = KR_RANK_INSECURE | KR_RANK_AUTH;
+		const bool ok = /* For NS any kr_rank is accepted,
+				 * as insecure or even nonauth is OK */
+				(type == KNOT_RRTYPE_NS || eh->rank >= rank_min)
+				/* Not interested in negative bogus or outdated RRs. */
+				&& !eh->is_packet && log_new_ttl >= 0;
+		WITH_VERBOSE(qry) { if (!ok) {
+			auto_free char *type_str = kr_rrtype_text(type);
+			const char *packet_str = eh->is_packet ? "packet" : "RR";
+			VERBOSE_MSG(qry,
+				"=> skipping unfit %s %s: rank 0%.2o, new TTL %d\n",
+				type_str, packet_str, eh->rank, (int)log_new_ttl);
+		} }
+		if (!ok) return ESKIP;
+	}
+	k->type = type;
+	return kr_ok();
+}
+
diff --git a/lib/cookies/alg_containers.c b/lib/cookies/alg_containers.c
new file mode 100644
index 0000000..a80487d
--- /dev/null
+++ b/lib/cookies/alg_containers.c
@@ -0,0 +1,72 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include <libknot/cookies/alg-fnv64.h>
+
+#include "lib/cookies/alg_containers.h"
+#include "lib/cookies/alg_sha.h"
+
+const struct knot_cc_alg *kr_cc_alg_get(int id)
+{
+	/*
+	 * Client algorithm identifiers are used to index this array of
+	 * pointers.
+	 */
+	static const struct knot_cc_alg *const cc_algs[] = {
+		/* 0 */ &knot_cc_alg_fnv64,
+		/* 1 */ &knot_cc_alg_hmac_sha256_64
+	};
+
+	if (id >= 0 && id < 2) {
+		return cc_algs[id];
+	}
+
+	return NULL;
+}
+
+const knot_lookup_t kr_cc_alg_names[] = {
+	{ 0, "FNV-64" },
+	{ 1, "HMAC-SHA256-64" },
+	{ -1, NULL }
+};
+
+const struct knot_sc_alg *kr_sc_alg_get(int id)
+{
+	/*
+	 * Server algorithm identifiers are used to index this array of
+	 * pointers.
+	 */
+	static const struct knot_sc_alg *const sc_algs[] = {
+		/* 0 */ &knot_sc_alg_fnv64,
+		/* 1 */ &knot_sc_alg_hmac_sha256_64
+	};
+
+	if (id >= 0 && id < 2) {
+		return sc_algs[id];
+	}
+
+	return NULL;
+}
+
+const knot_lookup_t kr_sc_alg_names[] = {
+	{ 0, "FNV-64" },
+	{ 1, "HMAC-SHA256-64" },
+	{ -1, NULL }
+};
diff --git a/lib/cookies/alg_containers.h b/lib/cookies/alg_containers.h
new file mode 100644
index 0000000..1e2aef6
--- /dev/null
+++ b/lib/cookies/alg_containers.h
@@ -0,0 +1,49 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <libknot/cookies/client.h>
+#include <libknot/cookies/server.h>
+#include <libknot/lookup.h>
+
+#include "lib/defines.h"
+
+/**
+ * @brief Returns pointer to client cookie algorithm.
+ *
+ * @param id algorithm identifier as defined by lookup table
+ * @return   pointer to algorithm structure with given id or NULL on error
+ */
+KR_EXPORT
+const struct knot_cc_alg *kr_cc_alg_get(int id);
+
+/** Binds client algorithm identifiers onto names. */
+KR_EXPORT
+extern const knot_lookup_t kr_cc_alg_names[];
+
+/**
+ * @brief Returns pointer to server cookie algorithm.
+ *
+ * @param id algorithm identifier as defined by lookup table
+ * @return   pointer to algorithm structure with given id or NULL on error
+ */
+KR_EXPORT
+const struct knot_sc_alg *kr_sc_alg_get(int id);
+
+/** Binds server algorithm identifiers onto names. */
+KR_EXPORT
+extern const knot_lookup_t kr_sc_alg_names[];
diff --git a/lib/cookies/alg_sha.c b/lib/cookies/alg_sha.c
new file mode 100644
index 0000000..e23c983
--- /dev/null
+++ b/lib/cookies/alg_sha.c
@@ -0,0 +1,122 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <nettle/hmac.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include <libknot/errcode.h>
+#include <libknot/rrtype/opt-cookie.h>
+
+#include "lib/cookies/alg_sha.h"
+#include "lib/utils.h"
+
+/**
+ * @brief Update hash value.
+ *
+ * @param ctx HMAC-SHA256 context to be updated.
+ * @param sa  Socket address.
+ */
+static inline void update_hash(struct hmac_sha256_ctx *ctx,
+                               const struct sockaddr *sa)
+{
+	assert(ctx && sa);
+
+	int addr_len = kr_inaddr_len(sa);
+	const uint8_t *addr = (uint8_t *)kr_inaddr(sa);
+
+	if (addr && addr_len > 0) {
+		hmac_sha256_update(ctx, addr_len, addr);
+	}
+}
+
+/**
+ * @brief Compute client cookie using HMAC-SHA256-64.
+ * @note At least one of the arguments must be non-null.
+ * @param input  input parameters
+ * @param cc_out buffer for computed client cookie
+ * @param cc_len buffer size
+ * @return Non-zero size of written data on success, 0 in case of a failure.
+ */
+static uint16_t cc_gen_hmac_sha256_64(const struct knot_cc_input *input,
+                                      uint8_t *cc_out, uint16_t cc_len)
+{
+	if (!knot_cc_input_is_valid(input) ||
+	    !cc_out || cc_len < KNOT_OPT_COOKIE_CLNT) {
+		return 0;
+	}
+
+	struct hmac_sha256_ctx ctx;
+	hmac_sha256_set_key(&ctx, input->secret_len, input->secret_data);
+
+	if (input->clnt_sockaddr) {
+		update_hash(&ctx, input->clnt_sockaddr);
+	}
+
+	if (input->srvr_sockaddr) {
+		update_hash(&ctx, input->srvr_sockaddr);
+	}
+
+	/* KNOT_OPT_COOKIE_CLNT <= SHA256_DIGEST_SIZE */
+
+	hmac_sha256_digest(&ctx, KNOT_OPT_COOKIE_CLNT, cc_out);
+
+	return KNOT_OPT_COOKIE_CLNT;
+}
+
+#define SRVR_HMAC_SHA256_64_HASH_SIZE 8
+
+/**
+ * @brief Compute server cookie hash using HMAC-SHA256-64).
+ * @note Server cookie = nonce | time | HMAC-SHA256-64( server secret, client cookie | nonce| time | client IP )
+ * @param input    data to compute cookie from
+ * @param hash_out hash output buffer
+ * @param hash_len buffer size
+ * @return Non-zero size of written data on success, 0 in case of a failure.
+ */
+static uint16_t sc_gen_hmac_sha256_64(const struct knot_sc_input *input,
+                                      uint8_t *hash_out, uint16_t hash_len)
+{
+	if (!knot_sc_input_is_valid(input) ||
+	    !hash_out || hash_len < SRVR_HMAC_SHA256_64_HASH_SIZE) {
+		return 0;
+	}
+
+	struct hmac_sha256_ctx ctx;
+	hmac_sha256_set_key(&ctx, input->srvr_data->secret_len,
+	                    input->srvr_data->secret_data);
+
+	hmac_sha256_update(&ctx, input->cc_len, input->cc);
+
+	if (input->nonce && input->nonce_len) {
+		hmac_sha256_update(&ctx, input->nonce_len, input->nonce);
+	}
+
+	if (input->srvr_data->clnt_sockaddr) {
+		update_hash(&ctx, input->srvr_data->clnt_sockaddr);
+	}
+
+	/* SRVR_HMAC_SHA256_64_HASH_SIZE < SHA256_DIGEST_SIZE */
+
+	hmac_sha256_digest(&ctx, SRVR_HMAC_SHA256_64_HASH_SIZE, hash_out);
+
+	return SRVR_HMAC_SHA256_64_HASH_SIZE;
+}
+
+const struct knot_cc_alg knot_cc_alg_hmac_sha256_64 = { KNOT_OPT_COOKIE_CLNT, cc_gen_hmac_sha256_64 };
+
+const struct knot_sc_alg knot_sc_alg_hmac_sha256_64 = { SRVR_HMAC_SHA256_64_HASH_SIZE, sc_gen_hmac_sha256_64 };
diff --git a/lib/cookies/alg_sha.h b/lib/cookies/alg_sha.h
new file mode 100644
index 0000000..5b0d0c9
--- /dev/null
+++ b/lib/cookies/alg_sha.h
@@ -0,0 +1,30 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <libknot/cookies/client.h>
+#include <libknot/cookies/server.h>
+
+#include "lib/defines.h"
+
+/* These structures are not meant to be part of public interface. */
+
+/** HMAC-SHA256-64 client cookie algorithm. */
+extern const struct knot_cc_alg knot_cc_alg_hmac_sha256_64;
+
+/** HMAC-SHA256-64 server cookie algorithm. */
+extern const struct knot_sc_alg knot_sc_alg_hmac_sha256_64;
diff --git a/lib/cookies/control.h b/lib/cookies/control.h
new file mode 100644
index 0000000..1bf503f
--- /dev/null
+++ b/lib/cookies/control.h
@@ -0,0 +1,49 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "lib/defines.h"
+
+/** Holds secret quantity. */
+struct kr_cookie_secret {
+	size_t size; /*!< Secret quantity size. */
+	uint8_t data[]; /*!< Secret quantity data. */
+};
+
+/** Holds settings that have direct influence on cookie values computation. */
+struct kr_cookie_comp {
+	struct kr_cookie_secret *secr; /*!< Secret data. */
+	int alg_id; /*!< Cookie algorithm identifier. */
+};
+
+/** Holds settings that control client/server cookie behaviour. */
+struct kr_cookie_settings {
+	bool enabled; /**< Enable/disables DNS cookies functionality. */
+
+	struct kr_cookie_comp current; /**< Current cookie settings. */
+	struct kr_cookie_comp recent; /**< Recent cookie settings. */
+};
+
+/** DNS cookies controlling structure. */
+struct kr_cookie_ctx {
+	struct kr_cookie_settings clnt; /**< Client settings. */
+	struct kr_cookie_settings srvr; /**< Server settings. */
+};
diff --git a/lib/cookies/helper.c b/lib/cookies/helper.c
new file mode 100644
index 0000000..e07b8cb
--- /dev/null
+++ b/lib/cookies/helper.c
@@ -0,0 +1,296 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <libknot/rrtype/opt.h>
+#include <libknot/rrtype/opt-cookie.h>
+
+#include "lib/cookies/helper.h"
+#include "lib/defines.h"
+
+/**
+ * @brief Check whether there is a cached cookie that matches the current
+ *        client cookie.
+ */
+static const uint8_t *peek_and_check_cc(kr_cookie_lru_t *cache, const void *sa,
+                                        const uint8_t *cc, uint16_t cc_len)
+{
+	assert(cache && sa && cc && cc_len);
+
+	const uint8_t *cached_opt = kr_cookie_lru_get(cache, sa);
+	if (!cached_opt) {
+		return NULL;
+	}
+
+	const uint8_t *cached_cc = knot_edns_opt_get_data((uint8_t *) cached_opt);
+
+	if (cc_len == KNOT_OPT_COOKIE_CLNT &&
+	    0 == memcmp(cc, cached_cc, cc_len)) {
+		return cached_opt;
+	}
+
+	return NULL;
+}
+
+/**
+ * @brief Put a client cookie into the RR Set.
+ */
+static int opt_rr_put_cookie(knot_rrset_t *opt_rr, uint8_t *data,
+                             uint16_t data_len, knot_mm_t *mm)
+{
+	assert(opt_rr && data && data_len > 0);
+
+	const uint8_t *cc = NULL, *sc = NULL;
+	uint16_t cc_len = 0, sc_len = 0;
+
+	int ret = knot_edns_opt_cookie_parse(data, data_len, &cc, &cc_len,
+	                                     &sc, &sc_len);
+	if (ret != KNOT_EOK) {
+		return kr_error(EINVAL);
+	}
+	assert(data_len == cc_len + sc_len);
+
+	uint16_t cookies_size = data_len;
+	uint8_t *cookies_data = NULL;
+
+	ret = knot_edns_reserve_unique_option(opt_rr, KNOT_EDNS_OPTION_COOKIE,
+	                                      cookies_size, &cookies_data, mm);
+	if (ret != KNOT_EOK) {
+		return kr_error(EINVAL);
+	}
+	assert(cookies_data != NULL);
+
+	cookies_size = knot_edns_opt_cookie_write(cc, cc_len, sc, sc_len,
+	                                          cookies_data, cookies_size);
+	if (cookies_size == 0) {
+		return kr_error(EINVAL);
+	}
+	assert(cookies_size == data_len);
+
+	return kr_ok();
+}
+
+/**
+ * @brief Puts entire EDNS option into the RR Set.
+ */
+static int opt_rr_put_cookie_opt(knot_rrset_t *opt_rr, uint8_t *option, knot_mm_t *mm)
+{
+	assert(opt_rr && option);
+
+	uint16_t opt_code = knot_edns_opt_get_code(option);
+	if (opt_code != KNOT_EDNS_OPTION_COOKIE) {
+		return kr_error(EINVAL);
+	}
+
+	uint16_t opt_len = knot_edns_opt_get_length(option);
+	uint8_t *opt_data = knot_edns_opt_get_data(option);
+	if (!opt_data || opt_len == 0) {
+		return kr_error(EINVAL);
+	}
+
+	return opt_rr_put_cookie(opt_rr, opt_data, opt_len, mm);
+}
+
+int kr_request_put_cookie(const struct kr_cookie_comp *clnt_comp,
+                          kr_cookie_lru_t *cookie_cache,
+                          const struct sockaddr *clnt_sa,
+                          const struct sockaddr *srvr_sa,
+                          struct kr_request *req)
+{
+	if (!clnt_comp || !req) {
+		return kr_error(EINVAL);
+	}
+
+	if (!req->ctx->opt_rr) {
+		return kr_ok();
+	}
+
+	if (!clnt_comp->secr || (clnt_comp->alg_id < 0) || !cookie_cache) {
+		return kr_error(EINVAL);
+	}
+
+	/*
+	 * Generate client cookie from client address, server address and
+	 * secret quantity.
+	 */
+	struct knot_cc_input input = {
+		.clnt_sockaddr = clnt_sa,
+		.srvr_sockaddr = srvr_sa,
+		.secret_data = clnt_comp->secr->data,
+		.secret_len = clnt_comp->secr->size
+	};
+	uint8_t cc[KNOT_OPT_COOKIE_CLNT];
+	uint16_t cc_len = KNOT_OPT_COOKIE_CLNT;
+	const struct knot_cc_alg *cc_alg = kr_cc_alg_get(clnt_comp->alg_id);
+	if (!cc_alg) {
+		return kr_error(EINVAL);
+	}
+	assert(cc_alg->gen_func);
+	cc_len = cc_alg->gen_func(&input, cc, cc_len);
+	if (cc_len != KNOT_OPT_COOKIE_CLNT) {
+		return kr_error(EINVAL);
+	}
+
+	const uint8_t *cached_cookie = peek_and_check_cc(cookie_cache,
+	                                                 srvr_sa, cc, cc_len);
+
+	/* Add cookie option. */
+	int ret;
+	if (cached_cookie) {
+		ret = opt_rr_put_cookie_opt(req->ctx->opt_rr,
+		                            (uint8_t *)cached_cookie,
+		                            req->ctx->pool);
+	} else {
+		ret = opt_rr_put_cookie(req->ctx->opt_rr, cc, cc_len,
+		                        req->ctx->pool);
+	}
+
+	return ret;
+}
+
+int kr_answer_write_cookie(struct knot_sc_input *sc_input,
+                           const struct kr_nonce_input *nonce,
+                           const struct knot_sc_alg *alg, knot_pkt_t *pkt)
+{
+	if (!sc_input || !sc_input->cc || sc_input->cc_len == 0) {
+		return kr_error(EINVAL);
+	}
+
+	if (!sc_input->srvr_data || !sc_input->srvr_data->clnt_sockaddr ||
+	    !sc_input->srvr_data->secret_data ||
+	    !sc_input->srvr_data->secret_len) {
+		return kr_error(EINVAL);
+	}
+
+	if (!nonce) {
+		return kr_error(EINVAL);
+	}
+
+	if (!alg || !alg->hash_size || !alg->hash_func) {
+		return kr_error(EINVAL);
+	}
+
+	if (!pkt || !pkt->opt_rr) {
+		return kr_error(EINVAL);
+	}
+
+	uint16_t nonce_len = KR_NONCE_LEN;
+	uint16_t hash_len = alg->hash_size;
+
+	/*
+	 * Space for cookie is reserved inside the EDNS OPT RR of
+	 * the answer packet.
+	 */
+	uint8_t *cookie = NULL;
+	uint16_t cookie_len = knot_edns_opt_cookie_data_len(sc_input->cc_len,
+	                                                    nonce_len + hash_len);
+	if (cookie_len == 0) {
+		return kr_error(EINVAL);
+	}
+
+	int ret = knot_edns_reserve_unique_option(pkt->opt_rr,
+	                                          KNOT_EDNS_OPTION_COOKIE,
+	                                          cookie_len, &cookie,
+	                                          &pkt->mm);
+	if (ret != KNOT_EOK) {
+		return kr_error(ENOMEM);
+	}
+	assert(cookie != NULL);
+
+	/*
+	 * Function knot_edns_opt_cookie_data_len() returns the sum of its
+	 * parameters or zero. Anyway, let's check again.
+	 */
+	if (cookie_len < (sc_input->cc_len + nonce_len + hash_len)) {
+		return kr_error(EINVAL);
+	}
+
+	/* Copy client cookie data portion. */
+	memcpy(cookie, sc_input->cc, sc_input->cc_len);
+
+	if (nonce_len) {
+		/* Write nonce data portion. */
+		kr_nonce_write_wire(cookie + sc_input->cc_len, nonce_len,
+		                    nonce);
+		/* Adjust input for written nonce value. */
+		sc_input->nonce = cookie + sc_input->cc_len;
+		sc_input->nonce_len = nonce_len;
+	}
+
+	hash_len = alg->hash_func(sc_input,
+	                          cookie + sc_input->cc_len + nonce_len,
+	                          hash_len);
+	/* Zero nonce values. */
+	sc_input->nonce = NULL;
+	sc_input->nonce_len = 0;
+
+	return (hash_len != 0) ? kr_ok() : kr_error(EINVAL);
+}
+
+int kr_pkt_set_ext_rcode(knot_pkt_t *pkt, uint16_t whole_rcode)
+{
+	/*
+	 * RFC6891 6.1.3 -- extended RCODE forms the upper 8 bits of whole
+	 * 12-bit RCODE (together with the 4 bits of 'normal' RCODE).
+	 *
+	 * | 11 10 09 08 07 06 05 04 | 03 02 01 00 |
+	 * |          12-bit whole RCODE           |
+	 * |   8-bit extended RCODE  | 4-bit RCODE |
+	 */
+
+	if (!pkt || !knot_pkt_has_edns(pkt)) {
+		return kr_error(EINVAL);
+	}
+
+	uint8_t rcode = whole_rcode & 0x0f;
+	uint8_t ext_rcode = whole_rcode >> 4;
+	knot_wire_set_rcode(pkt->wire, rcode);
+	knot_edns_set_ext_rcode(pkt->opt_rr, ext_rcode);
+
+	return kr_ok();
+}
+
+uint8_t *kr_no_question_cookie_query(const knot_pkt_t *pkt)
+{
+	if (!pkt || knot_wire_get_qdcount(pkt->wire) > 0) {
+		return false;
+	}
+
+	if (knot_wire_get_qr(pkt->wire) != 0 || !pkt->opt_rr) {
+		return false;
+	}
+
+	return knot_edns_get_option(pkt->opt_rr, KNOT_EDNS_OPTION_COOKIE);
+}
+
+int kr_parse_cookie_opt(uint8_t *cookie_opt, struct knot_dns_cookies *cookies)
+{
+	if (!cookie_opt || !cookies) {
+		return kr_error(EINVAL);
+	}
+
+	const uint8_t *cookie_data = knot_edns_opt_get_data(cookie_opt);
+	uint16_t cookie_len = knot_edns_opt_get_length(cookie_opt);
+	if (!cookie_data || cookie_len == 0) {
+		return kr_error(EINVAL);
+	}
+
+	int ret =  knot_edns_opt_cookie_parse(cookie_data, cookie_len,
+	                                      &cookies->cc, &cookies->cc_len,
+	                                      &cookies->sc, &cookies->sc_len);
+
+	return (ret == KNOT_EOK) ? kr_ok() : kr_error(EINVAL);
+}
diff --git a/lib/cookies/helper.h b/lib/cookies/helper.h
new file mode 100644
index 0000000..e5659ce
--- /dev/null
+++ b/lib/cookies/helper.h
@@ -0,0 +1,86 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <libknot/packet/pkt.h>
+
+#include "lib/cookies/alg_containers.h"
+#include "lib/cookies/control.h"
+#include "lib/cookies/lru_cache.h"
+#include "lib/cookies/nonce.h"
+#include "lib/defines.h"
+#include "lib/resolve.h"
+
+/**
+ * @brief Updates DNS cookie in the request EDNS options.
+ * @note This function must be called before the request packet is finalised.
+ * @param clnt_comp    client cookie control structure
+ * @param cookie_cache cookie cache
+ * @param clnt_sa      client socket address
+ * @param srvr_sa      server socket address
+ * @param req          name resolution request
+ * @return kr_ok() or error code
+ */
+KR_EXPORT
+int kr_request_put_cookie(const struct kr_cookie_comp *clnt_comp,
+                          kr_cookie_lru_t *cookie_cache,
+                          const struct sockaddr *clnt_sa,
+                          const struct sockaddr *srvr_sa,
+                          struct kr_request *req);
+
+/**
+ * @brief Inserts a cookie option into the OPT RR. It does not write any
+ *        wire data.
+ * @note The content of @a sc_input is modified. Any pre-set nonce value is
+ *       ignored. After retuning its nonce value will be null.
+ * @param sc_input  data needed to compute server cookie, nonce is ignored
+ * @param nonce     nonce value that is actually used
+ * @param alg       hash algorithm
+ * @param pkt       DNS response packet
+ */
+KR_EXPORT
+int kr_answer_write_cookie(struct knot_sc_input *sc_input,
+                           const struct kr_nonce_input *nonce,
+                           const struct knot_sc_alg *alg, knot_pkt_t *pkt);
+
+/**
+ * @brief Set RCODE and extended RCODE.
+ * @param pkt DNS packet
+ * @param whole_rcode RCODE value
+ * @return kr_ok() or error code
+ */
+KR_EXPORT
+int kr_pkt_set_ext_rcode(knot_pkt_t *pkt, uint16_t whole_rcode);
+
+/**
+ * @brief Check whether packet is a server cookie request according to
+ *        RFC7873 5.4.
+ * @param pkt Packet to be examined.
+ * @return Pointer to entire cookie option if is a server cookie query, NULL on
+ *         errors or if packet doesn't contain cookies or if QDCOUNT > 0.
+ */
+KR_EXPORT
+uint8_t *kr_no_question_cookie_query(const knot_pkt_t *pkt);
+
+/**
+ * @brief Parse cookies from cookie option.
+ * @param cookie_opt Cookie option.
+ * @param cookies    Cookie structure to be set.
+ * @return kr_ok() on success, error if cookies are malformed.
+ */
+KR_EXPORT
+int kr_parse_cookie_opt(uint8_t *cookie_opt, struct knot_dns_cookies *cookies);
diff --git a/lib/cookies/lru_cache.c b/lib/cookies/lru_cache.c
new file mode 100644
index 0000000..8ea97ab
--- /dev/null
+++ b/lib/cookies/lru_cache.c
@@ -0,0 +1,70 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <libknot/rrtype/opt.h>
+#include <string.h>
+
+#include "lib/cookies/lru_cache.h"
+#include "lib/utils.h"
+
+const uint8_t *kr_cookie_lru_get(kr_cookie_lru_t *cache,
+                                 const struct sockaddr *sa)
+{
+	if (!cache || !sa) {
+		return NULL;
+	}
+
+	int addr_len = kr_inaddr_len(sa);
+	const char *addr = kr_inaddr(sa);
+	if (!addr || addr_len <= 0) {
+		return NULL;
+	}
+
+	struct cookie_opt_data *cached = lru_get_try(cache, addr, addr_len);
+	return cached ? cached->opt_data : NULL;
+}
+
+int kr_cookie_lru_set(kr_cookie_lru_t *cache, const struct sockaddr *sa,
+                      uint8_t *opt)
+{
+	if (!cache || !sa) {
+		return kr_error(EINVAL);
+	}
+
+	if (!opt) {
+		return kr_ok();
+	}
+
+	int addr_len = kr_inaddr_len(sa);
+	const char *addr = kr_inaddr(sa);
+	if (!addr || addr_len <= 0) {
+		return kr_error(EINVAL);
+	}
+
+	uint16_t opt_size = KNOT_EDNS_OPTION_HDRLEN +
+	                    knot_edns_opt_get_length(opt);
+
+	if (opt_size > KR_COOKIE_OPT_MAX_LEN) {
+		return kr_error(EINVAL);
+	}
+
+	struct cookie_opt_data *cached = lru_get_new(cache, addr, addr_len, NULL);
+	if (cached) {
+		memcpy(cached->opt_data, opt, opt_size);
+	}
+
+	return kr_ok();
+}
diff --git a/lib/cookies/lru_cache.h b/lib/cookies/lru_cache.h
new file mode 100644
index 0000000..8ce0a01
--- /dev/null
+++ b/lib/cookies/lru_cache.h
@@ -0,0 +1,69 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <netinet/in.h>
+#include <stdint.h>
+
+#if defined(ENABLE_COOKIES)
+#include <libknot/rrtype/opt.h>
+#include <libknot/rrtype/opt-cookie.h>
+#else
+#define KNOT_OPT_COOKIE_CLNT 8
+#define KNOT_OPT_COOKIE_SRVR_MAX 32
+#endif /* defined(ENABLE_COOKIES) */
+
+#include "lib/defines.h"
+#include "lib/generic/lru.h"
+
+/** Maximal size of a cookie option. */
+#define KR_COOKIE_OPT_MAX_LEN (KNOT_EDNS_OPTION_HDRLEN + KNOT_OPT_COOKIE_CLNT + KNOT_OPT_COOKIE_SRVR_MAX)
+
+/**
+ * Cookie option entry.
+ */
+struct cookie_opt_data {
+	uint8_t opt_data[KR_COOKIE_OPT_MAX_LEN];
+};
+
+/**
+ * DNS cookies tracking.
+ */
+typedef lru_t(struct cookie_opt_data) kr_cookie_lru_t;
+
+/**
+ * @brief Obtain LRU cache entry.
+ *
+ * @param cache cookie LRU cache
+ * @param sa socket address serving as key
+ * @return pointer to cached option or NULL if not found or error occurred
+ */
+KR_EXPORT
+const uint8_t *kr_cookie_lru_get(kr_cookie_lru_t *cache,
+                                 const struct sockaddr *sa);
+
+/**
+ * @brief Stores cookie option into LRU cache.
+ *
+ * @param cache cookie LRU cache
+ * @param sa socket address serving as key
+ * @param opt cookie option to be stored
+ * @return kr_ok() or error code
+ */
+KR_EXPORT
+int kr_cookie_lru_set(kr_cookie_lru_t *cache, const struct sockaddr *sa,
+                      uint8_t *opt);
diff --git a/lib/cookies/nonce.c b/lib/cookies/nonce.c
new file mode 100644
index 0000000..4ad72c8
--- /dev/null
+++ b/lib/cookies/nonce.c
@@ -0,0 +1,34 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+
+#include "contrib/wire.h"
+#include "lib/cookies/nonce.h"
+
+uint16_t kr_nonce_write_wire(uint8_t *buf, uint16_t buf_len,
+                             const struct kr_nonce_input *input)
+{
+	if (!buf || buf_len < KR_NONCE_LEN || !input) {
+		return 0;
+	}
+
+	wire_write_u32(buf, input->rand);
+	wire_write_u32(buf + sizeof(uint32_t), input->time);
+	buf_len = 2 * sizeof(uint32_t);
+
+	return buf_len;
+}
diff --git a/lib/cookies/nonce.h b/lib/cookies/nonce.h
new file mode 100644
index 0000000..99c54d3
--- /dev/null
+++ b/lib/cookies/nonce.h
@@ -0,0 +1,43 @@
+/*  Copyright (C) 2016-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "lib/defines.h"
+
+/* RFC7873 Appendix B.2 mentions an algorithm using two values before the
+ * actual server cookie hash. */
+
+/** Nonce value length. */
+#define KR_NONCE_LEN 8
+
+/** Input data to generate nonce from. */
+struct kr_nonce_input {
+	uint32_t rand; /**< some random value */
+	uint32_t time; /**< time stamp */
+};
+
+/**
+ * @brief Writes server cookie nonce value into given buffer.
+ *
+ * @param buf     buffer to write nonce data in wire format into
+ * @param buf_len buffer size
+ * @param input   data to generate wire data from
+ * @return non-zero size of written data on success, 0 on failure
+ */
+KR_EXPORT
+uint16_t kr_nonce_write_wire(uint8_t *buf, uint16_t buf_len,
+                             const struct kr_nonce_input *input);
diff --git a/lib/defines.h b/lib/defines.h
new file mode 100644
index 0000000..84da059
--- /dev/null
+++ b/lib/defines.h
@@ -0,0 +1,102 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <errno.h>
+#include <libknot/errcode.h>
+#include <libknot/dname.h>
+#include <libknot/rrset.h>
+
+/* Function attributes */
+#if __GNUC__ >= 4
+#define KR_EXPORT __attribute__ ((visibility ("default")))
+#define KR_CONST __attribute__((__const__))
+#define KR_PURE __attribute__((__pure__))
+#define KR_NORETURN __attribute__((__noreturn__))
+#define KR_COLD __attribute__((__cold__))
+#define KR_PRINTF(n) __attribute__((format (printf, n, (n+1))))
+#else
+#define KR_EXPORT
+#define KR_CONST
+#define KR_PURE
+#define KR_NORETURN
+#define KR_COLD
+#define KR_PRINTF(n)
+#endif
+
+#ifndef uint /* Redefining typedef is a C11 feature. */
+typedef unsigned int uint;
+#define uint uint
+#endif
+
+/*
+ * Error codes.
+ */
+#define kr_ok() 0
+/* Mark as cold to mark all branches as unlikely. */
+static inline int KR_COLD kr_error(int x) {
+    return x <= 0 ? x : -x;
+}
+#define kr_strerror(x) strerror(abs(x))
+
+/*
+ * Connection limits.
+ * @cond internal
+ */
+#define KR_CONN_RTT_MAX 2000 /* Timeout for network activity */
+#define KR_CONN_RETRY 200    /* Retry interval for network activity */
+#define KR_ITER_LIMIT 100    /* Built-in iterator limit */
+#define KR_RESOLVE_TIME_LIMIT 10000 /* Upper limit for resolution time of single query, ms */
+#define KR_CNAME_CHAIN_LIMIT 40 /* Built-in maximum CNAME chain length */
+#define KR_TIMEOUT_LIMIT 4   /* Maximum number of retries after timeout. */
+#define KR_QUERY_NSRETRY_LIMIT 4 /* Maximum number of retries per query. */
+
+/*
+ * Defines.
+ */
+#define KR_DNS_PORT   53
+#define KR_DNS_TLS_PORT 853
+#define KR_EDNS_VERSION 0
+#define KR_EDNS_PAYLOAD 4096 /* Default UDP payload (max unfragmented UDP is 1452B) */
+#define KR_CACHE_DEFAULT_TTL_MIN (5) /* avoid bursts of queries */
+#define KR_CACHE_DEFAULT_TTL_MAX (6 * 24 * 3600) /* 6 days, like the root NS TTL */
+
+#define KR_DNAME_STR_MAXLEN (KNOT_DNAME_TXT_MAXLEN + 1)
+#define KR_RRTYPE_STR_MAXLEN (16 + 1)
+
+/*
+ * Address sanitizer hints.
+ */
+#if !defined(__SANITIZE_ADDRESS__) && defined(__has_feature)
+# if __has_feature(address_sanitizer)
+#  define __SANITIZE_ADDRESS__ 1
+# endif
+#endif
+#if defined(__SANITIZE_ADDRESS__)
+void __asan_poison_memory_region(void const volatile *addr, size_t size);
+void __asan_unpoison_memory_region(void const volatile *addr, size_t size);
+#define kr_asan_poison(addr, size) __asan_poison_memory_region((addr), (size))
+#define kr_asan_unpoison(addr, size) __asan_unpoison_memory_region((addr), (size))
+#define kr_asan_custom_poison(fn, addr) fn ##_poison((addr))
+#define kr_asan_custom_unpoison(fn, addr) fn ##_unpoison((addr))
+#else
+#define kr_asan_poison(addr, size)
+#define kr_asan_unpoison(addr, size)
+#define kr_asan_custom_poison(fn, addr)
+#define kr_asan_custom_unpoison(fn, addr)
+#endif
+/* @endcond */
diff --git a/lib/dnssec.c b/lib/dnssec.c
new file mode 100644
index 0000000..4f8ad8a
--- /dev/null
+++ b/lib/dnssec.c
@@ -0,0 +1,473 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <libdnssec/binary.h>
+#include <libdnssec/crypto.h>
+#include <libdnssec/error.h>
+#include <libdnssec/key.h>
+#include <libdnssec/sign.h>
+#include <libknot/descriptor.h>
+#include <libknot/packet/wire.h>
+#include <libknot/rdataset.h>
+#include <libknot/rrset.h>
+#include <libknot/rrtype/dnskey.h>
+#include <libknot/rrtype/nsec.h>
+#include <libknot/rrtype/rrsig.h>
+#include <contrib/wire.h>
+
+#include "lib/defines.h"
+#include "lib/dnssec/nsec.h"
+#include "lib/dnssec/nsec3.h"
+#include "lib/dnssec/signature.h"
+#include "lib/dnssec.h"
+#include "lib/resolve.h"
+
+/* forward */
+static int kr_rrset_validate_with_key(kr_rrset_validation_ctx_t *vctx,
+	const knot_rrset_t *covered, size_t key_pos, const struct dseckey *key);
+
+void kr_crypto_init(void)
+{
+	dnssec_crypto_init();
+}
+
+void kr_crypto_cleanup(void)
+{
+	dnssec_crypto_cleanup();
+}
+
+void kr_crypto_reinit(void)
+{
+	dnssec_crypto_reinit();
+}
+
+#define FLG_WILDCARD_EXPANSION 0x01 /**< Possibly generated by using wildcard expansion. */
+
+/**
+ * Check the RRSIG RR validity according to RFC4035 5.3.1 .
+ * @param flags     The flags are going to be set according to validation result.
+ * @param cov_labels Covered RRSet owner label count.
+ * @param rrsigs    rdata containing the signatures.
+ * @param key_owner Associated DNSKEY's owner.
+ * @param key_rdata Associated DNSKEY's rdata.
+ * @param keytag    Used key tag.
+ * @param zone_name The name of the zone cut.
+ * @param timestamp Validation time.
+ */
+static int validate_rrsig_rr(int *flags, int cov_labels,
+                             const knot_rdata_t *rrsigs,
+                             const knot_dname_t *key_owner, const knot_rdata_t *key_rdata,
+			     uint16_t keytag,
+                             const knot_dname_t *zone_name, uint32_t timestamp,
+                             kr_rrset_validation_ctx_t *vctx)
+{
+	if (!flags || !rrsigs || !key_owner || !key_rdata || !zone_name) {
+		return kr_error(EINVAL);
+	}
+	/* bullet 5 */
+	if (knot_rrsig_sig_expiration(rrsigs) < timestamp) {
+		vctx->rrs_counters.expired++;
+		return kr_error(EINVAL);
+	}
+	/* bullet 6 */
+	if (knot_rrsig_sig_inception(rrsigs) > timestamp) {
+		vctx->rrs_counters.notyet++;
+		return kr_error(EINVAL);
+	}
+	/* bullet 2 */
+	const knot_dname_t *signer_name = knot_rrsig_signer_name(rrsigs);
+	if (!signer_name || !knot_dname_is_equal(signer_name, zone_name)) {
+		vctx->rrs_counters.signer_invalid++;
+		return kr_error(EAGAIN);
+	}
+	/* bullet 4 */
+	{
+		int rrsig_labels = knot_rrsig_labels(rrsigs);
+		if (rrsig_labels > cov_labels) {
+			vctx->rrs_counters.labels_invalid++;
+			return kr_error(EINVAL);
+		}
+		if (rrsig_labels < cov_labels) {
+			*flags |= FLG_WILDCARD_EXPANSION;
+		}
+	}
+
+	/* bullet 7 */
+	if ((!knot_dname_is_equal(key_owner, signer_name)) ||
+	    (knot_dnskey_alg(key_rdata) != knot_rrsig_alg(rrsigs)) ||
+	    (keytag != knot_rrsig_key_tag(rrsigs))) {
+		vctx->rrs_counters.key_invalid++;
+		return kr_error(EINVAL);
+	}
+	/* bullet 8 */
+	/* Checked somewhere else. */
+	/* bullet 9 and 10 */
+	/* One of the requirements should be always fulfilled. */
+
+	return kr_ok();
+}
+
+/**
+ * Returns the number of labels that have been added by wildcard expansion.
+ * @param expanded Expanded wildcard.
+ * @param rrsigs   RRSet containing the signatures.
+ * @param sig_pos  Specifies the signature within the RRSIG RRSet.
+ * @return         Number of added labels, -1 on error.
+ */
+static inline int wildcard_radix_len_diff(const knot_dname_t *expanded,
+					  const knot_rdata_t *rrsig)
+{
+	if (!expanded || !rrsig) {
+		return -1;
+	}
+
+	return knot_dname_labels(expanded, NULL) - knot_rrsig_labels(rrsig);
+}
+
+int kr_rrset_validate(kr_rrset_validation_ctx_t *vctx, const knot_rrset_t *covered)
+{
+	if (!vctx) {
+		return kr_error(EINVAL);
+	}
+	if (!vctx->pkt || !covered || !vctx->keys || !vctx->zone_name) {
+		return kr_error(EINVAL);
+	}
+
+	memset(&vctx->rrs_counters, 0, sizeof(vctx->rrs_counters));
+	for (unsigned i = 0; i < vctx->keys->rrs.count; ++i) {
+		int ret = kr_rrset_validate_with_key(vctx, covered, i, NULL);
+		if (ret == 0) {
+			return ret;
+		}
+	}
+
+	return kr_error(ENOENT);
+}
+
+/**
+ * Validate RRSet using a specific key.
+ * @param vctx    Pointer to validation context.
+ * @param covered RRSet covered by a signature. It must be in canonical format.
+ * @param key_pos Position of the key to be validated with.
+ * @param key     Key to be used to validate.
+ *		  If NULL, then key from DNSKEY RRSet is used.
+ * @return        0 or error code, same as vctx->result.
+ */
+static int kr_rrset_validate_with_key(kr_rrset_validation_ctx_t *vctx,
+				const knot_rrset_t *covered,
+				size_t key_pos, const struct dseckey *key)
+{
+	const knot_pkt_t *pkt         = vctx->pkt;
+	const knot_rrset_t *keys      = vctx->keys;
+	const knot_dname_t *zone_name = vctx->zone_name;
+	uint32_t timestamp            = vctx->timestamp;
+	bool has_nsec3		      = vctx->has_nsec3;
+	struct dseckey *created_key = NULL;
+
+	/* It's just caller's approximation that the RR is in that particular zone.
+	 * We MUST guard against attempts of zones signing out-of-bailiwick records. */
+	if (knot_dname_in_bailiwick(covered->owner, zone_name) < 0) {
+		vctx->result = kr_error(ENOENT);
+		return vctx->result;
+	}
+
+	const knot_rdata_t *key_rdata = knot_rdataset_at(&keys->rrs, key_pos);
+	if (key == NULL) {
+		int ret = kr_dnssec_key_from_rdata(&created_key, keys->owner,
+						   key_rdata->data, key_rdata->len);
+		if (ret != 0) {
+			vctx->result = ret;
+			return vctx->result;
+		}
+		key = created_key;
+	}
+	uint16_t keytag = dnssec_key_get_keytag((dnssec_key_t *)key);
+	int covered_labels = knot_dname_labels(covered->owner, NULL);
+	if (knot_dname_is_wildcard(covered->owner)) {
+		/* The asterisk does not count, RFC4034 3.1.3, paragraph 3. */
+		--covered_labels;
+	}
+
+	for (uint16_t i = 0; i < vctx->rrs->len; ++i) {
+		/* Consider every RRSIG that matches owner and covers the class/type. */
+		const knot_rrset_t *rrsig = vctx->rrs->at[i]->rr;
+		if (rrsig->type != KNOT_RRTYPE_RRSIG) {
+			continue;
+		}
+		if ((covered->rclass != rrsig->rclass) || !knot_dname_is_equal(covered->owner, rrsig->owner)) {
+			continue;
+		}
+		knot_rdata_t *rdata_j = rrsig->rrs.rdata;
+		for (uint16_t j = 0; j < rrsig->rrs.count; ++j, rdata_j = knot_rdataset_next(rdata_j)) {
+			int val_flgs = 0;
+			int trim_labels = 0;
+			if (knot_rrsig_type_covered(rdata_j) != covered->type) {
+				continue;
+			}
+			vctx->rrs_counters.matching_name_type++;
+			int retv = validate_rrsig_rr(&val_flgs, covered_labels, rdata_j,
+			                      keys->owner, key_rdata, keytag,
+			                      zone_name, timestamp, vctx);
+			if (retv == kr_error(EAGAIN)) {
+				kr_dnssec_key_free(&created_key);
+				vctx->result = retv;
+				return retv;
+			} else if (retv != 0) {
+				continue;
+			}
+			if (val_flgs & FLG_WILDCARD_EXPANSION) {
+				trim_labels = wildcard_radix_len_diff(covered->owner, rdata_j);
+				if (trim_labels < 0) {
+					break;
+				}
+			}
+			if (kr_check_signature(rdata_j, (dnssec_key_t *) key, covered, trim_labels) != 0) {
+				vctx->rrs_counters.crypto_invalid++;
+				continue;
+			}
+			if (val_flgs & FLG_WILDCARD_EXPANSION) {
+				int ret = 0;
+				if (!has_nsec3) {
+					ret = kr_nsec_wildcard_answer_response_check(pkt, KNOT_AUTHORITY, covered->owner);
+				} else {
+					ret = kr_nsec3_wildcard_answer_response_check(pkt, KNOT_AUTHORITY, covered->owner, trim_labels - 1);
+					if (ret == kr_error(KNOT_ERANGE)) {
+						ret = 0;
+						vctx->flags |= KR_DNSSEC_VFLG_OPTOUT;
+					}
+				}
+				if (ret != 0) {
+					vctx->rrs_counters.nsec_invalid++;
+					continue;
+				}
+				vctx->flags |= KR_DNSSEC_VFLG_WEXPAND;
+			}
+			/* Validated with current key, OK */
+			kr_dnssec_key_free(&created_key);
+			vctx->result = kr_ok();
+			return vctx->result;
+		}
+	}
+	/* No applicable key found, cannot be validated. */
+	kr_dnssec_key_free(&created_key);
+	vctx->result = kr_error(ENOENT);
+	return vctx->result;
+}
+
+static bool kr_ds_algo_support(const knot_rrset_t *ta)
+{
+	knot_rdata_t *rdata_i = ta->rrs.rdata;
+	for (uint16_t i = 0; i < ta->rrs.count;
+			++i, rdata_i = knot_rdataset_next(rdata_i)) {
+		if (dnssec_algorithm_digest_support(knot_ds_digest_type(rdata_i))
+		    && dnssec_algorithm_key_support(knot_ds_alg(rdata_i))) {
+			return true;
+		}
+	}
+	return false;
+}
+
+int kr_dnskeys_trusted(kr_rrset_validation_ctx_t *vctx, const knot_rrset_t *ta)
+{
+	const knot_pkt_t *pkt         = vctx->pkt;
+	const knot_rrset_t *keys      = vctx->keys;
+
+	const bool ok = pkt && keys && ta && ta->rrs.count && ta->rrs.rdata
+			&& ta->type == KNOT_RRTYPE_DS;
+	if (!ok) {
+		assert(false);
+		return kr_error(EINVAL);
+	}
+
+	/* Check if at least one DS has a usable algorithm pair. */
+	if (!kr_ds_algo_support(ta)) {
+		/* See RFC6840 5.2. */
+		return vctx->result = kr_error(DNSSEC_INVALID_DS_ALGORITHM);
+	}
+
+	/* RFC4035 5.2, bullet 1
+	 * The supplied DS record has been authenticated.
+	 * It has been validated or is part of a configured trust anchor.
+	 */
+	memset(&vctx->rrs_counters, 0, sizeof(vctx->rrs_counters));
+	for (uint16_t i = 0; i < keys->rrs.count; ++i) {
+		/* RFC4035 5.3.1, bullet 8 */ /* ZSK */
+		/* LATER(optim.): more efficient way to iterate than _at() */
+		const knot_rdata_t *krr = knot_rdataset_at(&keys->rrs, i);
+		if (!kr_dnssec_key_zsk(krr->data) || kr_dnssec_key_revoked(krr->data)) {
+			continue;
+		}
+		
+		struct dseckey *key = NULL;
+		if (kr_dnssec_key_from_rdata(&key, keys->owner, krr->data, krr->len) != 0) {
+			continue;
+		}
+		if (kr_authenticate_referral(ta, (dnssec_key_t *) key) != 0) {
+			kr_dnssec_key_free(&key);
+			continue;
+		}
+		if (kr_rrset_validate_with_key(vctx, keys, i, key) != 0) {
+			kr_dnssec_key_free(&key);
+			continue;
+		}
+		kr_dnssec_key_free(&key);
+		assert (vctx->result == 0);
+		return vctx->result;
+	}
+
+	/* No useable key found */
+	vctx->result = kr_error(ENOENT);
+	return vctx->result;
+}
+
+bool kr_dnssec_key_zsk(const uint8_t *dnskey_rdata)
+{
+	return wire_read_u16(dnskey_rdata) & 0x0100;
+}
+
+bool kr_dnssec_key_ksk(const uint8_t *dnskey_rdata)
+{
+	return wire_read_u16(dnskey_rdata) & 0x0001;
+}
+
+/** Return true if the DNSKEY is revoked. */
+bool kr_dnssec_key_revoked(const uint8_t *dnskey_rdata)
+{
+	return wire_read_u16(dnskey_rdata) & 0x0080;
+}
+
+int kr_dnssec_key_tag(uint16_t rrtype, const uint8_t *rdata, size_t rdlen)
+{
+	if (!rdata || rdlen == 0 || (rrtype != KNOT_RRTYPE_DS && rrtype != KNOT_RRTYPE_DNSKEY)) {
+		return kr_error(EINVAL);
+	}
+	if (rrtype == KNOT_RRTYPE_DS) {
+		return wire_read_u16(rdata);
+	} else if (rrtype == KNOT_RRTYPE_DNSKEY) {
+		struct dseckey *key = NULL;
+		int ret = kr_dnssec_key_from_rdata(&key, NULL, rdata, rdlen);
+		if (ret != 0) {
+			return ret;
+		}
+		uint16_t keytag = dnssec_key_get_keytag((dnssec_key_t *)key);
+		kr_dnssec_key_free(&key);
+		return keytag;
+	} else {
+		return kr_error(EINVAL);
+	}
+}
+
+int kr_dnssec_key_match(const uint8_t *key_a_rdata, size_t key_a_rdlen,
+                        const uint8_t *key_b_rdata, size_t key_b_rdlen)
+{
+	dnssec_key_t *key_a = NULL, *key_b = NULL;
+	int ret = kr_dnssec_key_from_rdata((struct dseckey **)&key_a, NULL, key_a_rdata, key_a_rdlen);
+	if (ret != 0) {
+		return ret;
+	}
+	ret = kr_dnssec_key_from_rdata((struct dseckey **)&key_b, NULL, key_b_rdata, key_b_rdlen);
+	if (ret != 0) {
+		dnssec_key_free(key_a);
+		return ret;
+	}
+	/* If the algorithm and the public key match, we can be sure
+	 * that they are the same key. */
+	ret = kr_error(ENOENT);
+	dnssec_binary_t pk_a, pk_b;
+	if (dnssec_key_get_algorithm(key_a) == dnssec_key_get_algorithm(key_b) &&
+	    dnssec_key_get_pubkey(key_a, &pk_a) == DNSSEC_EOK &&
+	    dnssec_key_get_pubkey(key_b, &pk_b) == DNSSEC_EOK) {
+		if (pk_a.size == pk_b.size && memcmp(pk_a.data, pk_b.data, pk_a.size) == 0) {
+			ret = 0;
+		}
+	}
+	dnssec_key_free(key_a);
+	dnssec_key_free(key_b);
+	return ret;
+}
+
+int kr_dnssec_key_from_rdata(struct dseckey **key, const knot_dname_t *kown, const uint8_t *rdata, size_t rdlen)
+{
+	if (!key || !rdata || rdlen == 0) {
+		return kr_error(EINVAL);
+	}
+
+	dnssec_key_t *new_key = NULL;
+	const dnssec_binary_t binary_key = {
+		.size = rdlen,
+		.data = (uint8_t *)rdata
+	};
+
+	int ret = dnssec_key_new(&new_key);
+	if (ret != DNSSEC_EOK) {
+		return kr_error(ENOMEM);
+	}
+	ret = dnssec_key_set_rdata(new_key, &binary_key);
+	if (ret != DNSSEC_EOK) {
+		dnssec_key_free(new_key);
+		return kr_error(ret);
+	}
+	if (kown) {
+		ret = dnssec_key_set_dname(new_key, kown);
+		if (ret != DNSSEC_EOK) {
+			dnssec_key_free(new_key);
+			return kr_error(ENOMEM);
+		}
+	}
+
+	*key = (struct dseckey *) new_key;
+	return kr_ok();
+}
+
+void kr_dnssec_key_free(struct dseckey **key)
+{
+	assert(key);
+
+	dnssec_key_free((dnssec_key_t *) *key);
+	*key = NULL;
+}
+
+int kr_dnssec_matches_name_and_type(const ranked_rr_array_t *rrs, uint32_t qry_uid,
+				    const knot_dname_t *name, uint16_t type)
+{
+	int ret = kr_error(ENOENT);
+	for (size_t i = 0; i < rrs->len; ++i) {
+		const ranked_rr_array_entry_t *entry = rrs->at[i];
+		const knot_rrset_t *nsec = entry->rr;
+		if (entry->qry_uid != qry_uid || entry->yielded) {
+			continue;
+		}
+		if (nsec->type != KNOT_RRTYPE_NSEC &&
+		    nsec->type != KNOT_RRTYPE_NSEC3) {
+			continue;
+		}
+		if (!kr_rank_test(entry->rank, KR_RANK_SECURE)) {
+			continue;
+		}
+		if (nsec->type == KNOT_RRTYPE_NSEC) {
+			ret = kr_nsec_matches_name_and_type(nsec, name, type);
+		} else {
+			ret = kr_nsec3_matches_name_and_type(nsec, name, type);
+		}
+		if (ret == kr_ok()) {
+			return kr_ok();
+		} else if (ret != kr_error(ENOENT)) {
+			return ret;
+		}
+	}
+	return ret;
+}
diff --git a/lib/dnssec.h b/lib/dnssec.h
new file mode 100644
index 0000000..b54908c
--- /dev/null
+++ b/lib/dnssec.h
@@ -0,0 +1,152 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "lib/defines.h"
+#include "lib/utils.h"
+#include <libknot/packet/pkt.h>
+
+/**
+ * Initialise cryptographic back-end.
+ */
+KR_EXPORT
+void kr_crypto_init(void);
+
+/**
+ * De-initialise cryptographic back-end.
+ */
+KR_EXPORT
+void kr_crypto_cleanup(void);
+
+/**
+ * Re-initialise cryptographic back-end.
+ * @note Must be called after fork() in the child.
+ */
+KR_EXPORT
+void kr_crypto_reinit(void);
+
+/** Opaque DNSSEC key pointer. */
+struct dseckey;
+
+#define KR_DNSSEC_VFLG_WEXPAND 0x01
+#define KR_DNSSEC_VFLG_OPTOUT  0x02
+
+/** DNSSEC validation context. */
+struct kr_rrset_validation_ctx {
+	const knot_pkt_t *pkt;		/*!< Packet to be validated. */
+	ranked_rr_array_t *rrs;		/*!< List of preselected RRs to be validated. */
+	knot_section_t section_id;	/*!< Section to work with. */
+	const knot_rrset_t *keys;	/*!< DNSKEY RRSet. */
+        const knot_dname_t *zone_name;	/*!< Name of the zone containing the RRSIG RRSet. */
+	uint32_t timestamp;		/*!< Validation time. */
+        bool has_nsec3;			/*!< Whether to use NSEC3 validation. */
+	uint32_t qry_uid;		/*!< Current query uid. */
+	uint32_t flags;			/*!< Output - Flags. */
+	uint32_t err_cnt;		/*!< Output - Number of validation failures. */
+	int result;			/*!< Output - 0 or error code. */
+	struct {
+		unsigned int matching_name_type;	/*!< Name + type matches */
+		unsigned int expired;
+		unsigned int notyet;
+		unsigned int signer_invalid;		/*!< Signer is not zone apex */
+		unsigned int labels_invalid;		/*!< Number of labels in RRSIG */
+		unsigned int key_invalid;		/*!< Algorithm/keytag/key owner */
+		unsigned int crypto_invalid;
+		unsigned int nsec_invalid;
+	} rrs_counters;	/*!< Error counters for single RRset validation. */
+};
+
+typedef struct kr_rrset_validation_ctx kr_rrset_validation_ctx_t;
+
+/**
+ * Validate RRSet.
+ * @param vctx    Pointer to validation context.
+ * @param covered RRSet covered by a signature. It must be in canonical format.
+ * @return        0 or error code, same as vctx->result.
+ */
+int kr_rrset_validate(kr_rrset_validation_ctx_t *vctx,
+			const knot_rrset_t *covered);
+
+/**
+ * Check whether the DNSKEY rrset matches the supplied trust anchor RRSet.
+ * @param vctx  Pointer to validation context.
+ * @param ta    Trust anchor RRSet against which to validate the DNSKEY RRSet.
+ * @return      0 or error code, same as vctx->result.  In particular,
+ * 		DNSSEC_INVALID_DS_ALGORITHM if *each* DS records is unusable
+ * 		due to unimplemented DNSKEY or DS algorithm.
+ */
+int kr_dnskeys_trusted(kr_rrset_validation_ctx_t *vctx, const knot_rrset_t *ta);
+
+/** Return true if the DNSKEY can be used as a ZSK.  */
+KR_EXPORT KR_PURE
+bool kr_dnssec_key_zsk(const uint8_t *dnskey_rdata);
+
+/** Return true if the DNSKEY indicates being KSK (=> has SEP).  */
+KR_EXPORT KR_PURE
+bool kr_dnssec_key_ksk(const uint8_t *dnskey_rdata);
+
+/** Return true if the DNSKEY is revoked. */
+KR_EXPORT KR_PURE
+bool kr_dnssec_key_revoked(const uint8_t *dnskey_rdata);
+
+/** Return DNSKEY tag.
+  * @param rrtype RR type (either DS or DNSKEY are supported)
+  * @param rdata  Key/digest RDATA.
+  * @param rdlen  RDATA length.
+  * @return Key tag (positive number), or an error code
+  */
+KR_EXPORT KR_PURE
+int kr_dnssec_key_tag(uint16_t rrtype, const uint8_t *rdata, size_t rdlen);
+
+/** Return 0 if the two keys are identical.
+  * @note This compares RDATA only, algorithm and public key must match.
+  * @param key_a_rdata First key RDATA
+  * @param key_a_rdlen First key RDATA length
+  * @param key_b_rdata Second key RDATA
+  * @param key_b_rdlen Second key RDATA length
+  * @return 0 if they match or an error code
+  */
+KR_EXPORT KR_PURE
+int kr_dnssec_key_match(const uint8_t *key_a_rdata, size_t key_a_rdlen,
+                        const uint8_t *key_b_rdata, size_t key_b_rdlen);
+
+/**
+ * Construct a DNSSEC key.
+ * @param key   Pointer to be set to newly created DNSSEC key.
+ * @param kown  DNSKEY owner name.
+ * @param rdata DNSKEY RDATA
+ * @param rdlen DNSKEY RDATA length
+ * @return 0 or error code; in particular: DNSSEC_INVALID_KEY_ALGORITHM
+ */
+int kr_dnssec_key_from_rdata(struct dseckey **key, const knot_dname_t *kown, const uint8_t *rdata, size_t rdlen);
+
+/**
+ * Frees the DNSSEC key.
+ * @param key Pointer to freed key.
+ */
+void kr_dnssec_key_free(struct dseckey **key);
+
+/**
+ * Checks whether NSEC/NSEC3 RR selected by iterator matches the supplied name and type.
+ * @param rrs     Records selected by iterator.
+ * @param qry_uid Query unique identifier where NSEC/NSEC3 belongs to.
+ * @param name    Name to be checked.
+ * @param type    Type to be checked.
+ * @return        0 or error code.
+ */
+int kr_dnssec_matches_name_and_type(const ranked_rr_array_t *rrs, uint32_t qry_uid,
+				    const knot_dname_t *name, uint16_t type);
diff --git a/lib/dnssec/nsec.c b/lib/dnssec/nsec.c
new file mode 100644
index 0000000..4ae13b2
--- /dev/null
+++ b/lib/dnssec/nsec.c
@@ -0,0 +1,540 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <stdlib.h>
+
+#include <libknot/descriptor.h>
+#include <libknot/dname.h>
+#include <libknot/packet/wire.h>
+#include <libknot/rrset.h>
+#include <libknot/rrtype/nsec.h>
+#include <libknot/rrtype/rrsig.h>
+#include <libdnssec/error.h>
+#include <libdnssec/nsec.h>
+
+#include "lib/defines.h"
+#include "lib/dnssec/nsec.h"
+
+
+int kr_nsec_children_in_zone_check(const uint8_t *bm, uint16_t bm_size)
+{
+	if (!bm) {
+		return kr_error(EINVAL);
+	}
+	const bool parent_side =
+		dnssec_nsec_bitmap_contains(bm, bm_size, KNOT_RRTYPE_DNAME)
+		|| (dnssec_nsec_bitmap_contains(bm, bm_size, KNOT_RRTYPE_NS)
+		    && !dnssec_nsec_bitmap_contains(bm, bm_size, KNOT_RRTYPE_SOA)
+		);
+	return parent_side ? abs(ENOENT) : kr_ok();
+	/* LATER: after refactoring, probably also check if signer name equals owner,
+	 * but even without that it's not possible to attack *correctly* signed zones.
+	 */
+}
+
+/**
+ * Check whether the NSEC RR proves that there is no closer match for <SNAME, SCLASS>.
+ * @param nsec  NSEC RRSet.
+ * @param sname Searched name.
+ * @return      0 if proves, >0 if not (abs(ENOENT)), or error code (<0).
+ */
+static int nsec_covers(const knot_rrset_t *nsec, const knot_dname_t *sname)
+{
+	assert(nsec && sname);
+	if (knot_dname_cmp(sname, nsec->owner) <= 0) {
+		return abs(ENOENT); /* 'sname' before 'owner', so can't be covered */
+	}
+
+	/* If NSEC 'owner' >= 'next', it means that there is nothing after 'owner' */
+	/* We have to lower-case it with libknot >= 2.7; see also RFC 6840 5.1. */
+	knot_dname_t next[KNOT_DNAME_MAXLEN];
+	int ret = knot_dname_to_wire(next, knot_nsec_next(nsec->rrs.rdata), sizeof(next));
+	if (ret < 0) {
+		assert(!ret);
+		return kr_error(ret);
+	}
+	knot_dname_to_lower(next);
+
+	const bool is_last_nsec = knot_dname_cmp(nsec->owner, next) >= 0;
+	const bool in_range = is_last_nsec || knot_dname_cmp(sname, next) < 0;
+	if (!in_range) {
+		return abs(ENOENT);
+	}
+	/* Before returning kr_ok(), we have to check a special case:
+	 * sname might be under delegation from owner and thus
+	 * not in the zone of this NSEC at all.
+	 */
+	if (knot_dname_in_bailiwick(sname, nsec->owner) <= 0) {
+		return kr_ok();
+	}
+	const uint8_t *bm = knot_nsec_bitmap(nsec->rrs.rdata);
+	uint16_t bm_size = knot_nsec_bitmap_len(nsec->rrs.rdata);
+
+	return kr_nsec_children_in_zone_check(bm, bm_size);
+}
+
+#define FLG_NOEXIST_RRTYPE (1 << 0) /**< <SNAME, SCLASS> exists, <SNAME, SCLASS, STYPE> does not exist. */
+#define FLG_NOEXIST_RRSET  (1 << 1) /**< <SNAME, SCLASS> does not exist. */
+#define FLG_NOEXIST_WILDCARD (1 << 2) /**< No wildcard covering <SNAME, SCLASS> exists. */
+#define FLG_NOEXIST_CLOSER (1 << 3) /**< Wildcard covering <SNAME, SCLASS> exists, but doesn't match STYPE. */
+
+
+/**
+ * According to set flags determine whether NSEC proving
+ * RRset or RRType non-existense has been found.
+ * @param f Flags to inspect.
+ * @return  True if required NSEC exists.
+ */
+#define kr_nsec_rrset_noexist(f) \
+        ((f) & (FLG_NOEXIST_RRTYPE | FLG_NOEXIST_RRSET))
+/**
+ * According to set flags determine whether wildcard non-existense
+ * has been proven.
+ * @param f Flags to inspect.
+ * @return  True if wildcard not exists.
+ */
+#define kr_nsec_wcard_noexist(f) ((f) & FLG_NOEXIST_WILDCARD)
+
+/**
+ * According to set flags determine whether authenticated denial of existence has been proven.
+ * @param f Flags to inspect.
+ * @return  True if denial of existence proven.
+ */
+#define kr_nsec_existence_denied(f) \
+	((kr_nsec_rrset_noexist(f)) && (kr_nsec_wcard_noexist(f)))
+
+/**
+ * Name error response check (RFC4035 3.1.3.2; RFC4035 5.4, bullet 2).
+ * @note Returned flags must be checked in order to prove denial.
+ * @param flags Flags to be set according to check outcome.
+ * @param nsec  NSEC RR.
+ * @param name  Name to be checked.
+ * @param pool
+ * @return      0 or error code.
+ */
+static int name_error_response_check_rr(int *flags, const knot_rrset_t *nsec,
+                                        const knot_dname_t *name)
+{
+	assert(flags && nsec && name);
+
+	if (nsec_covers(nsec, name) == 0) {
+		*flags |= FLG_NOEXIST_RRSET;
+	}
+
+	/* Try to find parent wildcard that is proved by this NSEC. */ 
+	uint8_t namebuf[KNOT_DNAME_MAXLEN];
+	int ret = knot_dname_to_wire(namebuf, name, sizeof(namebuf));
+	if (ret < 0)
+		return ret;
+	knot_dname_t *ptr = namebuf;
+	while (ptr[0]) {
+		/* Remove leftmost label and replace it with '\1*'. */
+		ptr = (uint8_t *) knot_wire_next_label(ptr, NULL);
+		if (!ptr) {
+			return kr_error(EINVAL);
+		}
+		*(--ptr) = '*';
+		*(--ptr) = 1;
+		/* True if this wildcard provably doesn't exist. */
+		if (nsec_covers(nsec, ptr) == 0) {
+			*flags |= FLG_NOEXIST_WILDCARD;
+			break;
+		}
+		/* Remove added leftmost asterisk. */
+		ptr += 2;
+	}
+
+	return kr_ok();
+}
+
+int kr_nsec_name_error_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                      const knot_dname_t *sname)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, section_id);
+	if (!sec || !sname) {
+		return kr_error(EINVAL);
+	}
+
+	int flags = 0;
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rrset = knot_pkt_rr(sec, i);
+		if (rrset->type != KNOT_RRTYPE_NSEC) {
+			continue;
+		}
+		int ret = name_error_response_check_rr(&flags, rrset, sname);
+		if (ret != 0) {
+			return ret;
+		}
+	}
+
+	return kr_nsec_existence_denied(flags) ? kr_ok() : kr_error(ENOENT);
+}
+
+/**
+ * Returns the labels from the covering RRSIG RRs.
+ * @note The number must be the same in all covering RRSIGs.
+ * @param nsec NSEC RR.
+ * @param sec  Packet section.
+ * @param      Number of labels or (negative) error code.
+ */
+static int coverign_rrsig_labels(const knot_rrset_t *nsec, const knot_pktsection_t *sec)
+{
+	assert(nsec && sec);
+
+	int ret = kr_error(ENOENT);
+
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rrset = knot_pkt_rr(sec, i);
+		if ((rrset->type != KNOT_RRTYPE_RRSIG) ||
+		    (!knot_dname_is_equal(rrset->owner, nsec->owner))) {
+			continue;
+		}
+
+		knot_rdata_t *rdata_j = rrset->rrs.rdata;
+		for (uint16_t j = 0; j < rrset->rrs.count;
+				++j, rdata_j = knot_rdataset_next(rdata_j)) {
+			if (knot_rrsig_type_covered(rdata_j) != KNOT_RRTYPE_NSEC) {
+				continue;
+			}
+
+			if (ret < 0) {
+				ret = knot_rrsig_labels(rdata_j);
+			} else {
+				if (ret != knot_rrsig_labels(rdata_j)) {
+					return kr_error(EINVAL);
+				}
+			}
+		}
+	}
+
+	return ret;
+}
+
+
+int kr_nsec_bitmap_nodata_check(const uint8_t *bm, uint16_t bm_size, uint16_t type, const knot_dname_t *owner)
+{
+	const int NO_PROOF = abs(ENOENT);
+	if (!bm || !owner) {
+		return kr_error(EINVAL);
+	}
+	if (dnssec_nsec_bitmap_contains(bm, bm_size, type)) {
+		return NO_PROOF;
+	}
+
+	if (type != KNOT_RRTYPE_CNAME
+	    && dnssec_nsec_bitmap_contains(bm, bm_size, KNOT_RRTYPE_CNAME)) {
+		return NO_PROOF;
+	}
+	/* Special behavior around zone cuts. */
+	switch (type) {
+	case KNOT_RRTYPE_DS:
+		/* Security feature: in case of DS also check for SOA
+		 * non-existence to be more certain that we don't hold
+		 * a child-side NSEC by some mistake (e.g. when forwarding).
+		 * See RFC4035 5.2, next-to-last paragraph.
+		 * This doesn't apply for root DS as it doesn't exist in DNS hierarchy.
+		 */
+		if (owner[0] != '\0' && dnssec_nsec_bitmap_contains(bm, bm_size, KNOT_RRTYPE_SOA)) {
+			return NO_PROOF;
+		}
+		break;
+	case KNOT_RRTYPE_CNAME:
+		/* Exception from the `default` rule.  It's perhaps disputable,
+		 * but existence of CNAME at zone apex is not allowed, so we
+		 * consider a parent-side record to be enough to prove non-existence. */
+		break;
+	default:
+		/* Parent-side delegation record isn't authoritative for non-DS;
+		 * see RFC6840 4.1. */
+		if (dnssec_nsec_bitmap_contains(bm, bm_size, KNOT_RRTYPE_NS)
+		    && !dnssec_nsec_bitmap_contains(bm, bm_size, KNOT_RRTYPE_SOA)) {
+			return NO_PROOF;
+		}
+		/* LATER(opt): perhaps short-circuit test if we repeat it here. */
+	}
+
+	return kr_ok();
+}
+
+/**
+ * Attempt to prove NODATA given a matching NSEC.
+ * @param flags Flags to be set according to check outcome.
+ * @param nsec  NSEC RR.
+ * @param type  Type to be checked.
+ * @return      0 on success, abs(ENOENT) for no proof, or error code (<0).
+ * @note        It's not a *full* proof, of course (wildcards, etc.)
+ * @TODO returning result via `flags` is just ugly.
+ */
+static int no_data_response_check_rrtype(int *flags, const knot_rrset_t *nsec,
+                                         uint16_t type)
+{
+	assert(flags && nsec);
+
+	const uint8_t *bm = knot_nsec_bitmap(nsec->rrs.rdata);
+	uint16_t bm_size = knot_nsec_bitmap_len(nsec->rrs.rdata);
+	int ret = kr_nsec_bitmap_nodata_check(bm, bm_size, type, nsec->owner);
+	if (ret == kr_ok()) {
+		*flags |= FLG_NOEXIST_RRTYPE;
+	}
+	return ret <= 0 ? ret : kr_ok();
+}
+
+/**
+ * Perform check for RR type wildcard existence denial according to RFC4035 5.4, bullet 1.
+ * @param flags Flags to be set according to check outcome.
+ * @param nsec  NSEC RR.
+ * @param sec   Packet section to work with.
+ * @return      0 or error code.
+ */
+static int no_data_wildcard_existence_check(int *flags, const knot_rrset_t *nsec,
+                                            const knot_pktsection_t *sec)
+{
+	assert(flags && nsec && sec);
+
+	int rrsig_labels = coverign_rrsig_labels(nsec, sec);
+	if (rrsig_labels < 0) {
+		return rrsig_labels;
+	}
+	int nsec_labels = knot_dname_labels(nsec->owner, NULL);
+	if (nsec_labels < 0) {
+		return nsec_labels;
+	}
+
+	if (rrsig_labels == nsec_labels) {
+		*flags |= FLG_NOEXIST_WILDCARD;
+	}
+
+	return kr_ok();
+}
+
+/**
+ * Perform check for NSEC wildcard existence that covers sname and
+ * have no stype bit set.
+ * @param pkt   Packet structure to be processed.
+ * @param sec   Packet section to work with.
+ * @param sname Queried domain name.
+ * @param stype Queried type.
+ * @return      0 or error code.
+ */
+static int wildcard_match_check(const knot_pkt_t *pkt, const knot_pktsection_t *sec,
+				const knot_dname_t *sname, uint16_t stype)
+{
+	if (!sec || !sname) {
+		return kr_error(EINVAL);
+	}
+
+	int flags = 0;
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rrset = knot_pkt_rr(sec, i);
+		if (rrset->type != KNOT_RRTYPE_NSEC) {
+			continue;
+		}
+		if (!knot_dname_is_wildcard(rrset->owner)) {
+			continue;
+		}
+		if (!knot_dname_is_equal(rrset->owner, sname)) {
+			int wcard_labels = knot_dname_labels(rrset->owner, NULL);
+			int common_labels = knot_dname_matched_labels(rrset->owner, sname);
+			int rrsig_labels = coverign_rrsig_labels(rrset, sec);
+			if (wcard_labels < 1 ||
+			    common_labels != wcard_labels - 1 ||
+			    common_labels != rrsig_labels) {
+				continue;
+			}
+		}
+		int ret = no_data_response_check_rrtype(&flags, rrset, stype);
+		if (ret != 0) {
+			return ret;
+		}
+	}
+	return (flags & FLG_NOEXIST_RRTYPE) ? kr_ok() : kr_error(ENOENT);
+}
+
+int kr_nsec_no_data_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                   const knot_dname_t *sname, uint16_t stype)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, section_id);
+	if (!sec || !sname) {
+		return kr_error(EINVAL);
+	}
+
+	int flags = 0;
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rrset = knot_pkt_rr(sec, i);
+		if (rrset->type != KNOT_RRTYPE_NSEC) {
+			continue;
+		}
+		if (knot_dname_is_equal(rrset->owner, sname)) {
+			int ret = no_data_response_check_rrtype(&flags, rrset, stype);
+			if (ret != 0) {
+				return ret;
+			}
+		}
+	}
+
+	return (flags & FLG_NOEXIST_RRTYPE) ? kr_ok() : kr_error(ENOENT);
+}
+
+int kr_nsec_wildcard_answer_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                           const knot_dname_t *sname)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, section_id);
+	if (!sec || !sname) {
+		return kr_error(EINVAL);
+	}
+
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rrset = knot_pkt_rr(sec, i);
+		if (rrset->type != KNOT_RRTYPE_NSEC) {
+			continue;
+		}
+		if (nsec_covers(rrset, sname) == 0) {
+			return kr_ok();
+		}
+	}
+
+	return kr_error(ENOENT);
+}
+
+int kr_nsec_existence_denial(const knot_pkt_t *pkt, knot_section_t section_id,
+                             const knot_dname_t *sname, uint16_t stype)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, section_id);
+	if (!sec || !sname) {
+		return kr_error(EINVAL);
+	}
+
+	int flags = 0;
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rrset = knot_pkt_rr(sec, i);
+		if (rrset->type != KNOT_RRTYPE_NSEC) {
+			continue;
+		}
+		/* NSEC proves that name exists, but has no data (RFC4035 4.9, 1) */
+		if (knot_dname_is_equal(rrset->owner, sname)) {
+			no_data_response_check_rrtype(&flags, rrset, stype);
+		} else {
+			/* NSEC proves that name doesn't exist (RFC4035, 4.9, 2) */
+			name_error_response_check_rr(&flags, rrset, sname);
+		}
+		no_data_wildcard_existence_check(&flags, rrset, sec);
+	}
+	if (kr_nsec_existence_denied(flags)) {
+		/* denial of existence proved accordignly to 4035 5.4 -
+		 * NSEC proving either rrset non-existance or
+		 * qtype non-existance has been found,
+		 * and no wildcard expansion occurred.
+		 */
+		return kr_ok();
+	} else if (kr_nsec_rrset_noexist(flags)) {
+		/* NSEC proving either rrset non-existance or
+		 * qtype non-existance has been found,
+		 * but wildcard expansion occurs.
+		 * Try to find matching wildcard and check
+		 * corresponding types.
+		 */
+		return wildcard_match_check(pkt, sec, sname, stype);
+	}
+	return kr_error(ENOENT);
+}
+
+int kr_nsec_ref_to_unsigned(const knot_pkt_t *pkt)
+{
+	int nsec_found = 0;
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, KNOT_AUTHORITY);
+	if (!sec) {
+		return kr_error(EINVAL);
+	}
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *ns = knot_pkt_rr(sec, i);
+		if (ns->type == KNOT_RRTYPE_DS) {
+			return kr_error(EEXIST);
+		}
+		if (ns->type != KNOT_RRTYPE_NS) {
+			continue;
+		}
+		nsec_found = 0;
+		for (unsigned j = 0; j < sec->count; ++j) {
+			const knot_rrset_t *nsec = knot_pkt_rr(sec, j);
+			if (nsec->type == KNOT_RRTYPE_DS) {
+				return kr_error(EEXIST);
+			}
+			if (nsec->type != KNOT_RRTYPE_NSEC) {
+				continue;
+			}
+			/* nsec found
+			 * check if owner name matches the delegation name
+			 */
+			if (!knot_dname_is_equal(nsec->owner, ns->owner)) {
+				/* nsec does not match the delegation */
+				continue;
+			}
+			nsec_found = 1;
+			const uint8_t *bm = knot_nsec_bitmap(nsec->rrs.rdata);
+			uint16_t bm_size = knot_nsec_bitmap_len(nsec->rrs.rdata);
+			if (!bm) {
+				return kr_error(EINVAL);
+			}
+			if (dnssec_nsec_bitmap_contains(bm, bm_size,
+							  KNOT_RRTYPE_NS) &&
+			    !dnssec_nsec_bitmap_contains(bm, bm_size,
+							  KNOT_RRTYPE_DS) &&
+			    !dnssec_nsec_bitmap_contains(bm, bm_size,
+							  KNOT_RRTYPE_SOA)) {
+				/* rfc4035, 5.2 */
+				return kr_ok();
+			}
+		}
+		if (nsec_found) {
+			/* nsec which owner matches
+			 * the delegation name was found,
+			 * but nsec type bitmap contains wrong types
+			 */
+			return kr_error(EINVAL);
+		} else {
+			/* nsec that matches delegation was not found */
+			return kr_error(DNSSEC_NOT_FOUND);
+		}
+	}
+
+	return kr_error(EINVAL);
+}
+
+int kr_nsec_matches_name_and_type(const knot_rrset_t *nsec,
+				   const knot_dname_t *name, uint16_t type)
+{
+	/* It's not secure enough to just check a single bit for (some) other types,
+	 * but we don't (currently) only use this API for NS.  See RFC 6840 sec. 4.
+	 */
+	if (type != KNOT_RRTYPE_NS || !nsec || !name) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+	if (!knot_dname_is_equal(nsec->owner, name)) {
+		return kr_error(ENOENT);
+	}
+	const uint8_t *bm = knot_nsec_bitmap(nsec->rrs.rdata);
+	uint16_t bm_size = knot_nsec_bitmap_len(nsec->rrs.rdata);
+	if (!bm) {
+		return kr_error(EINVAL);
+	}
+	if (dnssec_nsec_bitmap_contains(bm, bm_size, type)) {
+		return kr_ok();
+	} else {
+		return kr_error(ENOENT);
+	}
+}
diff --git a/lib/dnssec/nsec.h b/lib/dnssec/nsec.h
new file mode 100644
index 0000000..9439a88
--- /dev/null
+++ b/lib/dnssec/nsec.h
@@ -0,0 +1,105 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <libknot/packet/pkt.h>
+
+/**
+ * Check bitmap that child names are contained in the same zone.
+ * @note see RFC6840 4.1.
+ * @param bm      Bitmap from NSEC or NSEC3.
+ * @param bm_size Bitmap size.
+ * @return 0 if they are, >0 if not (abs(ENOENT)), <0 on error.
+ */
+int kr_nsec_children_in_zone_check(const uint8_t *bm, uint16_t bm_size);
+
+/**
+ * Check an NSEC or NSEC3 bitmap for NODATA for a type.
+ * @param bm      Bitmap.
+ * @param bm_size Bitmap size.
+ * @param type    RR type to check.
+ * @param owner   NSEC record owner.
+ * @note This includes special checks for zone cuts, e.g. from RFC 6840 sec. 4.
+ * @return 0, abs(ENOENT) (no proof), kr_error(EINVAL)
+ */
+int kr_nsec_bitmap_nodata_check(const uint8_t *bm, uint16_t bm_size, uint16_t type, const knot_dname_t *owner);
+
+/**
+ * Name error response check (RFC4035 3.1.3.2; RFC4035 5.4, bullet 2).
+ * @note No RRSIGs are validated.
+ * @param pkt        Packet structure to be processed.
+ * @param section_id Packet section to be processed.
+ * @param sname      Name to be checked.
+ * @return           0 or error code.
+ */
+int kr_nsec_name_error_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                      const knot_dname_t *sname);
+
+/**
+ * No data response check (RFC4035 3.1.3.1; RFC4035 5.4, bullet 1).
+ * @param pkt        Packet structure to be processed.
+ * @param section_id Packet section to be processed.
+ * @param sname      Name to be checked.
+ * @param stype      Type to be checked.
+ * @return           0 or error code.
+ */
+int kr_nsec_no_data_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                   const knot_dname_t *sname, uint16_t stype);
+
+/**
+ * Wildcard answer response check (RFC4035 3.1.3.3).
+ * @param pkt        Packet structure to be processed.
+ * @param section_id Packet section to be processed.
+ * @param sname      Name to be checked.
+ * @return           0 or error code.
+ */
+int kr_nsec_wildcard_answer_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                           const knot_dname_t *sname);
+
+/**
+ * Authenticated denial of existence according to RFC4035 5.4.
+ * @note No RRSIGs are validated.
+ * @param pkt        Packet structure to be processed.
+ * @param section_id Packet section to be processed.
+ * @param sname      Queried domain name.
+ * @param stype      Queried type.
+ * @return           0 or error code.
+ */
+int kr_nsec_existence_denial(const knot_pkt_t *pkt, knot_section_t section_id,
+                             const knot_dname_t *sname, uint16_t stype);
+
+/**
+ * Referral to unsigned subzone check (RFC4035 5.2).
+ * @note 	     No RRSIGs are validated.
+ * @param pkt        Packet structure to be processed.
+ * @return           0 or error code:
+ * 		     DNSSEC_NOT_FOUND - neither ds nor nsec records
+ *		     were not found.
+ *		     EEXIST - ds record was found.
+ *		     EINVAL - bogus.
+ */
+int kr_nsec_ref_to_unsigned(const knot_pkt_t *pkt);
+
+/**
+ * Checks whether supplied NSEC RR matches the supplied name and type.
+ * @param nsec  NSEC RR.
+ * @param name  Name to be checked.
+ * @param type  Type to be checked.  Only use with NS!  TODO (+copy&paste NSEC3)
+ * @return      0 or error code.
+ */
+int kr_nsec_matches_name_and_type(const knot_rrset_t *nsec,
+				   const knot_dname_t *name, uint16_t type);
diff --git a/lib/dnssec/nsec3.c b/lib/dnssec/nsec3.c
new file mode 100644
index 0000000..4c2ef95
--- /dev/null
+++ b/lib/dnssec/nsec3.c
@@ -0,0 +1,776 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <string.h>
+
+#include <libdnssec/binary.h>
+#include <libdnssec/error.h>
+#include <libdnssec/nsec.h>
+#include <libknot/descriptor.h>
+#include <contrib/base32hex.h>
+#include <libknot/rrset.h>
+#include <libknot/rrtype/nsec3.h>
+
+#include "lib/defines.h"
+#include "lib/dnssec/nsec.h"
+#include "lib/dnssec/nsec3.h"
+
+#define OPT_OUT_BIT 0x01
+
+//#define FLG_CLOSEST_ENCLOSER (1 << 0)
+#define FLG_CLOSEST_PROVABLE_ENCLOSER (1 << 1)
+#define FLG_NAME_COVERED (1 << 2)
+#define FLG_NAME_MATCHED (1 << 3)
+#define FLG_TYPE_BIT_MISSING (1 << 4)
+#define FLG_CNAME_BIT_MISSING (1 << 5)
+
+/**
+ * Obtains NSEC3 parameters from RR.
+ * @param params NSEC3 parameters structure to be set.
+ * @param nsec3  NSEC3 RR containing the parameters.
+ * @return       0 or error code.
+ */
+static int nsec3_parameters(dnssec_nsec3_params_t *params, const knot_rrset_t *nsec3)
+{
+	assert(params && nsec3);
+
+	const knot_rdata_t *rr = knot_rdataset_at(&nsec3->rrs, 0);
+	assert(rr);
+
+	/* Every NSEC3 RR contains data from NSEC3PARAMS. */
+	const size_t SALT_OFFSET = 5; /* First 5 octets contain { Alg, Flags, Iterations, Salt length } */
+	dnssec_binary_t rdata = {
+		.size = SALT_OFFSET + (size_t)knot_nsec3_salt_len(nsec3->rrs.rdata),
+		.data = /*const-cast*/(uint8_t *)rr->data,
+	};
+	if (rdata.size > rr->len)
+		return kr_error(EMSGSIZE);
+
+	int ret = dnssec_nsec3_params_from_rdata(params, &rdata);
+	if (ret != DNSSEC_EOK) {
+		return kr_error(EINVAL);
+	}
+
+	return kr_ok();
+}
+
+/**
+ * Computes a hash of a given domain name.
+ * @param hash   Resulting hash, must be freed.
+ * @param params NSEC3 parameters.
+ * @param name   Domain name to be hashed.
+ * @return       0 or error code.
+ */
+static int hash_name(dnssec_binary_t *hash, const dnssec_nsec3_params_t *params,
+                     const knot_dname_t *name)
+{
+	assert(hash && params);
+	if (!name)
+		return kr_error(EINVAL);
+
+	dnssec_binary_t dname = {
+		.size = knot_dname_size(name),
+		.data = (uint8_t *) name,
+	};
+
+	int ret = dnssec_nsec3_hash(&dname, params, hash);
+	if (ret != DNSSEC_EOK) {
+		return kr_error(EINVAL);
+	}
+
+	return kr_ok();
+}
+
+/**
+ * Read hash from NSEC3 owner name and store its binary form.
+ * @param hash          Buffer to be written.
+ * @param max_hash_size Maximal has size.
+ * @param nsec3         NSEC3 RR.
+ * @return              0 or error code.
+ */
+static int read_owner_hash(dnssec_binary_t *hash, size_t max_hash_size, const knot_rrset_t *nsec3)
+{
+	assert(hash && nsec3);
+	assert(hash->data);
+
+	int32_t ret = base32hex_decode(nsec3->owner + 1, nsec3->owner[0], hash->data, max_hash_size);
+	if (ret < 0) {
+		return kr_error(EILSEQ);
+	}
+	hash->size = ret;
+
+	return kr_ok();
+}
+
+#define MAX_HASH_BYTES 64
+/**
+ * Closest (provable) encloser match (RFC5155 7.2.1, bullet 1).
+ * @param flags   Flags to be set according to check outcome.
+ * @param nsec3   NSEC3 RR.
+ * @param name    Name to be checked.
+ * @param skipped Number of skipped labels to find closest (provable) match.
+ * @return        0 or error code.
+ */
+static int closest_encloser_match(int *flags, const knot_rrset_t *nsec3,
+                                  const knot_dname_t *name, unsigned *skipped)
+{
+	assert(flags && nsec3 && name && skipped);
+
+	uint8_t hash_data[MAX_HASH_BYTES] = {0, };
+	dnssec_binary_t owner_hash = { 0, hash_data };
+	dnssec_nsec3_params_t params = { 0, };
+	dnssec_binary_t name_hash = { 0, };
+
+	int ret = read_owner_hash(&owner_hash, MAX_HASH_BYTES, nsec3);
+	if (ret != 0) {
+		goto fail;
+	}
+
+	ret = nsec3_parameters(&params, nsec3);
+	if (ret != 0) {
+		goto fail;
+	}
+
+	/* Root label has no encloser */
+	if (!name[0]) {
+		ret = kr_error(ENOENT);
+		goto fail;
+	}
+
+	const knot_dname_t *encloser = knot_wire_next_label(name, NULL);
+	*skipped = 1;
+
+	while(encloser) {
+		ret = hash_name(&name_hash, &params, encloser);
+		if (ret != 0) {
+			goto fail;
+		}
+
+		if ((owner_hash.size == name_hash.size) &&
+		    (memcmp(owner_hash.data, name_hash.data, owner_hash.size) == 0)) {
+			dnssec_binary_free(&name_hash);
+			*flags |= FLG_CLOSEST_PROVABLE_ENCLOSER;
+			break;
+		}
+
+		dnssec_binary_free(&name_hash);
+
+		if (!encloser[0])
+			break;
+		encloser = knot_wire_next_label(encloser, NULL);
+		++(*skipped);
+	}
+
+	ret = kr_ok();
+
+fail:
+	if (params.salt.data) {
+		dnssec_nsec3_params_free(&params);
+	}
+	if (name_hash.data) {
+		dnssec_binary_free(&name_hash);
+	}
+	return ret;
+}
+
+/**
+ * Checks whether NSEC3 RR covers the supplied name (RFC5155 7.2.1, bullet 2).
+ * @param flags Flags to be set according to check outcome.
+ * @param nsec3 NSEC3 RR.
+ * @param name  Name to be checked.
+ * @return      0 or error code.
+ */
+static int covers_name(int *flags, const knot_rrset_t *nsec3, const knot_dname_t *name)
+{
+	assert(flags && nsec3 && name);
+
+	uint8_t hash_data[MAX_HASH_BYTES] = { 0, };
+	dnssec_binary_t owner_hash = { 0, hash_data };
+	dnssec_nsec3_params_t params = { 0, };
+	dnssec_binary_t name_hash = { 0, };
+
+	int ret = read_owner_hash(&owner_hash, MAX_HASH_BYTES, nsec3);
+	if (ret != 0) {
+		goto fail;
+	}
+
+	ret = nsec3_parameters(&params, nsec3);
+	if (ret != 0) {
+		goto fail;
+	}
+
+	ret = hash_name(&name_hash, &params, name);
+	if (ret != 0) {
+		goto fail;
+	}
+
+	uint8_t next_size = knot_nsec3_next_len(nsec3->rrs.rdata);
+	const uint8_t *next_hash = knot_nsec3_next(nsec3->rrs.rdata);
+
+	if ((next_size > 0) && (owner_hash.size == next_size) && (name_hash.size == next_size)) {
+		/* All hash lengths must be same. */
+		const uint8_t *ownrd = owner_hash.data;
+		const uint8_t *nextd = next_hash;
+		int covered = 0;
+		int greater_then_owner = (memcmp(ownrd, name_hash.data, next_size) < 0);
+		int less_then_next = (memcmp(name_hash.data, nextd, next_size) < 0);
+		if (memcmp(ownrd, nextd, next_size) < 0) {
+			/*
+			 * 0 (...) owner ... next (...) MAX
+			 *                ^
+			 *                name
+			 * ==>
+			 * (owner < name) && (name < next)
+			 */
+			covered = ((greater_then_owner) && (less_then_next));
+		} else {
+			/*
+			 * owner ... MAX, 0 ... next
+			 *        ^     ^    ^
+			 *        name  name name
+			 * =>
+			 * (owner < name) || (name < next)
+			 */
+			covered = ((greater_then_owner) || (less_then_next));
+		}
+
+		if (covered) {
+			*flags |= FLG_NAME_COVERED;
+
+			uint8_t nsec3_flags = knot_nsec3_flags(nsec3->rrs.rdata);
+			if (nsec3_flags & ~OPT_OUT_BIT) {
+				/* RFC5155 3.1.2 */
+				ret = kr_error(EINVAL);
+			} else {
+				ret = kr_ok();
+			}
+		}
+	}
+
+fail:
+	if (params.salt.data) {
+		dnssec_nsec3_params_free(&params);
+	}
+	if (name_hash.data) {
+		dnssec_binary_free(&name_hash);
+	}
+	return ret;
+}
+
+/**
+ * Checks whether NSEC3 RR has the opt-out bit set.
+ * @param flags Flags to be set according to check outcome.
+ * @param nsec3 NSEC3 RR.
+ * @param name  Name to be checked.
+ * @return      0 or error code.
+ */
+static bool has_optout(const knot_rrset_t *nsec3)
+{
+	if (!nsec3) {
+		return false;
+	}
+
+	uint8_t nsec3_flags = knot_nsec3_flags(nsec3->rrs.rdata);
+	if (nsec3_flags & ~OPT_OUT_BIT) {
+		/* RFC5155 3.1.2 */
+		return false;
+	}
+
+	return nsec3_flags & OPT_OUT_BIT;
+}
+
+/**
+ * Checks whether NSEC3 RR matches the supplied name.
+ * @param flags Flags to be set according to check outcome.
+ * @param nsec3 NSEC3 RR.
+ * @param name  Name to be checked.
+ * @return      0 if matching, >0 if not (abs(ENOENT)), or error code (<0).
+ */
+static int matches_name(const knot_rrset_t *nsec3, const knot_dname_t *name)
+{
+	assert(nsec3 && name);
+
+	uint8_t hash_data[MAX_HASH_BYTES] = { 0, };
+	dnssec_binary_t owner_hash = { 0, hash_data };
+	dnssec_nsec3_params_t params = { 0, };
+	dnssec_binary_t name_hash = { 0, };
+
+	int ret = read_owner_hash(&owner_hash, MAX_HASH_BYTES, nsec3);
+	if (ret != 0) {
+		goto fail;
+	}
+
+	ret = nsec3_parameters(&params, nsec3);
+	if (ret != 0) {
+		goto fail;
+	}
+
+	ret = hash_name(&name_hash, &params, name);
+	if (ret != 0) {
+		goto fail;
+	}
+
+	if ((owner_hash.size == name_hash.size) &&
+	    (memcmp(owner_hash.data, name_hash.data, owner_hash.size) == 0)) {
+		ret = kr_ok();
+	} else {
+		ret = abs(ENOENT);
+	}
+
+fail:
+	if (params.salt.data) {
+		dnssec_nsec3_params_free(&params);
+	}
+	if (name_hash.data) {
+		dnssec_binary_free(&name_hash);
+	}
+	return ret;
+}
+#undef MAX_HASH_BYTES
+
+/**
+ * Prepends an asterisk label to given name.
+ *
+ * @param tgt  Target buffer to write domain name into.
+ * @param name Name to be added to the asterisk.
+ * @return     Size of the resulting name or error code.
+ */
+static int prepend_asterisk(uint8_t *tgt, size_t maxlen, const knot_dname_t *name)
+{
+	assert(maxlen >= 3);
+	memcpy(tgt, "\1*", 3);
+	return knot_dname_to_wire(tgt + 2, name, maxlen - 2);
+}
+
+/**
+ * Closest encloser proof (RFC5155 7.2.1).
+ * @note No RRSIGs are validated.
+ * @param pkt                     Packet structure to be processed.
+ * @param section_id              Packet section to be processed.
+ * @param sname                   Name to be checked.
+ * @param encloser_name           Returned matching encloser name, if found.
+ * @param matching_encloser_nsec3 Pointer to matching encloser NSEC RRSet.
+ * @param covering_next_nsec3     Pointer to covering next closer NSEC3 RRSet.
+ * @return                        0 or error code.
+ */
+static int closest_encloser_proof(const knot_pkt_t *pkt,
+				  knot_section_t section_id,
+				  const knot_dname_t *sname,
+				  const knot_dname_t **encloser_name,
+				  const knot_rrset_t **matching_encloser_nsec3,
+				  const knot_rrset_t **covering_next_nsec3)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, section_id);
+	if (!sec || !sname) {
+		return kr_error(EINVAL);
+	}
+
+	const knot_rrset_t *matching = NULL;
+	const knot_rrset_t *covering = NULL;
+
+	int flags = 0;
+	const knot_dname_t *next_closer = NULL;
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rrset = knot_pkt_rr(sec, i);
+		if (rrset->type != KNOT_RRTYPE_NSEC3) {
+			continue;
+		}
+		/* Also skip the NSEC3-to-match an ancestor of sname if it's
+		 * a parent-side delegation, as that would mean the owner
+		 * does not really exist (authoritatively in this zone,
+		 * even in case of opt-out).
+		 */
+		const uint8_t *bm = knot_nsec3_bitmap(rrset->rrs.rdata);
+		uint16_t bm_size = knot_nsec3_bitmap_len(rrset->rrs.rdata);
+		if (kr_nsec_children_in_zone_check(bm, bm_size) != 0) {
+			continue; /* no fatal errors from bad RRs */
+		}
+		/* Match the NSEC3 to sname or one of its ancestors. */
+		unsigned skipped = 0;
+		flags = 0;
+		int ret = closest_encloser_match(&flags, rrset, sname, &skipped);
+		if (ret != 0) {
+			return ret;
+		}
+		if (!(flags & FLG_CLOSEST_PROVABLE_ENCLOSER)) {
+			continue;
+		}
+		matching = rrset;
+		/* Construct the next closer name and try to cover it. */
+		--skipped;
+		next_closer = sname;
+		for (unsigned j = 0; j < skipped; ++j) {
+			assert(next_closer[0]);
+			next_closer = knot_wire_next_label(next_closer, NULL);
+		}
+		for (unsigned j = 0; j < sec->count; ++j) {
+			const knot_rrset_t *rrset_j = knot_pkt_rr(sec, j);
+			if (rrset_j->type != KNOT_RRTYPE_NSEC3) {
+				continue;
+			}
+			ret = covers_name(&flags, rrset_j, next_closer);
+			if (ret != 0) {
+				return ret;
+			}
+			if (flags & FLG_NAME_COVERED) {
+				covering = rrset_j;
+				break;
+			}
+		}
+		if (flags & FLG_NAME_COVERED) {
+			break;
+		}
+		flags = 0; //
+	}
+
+	if ((flags & FLG_CLOSEST_PROVABLE_ENCLOSER) && (flags & FLG_NAME_COVERED) && next_closer) {
+		if (encloser_name && next_closer[0]) {
+			*encloser_name = knot_wire_next_label(next_closer, NULL);
+		}
+		if (matching_encloser_nsec3) {
+			*matching_encloser_nsec3 = matching;
+		}
+		if (covering_next_nsec3) {
+			*covering_next_nsec3 = covering;
+		}
+		return kr_ok();
+	}
+
+	return kr_error(ENOENT);
+}
+
+/**
+ * Check whether any NSEC3 RR covers a wildcard RR at the closer encloser.
+ * @param pkt        Packet structure to be processed.
+ * @param section_id Packet section to be processed.
+ * @param encloser   Closest (provable) encloser domain name.
+ * @return           0 or error code:
+ *                   KNOT_ERANGE - NSEC3 RR (that covers a wildcard)
+ *                   has been found, but has opt-out flag set;
+ *                   otherwise - error.
+ */
+static int covers_closest_encloser_wildcard(const knot_pkt_t *pkt, knot_section_t section_id,
+                                            const knot_dname_t *encloser)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, section_id);
+	if (!sec || !encloser) {
+		return kr_error(EINVAL);
+	}
+
+	uint8_t wildcard[KNOT_DNAME_MAXLEN];
+	wildcard[0] = 1;
+	wildcard[1] = '*';
+	int encloser_len = knot_dname_size(encloser);
+	if (encloser_len < 0) {
+		return encloser_len;
+	}
+	memcpy(wildcard + 2, encloser, encloser_len);
+
+	int flags = 0;
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rrset = knot_pkt_rr(sec, i);
+		if (rrset->type != KNOT_RRTYPE_NSEC3) {
+			continue;
+		}
+		int ret = covers_name(&flags, rrset, wildcard);
+		if (ret != 0) {
+			return ret;
+		}
+		if (flags & FLG_NAME_COVERED) {
+			return has_optout(rrset) ?
+			       kr_error(KNOT_ERANGE) : kr_ok();
+		}
+	}
+
+	return kr_error(ENOENT);
+}
+
+int kr_nsec3_name_error_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                       const knot_dname_t *sname)
+{
+	const knot_dname_t *encloser = NULL;
+	const knot_rrset_t *covering_next_nsec3 = NULL;
+	int ret = closest_encloser_proof(pkt, section_id, sname,
+					 &encloser, NULL, &covering_next_nsec3);
+	if (ret != 0) {
+		return ret;
+	}
+	ret = covers_closest_encloser_wildcard(pkt, section_id, encloser);
+	if (ret != 0) {
+		/* OK, but NSEC3 for wildcard at encloser has opt-out;
+		 * or error */
+		return ret;
+	}
+	/* Closest encloser proof is OK and
+	 * NSEC3 for wildcard has been found and optout flag is not set.
+	 * Now check if NSEC3 that covers next closer name has opt-out. */
+	return has_optout(covering_next_nsec3) ?
+	       kr_error(KNOT_ERANGE) : kr_ok();
+}
+
+/**
+ * Search the packet section for a matching NSEC3 with nodata-proving bitmap.
+ * @param pkt        Packet structure to be processed.
+ * @param section_id Packet section to be processed.
+ * @param sname      Name to be checked.
+ * @param stype      Type to be checked.
+ * @return           0 or error code.
+ * @note             This does NOT check the opt-out case if type is DS;
+ *                   see RFC 5155 8.6.
+ */
+static int nodata_find(const knot_pkt_t *pkt, knot_section_t section_id,
+			const knot_dname_t *name, const uint16_t type)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, section_id);
+	if (!sec || !name) {
+		return kr_error(EINVAL);
+	}
+
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *nsec3 = knot_pkt_rr(sec, i);
+		/* Records causing any errors are simply skipped. */
+		if (nsec3->type != KNOT_RRTYPE_NSEC3
+		    || matches_name(nsec3, name) != kr_ok()) {
+			continue;
+			/* LATER(optim.): we repeatedly recompute the hash of `name` */
+		}
+
+		const uint8_t *bm = knot_nsec3_bitmap(nsec3->rrs.rdata);
+		uint16_t bm_size = knot_nsec3_bitmap_len(nsec3->rrs.rdata);
+		if (kr_nsec_bitmap_nodata_check(bm, bm_size, type, nsec3->owner) == kr_ok()) {
+			return kr_ok();
+		}
+	}
+
+	return kr_error(ENOENT);
+}
+
+/**
+ * Check whether NSEC3 RR matches a wildcard at the closest encloser and has given type bit missing.
+ * @param pkt        Packet structure to be processed.
+ * @param section_id Packet section to be processed.
+ * @param encloser   Closest (provable) encloser domain name.
+ * @param stype      Type to be checked.
+ * @return           0 or error code.
+ */
+static int matches_closest_encloser_wildcard(const knot_pkt_t *pkt, knot_section_t section_id,
+                                             const knot_dname_t *encloser, uint16_t stype)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, section_id);
+	if (!sec || !encloser) {
+		return kr_error(EINVAL);
+	}
+
+	uint8_t wildcard[KNOT_DNAME_MAXLEN]; /**< the source of synthesis */
+	int ret = prepend_asterisk(wildcard, sizeof(wildcard), encloser);
+	if (ret < 0) {
+		return ret;
+	}
+	assert(ret >= 3);
+	return nodata_find(pkt, section_id, wildcard, stype);
+}
+
+int kr_nsec3_wildcard_answer_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                            const knot_dname_t *sname, int trim_to_next)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, section_id);
+	if (!sec || !sname) {
+		return kr_error(EINVAL);
+	}
+
+	/* Compute the next closer name. */
+	for (int i = 0; i < trim_to_next; ++i) {
+		assert(sname[0]);
+		sname = knot_wire_next_label(sname, NULL);
+	}
+
+	int flags = 0;
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rrset = knot_pkt_rr(sec, i);
+		if (rrset->type != KNOT_RRTYPE_NSEC3) {
+			continue;
+		}
+		int ret = covers_name(&flags, rrset, sname);
+		if (ret != 0) {
+			return ret;
+		}
+		if (flags & FLG_NAME_COVERED) {
+			return has_optout(rrset) ?
+			       kr_error(KNOT_ERANGE) : kr_ok();
+		}
+	}
+
+	return kr_error(ENOENT);
+}
+
+
+int kr_nsec3_no_data(const knot_pkt_t *pkt, knot_section_t section_id,
+                     const knot_dname_t *sname, uint16_t stype)
+{
+	/* DS record may be also matched by an existing NSEC3 RR. */
+	int ret = nodata_find(pkt, section_id, sname, stype);
+	if (ret == 0) {
+		/* Satisfies RFC5155 8.5 and 8.6, both first paragraph. */
+		return ret;
+	}
+
+	/* Find closest provable encloser. */
+	const knot_dname_t *encloser_name = NULL;
+	const knot_rrset_t *covering_next_nsec3 = NULL;
+	ret = closest_encloser_proof(pkt, section_id, sname, &encloser_name,
+                                     NULL, &covering_next_nsec3);
+	if (ret != 0) {
+		return ret;
+	}
+
+	assert(encloser_name && covering_next_nsec3);
+	ret = matches_closest_encloser_wildcard(pkt, section_id,
+	                                         encloser_name, stype);
+	if (ret == 0) {
+		/* Satisfies RFC5155 8.7 */
+		if (has_optout(covering_next_nsec3)) {
+			/* Opt-out is detected.
+			 * Despite the fact that all records
+			 * in the packet can be properly signed,
+			 * AD bit must not be set due to rfc5155 9.2.
+			 * Return appropriate code to the caller */
+			ret = kr_error(KNOT_ERANGE);
+		}
+		return ret;
+	}
+
+	if (!has_optout(covering_next_nsec3)) {
+		/* Bogus */
+		ret = kr_error(ENOENT);
+	} else {
+		/* 
+		 * Satisfies RFC5155 8.6 (QTYPE == DS), 2nd paragraph.
+		 * Also satisfies ERRATA 3441 8.5 (QTYPE != DS), 3rd paragraph.
+		 * - (wildcard) empty nonterminal
+		 * derived from unsecure delegation.
+		 * Denial of existence can not be proven.
+		 * Set error code to proceed unsecure.
+		 */
+		ret = kr_error(KNOT_ERANGE);
+	}
+
+	return ret;
+}
+
+int kr_nsec3_ref_to_unsigned(const knot_pkt_t *pkt)
+{
+	const knot_pktsection_t *sec = knot_pkt_section(pkt, KNOT_AUTHORITY);
+	if (!sec) {
+		return kr_error(EINVAL);
+	}
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *ns = knot_pkt_rr(sec, i);
+		if (ns->type == KNOT_RRTYPE_DS) {
+			return kr_error(EEXIST);
+		}
+		if (ns->type != KNOT_RRTYPE_NS) {
+			continue;
+		}
+
+		int flags = 0;
+		bool nsec3_found = false;
+		for (unsigned j = 0; j < sec->count; ++j) {
+			const knot_rrset_t *nsec3 = knot_pkt_rr(sec, j);
+			if (nsec3->type == KNOT_RRTYPE_DS) {
+				return kr_error(EEXIST);
+			}
+			if (nsec3->type != KNOT_RRTYPE_NSEC3) {
+				continue;
+			}
+			nsec3_found = true;
+			/* nsec3 found, check if owner name matches the delegation name.
+			 * Just skip in case of *any* errors. */
+			if (matches_name(nsec3, ns->owner) != kr_ok()) {
+				continue;
+			}
+
+			const uint8_t *bm = knot_nsec3_bitmap(nsec3->rrs.rdata);
+			uint16_t bm_size = knot_nsec3_bitmap_len(nsec3->rrs.rdata);
+			if (!bm) {
+				return kr_error(EINVAL);
+			}
+			if (dnssec_nsec_bitmap_contains(bm, bm_size,
+							  KNOT_RRTYPE_NS) &&
+			    !dnssec_nsec_bitmap_contains(bm, bm_size,
+							  KNOT_RRTYPE_DS) &&
+			    !dnssec_nsec_bitmap_contains(bm, bm_size,
+							  KNOT_RRTYPE_SOA)) {
+				/* Satisfies rfc5155, 8.9. paragraph 2 */
+				return kr_ok();
+			}
+		}
+		if (!nsec3_found) {
+			return kr_error(DNSSEC_NOT_FOUND);
+		}
+		if (flags & FLG_NAME_MATCHED) {
+			/* nsec3 which owner matches
+			 * the delegation name was found,
+			 * but nsec3 type bitmap contains wrong types
+			 */
+			return kr_error(EINVAL);
+		}
+		/* nsec3 that matches the delegation was not found.
+		 * Check rfc5155, 8.9. paragraph 4.
+		 * Find closest provable encloser.
+		 */
+		const knot_dname_t *encloser_name = NULL;
+		const knot_rrset_t *covering_next_nsec3 = NULL;
+		int ret = closest_encloser_proof(pkt, KNOT_AUTHORITY, ns->owner,
+				&encloser_name, NULL, &covering_next_nsec3);
+		if (ret != 0) {
+			return kr_error(EINVAL);
+		}
+
+		if (has_optout(covering_next_nsec3)) {
+			return kr_error(KNOT_ERANGE);
+		} else {
+			return kr_error(EINVAL);
+		}
+	}
+	return kr_error(EINVAL);
+}
+
+int kr_nsec3_matches_name_and_type(const knot_rrset_t *nsec3,
+				   const knot_dname_t *name, uint16_t type)
+{
+	/* It's not secure enough to just check a single bit for (some) other types,
+	 * but we don't (currently) only use this API for NS.  See RFC 6840 sec. 4.
+	 */
+	if (type != KNOT_RRTYPE_NS) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+	int ret = matches_name(nsec3, name);
+	if (ret) {
+		return kr_error(ret);
+	}
+	const uint8_t *bm = knot_nsec3_bitmap(nsec3->rrs.rdata);
+	uint16_t bm_size = knot_nsec3_bitmap_len(nsec3->rrs.rdata);
+	if (!bm) {
+		return kr_error(EINVAL);
+	}
+	if (dnssec_nsec_bitmap_contains(bm, bm_size, type)) {
+		return kr_ok();
+	} else {
+		return kr_error(ENOENT);
+	}
+}
diff --git a/lib/dnssec/nsec3.h b/lib/dnssec/nsec3.h
new file mode 100644
index 0000000..527ccce
--- /dev/null
+++ b/lib/dnssec/nsec3.h
@@ -0,0 +1,82 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <libknot/packet/pkt.h>
+
+/**
+ * Name error response check (RFC5155 7.2.2).
+ * @note No RRSIGs are validated.
+ * @param pkt        Packet structure to be processed.
+ * @param section_id Packet section to be processed.
+ * @param sname      Name to be checked.
+ * @return           0 or error code.
+ */
+int kr_nsec3_name_error_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                       const knot_dname_t *sname);
+
+/**
+ * Wildcard answer response check (RFC5155 7.2.6).
+ * @param pkt          Packet structure to be processed.
+ * @param section_id   Packet section to be processed.
+ * @param sname        Name to be checked.
+ * @param trim_to_next Number of labels to remove to obtain next closer name.
+ * @return             0 or error code:
+ *                     KNOT_ERANGE - NSEC3 RR that covers a wildcard
+ *                     has been found, but has opt-out flag set;
+ *                     otherwise - error.
+ */
+int kr_nsec3_wildcard_answer_response_check(const knot_pkt_t *pkt, knot_section_t section_id,
+                                            const knot_dname_t *sname, int trim_to_next);
+
+/**
+ * Authenticated denial of existence according to RFC5155 8.5 and 8.7.
+ * @note No RRSIGs are validated.
+ * @param pkt        Packet structure to be processed.
+ * @param section_id Packet section to be processed.
+ * @param sname      Queried domain name.
+ * @param stype      Queried type.
+ * @return           0 or error code:
+ *                   DNSSEC_NOT_FOUND - neither ds nor nsec records
+ *                   were not found.
+ *                   KNOT_ERANGE - denial of existence can't be proven
+ *                   due to opt-out, otherwise - bogus.
+ */
+int kr_nsec3_no_data(const knot_pkt_t *pkt, knot_section_t section_id,
+                     const knot_dname_t *sname, uint16_t stype);
+
+/**
+ * Referral to unsigned subzone check (RFC5155 8.9).
+ * @note 	     No RRSIGs are validated.
+ * @param pkt        Packet structure to be processed.
+ * @return           0 or error code:
+ *                   KNOT_ERANGE - denial of existence can't be proven
+ *                   due to opt-out.
+ *                   EEXIST - ds record was found.
+ *                   EINVAL - bogus.
+ */
+int kr_nsec3_ref_to_unsigned(const knot_pkt_t *pkt);
+
+/**
+ * Checks whether supplied NSEC3 RR matches the supplied name and NS type.
+ * @param nsec3 NSEC3 RR.
+ * @param name  Name to be checked.
+ * @param type  Type to be checked.  Only use with NS!  TODO
+ * @return      0 or error code.
+ */
+int kr_nsec3_matches_name_and_type(const knot_rrset_t *nsec3,
+				   const knot_dname_t *name, uint16_t type);
diff --git a/lib/dnssec/signature.c b/lib/dnssec/signature.c
new file mode 100644
index 0000000..356bf14
--- /dev/null
+++ b/lib/dnssec/signature.c
@@ -0,0 +1,307 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <arpa/inet.h>
+#include <assert.h>
+#include <string.h>
+
+#include <libdnssec/error.h>
+#include <libdnssec/key.h>
+#include <libdnssec/sign.h>
+#include <libknot/descriptor.h>
+#include <libknot/packet/rrset-wire.h>
+#include <libknot/packet/wire.h>
+#include <libknot/rrset.h>
+#include <libknot/rrtype/rrsig.h>
+#include <libknot/rrtype/ds.h>
+
+#include "lib/defines.h"
+#include "lib/utils.h"
+#include "lib/dnssec/signature.h"
+
+#include "contrib/wire.h"
+
+static int authenticate_ds(const dnssec_key_t *key, dnssec_binary_t *ds_rdata, uint8_t digest_type)
+{
+	/* Compute DS RDATA from the DNSKEY. */
+	dnssec_binary_t computed_ds = { 0, };
+	int ret = dnssec_key_create_ds(key, digest_type, &computed_ds);
+	if (ret != DNSSEC_EOK) {
+		goto fail;
+	}
+
+	/* DS records contain algorithm, key tag and the digest.
+	 * Therefore the comparison of the two DS is sufficient.
+	 */
+	ret = (ds_rdata->size == computed_ds.size) &&
+	    (memcmp(ds_rdata->data, computed_ds.data, ds_rdata->size) == 0);
+	ret = ret ? kr_ok() : kr_error(ENOENT);
+
+fail:
+	dnssec_binary_free(&computed_ds);
+	return kr_error(ret);
+}
+
+int kr_authenticate_referral(const knot_rrset_t *ref, const dnssec_key_t *key)
+{
+	assert(ref && key);
+	if (ref->type != KNOT_RRTYPE_DS) {
+		return kr_error(EINVAL);
+	}
+
+	/* Try all possible DS records */
+	int ret = 0;
+	knot_rdata_t *rd = ref->rrs.rdata;
+	for (uint16_t i = 0; i < ref->rrs.count; ++i) {
+		dnssec_binary_t ds_rdata = {
+			.size = rd->len,
+			.data = rd->data
+		};
+		ret = authenticate_ds(key, &ds_rdata, knot_ds_digest_type(rd));
+		if (ret == 0) { /* Found a good DS */
+			return kr_ok();
+		}
+		rd = knot_rdataset_next(rd);
+	}
+
+	return kr_error(ret);
+}
+
+/**
+ * Adjust TTL in wire format.
+ * @param wire      RR Set in wire format.
+ * @param wire_size Size of the wire data portion.
+ * @param new_ttl   TTL value to be set for all RRs.
+ * @return          0 or error code.
+ */
+static int adjust_wire_ttl(uint8_t *wire, size_t wire_size, uint32_t new_ttl)
+{
+	assert(wire);
+	assert(sizeof(uint16_t) == 2);
+	assert(sizeof(uint32_t) == 4);
+	uint16_t rdlen;
+
+	int ret;
+
+	new_ttl = htonl(new_ttl);
+
+	size_t i = 0;
+	/* RR wire format in RFC1035 3.2.1 */
+	while(i < wire_size) {
+		ret = knot_dname_size(wire + i);
+		if (ret < 0) {
+			return ret;
+		}
+		i += ret + 4;
+		memcpy(wire + i, &new_ttl, sizeof(uint32_t));
+		i += sizeof(uint32_t);
+
+		memcpy(&rdlen, wire + i, sizeof(uint16_t));
+		rdlen = ntohs(rdlen);
+		i += sizeof(uint16_t) + rdlen;
+
+		assert(i <= wire_size);
+	}
+
+	return kr_ok();
+}
+
+/*!
+ * \brief Add RRSIG RDATA without signature to signing context.
+ *
+ * Requires signer name in RDATA in canonical form.
+ *
+ * \param ctx   Signing context.
+ * \param rdata Pointer to RRSIG RDATA.
+ *
+ * \return Error code, KNOT_EOK if successful.
+ */
+#define RRSIG_RDATA_SIGNER_OFFSET 18
+static int sign_ctx_add_self(dnssec_sign_ctx_t *ctx, const uint8_t *rdata)
+{
+	assert(ctx);
+	assert(rdata);
+
+	int result;
+
+	// static header
+
+	dnssec_binary_t header = {
+		.data = (uint8_t *)rdata,
+		.size = RRSIG_RDATA_SIGNER_OFFSET,
+	};
+
+	result = dnssec_sign_add(ctx, &header);
+	if (result != DNSSEC_EOK) {
+		return result;
+	}
+
+	// signer name
+
+	const uint8_t *rdata_signer = rdata + RRSIG_RDATA_SIGNER_OFFSET;
+	dnssec_binary_t signer = { 0 };
+	signer.data = knot_dname_copy(rdata_signer, NULL);
+	signer.size = knot_dname_size(signer.data);
+
+	result = dnssec_sign_add(ctx, &signer);
+	free(signer.data);
+
+	return result;
+}
+#undef RRSIG_RDATA_SIGNER_OFFSET
+
+/*!
+ * \brief Add covered RRs to signing context.
+ *
+ * Requires all DNAMEs in canonical form and all RRs ordered canonically.
+ *
+ * \param ctx      Signing context.
+ * \param covered  Covered RRs.
+ *
+ * \return Error code, KNOT_EOK if successful.
+ */
+static int sign_ctx_add_records(dnssec_sign_ctx_t *ctx, const knot_rrset_t *covered,
+                                uint32_t orig_ttl, int trim_labels)
+{
+	if (!ctx || !covered || trim_labels < 0) {
+		return kr_error(EINVAL);
+	}
+
+	// huge block of rrsets can be optionally created
+	static uint8_t wire_buffer[KNOT_WIRE_MAX_PKTSIZE];
+	int written = knot_rrset_to_wire(covered, wire_buffer, sizeof(wire_buffer), NULL);
+	if (written < 0) {
+		return written;
+	}
+
+	/* Set original ttl. */
+	int ret = adjust_wire_ttl(wire_buffer, written, orig_ttl);
+	if (ret != 0) {
+		return ret;
+	}
+
+	if (!trim_labels) {
+		const dnssec_binary_t wire_binary = {
+			.size = written,
+			.data = wire_buffer
+		};
+		return dnssec_sign_add(ctx, &wire_binary);
+	}
+
+	/* RFC4035 5.3.2
+	 * Remove leftmost labels and replace them with '*.'
+	 * for each RR in covered.
+	 */
+	uint8_t *beginp = wire_buffer;
+	for (uint16_t i = 0; i < covered->rrs.count; ++i) {
+		/* RR(i) = name | type | class | OrigTTL | RDATA length | RDATA */
+		for (int j = 0; j < trim_labels; ++j) {
+			assert(beginp[0]);
+			beginp = (uint8_t *) knot_wire_next_label(beginp, NULL);
+			assert(beginp != NULL);
+		}
+		*(--beginp) = '*';
+		*(--beginp) = 1;
+		const size_t rdatalen_offset = knot_dname_size(beginp) + /* name */
+			sizeof(uint16_t) + /* type */
+			sizeof(uint16_t) + /* class */
+			sizeof(uint32_t);  /* OrigTTL */
+		const uint8_t *rdatalen_ptr = beginp + rdatalen_offset;
+		const uint16_t rdata_size = wire_read_u16(rdatalen_ptr);
+		const size_t rr_size = rdatalen_offset +
+			sizeof(uint16_t) + /* RDATA length */
+			rdata_size;        /* RDATA */
+		const dnssec_binary_t wire_binary = {
+			.size = rr_size,
+			.data = beginp
+		};
+		ret = dnssec_sign_add(ctx, &wire_binary);
+		if (ret != 0) {
+			break;
+		}
+		beginp += rr_size;
+	}
+	return ret;
+}
+
+/*!
+ * \brief Add all data covered by signature into signing context.
+ *
+ * RFC 4034: The signature covers RRSIG RDATA field (excluding the signature)
+ * and all matching RR records, which are ordered canonically.
+ *
+ * Requires all DNAMEs in canonical form and all RRs ordered canonically.
+ *
+ * \param ctx          Signing context.
+ * \param rrsig_rdata  RRSIG RDATA with populated fields except signature.
+ * \param covered      Covered RRs.
+ *
+ * \return Error code, KNOT_EOK if successful.
+ */
+/* TODO -- Taken from knot/src/knot/dnssec/rrset-sign.c. Re-write for better fit needed. */
+static int sign_ctx_add_data(dnssec_sign_ctx_t *ctx, const uint8_t *rrsig_rdata,
+                             const knot_rrset_t *covered, uint32_t orig_ttl, int trim_labels)
+{
+	int result = sign_ctx_add_self(ctx, rrsig_rdata);
+	if (result != KNOT_EOK) {
+		return result;
+	}
+
+	return sign_ctx_add_records(ctx, covered, orig_ttl, trim_labels);
+}
+
+int kr_check_signature(const knot_rdata_t *rrsig,
+                       const dnssec_key_t *key, const knot_rrset_t *covered,
+                       int trim_labels)
+{
+	if (!rrsig || !key || !dnssec_key_can_verify(key)) {
+		return kr_error(EINVAL);
+	}
+
+	int ret = 0;
+	dnssec_sign_ctx_t *sign_ctx = NULL;
+	dnssec_binary_t signature = {
+		.data = /*const-cast*/(uint8_t*)knot_rrsig_signature(rrsig),
+		.size = knot_rrsig_signature_len(rrsig),
+	};
+	if (!signature.data || !signature.size) {
+		ret = kr_error(EINVAL);
+		goto fail;
+	}
+
+	if (dnssec_sign_new(&sign_ctx, key) != 0) {
+		ret = kr_error(ENOMEM);
+		goto fail;
+	}
+
+	uint32_t orig_ttl = knot_rrsig_original_ttl(rrsig);
+
+	if (sign_ctx_add_data(sign_ctx, rrsig->data, covered, orig_ttl, trim_labels) != 0) {
+		ret = kr_error(ENOMEM);
+		goto fail;
+	}
+
+	if (dnssec_sign_verify(sign_ctx, &signature) != 0) {
+		ret = kr_error(EBADMSG);
+		goto fail;
+	}
+
+	ret = kr_ok();
+
+fail:
+	dnssec_sign_free(sign_ctx);
+	return ret;
+}
diff --git a/lib/dnssec/signature.h b/lib/dnssec/signature.h
new file mode 100644
index 0000000..b756483
--- /dev/null
+++ b/lib/dnssec/signature.h
@@ -0,0 +1,42 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <libdnssec/key.h>
+#include <libknot/rrset.h>
+
+/**
+ * Performs referral authentication according to RFC4035 5.2, bullet 2
+ * @param ref Referral RRSet. Currently only DS can be used.
+ * @param key Already parsed key.
+ * @return    0 or error code.  In particular: DNSSEC_INVALID_DS_ALGORITHM
+ *            in case *all* DSs in ref use an unimplemented algorithm.
+ */
+int kr_authenticate_referral(const knot_rrset_t *ref, const dnssec_key_t *key);
+
+/**
+ * Check the signature of the supplied RRSet.
+ * @param rrsigs      RRSet containing signatures.
+ * @param pos         Index of the signature record in the signature RRSet.
+ * @param key         Key to be used to validate the signature.
+ * @param covered     The covered RRSet.
+ * @param trim_labels Number of the leftmost labels to be removed and replaced with '*.'.
+ * @return            0 if signature valid, error code else.
+ */
+int kr_check_signature(const knot_rdata_t *rrsig,
+                       const dnssec_key_t *key, const knot_rrset_t *covered,
+                       int trim_labels);
diff --git a/lib/dnssec/ta.c b/lib/dnssec/ta.c
new file mode 100644
index 0000000..12629c9
--- /dev/null
+++ b/lib/dnssec/ta.c
@@ -0,0 +1,185 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <contrib/cleanup.h>
+#include <libknot/descriptor.h>
+#include <libknot/rdataset.h>
+#include <libknot/rrset.h>
+#include <libknot/packet/wire.h>
+#include <libdnssec/key.h>
+#include <libdnssec/error.h>
+
+#include "lib/defines.h"
+#include "lib/dnssec.h"
+#include "lib/dnssec/ta.h"
+#include "lib/resolve.h"
+#include "lib/utils.h"
+
+knot_rrset_t *kr_ta_get(map_t *trust_anchors, const knot_dname_t *name)
+{
+	return map_get(trust_anchors, (const char *)name);
+}
+
+const knot_dname_t *kr_ta_get_longest_name(map_t *trust_anchors, const knot_dname_t *name)
+{
+	while(name) {
+		if (kr_ta_get(trust_anchors, name)) {
+			return name;
+		}
+		if (name[0] == '\0') {
+			break;
+		}
+		name = knot_wire_next_label(name, NULL);
+	}
+	return NULL;
+}
+
+/* @internal Create DS from DNSKEY, caller MUST free dst if successful. */
+static int dnskey2ds(dnssec_binary_t *dst, const knot_dname_t *owner, const uint8_t *rdata, uint16_t rdlen)
+{
+	dnssec_key_t *key = NULL;
+	int ret = dnssec_key_new(&key);
+	if (ret) goto cleanup;
+	/* Create DS from DNSKEY and reinsert */
+	const dnssec_binary_t key_data = { .size = rdlen, .data = (uint8_t *)rdata };
+	ret = dnssec_key_set_rdata(key, &key_data);
+	if (ret) goto cleanup;
+	/* Accept only keys with Zone and SEP flags that aren't revoked,
+	 * as a precaution.  RFC 5011 also utilizes these flags.
+	 * TODO: kr_dnssec_key_* names are confusing. */
+	const bool flags_ok = kr_dnssec_key_zsk(rdata) && !kr_dnssec_key_revoked(rdata);
+	if (!flags_ok) {
+		auto_free char *owner_str = kr_dname_text(owner);
+		kr_log_error("[ ta ] refusing to trust %s DNSKEY because of flags %d\n",
+			owner_str, dnssec_key_get_flags(key));
+		ret = kr_error(EILSEQ);
+		goto cleanup;
+	} else if (!kr_dnssec_key_ksk(rdata)) {
+		auto_free char *owner_str = kr_dname_text(owner);
+		int flags = dnssec_key_get_flags(key);
+		kr_log_info("[ ta ] warning: %s DNSKEY is missing the SEP bit; "
+			"flags %d instead of %d\n",
+			owner_str, flags, flags + 1/*a little ugly*/);
+	}
+	ret = dnssec_key_set_dname(key, owner);
+	if (ret) goto cleanup;
+	ret = dnssec_key_create_ds(key, DNSSEC_KEY_DIGEST_SHA256, dst);
+cleanup:
+	dnssec_key_free(key);
+	return kr_error(ret);
+}
+
+/* @internal Insert new TA to trust anchor set, rdata MUST be of DS type. */
+static int insert_ta(map_t *trust_anchors, const knot_dname_t *name,
+                     uint32_t ttl, const uint8_t *rdata, uint16_t rdlen)
+{
+	bool is_new_key = false;
+	knot_rrset_t *ta_rr = kr_ta_get(trust_anchors, name);
+	if (!ta_rr) {
+		ta_rr = knot_rrset_new(name, KNOT_RRTYPE_DS, KNOT_CLASS_IN, ttl, NULL);
+		is_new_key = true;
+	}
+	/* Merge-in new key data */
+	if (!ta_rr || (rdlen > 0 && knot_rrset_add_rdata(ta_rr, rdata, rdlen, NULL) != 0)) {
+		knot_rrset_free(ta_rr, NULL);
+		return kr_error(ENOMEM);
+	}
+	if (is_new_key) {
+		return map_set(trust_anchors, (const char *)name, ta_rr);
+	}
+	return kr_ok();
+}
+
+int kr_ta_add(map_t *trust_anchors, const knot_dname_t *name, uint16_t type,
+              uint32_t ttl, const uint8_t *rdata, uint16_t rdlen)
+{
+	if (!trust_anchors || !name) {
+		return kr_error(EINVAL);
+	}
+
+	/* DS/DNSEY types are accepted, for DNSKEY we
+	 * need to compute a DS digest. */
+	if (type == KNOT_RRTYPE_DS) {
+		return insert_ta(trust_anchors, name, ttl, rdata, rdlen);
+	} else if (type == KNOT_RRTYPE_DNSKEY) {
+		dnssec_binary_t ds_rdata = { 0, };
+		int ret = dnskey2ds(&ds_rdata, name, rdata, rdlen);
+		if (ret != 0) {
+			return ret;
+		}
+		ret = insert_ta(trust_anchors, name, ttl, ds_rdata.data, ds_rdata.size);
+		dnssec_binary_free(&ds_rdata);
+		return ret;
+	} else { /* Invalid type for TA */
+		return kr_error(EINVAL);
+	}
+}
+
+int kr_ta_covers(map_t *trust_anchors, const knot_dname_t *name)
+{
+	while(name) {
+		if (kr_ta_get(trust_anchors, name)) {
+			return true;
+		}
+		if (name[0] == '\0') {
+			return false;
+		}
+		name = knot_wire_next_label(name, NULL);
+	}
+	return false;
+}
+
+bool kr_ta_covers_qry(struct kr_context *ctx, const knot_dname_t *name,
+		      const uint16_t type)
+{
+	assert(ctx && name);
+	if (type == KNOT_RRTYPE_DS && name[0] != '\0') {
+		/* DS is parent-side record, so the parent name needs to be covered. */
+		name = knot_wire_next_label(name, NULL);
+		if (!name) {
+			assert(false);
+			return false;
+		}
+	}
+	return kr_ta_covers(&ctx->trust_anchors, name)
+		&& !kr_ta_covers(&ctx->negative_anchors, name);
+}
+
+/* Delete record data */
+static int del_record(const char *k, void *v, void *ext)
+{
+	knot_rrset_t *ta_rr = v;
+	if (ta_rr) {
+		knot_rrset_free(ta_rr, NULL);
+	}
+	return 0;
+}
+
+int kr_ta_del(map_t *trust_anchors, const knot_dname_t *name)
+{
+	knot_rrset_t *ta_rr = kr_ta_get(trust_anchors, name);
+	if (ta_rr) {
+		del_record(NULL, ta_rr, NULL);
+		map_del(trust_anchors, (const char *)name);
+	}
+	return kr_ok();
+}
+
+void kr_ta_clear(map_t *trust_anchors)
+{
+	map_walk(trust_anchors, del_record, NULL);
+	map_clear(trust_anchors);
+}
diff --git a/lib/dnssec/ta.h b/lib/dnssec/ta.h
new file mode 100644
index 0000000..dcc55e7
--- /dev/null
+++ b/lib/dnssec/ta.h
@@ -0,0 +1,87 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "lib/generic/map.h"
+#include <libknot/rrset.h>
+
+/**
+ * Find TA RRSet by name.
+ * @param  trust_anchors trust store
+ * @param  name          name of the TA
+ * @return non-empty RRSet or NULL
+ */
+KR_EXPORT
+knot_rrset_t *kr_ta_get(map_t *trust_anchors, const knot_dname_t *name);
+
+/**
+ * Add TA to trust store. DS or DNSKEY types are supported.
+ * @param  trust_anchors trust store
+ * @param  name          name of the TA
+ * @param  type          RR type of the TA (DS or DNSKEY)
+ * @param  ttl           
+ * @param  rdata         
+ * @param  rdlen         
+ * @return 0 or an error
+ */
+KR_EXPORT
+int kr_ta_add(map_t *trust_anchors, const knot_dname_t *name, uint16_t type,
+               uint32_t ttl, const uint8_t *rdata, uint16_t rdlen);
+
+/**
+ * Return true if the name is below/at any TA in the store.
+ * This can be useful to check if it's possible to validate a name beforehand.
+ * @param  trust_anchors trust store
+ * @param  name          name of the TA
+ * @return boolean
+ */
+KR_EXPORT KR_PURE
+int kr_ta_covers(map_t *trust_anchors, const knot_dname_t *name);
+
+struct kr_context;
+/**
+ * A wrapper around kr_ta_covers that is aware of negative TA and types.
+ */
+KR_EXPORT KR_PURE
+bool kr_ta_covers_qry(struct kr_context *ctx, const knot_dname_t *name,
+		      const uint16_t type);
+
+/**
+ * Remove TA from trust store.
+ * @param  trust_anchors trust store
+ * @param  name          name of the TA
+ * @return 0 or an error
+ */
+KR_EXPORT
+int kr_ta_del(map_t *trust_anchors, const knot_dname_t *name);
+
+/**
+ * Clear trust store.
+ * @param trust_anchors trust store
+ */
+KR_EXPORT
+void kr_ta_clear(map_t *trust_anchors);
+
+/**
+ * Return TA with the longest name that covers given name.
+ * @param trust_anchors trust store
+ * @param name name of the TA
+ * @return pointer to name or NULL.
+	   if not NULL, points inside the name parameter.
+ */
+KR_EXPORT
+const knot_dname_t *kr_ta_get_longest_name(map_t *trust_anchors, const knot_dname_t *name);
diff --git a/lib/generic/README.rst b/lib/generic/README.rst
new file mode 100644
index 0000000..7adff86
--- /dev/null
+++ b/lib/generic/README.rst
@@ -0,0 +1,60 @@
+Generics library
+----------------
+
+This small collection of "generics" was born out of frustration that I couldn't find no
+such thing for C. It's either bloated, has poor interface, null-checking is absent or
+doesn't allow custom allocation scheme. BSD-licensed (or compatible) code is allowed here,
+as long as it comes with a test case in `tests/test_generics.c`.
+
+* array_ - a set of simple macros to make working with dynamic arrays easier.
+* queue_ - a FIFO + LIFO queue.
+* map_ - a `Crit-bit tree`_ key-value map implementation (public domain) that comes with tests.
+* set_ - set abstraction implemented on top of ``map`` (unused now).
+* pack_ - length-prefixed list of objects (i.e. array-list).
+* lru_ - LRU-like hash table
+* trie_ - a trie-based key-value map, taken from knot-dns
+
+array
+~~~~~
+
+.. doxygenfile:: array.h
+   :project: libkres
+
+queue
+~~~~~
+
+.. doxygenfile:: queue.h
+   :project: libkres
+
+map
+~~~
+
+.. doxygenfile:: map.h
+   :project: libkres
+
+set
+~~~
+
+.. doxygenfile:: set.h
+   :project: libkres
+
+pack
+~~~~
+
+.. doxygenfile:: pack.h
+   :project: libkres
+
+lru
+~~~
+
+.. doxygenfile:: lru.h
+   :project: libkres
+
+trie
+~~~~
+
+.. doxygenfile:: trie.h
+   :project: libkres
+
+
+.. _`Crit-bit tree`: https://cr.yp.to/critbit.html 
diff --git a/lib/generic/array.h b/lib/generic/array.h
new file mode 100644
index 0000000..ece4dd1
--- /dev/null
+++ b/lib/generic/array.h
@@ -0,0 +1,166 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ *
+ * @file array.h
+ * @brief A set of simple macros to make working with dynamic arrays easier.
+ *
+ * @note The C has no generics, so it is implemented mostly using macros.
+ * Be aware of that, as direct usage of the macros in the evaluating macros
+ * may lead to different expectations:
+ *
+ * @code{.c}
+ *     MIN(array_push(arr, val), other)
+ * @endcode
+ *
+ * May evaluate the code twice, leading to unexpected behaviour.
+ * This is a price to pay for the absence of proper generics.
+ *
+ * # Example usage:
+ *
+ * @code{.c}
+ *      array_t(const char*) arr;
+ *      array_init(arr);
+ *
+ *      // Reserve memory in advance
+ *      if (array_reserve(arr, 2) < 0) {
+ *          return ENOMEM;
+ *      }
+ *
+ *      // Already reserved, cannot fail
+ *      array_push(arr, "princess");
+ *      array_push(arr, "leia");
+ *
+ *      // Not reserved, may fail
+ *      if (array_push(arr, "han") < 0) {
+ *          return ENOMEM;
+ *      }
+ *
+ *      // It does not hide what it really is
+ *      for (size_t i = 0; i < arr.len; ++i) {
+ *          printf("%s\n", arr.at[i]);
+ *      }
+ *
+ *      // Random delete
+ *      array_del(arr, 0);
+ * @endcode
+ * \addtogroup generics
+ * @{
+ */
+
+#pragma once
+#include <stdlib.h>
+
+/** Simplified Qt containers growth strategy. */
+static inline size_t array_next_count(size_t want)
+{
+	if (want < 2048) {
+		return (want < 20) ? want + 4 : want * 2;
+	} else {
+		return want + 2048;
+	}
+}
+
+/** @internal Incremental memory reservation */
+static inline int array_std_reserve(void *baton, char **mem, size_t elm_size, size_t want, size_t *have)
+{
+	if (*have >= want) {
+		return 0;
+	}
+	/* Simplified Qt containers growth strategy */
+	size_t next_size = array_next_count(want);
+	void *mem_new = realloc(*mem, next_size * elm_size);
+	if (mem_new != NULL) {
+		*mem = mem_new;
+		*have = next_size;
+		return 0;
+	}
+	return -1;
+}
+
+/** @internal Wrapper for stdlib free. */
+static inline void array_std_free(void *baton, void *p)
+{
+	free(p);
+}
+
+/** Declare an array structure. */
+#define array_t(type) struct {type * at; size_t len; size_t cap; }
+
+/** Zero-initialize the array. */
+#define array_init(array) ((array).at = NULL, (array).len = (array).cap = 0)
+
+/** Free and zero-initialize the array (plain malloc/free). */
+#define array_clear(array) \
+	array_clear_mm(array, array_std_free, NULL)
+
+/** Make the array empty and free pointed-to memory.
+ * Mempool usage: pass mm_free and a knot_mm_t* . */
+#define array_clear_mm(array, free, baton) \
+	(free)((baton), (array).at), array_init(array)
+
+/** Reserve capacity for at least n elements.
+ * @return 0 if success, <0 on failure */
+#define array_reserve(array, n) \
+	array_reserve_mm(array, n, array_std_reserve, NULL)
+
+/** Reserve capacity for at least n elements.
+ * Mempool usage: pass kr_memreserve and a knot_mm_t* .
+ * @return 0 if success, <0 on failure */
+#define array_reserve_mm(array, n, reserve, baton) \
+	(reserve)((baton), (char **) &(array).at, sizeof((array).at[0]), (n), &(array).cap)
+
+/**
+ * Push value at the end of the array, resize it if necessary.
+ * Mempool usage: pass kr_memreserve and a knot_mm_t* .
+ * @note May fail if the capacity is not reserved.
+ * @return element index on success, <0 on failure
+ */
+#define array_push_mm(array, val, reserve, baton) \
+	(int)((array).len < (array).cap ? ((array).at[(array).len] = val, (array).len++) \
+		: (array_reserve_mm(array, ((array).cap + 1), reserve, baton) < 0 ? -1 \
+			: ((array).at[(array).len] = val, (array).len++)))
+
+/**
+ * Push value at the end of the array, resize it if necessary (plain malloc/free).
+ * @note May fail if the capacity is not reserved.
+ * @return element index on success, <0 on failure
+ */
+#define array_push(array, val) \
+	array_push_mm(array, val, array_std_reserve, NULL)
+
+/**
+ * Pop value from the end of the array.
+ */
+#define array_pop(array) \
+ 	(array).len -= 1
+
+/**
+ * Remove value at given index.
+ * @return 0 on success, <0 on failure
+ */
+#define array_del(array, i) \
+	(int)((i) < (array).len ? ((array).len -= 1,(array).at[i] = (array).at[(array).len], 0) : -1)
+
+/**
+ * Return last element of the array.
+ * @warning Undefined if the array is empty.
+ */
+#define array_tail(array) \
+    (array).at[(array).len - 1]
+
+/** @} */
diff --git a/lib/generic/lru.c b/lib/generic/lru.c
new file mode 100644
index 0000000..12bba4e
--- /dev/null
+++ b/lib/generic/lru.c
@@ -0,0 +1,236 @@
+/*  Copyright (C) 2016-2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "lib/generic/lru.h"
+#include "contrib/murmurhash3/murmurhash3.h"
+
+typedef struct lru_group lru_group_t;
+
+struct lru_item {
+	uint16_t key_len, val_len; /**< Two bytes should be enough for our purposes. */
+	char data[];
+	/**< Place for both key and value.
+	 *
+	 * We use "char" to satisfy the C99+ aliasing rules.
+	 * See C99 section 6.5 Expressions, paragraph 7.
+	 * Any type can be accessed through char-pointer,
+	 * so we can use a common struct definition
+	 * for all types being held.
+	 */
+};
+
+/** @internal Compute offset of value in struct lru_item. */
+static uint val_offset(uint key_len)
+{
+	uint key_end = offsetof(struct lru_item, data) + key_len;
+	// align it to the closest multiple of four
+	return round_power(key_end, 2);
+}
+
+/** @internal Return pointer to value in an item. */
+static void * item_val(struct lru_item *it)
+{
+	return it->data + val_offset(it->key_len) - offsetof(struct lru_item, data);
+}
+
+/** @internal Compute the size of an item. ATM we don't align/pad the end of it. */
+static uint item_size(uint key_len, uint val_len)
+{
+	return val_offset(key_len) + val_len;
+}
+
+/** @internal Free each item. */
+KR_EXPORT void lru_free_items_impl(struct lru *lru)
+{
+	assert(lru);
+	for (size_t i = 0; i < (1 << (size_t)lru->log_groups); ++i) {
+		lru_group_t *g = &lru->groups[i];
+		for (int j = 0; j < LRU_ASSOC; ++j)
+			mm_free(lru->mm, g->items[j]);
+	}
+}
+
+/** @internal See lru_apply. */
+KR_EXPORT void lru_apply_impl(struct lru *lru, lru_apply_fun f, void *baton)
+{
+	bool ok = lru && f;
+	if (!ok) {
+		assert(false);
+		return;
+	}
+	for (size_t i = 0; i < (1 << (size_t)lru->log_groups); ++i) {
+		lru_group_t *g = &lru->groups[i];
+		for (uint j = 0; j < LRU_ASSOC; ++j) {
+			struct lru_item *it = g->items[j];
+			if (!it)
+				continue;
+			enum lru_apply_do ret =
+				f(it->data, it->key_len, item_val(it), baton);
+			switch(ret) {
+			case LRU_APPLY_DO_EVICT: // evict
+				mm_free(lru->mm, it);
+				g->items[j] = NULL;
+				g->counts[j] = 0;
+				g->hashes[j] = 0;
+				break;
+			default:
+				assert(ret == LRU_APPLY_DO_NOTHING);
+			}
+		}
+	}
+}
+
+/** @internal See lru_create. */
+KR_EXPORT struct lru * lru_create_impl(uint max_slots, knot_mm_t *mm_array, knot_mm_t *mm)
+{
+	assert(max_slots);
+	if (!max_slots)
+		return NULL;
+	// let lru->log_groups = ceil(log2(max_slots / (float) assoc))
+	//   without trying for efficiency
+	uint group_count = (max_slots - 1) / LRU_ASSOC + 1;
+	uint log_groups = 0;
+	for (uint s = group_count - 1; s; s /= 2)
+		++log_groups;
+	group_count = 1 << log_groups;
+	assert(max_slots <= group_count * LRU_ASSOC && group_count * LRU_ASSOC < 2 * max_slots);
+
+	size_t size = offsetof(struct lru, groups[group_count]);
+	struct lru *lru = mm_alloc(mm_array, size);
+	if (unlikely(lru == NULL))
+		return NULL;
+	*lru = (struct lru){
+		.mm = mm,
+		.mm_array = mm_array,
+		.log_groups = log_groups,
+	};
+	// zeros are a good init
+	memset(lru->groups, 0, size - offsetof(struct lru, groups));
+	return lru;
+}
+
+/** @internal Decrement all counters within a group. */
+static void group_dec_counts(lru_group_t *g) {
+	g->counts[LRU_TRACKED] = LRU_TRACKED;
+	for (uint i = 0; i < LRU_TRACKED + 1; ++i)
+		if (likely(g->counts[i]))
+			--g->counts[i];
+}
+
+/** @internal Increment a counter within a group. */
+static void group_inc_count(lru_group_t *g, int i) {
+	if (likely(++(g->counts[i])))
+       		return;
+	g->counts[i] = -1;
+	// We could've decreased or halved all of them, but let's keep the max.
+}
+
+/** @internal Implementation of both getting and insertion.
+ * Note: val_len is only meaningful if do_insert.
+ *       *is_new is only meaningful when return value isn't NULL, contains
+ *	 true when returned lru entry has been allocated right now
+ *	 if return value is NULL, *is_new remains untouched.
+ */
+KR_EXPORT void * lru_get_impl(struct lru *lru, const char *key, uint key_len,
+			      uint val_len, bool do_insert, bool *is_new)
+{
+	bool ok = lru && (key || !key_len) && key_len <= UINT16_MAX
+		   && (!do_insert || val_len <= UINT16_MAX);
+	if (!ok) {
+		assert(false);
+		return NULL; // reasonable fallback when not debugging
+	}
+	bool is_new_entry = false;
+	// find the right group
+	uint32_t khash = hash(key, key_len);
+	uint16_t khash_top = khash >> 16;
+	lru_group_t *g = &lru->groups[khash & ((1 << lru->log_groups) - 1)];
+	struct lru_item *it = NULL;
+	uint i;
+	// scan the *stored* elements in the group
+	for (i = 0; i < LRU_ASSOC; ++i) {
+		if (g->hashes[i] == khash_top) {
+			it = g->items[i];
+			if (likely(it && it->key_len == key_len
+					&& (key_len == 0 || memcmp(it->data, key, key_len) == 0))) {
+				/* Found a key, but trying to insert a value larger than available
+				 * space in the allocated slot, so the entry must be resized to fit. */
+				if (unlikely(do_insert && val_len > it->val_len)) {
+					goto insert;
+				} else {
+					goto found; // to reduce huge nesting depth	
+				}
+			}
+		}
+	}
+	// key not found; first try an empty/counted-out place to insert
+	if (do_insert)
+		for (i = 0; i < LRU_ASSOC; ++i)
+			if (g->items[i] == NULL || g->counts[i] == 0)
+				goto insert;
+	// check if we track key's count at least
+	for (i = LRU_ASSOC; i < LRU_TRACKED; ++i) {
+		if (g->hashes[i] == khash_top) {
+			group_inc_count(g, i);
+			if (!do_insert)
+				return NULL;
+			// check if we trumped some stored key
+			for (uint j = 0; j < LRU_ASSOC; ++j)
+				if (unlikely(g->counts[i] > g->counts[j])) {
+					// evict key j, i.e. swap with i
+					--g->counts[i]; // we increment it below
+					SWAP(g->counts[i], g->counts[j]);
+					SWAP(g->hashes[i], g->hashes[j]);
+					i = j;
+					goto insert;
+				}
+			return NULL;
+		}
+	}
+	// not found at all: decrement all counts but only on every LRU_TRACKED occasion
+	if (g->counts[LRU_TRACKED])
+		--g->counts[LRU_TRACKED];
+	else
+		group_dec_counts(g);
+	return NULL;
+insert: // insert into position i (incl. key)
+	assert(i < LRU_ASSOC);
+	g->hashes[i] = khash_top;
+	it = g->items[i];
+	uint new_size = item_size(key_len, val_len);
+	if (it == NULL || new_size != item_size(it->key_len, it->val_len)) {
+		// (re)allocate
+		mm_free(lru->mm, it);
+		it = g->items[i] = mm_alloc(lru->mm, new_size);
+		if (it == NULL)
+			return NULL;
+	}
+	it->key_len = key_len;
+	it->val_len = val_len;
+	if (key_len > 0) {
+		memcpy(it->data, key, key_len);
+	}
+	memset(item_val(it), 0, val_len); // clear the value
+	is_new_entry = true;
+found: // key and hash OK on g->items[i]; now update stamps
+	assert(i < LRU_ASSOC);
+	group_inc_count(g, i);
+	if (is_new) {
+		*is_new = is_new_entry;
+	}
+	return item_val(g->items[i]);
+}
+
diff --git a/lib/generic/lru.h b/lib/generic/lru.h
new file mode 100644
index 0000000..b5c9bcd
--- /dev/null
+++ b/lib/generic/lru.h
@@ -0,0 +1,249 @@
+/*  Copyright (C) 2016-2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+/**
+ * @file lru.h
+ * @brief A lossy cache.
+ *
+ * @note The implementation tries to keep frequent keys and avoid others,
+ *  even if "used recently", so it may refuse to store it on lru_get_new().
+ *  It uses hashing to split the problem pseudo-randomly into smaller groups,
+ *  and within each it tries to approximate relative usage counts of several
+ *  most frequent keys/hashes.  This tracking is done for *more* keys than
+ *  those that are actually stored.
+ *
+ * Example usage:
+ * @code{.c}
+ * 	// Define new LRU type
+ * 	typedef lru_t(int) lru_int_t;
+ *
+ * 	// Create LRU
+ * 	lru_int_t *lru;
+ * 	lru_create(&lru, 5, NULL, NULL);
+ *
+ * 	// Insert some values
+ * 	int *pi = lru_get_new(lru, "luke", strlen("luke"), NULL);
+ * 	if (pi)
+ * 		*pi = 42;
+ * 	pi = lru_get_new(lru, "leia", strlen("leia"), NULL);
+ * 	if (pi)
+ * 		*pi = 24;
+ *
+ * 	// Retrieve values
+ * 	int *ret = lru_get_try(lru, "luke", strlen("luke"), NULL);
+ * 	if (!ret) printf("luke dropped out!\n");
+ * 	    else  printf("luke's number is %d\n", *ret);
+ *
+ * 	char *enemies[] = {"goro", "raiden", "subzero", "scorpion"};
+ * 	for (int i = 0; i < 4; ++i) {
+ * 		int *val = lru_get_new(lru, enemies[i], strlen(enemies[i]), NULL);
+ * 		if (val)
+ * 			*val = i;
+ * 	}
+ *
+ * 	// We're done
+ * 	lru_free(lru);
+ * @endcode
+ *
+ * \addtogroup generics
+ * @{
+ */
+
+#pragma once
+
+#include <assert.h>
+#include <stdint.h>
+#include <stddef.h>
+
+#include "contrib/ucw/lib.h"
+#include "lib/utils.h"
+#include "libknot/mm_ctx.h"
+
+/* ================================ Interface ================================ */
+
+/** @brief The type for LRU, parametrized by value type. */
+#define lru_t(type) \
+	union { \
+		type *pdata_t; /* only the *type* information is used */ \
+		struct lru lru; \
+	}
+
+/**
+ * @brief Allocate and initialize an LRU with default associativity.
+ *
+ * The real limit on the number of slots can be a bit larger but less than double.
+ *
+ * @param ptable pointer to a pointer to the LRU
+ * @param max_slots number of slots
+ * @param mm_ctx_array memory context to use for the huge array, NULL for default
+ * @param mm_ctx memory context to use for individual key-value pairs, NULL for default
+ *
+ * @note The pointers to memory contexts need to remain valid
+ * 	during the whole life of the structure (or be NULL).
+ */
+#define lru_create(ptable, max_slots, mm_ctx_array, mm_ctx) do { \
+	(void)(((__typeof__((*(ptable))->pdata_t))0) == (void *)0); /* typecheck lru_t */ \
+	*(ptable) = (__typeof__(*(ptable))) \
+		lru_create_impl((max_slots), (mm_ctx_array), (mm_ctx)); \
+	} while (false)
+
+/** @brief Free an LRU created by lru_create (it can be NULL). */
+#define lru_free(table) \
+	lru_free_impl(&(table)->lru)
+
+/** @brief Reset an LRU to the empty state (but preserve any settings). */
+#define lru_reset(table) \
+	lru_reset_impl(&(table)->lru)
+
+/**
+ * @brief Find key in the LRU and return pointer to the corresponding value.
+ *
+ * @param table pointer to LRU
+ * @param key_ lookup key
+ * @param len_ key length
+ * @return pointer to data or NULL if not found
+ */
+#define lru_get_try(table, key_, len_) \
+	(__typeof__((table)->pdata_t)) \
+		lru_get_impl(&(table)->lru, (key_), (len_), -1, false, NULL)
+
+/**
+ * @brief Return pointer to value, inserting if needed (zeroed).
+ *
+ * @param table pointer to LRU
+ * @param key_ lookup key
+ * @param len_ key lengthkeys
+ * @param is_new pointer to bool to store result of operation
+ *             (true if entry is newly added, false otherwise; can be NULL).
+ * @return pointer to data or NULL (can be even if memory could be allocated!)
+ */
+#define lru_get_new(table, key_, len_, is_new) \
+	(__typeof__((table)->pdata_t)) \
+		lru_get_impl(&(table)->lru, (key_), (len_), \
+		sizeof(*(table)->pdata_t), true, is_new)
+
+/**
+ * @brief Apply a function to every item in LRU.
+ *
+ * @param table pointer to LRU
+ * @param function enum lru_apply_do (*function)(const char *key, uint len, val_type *val, void *baton)
+ *        See enum lru_apply_do for the return type meanings.
+ * @param baton extra pointer passed to each function invocation
+ */
+#define lru_apply(table, function, baton) do { \
+	lru_apply_fun_g(fun_dummy, __typeof__(*(table)->pdata_t)) = 0; \
+	(void)(fun_dummy == (function)); /* produce a warning with incompatible function type */ \
+	lru_apply_impl(&(table)->lru, (lru_apply_fun)(function), (baton)); \
+	} while (false)
+
+/** @brief Possible actions to do with an element. */
+enum lru_apply_do {
+	LRU_APPLY_DO_NOTHING,
+	LRU_APPLY_DO_EVICT,
+	/* maybe more in future*/
+};
+
+/**
+ * @brief Return the real capacity - maximum number of keys holdable within.
+ *
+ * @param table pointer to LRU
+ */
+#define lru_capacity(table) lru_capacity_impl(&(table)->lru)
+
+
+/** @brief Round the value up to a multiple of (1 << power). */
+static inline uint round_power(uint size, uint power)
+{
+	uint res = ((size - 1) & ~((1 << power) - 1)) + (1 << power);
+	assert(__builtin_ctz(res) >= power);
+	assert(size <= res && res < size + (1 << power));
+	return res;
+}
+
+
+/* ======================== Inlined part of implementation ======================== */
+/** @cond internal */
+
+#define lru_apply_fun_g(name, val_type) \
+	enum lru_apply_do (*(name))(const char *key, uint len, val_type *val, void *baton)
+typedef lru_apply_fun_g(lru_apply_fun, void);
+
+#if __GNUC__ >= 4
+	#define CACHE_ALIGNED __attribute__((aligned(64)))
+#else
+	#define CACHE_ALIGNED
+#endif
+
+struct lru;
+void lru_free_items_impl(struct lru *lru);
+struct lru * lru_create_impl(uint max_slots, knot_mm_t *mm_array, knot_mm_t *mm);
+void * lru_get_impl(struct lru *lru, const char *key, uint key_len,
+		    uint val_len, bool do_insert, bool *is_new);
+void lru_apply_impl(struct lru *lru, lru_apply_fun f, void *baton);
+
+struct lru_item;
+
+#if SIZE_MAX > (1 << 32)
+	/** @internal The number of keys stored within each group. */
+	#define LRU_ASSOC 3
+#else
+	#define LRU_ASSOC 4
+#endif
+/** @internal The number of hashes tracked within each group: 10-1 or 12-1. */
+#define LRU_TRACKED ((64 - sizeof(size_t) * LRU_ASSOC) / 4 - 1)
+
+struct lru_group {
+	uint16_t counts[LRU_TRACKED+1]; /*!< Occurrence counters; the last one is special. */
+	uint16_t hashes[LRU_TRACKED+1]; /*!< Top halves of hashes; the last one is unused. */
+	struct lru_item *items[LRU_ASSOC]; /*!< The full items. */
+} CACHE_ALIGNED;
+
+/* The sizes are chosen so lru_group just fits into a single x86 cache line. */
+static_assert(64 == sizeof(struct lru_group)
+		&& 64 == LRU_ASSOC * sizeof(void*) + (LRU_TRACKED+1) * 4,
+		"bad sizing for your sizeof(void*)");
+
+struct lru {
+	struct knot_mm *mm, /**< Memory context to use for keys. */
+		*mm_array; /**< Memory context to use for this structure itself. */
+	uint log_groups; /**< Logarithm of the number of LRU groups. */
+	struct lru_group groups[] CACHE_ALIGNED; /**< The groups of items. */
+};
+
+/** @internal See lru_free. */
+static inline void lru_free_impl(struct lru *lru)
+{
+	if (!lru)
+		return;
+	lru_free_items_impl(lru);
+	mm_free(lru->mm_array, lru);
+}
+
+/** @internal See lru_reset. */
+static inline void lru_reset_impl(struct lru *lru)
+{
+	lru_free_items_impl(lru);
+	memset(lru->groups, 0, sizeof(lru->groups[0]) * (1 << lru->log_groups));
+}
+
+/** @internal See lru_capacity. */
+static inline uint lru_capacity_impl(struct lru *lru)
+{
+	assert(lru);
+	return (1 << lru->log_groups) * LRU_ASSOC;
+}
+
+/** @endcond */
+/** @} (addtogroup generics) */
diff --git a/lib/generic/map.c b/lib/generic/map.c
new file mode 100644
index 0000000..3e06520
--- /dev/null
+++ b/lib/generic/map.c
@@ -0,0 +1,354 @@
+/*
+ * critbit89 - A crit-bit tree implementation for strings in C89
+ * Written by Jonas Gehring <jonas@jgehring.net>
+ * Implemented key-value storing by Marek Vavrusa <marek.vavrusa@nic.cz>
+ *
+ * The code makes the assumption that malloc returns pointers aligned at at
+ * least a two-byte boundary. Since the C standard requires that malloc return
+ * pointers that can store any type, there are no commonly-used toolchains for
+ * which this assumption is false.
+ *
+ * See https://github.com/agl/critbit/blob/master/critbit.pdf for reference.
+ */
+
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "map.h"
+#include "lib/utils.h"
+
+ /* Exports */
+#if defined _WIN32 || defined __CYGWIN__
+  #define EXPORT __attribute__ ((dllexport))
+#else
+  #define EXPORT __attribute__ ((visibility ("default")))
+#endif
+
+#ifdef _MSC_VER /* MSVC */
+ typedef unsigned __int8 uint8_t;
+ typedef unsigned __int32 uint32_t;
+ #ifdef _WIN64
+  typedef signed __int64 intptr_t;
+ #else
+  typedef _W64 signed int intptr_t;
+ #endif
+#else /* Not MSVC */
+ #include <stdint.h>
+#endif
+
+typedef struct {
+	void* value;
+	uint8_t key[];
+} cb_data_t;
+
+typedef struct {
+	void *child[2];
+	uint32_t byte;
+	uint8_t otherbits;
+} cb_node_t;
+
+/* Return true if ptr is internal node. */
+static inline int ref_is_internal(const uint8_t *p)
+{
+	return 1 & (intptr_t)p;
+}
+
+/* Get internal node. */
+static inline cb_node_t *ref_get_internal(uint8_t *p)
+{
+	return (cb_node_t *)(p - 1);
+}
+
+/* Static helper functions */
+static void cbt_traverse_delete(map_t *map, void *top)
+{
+	uint8_t *p = top;
+	if (ref_is_internal(p)) {
+		cb_node_t *q = ref_get_internal(p);
+		cbt_traverse_delete(map, q->child[0]);
+		cbt_traverse_delete(map, q->child[1]);
+		mm_free(map->pool, q);
+	} else {
+		mm_free(map->pool, p);
+	}
+}
+
+static int cbt_traverse_prefixed(void *top,
+	int (*callback)(const char *, void *, void *), void *baton)
+{
+	uint8_t *p = top;
+	cb_data_t *x = (cb_data_t *)top;
+
+	if (ref_is_internal(p)) {
+		cb_node_t *q = ref_get_internal(p);
+		int ret = 0;
+
+		ret = cbt_traverse_prefixed(q->child[0], callback, baton);
+		if (ret != 0) {
+			return ret;
+		}
+		ret = cbt_traverse_prefixed(q->child[1], callback, baton);
+		if (ret != 0) {
+			return ret;
+		}
+		return 0;
+	}
+
+	return (callback)((const char *)x->key, x->value, baton);
+}
+
+static cb_data_t *cbt_make_data(map_t *map, const uint8_t *str, size_t len, void *value)
+{
+	cb_data_t *x = mm_alloc(map->pool, sizeof(cb_data_t) + len);
+	if (x != NULL) {
+		x->value = value;
+		memcpy(x->key, str, len);
+	}
+	return x;
+}
+
+/*! Like map_contains, but also set the value, if passed and found. */
+static int cbt_get(map_t *map, const char *str, void **value)
+{
+	const uint8_t *ubytes = (void *)str;
+	const size_t ulen = strlen(str);
+	uint8_t *p = map->root;
+	cb_data_t *x = NULL;
+
+	if (p == NULL) {
+		return 0;
+	}
+
+	while (ref_is_internal(p)) {
+		cb_node_t *q = ref_get_internal(p);
+		uint8_t c = 0;
+		int direction;
+
+		if (q->byte < ulen) {
+			c = ubytes[q->byte];
+		}
+		direction = (1 + (q->otherbits | c)) >> 8;
+
+		p = q->child[direction];
+	}
+
+	x = (cb_data_t *)p;
+	if (strcmp(str, (const char *)x->key) == 0) {
+		if (value != NULL) {
+			*value = x->value;
+		}
+		return 1;
+	}
+
+	return 0;
+}
+
+/*! Returns non-zero if map contains str */
+EXPORT int map_contains(map_t *map, const char *str)
+{
+	return cbt_get(map, str, NULL);
+}
+
+EXPORT void *map_get(map_t *map, const char *str)
+{
+	void *v = NULL;
+	cbt_get(map, str, &v);
+	return v;
+}
+
+EXPORT int map_set(map_t *map, const char *str, void *val)
+{
+	const uint8_t *const ubytes = (void *)str;
+	const size_t ulen = strlen(str);
+	uint8_t *p = map->root;
+	uint8_t c = 0, *x = NULL;
+	uint32_t newbyte = 0;
+	uint32_t newotherbits = 0;
+	int direction = 0, newdirection = 0;
+	cb_node_t *newnode = NULL;
+	cb_data_t *data = NULL;
+	void **wherep = NULL;
+
+	if (p == NULL) {
+		map->root = cbt_make_data(map, (const uint8_t *)str, ulen + 1, val);
+		if (map->root == NULL) {
+			return ENOMEM;
+		}
+		return 0;
+	}
+
+	while (ref_is_internal(p)) {
+		cb_node_t *q = ref_get_internal(p);
+		c = 0;
+		if (q->byte < ulen) {
+			c = ubytes[q->byte];
+		}
+		direction = (1 + (q->otherbits | c)) >> 8;
+
+		p = q->child[direction];
+	}
+
+	data = (cb_data_t *)p;
+	for (newbyte = 0; newbyte < ulen; ++newbyte) {
+		if (data->key[newbyte] != ubytes[newbyte]) {
+			newotherbits = data->key[newbyte] ^ ubytes[newbyte];
+			goto different_byte_found;
+		}
+	}
+
+	if (data->key[newbyte] != 0) {
+		newotherbits = data->key[newbyte];
+		goto different_byte_found;
+	}
+	data->value = val;
+	return 1;
+
+different_byte_found:
+	newotherbits |= newotherbits >> 1;
+	newotherbits |= newotherbits >> 2;
+	newotherbits |= newotherbits >> 4;
+	newotherbits = (newotherbits & ~(newotherbits >> 1)) ^ 255;
+	c = data->key[newbyte];
+	newdirection = (1 + (newotherbits | c)) >> 8;
+
+	newnode = mm_alloc(map->pool, sizeof(cb_node_t));
+	if (newnode == NULL) {
+		return ENOMEM;
+	}
+
+	x = (uint8_t *)cbt_make_data(map, ubytes, ulen + 1, val);
+	if (x == NULL) {
+		mm_free(map->pool, newnode);
+		return ENOMEM;
+	}
+
+	newnode->byte = newbyte;
+	newnode->otherbits = newotherbits;
+	newnode->child[1 - newdirection] = x;
+
+	/* Insert into map */
+	wherep = &map->root;
+	for (;;) {
+		cb_node_t *q;
+		p = *wherep;
+		if (!ref_is_internal(p)) {
+			break;
+		}
+
+		q = ref_get_internal(p);
+		if (q->byte > newbyte) {
+			break;
+		}
+		if (q->byte == newbyte && q->otherbits > newotherbits) {
+			break;
+		}
+
+		c = 0;
+		if (q->byte < ulen) {
+			c = ubytes[q->byte];
+		}
+		direction = (1 + (q->otherbits | c)) >> 8;
+		wherep = q->child + direction;
+	}
+
+	newnode->child[newdirection] = *wherep;
+	*wherep = (void *)(1 + (char *)newnode);
+	return 0;
+}
+
+/*! Deletes str from the map, returns 0 on success */
+EXPORT int map_del(map_t *map, const char *str)
+{
+	const uint8_t *ubytes = (void *)str;
+	const size_t ulen = strlen(str);
+	uint8_t *p = map->root;
+	void **wherep = NULL, **whereq = NULL;
+	cb_node_t *q = NULL;
+	cb_data_t *data = NULL;
+	int direction = 0;
+
+	if (map->root == NULL) {
+		return 1;
+	}
+	wherep = &map->root;
+
+	while (ref_is_internal(p)) {
+		uint8_t c = 0;
+		whereq = wherep;
+		q = ref_get_internal(p);
+
+		if (q->byte < ulen) {
+			c = ubytes[q->byte];
+		}
+		direction = (1 + (q->otherbits | c)) >> 8;
+		wherep = q->child + direction;
+		p = *wherep;
+	}
+
+	data = (cb_data_t *)p;
+	if (strcmp(str, (const char *)data->key) != 0) {
+		return 1;
+	}
+	mm_free(map->pool, p);
+
+	if (!whereq) {
+		map->root = NULL;
+		return 0;
+	}
+
+	*whereq = q->child[1 - direction];
+	mm_free(map->pool, q);
+	return 0;
+}
+
+/*! Clears the given map */
+EXPORT void map_clear(map_t *map)
+{
+	if (map->root) {
+		cbt_traverse_delete(map, map->root);
+	}
+	map->root = NULL;
+}
+
+/*! Calls callback for all strings in map with the given prefix */
+EXPORT int map_walk_prefixed(map_t *map, const char *prefix,
+	int (*callback)(const char *, void *, void *), void *baton)
+{
+	if (!map) {
+		return 0;
+	}
+
+	const uint8_t *ubytes = (void *)prefix;
+	const size_t ulen = strlen(prefix);
+	uint8_t *p = map->root;
+	uint8_t *top = p;
+	cb_data_t *data = NULL;
+
+	if (p == NULL) {
+		return 0;
+	}
+
+	while (ref_is_internal(p)) {
+		cb_node_t *q = ref_get_internal(p);
+		uint8_t c = 0;
+		int direction;
+
+		if (q->byte < ulen) {
+			c = ubytes[q->byte];
+		}
+		direction = (1 + (q->otherbits | c)) >> 8;
+
+		p = q->child[direction];
+		if (q->byte < ulen) {
+			top = p;
+		}
+	}
+
+	data = (cb_data_t *)p;
+	if (strlen((const char *)data->key) < ulen || memcmp(data->key, prefix, ulen) != 0) {
+		return 0; /* No strings match */
+	}
+
+	return cbt_traverse_prefixed(top, callback, baton);
+}
diff --git a/lib/generic/map.h b/lib/generic/map.h
new file mode 100644
index 0000000..73ce4c0
--- /dev/null
+++ b/lib/generic/map.h
@@ -0,0 +1,115 @@
+/*
+ * critbit89 - A crit-bit map implementation for strings in C89
+ * Written by Jonas Gehring <jonas@jgehring.net>
+ */
+
+/**
+ * @file map.h
+ * @brief A Crit-bit tree key-value map implementation.
+ *
+ * @warning If the user provides a custom allocator, it must return addresses aligned to 2B boundary.
+ *
+ * # Example usage:
+ *
+ * @code{.c}
+ *      map_t map = map_make(NULL);
+ *
+ *      // Custom allocator (optional)
+ *      map.malloc = &mymalloc;
+ *      map.baton  = &mymalloc_context;
+ *
+ *      // Insert k-v pairs
+ *      int values = { 42, 53, 64 };
+ *      if (map_set(&map, "princess", &values[0]) != 0 ||
+ *          map_set(&map, "prince", &values[1])   != 0 ||
+ *          map_set(&map, "leia", &values[2])     != 0) {
+ *          fail();
+ *      }
+ *
+ *      // Test membership
+ *      if (map_contains(&map, "leia")) {
+ *          success();
+ *      }
+ *
+ *      // Prefix search
+ *      int i = 0;
+ *      int count(const char *k, void *v, void *ext) { (*(int *)ext)++; return 0; }
+ *      if (map_walk_prefixed(map, "princ", count, &i) == 0) {
+ *          printf("%d matches\n", i);
+ *      }
+ *
+ *      // Delete
+ *      if (map_del(&map, "badkey") != 0) {
+ *          fail(); // No such key
+ *      }
+ *
+ *      // Clear the map
+ *      map_clear(&map);
+ * @endcode
+ *
+ * \addtogroup generics
+ * @{
+ */
+
+#pragma once
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct knot_mm; /* avoid the unnecessary include */
+
+/** Main data structure */
+typedef struct {
+	void *root;
+	struct knot_mm *pool;
+} map_t;
+
+/** Creates an new empty critbit map.  Pass NULL for malloc+free. */
+static inline map_t map_make(struct knot_mm *pool)
+{
+	return (map_t){ .root = NULL, .pool = pool };
+}
+
+/** Returns non-zero if map contains str */
+int map_contains(map_t *map, const char *str);
+
+/** Returns value if map contains str.  Note: NULL may mean two different things. */
+void *map_get(map_t *map, const char *str);
+
+/** Inserts str into map.  Returns 0 if new, 1 if replaced, or ENOMEM. */
+int map_set(map_t *map, const char *str, void *val);
+
+/** Deletes str from the map, returns 0 on suceess */
+int map_del(map_t *map, const char *str);
+
+/** Clears the given map */
+void map_clear(map_t *map);
+
+/**
+ * Calls callback for all strings in map
+ * See @fn map_walk_prefixed() for documentation on parameters.
+ */
+#define map_walk(map, callback, baton) \
+	map_walk_prefixed((map), "", (callback), (baton))
+
+/**
+ * Calls callback for all strings in map with the given prefix.
+ * Returns value immediately if a callback returns nonzero.
+ *
+ * @param map
+ * @param prefix   required string prefix (empty => all strings)
+ * @param callback callback parameters are (key, value, baton)
+ * @param baton    passed uservalue
+ */
+int map_walk_prefixed(map_t *map, const char *prefix,
+	int (*callback)(const char *, void *, void *), void *baton);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+/** @} */
diff --git a/lib/generic/pack.h b/lib/generic/pack.h
new file mode 100644
index 0000000..dc7a975
--- /dev/null
+++ b/lib/generic/pack.h
@@ -0,0 +1,249 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @file pack.h
+ * @brief A length-prefixed list of objects, also an array list.
+ * 
+ * Each object is prefixed by item length, unlike array this structure 
+ * permits variable-length data. It is also equivallent to forward-only list
+ * backed by an array.
+ *
+ * @note Maximum object size is 2^16 bytes, see  ::pack_objlen_t
+ * @TODO If some mistake happens somewhere, the access may end up in an infinite loop.
+ *       (equality comparison on pointers)
+ *
+ * # Example usage:
+ *
+ * @code{.c}
+ *      pack_t pack;
+ *      pack_init(pack);
+ *
+ *      // Reserve 2 objects, 6 bytes total
+ *      pack_reserve(pack, 2, 4 + 2);
+ * 
+ *      // Push 2 objects
+ *      pack_obj_push(pack, U8("jedi"), 4)
+ *      pack_obj_push(pack, U8("\xbe\xef"), 2);
+ *
+ *      // Iterate length-value pairs
+ *      uint8_t *it = pack_head(pack);
+ *      while (it != pack_tail(pack)) {
+ *          uint8_t *val = pack_obj_val(it);
+ *          it = pack_obj_next(it);
+ *      }
+ *
+ *      // Remove object
+ *      pack_obj_del(pack, U8("jedi"), 4);
+ *
+ *      pack_clear(pack);
+ * @endcode
+ *
+ * \addtogroup generics
+ * @{
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <string.h>
+#include "array.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** Packed object length type. */
+typedef uint16_t pack_objlen_t;
+
+/** Pack is defined as an array of bytes */
+typedef array_t(uint8_t) pack_t;
+
+/** Zero-initialize the pack. */
+#define pack_init(pack) \
+	array_init(pack)
+
+/** Make the pack empty and free pointed-to memory (plain malloc/free). */
+#define pack_clear(pack) \
+	array_clear(pack)
+
+/** Make the pack empty and free pointed-to memory.
+ * Mempool usage: pass mm_free and a knot_mm_t* . */
+#define pack_clear_mm(pack, free, baton) \
+	array_clear_mm((pack), (free), (baton))
+
+/** Reserve space for *additional* objects in the pack (plain malloc/free).
+ * @return 0 if success, <0 on failure */
+#define pack_reserve(pack, objs_count, objs_len) \
+	pack_reserve_mm((pack), (objs_count), (objs_len), array_std_reserve, NULL)
+
+/** Reserve space for *additional* objects in the pack.
+ * Mempool usage: pass kr_memreserve and a knot_mm_t* .
+ * @return 0 if success, <0 on failure */
+#define pack_reserve_mm(pack, objs_count, objs_len, reserve, baton) \
+	array_reserve_mm((pack), (pack).len + (sizeof(pack_objlen_t)*(objs_count) + (objs_len)), (reserve), (baton))
+
+/** Return pointer to first packed object.
+ *
+ * Recommended way to iterate:
+ *   for (uint8_t *it = pack_head(pack); it != pack_tail(pack); it = pack_obj_next(it))
+ */
+#define pack_head(pack) \
+	((pack).len > 0 ? &((pack).at[0]) : NULL)
+
+/** Return pack end pointer. */
+#define pack_tail(pack) \
+	((pack).len > 0 ? &((pack).at[(pack).len]) : NULL)
+
+/** Return packed object length. */
+static inline pack_objlen_t pack_obj_len(uint8_t *it)
+{
+	pack_objlen_t len = 0;
+	if (it != NULL)
+		memcpy(&len, it, sizeof(len));
+	return len;
+}
+
+/** Return packed object value. */
+static inline uint8_t *pack_obj_val(uint8_t *it)
+{
+	if (it == NULL) {
+		assert(it);
+		return NULL;
+	}
+	return it + sizeof(pack_objlen_t);
+}
+
+/** Return pointer to next packed object. */
+static inline uint8_t *pack_obj_next(uint8_t *it)
+{
+	if (it == NULL) {
+		assert(it);
+		return NULL;
+	}
+	return pack_obj_val(it) + pack_obj_len(it);
+}
+
+/** Return pointer to the last packed object. */
+static inline uint8_t *pack_last(pack_t pack)
+{
+	if (pack.len == 0) {
+		return NULL;
+	}
+	uint8_t *it = pack_head(pack);
+	uint8_t *tail = pack_tail(pack);
+	while (true) {
+		uint8_t *next = pack_obj_next(it);
+		if (next == tail) {
+			return it;
+		}
+		it = next;
+	}
+}
+
+/** Push object to the end of the pack
+  * @return 0 on success, negative number on failure
+  */
+static inline int pack_obj_push(pack_t *pack, const uint8_t *obj, pack_objlen_t len)
+{
+	if (pack == NULL || obj == NULL) {
+		assert(false);
+		return kr_error(EINVAL);
+	}
+	size_t packed_len = len + sizeof(len);
+	if (pack->len + packed_len > pack->cap) {
+		return kr_error(ENOSPC);
+	}
+
+	uint8_t *endp = pack->at + pack->len;
+	memcpy(endp, (char *)&len, sizeof(len));
+	memcpy(endp + sizeof(len), obj, len);
+	pack->len += packed_len;
+	return 0;
+}
+
+/** Returns a pointer to packed object.
+  * @return pointer to packed object or NULL
+  */
+static inline uint8_t *pack_obj_find(pack_t *pack, const uint8_t *obj, pack_objlen_t len)
+{
+		if (pack == NULL || obj == NULL) {
+			assert(obj != NULL);
+			return NULL;
+		}
+		uint8_t *endp = pack_tail(*pack);
+		uint8_t *it = pack_head(*pack);
+		while (it != endp) {
+			uint8_t *val = pack_obj_val(it);
+			if (pack_obj_len(it) == len && memcmp(obj, val, len) == 0) {
+				return it;
+			}
+			it = pack_obj_next(it);
+		}
+		return NULL;
+}
+
+/** Delete object from the pack
+  * @return 0 on success, negative number on failure
+  */
+static inline int pack_obj_del(pack_t *pack, const uint8_t *obj, pack_objlen_t len)
+{
+	if (pack == NULL || obj == NULL) {
+		assert(obj != NULL);
+		return kr_error(EINVAL);
+	}
+	uint8_t *endp = pack_tail(*pack);
+	uint8_t *it = pack_obj_find(pack, obj, len);
+	if (it) {
+		size_t packed_len = len + sizeof(len);
+		memmove(it, it + packed_len, endp - it - packed_len);
+		pack->len -= packed_len;
+		return 0;
+	}
+	return -1;
+}
+
+/** Clone a pack, replacing destination pack; (*dst == NULL) is valid input.
+ * @return kr_error(ENOMEM) on allocation failure. */
+static inline int pack_clone(pack_t **dst, const pack_t *src, knot_mm_t *pool)
+{
+	if (!dst || !src) {
+		assert(false);
+		return kr_error(EINVAL);
+	}
+	/* Get a valid pack_t. */
+	if (!*dst) {
+		*dst = mm_alloc(pool, sizeof(pack_t));
+		if (!*dst) return kr_error(ENOMEM);
+		pack_init(**dst);
+		/* Clone data only if needed */
+		if (src->len == 0) return kr_ok();
+	}
+	/* Replace the contents of the pack_t. */
+	int ret = array_reserve_mm(**dst, src->len, kr_memreserve, pool);
+	if (ret < 0) {
+		return kr_error(ENOMEM);
+	}
+	memcpy((*dst)->at, src->at, src->len);
+	(*dst)->len = src->len;
+	return kr_ok();
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+/** @} */
diff --git a/lib/generic/queue.c b/lib/generic/queue.c
new file mode 100644
index 0000000..45657c7
--- /dev/null
+++ b/lib/generic/queue.c
@@ -0,0 +1,124 @@
+/*  Copyright (C) 2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "lib/generic/queue.h"
+#include <string.h>
+
+KR_EXPORT void queue_init_impl(struct queue *q, size_t item_size)
+{
+	q->len = 0;
+	q->item_size = item_size;
+	q->head = q->tail = NULL;
+	/* Take 128 B (two x86 cache lines), except a small margin
+	 * that the allocator can use for its overhead.
+	 * Normally (64-bit pointers) this means 16 B header + 13*8 B data. */
+	q->chunk_cap = (128 - offsetof(struct queue_chunk, data)
+			- sizeof(size_t)
+			) / item_size;
+	if (!q->chunk_cap) q->chunk_cap = 1; /* item_size big enough by itself */
+}
+
+KR_EXPORT void queue_deinit_impl(struct queue *q)
+{
+	assert(q);
+	struct queue_chunk *p = q->head;
+	while (p != NULL) {
+		struct queue_chunk *pf = p;
+		p = p->next;
+		free(pf);
+	}
+#ifndef NDEBUG
+	memset(q, 0, sizeof(*q));
+#endif
+}
+
+static struct queue_chunk * queue_chunk_new(const struct queue *q)
+{
+	struct queue_chunk *c = malloc(offsetof(struct queue_chunk, data)
+					+ q->chunk_cap * q->item_size);
+	if (unlikely(!c)) abort(); // simplify stuff
+	memset(c, 0, offsetof(struct queue_chunk, data));
+	c->cap = q->chunk_cap;
+	/* ->begin and ->end are zero, i.e. we optimize for _push
+	 * and not _push_head, by default. */
+	return c;
+}
+
+/* Return pointer to the space for the new element. */
+KR_EXPORT void * queue_push_impl(struct queue *q)
+{
+	assert(q);
+	struct queue_chunk *t = q->tail; // shorthand
+	if (unlikely(!t)) {
+		assert(!q->head && !q->len);
+		q->head = q->tail = t = queue_chunk_new(q);
+	} else
+	if (t->end == t->cap) {
+		if (t->begin * 2 >= t->cap) {
+			/* Utilization is below 50%, so let's shift (no overlap). */
+			memcpy(t->data, t->data + t->begin * q->item_size,
+				(t->end - t->begin) * q->item_size);
+			t->end -= t->begin;
+			t->begin = 0;
+		} else {
+			/* Let's grow the tail by another chunk. */
+			assert(!t->next);
+			t->next = queue_chunk_new(q);
+			t = q->tail = t->next;
+		}
+	}
+	assert(t->end < t->cap);
+	++(q->len);
+	++(t->end);
+	return t->data + q->item_size * (t->end - 1);
+}
+
+/* Return pointer to the space for the new element. */
+KR_EXPORT void * queue_push_head_impl(struct queue *q)
+{
+	/* When we have choice, we optimize for further _push_head,
+	 * i.e. when shifting or allocating a chunk,
+	 * we store items on the tail-end of the chunk. */
+	assert(q);
+	struct queue_chunk *h = q->head; // shorthand
+	if (unlikely(!h)) {
+		assert(!q->tail && !q->len);
+		h = q->head = q->tail = queue_chunk_new(q);
+		h->begin = h->end = h->cap;
+	} else
+	if (h->begin == 0) {
+		if (h->end * 2 <= h->cap) {
+			/* Utilization is below 50%, so let's shift (no overlap).
+			 * Computations here are simplified due to h->begin == 0. */
+			const int cnt = h->end;
+			memcpy(h->data + (h->cap - cnt) * q->item_size, h->data,
+				cnt * q->item_size);
+			h->begin = h->cap - cnt;
+			h->end = h->cap;
+		} else {
+			/* Let's grow the head by another chunk. */
+			h = queue_chunk_new(q);
+			h->next = q->head;
+			q->head = h;
+			h->begin = h->end = h->cap;
+		}
+	}
+	assert(h->begin > 0);
+	--(h->begin);
+	++(q->len);
+	return h->data + q->item_size * h->begin;
+}
+
diff --git a/lib/generic/queue.h b/lib/generic/queue.h
new file mode 100644
index 0000000..755e759
--- /dev/null
+++ b/lib/generic/queue.h
@@ -0,0 +1,260 @@
+/*  Copyright (C) 2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/**
+ * @file queue.h
+ * @brief A queue, usable for FIFO and LIFO simultaneously.
+ *
+ * Both the head and tail of the queue can be accessed and pushed to,
+ * but only the head can be popped from.
+ *
+ * @note The implementation uses a singly linked list of blocks
+ * where each block stores an array of values (for better efficiency).
+ *
+ * Example usage:
+ * @code{.c}
+	// define new queue type, and init a new queue instance
+	typedef queue_t(int) queue_int_t;
+	queue_int_t q;
+	queue_init(q);
+	// do some operations
+	queue_push(q, 1);
+	queue_push(q, 2);
+	queue_push(q, 3);
+	queue_push(q, 4);
+	queue_pop(q);
+	assert(queue_head(q) == 2);
+	assert(queue_tail(q) == 4);
+
+	// you may iterate
+	typedef queue_it_t(int) queue_it_int_t;
+	for (queue_it_int_t it = queue_it_begin(q); !queue_it_finished(it);
+	     queue_it_next(it)) {
+		++queue_it_val(it);
+	}
+	assert(queue_tail(q) == 5);
+
+	queue_push_head(q, 0);
+	++queue_tail(q);
+	assert(queue_tail(q) == 6);
+	// free it up
+	queue_deinit(q);
+
+	// you may use dynamic allocation for the type itself
+	queue_int_t *qm = malloc(sizeof(queue_int_t));
+	queue_init(*qm);
+	queue_deinit(*qm);
+	free(qm);
+ * @endcode
+ *
+ * \addtogroup generics
+ * @{
+ */
+
+#pragma once
+
+#include "lib/defines.h"
+#include "contrib/ucw/lib.h"
+#include <assert.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+/** @brief The type for queue, parametrized by value type. */
+#define queue_t(type) \
+	union { \
+		type *pdata_t; /* only the *type* information is used */ \
+		struct queue queue; \
+	}
+
+/** @brief Initialize a queue.  You can malloc() it the usual way. */
+#define queue_init(q) do { \
+	(void)(((__typeof__(((q).pdata_t)))0) == (void *)0); /* typecheck queue_t */ \
+	queue_init_impl(&(q).queue, sizeof(*(q).pdata_t)); \
+	} while (false)
+
+/** @brief De-initialize a queue: make it invalid and free any inner allocations. */
+#define queue_deinit(q) \
+	queue_deinit_impl(&(q).queue)
+
+/** @brief Push data to queue's tail.  (Type-safe version; use _impl() otherwise.) */
+#define queue_push(q, data) \
+	*((__typeof__((q).pdata_t)) queue_push_impl(&(q).queue)) = data
+
+/** @brief Push data to queue's head.  (Type-safe version; use _impl() otherwise.) */
+#define queue_push_head(q, data) \
+	*((__typeof__((q).pdata_t)) queue_push_head_impl(&(q).queue)) = data
+
+/** @brief Remove the element at the head.
+ * The queue must not be empty. */
+#define queue_pop(q) \
+	queue_pop_impl(&(q).queue)
+
+/** @brief Return a "reference" to the element at the head (it's an L-value).
+ * The queue must not be empty. */
+#define queue_head(q) \
+	( *(__typeof__((q).pdata_t)) queue_head_impl(&(q).queue) )
+
+/** @brief Return a "reference" to the element at the tail (it's an L-value).
+ * The queue must not be empty. */
+#define queue_tail(q) \
+	( *(__typeof__((q).pdata_t)) queue_tail_impl(&(q).queue) )
+
+/** @brief Return the number of elements in the queue (very efficient). */
+#define queue_len(q) \
+	((const size_t)(q).queue.len)
+
+
+/** @brief Type for queue iterator, parametrized by value type.
+ * It's a simple structure that owns no other resources.
+ * You may NOT use it after doing any push or pop (without _begin again). */
+#define queue_it_t(type) \
+	union { \
+		type *pdata_t; /* only the *type* information is used */ \
+		struct queue_it iter; \
+	}
+
+/** @brief Initialize a queue iterator at the head of the queue.
+ * If you use this in assignment (instead of initialization),
+ * you will unfortunately need to add corresponding type-cast in front.
+ * Beware: there's no type-check between queue and iterator! */
+#define queue_it_begin(q) \
+	{ .iter = queue_it_begin_impl(&(q).queue) }
+
+/** @brief Return a "reference" to the current element (it's an L-value) . */
+#define queue_it_val(it) \
+	( *(__typeof__((it).pdata_t)) queue_it_val_impl(&(it).iter) )
+
+/** @brief Test if the iterator has gone past the last element.
+ * If it has, you may not use _val or _next. */
+#define queue_it_finished(it) \
+	queue_it_finished_impl(&(it).iter)
+
+/** @brief Advance the iterator to the next element. */
+#define queue_it_next(it) \
+	queue_it_next_impl(&(it).iter)
+
+
+
+/* ====================== Internal for the implementation ================== */
+/** @cond internal */
+
+struct queue;
+/* Non-inline functions are exported to be usable from daemon. */
+void queue_init_impl(struct queue *q, size_t item_size);
+void queue_deinit_impl(struct queue *q);
+void * queue_push_impl(struct queue *q);
+void * queue_push_head_impl(struct queue *q);
+
+struct queue_chunk;
+struct queue {
+	size_t len;
+	uint16_t chunk_cap, item_size;
+	struct queue_chunk *head, *tail;
+};
+
+struct queue_chunk {
+	struct queue_chunk *next; /*< head -> ... -> tail */
+	int16_t begin, end, cap, pad_; /*< indices: zero is closest to head */
+	/*< We could fit into uint8_t for example, but the choice of (3+1)*2 bytes
+	 * is a compromise between wasting space and getting a good alignment.
+	 * In particular, queue_t(type*) will store the pointers on addresses
+	 * aligned to the pointer size, in both 64-bit and 32-bit platforms.
+	 */
+	char data[];
+	/**< The item data.  We use "char" to satisfy the C99+ aliasing rules.
+	 * See C99 section 6.5 Expressions, paragraph 7.
+	 * Any type can be accessed through char-pointer,
+	 * so we can use a common struct definition
+	 * for all types being held.
+	 */
+};
+
+static inline void * queue_head_impl(const struct queue *q)
+{
+	assert(q);
+	struct queue_chunk *h = q->head;
+	if (unlikely(!h))
+		return NULL;
+	assert(h->end > h->begin);
+	return h->data + h->begin * q->item_size;
+}
+
+static inline void * queue_tail_impl(const struct queue *q)
+{
+	assert(q);
+	struct queue_chunk *t = q->tail;
+	if (unlikely(!t))
+		return NULL;
+	assert(t->end > t->begin);
+	return t->data + (t->end - 1) * q->item_size;
+}
+
+static inline void queue_pop_impl(struct queue *q)
+{
+	assert(q);
+	struct queue_chunk *h = q->head;
+	assert(h && h->end > h->begin);
+	if (h->end - h->begin == 1) {
+		/* removing the last element in the chunk */
+		q->head = h->next;
+		free(h);
+	} else {
+		++(h->begin);
+	}
+	--(q->len);
+}
+
+
+struct queue_it {
+	struct queue_chunk *chunk;
+	int16_t pos, item_size;
+};
+
+static inline struct queue_it queue_it_begin_impl(struct queue *q)
+{
+	assert(q);
+	return (struct queue_it){
+		.chunk = q->head,
+		.pos = q->head ? q->head->begin : -1,
+		.item_size = q->item_size,
+	};
+}
+
+static inline bool queue_it_finished_impl(struct queue_it *it)
+{
+	return it->chunk == NULL || it->pos >= it->chunk->end;
+}
+
+static inline void * queue_it_val_impl(struct queue_it *it)
+{
+	assert(!queue_it_finished_impl(it));
+	return it->chunk->data + it->pos * it->item_size;
+}
+
+static inline void queue_it_next_impl(struct queue_it *it)
+{
+	assert(!queue_it_finished_impl(it));
+	++(it->pos);
+	if (it->pos < it->chunk->end)
+		return;
+	it->chunk = it->chunk->next;
+	it->pos = it->chunk ? it->chunk->begin : -1;
+}
+
+/** @endcond (internal) */
+/** @} (addtogroup generics) */
+
diff --git a/lib/generic/set.h b/lib/generic/set.h
new file mode 100644
index 0000000..332c1aa
--- /dev/null
+++ b/lib/generic/set.h
@@ -0,0 +1,105 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @file set.h
+ * @brief A set abstraction implemented on top of map.
+ *
+ * @note The API is based on map.h, see it for more examples.
+ *
+ * # Example usage:
+ *
+ * @code{.c}
+ *      set_t set = set_make(NULL);
+ *
+ *      // Insert keys
+ *      if (set_add(&set, "princess") != 0 ||
+ *          set_add(&set, "prince")   != 0 ||
+ *          set_add(&set, "leia")     != 0) {
+ *          fail();
+ *      }
+ *
+ *      // Test membership
+ *      if (set_contains(&set, "leia")) {
+ *          success();
+ *      }
+ *
+ *      // Prefix search
+ *      int i = 0;
+ *      int count(const char *s, void *n) { (*(int *)n)++; return 0; }
+ *      if (set_walk_prefixed(set, "princ", count, &i) == 0) {
+ *          printf("%d matches\n", i);
+ *      }
+ *
+ *      // Delete
+ *      if (set_del(&set, "badkey") != 0) {
+ *          fail(); // No such key
+ *      }
+ *
+ *      // Clear the set
+ *      set_clear(&set);
+ * @endcode
+ *
+ * \addtogroup generics
+ * @{
+ */
+
+#pragma once
+
+#include <stddef.h>
+#include "map.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef map_t set_t;
+typedef int (set_walk_cb)(const char *, void *);
+
+/*! Creates an new, empty critbit set */
+#define set_make \
+	map_make
+
+/*! Returns non-zero if set contains str */
+#define set_contains(set, str) \
+	map_contains((set), (str))
+
+/*! Inserts str into set.  Returns 0 if new, 1 if already present, or ENOMEM. */
+#define set_add(set, str) \
+	map_set((set), (str), (void *)1)
+
+/*! Deletes str from the set, returns 0 on suceess */
+#define set_del(set, str) \
+	map_del((set), (str))
+
+/*! Clears the given set */
+#define set_clear(set) \
+	map_clear(set)
+
+/*! Calls callback for all strings in map  */
+#define set_walk(set, callback, baton) \
+	map_walk_prefixed((set), "", (callback), (baton))
+
+/*! Calls callback for all strings in set with the given prefix  */
+#define set_walk_prefixed(set, prefix, callback, baton) \
+	map_walk_prefixed((set), (prefix), (callback), (baton))
+
+
+#ifdef __cplusplus
+}
+#endif
+
+/** @} */
diff --git a/lib/generic/trie.c b/lib/generic/trie.c
new file mode 100644
index 0000000..0009eef
--- /dev/null
+++ b/lib/generic/trie.c
@@ -0,0 +1,912 @@
+/*  Copyright (C) 2016-2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+    The code originated from https://github.com/fanf2/qp/blob/master/qp.c
+    at revision 5f6d93753.
+ */
+
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "lib/generic/trie.h"
+#include "lib/utils.h"
+#include "contrib/ucw/lib.h"
+
+#if defined(__i386) || defined(__x86_64) || defined(_M_IX86) \
+	|| (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN) \
+		&& __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
+
+	/*!
+	 * \brief Use a pointer alignment hack to save memory.
+	 *
+	 * When on, isbranch() relies on the fact that in leaf_t the first pointer
+	 * is aligned on multiple of 4 bytes and that the flags bitfield is
+	 * overlaid over the lowest two bits of that pointer.
+	 * Neither is really guaranteed by the C standards; the second part should
+	 * be OK with x86_64 ABI and most likely any other little-endian platform.
+	 * It would be possible to manipulate the right bits portably, but it would
+	 * complicate the code nontrivially. C++ doesn't even guarantee type-punning.
+	 * In debug mode we check this works OK when creating a new trie instance.
+	 */
+	#define FLAGS_HACK 1
+#else
+	#define FLAGS_HACK 0
+#endif
+
+typedef unsigned char byte;
+#ifndef uint
+typedef unsigned int uint;
+#define uint uint
+#endif
+typedef uint bitmap_t; /*! Bit-maps, using the range of 1<<0 to 1<<16 (inclusive). */
+
+typedef struct {
+	uint32_t len; // 32 bits are enough for key lengths; probably even 16 bits would be.
+	char chars[];
+} tkey_t;
+
+/*! \brief Leaf of trie. */
+typedef struct {
+	#if !FLAGS_HACK
+		byte flags;
+	#endif
+	tkey_t *key; /*!< The pointer must be aligned to 4-byte multiples! */
+	trie_val_t val;
+} leaf_t;
+
+/*! \brief A trie node is either leaf_t or branch_t. */
+typedef union node node_t;
+
+/*!
+ * \brief Branch node of trie.
+ *
+ * - The flags distinguish whether the node is a leaf_t (0), or a branch
+ *   testing the more-important nibble (1) or the less-important one (2).
+ * - It stores the index of the byte that the node tests.  The combined
+ *   value (index*4 + flags) increases in branch nodes as you go deeper
+ *   into the trie.  All the keys below a branch are identical up to the
+ *   nibble identified by the branch.  Indices have to be stored because
+ *   we skip any branch nodes that would have a single child.
+ *   (Consequently, the skipped parts of key have to be validated in a leaf.)
+ * - The bitmap indicates which subtries are present.  The present child nodes
+ *   are stored in the twigs array (with no holes between them).
+ * - To simplify storing keys that are prefixes of each other, the end-of-string
+ *   position is treated as another nibble value, ordered before all others.
+ *   That affects the bitmap and twigs fields.
+ *
+ * \note The branch nodes are never allocated individually, but they are
+ *   always part of either the root node or the twigs array of the parent.
+ */
+typedef struct {
+	#if FLAGS_HACK
+		uint32_t flags  : 2,
+		         bitmap : 17; /*!< The first bitmap bit is for end-of-string child. */
+	#else
+		byte flags;
+		uint32_t bitmap;
+	#endif
+	uint32_t index;
+	node_t *twigs;
+} branch_t;
+
+union node {
+	leaf_t leaf;
+	branch_t branch;
+};
+
+struct trie {
+	node_t root; // undefined when weight == 0, see empty_root()
+	size_t weight;
+	knot_mm_t mm;
+};
+
+/*! \brief Make the root node empty (debug-only). */
+static inline void empty_root(node_t *root) {
+#ifndef NDEBUG
+	*root = (node_t){ .branch = {
+		.flags = 3, // invalid value that fits
+		.bitmap = 0,
+		.index = -1,
+		.twigs = NULL
+	} };
+#endif
+}
+
+/*! \brief Check that unportable code works OK (debug-only). */
+static void assert_portability(void) {
+#if FLAGS_HACK
+	assert(((union node){ .leaf = {
+			.key = (tkey_t *)(((uint8_t *)NULL) + 1),
+			.val = NULL
+		} }).branch.flags == 1);
+#endif
+}
+
+/*! \brief Propagate error codes. */
+#define ERR_RETURN(x) \
+	do { \
+		int err_code_ = x; \
+		if (unlikely(err_code_ != KNOT_EOK)) \
+			return err_code_; \
+	} while (false)
+
+/*!
+ * \brief Count the number of set bits.
+ *
+ * \TODO This implementation may be relatively slow on some HW.
+ */
+static uint bitmap_weight(bitmap_t w)
+{
+	assert((w & ~((1 << 17) - 1)) == 0); // using the least-important 17 bits
+	return __builtin_popcount(w);
+}
+
+/*! \brief Only keep the lowest bit in the bitmap (least significant -> twigs[0]). */
+static bitmap_t bitmap_lowest_bit(bitmap_t w)
+{
+	assert((w & ~((1 << 17) - 1)) == 0); // using the least-important 17 bits
+	return 1 << __builtin_ctz(w);
+}
+
+/*! \brief Test flags to determine type of this node. */
+static bool isbranch(const node_t *t)
+{
+	uint f = t->branch.flags;
+	assert(f <= 2);
+	return f != 0;
+}
+
+/*! \brief Make a bitmask for testing a branch bitmap. */
+static bitmap_t nibbit(byte k, uint flags)
+{
+	uint shift = (2 - flags) << 2;
+	uint nibble = (k >> shift) & 0xf;
+	return 1 << (nibble + 1/*because of prefix keys*/);
+}
+
+/*! \brief Extract a nibble from a key and turn it into a bitmask. */
+static bitmap_t twigbit(const node_t *t, const char *key, uint32_t len)
+{
+	assert(isbranch(t));
+	uint i = t->branch.index;
+
+	if (i >= len)
+		return 1 << 0; // leaf position
+
+	return nibbit((byte)key[i], t->branch.flags);
+}
+
+/*! \brief Test if a branch node has a child indicated by a bitmask. */
+static bool hastwig(const node_t *t, bitmap_t bit)
+{
+	assert(isbranch(t));
+	return t->branch.bitmap & bit;
+}
+
+/*! \brief Compute offset of an existing child in a branch node. */
+static uint twigoff(const node_t *t, bitmap_t b)
+{
+	assert(isbranch(t));
+	return bitmap_weight(t->branch.bitmap & (b - 1));
+}
+
+/*! \brief Get pointer to a particular child of a branch node. */
+static node_t* twig(node_t *t, uint i)
+{
+	assert(isbranch(t));
+	return &t->branch.twigs[i];
+}
+
+/*!
+ * \brief For a branch nod, compute offset of a child and child count.
+ *
+ * Having this separate might be meaningful for performance optimization.
+ */
+#define TWIGOFFMAX(off, max, t, b) do {			\
+		off = twigoff(t, b);			\
+		max = bitmap_weight(t->branch.bitmap);	\
+	} while(0)
+
+/*! \brief Simple string comparator. */
+static int key_cmp(const char *k1, uint32_t k1_len, const char *k2, uint32_t k2_len)
+{
+	int ret = memcmp(k1, k2, MIN(k1_len, k2_len));
+	if (ret != 0) {
+		return ret;
+	}
+
+	/* Key string is equal, compare lengths. */
+	if (k1_len == k2_len) {
+		return 0;
+	} else if (k1_len < k2_len) {
+		return -1;
+	} else {
+		return 1;
+	}
+}
+
+trie_t* trie_create(knot_mm_t *mm)
+{
+	assert_portability();
+	trie_t *trie = mm_alloc(mm, sizeof(trie_t));
+	if (trie != NULL) {
+		empty_root(&trie->root);
+		trie->weight = 0;
+		if (mm != NULL)
+			trie->mm = *mm;
+		else
+			mm_ctx_init(&trie->mm);
+	}
+	return trie;
+}
+
+/*! \brief Free anything under the trie node, except for the passed pointer itself. */
+static void clear_trie(node_t *trie, knot_mm_t *mm)
+{
+	if (!isbranch(trie)) {
+		mm_free(mm, trie->leaf.key);
+	} else {
+		branch_t *b = &trie->branch;
+		int len = bitmap_weight(b->bitmap);
+		for (int i = 0; i < len; ++i)
+			clear_trie(b->twigs + i, mm);
+		mm_free(mm, b->twigs);
+	}
+}
+
+void trie_free(trie_t *tbl)
+{
+	if (tbl == NULL)
+		return;
+	if (tbl->weight)
+		clear_trie(&tbl->root, &tbl->mm);
+	mm_free(&tbl->mm, tbl);
+}
+
+void trie_clear(trie_t *tbl)
+{
+	assert(tbl);
+	if (!tbl->weight)
+		return;
+	clear_trie(&tbl->root, &tbl->mm);
+	empty_root(&tbl->root);
+	tbl->weight = 0;
+}
+
+size_t trie_weight(const trie_t *tbl)
+{
+	assert(tbl);
+	return tbl->weight;
+}
+
+struct found {
+	leaf_t *l;	/**< the found leaf (NULL if not found) */
+	branch_t *p;	/**< the leaf's parent (if exists) */
+	bitmap_t b;	/**< bit-mask with a single bit marking l under p */
+};
+/** Search trie for an item with the given key (equality only). */
+static struct found find_equal(trie_t *tbl, const char *key, uint32_t len)
+{
+	assert(tbl);
+	struct found ret0;
+	memset(&ret0, 0, sizeof(ret0));
+	if (!tbl->weight)
+		return ret0;
+	/* Current node and parent while descending (returned values basically). */
+	node_t *t = &tbl->root;
+	branch_t *p = NULL;
+	bitmap_t b = 0;
+	while (isbranch(t)) {
+		__builtin_prefetch(t->branch.twigs);
+		b = twigbit(t, key, len);
+		if (!hastwig(t, b))
+			return ret0;
+		p = &t->branch;
+		t = twig(t, twigoff(t, b));
+	}
+	if (key_cmp(key, len, t->leaf.key->chars, t->leaf.key->len) != 0)
+		return ret0;
+	return (struct found) {
+		.l = &t->leaf,
+		.p = p,
+		.b = b,
+	};
+}
+/** Find item with the first key (lexicographical order). */
+static struct found find_first(trie_t *tbl)
+{
+	assert(tbl);
+	if (!tbl->weight) {
+		struct found ret0;
+		memset(&ret0, 0, sizeof(ret0));
+		return ret0;
+	}
+	/* Current node and parent while descending (returned values basically). */
+	node_t *t = &tbl->root;
+	branch_t *p = NULL;
+	while (isbranch(t)) {
+		p = &t->branch;
+		t = &p->twigs[0];
+	}
+	return (struct found) {
+		.l = &t->leaf,
+		.p = p,
+		.b = p ? bitmap_lowest_bit(p->bitmap) : 0,
+	};
+}
+
+trie_val_t* trie_get_try(trie_t *tbl, const char *key, uint32_t len)
+{
+	struct found found = find_equal(tbl, key, len);
+	return found.l ? &found.l->val : NULL;
+}
+
+trie_val_t* trie_get_first(trie_t *tbl, char **key, uint32_t *len)
+{
+	struct found found = find_first(tbl);
+	if (!found.l)
+		return NULL;
+	if (key)
+		*key = found.l->key->chars;
+	if (len)
+		*len = found.l->key->len;
+	return &found.l->val;
+}
+
+/** Delete the found element (if any) and return value (unless NULL is passed) */
+static int del_found(trie_t *tbl, struct found found, trie_val_t *val)
+{
+	if (!found.l)
+		return KNOT_ENOENT;
+	mm_free(&tbl->mm, found.l->key);
+	if (val != NULL)
+		*val = found.l->val; // we return trie_val_t directly when deleting
+	--tbl->weight;
+	branch_t * const p = found.p; // short-hand
+	if (unlikely(!p)) { // whole trie was a single leaf
+		assert(tbl->weight == 0);
+		empty_root(&tbl->root);
+		return KNOT_EOK;
+	}
+	// remove leaf t as child of p; get child index via pointer arithmetic
+	int ci = ((union node *)found.l) - p->twigs,
+	    cc = bitmap_weight(p->bitmap); // child count
+	assert(ci >= 0 && ci < cc);
+
+	if (cc == 2) { // collapse binary node p: move the other child to this node
+		node_t *twigs = p->twigs;
+		(*(union node *)p) = twigs[1 - ci]; // it might be a leaf or branch
+		mm_free(&tbl->mm, twigs);
+		return KNOT_EOK;
+	}
+	memmove(p->twigs + ci, p->twigs + ci + 1, sizeof(node_t) * (cc - ci - 1));
+	p->bitmap &= ~found.b;
+	node_t *twigs = mm_realloc(&tbl->mm, p->twigs, sizeof(node_t) * (cc - 1),
+	                           sizeof(node_t) * cc);
+	if (likely(twigs != NULL))
+		p->twigs = twigs;
+		/* We can ignore mm_realloc failure, only beware that next time
+		 * the prev_size passed to it wouldn't be correct; TODO? */
+	return KNOT_EOK;
+}
+
+int trie_del(trie_t *tbl, const char *key, uint32_t len, trie_val_t *val)
+{
+	struct found found = find_equal(tbl, key, len);
+	return del_found(tbl, found, val);
+}
+
+int trie_del_first(trie_t *tbl, char *key, uint32_t *len, trie_val_t *val)
+{
+	struct found found = find_first(tbl);
+	if (!found.l)
+		return KNOT_ENOENT;
+	if (key) {
+		if (!len)
+			return KNOT_EINVAL;
+		if (*len < found.l->key->len)
+			return kr_error(ENOSPC);
+		memcpy(key, found.l->key->chars, found.l->key->len);
+	}
+	if (len) { // makes sense even with key == NULL
+		*len = found.l->key->len;
+	}
+	return del_found(tbl, found, val);
+}
+
+/*!
+ * \brief Stack of nodes, storing a path down a trie.
+ *
+ * The structure also serves directly as the public trie_it_t type,
+ * in which case it always points to the current leaf, unless we've finished
+ * (i.e. it->len == 0).
+ */
+typedef struct trie_it {
+	node_t* *stack; /*!< The stack; malloc is used directly instead of mm. */
+	uint32_t len;   /*!< Current length of the stack. */
+	uint32_t alen;  /*!< Allocated/available length of the stack. */
+	/*! \brief Initial storage for \a stack; it should fit in many use cases. */
+	node_t* stack_init[60];
+} nstack_t;
+
+/*! \brief Create a node stack containing just the root (or empty). */
+static void ns_init(nstack_t *ns, trie_t *tbl)
+{
+	assert(tbl);
+	ns->stack = ns->stack_init;
+	ns->alen = sizeof(ns->stack_init) / sizeof(ns->stack_init[0]);
+	if (tbl->weight) {
+		ns->len = 1;
+		ns->stack[0] = &tbl->root;
+	} else {
+		ns->len = 0;
+	}
+}
+
+/*! \brief Free inside of the stack, i.e. not the passed pointer itself. */
+static void ns_cleanup(nstack_t *ns)
+{
+	assert(ns && ns->stack);
+	if (likely(ns->stack == ns->stack_init))
+		return;
+	free(ns->stack);
+	#ifndef NDEBUG
+		ns->stack = NULL;
+		ns->alen = 0;
+	#endif
+}
+
+/*! \brief Allocate more space for the stack. */
+static int ns_longer_alloc(nstack_t *ns)
+{
+	ns->alen *= 2;
+	size_t new_size = sizeof(nstack_t) + ns->alen * sizeof(node_t *);
+	node_t **st;
+	if (ns->stack == ns->stack_init) {
+		st = malloc(new_size);
+		if (st != NULL)
+			memcpy(st, ns->stack, ns->len * sizeof(node_t *));
+	} else {
+		st = realloc(ns->stack, new_size);
+	}
+	if (st == NULL)
+		return KNOT_ENOMEM;
+	ns->stack = st;
+	return KNOT_EOK;
+}
+
+/*! \brief Ensure the node stack can be extended by one. */
+static inline int ns_longer(nstack_t *ns)
+{
+	// get a longer stack if needed
+	if (likely(ns->len < ns->alen))
+		return KNOT_EOK;
+	return ns_longer_alloc(ns); // hand-split the part suitable for inlining
+}
+
+/*!
+ * \brief Find the "branching point" as if searching for a key.
+ *
+ *  The whole path to the point is kept on the passed stack;
+ *  always at least the root will remain on the top of it.
+ *  Beware: the precise semantics of this function is rather tricky.
+ *  The top of the stack will contain: the corresponding leaf if exact match is found;
+ *  or the immediate node below a branching-point-on-edge or the branching-point itself.
+ *
+ *  \param info   Set position of the point of first mismatch (in index and flags).
+ *  \param first  Set the value of the first non-matching character (from trie),
+ *                optionally; end-of-string character has value -256 (that's why it's int).
+ *                Note: the character is converted to *unsigned* char (i.e. 0..255),
+ *                as that's the ordering used in the trie.
+ *
+ *  \return KNOT_EOK or KNOT_ENOMEM.
+ */
+static int ns_find_branch(nstack_t *ns, const char *key, uint32_t len,
+                          branch_t *info, int *first)
+{
+	assert(ns && ns->len && info);
+	// First find some leaf with longest matching prefix.
+	while (isbranch(ns->stack[ns->len - 1])) {
+		ERR_RETURN(ns_longer(ns));
+		node_t *t = ns->stack[ns->len - 1];
+		__builtin_prefetch(t->branch.twigs);
+		bitmap_t b = twigbit(t, key, len);
+		// Even if our key is missing from this branch we need to
+		// keep iterating down to a leaf. It doesn't matter which
+		// twig we choose since the keys are all the same up to this
+		// index. Note that blindly using twigoff(t, b) can cause
+		// an out-of-bounds index if it equals twigmax(t).
+		uint i = hastwig(t, b) ? twigoff(t, b) : 0;
+		ns->stack[ns->len++] = twig(t, i);
+	}
+	tkey_t *lkey = ns->stack[ns->len-1]->leaf.key;
+	// Find index of the first char that differs.
+	uint32_t index = 0;
+	while (index < MIN(len,lkey->len)) {
+		if (key[index] != lkey->chars[index])
+			break;
+		else
+			++index;
+	}
+	info->index = index;
+	if (first)
+		*first = lkey->len > index ? (unsigned char)lkey->chars[index] : -256;
+	// Find flags: which half-byte has matched.
+	uint flags;
+	if (index == len && len == lkey->len) { // found equivalent key
+		info->flags = flags = 0;
+		goto success;
+	}
+	if (likely(index < MIN(len,lkey->len))) {
+		byte k2 = (byte)lkey->chars[index];
+		byte k1 = (byte)key[index];
+		flags = ((k1 ^ k2) & 0xf0) ? 1 : 2;
+	} else { // one is prefix of another
+		flags = 1;
+	}
+	info->flags = flags;
+	// now go up the trie from the current leaf
+	branch_t *t;
+	do {
+		if (unlikely(ns->len == 1))
+			goto success; // only the root stays on the stack
+		t = (branch_t*)ns->stack[ns->len - 2];
+		if (t->index < index || (t->index == index && t->flags < flags))
+			goto success;
+		--ns->len;
+	} while (true);
+success:
+	#ifndef NDEBUG // invariants on successful return
+		assert(ns->len);
+		if (isbranch(ns->stack[ns->len - 1])) {
+			t = &ns->stack[ns->len - 1]->branch;
+			assert(t->index > index || (t->index == index && t->flags >= flags));
+		}
+		if (ns->len > 1) {
+			t = &ns->stack[ns->len - 2]->branch;
+			assert(t->index < index || (t->index == index
+			       && (t->flags < flags || (t->flags == 1 && flags == 0))));
+		}
+	#endif
+	return KNOT_EOK;
+}
+
+/*!
+ * \brief Advance the node stack to the last leaf in the subtree.
+ *
+ * \return KNOT_EOK or KNOT_ENOMEM.
+ */
+static int ns_last_leaf(nstack_t *ns)
+{
+	assert(ns);
+	do {
+		ERR_RETURN(ns_longer(ns));
+		node_t *t = ns->stack[ns->len - 1];
+		if (!isbranch(t))
+			return KNOT_EOK;
+		int lasti = bitmap_weight(t->branch.bitmap) - 1;
+		assert(lasti >= 0);
+		ns->stack[ns->len++] = twig(t, lasti);
+	} while (true);
+}
+
+/*!
+ * \brief Advance the node stack to the first leaf in the subtree.
+ *
+ * \return KNOT_EOK or KNOT_ENOMEM.
+ */
+static int ns_first_leaf(nstack_t *ns)
+{
+	assert(ns && ns->len);
+	do {
+		ERR_RETURN(ns_longer(ns));
+		node_t *t = ns->stack[ns->len - 1];
+		if (!isbranch(t))
+			return KNOT_EOK;
+		ns->stack[ns->len++] = twig(t, 0);
+	} while (true);
+}
+
+/*!
+ * \brief Advance the node stack to the leaf that is previous to the current node.
+ *
+ * \note Prefix leaf under the current node DOES count (if present; perhaps questionable).
+ * \return KNOT_EOK on success, KNOT_ENOENT on not-found, or possibly KNOT_ENOMEM.
+ */
+static int ns_prev_leaf(nstack_t *ns)
+{
+	assert(ns && ns->len > 0);
+
+	node_t *t = ns->stack[ns->len - 1];
+	if (hastwig(t, 1 << 0)) { // the prefix leaf
+		t = twig(t, 0);
+		ERR_RETURN(ns_longer(ns));
+		ns->stack[ns->len++] = t;
+		return KNOT_EOK;
+	}
+
+	do {
+		if (ns->len < 2)
+			return KNOT_ENOENT; // root without empty key has no previous leaf
+		t = ns->stack[ns->len - 1];
+		node_t *p = ns->stack[ns->len - 2];
+		int pindex = t - p->branch.twigs; // index in parent via pointer arithmetic
+		assert(pindex >= 0 && pindex <= 16);
+		if (pindex > 0) { // t isn't the first child -> go down the previous one
+			ns->stack[ns->len - 1] = twig(p, pindex - 1);
+			return ns_last_leaf(ns);
+		}
+		// we've got to go up again
+		--ns->len;
+	} while (true);
+}
+
+/*!
+ * \brief Advance the node stack to the leaf that is successor to the current node.
+ *
+ * \note Prefix leaf or anything else under the current node DOES count.
+ * \return KNOT_EOK on success, KNOT_ENOENT on not-found, or possibly KNOT_ENOMEM.
+ */
+static int ns_next_leaf(nstack_t *ns)
+{
+	assert(ns && ns->len > 0);
+
+	node_t *t = ns->stack[ns->len - 1];
+	if (isbranch(t))
+		return ns_first_leaf(ns);
+	do {
+		if (ns->len < 2)
+			return KNOT_ENOENT; // not found, as no more parent is available
+		t = ns->stack[ns->len - 1];
+		node_t *p = ns->stack[ns->len - 2];
+		int pindex = t - p->branch.twigs; // index in parent via pointer arithmetic
+		assert(pindex >= 0 && pindex <= 16);
+		int pcount = bitmap_weight(p->branch.bitmap);
+		if (pindex + 1 < pcount) { // t isn't the last child -> go down the next one
+			ns->stack[ns->len - 1] = twig(p, pindex + 1);
+			return ns_first_leaf(ns);
+		}
+		// we've got to go up again
+		--ns->len;
+	} while (true);
+}
+
+int trie_get_leq(trie_t *tbl, const char *key, uint32_t len, trie_val_t **val)
+{
+	assert(tbl && val);
+	*val = NULL; // so on failure we can just return;
+	if (tbl->weight == 0)
+		return KNOT_ENOENT;
+	{ // Intentionally un-indented; until end of function, to bound cleanup attr.
+	// First find a key with longest-matching prefix
+	__attribute__((cleanup(ns_cleanup)))
+		nstack_t ns_local;
+	ns_init(&ns_local, tbl);
+	nstack_t *ns = &ns_local;
+	branch_t bp;
+	int un_leaf; // first unmatched character in the leaf
+	ERR_RETURN(ns_find_branch(ns, key, len, &bp, &un_leaf));
+	int un_key = bp.index < len ? (unsigned char)key[bp.index] : -256;
+	node_t *t = ns->stack[ns->len - 1];
+	if (bp.flags == 0) { // found exact match
+		*val = &t->leaf.val;
+		return KNOT_EOK;
+	}
+	// Get t: the last node on matching path
+	if (isbranch(t) && t->branch.index == bp.index && t->branch.flags == bp.flags) {
+		// t is OK
+	} else {
+		// the top of the stack was the first unmatched node -> step up
+		if (ns->len == 1) {
+			// root was unmatched already
+			if (un_key < un_leaf)
+				return KNOT_ENOENT;
+			ERR_RETURN(ns_last_leaf(ns));
+			goto success;
+		}
+		--ns->len;
+		t = ns->stack[ns->len - 1];
+	}
+	// Now we re-do the first "non-matching" step in the trie
+	// but try the previous child if key was less (it may not exist)
+	bitmap_t b = twigbit(t, key, len);
+	int i = hastwig(t, b)
+		? twigoff(t, b) - (un_key < un_leaf)
+		: twigoff(t, b) - 1 /*twigoff returns successor when !hastwig*/;
+	if (i >= 0) {
+		ERR_RETURN(ns_longer(ns));
+		ns->stack[ns->len++] = twig(t, i);
+		ERR_RETURN(ns_last_leaf(ns));
+	} else {
+		ERR_RETURN(ns_prev_leaf(ns));
+	}
+success:
+	assert(!isbranch(ns->stack[ns->len - 1]));
+	*val = &ns->stack[ns->len - 1]->leaf.val;
+	return 1;
+	}
+}
+
+/*! \brief Initialize a new leaf, copying the key, and returning failure code. */
+static int mk_leaf(node_t *leaf, const char *key, uint32_t len, knot_mm_t *mm)
+{
+	tkey_t *k = mm_alloc(mm, sizeof(tkey_t) + len);
+	#if FLAGS_HACK
+		assert(((uintptr_t)k) % 4 == 0); // we need an aligned pointer
+	#endif
+	if (unlikely(!k))
+		return KNOT_ENOMEM;
+	k->len = len;
+	memcpy(k->chars, key, len);
+	leaf->leaf = (leaf_t){
+		#if !FLAGS_HACK
+			.flags = 0,
+		#endif
+		.val = NULL,
+		.key = k
+	};
+	return KNOT_EOK;
+}
+
+trie_val_t* trie_get_ins(trie_t *tbl, const char *key, uint32_t len)
+{
+	assert(tbl);
+	// First leaf in an empty tbl?
+	if (unlikely(!tbl->weight)) {
+		if (unlikely(mk_leaf(&tbl->root, key, len, &tbl->mm)))
+			return NULL;
+		++tbl->weight;
+		return &tbl->root.leaf.val;
+	}
+	{ // Intentionally un-indented; until end of function, to bound cleanup attr.
+	// Find the branching-point
+	__attribute__((cleanup(ns_cleanup)))
+		nstack_t ns_local;
+	ns_init(&ns_local, tbl);
+	nstack_t *ns = &ns_local;
+	branch_t bp; // branch-point: index and flags signifying the longest common prefix
+	int k2; // the first unmatched character in the leaf
+	if (unlikely(ns_find_branch(ns, key, len, &bp, &k2)))
+		return NULL;
+	node_t *t = ns->stack[ns->len - 1];
+	if (bp.flags == 0) // the same key was already present
+		return &t->leaf.val;
+	node_t leaf;
+	if (unlikely(mk_leaf(&leaf, key, len, &tbl->mm)))
+		return NULL;
+
+	if (isbranch(t) && bp.index == t->branch.index && bp.flags == t->branch.flags) {
+		// The node t needs a new leaf child.
+		bitmap_t b1 = twigbit(t, key, len);
+		assert(!hastwig(t, b1));
+		uint s, m; TWIGOFFMAX(s, m, t, b1); // new child position and original child count
+		node_t *twigs = mm_realloc(&tbl->mm, t->branch.twigs,
+				sizeof(node_t) * (m + 1), sizeof(node_t) * m);
+		if (unlikely(!twigs))
+			goto err_leaf;
+		memmove(twigs + s + 1, twigs + s, sizeof(node_t) * (m - s));
+		twigs[s] = leaf;
+		t->branch.twigs = twigs;
+		t->branch.bitmap |= b1;
+		++tbl->weight;
+		return &twigs[s].leaf.val;
+	} else {
+		// We need to insert a new binary branch with leaf at *t.
+		// Note: it works the same for the case where we insert above root t.
+		#ifndef NDEBUG
+			if (ns->len > 1) {
+				node_t *pt = ns->stack[ns->len - 2];
+				assert(hastwig(pt, twigbit(pt, key, len)));
+			}
+		#endif
+		node_t *twigs = mm_alloc(&tbl->mm, sizeof(node_t) * 2);
+		if (unlikely(!twigs))
+			goto err_leaf;
+		node_t t2 = *t; // Save before overwriting t.
+		t->branch.flags = bp.flags;
+		t->branch.index = bp.index;
+		t->branch.twigs = twigs;
+		bitmap_t b1 = twigbit(t, key, len);
+		bitmap_t b2 = unlikely(k2 == -256) ? (1 << 0) : nibbit(k2, bp.flags);
+		t->branch.bitmap = b1 | b2;
+		*twig(t, twigoff(t, b1)) = leaf;
+		*twig(t, twigoff(t, b2)) = t2;
+		++tbl->weight;
+		return &twig(t, twigoff(t, b1))->leaf.val;
+	};
+err_leaf:
+	mm_free(&tbl->mm, leaf.leaf.key);
+	return NULL;
+	}
+}
+
+/*! \brief Apply a function to every trie_val_t*, in order; a recursive solution. */
+static int apply_trie(node_t *t, int (*f)(trie_val_t *, void *), void *d)
+{
+	assert(t);
+	if (!isbranch(t))
+		return f(&t->leaf.val, d);
+	int child_count = bitmap_weight(t->branch.bitmap);
+	for (int i = 0; i < child_count; ++i)
+		ERR_RETURN(apply_trie(twig(t, i), f, d));
+	return KNOT_EOK;
+}
+
+int trie_apply(trie_t *tbl, int (*f)(trie_val_t *, void *), void *d)
+{
+	assert(tbl && f);
+	if (!tbl->weight)
+		return KNOT_EOK;
+	return apply_trie(&tbl->root, f, d);
+}
+
+/* These are all thin wrappers around static Tns* functions. */
+trie_it_t* trie_it_begin(trie_t *tbl)
+{
+	assert(tbl);
+	trie_it_t *it = malloc(sizeof(nstack_t));
+	if (!it)
+		return NULL;
+	ns_init(it, tbl);
+	if (it->len == 0) // empty tbl
+		return it;
+	if (ns_first_leaf(it)) {
+		ns_cleanup(it);
+		free(it);
+		return NULL;
+	}
+	return it;
+}
+
+void trie_it_next(trie_it_t *it)
+{
+	assert(it && it->len);
+	if (ns_next_leaf(it) != KNOT_EOK)
+		it->len = 0;
+}
+
+bool trie_it_finished(trie_it_t *it)
+{
+	assert(it);
+	return it->len == 0;
+}
+
+void trie_it_free(trie_it_t *it)
+{
+	if (!it)
+		return;
+	ns_cleanup(it);
+	free(it);
+}
+
+const char* trie_it_key(trie_it_t *it, size_t *len)
+{
+	assert(it && it->len);
+	node_t *t = it->stack[it->len - 1];
+	assert(!isbranch(t));
+	tkey_t *key = t->leaf.key;
+	if (len)
+		*len = key->len;
+	return key->chars;
+}
+
+trie_val_t* trie_it_val(trie_it_t *it)
+{
+	assert(it && it->len);
+	node_t *t = it->stack[it->len - 1];
+	assert(!isbranch(t));
+	return &t->leaf.val;
+}
diff --git a/lib/generic/trie.h b/lib/generic/trie.h
new file mode 100644
index 0000000..0550e95
--- /dev/null
+++ b/lib/generic/trie.h
@@ -0,0 +1,150 @@
+/*  Copyright (C) 2017-2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include <libknot/mm_ctx.h>
+#include "lib/defines.h"
+
+/*!
+ * \brief Native API of QP-tries:
+ *
+ * - keys are char strings, not necessarily zero-terminated,
+ *   the structure copies the contents of the passed keys
+ * - values are void* pointers, typically you get an ephemeral pointer to it
+ * - key lengths are limited by 2^32-1 ATM
+ *
+ * XXX EDITORS: trie.{h,c} are synced from
+ * https://gitlab.labs.nic.cz/knot/knot-dns/tree/68352fc969/src/contrib/qp-trie
+ * only with tiny adjustments, mostly #includes and KR_EXPORT.
+ */
+
+/*! \brief Element value. */
+typedef void* trie_val_t;
+
+/*! \brief Opaque structure holding a QP-trie. */
+typedef struct trie trie_t;
+
+/*! \brief Opaque type for holding a QP-trie iterator. */
+typedef struct trie_it trie_it_t;
+
+/*! \brief Create a trie instance.  Pass NULL to use malloc+free. */
+KR_EXPORT
+trie_t* trie_create(knot_mm_t *mm);
+
+/*! \brief Free a trie instance. */
+KR_EXPORT
+void trie_free(trie_t *tbl);
+
+/*! \brief Clear a trie instance (make it empty). */
+KR_EXPORT
+void trie_clear(trie_t *tbl);
+
+/*! \brief Return the number of keys in the trie. */
+KR_EXPORT
+size_t trie_weight(const trie_t *tbl);
+
+/*! \brief Search the trie, returning NULL on failure. */
+KR_EXPORT
+trie_val_t* trie_get_try(trie_t *tbl, const char *key, uint32_t len);
+
+/*!
+ * \brief Return pointer to the minimum.  Optionally with key and its length. */
+KR_EXPORT
+trie_val_t* trie_get_first(trie_t *tbl, char **key, uint32_t *len);
+
+/*! \brief Search the trie, inserting NULL trie_val_t on failure. */
+KR_EXPORT
+trie_val_t* trie_get_ins(trie_t *tbl, const char *key, uint32_t len);
+
+/*!
+ * \brief Search for less-or-equal element.
+ *
+ * \param tbl  Trie.
+ * \param key  Searched key.
+ * \param len  Key length.
+ * \param val  Must be valid; it will be set to NULL if not found or errored.
+ * \return KNOT_EOK for exact match, 1 for previous, KNOT_ENOENT for not-found,
+ *         or KNOT_E*.
+ */
+KR_EXPORT
+int trie_get_leq(trie_t *tbl, const char *key, uint32_t len, trie_val_t **val);
+
+/*!
+ * \brief Apply a function to every trie_val_t, in order.
+ *
+ * \param d Parameter passed as the second argument to f().
+ * \return First nonzero from f() or zero (i.e. KNOT_EOK).
+ */
+int trie_apply(trie_t *tbl, int (*f)(trie_val_t *, void *), void *d);
+
+/*!
+ * \brief Remove an item, returning KNOT_EOK if succeeded or KNOT_ENOENT if not found.
+ *
+ * If val!=NULL and deletion succeeded, the deleted value is set.
+ */
+KR_EXPORT
+int trie_del(trie_t *tbl, const char *key, uint32_t len, trie_val_t *val);
+
+/*!
+ * \brief Remove the first item, returning KNOT_EOK on success.
+ *
+ * You may optionally get the key and/or value.
+ * The key is copied, so you need to pass sufficient len,
+ * otherwise kr_error(ENOSPC) is returned.
+ */
+KR_EXPORT
+int trie_del_first(trie_t *tbl, char *key, uint32_t *len, trie_val_t *val);
+
+/*! \brief Create a new iterator pointing to the first element (if any). */
+KR_EXPORT
+trie_it_t* trie_it_begin(trie_t *tbl);
+
+/*!
+ * \brief Advance the iterator to the next element.
+ *
+ * Iteration is in ascending lexicographical order.
+ * In particular, the empty string would be considered as the very first.
+ *
+ * \note You may not use this function if the trie's key-set has been modified
+ * during the lifetime of the iterator (modifying values only is OK).
+ */
+KR_EXPORT
+void trie_it_next(trie_it_t *it);
+
+/*! \brief Test if the iterator has gone past the last element. */
+KR_EXPORT
+bool trie_it_finished(trie_it_t *it);
+
+/*! \brief Free any resources of the iterator. It's OK to call it on NULL. */
+KR_EXPORT
+void trie_it_free(trie_it_t *it);
+
+/*!
+ * \brief Return pointer to the key of the current element.
+ *
+ * \note The optional len is uint32_t internally but size_t is better for our usage,
+ *       as it is without an additional type conversion.
+ */
+KR_EXPORT
+const char* trie_it_key(trie_it_t *it, size_t *len);
+
+/*! \brief Return pointer to the value of the current element (writable). */
+KR_EXPORT
+trie_val_t* trie_it_val(trie_it_t *it);
diff --git a/lib/layer.h b/lib/layer.h
new file mode 100644
index 0000000..0909cb7
--- /dev/null
+++ b/lib/layer.h
@@ -0,0 +1,107 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "lib/defines.h"
+#include "lib/utils.h"
+
+#ifdef NOVERBOSELOG
+	#define QRVERBOSE(query, cls, ...)
+#else
+	/** Print a debug message related to resolution.
+	 * \param _query	associated kr_query, may be NULL
+	 * \param _cls	identifying string, typically of length exactly four (padded)
+	 * \param ...	printf-compatible list of parameters
+	 */
+	#define QRVERBOSE(_query, _cls, ...) do { \
+		const struct kr_query *_qry = (_query); \
+		if (kr_log_trace_enabled(_qry)) { \
+			kr_log_trace(_qry, (_cls), __VA_ARGS__); \
+		} else if (VERBOSE_STATUS) { \
+			kr_log_qverbose_impl(_qry, (_cls), __VA_ARGS__); \
+		}  \
+	} while (false)
+#endif
+
+/** Layer processing states.  Only one value at a time (but see TODO).
+ *
+ *  Each state represents the state machine transition,
+ *  and determines readiness for the next action.
+ *  See struct kr_layer_api for the actions.
+ *
+ *  TODO: the cookie module sometimes sets (_FAIL | _DONE) on purpose (!)
+ */
+enum kr_layer_state {
+	KR_STATE_CONSUME = 1 << 0, /*!< Consume data. */
+	KR_STATE_PRODUCE = 1 << 1, /*!< Produce data. */
+	KR_STATE_DONE    = 1 << 2, /*!< Finished successfully. */
+	KR_STATE_FAIL    = 1 << 3, /*!< Error. */
+	KR_STATE_YIELD   = 1 << 4, /*!< Paused, waiting for a sub-query. */
+};
+
+/* Forward declarations. */
+struct kr_layer_api;
+
+/** Packet processing context. */
+typedef struct kr_layer {
+	int state; /*!< The current state; bitmap of enum kr_layer_state. */
+	struct kr_request *req; /*!< The corresponding request. */
+	const struct kr_layer_api *api;
+} kr_layer_t;
+
+/** Packet processing module API.  All functions return the new kr_layer_state. */
+struct kr_layer_api {
+      	/** Start of processing the DNS request. */
+	int (*begin)(kr_layer_t *ctx);
+
+	int (*reset)(kr_layer_t *ctx);
+
+	/** Paired to begin, called both on successes and failures. */
+	int (*finish)(kr_layer_t *ctx);
+
+	/** Processing an answer from upstream or the answer to the request. */
+	int (*consume)(kr_layer_t *ctx, knot_pkt_t *pkt);
+
+	/** Produce either an answer to the request or a query for upstream (or fail). */
+	int (*produce)(kr_layer_t *ctx, knot_pkt_t *pkt);
+
+	/** Finalises the outbound query packet with the knowledge of the IP addresses.
+	 * The checkout layer doesn't persist the state, so canceled subrequests
+	 * don't affect the resolution or rest of the processing. */
+	int (*checkout)(kr_layer_t *ctx, knot_pkt_t *packet, struct sockaddr *dst, int type);
+
+	/** Finalises the answer.
+	 * Last chance to affect what will get into the answer, including EDNS.*/
+	int (*answer_finalize)(kr_layer_t *ctx);
+
+	/** The module can store anything in here. */
+	void *data;
+
+	/** Internal to ./daemon/ffimodule.c. */
+	int cb_slots[];
+};
+
+typedef struct kr_layer_api kr_layer_api_t;
+
+/** Pickled layer state (api, input, state). */
+struct kr_layer_pickle {
+    struct kr_layer_pickle *next;
+    const struct kr_layer_api *api;
+    knot_pkt_t *pkt;
+    unsigned state;
+};
+
diff --git a/lib/layer/cache.c b/lib/layer/cache.c
new file mode 100644
index 0000000..c7bbc1a
--- /dev/null
+++ b/lib/layer/cache.c
@@ -0,0 +1,31 @@
+/*  Copyright (C) 2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "lib/module.h"
+#include "lib/cache/api.h"
+
+/** Module implementation. */
+const kr_layer_api_t *cache_layer(struct kr_module *module)
+{
+	static const kr_layer_api_t _layer = {
+		.produce = &cache_peek,
+		.consume = &cache_stash,
+	};
+
+	return &_layer;
+}
+
+KR_MODULE_EXPORT(cache)
diff --git a/lib/layer/iterate.c b/lib/layer/iterate.c
new file mode 100644
index 0000000..cf57cc5
--- /dev/null
+++ b/lib/layer/iterate.c
@@ -0,0 +1,1135 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file iterate.c
+ *
+ * This builtin module is mainly active in the consume phase.
+ * Primary responsibilities:
+ *  - Classify the packet as auth/nonauth and change its AA flag accordingly.
+ *  - Pick interesting RRs to kr_request::answ_selected and ::auth_selected,
+ *    NEW: and classify their rank, except for validation status.
+ *  - Update kr_query::zone_cut (in case of referral).
+ *  - Interpret CNAMEs.
+ *  - Prepare the followup query - either inline or as another kr_query
+ *    (CNAME jumps create a new "sibling" query).
+ */
+
+#include <sys/time.h>
+#include <assert.h>
+#include <arpa/inet.h>
+
+#include <contrib/cleanup.h>
+#include <libknot/descriptor.h>
+#include <libknot/rrtype/rdname.h>
+#include <libknot/rrtype/rrsig.h>
+
+#include "lib/layer/iterate.h"
+#include "lib/resolve.h"
+#include "lib/rplan.h"
+#include "lib/defines.h"
+#include "lib/nsrep.h"
+#include "lib/module.h"
+#include "lib/dnssec/ta.h"
+
+#define VERBOSE_MSG(...) QRVERBOSE(req->current_query, "iter", __VA_ARGS__)
+#define QVERBOSE_MSG(qry, ...) QRVERBOSE(qry, "iter", __VA_ARGS__)
+
+/* Iterator often walks through packet section, this is an abstraction. */
+typedef int (*rr_callback_t)(const knot_rrset_t *, unsigned, struct kr_request *);
+
+/** Return minimized QNAME/QTYPE for current zone cut. */
+static const knot_dname_t *minimized_qname(struct kr_query *query, uint16_t *qtype)
+{
+	/* Minimization disabled. */
+	const knot_dname_t *qname = query->sname;
+	if (qname[0] == '\0' || query->flags.NO_MINIMIZE || query->flags.STUB) {
+		return qname;
+	}
+
+	/* Minimize name to contain current zone cut + 1 label. */
+	int cut_labels = knot_dname_labels(query->zone_cut.name, NULL);
+	int qname_labels = knot_dname_labels(qname, NULL);
+	while(qname[0] && qname_labels > cut_labels + 1) {
+		qname = knot_wire_next_label(qname, NULL);
+		qname_labels -= 1;
+	}
+
+	/* Hide QTYPE if minimized. */
+	if (qname != query->sname) {
+		*qtype = KNOT_RRTYPE_NS;
+	}
+
+	return qname;
+}
+
+/** Answer is paired to query. */
+static bool is_paired_to_query(const knot_pkt_t *answer, struct kr_query *query)
+{
+	uint16_t qtype = query->stype;
+	const knot_dname_t *qname = minimized_qname(query, &qtype);
+
+	return query->id      == knot_wire_get_id(answer->wire) &&
+	       knot_wire_get_qdcount(answer->wire) > 0 &&
+	       query->sclass  == knot_pkt_qclass(answer) &&
+	       qtype          == knot_pkt_qtype(answer) &&
+	       knot_dname_is_equal(qname, knot_pkt_qname(answer));
+}
+
+/** Relaxed rule for AA, either AA=1 or SOA matching zone cut is required. */
+static bool is_authoritative(const knot_pkt_t *answer, struct kr_query *query)
+{
+	if (knot_wire_get_aa(answer->wire)) {
+		return true;
+	}
+
+	const knot_pktsection_t *ns = knot_pkt_section(answer, KNOT_AUTHORITY);
+	for (unsigned i = 0; i < ns->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(ns, i);
+		if (rr->type == KNOT_RRTYPE_SOA
+		    && knot_dname_in_bailiwick(rr->owner, query->zone_cut.name) >= 0) {
+			return true;
+		}
+	}
+
+#ifndef STRICT_MODE
+	/* Last resort to work around broken auths, if the zone cut is at/parent of the QNAME. */
+	if (knot_dname_is_equal(query->zone_cut.name, knot_pkt_qname(answer))) {
+		return true;
+	}
+#endif
+
+	/* Some authoritative servers are hopelessly broken, allow lame answers in permissive mode. */
+	if (query->flags.PERMISSIVE) {
+		return true;
+	}
+
+	return false;
+}
+
+int kr_response_classify(const knot_pkt_t *pkt)
+{
+	const knot_pktsection_t *an = knot_pkt_section(pkt, KNOT_ANSWER);
+	switch (knot_wire_get_rcode(pkt->wire)) {
+	case KNOT_RCODE_NOERROR:
+		return (an->count == 0) ? PKT_NODATA : PKT_NOERROR;
+	case KNOT_RCODE_NXDOMAIN:
+		return PKT_NXDOMAIN;
+	case KNOT_RCODE_REFUSED:
+		return PKT_REFUSED;
+	default:
+		return PKT_ERROR;
+	}
+}
+
+/** @internal Filter ANY or loopback addresses. */
+static bool is_valid_addr(const uint8_t *addr, size_t len)
+{
+	if (len == sizeof(struct in_addr)) {
+		/* Filter ANY and 127.0.0.0/8 */
+		uint32_t ip_host = ntohl(*(const uint32_t *)(addr));
+		if (ip_host == 0 || (ip_host & 0xff000000) == 0x7f000000) {
+			return false;
+		}
+	} else if (len == sizeof(struct in6_addr)) {
+		struct in6_addr ip6_mask;
+		memset(&ip6_mask, 0, sizeof(ip6_mask));
+		/* All except last byte are zeroed, last byte defines ANY/::1 */
+		if (memcmp(addr, ip6_mask.s6_addr, sizeof(ip6_mask.s6_addr) - 1) == 0) {
+			return (addr[len - 1] > 1);
+		}
+	}
+	return true;
+}
+
+/** @internal Update NS address from record \a rr.  Return _FAIL on error. */
+static int update_nsaddr(const knot_rrset_t *rr, struct kr_query *query, int *glue_cnt)
+{
+	if (rr->type == KNOT_RRTYPE_A || rr->type == KNOT_RRTYPE_AAAA) {
+		const knot_rdata_t *rdata = rr->rrs.rdata;
+		const int a_len = rr->type == KNOT_RRTYPE_A
+			? sizeof(struct in_addr) : sizeof(struct in6_addr);
+		if (a_len != rdata->len) {
+			QVERBOSE_MSG(query, "<= ignoring invalid glue, length %d != %d\n",
+					(int)rdata->len, a_len);
+			return KR_STATE_FAIL;
+		}
+		char name_str[KR_DNAME_STR_MAXLEN];
+		char addr_str[INET6_ADDRSTRLEN];
+		WITH_VERBOSE(query) {
+			const int af = (rr->type == KNOT_RRTYPE_A) ? AF_INET : AF_INET6;
+			knot_dname_to_str(name_str, rr->owner, sizeof(name_str));
+			name_str[sizeof(name_str) - 1] = 0;
+			inet_ntop(af, rdata->data, addr_str, sizeof(addr_str));
+		}
+		if (!(query->flags.ALLOW_LOCAL) &&
+			!is_valid_addr(rdata->data, rdata->len)) {
+			QVERBOSE_MSG(query, "<= ignoring invalid glue for "
+				     "'%s': '%s'\n", name_str, addr_str);
+			return KR_STATE_CONSUME; /* Ignore invalid addresses */
+		}
+		int ret = kr_zonecut_add(&query->zone_cut, rr->owner, rdata->data, rdata->len);
+		if (ret != 0) {
+			return KR_STATE_FAIL;
+		}
+
+		++*glue_cnt; /* reduced verbosity */
+		/* QVERBOSE_MSG(query, "<= using glue for "
+			     "'%s': '%s'\n", name_str, addr_str);
+		*/
+	}
+	return KR_STATE_CONSUME;
+}
+
+/** @internal From \a pkt, fetch glue records for name \a ns, and update the cut etc.
+ *
+ * \param glue_cnt the number of accepted addresses (to be incremented)
+ */
+static void fetch_glue(knot_pkt_t *pkt, const knot_dname_t *ns, bool in_bailiwick,
+			struct kr_request *req, const struct kr_query *qry, int *glue_cnt)
+{
+	ranked_rr_array_t *selected[] = kr_request_selected(req);
+	for (knot_section_t i = KNOT_ANSWER; i <= KNOT_ADDITIONAL; ++i) {
+		const knot_pktsection_t *sec = knot_pkt_section(pkt, i);
+		for (unsigned k = 0; k < sec->count; ++k) {
+			const knot_rrset_t *rr = knot_pkt_rr(sec, k);
+			if (!knot_dname_is_equal(ns, rr->owner)) {
+				continue;
+			}
+			if ((rr->type != KNOT_RRTYPE_A) &&
+			    (rr->type != KNOT_RRTYPE_AAAA)) {
+				continue;
+			}
+
+			uint8_t rank = (in_bailiwick && i == KNOT_ANSWER)
+				? (KR_RANK_INITIAL | KR_RANK_AUTH) : KR_RANK_OMIT;
+			(void) kr_ranked_rrarray_add(selected[i], rr, rank,
+							false, qry->uid, &req->pool);
+
+			if ((rr->type == KNOT_RRTYPE_A) &&
+			    (req->ctx->options.NO_IPV4)) {
+				continue;
+			}
+			if ((rr->type == KNOT_RRTYPE_AAAA) &&
+			    (req->ctx->options.NO_IPV6)) {
+				continue;
+			}
+			(void) update_nsaddr(rr, req->current_query, glue_cnt);
+		}
+	}
+}
+
+/** Attempt to find glue for given nameserver name (best effort). */
+static bool has_glue(knot_pkt_t *pkt, const knot_dname_t *ns)
+{
+	for (knot_section_t i = KNOT_ANSWER; i <= KNOT_ADDITIONAL; ++i) {
+		const knot_pktsection_t *sec = knot_pkt_section(pkt, i);
+		for (unsigned k = 0; k < sec->count; ++k) {
+			const knot_rrset_t *rr = knot_pkt_rr(sec, k);
+			if (knot_dname_is_equal(ns, rr->owner) &&
+			    (rr->type == KNOT_RRTYPE_A || rr->type == KNOT_RRTYPE_AAAA)) {
+				return true;
+			}
+		}
+	}
+	return false;
+}
+
+/** @internal Update the cut with another NS(+glue) record.
+ * @param current_cut is cut name before this packet.
+ * @return _DONE if cut->name changes, _FAIL on error, and _CONSUME otherwise. */
+static int update_cut(knot_pkt_t *pkt, const knot_rrset_t *rr,
+		      struct kr_request *req, const knot_dname_t *current_cut,
+		      int *glue_cnt)
+{
+	struct kr_query *qry = req->current_query;
+	struct kr_zonecut *cut = &qry->zone_cut;
+	int state = KR_STATE_CONSUME;
+
+	/* New authority MUST be at/below the authority of the current cut;
+	 * also qname must be below new authority;
+	 * otherwise it's a possible cache injection attempt. */
+	const bool ok = knot_dname_in_bailiwick(rr->owner, current_cut) >= 0
+		     && knot_dname_in_bailiwick(qry->sname, rr->owner)  >= 0;
+	if (!ok) {
+		VERBOSE_MSG("<= authority: ns outside bailiwick\n");
+#ifdef STRICT_MODE
+		return KR_STATE_FAIL;
+#else
+		/* Workaround: ignore out-of-bailiwick NSs for authoritative answers,
+		 * but fail for referrals. This is important to detect lame answers. */
+		if (knot_pkt_section(pkt, KNOT_ANSWER)->count == 0) {
+			state = KR_STATE_FAIL;
+		}
+		return state;
+#endif
+	}
+
+	/* Update zone cut name */
+	if (!knot_dname_is_equal(rr->owner, cut->name)) {
+		/* Remember parent cut and descend to new (keep keys and TA). */
+		struct kr_zonecut *parent = mm_alloc(&req->pool, sizeof(*parent));
+		if (parent) {
+			memcpy(parent, cut, sizeof(*parent));
+			kr_zonecut_init(cut, rr->owner, &req->pool);
+			cut->key = parent->key;
+			cut->trust_anchor = parent->trust_anchor;
+			cut->parent = parent;
+		} else {
+			kr_zonecut_set(cut, rr->owner);
+		}
+		state = KR_STATE_DONE;
+	}
+
+	/* Fetch glue for each NS */
+	knot_rdata_t *rdata_i = rr->rrs.rdata;
+	for (unsigned i = 0; i < rr->rrs.count;
+			++i, rdata_i = knot_rdataset_next(rdata_i)) {
+		const knot_dname_t *ns_name = knot_ns_name(rdata_i);
+		/* Glue is mandatory for NS below zone */
+		if (knot_dname_in_bailiwick(ns_name, rr->owner) >= 0
+		    && !has_glue(pkt, ns_name)) {
+			const char *msg =
+				"<= authority: missing mandatory glue, skipping NS";
+			WITH_VERBOSE(qry) {
+				auto_free char *ns_str = kr_dname_text(ns_name);
+				VERBOSE_MSG("%s %s\n", msg, ns_str);
+			}
+			continue;
+		}
+		int ret = kr_zonecut_add(cut, ns_name, NULL, 0);
+		assert(!ret); (void)ret;
+
+		/* Choose when to use glue records. */
+		const bool in_bailiwick =
+			knot_dname_in_bailiwick(ns_name, current_cut) >= 0;
+		bool do_fetch;
+		if (qry->flags.PERMISSIVE) {
+			do_fetch = true;
+		} else if (qry->flags.STRICT) {
+			/* Strict mode uses only mandatory glue. */
+			do_fetch = knot_dname_in_bailiwick(ns_name, cut->name) >= 0;
+		} else {
+			/* Normal mode uses in-bailiwick glue. */
+			do_fetch = in_bailiwick;
+		}
+		if (do_fetch) {
+			fetch_glue(pkt, ns_name, in_bailiwick, req, qry, glue_cnt);
+		}
+	}
+
+	return state;
+}
+
+/** Compute rank appropriate for RRs present in the packet.
+ * @param answer whether the RR is from answer or authority section
+ * @param is_nonauth: from referral or forwarding (etc.) */
+static uint8_t get_initial_rank(const knot_rrset_t *rr, const struct kr_query *qry,
+				const bool answer, const bool is_nonauth)
+{
+	/* For RRSIGs, ensure the KR_RANK_AUTH flag corresponds to the signed RR. */
+	uint16_t type = kr_rrset_type_maysig(rr);
+
+	if (qry->flags.CACHED) {
+		return rr->additional ? *(uint8_t *)rr->additional : KR_RANK_OMIT;
+		/* ^^ Current use case for "cached" RRs without rank: hints module. */
+	}
+	if (answer || type == KNOT_RRTYPE_DS
+	    || type == KNOT_RRTYPE_SOA /* needed for aggressive negative caching */
+	    || type == KNOT_RRTYPE_NSEC || type == KNOT_RRTYPE_NSEC3) {
+		/* We almost always want these validated, and it should be possible. */
+		return KR_RANK_INITIAL | KR_RANK_AUTH;
+	}
+	/* Be aggressive: try to validate anything else (almost never extra latency). */
+	return KR_RANK_TRY;
+	/* TODO: this classifier of authoritativity may not be perfect yet. */
+}
+
+static int pick_authority(knot_pkt_t *pkt, struct kr_request *req, bool to_wire)
+{
+	struct kr_query *qry = req->current_query;
+	const knot_pktsection_t *ns = knot_pkt_section(pkt, KNOT_AUTHORITY);
+
+	const knot_dname_t *zonecut_name = qry->zone_cut.name;
+	bool referral = !knot_wire_get_aa(pkt->wire);
+	if (referral) {
+		/* zone cut already updated by process_authority()
+		 * use parent zonecut name */
+		zonecut_name = qry->zone_cut.parent ? qry->zone_cut.parent->name : qry->zone_cut.name;
+		to_wire = false;
+	}
+
+	for (unsigned i = 0; i < ns->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(ns, i);
+		if (rr->rclass != KNOT_CLASS_IN
+		    || knot_dname_in_bailiwick(rr->owner, zonecut_name) < 0) {
+			continue;
+		}
+		uint8_t rank = get_initial_rank(rr, qry, false,
+						qry->flags.FORWARD || referral);
+		int ret = kr_ranked_rrarray_add(&req->auth_selected, rr,
+						rank, to_wire, qry->uid, &req->pool);
+		if (ret != kr_ok()) {
+			return ret;
+		}
+	}
+
+	return kr_ok();
+}
+
+static int process_authority(knot_pkt_t *pkt, struct kr_request *req)
+{
+	struct kr_query *qry = req->current_query;
+	assert(!(qry->flags.STUB));
+
+	int result = KR_STATE_CONSUME;
+	if (qry->flags.FORWARD) {
+		return result;
+	}
+
+	const knot_pktsection_t *ns = knot_pkt_section(pkt, KNOT_AUTHORITY);
+	const knot_pktsection_t *an = knot_pkt_section(pkt, KNOT_ANSWER);
+
+#ifdef STRICT_MODE
+	/* AA, terminate resolution chain. */
+	if (knot_wire_get_aa(pkt->wire)) {
+		return KR_STATE_CONSUME;
+	}
+#else
+	/* Work around servers sending back CNAME with different delegation and no AA. */
+	if (an->count > 0 && ns->count > 0) {
+		const knot_rrset_t *rr = knot_pkt_rr(an, 0);
+		if (rr->type == KNOT_RRTYPE_CNAME) {
+			return KR_STATE_CONSUME;
+		}
+		/* Work around for these NSs which are authoritative both for
+		 * parent and child and mixes data from both zones in single answer */
+		if (knot_wire_get_aa(pkt->wire) &&
+		    (rr->type == qry->stype) &&
+		    (knot_dname_is_equal(rr->owner, qry->sname))) {
+			return KR_STATE_CONSUME;
+		}
+	}
+#endif
+	/* Remember current bailiwick for NS processing. */
+	const knot_dname_t *current_zone_cut = qry->zone_cut.name;
+	bool ns_record_exists = false;
+	int glue_cnt = 0;
+	/* Update zone cut information. */
+	for (unsigned i = 0; i < ns->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(ns, i);
+		if (rr->type == KNOT_RRTYPE_NS) {
+			ns_record_exists = true;
+			int state = update_cut(pkt, rr, req, current_zone_cut, &glue_cnt);
+			switch(state) {
+			case KR_STATE_DONE: result = state; break;
+			case KR_STATE_FAIL: return state; break;
+			default:              /* continue */ break;
+			}
+		} else if (rr->type == KNOT_RRTYPE_SOA
+			   && knot_dname_in_bailiwick(rr->owner, qry->zone_cut.name) > 0) {
+			/* SOA below cut in authority indicates different authority,
+			 * but same NS set. */
+			qry->zone_cut.name = knot_dname_copy(rr->owner, &req->pool);
+		}
+	}
+
+	/* Nameserver is authoritative for both parent side and the child side of the
+	 * delegation may respond with an NS record in the answer section, and still update
+	 * the zone cut (e.g. what a.gtld-servers.net would respond for `com NS`) */
+	if (!ns_record_exists && knot_wire_get_aa(pkt->wire)) {
+		for (unsigned i = 0; i < an->count; ++i) {
+			const knot_rrset_t *rr = knot_pkt_rr(an, i);
+			if (rr->type == KNOT_RRTYPE_NS
+			    && knot_dname_in_bailiwick(rr->owner, qry->zone_cut.name) > 0) {
+				/* NS below cut in authority indicates different authority,
+				 * but same NS set. */
+				qry->zone_cut.name = knot_dname_copy(rr->owner, &req->pool);
+			}
+		}
+	}
+
+	if (glue_cnt) {
+		VERBOSE_MSG("<= loaded %d glue addresses\n", glue_cnt);
+	}
+
+
+	if ((qry->flags.DNSSEC_WANT) && (result == KR_STATE_CONSUME)) {
+		if (knot_wire_get_aa(pkt->wire) == 0 &&
+		    knot_wire_get_ancount(pkt->wire) == 0 &&
+		    ns_record_exists) {
+			/* Unhelpful referral
+			   Prevent from validating as an authoritative answer */
+			result = KR_STATE_DONE;
+		}
+	}
+
+	/* CONSUME => Unhelpful referral.
+	 * DONE    => Zone cut updated.  */
+	return result;
+}
+
+static void finalize_answer(knot_pkt_t *pkt, struct kr_query *qry, struct kr_request *req)
+{
+	/* Finalize header */
+	knot_pkt_t *answer = req->answer;
+	knot_wire_set_rcode(answer->wire, knot_wire_get_rcode(pkt->wire));
+}
+
+static int unroll_cname(knot_pkt_t *pkt, struct kr_request *req, bool referral, const knot_dname_t **cname_ret)
+{
+	struct kr_query *query = req->current_query;
+	assert(!(query->flags.STUB));
+	/* Process answer type */
+	const knot_pktsection_t *an = knot_pkt_section(pkt, KNOT_ANSWER);
+	const knot_dname_t *cname = NULL;
+	const knot_dname_t *pending_cname = query->sname;
+	unsigned cname_chain_len = 0;
+	bool is_final = (query->parent == NULL);
+	uint32_t iter_count = 0;
+	bool strict_mode = (query->flags.STRICT);
+	do {
+		/* CNAME was found at previous iteration, but records may not follow the correct order.
+		 * Try to find records for pending_cname owner from section start. */
+		cname = pending_cname;
+		pending_cname = NULL;
+		const int cname_labels = knot_dname_labels(cname, NULL);
+		for (unsigned i = 0; i < an->count; ++i) {
+			const knot_rrset_t *rr = knot_pkt_rr(an, i);
+
+			/* Skip the RR if its owner+type doesn't interest us. */
+			const uint16_t type = kr_rrset_type_maysig(rr);
+			const bool type_OK = rr->type == query->stype || type == query->stype
+				|| type == KNOT_RRTYPE_CNAME || type == KNOT_RRTYPE_DNAME;
+				/* TODO: actually handle DNAMEs */
+			if (rr->rclass != KNOT_CLASS_IN || !type_OK
+			    || !knot_dname_is_equal(rr->owner, cname)
+			    || knot_dname_in_bailiwick(rr->owner, query->zone_cut.name) < 0) {
+				continue;
+			}
+
+			if (rr->type == KNOT_RRTYPE_RRSIG) {
+				int rrsig_labels = knot_rrsig_labels(rr->rrs.rdata);
+				if (rrsig_labels > cname_labels) {
+					/* clearly wrong RRSIG, don't pick it.
+					 * don't fail immediately,
+					 * let validator work. */
+					continue;
+				}
+				if (rrsig_labels < cname_labels) {
+					query->flags.DNSSEC_WEXPAND = true;
+				}
+			}
+
+			/* Process records matching current SNAME */
+			int state = KR_STATE_FAIL;
+			bool to_wire = false;
+			if (is_final) {
+				/* if not referral, mark record to be written to final answer */
+				to_wire = !referral;
+			} else {
+				int cnt_ = 0;
+				state = update_nsaddr(rr, query->parent, &cnt_);
+				if (state == KR_STATE_FAIL) {
+					return state;
+				}
+			}
+			uint8_t rank = get_initial_rank(rr, query, true,
+					query->flags.FORWARD || referral);
+			state = kr_ranked_rrarray_add(&req->answ_selected, rr,
+						      rank, to_wire, query->uid, &req->pool);
+			if (state != kr_ok()) {
+				return KR_STATE_FAIL;
+			}
+			/* Jump to next CNAME target */
+			if ((query->stype == KNOT_RRTYPE_CNAME) || (rr->type != KNOT_RRTYPE_CNAME)) {
+				continue;
+			}
+			cname_chain_len += 1;
+			pending_cname = knot_cname_name(rr->rrs.rdata);
+			if (!pending_cname) {
+				break;
+			}
+			if (cname_chain_len > an->count || cname_chain_len > KR_CNAME_CHAIN_LIMIT) {
+				VERBOSE_MSG("<= too long cname chain\n");
+				return KR_STATE_FAIL;
+			}
+			/* Don't use pending_cname immediately.
+			 * There are can be records for "old" cname. */
+		}
+		if (!pending_cname) {
+			break;
+		}
+		if (knot_dname_is_equal(cname, pending_cname)) {
+			VERBOSE_MSG("<= cname chain loop\n");
+			return KR_STATE_FAIL;
+		}
+		/* In strict mode, explicitly fetch each CNAME target. */
+		if (strict_mode) {
+			cname = pending_cname;
+			break;
+		}
+		/* Information outside bailiwick is not trusted. */
+		if (knot_dname_in_bailiwick(pending_cname, query->zone_cut.name) < 0) {
+			cname = pending_cname;
+			break;
+		}
+		/* The validator still can't handle multiple zones in one answer,
+		 * so we only follow if a single label is replaced.
+		 * TODO: this still isn't 100%, as the target might have a NS+DS,
+		 * possibly leading to a SERVFAIL for the in-bailiwick name. */
+		const int pending_labels = knot_dname_labels(pending_cname, NULL);
+		if (pending_labels != cname_labels) {
+			cname = pending_cname;
+			break;
+		}
+		if (knot_dname_matched_labels(pending_cname, cname) !=
+		    (cname_labels - 1)) {
+			cname = pending_cname;
+			break;
+		}
+	} while (++iter_count < KR_CNAME_CHAIN_LIMIT);
+	if (iter_count >= KR_CNAME_CHAIN_LIMIT) {
+		VERBOSE_MSG("<= too long cname chain\n");
+		return KR_STATE_FAIL;
+	}
+	*cname_ret = cname;
+	return kr_ok();
+}
+
+static int process_referral_answer(knot_pkt_t *pkt, struct kr_request *req)
+{
+	const knot_dname_t *cname = NULL;
+	int state = unroll_cname(pkt, req, true, &cname);
+	if (state != kr_ok()) {
+		return KR_STATE_FAIL;
+	}
+	struct kr_query *query = req->current_query;
+	if (!(query->flags.CACHED)) {
+		/* If not cached (i.e. got from upstream)
+		 * make sure that this is not an authoritative answer
+		 * (even with AA=1) for other layers.
+		 * There can be answers with AA=1,
+		 * empty answer section and NS in authority.
+		 * Clearing of AA prevents them from
+		 * caching in the packet cache.
+		 * If packet already cached, don't touch him. */
+		knot_wire_clear_aa(pkt->wire);
+	}
+	state = pick_authority(pkt, req, false);
+	return state == kr_ok() ? KR_STATE_DONE : KR_STATE_FAIL;
+}
+
+static int process_final(knot_pkt_t *pkt, struct kr_request *req,
+			 const knot_dname_t *cname)
+{
+	const int pkt_class = kr_response_classify(pkt);
+	struct kr_query *query = req->current_query;
+	ranked_rr_array_t *array = &req->answ_selected;
+	for (size_t i = 0; i < array->len; ++i) {
+		const knot_rrset_t *rr = array->at[i]->rr;
+		if (!knot_dname_is_equal(rr->owner, cname)) {
+			continue;
+		}
+		if ((rr->rclass != query->sclass) ||
+		    (rr->type != query->stype)) {
+			continue;
+		}
+		const bool to_wire = ((pkt_class & (PKT_NXDOMAIN|PKT_NODATA)) != 0);
+		const int state = pick_authority(pkt, req, to_wire);
+		if (state != kr_ok()) {
+			return KR_STATE_FAIL;
+		}
+		if (!array->at[i]->to_wire) {
+			const size_t last_idx = array->len - 1;
+			size_t j = i;
+			ranked_rr_array_entry_t *entry = array->at[i];
+			/* Relocate record to the end, after current cname */
+			while (j < last_idx) {
+				array->at[j] = array->at[j + 1];
+				++j;
+			}
+			array->at[last_idx] = entry;
+			entry->to_wire = true;
+		}
+		finalize_answer(pkt, query, req);
+		return KR_STATE_DONE;
+	}
+	return kr_ok();
+}
+
+static int process_answer(knot_pkt_t *pkt, struct kr_request *req)
+{
+	struct kr_query *query = req->current_query;
+
+	/* Response for minimized QNAME.  Note that current iterator's minimization
+	 * is only able ask one label below a zone cut.
+	 * NODATA   => may be empty non-terminal, retry (found zone cut)
+	 * NOERROR  => found zone cut, retry, except the case described below
+	 * NXDOMAIN => parent is zone cut, retry as a workaround for bad authoritatives
+	 */
+	const bool is_final = (query->parent == NULL);
+	const int pkt_class = kr_response_classify(pkt);
+	const knot_dname_t * pkt_qname = knot_pkt_qname(pkt);
+	if (!knot_dname_is_equal(pkt_qname, query->sname) &&
+	    (pkt_class & (PKT_NOERROR|PKT_NXDOMAIN|PKT_REFUSED|PKT_NODATA))) {
+		/* Check for parent server that is authoritative for child zone,
+		 * several CCTLDs where the SLD and TLD have the same name servers */
+		const knot_pktsection_t *ans = knot_pkt_section(pkt, KNOT_ANSWER);
+		if ((pkt_class & (PKT_NOERROR)) && ans->count > 0 &&
+		     knot_dname_is_equal(pkt_qname, query->zone_cut.name)) {
+			VERBOSE_MSG("<= continuing with qname minimization\n");
+		} else {
+			/* fall back to disabling minimization */
+			VERBOSE_MSG("<= retrying with non-minimized name\n");
+			query->flags.NO_MINIMIZE = true;
+		}
+		return KR_STATE_CONSUME;
+	}
+
+	/* This answer didn't improve resolution chain, therefore must be authoritative (relaxed to negative). */
+	if (!is_authoritative(pkt, query)) {
+		if (!(query->flags.FORWARD) &&
+		    pkt_class & (PKT_NXDOMAIN|PKT_NODATA)) {
+			VERBOSE_MSG("<= lame response: non-auth sent negative response\n");
+			return KR_STATE_FAIL;
+		}
+	}
+
+	const knot_dname_t *cname = NULL;
+	/* Process answer type */
+	int state = unroll_cname(pkt, req, false, &cname);
+	if (state != kr_ok()) {
+		return state;
+	}
+	/* Make sure that this is an authoritative answer (even with AA=0) for other layers */
+	knot_wire_set_aa(pkt->wire);
+	/* Either way it resolves current query. */
+	query->flags.RESOLVED = true;
+	/* Follow canonical name as next SNAME. */
+	if (!knot_dname_is_equal(cname, query->sname)) {
+		/* Check if target record has been already copied */
+		query->flags.CNAME = true;
+		if (is_final) {
+			state = process_final(pkt, req, cname);
+			if (state != kr_ok()) {
+				return state;
+			}
+		} else if ((query->flags.FORWARD) &&
+			   ((query->stype == KNOT_RRTYPE_DS) ||
+			    (query->stype == KNOT_RRTYPE_NS))) {
+			/* CNAME'ed answer for DS or NS subquery.
+			 * Treat it as proof of zonecut nonexistance. */
+			return KR_STATE_DONE;
+		}
+		VERBOSE_MSG("<= cname chain, following\n");
+		/* Check if the same query was followed in the same CNAME chain. */
+		for (const struct kr_query *q = query->cname_parent; q != NULL;
+				q = q->cname_parent) {
+			if (q->sclass == query->sclass &&
+			    q->stype == query->stype   &&
+			    knot_dname_is_equal(q->sname, cname)) {
+				VERBOSE_MSG("<= cname chain loop\n");
+				return KR_STATE_FAIL;
+			}
+		}
+		struct kr_query *next = kr_rplan_push(&req->rplan, query->parent, cname, query->sclass, query->stype);
+		if (!next) {
+			return KR_STATE_FAIL;
+		}
+		next->flags.AWAIT_CUT = true;
+
+		/* Copy transitive flags from original query to CNAME followup. */
+		next->flags.TRACE = query->flags.TRACE;
+		next->flags.ALWAYS_CUT = query->flags.ALWAYS_CUT;
+		next->flags.NO_MINIMIZE = query->flags.NO_MINIMIZE;
+		next->flags.NO_THROTTLE = query->flags.NO_THROTTLE;
+
+		if (query->flags.FORWARD) {
+			next->forward_flags.CNAME = true;
+			if (query->parent == NULL) {
+				state = kr_nsrep_copy_set(&next->ns, &query->ns);
+				if (state != kr_ok()) {
+					return KR_STATE_FAIL;
+				}
+			}
+		}
+		next->cname_parent = query;
+		/* Want DNSSEC if and only if it's posible to secure
+		 * this name (i.e. iff it is covered by a TA) */
+		if (kr_ta_covers_qry(req->ctx, cname, query->stype)) {
+			next->flags.DNSSEC_WANT = true;
+		} else {
+			next->flags.DNSSEC_WANT = false;
+		}
+		if (!(query->flags.FORWARD) ||
+		    (query->flags.DNSSEC_WEXPAND)) {
+			state = pick_authority(pkt, req, false);
+			if (state != kr_ok()) {
+				return KR_STATE_FAIL;
+			}
+		}
+	} else if (!query->parent) {
+		/* Answer for initial query */
+		const bool to_wire = ((pkt_class & (PKT_NXDOMAIN|PKT_NODATA)) != 0);
+		state = pick_authority(pkt, req, to_wire);
+		if (state != kr_ok()) {
+			return KR_STATE_FAIL;
+		}
+		finalize_answer(pkt, query, req);
+	} else {
+		/* Answer for sub-query; DS, IP for NS etc.
+		 * It may contains NSEC \ NSEC3 records for
+		 * data non-existence or wc expansion proving.
+		 * If yes, they must be validated by validator.
+		 * If no, authority section is unuseful.
+		 * dnssec\nsec.c & dnssec\nsec3.c use
+		 * rrsets from incoming packet.
+		 * validator uses answer_selected & auth_selected.
+		 * So, if nsec\nsec3 records are present in authority,
+		 * pick_authority() must be called.
+		 * TODO refactor nsec\nsec3 modules to work with
+		 * answer_selected & auth_selected instead of incoming pkt. */
+		bool auth_is_unuseful = true;
+		const knot_pktsection_t *ns = knot_pkt_section(pkt, KNOT_AUTHORITY);
+		for (unsigned i = 0; i < ns->count; ++i) {
+			const knot_rrset_t *rr = knot_pkt_rr(ns, i);
+			if (rr->type == KNOT_RRTYPE_NSEC ||
+			    rr->type == KNOT_RRTYPE_NSEC3) {
+				auth_is_unuseful = false;
+				break;
+			}
+		}
+		if (!auth_is_unuseful) {
+			state = pick_authority(pkt, req, false);
+			if (state != kr_ok()) {
+				return KR_STATE_FAIL;
+			}
+		}
+	}
+	return KR_STATE_DONE;
+}
+
+/** @internal like process_answer() but for the STUB mode. */
+static int process_stub(knot_pkt_t *pkt, struct kr_request *req)
+{
+	struct kr_query *query = req->current_query;
+	assert(query->flags.STUB);
+	/* Pick all answer RRs. */
+	const knot_pktsection_t *an = knot_pkt_section(pkt, KNOT_ANSWER);
+	for (unsigned i = 0; i < an->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(an, i);
+		int err = kr_ranked_rrarray_add(&req->answ_selected, rr,
+			      KR_RANK_OMIT | KR_RANK_AUTH, true, query->uid, &req->pool);
+		/* KR_RANK_AUTH: we don't have the records directly from
+		 * an authoritative source, but we do trust the server and it's
+		 * supposed to only send us authoritative records. */
+		if (err != kr_ok()) {
+			return KR_STATE_FAIL;
+		}
+	}
+
+	knot_wire_set_aa(pkt->wire);
+	query->flags.RESOLVED = true;
+	/* Pick authority RRs. */
+	int pkt_class = kr_response_classify(pkt);
+	const bool to_wire = ((pkt_class & (PKT_NXDOMAIN|PKT_NODATA)) != 0);
+	int err = pick_authority(pkt, req, to_wire);
+	if (err != kr_ok()) {
+		return KR_STATE_FAIL;
+	}
+
+	finalize_answer(pkt, query, req);
+	return KR_STATE_DONE;
+}
+
+
+/** Error handling, RFC1034 5.3.3, 4d. */
+static int resolve_error(knot_pkt_t *pkt, struct kr_request *req)
+{
+	return KR_STATE_FAIL;
+}
+
+/* State-less single resolution iteration step, not needed. */
+static int reset(kr_layer_t *ctx)  { return KR_STATE_PRODUCE; }
+
+/* Set resolution context and parameters. */
+static int begin(kr_layer_t *ctx)
+{
+	if (ctx->state & (KR_STATE_DONE|KR_STATE_FAIL)) {
+		return ctx->state;
+	}
+	/*
+	 * RFC7873 5.4 extends the QUERY operation code behaviour in order to
+	 * be able to generate requests for server cookies. Such requests have
+	 * QDCOUNT equal to zero and must contain a cookie option.
+	 * Server cookie queries must be handled by the cookie module/layer
+	 * before this layer.
+	 */
+	const knot_pkt_t *pkt = ctx->req->qsource.packet;
+	if (!pkt || knot_wire_get_qdcount(pkt->wire) == 0) {
+		return KR_STATE_FAIL;
+	}
+
+	struct kr_query *qry = ctx->req->current_query;
+	/* Avoid any other classes, and avoid any meta-types ~~except for ANY~~. */
+	if (qry->sclass != KNOT_CLASS_IN
+	    || (knot_rrtype_is_metatype(qry->stype)
+		    /* && qry->stype != KNOT_RRTYPE_ANY hmm ANY seems broken ATM */)) {
+		knot_wire_set_rcode(ctx->req->answer->wire, KNOT_RCODE_NOTIMPL);
+		return KR_STATE_FAIL;
+	}
+
+	return reset(ctx);
+}
+
+int kr_make_query(struct kr_query *query, knot_pkt_t *pkt)
+{
+	/* Minimize QNAME (if possible). */
+	uint16_t qtype = query->stype;
+	const knot_dname_t *qname = minimized_qname(query, &qtype);
+
+	/* Form a query for the authoritative. */
+	knot_pkt_clear(pkt);
+	int ret = knot_pkt_put_question(pkt, qname, query->sclass, qtype);
+	if (ret != KNOT_EOK) {
+		return ret;
+	}
+
+	/* Query built, expect answer. */
+	query->id = kr_rand_bytes(2);
+	/* We must respect https://tools.ietf.org/html/rfc7766#section-6.2.1
+	 * -  When sending multiple queries over a TCP connection, clients MUST NOT
+	 *    reuse the DNS Message ID of an in-flight query on that connection.
+	 *
+	 * So, if query is going to be sent over TCP connection
+	 * this id can be changed to avoid duplication with query that already was sent
+	 * but didn't receive answer yet.
+	 */
+	knot_wire_set_id(pkt->wire, query->id);
+	pkt->parsed = pkt->size;
+
+	return kr_ok();
+}
+
+static int prepare_query(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	assert(pkt && ctx);
+	struct kr_request *req = ctx->req;
+	struct kr_query *query = req->current_query;
+	if (!query || ctx->state & (KR_STATE_DONE|KR_STATE_FAIL)) {
+		return ctx->state;
+	}
+
+	/* Make query */
+	int ret = kr_make_query(query, pkt);
+	if (ret != 0) {
+		return KR_STATE_FAIL;
+	}
+
+	WITH_VERBOSE(query) {
+		KR_DNAME_GET_STR(name_str, query->sname);
+		KR_RRTYPE_GET_STR(type_str, query->stype);
+		QVERBOSE_MSG(query, "'%s' type '%s' new uid was assigned .%02u, parent uid .%02u\n",
+			    name_str, type_str, req->rplan.next_uid,
+			    query->parent ? query->parent->uid : 0);
+	}
+
+	query->uid = req->rplan.next_uid;
+	req->rplan.next_uid += 1;
+
+	return KR_STATE_CONSUME;
+}
+
+static int resolve_badmsg(knot_pkt_t *pkt, struct kr_request *req, struct kr_query *query)
+{
+
+#ifndef STRICT_MODE
+	/* Work around broken auths/load balancers */
+	if (query->flags.SAFEMODE) {
+		return resolve_error(pkt, req);
+	} else if (query->flags.NO_MINIMIZE) {
+		query->flags.SAFEMODE = true;
+		return KR_STATE_DONE;
+	} else {
+		query->flags.NO_MINIMIZE = true;
+		return KR_STATE_DONE;
+	}
+#else
+		return resolve_error(pkt, req);
+#endif
+}
+
+static int resolve_notimpl(knot_pkt_t *pkt, struct kr_request *req, struct kr_query *qry)
+{
+	if (qry->stype == KNOT_RRTYPE_RRSIG && qry->parent != NULL) {
+		/* RRSIG subquery have got NOTIMPL.
+		 * Possible scenario - same NS is autoritative for child and parent,
+		 * but child isn't signed.
+		 * We got delegation to parent,
+		 * then NS responded as NS for child zone.
+		 * Answer contained record been requested, but no RRSIGs,
+		 * Validator issued RRSIG query then. If qname is zone name,
+		 * we can get NOTIMPL. Ask for DS to find out security status.
+		 * TODO - maybe it would be better to do this in validator, when
+		 * RRSIG revalidation occurs.
+		 */
+		struct kr_rplan *rplan = &req->rplan;
+		struct kr_query *next = kr_rplan_push(rplan, qry->parent, qry->sname,
+						qry->sclass, KNOT_RRTYPE_DS);
+		if (!next) {
+			return KR_STATE_FAIL;
+		}
+		kr_zonecut_set(&next->zone_cut, qry->parent->zone_cut.name);
+		kr_zonecut_copy(&next->zone_cut, &qry->parent->zone_cut);
+		kr_zonecut_copy_trust(&next->zone_cut, &qry->parent->zone_cut);
+		next->flags.DNSSEC_WANT = true;
+		qry->flags.RESOLVED = true;
+		return KR_STATE_DONE;
+	}
+	return resolve_badmsg(pkt, req, qry);
+}
+
+/** Resolve input query or continue resolution with followups.
+ *
+ *  This roughly corresponds to RFC1034, 5.3.3 4a-d.
+ */
+static int resolve(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	assert(pkt && ctx);
+	struct kr_request *req = ctx->req;
+	struct kr_query *query = req->current_query;
+	if (!query) {
+		return ctx->state;
+	}
+
+	WITH_VERBOSE(query) {
+		if (query->flags.TRACE) {
+			auto_free char *pkt_text = kr_pkt_text(pkt);
+			VERBOSE_MSG("<= answer received: \n%s\n", pkt_text);
+		}
+	}
+
+	if (query->flags.RESOLVED || query->flags.BADCOOKIE_AGAIN) {
+		return ctx->state;
+	}
+
+	/* Check for packet processing errors first.
+	 * Note - we *MUST* check if it has at least a QUESTION,
+	 * otherwise it would crash on accessing QNAME. */
+#ifdef STRICT_MODE
+	if (pkt->parsed < pkt->size) {
+		VERBOSE_MSG("<= pkt contains excessive data\n");
+		return resolve_badmsg(pkt, req, query);
+	} else
+#endif
+	if (pkt->parsed <= KNOT_WIRE_HEADER_SIZE) {
+		VERBOSE_MSG("<= malformed response\n");
+		return resolve_badmsg(pkt, req, query);
+	} else if (!is_paired_to_query(pkt, query)) {
+		VERBOSE_MSG("<= ignoring mismatching response\n");
+		/* Force TCP, to work around authoritatives messing up question
+		 * without yielding to spoofed responses. */
+		query->flags.TCP = true;
+		return resolve_badmsg(pkt, req, query);
+	} else if (knot_wire_get_tc(pkt->wire)) {
+		VERBOSE_MSG("<= truncated response, failover to TCP\n");
+		if (query) {
+			/* Fail if already on TCP. */
+			if (query->flags.TCP) {
+				VERBOSE_MSG("<= TC=1 with TCP, bailing out\n");
+				return resolve_error(pkt, req);
+			}
+			query->flags.TCP = true;
+		}
+		return KR_STATE_CONSUME;
+	}
+
+#ifndef NOVERBOSELOG
+	const knot_lookup_t *rcode = knot_lookup_by_id(knot_rcode_names, knot_wire_get_rcode(pkt->wire));
+#endif
+
+	/* Check response code. */
+	switch(knot_wire_get_rcode(pkt->wire)) {
+	case KNOT_RCODE_NOERROR:
+	case KNOT_RCODE_NXDOMAIN:
+		break; /* OK */
+	case KNOT_RCODE_REFUSED:
+	case KNOT_RCODE_SERVFAIL: {
+		if (query->flags.STUB) {
+			 /* Pass through in stub mode */
+			break;
+		}
+		VERBOSE_MSG("<= rcode: %s\n", rcode ? rcode->name : "??");
+		query->fails += 1;
+		if (query->fails >= KR_QUERY_NSRETRY_LIMIT) {
+			query->fails = 0; /* Reset per-query counter. */
+			return resolve_error(pkt, req);
+		} else {
+			if (!query->flags.FORWARD) {
+				query->flags.NO_MINIMIZE = true; /* Drop minimisation as a safe-guard. */
+			}
+			return KR_STATE_CONSUME;
+		}
+	}
+	case KNOT_RCODE_FORMERR:
+		VERBOSE_MSG("<= rcode: %s\n", rcode ? rcode->name : "??");
+		return resolve_badmsg(pkt, req, query);
+	case KNOT_RCODE_NOTIMPL:
+		VERBOSE_MSG("<= rcode: %s\n", rcode ? rcode->name : "??");
+		return resolve_notimpl(pkt, req, query);
+	default:
+		VERBOSE_MSG("<= rcode: %s\n", rcode ? rcode->name : "??");
+		return resolve_error(pkt, req);
+	}
+
+	/* Forwarding/stub mode is special. */
+	if (query->flags.STUB) {
+		return process_stub(pkt, req);
+	}
+
+	/* Resolve authority to see if it's referral or authoritative. */
+	int state = process_authority(pkt, req);
+	switch(state) {
+	case KR_STATE_CONSUME: /* Not referral, process answer. */
+		VERBOSE_MSG("<= rcode: %s\n", rcode ? rcode->name : "??");
+		state = process_answer(pkt, req);
+		break;
+	case KR_STATE_DONE: /* Referral */
+		state = process_referral_answer(pkt,req);
+		VERBOSE_MSG("<= referral response, follow\n");
+		break;
+	default:
+		break;
+	}
+
+	return state;
+}
+
+/** Module implementation. */
+const kr_layer_api_t *iterate_layer(struct kr_module *module)
+{
+	static const kr_layer_api_t _layer = {
+		.begin = &begin,
+		.reset = &reset,
+		.consume = &resolve,
+		.produce = &prepare_query
+	};
+	return &_layer;
+}
+
+KR_MODULE_EXPORT(iterate)
+
+#undef VERBOSE_MSG
diff --git a/lib/layer/iterate.h b/lib/layer/iterate.h
new file mode 100644
index 0000000..a9395bf
--- /dev/null
+++ b/lib/layer/iterate.h
@@ -0,0 +1,36 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "lib/layer.h"
+#include "lib/rplan.h"
+
+/* Packet classification. */
+enum {
+	PKT_NOERROR   = 1 << 0, /* Positive response */
+	PKT_NODATA    = 1 << 1, /* No data response */
+	PKT_NXDOMAIN  = 1 << 2, /* Negative response */
+	PKT_REFUSED   = 1 << 3, /* Refused response */
+	PKT_ERROR     = 1 << 4  /* Bad message */
+};
+
+/** Classify response by type. */
+int kr_response_classify(const knot_pkt_t *pkt);
+
+/** Make next iterative query. */
+KR_EXPORT
+int kr_make_query(struct kr_query *query, knot_pkt_t *pkt);
diff --git a/lib/layer/validate.c b/lib/layer/validate.c
new file mode 100644
index 0000000..55c3ad7
--- /dev/null
+++ b/lib/layer/validate.c
@@ -0,0 +1,1133 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <sys/time.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <contrib/cleanup.h>
+#include <libknot/packet/wire.h>
+#include <libknot/rrtype/rdname.h>
+#include <libknot/rrtype/rrsig.h>
+#include <libdnssec/error.h>
+
+#include "lib/dnssec/nsec.h"
+#include "lib/dnssec/nsec3.h"
+#include "lib/dnssec.h"
+#include "lib/layer.h"
+#include "lib/resolve.h"
+#include "lib/rplan.h"
+#include "lib/utils.h"
+#include "lib/defines.h"
+#include "lib/module.h"
+
+#define VERBOSE_MSG(qry, ...) QRVERBOSE(qry, "vldr", __VA_ARGS__)
+
+#define MAX_REVALIDATION_CNT 2
+
+/**
+ * Search in section for given type.
+ * @param sec  Packet section.
+ * @param type Type to search for.
+ * @return     True if found.
+ */
+static bool section_has_type(const knot_pktsection_t *sec, uint16_t type)
+{
+	if (!sec) {
+		return false;
+	}
+
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(sec, i);
+		if (rr->type == type) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
+static bool pkt_has_type(const knot_pkt_t *pkt, uint16_t type)
+{
+	if (!pkt) {
+		return false;
+	}
+
+	if (section_has_type(knot_pkt_section(pkt, KNOT_ANSWER), type)) {
+		return true;
+	}
+	if (section_has_type(knot_pkt_section(pkt, KNOT_AUTHORITY), type)) {
+		return true;
+	}
+	return section_has_type(knot_pkt_section(pkt, KNOT_ADDITIONAL), type);
+}
+
+static void log_bogus_rrsig(kr_rrset_validation_ctx_t *vctx, const struct kr_query *qry,
+			    const knot_rrset_t *rr, const char *msg) {
+	WITH_VERBOSE(qry) {
+		auto_free char *name_text = kr_dname_text(rr->owner);
+		auto_free char *type_text = kr_rrtype_text(rr->type);
+		VERBOSE_MSG(qry, ">< %s: %s %s "
+			    "(%u matching RRSIGs, %u expired, %u not yet valid, "
+			    "%u invalid signer, %u invalid label count, %u invalid key, "
+			    "%u invalid crypto, %u invalid NSEC)\n",
+			    msg, name_text, type_text, vctx->rrs_counters.matching_name_type,
+			    vctx->rrs_counters.expired, vctx->rrs_counters.notyet,
+			    vctx->rrs_counters.signer_invalid, vctx->rrs_counters.labels_invalid,
+			    vctx->rrs_counters.key_invalid, vctx->rrs_counters.crypto_invalid,
+			    vctx->rrs_counters.nsec_invalid);
+	}
+}
+
+static int validate_section(kr_rrset_validation_ctx_t *vctx, const struct kr_query *qry,
+			    knot_mm_t *pool)
+{
+	if (!vctx) {
+		return kr_error(EINVAL);
+	}
+
+	/* Can't use qry->zone_cut.name directly, as this name can
+	 * change when updating cut information before validation.
+	 */
+	vctx->zone_name = vctx->keys ? vctx->keys->owner : NULL;
+
+	int validation_result = 0;
+	for (ssize_t i = 0; i < vctx->rrs->len; ++i) {
+		ranked_rr_array_entry_t *entry = vctx->rrs->at[i];
+		const knot_rrset_t *rr = entry->rr;
+
+		if (entry->yielded || vctx->qry_uid != entry->qry_uid) {
+			continue;
+		}
+
+		if (kr_rank_test(entry->rank, KR_RANK_OMIT)
+		    || kr_rank_test(entry->rank, KR_RANK_SECURE)) {
+			continue; /* these are already OK */
+		}
+
+		if (rr->type == KNOT_RRTYPE_RRSIG) {
+			const knot_dname_t *signer_name = knot_rrsig_signer_name(rr->rrs.rdata);
+			if (!knot_dname_is_equal(vctx->zone_name, signer_name)) {
+				kr_rank_set(&entry->rank, KR_RANK_MISMATCH);
+				vctx->err_cnt += 1;
+				break;
+			}
+			kr_rank_set(&entry->rank, KR_RANK_OMIT);
+			continue;
+		}
+
+		uint8_t rank_orig = entry->rank;
+		validation_result = kr_rrset_validate(vctx, rr);
+		if (validation_result == kr_ok()) {
+			kr_rank_set(&entry->rank, KR_RANK_SECURE);
+
+		} else if (kr_rank_test(rank_orig, KR_RANK_TRY)) {
+			log_bogus_rrsig(vctx, qry, rr,
+					"failed to validate non-authoritative data but continuing");
+			vctx->result = kr_ok();
+			kr_rank_set(&entry->rank, KR_RANK_TRY);
+			/* ^^ BOGUS would be more accurate, but it might change
+			 * to MISMATCH on revalidation, e.g. in test val_referral_nods :-/
+			 */
+
+		} else if (validation_result == kr_error(ENOENT)) {
+			/* no RRSIGs found */
+			kr_rank_set(&entry->rank, KR_RANK_MISSING);
+			vctx->err_cnt += 1;
+			log_bogus_rrsig(vctx, qry, rr, "no valid RRSIGs found");
+		} else {
+			kr_rank_set(&entry->rank, KR_RANK_BOGUS);
+			vctx->err_cnt += 1;
+			log_bogus_rrsig(vctx, qry, rr, "bogus signatures");
+		}
+	}
+	return kr_ok();
+}
+
+static int validate_records(struct kr_request *req, knot_pkt_t *answer, knot_mm_t *pool, bool has_nsec3)
+{
+	struct kr_query *qry = req->current_query;
+	if (!qry->zone_cut.key) {
+		VERBOSE_MSG(qry, "<= no DNSKEY, can't validate\n");
+		return kr_error(EBADMSG);
+	}
+
+	kr_rrset_validation_ctx_t vctx = {
+		.pkt		= answer,
+		.rrs		= &req->answ_selected,
+		.section_id	= KNOT_ANSWER,
+		.keys		= qry->zone_cut.key,
+		.zone_name	= qry->zone_cut.name,
+		.timestamp	= qry->timestamp.tv_sec,
+		.qry_uid	= qry->uid,
+		.has_nsec3	= has_nsec3,
+		.flags		= 0,
+		.err_cnt	= 0,
+		.result		= 0
+	};
+
+	int ret = validate_section(&vctx, qry, pool);
+	req->answ_validated = (vctx.err_cnt == 0);
+	if (ret != kr_ok()) {
+		return ret;
+	}
+
+	uint32_t an_flags = vctx.flags;
+	vctx.rrs	  = &req->auth_selected;
+	vctx.section_id   = KNOT_AUTHORITY;
+	vctx.flags	  = 0;
+	vctx.err_cnt	  = 0;
+	vctx.result	  = 0;
+
+	ret = validate_section(&vctx, qry, pool);
+	req->auth_validated = (vctx.err_cnt == 0);
+	if (ret != kr_ok()) {
+		return ret;
+	}
+
+	/* Records were validated.
+	 * If there is wildcard expansion in answer,
+	 * or optout - flag the query.
+         */
+	if (an_flags & KR_DNSSEC_VFLG_WEXPAND) {
+		qry->flags.DNSSEC_WEXPAND = true;
+	}
+	if (an_flags & KR_DNSSEC_VFLG_OPTOUT) {
+		qry->flags.DNSSEC_OPTOUT = true;
+	}
+
+	return ret;
+}
+
+static int validate_keyset(struct kr_request *req, knot_pkt_t *answer, bool has_nsec3)
+{
+	/* Merge DNSKEY records from answer that are below/at current cut. */
+	struct kr_query *qry = req->current_query;
+	bool updated_key = false;
+	const knot_pktsection_t *an = knot_pkt_section(answer, KNOT_ANSWER);
+	for (unsigned i = 0; i < an->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(an, i);
+		if (rr->type != KNOT_RRTYPE_DNSKEY
+		    || knot_dname_in_bailiwick(rr->owner, qry->zone_cut.name) < 0) {
+			continue;
+		}
+		/* Merge with zone cut (or replace ancestor key). */
+		if (!qry->zone_cut.key || !knot_dname_is_equal(qry->zone_cut.key->owner, rr->owner)) {
+			qry->zone_cut.key = knot_rrset_copy(rr, qry->zone_cut.pool);
+			if (!qry->zone_cut.key) {
+				return kr_error(ENOMEM);
+			}
+			updated_key = true;
+		} else {
+			int ret = knot_rdataset_merge(&qry->zone_cut.key->rrs,
+			                              &rr->rrs, qry->zone_cut.pool);
+			if (ret != 0) {
+				knot_rrset_free(qry->zone_cut.key, qry->zone_cut.pool);
+				qry->zone_cut.key = NULL;
+				return ret;
+			}
+			updated_key = true;
+		}
+	}
+
+	/* Check if there's a key for current TA. */
+	if (updated_key && !(qry->flags.CACHED)) {
+
+		kr_rrset_validation_ctx_t vctx = {
+			.pkt		= answer,
+			.rrs		= &req->answ_selected,
+			.section_id	= KNOT_ANSWER,
+			.keys		= qry->zone_cut.key,
+			.zone_name	= qry->zone_cut.name,
+			.timestamp	= qry->timestamp.tv_sec,
+			.qry_uid	= qry->uid,
+			.has_nsec3	= has_nsec3,
+			.flags		= 0,
+			.result		= 0
+		};
+		int ret = kr_dnskeys_trusted(&vctx, qry->zone_cut.trust_anchor);
+		if (ret != 0) {
+			if (ret != kr_error(DNSSEC_INVALID_DS_ALGORITHM) &&
+			    ret != kr_error(EAGAIN)) {
+				log_bogus_rrsig(&vctx, qry, qry->zone_cut.key, "bogus key");
+			}
+			knot_rrset_free(qry->zone_cut.key, qry->zone_cut.pool);
+			qry->zone_cut.key = NULL;
+			return ret;
+		}
+
+		if (vctx.flags & KR_DNSSEC_VFLG_WEXPAND) {
+			qry->flags.DNSSEC_WEXPAND = true;
+		}
+		if (vctx.flags & KR_DNSSEC_VFLG_OPTOUT) {
+			qry->flags.DNSSEC_OPTOUT = true;
+		}
+
+	}
+	return kr_ok();
+}
+
+static knot_rrset_t *update_ds(struct kr_zonecut *cut, const knot_pktsection_t *sec)
+{
+	/* Aggregate DS records (if using multiple keys) */
+	knot_rrset_t *new_ds = NULL;
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(sec, i);
+		if (rr->type != KNOT_RRTYPE_DS) {
+			continue;
+		}
+		int ret = 0;
+		if (new_ds) {
+			ret = knot_rdataset_merge(&new_ds->rrs, &rr->rrs, cut->pool);
+		} else {
+			new_ds = knot_rrset_copy(rr, cut->pool);
+			if (!new_ds) {
+				return NULL;
+			}
+		}
+		if (ret != 0) {
+			knot_rrset_free(new_ds, cut->pool);
+			return NULL;
+		}
+	}
+	return new_ds;	
+}
+
+static void mark_insecure_parents(const struct kr_query *qry)
+{
+	/* If there is a chain of DS queries mark all of them,
+	 * then mark first non-DS parent.
+	 * Stop if parent is waiting for ns address.
+	 * NS can be located at unsigned zone, but still will return
+	 * valid DNSSEC records for initial query. */
+	struct kr_query *parent = qry->parent;
+	while (parent && !parent->flags.AWAIT_IPV4 && !parent->flags.AWAIT_IPV6) {
+		parent->flags.DNSSEC_WANT = false;
+		parent->flags.DNSSEC_INSECURE = true;
+		if (parent->stype != KNOT_RRTYPE_DS &&
+		    parent->stype != KNOT_RRTYPE_RRSIG) {
+			break;
+		}
+		parent = parent->parent;
+	}
+}
+
+static int update_parent_keys(struct kr_request *req, uint16_t answer_type)
+{
+	struct kr_query *qry = req->current_query;
+	struct kr_query *parent = qry->parent;
+	assert(parent);
+	switch(answer_type) {
+	case KNOT_RRTYPE_DNSKEY:
+		VERBOSE_MSG(qry, "<= parent: updating DNSKEY\n");
+		parent->zone_cut.key = knot_rrset_copy(qry->zone_cut.key, parent->zone_cut.pool);
+		if (!parent->zone_cut.key) {
+			return KR_STATE_FAIL;
+		}
+		break;
+	case KNOT_RRTYPE_DS:
+		VERBOSE_MSG(qry, "<= parent: updating DS\n");
+		if (qry->flags.DNSSEC_INSECURE) { /* DS non-existence proven. */
+			mark_insecure_parents(qry);
+		} else if (qry->flags.DNSSEC_NODS && !qry->flags.FORWARD) {
+			if (qry->flags.DNSSEC_OPTOUT) {
+				mark_insecure_parents(qry);
+			} else {
+				int ret = kr_dnssec_matches_name_and_type(&req->auth_selected, qry->uid,
+									  qry->sname, KNOT_RRTYPE_NS);
+				if (ret == kr_ok()) {
+					mark_insecure_parents(qry);
+				}
+			}
+		} else if (qry->flags.DNSSEC_NODS && qry->flags.FORWARD) {
+			int ret = kr_dnssec_matches_name_and_type(&req->auth_selected, qry->uid,
+								  qry->sname, KNOT_RRTYPE_NS);
+			if (ret == kr_ok()) {
+				mark_insecure_parents(qry);
+			}
+		} else { /* DS existence proven. */
+			parent->zone_cut.trust_anchor = knot_rrset_copy(qry->zone_cut.trust_anchor, parent->zone_cut.pool);
+			if (!parent->zone_cut.trust_anchor) {
+				return KR_STATE_FAIL;
+			}
+		}
+		break;
+	default: break;
+	}
+	return kr_ok();
+}
+
+static int update_delegation(struct kr_request *req, struct kr_query *qry, knot_pkt_t *answer, bool has_nsec3)
+{
+	struct kr_zonecut *cut = &qry->zone_cut;
+
+	/* RFC4035 3.1.4. authoritative must send either DS or proof of non-existence.
+	 * If it contains neither, resolver must query the parent for the DS (RFC4035 5.2.).
+	 * If DS exists, the referral is OK,
+	 * otherwise referral is bogus (or an attempted downgrade attack).
+	 */
+
+
+	unsigned section = KNOT_ANSWER;
+	const bool referral = !knot_wire_get_aa(answer->wire);
+	if (referral) {
+		section = KNOT_AUTHORITY;
+	} else if (knot_pkt_qtype(answer) == KNOT_RRTYPE_DS &&
+		   !(qry->flags.CNAME) &&
+		   (knot_wire_get_rcode(answer->wire) != KNOT_RCODE_NXDOMAIN)) {
+		section = KNOT_ANSWER;
+	} else { /* N/A */
+		return kr_ok();
+	}
+
+	int ret = 0;
+	const knot_dname_t *proved_name = knot_pkt_qname(answer);
+	/* Aggregate DS records (if using multiple keys) */
+	knot_rrset_t *new_ds = update_ds(cut, knot_pkt_section(answer, section));
+	if (!new_ds) {
+		/* No DS provided, check for proof of non-existence. */
+		if (!has_nsec3) {
+			if (referral) {
+				/* Check if it is referral to unsigned, rfc4035 5.2 */
+				ret = kr_nsec_ref_to_unsigned(answer);
+			} else {
+				/* No-data answer */
+				ret = kr_nsec_existence_denial(answer, KNOT_AUTHORITY, proved_name, KNOT_RRTYPE_DS);
+			}
+		} else {
+			if (referral) {
+				/* Check if it is referral to unsigned, rfc5155 8.9 */
+				ret = kr_nsec3_ref_to_unsigned(answer);
+			} else {
+				/* No-data answer, QTYPE is DS, rfc5155 8.6 */
+				ret = kr_nsec3_no_data(answer, KNOT_AUTHORITY, proved_name, KNOT_RRTYPE_DS);
+			}
+			if (ret == kr_error(KNOT_ERANGE)) {
+				/* Not bogus, going insecure due to optout */
+				ret = 0;
+			}
+		}
+
+		if (referral && qry->stype != KNOT_RRTYPE_DS &&
+		    ret == DNSSEC_NOT_FOUND) {
+			/* referral,
+			 * qtype is not KNOT_RRTYPE_DS, NSEC\NSEC3 were not found.
+			 * Check if DS already was fetched. */
+			knot_rrset_t *ta = cut->trust_anchor;
+			if (knot_dname_is_equal(cut->name, ta->owner)) {
+				/* DS is OK */
+				ret = 0;
+			}
+		} else if (ret != 0) {
+			VERBOSE_MSG(qry, "<= bogus proof of DS non-existence\n");
+			qry->flags.DNSSEC_BOGUS = true;
+		} else if (proved_name[0] != '\0') { /* don't go to insecure for . DS */
+			VERBOSE_MSG(qry, "<= DS doesn't exist, going insecure\n");
+			qry->flags.DNSSEC_NODS = true;
+			/* Rank the corresponding nonauth NS as insecure. */
+			for (int i = 0; i < req->auth_selected.len; ++i) {
+				ranked_rr_array_entry_t *ns = req->auth_selected.at[i];
+				if (ns->qry_uid != qry->uid
+				    || !ns->rr
+				    || ns->rr->type != KNOT_RRTYPE_NS) {
+					continue;
+				}
+				if (!referral && !knot_dname_is_equal(qry->sname, ns->rr->owner)) {
+					continue;
+				}
+				/* Found the record.  Note: this is slightly fragile
+				 * in case there were more NS records in the packet.
+				 * As it is now for referrals, kr_nsec*_ref_to_unsigned consider
+				 * (only) the first NS record in the packet. */
+				if (!kr_rank_test(ns->rank, KR_RANK_AUTH)) { /* sanity */
+					ns->rank = KR_RANK_INSECURE;
+				}
+				break;
+			}
+		}
+		return ret;
+	} else if (qry->flags.FORWARD && qry->parent) {
+		struct kr_query *parent = qry->parent;
+		parent->zone_cut.name = knot_dname_copy(qry->sname, parent->zone_cut.pool);
+	}
+
+	/* Extend trust anchor */
+	VERBOSE_MSG(qry, "<= DS: OK\n");
+	cut->trust_anchor = new_ds;
+	return ret;
+}
+
+static const knot_dname_t *find_first_signer(ranked_rr_array_t *arr)
+{
+	for (size_t i = 0; i < arr->len; ++i) {
+		ranked_rr_array_entry_t *entry = arr->at[i];
+		const knot_rrset_t *rr = entry->rr;
+		if (entry->yielded ||
+		    (!kr_rank_test(entry->rank, KR_RANK_INITIAL) &&
+		     !kr_rank_test(entry->rank, KR_RANK_TRY) &&
+		     !kr_rank_test(entry->rank, KR_RANK_MISMATCH))) {
+			continue;
+		}
+		if (rr->type == KNOT_RRTYPE_RRSIG) {
+			return knot_rrsig_signer_name(rr->rrs.rdata);
+		}
+	}
+	return NULL;
+}
+
+static const knot_dname_t *signature_authority(struct kr_request *req)
+{
+	const knot_dname_t *signer_name = find_first_signer(&req->answ_selected);
+	if (!signer_name) {
+		signer_name = find_first_signer(&req->auth_selected);
+	}
+	return signer_name;
+}
+
+static int rrsig_not_found(kr_layer_t *ctx, const knot_rrset_t *rr)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+
+	/* Parent-side record, so don't ask for RRSIG.
+	 * We won't receive it anyway. */
+	if (qry->stype == KNOT_RRTYPE_DS) {
+		return KR_STATE_FAIL;
+	}
+
+	struct kr_zonecut *cut = &qry->zone_cut;
+	const knot_dname_t *cut_name_start = qry->zone_cut.name;
+	bool use_cut = true;
+	if (knot_dname_in_bailiwick(rr->owner, cut_name_start) < 0) {
+		int zone_labels = knot_dname_labels(qry->zone_cut.name, NULL);
+		int matched_labels = knot_dname_matched_labels(qry->zone_cut.name, rr->owner);
+		int skip_labels = zone_labels - matched_labels;
+		while (skip_labels--) {
+			cut_name_start = knot_wire_next_label(cut_name_start, NULL);
+		}
+		/* try to find the name wanted among ancestors */
+		use_cut = false;
+		while (cut->parent) {
+			cut = cut->parent;
+			if (knot_dname_is_equal(cut_name_start, cut->name)) {
+				use_cut = true;
+				break;
+			}
+		};
+	}
+	struct kr_rplan *rplan = &req->rplan;
+	struct kr_query *next = kr_rplan_push(rplan, qry, rr->owner, rr->rclass, KNOT_RRTYPE_RRSIG);
+	if (!next) {
+		return KR_STATE_FAIL;
+	}
+	kr_zonecut_init(&next->zone_cut, cut_name_start, &req->pool);
+	if (use_cut) {
+		kr_zonecut_copy(&next->zone_cut, cut);
+		kr_zonecut_copy_trust(&next->zone_cut, cut);
+	} else {
+		next->flags.AWAIT_CUT = true;
+	}
+	if (qry->flags.FORWARD) {
+		next->flags.AWAIT_CUT = false;
+	}
+	next->flags.DNSSEC_WANT = true;
+	return KR_STATE_YIELD;
+}
+
+static int check_validation_result(kr_layer_t *ctx, ranked_rr_array_t *arr)
+{
+	int ret = KR_STATE_DONE;
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	ranked_rr_array_entry_t *invalid_entry = NULL;
+	for (size_t i = 0; i < arr->len; ++i) {
+		ranked_rr_array_entry_t *entry = arr->at[i];
+		if (entry->yielded || entry->qry_uid != qry->uid) {
+			continue;
+		}
+		if (kr_rank_test(entry->rank, KR_RANK_MISMATCH)) {
+			invalid_entry = entry;
+			break;
+		} else if (kr_rank_test(entry->rank, KR_RANK_MISSING) &&
+			   !invalid_entry) {
+			invalid_entry = entry;
+		} else if (kr_rank_test(entry->rank, KR_RANK_OMIT)) {
+			continue;
+		} else if (!kr_rank_test(entry->rank, KR_RANK_SECURE) &&
+			   !invalid_entry) {
+			invalid_entry = entry;
+		}
+	}
+
+	if (!invalid_entry) {
+		return ret;
+	}
+
+	if (!kr_rank_test(invalid_entry->rank, KR_RANK_SECURE) &&
+	    (++(invalid_entry->revalidation_cnt) > MAX_REVALIDATION_CNT)) {
+		VERBOSE_MSG(qry, "<= continuous revalidation, fails\n");
+		qry->flags.DNSSEC_BOGUS = true;
+		return KR_STATE_FAIL;
+	}
+
+	const knot_rrset_t *rr = invalid_entry->rr;
+	if (kr_rank_test(invalid_entry->rank, KR_RANK_MISMATCH)) {
+		const knot_dname_t *signer_name = knot_rrsig_signer_name(rr->rrs.rdata);
+		if (knot_dname_in_bailiwick(signer_name, qry->zone_cut.name) > 0) {
+			qry->zone_cut.name = knot_dname_copy(signer_name, &req->pool);
+			qry->flags.AWAIT_CUT = true;
+		} else if (!knot_dname_is_equal(signer_name, qry->zone_cut.name)) {
+			if (qry->zone_cut.parent) {
+				memcpy(&qry->zone_cut, qry->zone_cut.parent, sizeof(qry->zone_cut));
+			} else {
+				qry->flags.AWAIT_CUT = true;
+			}
+			qry->zone_cut.name = knot_dname_copy(signer_name, &req->pool);
+		}
+		VERBOSE_MSG(qry, ">< cut changed (new signer), needs revalidation\n");
+		ret = KR_STATE_YIELD;
+	} else if (kr_rank_test(invalid_entry->rank, KR_RANK_MISSING)) {
+		ret = rrsig_not_found(ctx, rr);
+	} else if (!kr_rank_test(invalid_entry->rank, KR_RANK_SECURE)) {
+		qry->flags.DNSSEC_BOGUS = true;
+		ret = KR_STATE_FAIL;
+	}
+
+	return ret;
+}
+
+static bool check_empty_answer(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req	= ctx->req;
+	struct kr_query *qry	= req->current_query;
+	ranked_rr_array_t *arr	= &req->answ_selected;
+	size_t num_entries = 0;
+	for (size_t i = 0; i < arr->len; ++i) {
+		ranked_rr_array_entry_t *entry = arr->at[i];
+		const knot_rrset_t *rr = entry->rr;
+		if (rr->type == KNOT_RRTYPE_RRSIG && qry->stype != KNOT_RRTYPE_RRSIG) {
+			continue;
+		}
+		if (entry->qry_uid == qry->uid) {
+			++num_entries;
+		}
+	}
+	const knot_pktsection_t *an = knot_pkt_section(pkt, KNOT_ANSWER);
+	return ((an->count != 0) && (num_entries == 0)) ? false : true;
+}
+
+static int unsigned_forward(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	const uint16_t qtype = knot_pkt_qtype(pkt);
+	const uint8_t pkt_rcode = knot_wire_get_rcode(pkt->wire);
+	bool nods = false;
+	bool ns_exist = true;
+	for (int i = 0; i < req->rplan.resolved.len; ++i) {
+		struct kr_query *q = req->rplan.resolved.at[i];
+		if (q->sclass == qry->sclass &&
+		    q->stype == KNOT_RRTYPE_DS &&
+		    knot_dname_is_equal(q->sname, qry->sname)) {
+			nods = true;
+			if (!(q->flags.DNSSEC_OPTOUT)) {
+				int ret = kr_dnssec_matches_name_and_type(&req->auth_selected, q->uid,
+									  qry->sname, KNOT_RRTYPE_NS);
+				ns_exist = (ret == kr_ok());
+			}
+		}
+	}
+
+	if (nods && ns_exist && qtype == KNOT_RRTYPE_NS) {
+		qry->flags.DNSSEC_WANT = false;
+		qry->flags.DNSSEC_INSECURE = true;
+		if (qry->forward_flags.CNAME) {
+			assert(qry->cname_parent);
+			qry->cname_parent->flags.DNSSEC_WANT = false;
+			qry->cname_parent->flags.DNSSEC_INSECURE = true;
+		} else if (pkt_rcode == KNOT_RCODE_NOERROR && qry->parent != NULL) {
+			const knot_pktsection_t *sec = knot_pkt_section(pkt, KNOT_ANSWER);
+			const knot_rrset_t *rr = knot_pkt_rr(sec, 0);
+			if (rr->type == KNOT_RRTYPE_NS) {
+				qry->parent->zone_cut.name = knot_dname_copy(rr->owner, &req->pool);
+				qry->parent->flags.DNSSEC_WANT = false;
+				qry->parent->flags.DNSSEC_INSECURE = true;
+			}
+		}
+		while (qry->parent) {
+			qry = qry->parent;
+			qry->flags.DNSSEC_WANT = false;
+			qry->flags.DNSSEC_INSECURE = true;
+			if (qry->forward_flags.CNAME) {
+				assert(qry->cname_parent);
+				qry->cname_parent->flags.DNSSEC_WANT = false;
+				qry->cname_parent->flags.DNSSEC_INSECURE = true;
+			}
+		}
+		return KR_STATE_DONE;
+	}
+
+	if (ctx->state == KR_STATE_YIELD) {
+		return KR_STATE_DONE;
+	}
+
+	if (!nods && qtype != KNOT_RRTYPE_DS) {
+		struct kr_rplan *rplan = &req->rplan;
+		struct kr_query *next = kr_rplan_push(rplan, qry, qry->sname, qry->sclass, KNOT_RRTYPE_DS);
+		if (!next) {
+			return KR_STATE_FAIL;
+		}
+		kr_zonecut_set(&next->zone_cut, qry->zone_cut.name);
+		kr_zonecut_copy_trust(&next->zone_cut, &qry->zone_cut);
+		next->flags.DNSSEC_WANT = true;
+	}
+
+	return KR_STATE_YIELD;
+}
+
+static int check_signer(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	const knot_dname_t *ta_name = qry->zone_cut.trust_anchor ? qry->zone_cut.trust_anchor->owner : NULL;
+	const knot_dname_t *signer = signature_authority(req);
+	if (ta_name && (!signer || !knot_dname_is_equal(ta_name, signer))) {
+		/* check all newly added RRSIGs */
+		if (!signer) {
+			if (qry->flags.FORWARD) {
+				return unsigned_forward(ctx, pkt);
+			}
+			/* Not a DNSSEC-signed response. */
+			if (ctx->state == KR_STATE_YIELD) {
+				/* Already yielded for revalidation.
+				 * It means that trust chain is OK and
+				 * transition to INSECURE hasn't occurred.
+				 * Let the validation logic ask about RRSIG. */
+				return KR_STATE_DONE;
+			}
+			/* Ask parent for DS
+			 * to prove transition to INSECURE. */
+			const uint16_t qtype = knot_pkt_qtype(pkt);
+			const knot_dname_t *qname = knot_pkt_qname(pkt);
+			if (qtype == KNOT_RRTYPE_NS &&
+			    knot_dname_in_bailiwick(qname, qry->zone_cut.name) > 0) {
+				/* Server is authoritative
+				 * for both parent and child,
+				 * and child zone is not signed. */
+				qry->zone_cut.name = knot_dname_copy(qname, &req->pool);
+			}
+		} else if (knot_dname_in_bailiwick(signer, qry->zone_cut.name) > 0) {
+			if (!(qry->flags.FORWARD)) {
+				/* Key signer is below current cut, advance and refetch keys. */
+				qry->zone_cut.name = knot_dname_copy(signer, &req->pool);
+			} else {
+				/* Check if DS does not exist. */
+				struct kr_query *q = kr_rplan_find_resolved(&req->rplan, NULL,
+									    signer, qry->sclass, KNOT_RRTYPE_DS);
+				if (q && q->flags.DNSSEC_NODS) {
+					qry->flags.DNSSEC_WANT = false;
+					qry->flags.DNSSEC_INSECURE = true;
+					if (qry->parent) {
+						qry->parent->flags.DNSSEC_WANT = false;
+						qry->parent->flags.DNSSEC_INSECURE = true;
+					}
+				} else if (qry->stype != KNOT_RRTYPE_DS) {
+					struct kr_rplan *rplan = &req->rplan;
+					struct kr_query *next = kr_rplan_push(rplan, qry, qry->sname,
+									      qry->sclass, KNOT_RRTYPE_DS);
+					if (!next) {
+						return KR_STATE_FAIL;
+					}
+					kr_zonecut_set(&next->zone_cut, qry->zone_cut.name);
+					kr_zonecut_copy_trust(&next->zone_cut, &qry->zone_cut);
+					next->flags.DNSSEC_WANT = true;
+				}
+			}
+		} else if (!knot_dname_is_equal(signer, qry->zone_cut.name)) {
+			/* Key signer is above the current cut, so we can't validate it. This happens when
+			   a server is authoritative for both grandparent, parent and child zone.
+			   Ascend to parent cut, and refetch authority for signer. */
+			if (qry->zone_cut.parent) {
+				memcpy(&qry->zone_cut, qry->zone_cut.parent, sizeof(qry->zone_cut));
+			} else {
+				qry->flags.AWAIT_CUT = true;
+			}
+			qry->zone_cut.name = knot_dname_copy(signer, &req->pool);
+		}
+
+		/* zone cut matches, but DS/DNSKEY doesn't => refetch. */
+		VERBOSE_MSG(qry, ">< cut changed, needs revalidation\n");
+		if ((qry->flags.FORWARD) && qry->stype != KNOT_RRTYPE_DS) {
+			struct kr_rplan *rplan = &req->rplan;
+			struct kr_query *next = kr_rplan_push(rplan, qry, signer,
+							qry->sclass, KNOT_RRTYPE_DS);
+			if (!next) {
+				return KR_STATE_FAIL;
+			}
+			kr_zonecut_set(&next->zone_cut, qry->zone_cut.name);
+			kr_zonecut_copy_trust(&next->zone_cut, &qry->zone_cut);
+			next->flags.DNSSEC_WANT = true;
+			return KR_STATE_YIELD;
+		}
+		if (!(qry->flags.FORWARD)) {
+			return KR_STATE_YIELD;
+		}
+	}
+	return KR_STATE_DONE;
+}
+
+/** Change ranks of RRs from this single iteration:
+ * _INITIAL or _TRY or _MISSING -> rank_to_set.
+ *
+ * Optionally do this only in a `bailiwick` (if not NULL).
+ * Iterator shouldn't have selected such records, but we check to be sure. */
+static void rank_records(kr_layer_t *ctx, enum kr_rank rank_to_set,
+			 const knot_dname_t *bailiwick)
+{
+	struct kr_request *req	   = ctx->req;
+	struct kr_query *qry	   = req->current_query;
+	ranked_rr_array_t *ptrs[2] = { &req->answ_selected, &req->auth_selected };
+	for (size_t i = 0; i < 2; ++i) {
+		ranked_rr_array_t *arr = ptrs[i];
+		for (size_t j = 0; j < arr->len; ++j) {
+			ranked_rr_array_entry_t *entry = arr->at[j];
+			if (entry->qry_uid != qry->uid) {
+				continue;
+			}
+			if (bailiwick && knot_dname_in_bailiwick(entry->rr->owner,
+								 bailiwick) < 0) {
+				continue;
+			}
+			if (kr_rank_test(entry->rank, KR_RANK_INITIAL)
+			    || kr_rank_test(entry->rank, KR_RANK_TRY)
+			    || kr_rank_test(entry->rank, KR_RANK_MISSING)) {
+				kr_rank_set(&entry->rank, rank_to_set);
+			}
+		}
+	}
+}
+
+static void check_wildcard(kr_layer_t *ctx)
+{
+	struct kr_request *req	   = ctx->req;
+	struct kr_query *qry	   = req->current_query;
+	ranked_rr_array_t *ptrs[2] = { &req->answ_selected, &req->auth_selected };
+
+	for (int i = 0; i < 2; ++i) {
+		ranked_rr_array_t *arr = ptrs[i];
+		for (ssize_t j = 0; j < arr->len; ++j) {
+			ranked_rr_array_entry_t *entry = arr->at[j];
+			const knot_rrset_t *rrsigs = entry->rr;
+
+			if (qry->uid != entry->qry_uid) {
+				continue;
+			}
+
+			if (rrsigs->type != KNOT_RRTYPE_RRSIG) {
+				continue;
+			}
+
+			int owner_labels = knot_dname_labels(rrsigs->owner, NULL);
+
+			knot_rdata_t *rdata_k = rrsigs->rrs.rdata;
+			for (int k = 0; k < rrsigs->rrs.count;
+					++k, rdata_k = knot_rdataset_next(rdata_k)) {
+				if (knot_rrsig_labels(rdata_k) != owner_labels) {
+					qry->flags.DNSSEC_WEXPAND = true;
+				}
+			}
+		}
+	}
+}
+
+/** Just for wildcard_adjust_to_wire() */
+static bool rr_is_for_wildcard(const ranked_rr_array_entry_t *entry)
+{
+	switch (kr_rrset_type_maysig(entry->rr)) {
+	case KNOT_RRTYPE_NSEC:
+	case KNOT_RRTYPE_NSEC3:
+		return true;
+	default:
+		return false;
+	}
+}
+/** In case of wildcard expansion, mark required authority RRs by to_wire. */
+static int wildcard_adjust_to_wire(struct kr_request *req, const struct kr_query *qry)
+{
+	if (!qry->parent && qry->flags.DNSSEC_WEXPAND) {
+		return kr_ranked_rrarray_set_wire(&req->auth_selected, true,
+				qry->uid, true, &rr_is_for_wildcard);
+	}
+	return kr_ok();
+}
+
+static int validate(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	int ret = 0;
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+
+	/* Ignore faulty or unprocessed responses. */
+	if (ctx->state & (KR_STATE_FAIL|KR_STATE_CONSUME)) {
+		return ctx->state;
+	}
+
+	/* Pass-through if user doesn't want secure answer or stub. */
+	/* @todo: Validating stub resolver mode. */
+	if (qry->flags.STUB) {
+		rank_records(ctx, KR_RANK_OMIT, NULL);
+		return ctx->state;
+	}
+	uint8_t pkt_rcode = knot_wire_get_rcode(pkt->wire);
+	if ((qry->flags.FORWARD) &&
+	    pkt_rcode != KNOT_RCODE_NOERROR &&
+	    pkt_rcode != KNOT_RCODE_NXDOMAIN) {
+		do {
+			qry->flags.DNSSEC_BOGUS = true;
+			if (qry->cname_parent) {
+				qry->cname_parent->flags.DNSSEC_BOGUS = true;
+			}
+			qry = qry->parent;
+		} while (qry);
+		ctx->state = KR_STATE_DONE;
+		return ctx->state;
+	}
+
+	if (!(qry->flags.DNSSEC_WANT)) {
+		const bool is_insec = qry->flags.CACHED && qry->flags.DNSSEC_INSECURE;
+		if ((qry->flags.DNSSEC_INSECURE)) {
+			rank_records(ctx, KR_RANK_INSECURE, qry->zone_cut.name);
+		}
+		if (is_insec && qry->parent != NULL) {
+			/* We have got insecure answer from cache.
+			 * Mark parent(s) as insecure. */
+			mark_insecure_parents(qry);
+			VERBOSE_MSG(qry, "<= cached insecure response, going insecure\n");
+			ctx->state = KR_STATE_DONE;
+		} else if (ctx->state == KR_STATE_YIELD) {
+			/* Transition to unsecure state
+			   occurred during revalidation.
+			   if state remains YIELD, answer will not be cached.
+			   Let cache layers to work. */
+			ctx->state = KR_STATE_DONE;
+		}
+		return ctx->state;
+	}
+
+	/* Pass-through if CD bit is set. */
+	if (knot_wire_get_cd(req->qsource.packet->wire)) {
+		check_wildcard(ctx);
+		wildcard_adjust_to_wire(req, qry);
+		rank_records(ctx, KR_RANK_OMIT, NULL);
+		return ctx->state;
+	}
+	/* Answer for RRSIG may not set DO=1, but all records MUST still validate. */
+	bool use_signatures = (knot_pkt_qtype(pkt) != KNOT_RRTYPE_RRSIG);
+	if (!(qry->flags.CACHED) && !knot_pkt_has_dnssec(pkt) && !use_signatures) {
+		VERBOSE_MSG(qry, "<= got insecure response\n");
+		qry->flags.DNSSEC_BOGUS = true;
+		return KR_STATE_FAIL;
+	}
+
+	/* Check if this is a DNSKEY answer, check trust chain and store. */
+	uint16_t qtype = knot_pkt_qtype(pkt);
+	bool has_nsec3 = pkt_has_type(pkt, KNOT_RRTYPE_NSEC3);
+	const knot_pktsection_t *an = knot_pkt_section(pkt, KNOT_ANSWER);
+	const bool referral = (an->count == 0 && !knot_wire_get_aa(pkt->wire));
+
+	if (!(qry->flags.CACHED) && knot_wire_get_aa(pkt->wire)) {
+		/* Check if answer if not empty,
+		 * but iterator has not selected any records. */
+		if (!check_empty_answer(ctx, pkt)) {
+			VERBOSE_MSG(qry, "<= no useful RR in authoritative answer\n");
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		}
+		/* Track difference between current TA and signer name.
+		 * This indicates that the NS is auth for both parent-child,
+		 * and we must update DS/DNSKEY to validate it.
+		 */
+		ret = check_signer(ctx, pkt);
+		if (ret != KR_STATE_DONE) {
+			return ret;
+		}
+		if (qry->flags.FORWARD && qry->flags.DNSSEC_INSECURE) {
+			return KR_STATE_DONE;
+		}
+	}
+
+	if (knot_wire_get_aa(pkt->wire) && qtype == KNOT_RRTYPE_DNSKEY) {
+		ret = validate_keyset(req, pkt, has_nsec3);
+		if (ret == kr_error(EAGAIN)) {
+			VERBOSE_MSG(qry, ">< cut changed, needs revalidation\n");
+			return KR_STATE_YIELD;
+		} else if (ret == kr_error(DNSSEC_INVALID_DS_ALGORITHM)) {
+			VERBOSE_MSG(qry, ">< all DS entries use unsupported algorithm pairs, going insecure\n");
+			/* ^ the message is a bit imprecise to avoid being too verbose */
+			qry->flags.DNSSEC_WANT = false;
+			qry->flags.DNSSEC_INSECURE = true;
+			rank_records(ctx, KR_RANK_INSECURE, qry->zone_cut.name);
+			mark_insecure_parents(qry);
+			return KR_STATE_DONE;
+		} else if (ret != 0) {
+			VERBOSE_MSG(qry, "<= bad keys, broken trust chain\n");
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		}
+	}
+
+	/* Validate non-existence proof if not positive answer.
+	 * In case of CNAME, iterator scheduled a sibling query for the target,
+	 * so we just drop the negative piece of information and don't try to prove it.
+	 * TODO: not ideal; with aggressive cache we'll at least avoid the extra packet. */
+	if (!qry->flags.CACHED && pkt_rcode == KNOT_RCODE_NXDOMAIN && !qry->flags.CNAME) {
+		/* @todo If knot_pkt_qname(pkt) is used instead of qry->sname then the tests crash. */
+		if (!has_nsec3) {
+			ret = kr_nsec_name_error_response_check(pkt, KNOT_AUTHORITY, qry->sname);
+		} else {
+			ret = kr_nsec3_name_error_response_check(pkt, KNOT_AUTHORITY, qry->sname);
+		}
+		if (has_nsec3 && (ret == kr_error(KNOT_ERANGE))) {
+			/* NXDOMAIN proof is OK,
+			 * but NSEC3 that covers next closer name
+			 * (or wildcard at next closer name) has opt-out flag.
+			 * RFC5155 9.2; AD flag can not be set */
+			qry->flags.DNSSEC_OPTOUT = true;
+			VERBOSE_MSG(qry, "<= can't prove NXDOMAIN due to optout, going insecure\n");
+		} else if (ret != 0) {
+			VERBOSE_MSG(qry, "<= bad NXDOMAIN proof\n");
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		}
+	}
+
+	/* @todo WTH, this needs API that just tries to find a proof and the caller
+	 * doesn't have to worry about NSEC/NSEC3
+	 * @todo rework this
+	 * CNAME: same as the NXDOMAIN case above */
+	if (!qry->flags.CACHED && pkt_rcode == KNOT_RCODE_NOERROR && !qry->flags.CNAME) {
+		bool no_data = (an->count == 0 && knot_wire_get_aa(pkt->wire));
+		if (no_data) {
+			/* @todo
+			 * ? quick mechanism to determine which check to preform first
+			 * ? merge the functionality together to share code/resources
+			 */
+			if (!has_nsec3) {
+				ret = kr_nsec_existence_denial(pkt, KNOT_AUTHORITY, knot_pkt_qname(pkt), knot_pkt_qtype(pkt));
+			} else {
+				ret = kr_nsec3_no_data(pkt, KNOT_AUTHORITY, knot_pkt_qname(pkt), knot_pkt_qtype(pkt));
+			}
+			if (ret != 0) {
+				if (has_nsec3 && (ret == kr_error(KNOT_ERANGE))) {
+					VERBOSE_MSG(qry, "<= can't prove NODATA due to optout, going insecure\n");
+					qry->flags.DNSSEC_OPTOUT = true;
+					/* Could not return from here,
+					 * we must continue, validate NSEC\NSEC3 and
+					 * call update_parent_keys() to mark
+					 * parent queries as insecured */
+				} else {
+					VERBOSE_MSG(qry, "<= bad NODATA proof\n");
+					qry->flags.DNSSEC_BOGUS = true;
+					return KR_STATE_FAIL;
+				}
+			}
+		}
+	}
+
+	/* Validate all records, fail as bogus if it doesn't match.
+	 * Do not revalidate data from cache, as it's already trusted. */
+	if (!(qry->flags.CACHED)) {
+		ret = validate_records(req, pkt, req->rplan.pool, has_nsec3);
+		if (ret != 0) {
+			/* something exceptional - no DNS key, empty pointers etc
+			 * normally it shoudn't happen */
+			VERBOSE_MSG(qry, "<= couldn't validate RRSIGs\n");
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		}
+		/* check validation state and spawn subrequests */
+		if (!req->answ_validated) {
+			ret = check_validation_result(ctx, &req->answ_selected);
+			if (ret != KR_STATE_DONE) {
+				return ret;
+			}
+		}
+		if (!req->auth_validated) {
+			ret = check_validation_result(ctx, &req->auth_selected);
+			if (ret != KR_STATE_DONE) {
+				return ret;
+			}
+		}
+	}
+
+	wildcard_adjust_to_wire(req, qry);
+
+	/* Check and update current delegation point security status. */
+	ret = update_delegation(req, qry, pkt, has_nsec3);
+	if (ret == DNSSEC_NOT_FOUND && qry->stype != KNOT_RRTYPE_DS) {
+		if (ctx->state == KR_STATE_YIELD) {
+			VERBOSE_MSG(qry, "<= can't validate referral\n");
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		} else {
+			/* Check the trust chain and query DS\DNSKEY if needed. */
+			VERBOSE_MSG(qry, "<= DS\\NSEC was not found, querying for DS\n");
+			return KR_STATE_YIELD;
+		}
+	} else if (ret != 0) {
+		return KR_STATE_FAIL;
+	} else if (pkt_rcode == KNOT_RCODE_NOERROR &&
+		   referral &&
+		   ((!qry->flags.DNSSEC_WANT && qry->flags.DNSSEC_INSECURE) ||
+		   (qry->flags.DNSSEC_NODS))) {
+		/* referral with proven DS non-existance */
+		qtype = KNOT_RRTYPE_DS;
+	}
+	/* Update parent query zone cut */
+	if (qry->parent) {
+		if (update_parent_keys(req, qtype) != 0) {
+			return KR_STATE_FAIL;
+		}
+	}
+
+	if (qry->flags.FORWARD && qry->parent) {
+		if (pkt_rcode == KNOT_RCODE_NXDOMAIN) {
+			qry->parent->forward_flags.NO_MINIMIZE = true;
+		}
+	}
+	VERBOSE_MSG(qry, "<= answer valid, OK\n");
+	return KR_STATE_DONE;
+}
+/** Module implementation. */
+const kr_layer_api_t *validate_layer(struct kr_module *module)
+{
+	static const kr_layer_api_t _layer = {
+		.consume = &validate,
+	};
+	/* Store module reference */
+	return &_layer;
+}
+
+int validate_init(struct kr_module *module)
+{
+	return kr_ok();
+}
+
+KR_MODULE_EXPORT(validate)
+
+#undef VERBOSE_MSG
diff --git a/lib/lib.mk b/lib/lib.mk
new file mode 100644
index 0000000..8ac4e91
--- /dev/null
+++ b/lib/lib.mk
@@ -0,0 +1,110 @@
+libkres_SOURCES := \
+	lib/cache/api.c \
+	lib/cache/cdb_lmdb.c \
+	lib/cache/entry_list.c \
+	lib/cache/entry_pkt.c \
+	lib/cache/entry_rr.c \
+	lib/cache/knot_pkt.c \
+	lib/cache/nsec1.c \
+	lib/cache/nsec3.c \
+	lib/cache/peek.c \
+	lib/dnssec.c \
+	lib/dnssec/nsec.c \
+	lib/dnssec/nsec3.c \
+	lib/dnssec/signature.c \
+	lib/dnssec/ta.c \
+	lib/generic/lru.c \
+	lib/generic/map.c \
+	lib/generic/queue.c \
+	lib/generic/trie.c \
+	lib/layer/cache.c \
+	lib/layer/iterate.c \
+	lib/layer/validate.c \
+	lib/module.c \
+	lib/nsrep.c \
+	lib/resolve.c \
+	lib/rplan.c \
+	lib/utils.c \
+	lib/zonecut.c
+
+libkres_HEADERS := \
+	lib/cache/api.h \
+	lib/cache/cdb_api.h \
+	lib/cache/cdb_lmdb.h \
+	lib/cache/impl.h \
+	lib/defines.h \
+	lib/dnssec.h \
+	lib/dnssec/nsec.h \
+	lib/dnssec/nsec3.h \
+	lib/dnssec/signature.h \
+	lib/dnssec/ta.h \
+	lib/generic/array.h \
+	lib/generic/lru.h \
+	lib/generic/map.h \
+	lib/generic/pack.h \
+	lib/generic/queue.h \
+	lib/generic/trie.h \
+	lib/layer.h \
+	lib/layer/iterate.h \
+	lib/module.h \
+	lib/nsrep.h \
+	lib/resolve.h \
+	lib/rplan.h \
+	lib/utils.h \
+	lib/zonecut.h
+
+# Dependencies
+libkres_DEPEND := $(contrib)
+libkres_CFLAGS := -fPIC $(lmdb_CFLAGS)
+libkres_LIBS := $(contrib_TARGET) $(libknot_LIBS) $(libdnssec_LIBS) $(lmdb_LIBS) \
+				$(libuv_LIBS) $(gnutls_LIBS)
+libkres_TARGET := -L$(abspath lib) -lkres
+
+ifeq ($(ENABLE_COOKIES),yes)
+libkres_SOURCES += \
+	lib/cookies/alg_containers.c \
+	lib/cookies/alg_sha.c \
+	lib/cookies/helper.c \
+	lib/cookies/lru_cache.c \
+	lib/cookies/nonce.c
+
+libkres_HEADERS += \
+	lib/cookies/alg_containers.h \
+	lib/cookies/alg_sha.h \
+	lib/cookies/control.h \
+	lib/cookies/helper.h \
+	lib/cookies/lru_cache.h \
+	lib/cookies/nonce.h
+
+libkres_LIBS += $(nettle_LIBS)
+endif
+
+# Make library
+ifeq ($(BUILDMODE), static)
+$(eval $(call make_static,libkres,lib,yes))
+else
+$(eval $(call make_lib,libkres,lib,yes,$(ABIVER)))
+endif
+
+# Generate pkg-config file
+libkres.pc:
+	@echo 'prefix='$(PREFIX) > $@
+	@echo 'exec_prefix=$${prefix}' >> $@
+	@echo 'libdir='$(LIBDIR) >> $@
+	@echo 'includedir='$(INCLUDEDIR) >> $@
+	@echo 'Name: libkres' >> $@
+	@echo 'Description: Knot Resolver library' >> $@
+	@echo 'URL: https://www.knot-resolver.cz' >> $@
+	@echo 'Version: $(VERSION)' >> $@
+	@echo 'Libs: -L$${libdir} -lkres' >> $@
+	@echo 'Cflags: -I$${includedir}' >> $@
+libkres-pcinstall: libkres.pc libkres-install
+	$(INSTALL) -d -m 755 $(DESTDIR)$(PKGCONFIGDIR)
+	$(INSTALL)    -m 644 $< $(DESTDIR)$(PKGCONFIGDIR)
+
+# Targets
+lib: $(libkres)
+lib-install: libkres-install libkres-pcinstall
+lib-clean: libkres-clean
+
+.PHONY: lib lib-install lib-clean libkres.pc
diff --git a/lib/module.c b/lib/module.c
new file mode 100644
index 0000000..68abc84
--- /dev/null
+++ b/lib/module.c
@@ -0,0 +1,170 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <stdlib.h>
+#include <dlfcn.h>
+#include <pthread.h>
+#include <contrib/cleanup.h>
+
+#include "lib/defines.h"
+#include "lib/utils.h"
+#include "lib/module.h"
+
+/* List of embedded modules */
+const kr_layer_api_t *iterate_layer(struct kr_module *module);
+const kr_layer_api_t *validate_layer(struct kr_module *module);
+const kr_layer_api_t *cache_layer(struct kr_module *module);
+static const struct kr_module embedded_modules[] = {
+	{ "iterate",  NULL, NULL, NULL, iterate_layer,  NULL, NULL, NULL },
+	{ "validate", NULL, NULL, NULL, validate_layer, NULL, NULL, NULL },
+	{ "cache",    NULL, NULL, NULL, cache_layer,    NULL, NULL, NULL },
+};
+
+/** Library extension. */
+#if defined(__APPLE__)
+ #define LIBEXT ".dylib"
+#elif _WIN32
+ #define LIBEXT ".dll"
+#else
+ #define LIBEXT ".so"
+#endif
+
+
+/** Load prefixed symbol. */
+static void *load_symbol(void *lib, const char *prefix, const char *name)
+{
+	auto_free char *symbol = kr_strcatdup(2, prefix, name);
+	return dlsym(lib, symbol);
+}
+
+static int load_library(struct kr_module *module, const char *name, const char *path)
+{
+	assert(module && name && path);
+	/* Absolute or relative path (then only library search path is used). */
+	auto_free char *lib_path = kr_strcatdup(4, path, "/", name, LIBEXT);
+	if (lib_path == NULL) {
+		return kr_error(ENOMEM);
+	}
+
+	/* Workaround for buggy _fini/__attribute__((destructor)) and dlclose(),
+	 * this keeps the library mapped until the program finishes though. */
+	module->lib = dlopen(lib_path, RTLD_NOW | RTLD_NODELETE);
+	if (module->lib) {
+		return kr_ok();
+	}
+
+	return kr_error(ENOENT);
+}
+
+const struct kr_module * kr_module_embedded(const char *name)
+{
+	for (unsigned i = 0; i < sizeof(embedded_modules)/sizeof(embedded_modules[0]); ++i) {
+		if (strcmp(name, embedded_modules[i].name) == 0)
+			return embedded_modules + i;
+	}
+	return NULL;
+}
+
+/** Load C module symbols. */
+static int load_sym_c(struct kr_module *module, uint32_t api_required)
+{
+	#pragma GCC diagnostic push
+	#pragma GCC diagnostic ignored "-Wpedantic" /* casts after load_symbol() */
+	/* Check if it's embedded first */
+	const struct kr_module *embedded = kr_module_embedded(module->name);
+	if (embedded) {
+		module->init = embedded->init;
+		module->deinit = embedded->deinit;
+		module->config = embedded->config;
+		module->layer = embedded->layer;
+		module->props = embedded->props;
+		return kr_ok();
+	}
+	/* Load dynamic library module */
+	auto_free char *m_prefix = kr_strcatdup(2, module->name, "_");
+
+	/* Check ABI version, return error on mismatch. */
+	module_api_cb *api = load_symbol(module->lib, m_prefix, "api");
+	if (api == NULL) {
+		return kr_error(ENOENT);
+	}
+	if (api() != api_required) {
+		return kr_error(ENOTSUP);
+	}
+
+	/* Load ABI by symbol names. */
+	#define ML(symname) module->symname = \
+		load_symbol(module->lib, m_prefix, #symname)
+	ML(init);
+	ML(deinit);
+	ML(config);
+	ML(layer);
+	ML(props);
+	#undef ML
+
+	return kr_ok();
+	#pragma GCC diagnostic pop
+}
+
+int kr_module_load(struct kr_module *module, const char *name, const char *path)
+{
+	if (module == NULL || name == NULL) {
+		return kr_error(EINVAL);
+	}
+
+	/* Initialize, keep userdata */
+	void *data = module->data;
+	memset(module, 0, sizeof(struct kr_module));
+	module->data = data;
+	module->name = strdup(name);
+	if (module->name == NULL) {
+		return kr_error(ENOMEM);
+	}
+
+	/* Search for module library. */
+	if (!path || load_library(module, name, path) != 0) {
+		module->lib = RTLD_DEFAULT;
+	}
+
+	/* Try to load module ABI. */
+	int ret = load_sym_c(module, KR_MODULE_API);
+	if (ret == 0 && module->init) {
+		ret = module->init(module);
+	}
+	if (ret != 0) {
+		kr_module_unload(module);
+	}
+
+	return ret;
+}
+
+void kr_module_unload(struct kr_module *module)
+{
+	if (module == NULL) {
+		return;
+	}
+
+	if (module->deinit) {
+		module->deinit(module);
+	}
+
+	if (module->lib && module->lib != RTLD_DEFAULT) {
+		dlclose(module->lib);
+	}
+
+	free(module->name);
+	memset(module, 0, sizeof(struct kr_module));
+}
diff --git a/lib/module.h b/lib/module.h
new file mode 100644
index 0000000..295c1f9
--- /dev/null
+++ b/lib/module.h
@@ -0,0 +1,111 @@
+/*  Copyright (C) 2015-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ * Module API definition and functions for (un)loading modules.
+ */
+
+#pragma once
+
+#include "lib/defines.h"
+#include "lib/utils.h"
+#include "lib/layer.h"
+
+struct kr_module;
+struct kr_prop;
+
+
+/**
+ * Export module API version (place this at the end of your module).
+ *
+ * @param module module name (f.e. hints)
+ */
+#define KR_MODULE_EXPORT(module) \
+    KR_EXPORT uint32_t module ## _api() { return KR_MODULE_API; }
+#define KR_MODULE_API ((uint32_t) 0x20180401)
+
+typedef uint32_t (module_api_cb)(void);
+
+
+/**
+ * Module representation.
+ *
+ * The five symbols (init, ...) may be defined by the module as name_init(), etc;
+ * all are optional and missing symbols are represented as NULLs;
+ */
+struct kr_module {
+	char *name;
+
+	/** Constructor.  Called after loading the module.  @return error code. */
+	int (*init)(struct kr_module *self);
+	/** Destructor.  Called before unloading the module.  @return error code. */
+	int (*deinit)(struct kr_module *self);
+	/** Configure with encoded JSON (NULL if missing).  @return error code. */
+	int (*config)(struct kr_module *self, const char *input);
+	/** Get a pointer to packet processing API specs.  See docs on that type. */
+	const kr_layer_api_t * (*layer)(struct kr_module *self);
+	/** Get a pointer to list of properties, terminated by { NULL, NULL, NULL }. */
+	const struct kr_prop * (*props)(void);
+
+	void *lib;      /**< Shared library handle or RTLD_DEFAULT */
+	void *data;     /**< Custom data context. */
+};
+
+/**
+ * Module property callback.  Input and output is passed via a JSON encoded in a string.
+ *
+ * @param env pointer to the lua engine, i.e. struct engine *env (TODO: explicit type)
+ * @param input parameter (NULL if missing/nil on lua level)
+ * @return a free-form JSON output (malloc-ated)
+ * @note see l_trampoline() implementation for details about the input/output conversion.
+ */
+typedef char *(kr_prop_cb)(void *env, struct kr_module *self, const char *input);
+
+/**
+ * Module property (named callable).
+ */
+struct kr_prop {
+	kr_prop_cb *cb;
+	const char *name;
+	const char *info;
+};
+
+
+/**
+ * Load a C module instance into memory.
+ *
+ * @param module module structure
+ * @param name module name
+ * @param path module search path
+ * @return 0 or an error
+ */
+KR_EXPORT
+int kr_module_load(struct kr_module *module, const char *name, const char *path);
+
+/**
+ * Unload module instance.
+ *
+ * @param module module structure
+ */
+KR_EXPORT
+void kr_module_unload(struct kr_module *module);
+
+/**
+ * Get embedded module prototype by name (or NULL).
+ */
+KR_EXPORT
+const struct kr_module * kr_module_embedded(const char *name);
+
diff --git a/lib/nsrep.c b/lib/nsrep.c
new file mode 100644
index 0000000..2af12f2
--- /dev/null
+++ b/lib/nsrep.c
@@ -0,0 +1,563 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netdb.h>
+
+#include <arpa/inet.h>
+
+#include "lib/nsrep.h"
+#include "lib/rplan.h"
+#include "lib/resolve.h"
+#include "lib/defines.h"
+#include "lib/generic/pack.h"
+#include "contrib/ucw/lib.h"
+
+/** Some built-in unfairness ... */
+#ifndef FAVOUR_IPV6
+#define FAVOUR_IPV6 20 /* 20ms bonus for v6 */
+#endif
+
+/** @internal Macro to set address structure. */
+#define ADDR_SET(sa, family, addr, len, port) do {\
+    	memcpy(&sa ## _addr, (addr), (len)); \
+    	sa ## _family = (family); \
+	sa ## _port = htons(port); \
+} while (0)
+
+/** Update nameserver representation with current name/address pair. */
+static void update_nsrep(struct kr_nsrep *ns, size_t pos, uint8_t *addr, size_t addr_len, int port)
+{
+	if (addr == NULL) {
+		ns->addr[pos].ip.sa_family = AF_UNSPEC;
+		return;
+	}
+
+	/* Rotate previous addresses to the right. */
+	memmove(ns->addr + pos + 1, ns->addr + pos, (KR_NSREP_MAXADDR - pos - 1) * sizeof(ns->addr[0]));
+
+	switch(addr_len) {
+	case sizeof(struct in_addr):
+		ADDR_SET(ns->addr[pos].ip4.sin, AF_INET, addr, addr_len, port); break;
+	case sizeof(struct in6_addr):
+		ADDR_SET(ns->addr[pos].ip6.sin6, AF_INET6, addr, addr_len, port); break;
+	default: assert(0); break;
+	}
+}
+
+static void update_nsrep_set(struct kr_nsrep *ns, const knot_dname_t *name, uint8_t *addr[], unsigned score)
+{
+	/* NSLIST is not empty, empty NS cannot be a leader. */
+	if (!addr[0] && ns->addr[0].ip.sa_family != AF_UNSPEC) {
+		return;
+	}
+	/* Set new NS leader */
+	ns->name = name;
+	ns->score = score;
+	for (size_t i = 0; i < KR_NSREP_MAXADDR; ++i) {
+		if (addr[i]) {
+			void *addr_val = pack_obj_val(addr[i]);
+			size_t len = pack_obj_len(addr[i]);
+			update_nsrep(ns, i, addr_val, len, KR_DNS_PORT);
+		} else {
+			break;
+		}
+	}
+}
+
+#undef ADDR_SET
+
+/**
+ * \param addr_set pack with one IP address per element */
+static unsigned eval_addr_set(const pack_t *addr_set, struct kr_context *ctx,
+			      struct kr_qflags opts, unsigned score, uint8_t *addr[])
+{
+	kr_nsrep_rtt_lru_t *rtt_cache = ctx->cache_rtt;
+	kr_nsrep_rtt_lru_entry_t *rtt_cache_entry_ptr[KR_NSREP_MAXADDR] = { NULL, };
+	assert (KR_NSREP_MAXADDR >= 2);
+	unsigned rtt_cache_entry_score[KR_NSREP_MAXADDR] = { score, KR_NS_MAX_SCORE + 1, };
+	uint64_t now = kr_now();
+
+	/* Name server is better candidate if it has address record. */
+	for (uint8_t *it = pack_head(*addr_set); it != pack_tail(*addr_set);
+						it = pack_obj_next(it)) {
+		void *val = pack_obj_val(it);
+		size_t len = pack_obj_len(it);
+		unsigned favour = 0;
+		bool is_valid = false;
+		/* Check if the address isn't disabled. */
+		if (len == sizeof(struct in6_addr)) {
+			is_valid = !(opts.NO_IPV6);
+			favour = FAVOUR_IPV6;
+		} else if (len == sizeof(struct in_addr)) {
+			is_valid = !(opts.NO_IPV4);
+		} else {
+			assert(!EINVAL);
+			is_valid = false;
+		}
+
+		if (!is_valid) {
+			continue;
+		}
+
+		/* Get score for the current address. */
+		kr_nsrep_rtt_lru_entry_t *cached = rtt_cache ?
+						   lru_get_try(rtt_cache, val, len) :
+						   NULL;
+		unsigned cur_addr_score = KR_NS_GLUED;
+		if (cached) {
+			cur_addr_score = cached->score;
+			if (cached->score >= KR_NS_TIMEOUT) {
+				/* If NS once was marked as "timeouted",
+				 * it won't participate in NS elections
+				 * at least ctx->cache_rtt_tout_retry_interval milliseconds. */
+				uint64_t elapsed = now - cached->tout_timestamp;
+				elapsed = elapsed > UINT_MAX ? UINT_MAX : elapsed;
+				if (elapsed > ctx->cache_rtt_tout_retry_interval) {
+					/* Select this NS for probing in this particular query,
+					 * but don't change the cached score.
+					 * For other queries this NS will remain "timeouted". */
+					cur_addr_score = KR_NS_LONG - 1;
+				}
+			}
+		}
+
+		for (size_t i = 0; i < KR_NSREP_MAXADDR; ++i) {
+			if (cur_addr_score >= KR_NS_TIMEOUT) {
+				/* We can't use favour here.
+				 * If all of the conditions below are true
+				 *
+				 * rtt_cache_entry_score[i] < KR_NS_TIMEOUT
+				 * rtt_cache_entry_score[i] + favour > KR_NS_TIMEOUT
+				 * cur_addr_score < rtt_cache_entry_score[i] + favour
+				 *
+				 * we will prefer "certainly dead" cur_addr_score
+				 * instead of "almost dead, but alive" rtt_cache_entry_score[i]
+				 */
+				if (cur_addr_score >= rtt_cache_entry_score[i]) {
+					continue;
+				}
+			}
+			if (cur_addr_score >= KR_NS_TIMEOUT
+			    || cur_addr_score < rtt_cache_entry_score[i] + favour) {
+				/* Shake down previous contenders */
+				for (size_t j = KR_NSREP_MAXADDR - 1; j > i; --j) {
+					addr[j] = addr[j - 1];
+					rtt_cache_entry_ptr[j] = rtt_cache_entry_ptr[j - 1];
+					rtt_cache_entry_score[j] = rtt_cache_entry_score[j - 1];
+				}
+				addr[i] = it;
+				rtt_cache_entry_score[i] = cur_addr_score;
+				rtt_cache_entry_ptr[i] = cached;
+				break;
+			}
+		}
+	}
+
+	/* At this point, rtt_cache_entry_ptr contains up to KR_NSREP_MAXADDR
+	 * pointers to the rtt cache entries with the best scores for the given addr_set.
+	 * Check if there are timeouted NS. */
+
+	for (size_t i = 0; i < KR_NSREP_MAXADDR; ++i) {
+		if (rtt_cache_entry_ptr[i] == NULL)
+			continue;
+		if (rtt_cache_entry_ptr[i]->score < KR_NS_TIMEOUT)
+			continue;
+
+		uint64_t elapsed = now - rtt_cache_entry_ptr[i]->tout_timestamp;
+		elapsed = elapsed > UINT_MAX ? UINT_MAX : elapsed;
+		if (elapsed <= ctx->cache_rtt_tout_retry_interval)
+			continue;
+
+		/* rtt_cache_entry_ptr[i] points to "timeouted" rtt cache entry.
+		 * The period of the ban on participation in elections has expired. */
+
+		if (VERBOSE_STATUS) {
+			void *val = pack_obj_val(addr[i]);
+			size_t len = pack_obj_len(addr[i]);
+			char sa_str[INET6_ADDRSTRLEN];
+			int af = (len == sizeof(struct in6_addr)) ? AF_INET6 : AF_INET;
+			inet_ntop(af, val, sa_str, sizeof(sa_str));
+			kr_log_verbose("[     ][nsre] probing timeouted NS: %s, score %i\n",
+				       sa_str, rtt_cache_entry_ptr[i]->score);
+		}
+
+		rtt_cache_entry_ptr[i]->tout_timestamp = now;
+	}
+
+	return rtt_cache_entry_score[0];
+}
+
+static int eval_nsrep(const knot_dname_t *owner, const pack_t *addr_set, struct kr_query *qry)
+{
+	struct kr_nsrep *ns = &qry->ns;
+	struct kr_context *ctx = ns->ctx;
+	unsigned score = KR_NS_MAX_SCORE;
+	unsigned reputation = 0;
+	uint8_t *addr_choice[KR_NSREP_MAXADDR] = { NULL, };
+
+	/* Fetch NS reputation */
+	if (ctx->cache_rep) {
+		unsigned *cached = lru_get_try(ctx->cache_rep, (const char *)owner,
+					       knot_dname_size(owner));
+		if (cached) {
+			reputation = *cached;
+		}
+	}
+
+	/* Favour nameservers with unknown addresses to probe them,
+	 * otherwise discover the current best address for the NS. */
+	if (addr_set->len == 0) {
+		score = KR_NS_UNKNOWN;
+		/* If the server doesn't have IPv6, give it disadvantage. */
+		if (reputation & KR_NS_NOIP6) {
+			score += FAVOUR_IPV6;
+			/* If the server is unknown but has rep record, treat it as timeouted */
+			if (reputation & KR_NS_NOIP4) {
+				score = KR_NS_UNKNOWN;
+				/* Try to start with clean slate */
+				if (!(qry->flags.NO_IPV6)) {
+					reputation &= ~KR_NS_NOIP6;
+				}
+				if (!(qry->flags.NO_IPV4)) {
+					reputation &= ~KR_NS_NOIP4;
+				}
+			}
+		}
+	} else {
+		score = eval_addr_set(addr_set, ctx, qry->flags, score, addr_choice);
+	}
+
+	/* Probabilistic bee foraging strategy (naive).
+	 * The fastest NS is preferred by workers until it is depleted (timeouts or degrades),
+	 * at the same time long distance scouts probe other sources (low probability).
+	 * Servers on TIMEOUT will not have probed at all.
+	 * Servers with score above KR_NS_LONG will have periodically removed from
+	 * reputation cache, so that kresd can reprobe them. */
+	if (score >= KR_NS_TIMEOUT) {
+		return kr_ok();
+	} else if (score <= ns->score &&
+	   (score < KR_NS_LONG  || qry->flags.NO_THROTTLE)) {
+		update_nsrep_set(ns, owner, addr_choice, score);
+		ns->reputation = reputation;
+	} else if (kr_rand_coin(1, 10) &&
+		   !kr_rand_coin(score, KR_NS_MAX_SCORE)) {
+		/* With 10% chance probe server with a probability
+		 * given by its RTT / MAX_RTT. */
+		update_nsrep_set(ns, owner, addr_choice, score);
+		ns->reputation = reputation;
+		return 1; /* Stop evaluation */
+	} else if (ns->score > KR_NS_MAX_SCORE) {
+		/* Check if any server was already selected.
+		 * If no, pick current server and continue evaluation. */
+		update_nsrep_set(ns, owner, addr_choice, score);
+		ns->reputation = reputation;
+	}
+
+	return kr_ok();
+}
+
+int kr_nsrep_set(struct kr_query *qry, size_t index, const struct sockaddr *sock)
+{
+	if (!qry) {
+		return kr_error(EINVAL);
+	}
+	if (index >= KR_NSREP_MAXADDR) {
+		return kr_error(ENOSPC);
+	}
+
+	if (!sock) {
+		qry->ns.name = (const uint8_t *)"";
+		qry->ns.addr[index].ip.sa_family = AF_UNSPEC;
+		return kr_ok();
+	}
+
+	switch (sock->sa_family) {
+	case AF_INET:
+		if (qry->flags.NO_IPV4) {
+			return kr_error(ENOENT);
+		}
+		qry->ns.addr[index].ip4 = *(const struct sockaddr_in *)sock;
+		break;
+	case AF_INET6:
+		if (qry->flags.NO_IPV6) {
+			return kr_error(ENOENT);
+		}
+		qry->ns.addr[index].ip6 = *(const struct sockaddr_in6 *)sock;
+		break;
+	default:
+		qry->ns.addr[index].ip.sa_family = AF_UNSPEC;
+		return kr_error(EINVAL);
+	}
+
+	qry->ns.name = (const uint8_t *)"";
+	/* Reset score on first entry */
+	if (index == 0) {
+		qry->ns.score = KR_NS_UNKNOWN;
+		qry->ns.reputation = 0;
+	}
+
+	/* Retrieve RTT from cache */
+	struct kr_context *ctx = qry->ns.ctx;
+	kr_nsrep_rtt_lru_entry_t *rtt_cache_entry = ctx
+		? lru_get_try(ctx->cache_rtt, kr_inaddr(sock), kr_family_len(sock->sa_family))
+		: NULL;
+	if (rtt_cache_entry) {
+		qry->ns.score = MIN(qry->ns.score, rtt_cache_entry->score);
+	}
+
+	return kr_ok();
+}
+
+#define ELECT_INIT(ns, ctx_) do { \
+	(ns)->ctx = (ctx_); \
+	(ns)->addr[0].ip.sa_family = AF_UNSPEC; \
+	(ns)->reputation = 0; \
+	(ns)->score = KR_NS_MAX_SCORE + 1; \
+} while (0)
+
+int kr_nsrep_elect(struct kr_query *qry, struct kr_context *ctx)
+{
+	if (!qry || !ctx) {
+		//assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+
+	struct kr_nsrep *ns = &qry->ns;
+	ELECT_INIT(ns, ctx);
+
+	int ret = kr_ok();
+	trie_it_t *it;
+	for (it = trie_it_begin(qry->zone_cut.nsset); !trie_it_finished(it);
+							trie_it_next(it)) {
+		ret = eval_nsrep(/* we trust it's a correct dname */
+				 (const knot_dname_t *)trie_it_key(it, NULL),
+				 (const pack_t *)*trie_it_val(it), qry);
+		if (ret) break;
+	}
+	trie_it_free(it);
+
+	if (qry->ns.score <= KR_NS_MAX_SCORE && qry->ns.score >= KR_NS_LONG) {
+		/* This is a low-reliability probe,
+		 * go with TCP to get ICMP reachability check. */
+		qry->flags.TCP = true;
+	}
+	return ret;
+}
+
+int kr_nsrep_elect_addr(struct kr_query *qry, struct kr_context *ctx)
+{
+	if (!qry || !ctx) {
+		//assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+
+	/* Get address list for this NS */
+	struct kr_nsrep *ns = &qry->ns;
+	ELECT_INIT(ns, ctx);
+	pack_t *addr_set = kr_zonecut_find(&qry->zone_cut, ns->name);
+	if (!addr_set) {
+		return kr_error(ENOENT);
+	}
+	/* Evaluate addr list */
+	uint8_t *addr_choice[KR_NSREP_MAXADDR] = { NULL, };
+	unsigned score = eval_addr_set(addr_set, ctx, qry->flags, ns->score, addr_choice);
+	update_nsrep_set(ns, ns->name, addr_choice, score);
+	return kr_ok();
+}
+
+#undef ELECT_INIT
+
+int kr_nsrep_update_rtt(struct kr_nsrep *ns, const struct sockaddr *addr,
+			unsigned score, kr_nsrep_rtt_lru_t *cache, int umode)
+{
+	if (!cache || umode > KR_NS_MAX || umode < 0) {
+		return kr_error(EINVAL);
+	}
+
+	/* Get `addr`, and later its raw string. */
+	if (addr) {
+		/* Caller provided specific address, OK. */
+	} else if (ns != NULL) {
+		addr = &ns->addr[0].ip;
+	} else {
+		assert(false && "kr_nsrep_update_rtt: don't know what address to update");
+		return kr_error(EINVAL);
+	}
+	const char *addr_in = kr_inaddr(addr);
+	size_t addr_len = kr_inaddr_len(addr);
+	if (!addr_in || addr_len <= 0) {
+		assert(false && "kr_nsrep_update_rtt: incorrect address");
+		return kr_error(EINVAL);
+	}
+
+	bool is_new_entry = false;
+	kr_nsrep_rtt_lru_entry_t  *cur = lru_get_new(cache, addr_in, addr_len,
+						     (&is_new_entry));
+	if (!cur) {
+		return kr_ok();
+	}
+	if (score <= KR_NS_GLUED) {
+		score = KR_NS_GLUED + 1;
+	}
+	/* If there's nothing to update, we reset it unless KR_NS_UPDATE_NORESET
+	 * mode was requested.  New items are zeroed by LRU automatically. */
+	if (is_new_entry && umode != KR_NS_UPDATE_NORESET) {
+		umode = KR_NS_RESET;
+	}
+	unsigned new_score = 0;
+	/* Update score, by default smooth over last two measurements. */
+	switch (umode) {
+	case KR_NS_UPDATE:
+	case KR_NS_UPDATE_NORESET:
+		new_score = (cur->score + score) / 2; break;
+	case KR_NS_RESET:  new_score = score; break;
+	case KR_NS_ADD:    new_score = MIN(KR_NS_MAX_SCORE - 1, cur->score + score); break;
+	case KR_NS_MAX:    new_score = MAX(cur->score, score); break;
+	default:           return kr_error(EINVAL);
+	}
+	/* Score limits */
+	if (new_score > KR_NS_MAX_SCORE) {
+		new_score = KR_NS_MAX_SCORE;
+	}
+	if (new_score >= KR_NS_TIMEOUT && cur->score < KR_NS_TIMEOUT) {
+		/* Set the timestamp only when NS became "timeouted" */
+		cur->tout_timestamp = kr_now();
+	}
+	cur->score = new_score;
+	return kr_ok();
+}
+
+int kr_nsrep_update_rep(struct kr_nsrep *ns, unsigned reputation, kr_nsrep_lru_t *cache)
+{
+	if (!ns || !cache ) {
+		return kr_error(EINVAL);
+	}
+
+	/* Store in the struct */
+	ns->reputation = reputation;
+	/* Store reputation in the LRU cache */
+	unsigned *cur = lru_get_new(cache, (const char *)ns->name,
+				    knot_dname_size(ns->name), NULL);
+	if (cur) {
+		*cur = reputation;
+	}
+	return kr_ok();
+}
+
+int kr_nsrep_copy_set(struct kr_nsrep *dst, const struct kr_nsrep *src)
+{
+	if (!dst || !src ) {
+		return kr_error(EINVAL);
+	}
+
+	memcpy(dst, src, sizeof(struct kr_nsrep));
+	dst->name = (const uint8_t *)"";
+	dst->score = KR_NS_UNKNOWN;
+	dst->reputation = 0;
+
+	return kr_ok();
+}
+
+int kr_nsrep_sort(struct kr_nsrep *ns, struct kr_context *ctx)
+{
+	if (!ns || !ctx) {
+		assert(false);
+		return kr_error(EINVAL);
+	}
+
+	kr_nsrep_rtt_lru_t *rtt_cache = ctx->cache_rtt;
+
+	ns->reputation = 0;
+	ns->score = KR_NS_MAX_SCORE + 1;
+
+	if (ns->addr[0].ip.sa_family == AF_UNSPEC) {
+		return kr_error(EINVAL);
+	}
+
+	/* Compute the scores.  Unfortunately there's no space for scores
+	 * along the addresses. */
+	unsigned scores[KR_NSREP_MAXADDR];
+	int i;
+	bool timeouted_address_is_already_selected = false;
+	for (i = 0; i < KR_NSREP_MAXADDR; ++i) {
+		const struct sockaddr *sa = &ns->addr[i].ip;
+		if (sa->sa_family == AF_UNSPEC) {
+			break;
+		}
+		kr_nsrep_rtt_lru_entry_t *rtt_cache_entry = lru_get_try(rtt_cache,
+									kr_inaddr(sa),
+									kr_family_len(sa->sa_family));
+		if (!rtt_cache_entry) {
+			scores[i] = 1; /* prefer unknown to probe RTT */
+		} else if (rtt_cache_entry->score < KR_NS_FWD_TIMEOUT) {
+			/* some probability to bump bad ones up for re-probe */
+			scores[i] = rtt_cache_entry->score;
+			/* The lower the rtt, the more likely it will be selected. */
+			if (!kr_rand_coin(rtt_cache_entry->score, KR_NS_FWD_TIMEOUT)) {
+				scores[i] = 1;
+			}
+		} else {
+			uint64_t now = kr_now();
+			uint64_t elapsed = now - rtt_cache_entry->tout_timestamp;
+			scores[i] = KR_NS_MAX_SCORE + 1;
+			elapsed = elapsed > UINT_MAX ? UINT_MAX : elapsed;
+			if (elapsed > ctx->cache_rtt_tout_retry_interval &&
+			    !timeouted_address_is_already_selected) {
+				scores[i] = 1;
+				rtt_cache_entry->tout_timestamp = now;
+				timeouted_address_is_already_selected = true;
+			}
+		}
+
+		/* Give advantage to IPv6. */
+		if (scores[i] <= KR_NS_MAX_SCORE && sa->sa_family == AF_INET) {
+			scores[i] += FAVOUR_IPV6;
+		}
+
+		if (VERBOSE_STATUS) {
+			kr_log_verbose("[     ][nsre] score %d for %s;\t cached RTT: %d\n",
+					scores[i], kr_straddr(sa),
+					rtt_cache_entry ? rtt_cache_entry->score : -1);
+		}
+	}
+
+	/* Select-sort the addresses. */
+	const int count = i;
+	for (i = 0; i < count - 1; ++i) {
+		/* find min from i onwards */
+		int min_i = i;
+		for (int j = i + 1; j < count; ++j) {
+			if (scores[j] < scores[min_i]) {
+				min_i = j;
+			}
+		}
+		/* swap the indices */
+		if (min_i != i) {
+			SWAP(scores[min_i], scores[i]);
+			SWAP(ns->addr[min_i], ns->addr[i]);
+		}
+	}
+
+	if (count > 0) {
+		ns->score = scores[0];
+		ns->reputation = 0;
+	}
+
+	return kr_ok();
+}
diff --git a/lib/nsrep.h b/lib/nsrep.h
new file mode 100644
index 0000000..cc35ca4
--- /dev/null
+++ b/lib/nsrep.h
@@ -0,0 +1,188 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <netinet/in.h>
+#include <sys/socket.h>
+#include <libknot/dname.h>
+#include <limits.h>
+
+#include "lib/defines.h"
+#include "lib/generic/lru.h"
+
+struct kr_query;
+
+/** 
+  * NS RTT score (special values).
+  * @note RTT is measured in milliseconds.
+  */
+enum kr_ns_score {
+	KR_NS_MAX_SCORE     = 20 * KR_CONN_RTT_MAX, /* max possible value */
+	KR_NS_FWD_TIMEOUT   = (95 * 10000) / 100, /* timeout for upstream recursor,
+						   * 95 percents from max resolution time */
+	KR_NS_TIMEOUT       = (95 * KR_CONN_RTT_MAX) / 100, /* timeout for upstream auth */
+	KR_NS_LONG          = (3 * KR_NS_TIMEOUT) / 4,
+	KR_NS_UNKNOWN       = KR_NS_TIMEOUT / 2,
+	KR_NS_PENALTY       = 100,
+	KR_NS_GLUED         = 10
+};
+
+/**
+ *  See kr_nsrep_update_rtt()
+ */
+#define KR_NS_DEAD (((KR_NS_TIMEOUT * 4) + 3) / 3)
+#define KR_NS_FWD_DEAD (((KR_NS_FWD_TIMEOUT * 4) + 3) / 3)
+
+/** If once NS was marked as "timeouted", it won't participate in NS elections
+ * at least KR_NS_TIMEOUT_RETRY_INTERVAL milliseconds (now: one second). */
+#define KR_NS_TIMEOUT_RETRY_INTERVAL 1000
+
+/**
+ * NS QoS flags.
+ */
+enum kr_ns_rep {
+	KR_NS_NOIP4  = 1 << 0, /**< NS has no IPv4 */
+	KR_NS_NOIP6  = 1 << 1, /**< NS has no IPv6 */
+	KR_NS_NOEDNS = 1 << 2  /**< NS has no EDNS support */
+};
+
+/**
+ * NS RTT update modes.
+ * First update is always KR_NS_RESET unless
+ * KR_NS_UPDATE_NORESET mode had choosen.
+ */
+enum kr_ns_update_mode {
+	KR_NS_UPDATE = 0,     /**< Update as smooth over last two measurements */
+	KR_NS_UPDATE_NORESET, /**< Same as KR_NS_UPDATE, but disable fallback to
+			       *   KR_NS_RESET on newly added entries.
+			       *   Zero is used as initial value. */
+	KR_NS_RESET,          /**< Set to given value */
+	KR_NS_ADD,            /**< Increment current value */
+	KR_NS_MAX             /**< Set to maximum of current/proposed value. */
+};
+
+struct kr_nsrep_rtt_lru_entry {
+	unsigned score;	          /* combined rtt */
+	uint64_t tout_timestamp;  /* The time when score became
+				   * greater or equal then KR_NS_TIMEOUT.
+				   * Is meaningful only when score >= KR_NS_TIMEOUT */
+};
+
+typedef struct kr_nsrep_rtt_lru_entry kr_nsrep_rtt_lru_entry_t;
+
+/**
+ * NS QoS tracking.
+ */
+typedef lru_t(kr_nsrep_rtt_lru_entry_t) kr_nsrep_rtt_lru_t;
+
+/**
+ * NS reputation tracking.
+ */
+typedef lru_t(unsigned) kr_nsrep_lru_t;
+
+/* Maximum count of addresses probed in one go (last is left empty) */
+#define KR_NSREP_MAXADDR 4
+
+/**
+ * Name server representation.
+ * Contains extra information about the name server, e.g. score
+ * or other metadata.
+ */
+struct kr_nsrep
+{
+	unsigned score;                  /**< NS score */
+	unsigned reputation;             /**< NS reputation */
+	const knot_dname_t *name;        /**< NS name */
+	struct kr_context *ctx;          /**< Resolution context */
+	union inaddr addr[KR_NSREP_MAXADDR];        /**< NS address(es) */
+};
+
+/**
+ * Set given NS address.  (Very low-level access to the list.)
+ * @param  qry      updated query
+ * @param  index    index of the updated target
+ * @param  sock     socket address to use (sockaddr_in or sockaddr_in6 or NULL)
+ * @return          0 or an error code, in particular kr_error(ENOENT) for net.ipvX
+ */
+KR_EXPORT
+int kr_nsrep_set(struct kr_query *qry, size_t index, const struct sockaddr *sock);
+
+/**
+ * Elect best nameserver/address pair from the nsset.
+ * @param  qry          updated query
+ * @param  ctx          resolution context
+ * @return              0 or an error code
+ */
+KR_EXPORT
+int kr_nsrep_elect(struct kr_query *qry, struct kr_context *ctx);
+
+/**
+ * Elect best nameserver/address pair from the nsset.
+ * @param  qry          updated query
+ * @param  ctx          resolution context
+ * @return              0 or an error code
+ */
+KR_EXPORT
+int kr_nsrep_elect_addr(struct kr_query *qry, struct kr_context *ctx);
+
+/**
+ * Update NS address RTT information.
+ *
+ * @brief In KR_NS_UPDATE mode reputation is smoothed over last N measurements.
+ * 
+ * @param  ns           updated NS representation
+ * @param  addr         chosen address (NULL for first)
+ * @param  score        new score (i.e. RTT), see enum kr_ns_score
+ * @param  cache        RTT LRU cache
+ * @param  umode        update mode (KR_NS_UPDATE or KR_NS_RESET or KR_NS_ADD)
+ * @return              0 on success, error code on failure
+ */
+KR_EXPORT
+int kr_nsrep_update_rtt(struct kr_nsrep *ns, const struct sockaddr *addr,
+			unsigned score, kr_nsrep_rtt_lru_t *cache, int umode);
+
+/**
+ * Update NSSET reputation information.
+ * 
+ * @param  ns           updated NS representation
+ * @param  reputation   combined reputation flags, see enum kr_ns_rep
+ * @param  cache        LRU cache
+ * @return              0 on success, error code on failure
+ */
+KR_EXPORT
+int kr_nsrep_update_rep(struct kr_nsrep *ns, unsigned reputation, kr_nsrep_lru_t *cache);
+/**
+ * Copy NSSET reputation information and resets score.
+ *
+ * @param  dst          updated NS representation
+ * @param  src          source NS representation
+ * @return              0 on success, error code on failure
+ */
+int kr_nsrep_copy_set(struct kr_nsrep *dst, const struct kr_nsrep *src);
+
+/**
+ * Sort addresses in the query nsrep list by cached RTT.
+ * if RTT is greater then KR_NS_TIMEOUT, address will placed at the beginning of the
+ * nsrep list once in cache.ns_tout() milliseconds. Otherwise it will be sorted
+ * as if it has cached RTT equal to KR_NS_MAX_SCORE + 1.
+ * @param  ns           updated kr_nsrep
+ * @param  ctx          name resolution context.
+ * @return              0 or an error code
+ * @note   ns reputation is zeroed and score is set to KR_NS_MAX_SCORE + 1.
+ */
+KR_EXPORT
+int kr_nsrep_sort(struct kr_nsrep *ns,  struct kr_context *ctx);
diff --git a/lib/resolve.c b/lib/resolve.c
new file mode 100644
index 0000000..8718f25
--- /dev/null
+++ b/lib/resolve.c
@@ -0,0 +1,1648 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <ctype.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <arpa/inet.h>
+#include <libknot/rrtype/rdname.h>
+#include <libknot/descriptor.h>
+#include <ucw/mempool.h>
+#include "lib/resolve.h"
+#include "lib/layer.h"
+#include "lib/rplan.h"
+#include "lib/layer/iterate.h"
+#include "lib/dnssec/ta.h"
+#include "lib/dnssec.h"
+#if defined(ENABLE_COOKIES)
+#include "lib/cookies/control.h"
+#include "lib/cookies/helper.h"
+#include "lib/cookies/nonce.h"
+#else /* Define compatibility macros */
+#define KNOT_EDNS_OPTION_COOKIE 10
+#endif /* defined(ENABLE_COOKIES) */
+
+#define VERBOSE_MSG(qry, ...) QRVERBOSE((qry), "resl",  __VA_ARGS__)
+
+bool kr_rank_check(uint8_t rank)
+{
+	switch (rank & ~KR_RANK_AUTH) {
+	case KR_RANK_INITIAL:
+	case KR_RANK_OMIT:
+	case KR_RANK_TRY:
+	case KR_RANK_INDET:
+	case KR_RANK_BOGUS:
+	case KR_RANK_MISMATCH:
+	case KR_RANK_MISSING:
+	case KR_RANK_INSECURE:
+	case KR_RANK_SECURE:
+		return true;
+	default:
+		return false;
+	}
+}
+
+/** @internal Set @a yielded to all RRs with matching @a qry_uid. */
+static void set_yield(ranked_rr_array_t *array, const uint32_t qry_uid, const bool yielded)
+{
+	for (unsigned i = 0; i < array->len; ++i) {
+		ranked_rr_array_entry_t *entry = array->at[i];
+		if (entry->qry_uid == qry_uid) {
+			entry->yielded = yielded;
+		}
+	}
+}
+
+/**
+ * @internal Defer execution of current query.
+ * The current layer state and input will be pushed to a stack and resumed on next iteration.
+ */
+static int consume_yield(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req = ctx->req;
+	size_t pkt_size = pkt->size;
+	if (knot_pkt_has_tsig(pkt)) {
+		pkt_size += pkt->tsig_wire.len;
+	}
+	knot_pkt_t *pkt_copy = knot_pkt_new(NULL, pkt_size, &req->pool);
+	struct kr_layer_pickle *pickle = mm_alloc(&req->pool, sizeof(*pickle));
+	if (pickle && pkt_copy && knot_pkt_copy(pkt_copy, pkt) == 0) {
+		struct kr_query *qry = req->current_query;
+		pickle->api = ctx->api;
+		pickle->state = ctx->state;
+		pickle->pkt = pkt_copy;
+		pickle->next = qry->deferred;
+		qry->deferred = pickle;
+		set_yield(&req->answ_selected, qry->uid, true);
+		set_yield(&req->auth_selected, qry->uid, true);
+		return kr_ok();
+	}
+	return kr_error(ENOMEM);
+}
+static int begin_yield(kr_layer_t *ctx) { return kr_ok(); }
+static int reset_yield(kr_layer_t *ctx) { return kr_ok(); }
+static int finish_yield(kr_layer_t *ctx) { return kr_ok(); }
+static int produce_yield(kr_layer_t *ctx, knot_pkt_t *pkt) { return kr_ok(); }
+static int checkout_yield(kr_layer_t *ctx, knot_pkt_t *packet, struct sockaddr *dst, int type) { return kr_ok(); }
+static int answer_finalize_yield(kr_layer_t *ctx) { return kr_ok(); }
+
+/** @internal Macro for iterating module layers. */
+#define RESUME_LAYERS(from, r, qry, func, ...) \
+    (r)->current_query = (qry); \
+	for (size_t i = (from); i < (r)->ctx->modules->len; ++i) { \
+		struct kr_module *mod = (r)->ctx->modules->at[i]; \
+		if (mod->layer) { \
+			struct kr_layer layer = {.state = (r)->state, .api = mod->layer(mod), .req = (r)}; \
+			if (layer.api && layer.api->func) { \
+				(r)->state = layer.api->func(&layer, ##__VA_ARGS__); \
+				if ((r)->state == KR_STATE_YIELD) { \
+					func ## _yield(&layer, ##__VA_ARGS__); \
+					break; \
+				} \
+			} \
+		} \
+	} /* Invalidate current query. */ \
+	(r)->current_query = NULL
+
+/** @internal Macro for starting module iteration. */
+#define ITERATE_LAYERS(req, qry, func, ...) RESUME_LAYERS(0, req, qry, func, ##__VA_ARGS__)
+
+/** @internal Find layer id matching API. */
+static inline size_t layer_id(struct kr_request *req, const struct kr_layer_api *api) {
+	module_array_t *modules = req->ctx->modules;
+	for (size_t i = 0; i < modules->len; ++i) {
+		struct kr_module *mod = modules->at[i];
+		if (mod->layer && mod->layer(mod) == api) {
+			return i;
+		}
+	}
+	return 0; /* Not found, try all. */
+}
+
+/* @internal We don't need to deal with locale here */
+KR_CONST static inline bool isletter(unsigned chr)
+{ return (chr | 0x20 /* tolower */) - 'a' <= 'z' - 'a'; }
+
+/* Randomize QNAME letter case.
+ * This adds 32 bits of randomness at maximum, but that's more than an average domain name length.
+ * https://tools.ietf.org/html/draft-vixie-dnsext-dns0x20-00
+ */
+static void randomized_qname_case(knot_dname_t * restrict qname, uint32_t secret)
+{
+	if (secret == 0) {
+		return;
+	}
+	assert(qname);
+	const int len = knot_dname_size(qname) - 2; /* Skip first, last label. */
+	for (int i = 0; i < len; ++i) {
+		if (isletter(*++qname)) {
+				*qname ^= ((secret >> (i & 31)) & 1) * 0x20;
+		}
+	}
+}
+
+/** Invalidate current NS/addr pair. */
+static int invalidate_ns(struct kr_rplan *rplan, struct kr_query *qry)
+{
+	if (qry->ns.addr[0].ip.sa_family != AF_UNSPEC) {
+		const char *addr = kr_inaddr(&qry->ns.addr[0].ip);
+		int addr_len = kr_inaddr_len(&qry->ns.addr[0].ip);
+		return kr_zonecut_del(&qry->zone_cut, qry->ns.name, addr, addr_len);
+	} else {
+		return kr_zonecut_del_all(&qry->zone_cut, qry->ns.name);
+	}
+}
+
+/** This turns of QNAME minimisation if there is a non-terminal between current zone cut, and name target.
+ *  It save several minimization steps, as the zone cut is likely final one.
+ */
+static void check_empty_nonterms(struct kr_query *qry, knot_pkt_t *pkt, struct kr_cache *cache, uint32_t timestamp)
+{
+	// FIXME cleanup, etc.
+#if 0
+	if (qry->flags.NO_MINIMIZE) {
+		return;
+	}
+
+	const knot_dname_t *target = qry->sname;
+	const knot_dname_t *cut_name = qry->zone_cut.name;
+	if (!target || !cut_name)
+		return;
+
+	struct kr_cache_entry *entry = NULL;
+	/* @note: The non-terminal must be direct child of zone cut (e.g. label distance <= 2),
+	 *        otherwise this would risk leaking information to parent if the NODATA TTD > zone cut TTD. */
+	int labels = knot_dname_labels(target, NULL) - knot_dname_labels(cut_name, NULL);
+	while (target[0] && labels > 2) {
+		target = knot_wire_next_label(target, NULL);
+		--labels;
+	}
+	for (int i = 0; i < labels; ++i) {
+		int ret = kr_cache_peek(cache, KR_CACHE_PKT, target, KNOT_RRTYPE_NS, &entry, &timestamp);
+		if (ret == 0) { /* Either NXDOMAIN or NODATA, start here. */
+			/* @todo We could stop resolution here for NXDOMAIN, but we can't because of broken CDNs */
+			qry->flags.NO_MINIMIZE = true;
+			kr_make_query(qry, pkt);
+			break;
+		}
+		assert(target[0]);
+		target = knot_wire_next_label(target, NULL);
+	}
+	kr_cache_sync(cache);
+#endif
+}
+
+static int ns_fetch_cut(struct kr_query *qry, const knot_dname_t *requested_name,
+			struct kr_request *req, knot_pkt_t *pkt)
+{
+	/* It can occur that here parent query already have
+	 * provably insecured zonecut which not in the cache yet. */
+	struct kr_qflags pflags;
+	if (qry->parent) {
+		pflags = qry->parent->flags;
+	}
+	const bool is_insecured = qry->parent != NULL
+		&& !(pflags.AWAIT_IPV4 || pflags.AWAIT_IPV6)
+		&& (pflags.DNSSEC_INSECURE || pflags.DNSSEC_NODS);
+
+	/* Want DNSSEC if it's possible to secure this name
+	 * (e.g. is covered by any TA) */
+	if (is_insecured) {
+		/* If parent is unsecured we don't want DNSSEC
+		 * even if cut name is covered by TA. */
+		qry->flags.DNSSEC_WANT = false;
+		qry->flags.DNSSEC_INSECURE = true;
+		VERBOSE_MSG(qry, "=> going insecure because parent query is insecure\n");
+	} else if (kr_ta_covers_qry(req->ctx, qry->zone_cut.name, KNOT_RRTYPE_NS)) {
+		qry->flags.DNSSEC_WANT = true;
+	} else {
+		qry->flags.DNSSEC_WANT = false;
+		VERBOSE_MSG(qry, "=> going insecure because there's no covering TA\n");
+	}
+
+	struct kr_zonecut cut_found;
+	kr_zonecut_init(&cut_found, requested_name, req->rplan.pool);
+	/* Cut that has been found can differs from cut that has been requested.
+	 * So if not already insecured,
+	 * try to fetch ta & keys even if initial cut name not covered by TA */
+	bool secured = !is_insecured;
+	int ret = kr_zonecut_find_cached(req->ctx, &cut_found, requested_name,
+					 qry, &secured);
+	if (ret == kr_error(ENOENT)) {
+		/* No cached cut found, start from SBELT
+		 * and issue priming query. */
+		kr_zonecut_deinit(&cut_found);
+		ret = kr_zonecut_set_sbelt(req->ctx, &qry->zone_cut);
+		if (ret != 0) {
+			return KR_STATE_FAIL;
+		}
+		VERBOSE_MSG(qry, "=> using root hints\n");
+		qry->flags.AWAIT_CUT = false;
+		return KR_STATE_DONE;
+	} else if (ret != kr_ok()) {
+		kr_zonecut_deinit(&cut_found);
+		return KR_STATE_FAIL;
+	}
+
+	/* Find out security status.
+	 * Go insecure if the zone cut is provably insecure */
+	if ((qry->flags.DNSSEC_WANT) && !secured) {
+		VERBOSE_MSG(qry, "=> NS is provably without DS, going insecure\n");
+		qry->flags.DNSSEC_WANT = false;
+		qry->flags.DNSSEC_INSECURE = true;
+	}
+	/* Zonecut name can change, check it again
+	 * to prevent unnecessary DS & DNSKEY queries */
+	if (!(qry->flags.DNSSEC_INSECURE) &&
+	    kr_ta_covers_qry(req->ctx, cut_found.name, KNOT_RRTYPE_NS)) {
+		qry->flags.DNSSEC_WANT = true;
+	} else {
+		qry->flags.DNSSEC_WANT = false;
+	}
+	/* Check if any DNSKEY found for cached cut */
+	if (qry->flags.DNSSEC_WANT && cut_found.key == NULL &&
+	    kr_zonecut_is_empty(&cut_found)) {
+		/* Cut found and there are no proofs of zone insecurity.
+		 * But no DNSKEY found and no glue fetched.
+		 * We have got circular dependency - must fetch A\AAAA
+		 * from authoritative, but we have no key to verify it. */
+		kr_zonecut_deinit(&cut_found);
+		if (requested_name[0] != '\0' ) {
+			/* If not root - try next label */
+			return KR_STATE_CONSUME;
+		}
+		/* No cached cut & keys found, start from SBELT */
+		ret = kr_zonecut_set_sbelt(req->ctx, &qry->zone_cut);
+		if (ret != 0) {
+			return KR_STATE_FAIL;
+		}
+		VERBOSE_MSG(qry, "=> using root hints\n");
+		qry->flags.AWAIT_CUT = false;
+		return KR_STATE_DONE;
+	}
+	/* Use the found zone cut. */
+	kr_zonecut_move(&qry->zone_cut, &cut_found);
+	/* Check if there's a non-terminal between target and current cut. */
+	struct kr_cache *cache = &req->ctx->cache;
+	check_empty_nonterms(qry, pkt, cache, qry->timestamp.tv_sec);
+	/* Cut found */
+	return KR_STATE_PRODUCE;
+}
+
+static int ns_resolve_addr(struct kr_query *qry, struct kr_request *param)
+{
+	struct kr_rplan *rplan = &param->rplan;
+	struct kr_context *ctx = param->ctx;
+
+
+	/* Start NS queries from root, to avoid certain cases
+	 * where a NS drops out of cache and the rest is unavailable,
+	 * this would lead to dependency loop in current zone cut.
+	 * Prefer IPv6 and continue with IPv4 if not available.
+	 */
+	uint16_t next_type = 0;
+	if (!(qry->flags.AWAIT_IPV6) &&
+	    !(ctx->options.NO_IPV6)) {
+		next_type = KNOT_RRTYPE_AAAA;
+		qry->flags.AWAIT_IPV6 = true;
+	} else if (!(qry->flags.AWAIT_IPV4) &&
+		   !(ctx->options.NO_IPV4)) {
+		next_type = KNOT_RRTYPE_A;
+		qry->flags.AWAIT_IPV4 = true;
+		/* Hmm, no useable IPv6 then. */
+		qry->ns.reputation |= KR_NS_NOIP6;
+		kr_nsrep_update_rep(&qry->ns, qry->ns.reputation, ctx->cache_rep);
+	}
+	/* Bail out if the query is already pending or dependency loop. */
+	if (!next_type || kr_rplan_satisfies(qry->parent, qry->ns.name, KNOT_CLASS_IN, next_type)) {
+		/* Fall back to SBELT if root server query fails. */
+		if (!next_type && qry->zone_cut.name[0] == '\0') {
+			VERBOSE_MSG(qry, "=> fallback to root hints\n");
+			kr_zonecut_set_sbelt(ctx, &qry->zone_cut);
+			qry->flags.NO_THROTTLE = true; /* Pick even bad SBELT servers */
+			return kr_error(EAGAIN);
+		}
+		/* No IPv4 nor IPv6, flag server as unusable. */
+		VERBOSE_MSG(qry, "=> unresolvable NS address, bailing out\n");
+		qry->ns.reputation |= KR_NS_NOIP4 | KR_NS_NOIP6;
+		kr_nsrep_update_rep(&qry->ns, qry->ns.reputation, ctx->cache_rep);
+		invalidate_ns(rplan, qry);
+		return kr_error(EHOSTUNREACH);
+	}
+	/* Push new query to the resolution plan */
+	struct kr_query *next =
+		kr_rplan_push(rplan, qry, qry->ns.name, KNOT_CLASS_IN, next_type);
+	if (!next) {
+		return kr_error(ENOMEM);
+	}
+	next->flags.NONAUTH = true;
+
+	/* At the root level with no NS addresses, add SBELT subrequest. */
+	int ret = 0;
+	if (qry->zone_cut.name[0] == '\0') {
+		ret = kr_zonecut_set_sbelt(ctx, &next->zone_cut);
+		if (ret == 0) { /* Copy TA and key since it's the same cut to avoid lookup. */
+			kr_zonecut_copy_trust(&next->zone_cut, &qry->zone_cut);
+			kr_zonecut_set_sbelt(ctx, &qry->zone_cut); /* Add SBELT to parent in case query fails. */
+			qry->flags.NO_THROTTLE = true; /* Pick even bad SBELT servers */
+		}
+	} else {
+		next->flags.AWAIT_CUT = true;
+	}
+	return ret;
+}
+
+static int edns_put(knot_pkt_t *pkt, bool reclaim)
+{
+	if (!pkt->opt_rr) {
+		return kr_ok();
+	}
+	if (reclaim) {
+		/* Reclaim reserved size. */
+		int ret = knot_pkt_reclaim(pkt, knot_edns_wire_size(pkt->opt_rr));
+		if (ret != 0) {
+			return ret;
+		}
+	}
+	/* Write to packet. */
+	assert(pkt->current == KNOT_ADDITIONAL);
+	return knot_pkt_put(pkt, KNOT_COMPR_HINT_NONE, pkt->opt_rr, KNOT_PF_FREE);
+}
+
+/** Removes last EDNS OPT RR written to the packet. */
+static int edns_erase_and_reserve(knot_pkt_t *pkt)
+{
+	/* Nothing to be done. */
+	if (!pkt || !pkt->opt_rr) {
+		return 0;
+	}
+
+	/* Fail if the data are located elsewhere than at the end of packet. */
+	if (pkt->current != KNOT_ADDITIONAL ||
+	    pkt->opt_rr != &pkt->rr[pkt->rrset_count - 1]) {
+		return -1;
+	}
+
+	size_t len = knot_rrset_size(pkt->opt_rr);
+	int16_t rr_removed = pkt->opt_rr->rrs.count;
+	/* Decrease rrset counters. */
+	pkt->rrset_count -= 1;
+	pkt->sections[pkt->current].count -= 1;
+	pkt->size -= len;
+	knot_wire_add_arcount(pkt->wire, -rr_removed); /* ADDITIONAL */
+
+	pkt->opt_rr = NULL;
+
+	/* Reserve the freed space. */
+	return knot_pkt_reserve(pkt, len);
+}
+
+static int edns_create(knot_pkt_t *pkt, knot_pkt_t *template, struct kr_request *req)
+{
+	pkt->opt_rr = knot_rrset_copy(req->ctx->opt_rr, &pkt->mm);
+	size_t wire_size = knot_edns_wire_size(pkt->opt_rr);
+#if defined(ENABLE_COOKIES)
+	if (req->ctx->cookie_ctx.clnt.enabled ||
+	    req->ctx->cookie_ctx.srvr.enabled) {
+		wire_size += KR_COOKIE_OPT_MAX_LEN;
+	}
+#endif /* defined(ENABLE_COOKIES) */
+	if (req->qsource.flags.tls) {
+		if (req->ctx->tls_padding == -1)
+			/* FIXME: we do not know how to reserve space for the
+			 * default padding policy, since we can't predict what
+			 * it will select. So i'm just guessing :/ */
+			wire_size += KNOT_EDNS_OPTION_HDRLEN + 512;
+		if (req->ctx->tls_padding >= 2)
+			wire_size += KNOT_EDNS_OPTION_HDRLEN + req->ctx->tls_padding;
+	}
+	return knot_pkt_reserve(pkt, wire_size);
+}
+
+static int answer_prepare(struct kr_request *req, knot_pkt_t *query)
+{
+	knot_pkt_t *answer = req->answer;
+	if (knot_pkt_init_response(answer, query) != 0) {
+		return kr_error(ENOMEM); /* Failed to initialize answer */
+	}
+	/* Handle EDNS in the query */
+	if (knot_pkt_has_edns(query)) {
+		answer->opt_rr = knot_rrset_copy(req->ctx->opt_rr, &answer->mm);
+		if (answer->opt_rr == NULL){
+			return kr_error(ENOMEM);
+		}
+		/* Set DO bit if set (DNSSEC requested). */
+		if (knot_pkt_has_dnssec(query)) {
+			knot_edns_set_do(answer->opt_rr);
+		}
+	}
+	return kr_ok();
+}
+
+/** @return error code, ignoring if forced to truncate the packet. */
+static int write_extra_records(const rr_array_t *arr, uint16_t reorder, knot_pkt_t *answer)
+{
+	for (size_t i = 0; i < arr->len; ++i) {
+		int err = knot_pkt_put_rotate(answer, 0, arr->at[i], reorder, 0);
+		if (err != KNOT_EOK) {
+			return err == KNOT_ESPACE ? kr_ok() : kr_error(err);
+		}
+	}
+	return kr_ok();
+}
+
+/**
+ * @param all_secure optionally &&-combine security of written RRs into its value.
+ *		     (i.e. if you pass a pointer to false, it will always remain)
+ * @param all_cname optionally output if all written RRs are CNAMEs and RRSIGs of CNAMEs
+ * @return error code, ignoring if forced to truncate the packet.
+ */
+static int write_extra_ranked_records(const ranked_rr_array_t *arr, uint16_t reorder,
+				      knot_pkt_t *answer, bool *all_secure, bool *all_cname)
+{
+	const bool has_dnssec = knot_pkt_has_dnssec(answer);
+	bool all_sec = true;
+	bool all_cn = (all_cname != NULL); /* optim.: init as false if not needed */
+	int err = kr_ok();
+
+	for (size_t i = 0; i < arr->len; ++i) {
+		ranked_rr_array_entry_t * entry = arr->at[i];
+		if (!entry->to_wire) {
+			continue;
+		}
+		knot_rrset_t *rr = entry->rr;
+		if (!has_dnssec) {
+			if (rr->type != knot_pkt_qtype(answer) && knot_rrtype_is_dnssec(rr->type)) {
+				continue;
+			}
+		}
+		err = knot_pkt_put_rotate(answer, 0, rr, reorder, 0);
+		if (err != KNOT_EOK) {
+			if (err == KNOT_ESPACE) {
+				err = kr_ok();
+			}
+			break;
+		}
+
+		if (rr->type != KNOT_RRTYPE_RRSIG) {
+			all_sec = all_sec && kr_rank_test(entry->rank, KR_RANK_SECURE);
+		}
+		all_cn = all_cn && kr_rrset_type_maysig(entry->rr) == KNOT_RRTYPE_CNAME;
+	}
+
+	if (all_secure) {
+		*all_secure = *all_secure && all_sec;
+	}
+	if (all_cname) {
+		*all_cname = all_cn;
+	}
+	return err;
+}
+
+/** @internal Add an EDNS padding RR into the answer if requested and required. */
+static int answer_padding(struct kr_request *request)
+{
+	if (!request || !request->answer || !request->ctx) {
+		assert(false);
+		return kr_error(EINVAL);
+	}
+	int32_t padding = request->ctx->tls_padding;
+	knot_pkt_t *answer = request->answer;
+	knot_rrset_t *opt_rr = answer->opt_rr;
+	int32_t pad_bytes = -1;
+
+	if (padding == -1) { /* use the default padding policy from libknot */
+		pad_bytes =  knot_pkt_default_padding_size(answer, opt_rr);
+	}
+	if (padding >= 2) {
+		int32_t max_pad_bytes = knot_edns_get_payload(opt_rr) - (answer->size + knot_rrset_size(opt_rr));
+		pad_bytes = MIN(knot_edns_alignment_size(answer->size, knot_rrset_size(opt_rr), padding),
+				max_pad_bytes);
+	}
+
+	if (pad_bytes >= 0) {
+		uint8_t zeros[MAX(1, pad_bytes)];
+		memset(zeros, 0, sizeof(zeros));
+		int r = knot_edns_add_option(opt_rr, KNOT_EDNS_OPTION_PADDING,
+					     pad_bytes, zeros, &answer->mm);
+		if (r != KNOT_EOK) {
+			knot_rrset_clear(opt_rr, &answer->mm);
+			return kr_error(r);
+		}
+	}
+	return kr_ok();
+}
+
+static int answer_fail(struct kr_request *request)
+{
+	knot_pkt_t *answer = request->answer;
+	int ret = kr_pkt_clear_payload(answer);
+	knot_wire_clear_ad(answer->wire);
+	knot_wire_clear_aa(answer->wire);
+	knot_wire_set_rcode(answer->wire, KNOT_RCODE_SERVFAIL);
+	if (ret == 0 && answer->opt_rr) {
+		/* OPT in SERVFAIL response is still useful for cookies/additional info. */
+		knot_pkt_begin(answer, KNOT_ADDITIONAL);
+		answer_padding(request); /* Ignore failed padding in SERVFAIL answer. */
+		ret = edns_put(answer, false);
+	}
+	return ret;
+}
+
+static int answer_finalize(struct kr_request *request, int state)
+{
+	struct kr_rplan *rplan = &request->rplan;
+	knot_pkt_t *answer = request->answer;
+
+	/* Always set SERVFAIL for bogus answers. */
+	if (state == KR_STATE_FAIL && rplan->pending.len > 0) {
+		struct kr_query *last = array_tail(rplan->pending);
+		if ((last->flags.DNSSEC_WANT) && (last->flags.DNSSEC_BOGUS)) {
+			return answer_fail(request);
+		}
+	}
+
+	struct kr_query *last = rplan->resolved.len > 0 ? array_tail(rplan->resolved) : NULL;
+		/* TODO  ^^^^ this is slightly fragile */
+
+	/* AD flag.  We can only change `secure` from true to false.
+	 * Be conservative.  Primary approach: check ranks of all RRs in wire.
+	 * Only "negative answers" need special handling. */
+	bool secure = last != NULL && state == KR_STATE_DONE /*< suspicious otherwise */
+		&& knot_pkt_qtype(answer) != KNOT_RRTYPE_RRSIG;
+	if (last && (last->flags.STUB)) {
+		secure = false; /* don't trust forwarding for now */
+	}
+	if (last && (last->flags.DNSSEC_OPTOUT)) {
+		VERBOSE_MSG(NULL, "AD: opt-out\n");
+		secure = false; /* the last answer is insecure due to opt-out */
+	}
+
+	const uint16_t reorder = last ? last->reorder : 0;
+	bool answ_all_cnames = false/*arbitrary*/;
+	if (request->answ_selected.len > 0) {
+		assert(answer->current <= KNOT_ANSWER);
+		/* Write answer records. */
+		if (answer->current < KNOT_ANSWER) {
+			knot_pkt_begin(answer, KNOT_ANSWER);
+		}
+		if (write_extra_ranked_records(&request->answ_selected, reorder,
+						answer, &secure, &answ_all_cnames))
+		{
+			return answer_fail(request);
+		}
+	}
+
+	/* Write authority records. */
+	if (answer->current < KNOT_AUTHORITY) {
+		knot_pkt_begin(answer, KNOT_AUTHORITY);
+	}
+	if (write_extra_ranked_records(&request->auth_selected, reorder,
+	    answer, &secure, NULL)) {
+		return answer_fail(request);
+	}
+	/* Write additional records. */
+	knot_pkt_begin(answer, KNOT_ADDITIONAL);
+	if (write_extra_records(&request->additional, reorder, answer)) {
+		return answer_fail(request);
+	}
+	/* Write EDNS information */
+	if (answer->opt_rr) {
+		if (request->qsource.flags.tls) {
+			if (answer_padding(request) != kr_ok()) {
+				return answer_fail(request);
+			}
+		}
+		knot_pkt_begin(answer, KNOT_ADDITIONAL);
+		int ret = knot_pkt_put(answer, KNOT_COMPR_HINT_NONE,
+				       answer->opt_rr, KNOT_PF_FREE);
+		if (ret != KNOT_EOK) {
+			return answer_fail(request);
+		}
+	}
+
+	if (!last) secure = false; /*< should be no-op, mostly documentation */
+	/* AD: "negative answers" need more handling. */
+	if (kr_response_classify(answer) != PKT_NOERROR
+	    /* Additionally check for CNAME chains that "end in NODATA",
+	     * as those would also be PKT_NOERROR. */
+	    || (answ_all_cnames && knot_pkt_qtype(answer) != KNOT_RRTYPE_CNAME)) {
+
+		secure = secure && last->flags.DNSSEC_WANT
+			&& !last->flags.DNSSEC_BOGUS && !last->flags.DNSSEC_INSECURE;
+	}
+
+	if (secure) {
+		struct kr_query *cname_parent = last->cname_parent;
+		while (cname_parent != NULL) {
+			if (cname_parent->flags.DNSSEC_OPTOUT) {
+				secure = false;
+				break;
+			}
+			cname_parent = cname_parent->cname_parent;
+		}
+	}
+
+	/* No detailed analysis ATM, just _SECURE or not.
+	 * LATER: request->rank might better be computed in validator's finish phase. */
+	VERBOSE_MSG(last, "AD: request%s classified as SECURE\n", secure ? "" : " NOT");
+	request->rank = secure ? KR_RANK_SECURE : KR_RANK_INITIAL;
+
+	/* Clear AD if not secure.  ATM answer has AD=1 if requested secured answer. */
+	if (!secure) {
+		knot_wire_clear_ad(answer->wire);
+	}
+
+	return kr_ok();
+}
+
+static int query_finalize(struct kr_request *request, struct kr_query *qry, knot_pkt_t *pkt)
+{
+	int ret = 0;
+	knot_pkt_begin(pkt, KNOT_ADDITIONAL);
+	if (!(qry->flags.SAFEMODE)) {
+		/* Remove any EDNS records from any previous iteration. */
+		ret = edns_erase_and_reserve(pkt);
+		if (ret == 0) {
+			ret = edns_create(pkt, request->answer, request);
+		}
+		if (ret == 0) {
+			/* Stub resolution (ask for +rd and +do) */
+			if (qry->flags.STUB) {
+				knot_wire_set_rd(pkt->wire);
+				if (knot_pkt_has_dnssec(request->qsource.packet)) {
+					knot_edns_set_do(pkt->opt_rr);
+				}
+				if (knot_wire_get_cd(request->qsource.packet->wire)) {
+					knot_wire_set_cd(pkt->wire);
+				}
+			/* Full resolution (ask for +cd and +do) */
+			} else if (qry->flags.FORWARD) {
+				knot_wire_set_rd(pkt->wire);
+				knot_edns_set_do(pkt->opt_rr);
+				knot_wire_set_cd(pkt->wire);
+			} else if (qry->flags.DNSSEC_WANT) {
+				knot_edns_set_do(pkt->opt_rr);
+				knot_wire_set_cd(pkt->wire);
+			}
+		}
+	}
+	return ret;
+}
+
+int kr_resolve_begin(struct kr_request *request, struct kr_context *ctx, knot_pkt_t *answer)
+{
+	/* Initialize request */
+	request->ctx = ctx;
+	request->answer = answer;
+	request->options = ctx->options;
+	request->state = KR_STATE_CONSUME;
+	request->current_query = NULL;
+	array_init(request->additional);
+	array_init(request->answ_selected);
+	array_init(request->auth_selected);
+	array_init(request->add_selected);
+	request->answ_validated = false;
+	request->auth_validated = false;
+	request->rank = KR_RANK_INITIAL;
+	request->trace_log = NULL;
+	request->trace_finish = NULL;
+
+	/* Expect first query */
+	kr_rplan_init(&request->rplan, request, &request->pool);
+	return KR_STATE_CONSUME;
+}
+
+static int resolve_query(struct kr_request *request, const knot_pkt_t *packet)
+{
+	struct kr_rplan *rplan = &request->rplan;
+	const knot_dname_t *qname = knot_pkt_qname(packet);
+	uint16_t qclass = knot_pkt_qclass(packet);
+	uint16_t qtype = knot_pkt_qtype(packet);
+	struct kr_query *qry = NULL;
+	struct kr_context *ctx = request->ctx;
+	struct kr_cookie_ctx *cookie_ctx = ctx ? &ctx->cookie_ctx : NULL;
+
+	if (qname != NULL) {
+		qry = kr_rplan_push(rplan, NULL, qname, qclass, qtype);
+	} else if (cookie_ctx && cookie_ctx->srvr.enabled &&
+		   knot_wire_get_qdcount(packet->wire) == 0 &&
+		   knot_pkt_has_edns(packet) &&
+		   knot_pkt_edns_option(packet, KNOT_EDNS_OPTION_COOKIE)) {
+		/* Plan empty query only for cookies. */
+		qry = kr_rplan_push_empty(rplan, NULL);
+	}
+	if (!qry) {
+		return KR_STATE_FAIL;
+	}
+
+	if (qname != NULL) {
+		/* Deferred zone cut lookup for this query. */
+		qry->flags.AWAIT_CUT = true;
+		/* Want DNSSEC if it's posible to secure this name (e.g. is covered by any TA) */
+		if ((knot_wire_get_ad(packet->wire) || knot_pkt_has_dnssec(packet)) &&
+		    kr_ta_covers_qry(request->ctx, qname, qtype)) {
+			qry->flags.DNSSEC_WANT = true;
+		}
+	}
+
+	/* Initialize answer packet */
+	knot_pkt_t *answer = request->answer;
+	knot_wire_set_qr(answer->wire);
+	knot_wire_clear_aa(answer->wire);
+	knot_wire_set_ra(answer->wire);
+	knot_wire_set_rcode(answer->wire, KNOT_RCODE_NOERROR);
+
+	assert(request->qsource.packet);
+	if (knot_wire_get_cd(request->qsource.packet->wire)) {
+		knot_wire_set_cd(answer->wire);
+	} else if (qry->flags.DNSSEC_WANT) {
+		knot_wire_set_ad(answer->wire);
+	}
+
+	/* Expect answer, pop if satisfied immediately */
+	ITERATE_LAYERS(request, qry, begin);
+	if ((request->state & KR_STATE_DONE) != 0) {
+		kr_rplan_pop(rplan, qry);
+	} else if (qname == NULL) {
+		/* it is an empty query which must be resolved by
+		   `begin` layer of cookie module.
+		   If query isn't resolved, fail. */
+		request->state = KR_STATE_FAIL;
+	}
+	return request->state;
+}
+
+KR_PURE static bool kr_inaddr_equal(const struct sockaddr *a, const struct sockaddr *b)
+{
+	const int a_len = kr_inaddr_len(a);
+	const int b_len = kr_inaddr_len(b);
+	return a_len == b_len && memcmp(kr_inaddr(a), kr_inaddr(b), a_len) == 0;
+}
+
+static void update_nslist_rtt(struct kr_context *ctx, struct kr_query *qry, const struct sockaddr *src)
+{
+	/* Do not track in safe mode. */
+	if (qry->flags.SAFEMODE) {
+		return;
+	}
+
+	/* Calculate total resolution time from the time the query was generated. */
+	uint64_t elapsed = kr_now() - qry->timestamp_mono;
+	elapsed = elapsed > UINT_MAX ? UINT_MAX : elapsed;
+ 
+	/* NSs in the preference list prior to the one who responded will be penalised
+	 * with the RETRY timer interval. This is because we know they didn't respond
+	 * for N retries, so their RTT must be at least N * RETRY.
+	 * The NS in the preference list that responded will have RTT relative to the
+	 * time when the query was sent out, not when it was originated.
+	 */
+	for (size_t i = 0; i < KR_NSREP_MAXADDR; ++i) {
+		const struct sockaddr *addr = &qry->ns.addr[i].ip;
+		if (addr->sa_family == AF_UNSPEC) {
+			break;
+		}
+		/* If this address is the source of the answer, update its RTT */
+		if (kr_inaddr_equal(src, addr)) {
+			kr_nsrep_update_rtt(&qry->ns, addr, elapsed, ctx->cache_rtt, KR_NS_UPDATE);
+			WITH_VERBOSE(qry) {
+				char addr_str[INET6_ADDRSTRLEN];
+				inet_ntop(addr->sa_family, kr_inaddr(addr), addr_str, sizeof(addr_str));
+				VERBOSE_MSG(qry, "<= server: '%s' rtt: %"PRIu64" ms\n",
+						addr_str, elapsed);
+			}
+		} else {
+			/* Response didn't come from this IP, but we know the RTT must be at least
+			 * several RETRY timer tries, e.g. if we have addresses [a, b, c] and we have
+			 * tried [a, b] when the answer from 'a' came after 350ms, then we know
+			 * that 'b' didn't respond for at least 350 - (1 * 300) ms. We can't say that
+			 * its RTT is 50ms, but we can say that its score shouldn't be less than 50. */
+			 kr_nsrep_update_rtt(&qry->ns, addr, elapsed, ctx->cache_rtt, KR_NS_MAX);
+			 WITH_VERBOSE(qry) {
+			 	char addr_str[INET6_ADDRSTRLEN];
+			 	inet_ntop(addr->sa_family, kr_inaddr(addr), addr_str, sizeof(addr_str));
+				VERBOSE_MSG(qry, "<= server: '%s' rtt: >= %"PRIu64" ms\n",
+						addr_str, elapsed);
+			 }
+		}
+		/* Subtract query start time from elapsed time */
+		if (elapsed < KR_CONN_RETRY) {
+			break;
+		}
+		elapsed = elapsed - KR_CONN_RETRY;
+	}
+}
+
+static void update_nslist_score(struct kr_request *request, struct kr_query *qry, const struct sockaddr *src, knot_pkt_t *packet)
+{
+	struct kr_context *ctx = request->ctx;
+	/* On successful answer, update preference list RTT and penalise timer  */
+	if (request->state != KR_STATE_FAIL) {
+		/* Update RTT information for preference list */
+		update_nslist_rtt(ctx, qry, src);
+		/* Do not complete NS address resolution on soft-fail. */
+		const int rcode = packet ? knot_wire_get_rcode(packet->wire) : 0;
+		if (rcode != KNOT_RCODE_SERVFAIL && rcode != KNOT_RCODE_REFUSED) {
+			qry->flags.AWAIT_IPV6 = false;
+			qry->flags.AWAIT_IPV4 = false;
+		} else { /* Penalize SERVFAILs. */
+			kr_nsrep_update_rtt(&qry->ns, src, KR_NS_PENALTY, ctx->cache_rtt, KR_NS_ADD);
+		}
+	}
+}
+
+static bool resolution_time_exceeded(struct kr_query *qry, uint64_t now)
+{
+	uint64_t resolving_time = now - qry->creation_time_mono;
+	if (resolving_time > KR_RESOLVE_TIME_LIMIT) {
+		WITH_VERBOSE(qry) {
+			VERBOSE_MSG(qry, "query resolution time limit exceeded\n");
+		}
+		return true;
+	}
+	return false;
+}
+
+int kr_resolve_consume(struct kr_request *request, const struct sockaddr *src, knot_pkt_t *packet)
+{
+	struct kr_rplan *rplan = &request->rplan;
+
+	/* Empty resolution plan, push packet as the new query */
+	if (packet && kr_rplan_empty(rplan)) {
+		if (answer_prepare(request, packet) != 0) {
+			return KR_STATE_FAIL;
+		}
+		return resolve_query(request, packet);
+	}
+
+	/* Different processing for network error */
+	struct kr_query *qry = array_tail(rplan->pending);
+	/* Check overall resolution time */
+	if (resolution_time_exceeded(qry, kr_now())) {
+		return KR_STATE_FAIL;
+	}
+	bool tried_tcp = (qry->flags.TCP);
+	if (!packet || packet->size == 0) {
+		if (tried_tcp) {
+			request->state = KR_STATE_FAIL;
+		} else {
+			qry->flags.TCP = true;
+		}
+	} else {
+		/* Packet cleared, derandomize QNAME. */
+		knot_dname_t *qname_raw = knot_pkt_qname(packet);
+		if (qname_raw && qry->secret != 0) {
+			randomized_qname_case(qname_raw, qry->secret);
+		}
+		request->state = KR_STATE_CONSUME;
+		if (qry->flags.CACHED) {
+			ITERATE_LAYERS(request, qry, consume, packet);
+		} else {
+			/* Fill in source and latency information. */
+			request->upstream.rtt = kr_now() - qry->timestamp_mono;
+			request->upstream.addr = src;
+			ITERATE_LAYERS(request, qry, consume, packet);
+			/* Clear temporary information */
+			request->upstream.addr = NULL;
+			request->upstream.rtt = 0;
+		}
+	}
+
+	/* Track RTT for iterative answers */
+	if (src && !(qry->flags.CACHED)) {
+		update_nslist_score(request, qry, src, packet);
+	}
+	/* Resolution failed, invalidate current NS. */
+	if (request->state == KR_STATE_FAIL) {
+		invalidate_ns(rplan, qry);
+		qry->flags.RESOLVED = false;
+	}
+
+	/* Pop query if resolved. */
+	if (request->state == KR_STATE_YIELD) {
+		return KR_STATE_PRODUCE; /* Requery */
+	} else if (qry->flags.RESOLVED) {
+		kr_rplan_pop(rplan, qry);
+	} else if (!tried_tcp && (qry->flags.TCP)) {
+		return KR_STATE_PRODUCE; /* Requery over TCP */
+	} else { /* Clear query flags for next attempt */
+		qry->flags.CACHED = false;
+		if (!request->options.TCP) {
+			qry->flags.TCP = false;
+		}
+	}
+
+	ITERATE_LAYERS(request, qry, reset);
+
+	/* Do not finish with bogus answer. */
+	if (qry->flags.DNSSEC_BOGUS)  {
+		return KR_STATE_FAIL;
+	}
+
+	return kr_rplan_empty(&request->rplan) ? KR_STATE_DONE : KR_STATE_PRODUCE;
+}
+
+/** @internal Spawn subrequest in current zone cut (no minimization or lookup). */
+static struct kr_query *zone_cut_subreq(struct kr_rplan *rplan, struct kr_query *parent,
+                           const knot_dname_t *qname, uint16_t qtype)
+{
+	struct kr_query *next = kr_rplan_push(rplan, parent, qname, parent->sclass, qtype);
+	if (!next) {
+		return NULL;
+	}
+	kr_zonecut_set(&next->zone_cut, parent->zone_cut.name);
+	if (kr_zonecut_copy(&next->zone_cut, &parent->zone_cut) != 0 ||
+	    kr_zonecut_copy_trust(&next->zone_cut, &parent->zone_cut) != 0) {
+		return NULL;
+	}
+	next->flags.NO_MINIMIZE = true;
+	if (parent->flags.DNSSEC_WANT) {
+		next->flags.DNSSEC_WANT = true;
+	}
+	return next;
+}
+
+static int forward_trust_chain_check(struct kr_request *request, struct kr_query *qry, bool resume)
+{
+	struct kr_rplan *rplan = &request->rplan;
+	map_t *trust_anchors = &request->ctx->trust_anchors;
+	map_t *negative_anchors = &request->ctx->negative_anchors;
+
+	if (qry->parent != NULL &&
+	    !(qry->forward_flags.CNAME) &&
+	    !(qry->flags.DNS64_MARK) &&
+	    knot_dname_in_bailiwick(qry->zone_cut.name, qry->parent->zone_cut.name) >= 0) {
+		return KR_STATE_PRODUCE;
+	}
+
+	assert(qry->flags.FORWARD);
+
+	if (!trust_anchors) {
+		qry->flags.AWAIT_CUT = false;
+		return KR_STATE_PRODUCE;
+	}
+
+	if (qry->flags.DNSSEC_INSECURE) {
+		qry->flags.AWAIT_CUT = false;
+		return KR_STATE_PRODUCE;
+	}
+
+	if (qry->forward_flags.NO_MINIMIZE) {
+		qry->flags.AWAIT_CUT = false;
+		return KR_STATE_PRODUCE;
+	}
+
+	const knot_dname_t *start_name = qry->sname;
+	if ((qry->flags.AWAIT_CUT) && !resume) {
+		qry->flags.AWAIT_CUT = false;
+		const knot_dname_t *longest_ta = kr_ta_get_longest_name(trust_anchors, qry->sname);
+		if (longest_ta) {
+			start_name = longest_ta;
+			qry->zone_cut.name = knot_dname_copy(start_name, qry->zone_cut.pool);
+			qry->flags.DNSSEC_WANT = true;
+		} else {
+			qry->flags.DNSSEC_WANT = false;
+			return KR_STATE_PRODUCE;
+		}
+	}
+
+	bool has_ta = (qry->zone_cut.trust_anchor != NULL);
+	knot_dname_t *ta_name = (has_ta ? qry->zone_cut.trust_anchor->owner : NULL);
+	bool refetch_ta = (!has_ta || !knot_dname_is_equal(qry->zone_cut.name, ta_name));
+	bool is_dnskey_subreq = kr_rplan_satisfies(qry, ta_name, KNOT_CLASS_IN, KNOT_RRTYPE_DNSKEY);
+	bool refetch_key = has_ta && (!qry->zone_cut.key || !knot_dname_is_equal(ta_name, qry->zone_cut.key->owner));
+	if (refetch_key && !is_dnskey_subreq) {
+		struct kr_query *next = zone_cut_subreq(rplan, qry, ta_name, KNOT_RRTYPE_DNSKEY);
+		if (!next) {
+			return KR_STATE_FAIL;
+		}
+		return KR_STATE_DONE;
+	}
+
+	int name_offset = 1;
+	const knot_dname_t *wanted_name;
+	bool nods, ds_req, ns_req, minimized, ns_exist;
+	do {
+		wanted_name = start_name;
+		ds_req = false;
+		ns_req = false;
+		ns_exist = true;
+
+		int cut_labels = knot_dname_labels(qry->zone_cut.name, NULL);
+		int wanted_name_labels = knot_dname_labels(wanted_name, NULL);
+		while (wanted_name[0] && wanted_name_labels > cut_labels + name_offset) {
+			wanted_name = knot_wire_next_label(wanted_name, NULL);
+			wanted_name_labels -= 1;
+		}
+		minimized = (wanted_name != qry->sname);
+
+		for (int i = 0; i < request->rplan.resolved.len; ++i) {
+			struct kr_query *q = request->rplan.resolved.at[i];
+			if (q->parent == qry &&
+			    q->sclass == qry->sclass &&
+			    (q->stype == KNOT_RRTYPE_DS || q->stype == KNOT_RRTYPE_NS) &&
+			    knot_dname_is_equal(q->sname, wanted_name)) {
+				if (q->stype == KNOT_RRTYPE_DS) {
+					ds_req = true;
+					if (q->flags.CNAME) {
+						ns_exist = false;
+					} else if (!(q->flags.DNSSEC_OPTOUT)) {
+						int ret = kr_dnssec_matches_name_and_type(&request->auth_selected, q->uid,
+											  wanted_name, KNOT_RRTYPE_NS);
+						ns_exist = (ret == kr_ok());
+					}
+				} else {
+					if (q->flags.CNAME) {
+						ns_exist = false;
+					}
+					ns_req = true;
+				}
+			}
+		}
+
+		if (ds_req && ns_exist && !ns_req && (minimized || resume)) {
+			struct kr_query *next = zone_cut_subreq(rplan, qry, wanted_name,
+								KNOT_RRTYPE_NS);
+			if (!next) {
+				return KR_STATE_FAIL;
+			}
+			return KR_STATE_DONE;
+		}
+
+		if (qry->parent == NULL && (qry->flags.CNAME) &&
+		    ds_req && ns_req) {
+			return KR_STATE_PRODUCE;
+		}
+
+		/* set `nods` */
+		if ((qry->stype == KNOT_RRTYPE_DS) &&
+	            knot_dname_is_equal(wanted_name, qry->sname)) {
+			nods = true;
+		} else if (resume && !ds_req) {
+			nods = false;
+		} else if (!minimized && qry->stype != KNOT_RRTYPE_DNSKEY) {
+			nods = true;
+		} else {
+			nods = ds_req;
+		}
+		name_offset += 1;
+	} while (ds_req && (ns_req || !ns_exist) && minimized);
+
+	/* Disable DNSSEC if it enters NTA. */
+	if (kr_ta_get(negative_anchors, wanted_name)){
+		VERBOSE_MSG(qry, ">< negative TA, going insecure\n");
+		qry->flags.DNSSEC_WANT = false;
+	}
+
+	/* Enable DNSSEC if enters a new island of trust. */
+	bool want_secured = (qry->flags.DNSSEC_WANT) &&
+			    !knot_wire_get_cd(request->qsource.packet->wire);
+	if (!(qry->flags.DNSSEC_WANT) &&
+	    !knot_wire_get_cd(request->qsource.packet->wire) &&
+	    kr_ta_get(trust_anchors, wanted_name)) {
+		qry->flags.DNSSEC_WANT = true;
+		want_secured = true;
+		WITH_VERBOSE(qry) {
+		KR_DNAME_GET_STR(qname_str, wanted_name);
+		VERBOSE_MSG(qry, ">< TA: '%s'\n", qname_str);
+		}
+	}
+
+	if (want_secured && !qry->zone_cut.trust_anchor) {
+		knot_rrset_t *ta_rr = kr_ta_get(trust_anchors, wanted_name);
+		if (!ta_rr) {
+			char name[] = "\0";
+			ta_rr = kr_ta_get(trust_anchors, (knot_dname_t*)name);
+		}
+		if (ta_rr) {
+			qry->zone_cut.trust_anchor = knot_rrset_copy(ta_rr, qry->zone_cut.pool);
+		}
+	}
+
+	has_ta = (qry->zone_cut.trust_anchor != NULL);
+	ta_name = (has_ta ? qry->zone_cut.trust_anchor->owner : NULL);
+	refetch_ta = (!has_ta || !knot_dname_is_equal(wanted_name, ta_name));
+	if (!nods && want_secured && refetch_ta) {
+		struct kr_query *next = zone_cut_subreq(rplan, qry, wanted_name,
+							KNOT_RRTYPE_DS);
+		if (!next) {
+			return KR_STATE_FAIL;
+		}
+		return KR_STATE_DONE;
+	}
+
+	/* Try to fetch missing DNSKEY.
+	 * Do not fetch if this is a DNSKEY subrequest to avoid circular dependency. */
+	is_dnskey_subreq = kr_rplan_satisfies(qry, ta_name, KNOT_CLASS_IN, KNOT_RRTYPE_DNSKEY);
+	refetch_key = has_ta && (!qry->zone_cut.key || !knot_dname_is_equal(ta_name, qry->zone_cut.key->owner));
+	if (want_secured && refetch_key && !is_dnskey_subreq) {
+		struct kr_query *next = zone_cut_subreq(rplan, qry, ta_name, KNOT_RRTYPE_DNSKEY);
+		if (!next) {
+			return KR_STATE_FAIL;
+		}
+		return KR_STATE_DONE;
+	}
+
+	return KR_STATE_PRODUCE;
+}
+
+/* @todo: Validator refactoring, keep this in driver for now. */
+static int trust_chain_check(struct kr_request *request, struct kr_query *qry)
+{
+	struct kr_rplan *rplan = &request->rplan;
+	map_t *trust_anchors = &request->ctx->trust_anchors;
+	map_t *negative_anchors = &request->ctx->negative_anchors;
+
+	/* Disable DNSSEC if it enters NTA. */
+	if (kr_ta_get(negative_anchors, qry->zone_cut.name)){
+		VERBOSE_MSG(qry, ">< negative TA, going insecure\n");
+		qry->flags.DNSSEC_WANT = false;
+		qry->flags.DNSSEC_INSECURE = true;
+	}
+	if (qry->flags.DNSSEC_NODS) {
+		/* This is the next query iteration with minimized qname.
+		 * At previous iteration DS non-existance has been proven */
+		qry->flags.DNSSEC_NODS = false;
+		qry->flags.DNSSEC_WANT = false;
+		qry->flags.DNSSEC_INSECURE = true;
+	}
+	/* Enable DNSSEC if entering a new (or different) island of trust,
+	 * and update the TA RRset if required. */
+	bool want_secured = (qry->flags.DNSSEC_WANT) &&
+			    !knot_wire_get_cd(request->qsource.packet->wire);
+	knot_rrset_t *ta_rr = kr_ta_get(trust_anchors, qry->zone_cut.name);
+	if (!knot_wire_get_cd(request->qsource.packet->wire) && ta_rr) {
+		qry->flags.DNSSEC_WANT = true;
+		want_secured = true;
+
+		if (qry->zone_cut.trust_anchor == NULL
+		    || !knot_dname_is_equal(qry->zone_cut.trust_anchor->owner, qry->zone_cut.name)) {
+			mm_free(qry->zone_cut.pool, qry->zone_cut.trust_anchor);
+			qry->zone_cut.trust_anchor = knot_rrset_copy(ta_rr, qry->zone_cut.pool);
+
+			WITH_VERBOSE(qry) {
+			KR_DNAME_GET_STR(qname_str, ta_rr->owner);
+			VERBOSE_MSG(qry, ">< TA: '%s'\n", qname_str);
+			}
+		}
+	}
+
+	/* Try to fetch missing DS (from above the cut). */
+	const bool has_ta = (qry->zone_cut.trust_anchor != NULL);
+	const knot_dname_t *ta_name = (has_ta ? qry->zone_cut.trust_anchor->owner : NULL);
+	const bool refetch_ta = !has_ta || !knot_dname_is_equal(qry->zone_cut.name, ta_name);
+	if (want_secured && refetch_ta) {
+		/* @todo we could fetch the information from the parent cut, but we don't remember that now */
+		struct kr_query *next = kr_rplan_push(rplan, qry, qry->zone_cut.name, qry->sclass, KNOT_RRTYPE_DS);
+		if (!next) {
+			return KR_STATE_FAIL;
+		}
+		next->flags.AWAIT_CUT = true;
+		next->flags.DNSSEC_WANT = true;
+		return KR_STATE_DONE;
+	}
+	/* Try to fetch missing DNSKEY (either missing or above current cut).
+	 * Do not fetch if this is a DNSKEY subrequest to avoid circular dependency. */
+	const bool is_dnskey_subreq = kr_rplan_satisfies(qry, ta_name, KNOT_CLASS_IN, KNOT_RRTYPE_DNSKEY);
+	const bool refetch_key = has_ta && (!qry->zone_cut.key || !knot_dname_is_equal(ta_name, qry->zone_cut.key->owner));
+	if (want_secured && refetch_key && !is_dnskey_subreq) {
+		struct kr_query *next = zone_cut_subreq(rplan, qry, ta_name, KNOT_RRTYPE_DNSKEY);
+		if (!next) {
+			return KR_STATE_FAIL;
+		}
+		return KR_STATE_DONE;
+	}
+
+	return KR_STATE_PRODUCE;
+}
+
+/** @internal Check current zone cut status and credibility, spawn subrequests if needed. */
+static int zone_cut_check(struct kr_request *request, struct kr_query *qry, knot_pkt_t *packet)
+/* TODO: using cache on this point in this way just isn't nice; remove in time */
+{
+	/* Stub mode, just forward and do not solve cut. */
+	if (qry->flags.STUB) {
+		return KR_STATE_PRODUCE;
+	}
+
+	/* Forwarding to upstream resolver mode.
+	 * Since forwarding targets already are in qry->ns -
+	 * cut fetching is not needed. */
+	if (qry->flags.FORWARD) {
+		return forward_trust_chain_check(request, qry, false);
+	}
+	if (!(qry->flags.AWAIT_CUT)) {
+		/* The query was resolved from cache.
+		 * Spawn DS \ DNSKEY requests if needed and exit */
+		return trust_chain_check(request, qry);
+	}
+
+	/* The query wasn't resolved from cache,
+	 * now it's the time to look up closest zone cut from cache. */
+	struct kr_cache *cache = &request->ctx->cache;
+	if (!kr_cache_is_open(cache)) {
+		int ret = kr_zonecut_set_sbelt(request->ctx, &qry->zone_cut);
+		if (ret != 0) {
+			return KR_STATE_FAIL;
+		}
+		VERBOSE_MSG(qry, "=> no cache open, using root hints\n");
+		qry->flags.AWAIT_CUT = false;
+		return KR_STATE_DONE;
+	}
+
+	const knot_dname_t *requested_name = qry->sname;
+	/* If at/subdomain of parent zone cut, start from its encloser.
+	 * This is for case when we get to a dead end
+	 * (and need glue from parent), or DS refetch. */
+	if (qry->parent) {
+		const knot_dname_t *parent = qry->parent->zone_cut.name;
+		if (parent[0] != '\0'
+		    && knot_dname_in_bailiwick(qry->sname, parent) >= 0) {
+			requested_name = knot_wire_next_label(parent, NULL);
+		}
+	} else if ((qry->stype == KNOT_RRTYPE_DS) && (qry->sname[0] != '\0')) {
+		/* If this is explicit DS query, start from encloser too. */
+		requested_name = knot_wire_next_label(requested_name, NULL);
+	}
+
+	int state = KR_STATE_FAIL;
+	do {
+		state = ns_fetch_cut(qry, requested_name, request, packet);
+		if (state == KR_STATE_DONE || state == KR_STATE_FAIL) {
+			return state;
+		} else if (state == KR_STATE_CONSUME) {
+			requested_name = knot_wire_next_label(requested_name, NULL);
+		}
+	} while (state == KR_STATE_CONSUME);
+
+	/* Update minimized QNAME if zone cut changed */
+	if (qry->zone_cut.name && qry->zone_cut.name[0] != '\0' && !(qry->flags.NO_MINIMIZE)) {
+		if (kr_make_query(qry, packet) != 0) {
+			return KR_STATE_FAIL;
+		}
+	}
+	qry->flags.AWAIT_CUT = false;
+
+	/* Check trust chain */
+	return trust_chain_check(request, qry);
+}
+
+int kr_resolve_produce(struct kr_request *request, struct sockaddr **dst, int *type, knot_pkt_t *packet)
+{
+	struct kr_rplan *rplan = &request->rplan;
+	unsigned ns_election_iter = 0;
+
+	/* No query left for resolution */
+	if (kr_rplan_empty(rplan)) {
+		return KR_STATE_FAIL;
+	}
+	/* If we have deferred answers, resume them. */
+	struct kr_query *qry = array_tail(rplan->pending);
+	if (qry->deferred != NULL) {
+		/* @todo: Refactoring validator, check trust chain before resuming. */
+		int state = 0;
+		if (((qry->flags.FORWARD) == 0) ||
+		    ((qry->stype == KNOT_RRTYPE_DS) && (qry->flags.CNAME))) {
+			state = trust_chain_check(request, qry);
+		} else {
+			state = forward_trust_chain_check(request, qry, true);
+		}
+
+		switch(state) {
+		case KR_STATE_FAIL: return KR_STATE_FAIL;
+		case KR_STATE_DONE: return KR_STATE_PRODUCE;
+		default: break;
+		}
+		VERBOSE_MSG(qry, "=> resuming yielded answer\n");
+		struct kr_layer_pickle *pickle = qry->deferred;
+		request->state = KR_STATE_YIELD;
+		set_yield(&request->answ_selected, qry->uid, false);
+		set_yield(&request->auth_selected, qry->uid, false);
+		RESUME_LAYERS(layer_id(request, pickle->api), request, qry, consume, pickle->pkt);
+		if (request->state != KR_STATE_YIELD) {
+			/* No new deferred answers, take the next */
+			qry->deferred = pickle->next;
+		}
+	} else {
+		/* Caller is interested in always tracking a zone cut, even if the answer is cached
+		 * this is normally not required, and incurrs another cache lookups for cached answer. */
+		if (qry->flags.ALWAYS_CUT) {
+			if (!(qry->flags.STUB)) {
+				switch(zone_cut_check(request, qry, packet)) {
+				case KR_STATE_FAIL: return KR_STATE_FAIL;
+				case KR_STATE_DONE: return KR_STATE_PRODUCE;
+				default: break;
+				}
+			}
+		}
+		/* Resolve current query and produce dependent or finish */
+		request->state = KR_STATE_PRODUCE;
+		ITERATE_LAYERS(request, qry, produce, packet);
+		if (request->state != KR_STATE_FAIL && knot_wire_get_qr(packet->wire)) {
+			/* Produced an answer from cache, consume it. */
+			qry->secret = 0;
+			request->state = KR_STATE_CONSUME;
+			ITERATE_LAYERS(request, qry, consume, packet);
+		}
+	}
+	switch(request->state) {
+	case KR_STATE_FAIL: return request->state;
+	case KR_STATE_CONSUME: break;
+	case KR_STATE_DONE:
+	default: /* Current query is done */
+		if (qry->flags.RESOLVED && request->state != KR_STATE_YIELD) {
+			kr_rplan_pop(rplan, qry);
+		}
+		ITERATE_LAYERS(request, qry, reset);
+		return kr_rplan_empty(rplan) ? KR_STATE_DONE : KR_STATE_PRODUCE;
+	}
+	
+
+	/* This query has RD=0 or is ANY, stop here. */
+	if (qry->stype == KNOT_RRTYPE_ANY ||
+	    !knot_wire_get_rd(request->qsource.packet->wire)) {
+		VERBOSE_MSG(qry, "=> qtype is ANY or RD=0, bail out\n");
+		return KR_STATE_FAIL;
+	}
+
+	/* Update zone cut, spawn new subrequests. */
+	if (!(qry->flags.STUB)) {
+		int state = zone_cut_check(request, qry, packet);
+		switch(state) {
+		case KR_STATE_FAIL: return KR_STATE_FAIL;
+		case KR_STATE_DONE: return KR_STATE_PRODUCE;
+		default: break;
+		}
+	}
+
+ns_election:
+
+	/* If the query has already selected a NS and is waiting for IPv4/IPv6 record,
+	 * elect best address only, otherwise elect a completely new NS.
+	 */
+	if(++ns_election_iter >= KR_ITER_LIMIT) {
+		VERBOSE_MSG(qry, "=> couldn't converge NS selection, bail out\n");
+		return KR_STATE_FAIL;
+	}
+
+	const struct kr_qflags qflg = qry->flags;
+	const bool retry = qflg.TCP || qflg.BADCOOKIE_AGAIN;
+	if (qflg.AWAIT_IPV4 || qflg.AWAIT_IPV6) {
+		kr_nsrep_elect_addr(qry, request->ctx);
+	} else if (qflg.FORWARD || qflg.STUB) {
+		kr_nsrep_sort(&qry->ns, request->ctx);
+		if (qry->ns.score > KR_NS_MAX_SCORE) {
+			/* At the moment all NS have bad reputation.
+			 * But there can be existing connections*/
+			VERBOSE_MSG(qry, "=> no valid NS left\n");
+			return KR_STATE_FAIL;
+		}
+	} else if (!qry->ns.name || !retry) { /* Keep NS when requerying/stub/badcookie. */
+		/* Root DNSKEY must be fetched from the hints to avoid chicken and egg problem. */
+		if (qry->sname[0] == '\0' && qry->stype == KNOT_RRTYPE_DNSKEY) {
+			kr_zonecut_set_sbelt(request->ctx, &qry->zone_cut);
+			qry->flags.NO_THROTTLE = true; /* Pick even bad SBELT servers */
+		}
+		kr_nsrep_elect(qry, request->ctx);
+		if (qry->ns.score > KR_NS_MAX_SCORE) {
+			if (kr_zonecut_is_empty(&qry->zone_cut)) {
+				VERBOSE_MSG(qry, "=> no NS with an address\n");
+			} else {
+				VERBOSE_MSG(qry, "=> no valid NS left\n");
+			}
+			if (!qry->flags.NO_NS_FOUND) {
+				qry->flags.NO_NS_FOUND = true;
+			} else {
+				ITERATE_LAYERS(request, qry, reset);
+				kr_rplan_pop(rplan, qry);
+			}
+			return KR_STATE_PRODUCE;
+		}
+	}
+
+	/* Resolve address records */
+	if (qry->ns.addr[0].ip.sa_family == AF_UNSPEC) {
+		int ret = ns_resolve_addr(qry, request);
+		if (ret != 0) {
+			qry->flags.AWAIT_IPV6 = false;
+			qry->flags.AWAIT_IPV4 = false;
+			qry->flags.TCP = false;
+			qry->ns.name = NULL;
+			goto ns_election; /* Must try different NS */
+		}
+		ITERATE_LAYERS(request, qry, reset);
+		return KR_STATE_PRODUCE;
+	}
+
+	/* Randomize query case (if not in safe mode or turned off) */
+	qry->secret = (qry->flags.SAFEMODE || qry->flags.NO_0X20)
+			? 0 : kr_rand_bytes(sizeof(qry->secret));
+	knot_dname_t *qname_raw = knot_pkt_qname(packet);
+	randomized_qname_case(qname_raw, qry->secret);
+
+	/*
+	 * Additional query is going to be finalized when calling
+	 * kr_resolve_checkout().
+	 */
+	qry->timestamp_mono = kr_now();
+	*dst = &qry->ns.addr[0].ip;
+	*type = (qry->flags.TCP) ? SOCK_STREAM : SOCK_DGRAM;
+	return request->state;
+}
+
+#if defined(ENABLE_COOKIES)
+/** Update DNS cookie data in packet. */
+static bool outbound_request_update_cookies(struct kr_request *req,
+                                            const struct sockaddr *src,
+                                            const struct sockaddr *dst)
+{
+	assert(req);
+
+	/* RFC7873 4.1 strongly requires server address. */
+	if (!dst) {
+		return false;
+	}
+
+	struct kr_cookie_settings *clnt_sett = &req->ctx->cookie_ctx.clnt;
+
+	/* Cookies disabled or packet has no EDNS section. */
+	if (!clnt_sett->enabled) {
+		return true;
+	}
+
+	/*
+	 * RFC7873 4.1 recommends using also the client address. The matter is
+	 * also discussed in section 6.
+	 */
+
+	kr_request_put_cookie(&clnt_sett->current, req->ctx->cache_cookie,
+	                      src, dst, req);
+
+	return true;
+}
+#endif /* defined(ENABLE_COOKIES) */
+
+int kr_resolve_checkout(struct kr_request *request, const struct sockaddr *src,
+                        struct sockaddr *dst, int type, knot_pkt_t *packet)
+{
+	/* @todo: Update documentation if this function becomes approved. */
+
+	struct kr_rplan *rplan = &request->rplan;
+
+	if (knot_wire_get_qr(packet->wire) != 0) {
+		return kr_ok();
+	}
+
+	/* No query left for resolution */
+	if (kr_rplan_empty(rplan)) {
+		return kr_error(EINVAL);
+	}
+	struct kr_query *qry = array_tail(rplan->pending);
+
+#if defined(ENABLE_COOKIES)
+	/* Update DNS cookies in request. */
+	if (type == SOCK_DGRAM) { /* @todo: Add cookies also over TCP? */
+		/*
+		 * The actual server IP address is needed before generating the
+		 * actual cookie. If we don't know the server address then we
+		 * also don't know the actual cookie size.
+		 */
+		if (!outbound_request_update_cookies(request, src, dst)) {
+			return kr_error(EINVAL);
+		}
+	}
+#endif /* defined(ENABLE_COOKIES) */
+
+	int ret = query_finalize(request, qry, packet);
+	if (ret != 0) {
+		return kr_error(EINVAL);
+	}
+
+	/* Track changes in minimization secret to enable/disable minimization */
+	uint32_t old_minimization_secret = qry->secret;
+
+	/* Run the checkout layers and cancel on failure.
+	 * The checkout layer doesn't persist the state, so canceled subrequests
+	 * don't affect the resolution or rest of the processing. */
+	int state = request->state;
+	ITERATE_LAYERS(request, qry, checkout, packet, dst, type);
+	if (request->state == KR_STATE_FAIL) {
+		request->state = state; /* Restore */
+		return kr_error(ECANCELED);
+	}
+
+	/* Randomize query case (if secret changed) */
+	knot_dname_t *qname = (knot_dname_t *)knot_pkt_qname(packet);
+	if (qry->secret != old_minimization_secret) {
+		randomized_qname_case(qname, qry->secret);
+	}
+
+	/* Write down OPT unless in safemode */
+	if (!(qry->flags.SAFEMODE)) {
+		ret = edns_put(packet, true);
+		if (ret != 0) {
+			return kr_error(EINVAL);
+		}
+	}
+
+	WITH_VERBOSE(qry) {
+
+	KR_DNAME_GET_STR(qname_str, knot_pkt_qname(packet));
+	KR_DNAME_GET_STR(zonecut_str, qry->zone_cut.name);
+	KR_RRTYPE_GET_STR(type_str, knot_pkt_qtype(packet));
+
+	for (size_t i = 0; i < KR_NSREP_MAXADDR; ++i) {
+		struct sockaddr *addr = &qry->ns.addr[i].ip;
+		if (addr->sa_family == AF_UNSPEC) {
+			break;
+		}
+		if (!kr_inaddr_equal(dst, addr)) {
+			continue;
+		}
+		const char *ns_str = kr_straddr(addr);
+		VERBOSE_MSG(qry,
+			"=> id: '%05u' querying: '%s' score: %u zone cut: '%s' "
+			"qname: '%s' qtype: '%s' proto: '%s'\n",
+			qry->id, ns_str ? ns_str : "", qry->ns.score, zonecut_str,
+			qname_str, type_str, (qry->flags.TCP) ? "tcp" : "udp");
+
+		break;
+	}}
+
+	return kr_ok();
+}
+
+int kr_resolve_finish(struct kr_request *request, int state)
+{
+	/* Finalize answer and construct wire-buffer. */
+	ITERATE_LAYERS(request, NULL, answer_finalize);
+	if (request->state == KR_STATE_FAIL) {
+		state = KR_STATE_FAIL;
+	} else if (answer_finalize(request, state) != 0) {
+		state = KR_STATE_FAIL;
+	}
+
+	/* Error during processing, internal failure */
+	if (state != KR_STATE_DONE) {
+		knot_pkt_t *answer = request->answer;
+		if (knot_wire_get_rcode(answer->wire) == KNOT_RCODE_NOERROR) {
+			knot_wire_clear_ad(answer->wire);
+			knot_wire_clear_aa(answer->wire);
+			knot_wire_set_rcode(answer->wire, KNOT_RCODE_SERVFAIL);
+		}
+	}
+
+	request->state = state;
+	ITERATE_LAYERS(request, NULL, finish);
+
+#ifndef NOVERBOSELOG
+	struct kr_rplan *rplan = &request->rplan;
+	struct kr_query *last = kr_rplan_last(rplan);
+	VERBOSE_MSG(last, "finished: %d, queries: %zu, mempool: %zu B\n",
+	          request->state, rplan->resolved.len, (size_t) mp_total_size(request->pool.ctx));
+#endif
+
+	/* Trace request finish */
+	if (request->trace_finish) {
+		request->trace_finish(request);
+	}
+
+	/* Uninstall all tracepoints */
+	request->trace_finish = NULL;
+	request->trace_log = NULL;
+
+	return KR_STATE_DONE;
+}
+
+struct kr_rplan *kr_resolve_plan(struct kr_request *request)
+{
+	if (request) {
+		return &request->rplan;
+	}
+	return NULL;
+}
+
+knot_mm_t *kr_resolve_pool(struct kr_request *request)
+{
+	if (request) {
+		return &request->pool;
+	}
+	return NULL;
+}
+
+#undef VERBOSE_MSG
diff --git a/lib/resolve.h b/lib/resolve.h
new file mode 100644
index 0000000..60d80bb
--- /dev/null
+++ b/lib/resolve.h
@@ -0,0 +1,332 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <netinet/in.h>
+#include <sys/socket.h>
+#include <libknot/packet/pkt.h>
+
+#include "lib/cookies/control.h"
+#include "lib/cookies/lru_cache.h"
+#include "lib/layer.h"
+#include "lib/generic/map.h"
+#include "lib/generic/array.h"
+#include "lib/nsrep.h"
+#include "lib/rplan.h"
+#include "lib/module.h"
+#include "lib/cache/api.h"
+
+/**
+ * @file resolve.h
+ * @brief The API provides an API providing a "consumer-producer"-like interface to enable
+ * user to plug it into existing event loop or I/O code.
+ *
+ * # Example usage of the iterative API:
+ *
+ * @code{.c}
+ *
+ * // Create request and its memory pool
+ * struct kr_request req = {
+ * 	.pool = {
+ * 		.ctx = mp_new (4096),
+ * 		.alloc = (mm_alloc_t) mp_alloc
+ * 	}
+ * };
+ *
+ * // Setup and provide input query
+ * int state = kr_resolve_begin(&req, ctx, final_answer);
+ * state = kr_resolve_consume(&req, query);
+ *
+ * // Generate answer
+ * while (state == KR_STATE_PRODUCE) {
+ *
+ *     // Additional query generate, do the I/O and pass back answer
+ *     state = kr_resolve_produce(&req, &addr, &type, query);
+ *     while (state == KR_STATE_CONSUME) {
+ *         int ret = sendrecv(addr, proto, query, resp);
+ *
+ *         // If I/O fails, make "resp" empty
+ *         state = kr_resolve_consume(&request, addr, resp);
+ *         knot_pkt_clear(resp);
+ *     }
+ *     knot_pkt_clear(query);
+ * }
+ *
+ * // "state" is either DONE or FAIL
+ * kr_resolve_finish(&request, state);
+ *
+ * @endcode
+ */
+
+
+/**
+ * RRset rank - for cache and ranked_rr_*.
+ *
+ * The rank meaning consists of one independent flag - KR_RANK_AUTH,
+ * and the rest have meaning of values where only one can hold at any time.
+ * You can use one of the enums as a safe initial value, optionally | KR_RANK_AUTH;
+ * otherwise it's best to manipulate ranks via the kr_rank_* functions.
+ *
+ * @note The representation is complicated by restrictions on integer comparison:
+ * - AUTH must be > than !AUTH
+ * - AUTH INSECURE must be > than AUTH (because it attempted validation)
+ * - !AUTH SECURE must be > than AUTH (because it's valid)
+ *
+ * See also:
+ *   https://tools.ietf.org/html/rfc2181#section-5.4.1
+ *   https://tools.ietf.org/html/rfc4035#section-4.3
+ */
+enum kr_rank {
+	/* Initial-like states.  No validation has been attempted (yet). */
+	KR_RANK_INITIAL = 0, /**< Did not attempt to validate. It's assumed
+					compulsory to validate (or prove insecure). */
+	KR_RANK_OMIT,        /**< Do not attempt to validate.
+					(And don't consider it a validation failure.) */
+	KR_RANK_TRY,         /**< Attempt to validate, but failures are non-fatal. */
+
+	/* Failure states.  These have higher value because they have more information. */
+	KR_RANK_INDET = 4,   /**< Unable to determine whether it should be secure. */
+	KR_RANK_BOGUS,       /**< Ought to be secure but isn't. */
+	KR_RANK_MISMATCH,
+	KR_RANK_MISSING,     /**< Unable to obtain a good signature. */
+
+	/** Proven to be insecure, i.e. we have a chain of trust from TAs
+	 * that cryptographically denies the possibility of existence
+	 * of a positive chain of trust from the TAs to the record. */
+	KR_RANK_INSECURE = 8,
+
+	/** Authoritative data flag; the chain of authority was "verified".
+	 *  Even if not set, only in-bailiwick stuff is acceptable,
+	 *  i.e. almost authoritative (example: mandatory glue and its NS RR). */
+	KR_RANK_AUTH = 16,
+
+	KR_RANK_SECURE = 32,  /**< Verified whole chain of trust from the closest TA. */
+	/* @note Rank must not exceed 6 bits */
+};
+
+/** Check that a rank value is valid.  Meant for assertions. */
+bool kr_rank_check(uint8_t rank) KR_PURE;
+
+/** Test the presence of any flag/state in a rank, i.e. including KR_RANK_AUTH. */
+static inline bool kr_rank_test(uint8_t rank, uint8_t kr_flag)
+{
+	assert(kr_rank_check(rank) && kr_rank_check(kr_flag));
+	if (kr_flag == KR_RANK_AUTH) {
+		return rank & KR_RANK_AUTH;
+	}
+	assert(!(kr_flag & KR_RANK_AUTH));
+	/* The rest are exclusive values - exactly one has to be set. */
+	return (rank & ~KR_RANK_AUTH) == kr_flag;
+}
+
+/** Set the rank state. The _AUTH flag is kept as it was. */
+static inline void kr_rank_set(uint8_t *rank, uint8_t kr_flag)
+{
+	assert(rank && kr_rank_check(*rank));
+	assert(kr_rank_check(kr_flag) && !(kr_flag & KR_RANK_AUTH));
+	*rank = kr_flag | (*rank & KR_RANK_AUTH);
+}
+
+
+/** @cond internal Array of modules. */
+typedef array_t(struct kr_module *) module_array_t;
+/* @endcond */
+
+/**
+ * Name resolution context.
+ *
+ * Resolution context provides basic services like cache, configuration and options.
+ *
+ * @note This structure is persistent between name resolutions and may
+ *       be shared between threads.
+ */
+struct kr_context
+{
+	struct kr_qflags options;
+	knot_rrset_t *opt_rr;
+	map_t trust_anchors;
+	map_t negative_anchors;
+	struct kr_zonecut root_hints;
+	struct kr_cache cache;
+	kr_nsrep_rtt_lru_t *cache_rtt;
+	unsigned cache_rtt_tout_retry_interval;
+	kr_nsrep_lru_t *cache_rep;
+	module_array_t *modules;
+	/* The cookie context structure should not be held within the cookies
+	 * module because of better access. */
+	struct kr_cookie_ctx cookie_ctx;
+	kr_cookie_lru_t *cache_cookie;
+	int32_t tls_padding; /**< See net.tls_padding in ../daemon/README.rst -- -1 is "true" (default policy), 0 is "false" (no padding) */
+	knot_mm_t *pool;
+};
+
+/* Kept outside, because kres-gen.lua can't handle this depth
+ * (and lines here were too long anyway). */
+struct kr_request_qsource_flags {
+	bool tcp:1; /**< true if the request is on TCP (or TLS); only meaningful if (dst_addr). */
+	bool tls:1; /**< true if the request is on TLS; only meaningful if (dst_addr). */
+};
+
+/**
+ * Name resolution request.
+ *
+ * Keeps information about current query processing between calls to
+ * processing APIs, i.e. current resolved query, resolution plan, ...
+ * Use this instead of the simple interface if you want to implement
+ * multiplexing or custom I/O.
+ *
+ * @note All data for this request must be allocated from the given pool.
+ */
+struct kr_request {
+	struct kr_context *ctx;
+	knot_pkt_t *answer;
+	struct kr_query *current_query;    /**< Current evaluated query. */
+	struct {
+		/** Address that originated the request. NULL for internal origin. */
+		const struct sockaddr *addr;
+		/** Address that accepted the request.  NULL for internal origin. */
+		const struct sockaddr *dst_addr;
+		const knot_pkt_t *packet;
+		struct kr_request_qsource_flags flags; /**< See definition above. */
+		size_t size; /**< query packet size */
+	} qsource;
+	struct {
+		unsigned rtt;                  /**< Current upstream RTT */
+		const struct sockaddr *addr;   /**< Current upstream address */
+	} upstream;                        /**< Upstream information, valid only in consume() phase */
+	struct kr_qflags options;
+	int state;
+	ranked_rr_array_t answ_selected;
+	ranked_rr_array_t auth_selected;
+	ranked_rr_array_t add_selected;
+	rr_array_t additional;
+	bool answ_validated; /**< internal to validator; beware of caching, etc. */
+	bool auth_validated; /**< see answ_validated ^^ ; TODO */
+
+	/** Overall rank for the request.
+	 *
+	 * Values from kr_rank, currently just KR_RANK_SECURE and _INITIAL.
+	 * Only read this in finish phase and after validator, please.
+	 * Meaning of _SECURE: all RRs in answer+authority are _SECURE,
+	 *   including any negative results implied (NXDOMAIN, NODATA).
+	 */
+	uint8_t rank;
+
+	struct kr_rplan rplan;
+	trace_log_f trace_log; /**< Logging tracepoint */
+	trace_callback_f trace_finish; /**< Request finish tracepoint */
+	int vars_ref; /**< Reference to per-request variable table. LUA_NOREF if not set. */
+	knot_mm_t pool;
+	unsigned int uid; /** for logging purposes only */
+	void *daemon_context; /** pointer to worker from daemon. Can be used in modules. */
+};
+
+/** Initializer for an array of *_selected. */
+#define kr_request_selected(req) { \
+	[KNOT_ANSWER] = &(req)->answ_selected, \
+	[KNOT_AUTHORITY] = &(req)->auth_selected, \
+	[KNOT_ADDITIONAL] = &(req)->add_selected, \
+	}
+
+/**
+ * Begin name resolution.
+ *
+ * @note Expects a request to have an initialized mempool, the "answer" packet will
+ *       be kept during the resolution and will contain the final answer at the end.
+ *
+ * @param request request state with initialized mempool
+ * @param ctx     resolution context
+ * @param answer  allocated packet for final answer
+ * @return        CONSUME (expecting query)
+ */
+KR_EXPORT
+int kr_resolve_begin(struct kr_request *request, struct kr_context *ctx, knot_pkt_t *answer);
+
+/**
+ * Consume input packet (may be either first query or answer to query originated from kr_resolve_produce())
+ *
+ * @note If the I/O fails, provide an empty or NULL packet, this will make iterator recognize nameserver failure.
+ * 
+ * @param  request request state (awaiting input)
+ * @param  src     [in] packet source address
+ * @param  packet  [in] input packet
+ * @return         any state
+ */
+KR_EXPORT
+int kr_resolve_consume(struct kr_request *request, const struct sockaddr *src, knot_pkt_t *packet);
+
+/**
+ * Produce either next additional query or finish.
+ *
+ * If the CONSUME is returned then dst, type and packet will be filled with
+ * appropriate values and caller is responsible to send them and receive answer.
+ * If it returns any other state, then content of the variables is undefined.
+ * 
+ * @param  request request state (in PRODUCE state)
+ * @param  dst     [out] possible address of the next nameserver
+ * @param  type    [out] possible used socket type (SOCK_STREAM, SOCK_DGRAM)
+ * @param  packet  [out] packet to be filled with additional query
+ * @return         any state
+ */
+KR_EXPORT
+int kr_resolve_produce(struct kr_request *request, struct sockaddr **dst, int *type, knot_pkt_t *packet);
+
+/**
+ * Finalises the outbound query packet with the knowledge of the IP addresses.
+ *
+ * @note The function must be called before actual sending of the request packet.
+ *
+ * @param  request request state (in PRODUCE state)
+ * @param  src     address from which the query is going to be sent
+ * @param  dst     address of the name server
+ * @param  type    used socket type (SOCK_STREAM, SOCK_DGRAM)
+ * @param  packet  [in,out] query packet to be finalised
+ * @return         kr_ok() or error code
+ */
+KR_EXPORT
+int kr_resolve_checkout(struct kr_request *request, const struct sockaddr *src,
+                        struct sockaddr *dst, int type, knot_pkt_t *packet);
+
+/**
+ * Finish resolution and commit results if the state is DONE.
+ *
+ * @note The structures will be deinitialized, but the assigned memory pool is not going to
+ *       be destroyed, as it's owned by caller.
+ *
+ * @param  request request state
+ * @param  state   either DONE or FAIL state
+ * @return         DONE
+ */
+KR_EXPORT
+int kr_resolve_finish(struct kr_request *request, int state);
+
+/**
+ * Return resolution plan.
+ * @param  request request state
+ * @return         pointer to rplan
+ */
+KR_EXPORT KR_PURE
+struct kr_rplan *kr_resolve_plan(struct kr_request *request);
+
+/**
+ * Return memory pool associated with request.
+ * @param  request request state
+ * @return         mempool
+ */
+KR_EXPORT KR_PURE
+knot_mm_t *kr_resolve_pool(struct kr_request *request);
+
diff --git a/lib/rplan.c b/lib/rplan.c
new file mode 100644
index 0000000..6ed8e4e
--- /dev/null
+++ b/lib/rplan.c
@@ -0,0 +1,308 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <libknot/descriptor.h>
+#include <libknot/errcode.h>
+
+#include "lib/rplan.h"
+#include "lib/resolve.h"
+#include "lib/cache/api.h"
+#include "lib/defines.h"
+#include "lib/layer.h"
+
+#define VERBOSE_MSG(qry, ...) QRVERBOSE(qry, "plan",  __VA_ARGS__)
+#define QUERY_PROVIDES(q, name, cls, type) \
+    ((q)->sclass == (cls) && (q)->stype == type && knot_dname_is_equal((q)->sname, name))
+
+inline static unsigned char chars_or(const unsigned char a, const unsigned char b)
+{
+	return a | b;
+}
+
+/** Bits set to 1 in variable b will be set to zero in variable a. */
+inline static unsigned char chars_mask(const unsigned char a, const unsigned char b)
+{
+	return a & ~b;
+}
+
+/** Apply mod(a, b) to every byte a, b from fl1, fl2 and return result in fl1. */
+inline static void kr_qflags_mod(struct kr_qflags *fl1, struct kr_qflags fl2,
+			unsigned char mod(const unsigned char a, const unsigned char b))
+{
+	if (!fl1) abort();
+	union {
+		struct kr_qflags flags;
+		/* C99 section 6.5.3.4: sizeof(char) == 1 */
+		unsigned char chars[sizeof(struct kr_qflags)];
+	} tmp1, tmp2;
+	/* The compiler should be able to optimize all this into simple ORs. */
+	tmp1.flags = *fl1;
+	tmp2.flags = fl2;
+	for (size_t i = 0; i < sizeof(struct kr_qflags); ++i) {
+		tmp1.chars[i] = mod(tmp1.chars[i], tmp2.chars[i]);
+	}
+	*fl1 = tmp1.flags;
+}
+
+/**
+ * Set bits from variable fl2 in variable fl1.
+ * Bits which are not set in fl2 are not modified in fl1.
+ *
+ * @param[in,out] fl1
+ * @param[in] fl2
+ */
+void kr_qflags_set(struct kr_qflags *fl1, struct kr_qflags fl2)
+{
+	kr_qflags_mod(fl1, fl2, chars_or);
+}
+
+/**
+ * Clear bits from variable fl2 in variable fl1.
+ * Bits which are not set in fl2 are not modified in fl1.
+ *
+ * @param[in,out] fl1
+ * @param[in] fl2
+ */
+void kr_qflags_clear(struct kr_qflags *fl1, struct kr_qflags fl2)
+{
+	kr_qflags_mod(fl1, fl2, chars_mask);
+}
+
+static struct kr_query *query_create(knot_mm_t *pool, const knot_dname_t *name, uint32_t uid)
+{
+	struct kr_query *qry = mm_alloc(pool, sizeof(struct kr_query));
+	if (qry == NULL) {
+		return NULL;
+	}
+
+	memset(qry, 0, sizeof(struct kr_query));
+	if (name != NULL) {
+		qry->sname = knot_dname_copy(name, pool);
+		if (qry->sname == NULL) {
+			mm_free(pool, qry);
+			return NULL;
+		}
+	}
+
+	knot_dname_to_lower(qry->sname);
+	qry->uid = uid;
+	return qry;
+}
+
+static void query_free(knot_mm_t *pool, struct kr_query *qry)
+{
+	kr_zonecut_deinit(&qry->zone_cut);
+	mm_free(pool, qry->sname);
+	mm_free(pool, qry);
+}
+
+int kr_rplan_init(struct kr_rplan *rplan, struct kr_request *request, knot_mm_t *pool)
+{
+	if (rplan == NULL) {
+		return KNOT_EINVAL;
+	}
+
+	memset(rplan, 0, sizeof(struct kr_rplan));
+
+	rplan->pool = pool;
+	rplan->request = request;
+	array_init(rplan->pending);
+	array_init(rplan->resolved);
+	rplan->next_uid = 0;
+	return KNOT_EOK;
+}
+
+void kr_rplan_deinit(struct kr_rplan *rplan)
+{
+	if (rplan == NULL) {
+		return;
+	}
+
+	for (size_t i = 0; i < rplan->pending.len; ++i) {
+		query_free(rplan->pool, rplan->pending.at[i]);
+	}
+	for (size_t i = 0; i < rplan->resolved.len; ++i) {
+		query_free(rplan->pool, rplan->resolved.at[i]);
+	}
+	array_clear_mm(rplan->pending, mm_free, rplan->pool);
+	array_clear_mm(rplan->resolved, mm_free, rplan->pool);
+}
+
+bool kr_rplan_empty(struct kr_rplan *rplan)
+{
+	if (rplan == NULL) {
+		return true;
+	}
+
+	return rplan->pending.len == 0;
+}
+
+static struct kr_query *kr_rplan_push_query(struct kr_rplan *rplan,
+                                            struct kr_query *parent,
+                                            const knot_dname_t *name)
+{
+	if (rplan == NULL) {
+		return NULL;
+	}
+
+	/* Make sure there's enough space */
+	int ret = array_reserve_mm(rplan->pending, rplan->pending.len + 1, kr_memreserve, rplan->pool);
+	if (ret != 0) {
+		return NULL;
+	}
+
+	struct kr_query *qry = query_create(rplan->pool, name, rplan->next_uid);
+	if (qry == NULL) {
+		return NULL;
+	}
+	rplan->next_uid += 1;
+	/* Class and type must be set outside this function. */
+	qry->flags = rplan->request->options;
+	qry->parent = parent;
+	qry->request = rplan->request;
+	qry->ns.ctx = rplan->request->ctx;
+	qry->ns.addr[0].ip.sa_family = AF_UNSPEC;
+	gettimeofday(&qry->timestamp, NULL);
+	qry->timestamp_mono = kr_now();
+	qry->creation_time_mono = parent ? parent->creation_time_mono : qry->timestamp_mono;
+	kr_zonecut_init(&qry->zone_cut, (const uint8_t *)"", rplan->pool);
+	qry->reorder = qry->flags.REORDER_RR ? kr_rand_bytes(sizeof(qry->reorder)) : 0;
+
+	/* When forwarding, keep the nameserver addresses. */
+	if (parent && parent->flags.FORWARD && qry->flags.FORWARD) {
+		ret = kr_nsrep_copy_set(&qry->ns, &parent->ns);
+		if (ret) {
+			query_free(rplan->pool, qry);
+			return NULL;
+		}
+	}
+
+	array_push(rplan->pending, qry);
+
+	return qry;
+}
+
+struct kr_query *kr_rplan_push_empty(struct kr_rplan *rplan, struct kr_query *parent)
+{
+	if (rplan == NULL) {
+		return NULL;
+	}
+
+	struct kr_query *qry = kr_rplan_push_query(rplan, parent, NULL);
+	if (qry == NULL) {
+		return NULL;
+	}
+
+	WITH_VERBOSE(qry) {
+	VERBOSE_MSG(qry, "plan '%s' type '%s'  uid [%05u.%02u]\n", "", "",
+		    qry->request ? qry->request->uid : 0, qry->uid);
+	}
+	return qry;
+}
+
+struct kr_query *kr_rplan_push(struct kr_rplan *rplan, struct kr_query *parent,
+                               const knot_dname_t *name, uint16_t cls, uint16_t type)
+{
+	if (rplan == NULL || name == NULL) {
+		return NULL;
+	}
+
+	struct kr_query *qry = kr_rplan_push_query(rplan, parent, name);
+	if (qry == NULL) {
+		return NULL;
+	}
+
+	qry->sclass = cls;
+	qry->stype = type;
+
+	WITH_VERBOSE(qry) {
+	KR_DNAME_GET_STR(name_str, name);
+	KR_RRTYPE_GET_STR(type_str, type);
+	VERBOSE_MSG(parent, "plan '%s' type '%s' uid [%05u.%02u]\n",
+		    name_str, type_str,
+		    qry->request ? qry->request->uid : 0, qry->uid);
+	}
+	return qry;
+}
+
+int kr_rplan_pop(struct kr_rplan *rplan, struct kr_query *qry)
+{
+	if (rplan == NULL || qry == NULL) {
+		return KNOT_EINVAL;
+	}
+
+	/* Make sure there's enough space */
+	int ret = array_reserve_mm(rplan->resolved, rplan->resolved.len + 1, kr_memreserve, rplan->pool);
+	if (ret != 0) {
+		return ret;
+	}
+
+	/* Find the query, it will likely be on top */
+	for (size_t i = rplan->pending.len; i > 0; i--) {
+		if (rplan->pending.at[i - 1] == qry) {
+			array_del(rplan->pending, i - 1);
+			array_push(rplan->resolved, qry);
+			break;
+		}
+	}
+	return KNOT_EOK;
+}
+
+bool kr_rplan_satisfies(struct kr_query *closure, const knot_dname_t *name, uint16_t cls, uint16_t type)
+{
+	while (name && closure) {
+		if (QUERY_PROVIDES(closure, name, cls, type)) {
+			return true;
+		}
+		closure = closure->parent;
+	}
+	return false;
+}
+
+struct kr_query *kr_rplan_resolved(struct kr_rplan *rplan)
+{
+	if (rplan->resolved.len == 0) {
+		return NULL;
+	}
+	return array_tail(rplan->resolved);
+}
+
+struct kr_query *kr_rplan_last(struct kr_rplan *rplan)
+{
+	if (!kr_rplan_empty(rplan)) {
+		return array_tail(rplan->pending);
+	}
+
+	return kr_rplan_resolved(rplan);
+}
+
+struct kr_query *kr_rplan_find_resolved(struct kr_rplan *rplan, struct kr_query *parent,
+                               const knot_dname_t *name, uint16_t cls, uint16_t type)
+{
+	struct kr_query *ret = NULL;
+	for (int i = 0; i < rplan->resolved.len; ++i) {
+		struct kr_query *q = rplan->resolved.at[i];
+		if (q->stype == type && q->sclass == cls &&
+		    (parent == NULL || q->parent == parent) &&
+		    knot_dname_is_equal(q->sname, name)) {
+			ret = q;
+			break;
+		}
+	}
+	return ret;
+}
+
+#undef VERBOSE_MSG
diff --git a/lib/rplan.h b/lib/rplan.h
new file mode 100644
index 0000000..21b0b0b
--- /dev/null
+++ b/lib/rplan.h
@@ -0,0 +1,221 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <sys/time.h>
+#include <libknot/dname.h>
+#include <libknot/codes.h>
+
+#include "lib/cache/api.h"
+#include "lib/zonecut.h"
+#include "lib/nsrep.h"
+
+/** Query flags */
+struct kr_qflags {
+	bool NO_MINIMIZE : 1;    /**< Don't minimize QNAME. */
+	bool NO_THROTTLE : 1;    /**< No query/slow NS throttling. */
+	bool NO_IPV6 : 1;        /**< Disable IPv6 */
+	bool NO_IPV4 : 1;        /**< Disable IPv4 */
+	bool TCP : 1;            /**< Use TCP for this query. */
+	bool RESOLVED : 1;       /**< Query is resolved.  Note that kr_query gets
+				  *   RESOLVED before following a CNAME chain; see .CNAME. */
+	bool AWAIT_IPV4 : 1;     /**< Query is waiting for A address. */
+	bool AWAIT_IPV6 : 1;     /**< Query is waiting for AAAA address. */
+	bool AWAIT_CUT : 1;      /**< Query is waiting for zone cut lookup */
+	bool SAFEMODE : 1;       /**< Don't use fancy stuff (EDNS, 0x20, ...) */
+	bool CACHED : 1;         /**< Query response is cached. */
+	bool NO_CACHE : 1;       /**< No cache for lookup; exception: finding NSs and subqueries. */
+	bool EXPIRING : 1;       /**< Query response is cached, but expiring. */
+	bool ALLOW_LOCAL : 1;    /**< Allow queries to local or private address ranges. */
+	bool DNSSEC_WANT : 1;    /**< Want DNSSEC secured answer; exception: +cd,
+				  * i.e. knot_wire_set_cd(request->answer->wire). */
+	bool DNSSEC_BOGUS : 1;   /**< Query response is DNSSEC bogus. */
+	bool DNSSEC_INSECURE : 1;/**< Query response is DNSSEC insecure. */
+	bool DNSSEC_CD : 1;      /**< Instruction to set CD bit in request. */
+	bool STUB : 1;           /**< Stub resolution, accept received answer as solved. */
+	bool ALWAYS_CUT : 1;     /**< Always recover zone cut (even if cached). */
+	bool DNSSEC_WEXPAND : 1; /**< Query response has wildcard expansion. */
+	bool PERMISSIVE : 1;     /**< Permissive resolver mode. */
+	bool STRICT : 1;         /**< Strict resolver mode. */
+	bool BADCOOKIE_AGAIN : 1;/**< Query again because bad cookie returned. */
+	bool CNAME : 1;          /**< Query response contains CNAME in answer section. */
+	bool REORDER_RR : 1;     /**< Reorder cached RRs. */
+	bool TRACE : 1;          /**< Also log answers if --verbose. */
+	bool NO_0X20 : 1;        /**< Disable query case randomization . */
+	bool DNSSEC_NODS : 1;    /**< DS non-existance is proven */
+	bool DNSSEC_OPTOUT : 1;  /**< Closest encloser proof has optout */
+	bool NONAUTH : 1;        /**< Non-authoritative in-bailiwick records are enough.
+				  * TODO: utilize this also outside cache. */
+	bool FORWARD : 1;        /**< Forward all queries to upstream; validate answers. */
+	bool DNS64_MARK : 1;     /**< Internal mark for dns64 module. */
+	bool CACHE_TRIED : 1;    /**< Internal to cache module. */
+	bool NO_NS_FOUND : 1;    /**< No valid NS found during last PRODUCE stage. */
+};
+
+/** Combine flags together.  This means set union for simple flags. */
+KR_EXPORT
+void kr_qflags_set(struct kr_qflags *fl1, struct kr_qflags fl2);
+
+/** Remove flags.  This means set-theoretic difference. */
+KR_EXPORT
+void kr_qflags_clear(struct kr_qflags *fl1, struct kr_qflags fl2);
+
+/** Callback for serve-stale decisions.
+ * @param ttl the expired TTL (i.e. it's < 0)
+ * @return the adjusted TTL (typically 1) or < 0.
+ */
+typedef int32_t (*kr_stale_cb)(int32_t ttl, const knot_dname_t *owner, uint16_t type,
+				const struct kr_query *qry);
+
+/**
+ * Single query representation.
+ */
+struct kr_query {
+	struct kr_query *parent;
+	knot_dname_t *sname; /**< The name to resolve - lower-cased, uncompressed. */
+	uint16_t stype;
+	uint16_t sclass;
+	uint16_t id;
+	struct kr_qflags flags, forward_flags;
+	uint32_t secret;
+	uint16_t fails;
+	uint16_t reorder; /**< Seed to reorder (cached) RRs in answer or zero. */
+	uint64_t creation_time_mono; /* The time of query's creation (milliseconds).
+				 * Or time of creation of an oldest
+				 * ancestor if it is a subquery. */
+	uint64_t timestamp_mono; /**< Time of query created or time of
+	                           * query to upstream resolver (milliseconds). */
+	struct timeval timestamp; /**< Real time for TTL+DNSSEC checks (.tv_sec only). */
+	struct kr_zonecut zone_cut;
+	struct kr_layer_pickle *deferred;
+	uint32_t uid; /**< Query iteration number, unique within the kr_rplan. */
+	/** Pointer to the query that originated this one because of following a CNAME (or NULL). */
+	struct kr_query *cname_parent;
+	struct kr_request *request; /**< Parent resolution request. */
+	kr_stale_cb stale_cb; /**< See the type */
+	/* Beware: this must remain the last, because of lua bindings. */
+	struct kr_nsrep ns;
+};
+
+/** @cond internal Array of queries. */
+typedef array_t(struct kr_query *) kr_qarray_t;
+/* @endcond */
+
+/**
+ * Query resolution plan structure.
+ *
+ * The structure most importantly holds the original query, answer and the
+ * list of pending queries required to resolve the original query.
+ * It also keeps a notion of current zone cut.
+ */
+struct kr_rplan {
+	kr_qarray_t pending;        /**< List of pending queries. */
+	kr_qarray_t resolved;       /**< List of resolved queries. */
+	struct kr_request *request; /**< Parent resolution request. */
+	knot_mm_t *pool;            /**< Temporary memory pool. */
+	uint32_t next_uid;          /**< Next value for kr_query::uid (incremental). */
+};
+
+/**
+ * Initialize resolution plan (empty).
+ * @param rplan plan instance
+ * @param request resolution request
+ * @param pool ephemeral memory pool for whole resolution
+ */
+KR_EXPORT
+int kr_rplan_init(struct kr_rplan *rplan, struct kr_request *request, knot_mm_t *pool);
+
+/**
+ * Deinitialize resolution plan, aborting any uncommited transactions.
+ * @param rplan plan instance
+ */
+KR_EXPORT
+void kr_rplan_deinit(struct kr_rplan *rplan);
+
+/**
+ * Return true if the resolution plan is empty (i.e. finished or initialized)
+ * @param rplan plan instance
+ * @return true or false
+ */
+KR_EXPORT KR_PURE
+bool kr_rplan_empty(struct kr_rplan *rplan);
+
+/**
+ * Push empty query to the top of the resolution plan.
+ * @note This query serves as a cookie query only.
+ * @param rplan plan instance
+ * @param parent query parent (or NULL)
+ * @return query instance or NULL
+ */
+KR_EXPORT
+struct kr_query *kr_rplan_push_empty(struct kr_rplan *rplan,
+                                     struct kr_query *parent);
+
+/**
+ * Push a query to the top of the resolution plan.
+ * @note This means that this query takes precedence before all pending queries.
+ * @param rplan plan instance
+ * @param parent query parent (or NULL)
+ * @param name resolved name
+ * @param cls  resolved class
+ * @param type resolved type
+ * @return query instance or NULL
+ */
+KR_EXPORT
+struct kr_query *kr_rplan_push(struct kr_rplan *rplan, struct kr_query *parent,
+                               const knot_dname_t *name, uint16_t cls, uint16_t type);
+
+/**
+ * Pop existing query from the resolution plan.
+ * @note Popped queries are not discarded, but moved to the resolved list.
+ * @param rplan plan instance
+ * @param qry resolved query
+ * @return 0 or an error
+ */
+KR_EXPORT
+int kr_rplan_pop(struct kr_rplan *rplan, struct kr_query *qry);
+
+/**
+ * Return true if resolution chain satisfies given query.
+ */
+KR_EXPORT KR_PURE
+bool kr_rplan_satisfies(struct kr_query *closure, const knot_dname_t *name, uint16_t cls, uint16_t type);
+
+/** Return last resolved query. */
+KR_EXPORT KR_PURE
+struct kr_query *kr_rplan_resolved(struct kr_rplan *rplan);
+
+/**
+  * Return last query (either currently being solved or last resolved).
+  * This is necessary to retrieve the last query in case of resolution failures (e.g. time limit reached).
+  */
+KR_EXPORT KR_PURE
+struct kr_query *kr_rplan_last(struct kr_rplan *rplan);
+
+
+/**
+ * Check if a given query already resolved.
+ * @param rplan plan instance
+ * @param parent query parent (or NULL)
+ * @param name resolved name
+ * @param cls  resolved class
+ * @param type resolved type
+ * @return query instance or NULL
+ */
+KR_EXPORT KR_PURE
+struct kr_query *kr_rplan_find_resolved(struct kr_rplan *rplan, struct kr_query *parent,
+                               const knot_dname_t *name, uint16_t cls, uint16_t type);
diff --git a/lib/utils.c b/lib/utils.c
new file mode 100644
index 0000000..fe9ab03
--- /dev/null
+++ b/lib/utils.c
@@ -0,0 +1,1084 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <stdarg.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <arpa/inet.h>
+#include <sys/time.h>
+#include <contrib/cleanup.h>
+#include <contrib/ccan/asprintf/asprintf.h>
+#include <ucw/mempool.h>
+#include <gnutls/gnutls.h>
+#include <libknot/descriptor.h>
+#include <libknot/dname.h>
+#include <libknot/rrtype/rrsig.h>
+#include <libknot/rrset-dump.h>
+#include <libknot/version.h>
+#include <uv.h>
+
+#include "lib/defines.h"
+#include "lib/utils.h"
+#include "lib/generic/array.h"
+#include "lib/nsrep.h"
+#include "lib/module.h"
+#include "lib/resolve.h"
+
+
+/* Always compile-in log symbols, even if disabled. */
+#undef kr_verbose_status
+#undef kr_verbose_set
+#undef kr_log_verbose
+
+/* Logging & debugging */
+bool kr_verbose_status = false;
+
+void *mm_realloc(knot_mm_t *mm, void *what, size_t size, size_t prev_size)
+{
+	if (mm) {
+		void *p = mm->alloc(mm->ctx, size);
+		if (p == NULL) {
+			return NULL;
+		} else {
+			if (what) {
+				memcpy(p, what,
+				       prev_size < size ? prev_size : size);
+			}
+			mm_free(mm, what);
+			return p;
+		}
+	} else {
+		return realloc(what, size);
+	}
+}
+
+void *mm_malloc(void *ctx, size_t n)
+{
+	(void)ctx;
+	return malloc(n);
+}
+
+/*
+ * Macros.
+ */
+#define strlen_safe(x) ((x) ? strlen(x) : 0)
+
+/**
+ * @internal Convert 16bit unsigned to string, keeps leading spaces.
+ * @note Always fills dst length = 5
+ * Credit: http://computer-programming-forum.com/46-asm/7aa4b50bce8dd985.htm
+ */
+static inline int u16tostr(uint8_t *dst, uint16_t num)
+{
+	uint32_t tmp = num * (((1 << 28) / 10000) + 1) - (num / 4);
+	for(size_t i = 0; i < 5; i++) {
+		dst[i] = '0' + (char) (tmp >> 28);
+		tmp = (tmp & 0x0fffffff) * 10;
+	}
+	return 5;
+}
+
+/*
+ * Cleanup callbacks.
+ */
+
+static void kres_gnutls_log(int level, const char *message)
+{
+	kr_log_verbose("[gnutls] (%d) %s", level, message);
+}
+
+bool kr_verbose_set(bool status)
+{
+#ifndef NOVERBOSELOG
+	kr_verbose_status = status;
+
+	/* gnutls logs messages related to our TLS and also libdnssec,
+	 * and the logging is set up in a global way only */
+	if (status) {
+		gnutls_global_set_log_function(kres_gnutls_log);
+	}
+	gnutls_global_set_log_level(status ? 5 : 0);
+#endif
+	return kr_verbose_status;
+}
+
+void kr_log_verbose(const char *fmt, ...)
+{
+	if (kr_verbose_status) {
+		va_list args;
+		va_start(args, fmt);
+		vprintf(fmt, args);
+		va_end(args);
+		fflush(stdout);
+	}
+}
+
+void kr_log_qverbose_impl(const struct kr_query *qry, const char *cls, const char *fmt, ...)
+{
+	unsigned ind = 0;
+	for (const struct kr_query *q = qry; q; q = q->parent)
+		ind += 2;
+	uint32_t qry_uid = qry ? qry->uid : 0;
+	uint32_t req_uid = qry && qry->request ? qry->request->uid : 0;
+	/* Simplified kr_log_verbose() calls, first prefix then passed fmt...
+	 * Calling it would take about the same amount of code. */
+	printf("[%05u.%02u][%s] %*s", req_uid, qry_uid, cls, ind, "");
+	va_list args;
+	va_start(args, fmt);
+	vprintf(fmt, args);
+	va_end(args);
+	fflush(stdout);
+}
+
+bool kr_log_trace(const struct kr_query *query, const char *source, const char *fmt, ...)
+{
+	if (!kr_log_trace_enabled(query)) {
+		return false;
+	}
+
+	auto_free char *msg = NULL;
+
+	va_list args;
+	va_start(args, fmt);
+	int len = vasprintf(&msg, fmt, args);
+	va_end(args);
+
+	/* Check formatting result before logging */
+	if (len < 0) {
+		return false;
+	}
+
+	query->request->trace_log(query, source, msg);
+	return true;
+}
+
+char* kr_strcatdup(unsigned n, ...)
+{
+	if (n < 1) {
+		return NULL;
+	}
+
+	/* Calculate total length */
+	size_t total_len = 0;
+	va_list vl;
+	va_start(vl, n);
+	for (unsigned i = 0; i < n; ++i) {
+		char *item = va_arg(vl, char *);
+		const size_t new_len = total_len + strlen_safe(item);
+		if (unlikely(new_len < total_len)) {
+			va_end(vl);
+			return NULL;
+		}
+		total_len = new_len;
+	}
+	va_end(vl);
+
+	/* Allocate result and fill */
+	char *result = NULL;
+	if (total_len > 0) {
+		if (unlikely(total_len + 1 == 0)) return NULL;
+		result = malloc(total_len + 1);
+	}
+	if (result) {
+		char *stream = result;
+		va_start(vl, n);
+		for (unsigned i = 0; i < n; ++i) {
+			char *item = va_arg(vl, char *);
+			if (item) {
+				size_t len = strlen(item);
+				memcpy(stream, item, len + 1);
+				stream += len;
+			}
+		}
+		va_end(vl);
+	}
+
+	return result;
+}
+
+int kr_memreserve(void *baton, char **mem, size_t elm_size, size_t want, size_t *have)
+{
+    if (*have >= want) {
+        return 0;
+    } else {
+        knot_mm_t *pool = baton;
+        size_t next_size = array_next_count(want);
+        void *mem_new = mm_alloc(pool, next_size * elm_size);
+        if (mem_new != NULL) {
+            memcpy(mem_new, *mem, (*have)*(elm_size));
+            mm_free(pool, *mem);
+            *mem = mem_new;
+            *have = next_size;
+            return 0;
+        }
+    }
+    return -1;
+}
+
+static int pkt_recycle(knot_pkt_t *pkt, bool keep_question)
+{
+	/* The maximum size of a header + query name + (class, type) */
+	uint8_t buf[KNOT_WIRE_HEADER_SIZE + KNOT_DNAME_MAXLEN + 2 * sizeof(uint16_t)];
+
+	/* Save header and the question section */
+	size_t base_size = KNOT_WIRE_HEADER_SIZE;
+	if (keep_question) {
+		base_size += knot_pkt_question_size(pkt);
+	}
+	assert(base_size <= sizeof(buf));
+	memcpy(buf, pkt->wire, base_size);
+
+	/* Clear the packet and its auxiliary structures */
+	knot_pkt_clear(pkt);
+
+	/* Restore header and question section and clear counters */
+	pkt->size = base_size;
+	memcpy(pkt->wire, buf, base_size);
+	knot_wire_set_qdcount(pkt->wire, keep_question);
+	knot_wire_set_ancount(pkt->wire, 0);
+	knot_wire_set_nscount(pkt->wire, 0);
+	knot_wire_set_arcount(pkt->wire, 0);
+
+	/* Reparse question */
+	knot_pkt_begin(pkt, KNOT_ANSWER);
+	return knot_pkt_parse_question(pkt);
+}
+
+int kr_pkt_recycle(knot_pkt_t *pkt)
+{
+	return pkt_recycle(pkt, false);
+}
+
+int kr_pkt_clear_payload(knot_pkt_t *pkt)
+{
+	return pkt_recycle(pkt, knot_wire_get_qdcount(pkt->wire));
+}
+
+int kr_pkt_put(knot_pkt_t *pkt, const knot_dname_t *name, uint32_t ttl,
+               uint16_t rclass, uint16_t rtype, const uint8_t *rdata, uint16_t rdlen)
+{
+	/* LATER(opt.): there's relatively lots of copying, but ATM kr_pkt_put()
+	 * isn't considered to be used in any performance-critical parts (just lua). */
+	if (!pkt || !name)  {
+		return kr_error(EINVAL);
+	}
+	/* Create empty RR */
+	knot_rrset_t rr;
+	knot_rrset_init(&rr, knot_dname_copy(name, &pkt->mm), rtype, rclass, ttl);
+	/* Create RDATA */
+	knot_rdata_t *rdata_tmp = mm_alloc(&pkt->mm, offsetof(knot_rdata_t, data) + rdlen);
+	knot_rdata_init(rdata_tmp, rdlen, rdata);
+	knot_rdataset_add(&rr.rrs, rdata_tmp, &pkt->mm);
+	mm_free(&pkt->mm, rdata_tmp); /* we're always on mempool for now, but whatever */
+	/* Append RR */
+	return knot_pkt_put(pkt, 0, &rr, KNOT_PF_FREE);
+}
+
+void kr_pkt_make_auth_header(knot_pkt_t *pkt)
+{
+	assert(pkt && pkt->wire);
+	knot_wire_clear_ad(pkt->wire);
+	knot_wire_set_aa(pkt->wire);
+}
+
+const char *kr_inaddr(const struct sockaddr *addr)
+{
+	if (!addr) {
+		return NULL;
+	}
+	switch (addr->sa_family) {
+	case AF_INET:  return (const char *)&(((const struct sockaddr_in *)addr)->sin_addr);
+	case AF_INET6: return (const char *)&(((const struct sockaddr_in6 *)addr)->sin6_addr);
+	default:       return NULL;
+	}
+}
+
+int kr_inaddr_family(const struct sockaddr *addr)
+{
+	if (!addr)
+		return AF_UNSPEC;
+	return addr->sa_family;
+}
+
+int kr_inaddr_len(const struct sockaddr *addr)
+{
+	if (!addr) {
+		return kr_error(EINVAL);
+	}
+	return kr_family_len(addr->sa_family);
+}
+
+int kr_sockaddr_len(const struct sockaddr *addr)
+{
+	if (!addr) {
+		return kr_error(EINVAL);
+	}
+	switch (addr->sa_family) {
+	case AF_INET:  return sizeof(struct sockaddr_in);
+	case AF_INET6: return sizeof(struct sockaddr_in6);
+	default:       return kr_error(EINVAL);
+	}
+}
+
+int kr_sockaddr_cmp(const struct sockaddr *left, const struct sockaddr *right)
+{
+	if (!left || !right) {
+		return kr_error(EINVAL);
+	}
+	if (left->sa_family != right->sa_family) {
+		return kr_error(EFAULT);
+	}
+	if (left->sa_family == AF_INET) {
+		struct sockaddr_in *left_in = (struct sockaddr_in *)left;
+		struct sockaddr_in *right_in = (struct sockaddr_in *)right;
+		if (left_in->sin_addr.s_addr != right_in->sin_addr.s_addr) {
+			return kr_error(EFAULT);
+		}
+		if (left_in->sin_port != right_in->sin_port) {
+			return kr_error(EFAULT);
+		}
+	} else if (left->sa_family == AF_INET6) {
+		struct sockaddr_in6 *left_in6 = (struct sockaddr_in6 *)left;
+		struct sockaddr_in6 *right_in6 = (struct sockaddr_in6 *)right;
+		if (memcmp(&left_in6->sin6_addr, &right_in6->sin6_addr,
+			   sizeof(struct in6_addr)) != 0) {
+			return kr_error(EFAULT);
+		}
+		if (left_in6->sin6_port != right_in6->sin6_port) {
+			return kr_error(EFAULT);
+		}
+	} else {
+		return kr_error(ENOENT);
+	}
+	return kr_ok();
+}
+
+uint16_t kr_inaddr_port(const struct sockaddr *addr)
+{
+	if (!addr) {
+		return 0;
+	}
+	switch (addr->sa_family) {
+	case AF_INET:  return ntohs(((const struct sockaddr_in *)addr)->sin_port);
+	case AF_INET6: return ntohs(((const struct sockaddr_in6 *)addr)->sin6_port);
+	default:       return 0;
+	}
+}
+
+void kr_inaddr_set_port(struct sockaddr *addr, uint16_t port)
+{
+	if (!addr) {
+		return;
+	}
+	switch (addr->sa_family) {
+	case AF_INET:  ((struct sockaddr_in *)addr)->sin_port = htons(port);
+	case AF_INET6: ((struct sockaddr_in6 *)addr)->sin6_port = htons(port);
+	default: break;
+	}
+}
+
+int kr_inaddr_str(const struct sockaddr *addr, char *buf, size_t *buflen)
+{
+	if (!addr || !buf || !buflen) {
+		return kr_error(EINVAL);
+	}
+
+	if (!inet_ntop(addr->sa_family, kr_inaddr(addr), buf, *buflen)) {
+		return kr_error(errno);
+	}
+	const int len = strlen(buf);
+	const int len_need = len + 1 + 5 + 1;
+	if (len_need > *buflen) {
+		*buflen = len_need;
+		return kr_error(ENOSPC);
+	}
+	*buflen = len_need;
+	buf[len] = '#';
+	u16tostr((uint8_t *)&buf[len + 1], kr_inaddr_port(addr));
+	buf[len_need - 1] = 0;
+	return kr_ok();
+}
+
+int kr_straddr_family(const char *addr)
+{
+	if (!addr) {
+		return kr_error(EINVAL);
+	}
+	if (strchr(addr, ':')) {
+		return AF_INET6;
+	}
+	return AF_INET;
+}
+
+int kr_family_len(int family)
+{
+	switch (family) {
+	case AF_INET:  return sizeof(struct in_addr);
+	case AF_INET6: return sizeof(struct in6_addr);
+	default:       return kr_error(EINVAL);
+	}
+}
+
+struct sockaddr * kr_straddr_socket(const char *addr, int port)
+{
+	switch (kr_straddr_family(addr)) {
+	case AF_INET: {
+		struct sockaddr_in *res = malloc(sizeof(*res));
+		if (uv_ip4_addr(addr, port, res) >= 0) {
+			return (struct sockaddr *)res;
+		} else {
+			free(res);
+			return NULL;
+		}
+	}
+	case AF_INET6: {
+		struct sockaddr_in6 *res = malloc(sizeof(*res));
+		if (uv_ip6_addr(addr, port, res) >= 0) {
+			return (struct sockaddr *)res;
+		} else {
+			free(res);
+			return NULL;
+		}
+	}
+	default:
+		return NULL;
+	}
+}
+
+int kr_straddr_subnet(void *dst, const char *addr)
+{
+	if (!dst || !addr) {
+		return kr_error(EINVAL);
+	}
+	/* Parse subnet */
+	int bit_len = 0;
+	int family = kr_straddr_family(addr);
+	auto_free char *addr_str = strdup(addr);
+	char *subnet = strchr(addr_str, '/');
+	if (subnet) {
+		*subnet = '\0';
+		subnet += 1;
+		bit_len = strtol(subnet, NULL, 10);
+		/* Check client subnet length */
+		const int max_len = (family == AF_INET6) ? 128 : 32;
+		if (bit_len < 0 || bit_len > max_len) {
+			return kr_error(ERANGE);
+		}
+	} else {
+		/* No subnet, use maximal subnet length. */
+		bit_len = (family == AF_INET6) ? 128 : 32;
+	}
+	/* Parse address */
+	int ret = inet_pton(family, addr_str, dst);
+	if (ret < 0) {
+		return kr_error(EILSEQ);
+	}
+
+	return bit_len;
+}
+
+int kr_straddr_split(const char *addr, char *buf, size_t buflen, uint16_t *port)
+{
+	const int base = 10;
+	long p = 0;
+	size_t addrlen = strlen(addr);
+	char *p_start = strchr(addr, '@');
+	char *p_end;
+
+	if (!p_start) {
+		p_start = strchr(addr, '#');
+	}
+
+	if (p_start) {
+		if (p_start[1] != '\0'){
+			p = strtol(p_start + 1, &p_end, base);
+			if (*p_end != '\0' || p <= 0 || p > UINT16_MAX) {
+				return kr_error(EINVAL);
+			}
+		}
+		addrlen = p_start - addr;
+	}
+
+	/* Check if address is valid. */
+	if (addrlen >= INET6_ADDRSTRLEN) {
+		return kr_error(EINVAL);
+	}
+
+	char str[INET6_ADDRSTRLEN];
+	struct sockaddr_storage ss;
+
+	memcpy(str, addr, addrlen); str[addrlen] = '\0';
+
+	int family = kr_straddr_family(str);
+	if (family == kr_error(EINVAL) || !inet_pton(family, str, &ss)) {
+		return kr_error(EINVAL);
+	}
+
+	/* Address and port contains valid values, return it to caller */
+	if (buf) {
+		if (addrlen >= buflen) {
+			return kr_error(ENOSPC);
+		}
+		memcpy(buf, addr, addrlen); buf[addrlen] = '\0';
+	}
+	if (port) {
+		*port = (uint16_t)p;
+	}
+
+	return kr_ok();
+}
+
+int kr_straddr_join(const char *addr, uint16_t port, char *buf, size_t *buflen)
+{
+	if (!addr || !buf || !buflen) {
+		return kr_error(EINVAL);
+	}
+
+	struct sockaddr_storage ss;
+	int family = kr_straddr_family(addr);
+	if (family == kr_error(EINVAL) || !inet_pton(family, addr, &ss)) {
+		return kr_error(EINVAL);
+	}
+
+	int len = strlen(addr);
+	if (len + 6 >= *buflen) {
+		return kr_error(ENOSPC);
+	}
+
+	memcpy(buf, addr, len + 1);
+	buf[len] = '#';
+	u16tostr((uint8_t *)&buf[len + 1], port);
+	len += 6;
+	buf[len] = 0;
+	*buflen = len;
+
+	return kr_ok();
+}
+
+int kr_bitcmp(const char *a, const char *b, int bits)
+{
+	/* We're using the function from lua directly, so at least for now
+	 * we avoid crashing on bogus inputs.  Meaning: NULL is ordered before
+	 * anything else, and negative length is the same as zero.
+	 * TODO: review the call sites and probably remove the checks. */
+	if (bits <= 0 || (!a && !b)) {
+		return 0;
+	} else if (!a) {
+		return -1;
+	} else if (!b) {
+		return 1;
+	}
+
+	assert((a && b && bits >= 0)  ||  bits == 0);
+	/* Compare part byte-divisible part. */
+	const size_t chunk = bits / 8;
+	int ret = memcmp(a, b, chunk);
+	if (ret != 0) {
+		return ret;
+	}
+	a += chunk;
+	b += chunk;
+	bits -= chunk * 8;
+	/* Compare last partial byte address block. */
+	if (bits > 0) {
+		const size_t shift = (8 - bits);
+		ret = ((uint8_t)(*a >> shift) - (uint8_t)(*b >> shift));
+	}
+	return ret;
+}
+
+int kr_rrkey(char *key, uint16_t class, const knot_dname_t *owner,
+	     uint16_t type, uint16_t additional)
+{
+	if (!key || !owner) {
+		return kr_error(EINVAL);
+	}
+	uint8_t *key_buf = (uint8_t *)key;
+	int ret = u16tostr(key_buf, class);
+	if (ret <= 0) {
+		return ret;
+	}
+	key_buf += ret;
+	ret = knot_dname_to_wire(key_buf, owner, KNOT_DNAME_MAXLEN);
+	if (ret <= 0) {
+		return ret;
+	}
+	knot_dname_to_lower(key_buf);
+	key_buf += ret - 1;
+	ret = u16tostr(key_buf, type);
+	if (ret <= 0) {
+		return ret;
+	}
+	key_buf += ret;
+	ret = u16tostr(key_buf, additional);
+	if (ret <= 0) {
+		return ret;
+	}
+	key_buf[ret] = '\0';
+	return (char *)&key_buf[ret] - key;
+}
+
+/** Return whether two RRsets match, i.e. would form the same set; see ranked_rr_array_t */
+static inline bool rrsets_match(const knot_rrset_t *rr1, const knot_rrset_t *rr2)
+{
+	bool match = rr1->type == rr2->type && rr1->rclass == rr2->rclass;
+	if (match && rr2->type == KNOT_RRTYPE_RRSIG) {
+		match = match && knot_rrsig_type_covered(rr1->rrs.rdata)
+				  == knot_rrsig_type_covered(rr2->rrs.rdata);
+	}
+	match = match && knot_dname_is_equal(rr1->owner, rr2->owner);
+	return match;
+}
+
+/** Ensure that an index in a ranked array won't cause "duplicate" RRsets on wire.
+ *
+ * Other entries that would form the same RRset get to_wire = false.
+ * See also rrsets_match.
+ */
+static int to_wire_ensure_unique(ranked_rr_array_t *array, size_t index)
+{
+	bool ok = array && index < array->len;
+	if (!ok) {
+		assert(false);
+		return kr_error(EINVAL);
+	}
+
+	const struct ranked_rr_array_entry *e0 = array->at[index];
+	if (!e0->to_wire) {
+		return kr_ok();
+	}
+
+	for (ssize_t i = array->len - 1; i >= 0; --i) {
+		/* ^ iterate backwards, as the end is more likely in CPU caches */
+		struct ranked_rr_array_entry *ei = array->at[i];
+		if (ei->qry_uid == e0->qry_uid /* assumption: no duplicates within qry */
+		    || !ei->to_wire /* no use for complex comparison if @to_wire */
+		   ) {
+			continue;
+		}
+		if (rrsets_match(ei->rr, e0->rr)) {
+			ei->to_wire = false;
+		}
+	}
+	return kr_ok();
+}
+
+int kr_ranked_rrarray_add(ranked_rr_array_t *array, const knot_rrset_t *rr,
+			  uint8_t rank, bool to_wire, uint32_t qry_uid, knot_mm_t *pool)
+{
+	/* rr always has one record per rrset
+	 * check if another rrset with the same
+	 * rclass/type/owner combination exists within current query
+	 * and merge if needed */
+	for (ssize_t i = array->len - 1; i >= 0; --i) {
+		ranked_rr_array_entry_t *stashed = array->at[i];
+		if (stashed->yielded) {
+			break;
+		}
+		if (stashed->qry_uid != qry_uid) {
+			break;
+		}
+		if (!rrsets_match(stashed->rr, rr)) {
+			continue;
+		}
+		/* Found the entry to merge with.  Check consistency and merge. */
+		bool ok = stashed->rank == rank && !stashed->cached;
+		if (!ok) {
+			assert(false);
+			return kr_error(EEXIST);
+		}
+		/* It may happen that an RRset is first considered useful
+		 * (to_wire = false, e.g. due to being part of glue),
+		 * and later we may find we also want it in the answer. */
+		stashed->to_wire = stashed->to_wire || to_wire;
+
+		return knot_rdataset_merge(&stashed->rr->rrs, &rr->rrs, pool);
+	}
+
+	/* No stashed rrset found, add */
+	int ret = array_reserve_mm(*array, array->len + 1, kr_memreserve, pool);
+	if (ret != 0) {
+		return kr_error(ENOMEM);
+	}
+
+	ranked_rr_array_entry_t *entry = mm_alloc(pool, sizeof(ranked_rr_array_entry_t));
+	if (!entry) {
+		return kr_error(ENOMEM);
+	}
+	knot_rrset_t *copy = knot_rrset_copy(rr, pool);
+	if (!copy) {
+		mm_free(pool, entry);
+		return kr_error(ENOMEM);
+	}
+
+	entry->qry_uid = qry_uid;
+	entry->rr = copy;
+	entry->rank = rank;
+	entry->revalidation_cnt = 0;
+	entry->cached = false;
+	entry->yielded = false;
+	entry->to_wire = to_wire;
+	if (array_push(*array, entry) < 0) {
+		/* Silence coverity.  It shouldn't be possible to happen,
+		 * due to the array_reserve_mm call above. */
+		mm_free(pool, entry);
+		return kr_error(ENOMEM);
+	}
+
+	return to_wire_ensure_unique(array, array->len - 1);
+}
+
+int kr_ranked_rrarray_set_wire(ranked_rr_array_t *array, bool to_wire,
+			       uint32_t qry_uid, bool check_dups,
+			       bool (*extraCheck)(const ranked_rr_array_entry_t *))
+{
+	for (size_t i = 0; i < array->len; ++i) {
+		ranked_rr_array_entry_t *entry = array->at[i];
+		if (entry->qry_uid != qry_uid) {
+			continue;
+		}
+		if (extraCheck != NULL && !extraCheck(entry)) {
+			continue;
+		}
+		entry->to_wire = to_wire;
+		if (check_dups) {
+			int ret = to_wire_ensure_unique(array, i);
+			if (ret) return ret;
+		}
+	}
+	return kr_ok();
+}
+
+
+static char *callprop(struct kr_module *module, const char *prop, const char *input, void *env)
+{
+	if (!module || !module->props || !prop) {
+		return NULL;
+	}
+	for (const struct kr_prop *p = module->props(); p && p->name; ++p) {
+		if (p->cb != NULL && strcmp(p->name, prop) == 0) {
+			return p->cb(env, module, input);
+		}
+	}
+	return NULL;
+}
+
+char *kr_module_call(struct kr_context *ctx, const char *module, const char *prop, const char *input)
+{
+	if (!ctx || !ctx->modules || !module || !prop) {
+		return NULL;
+	}
+	module_array_t *mod_list = ctx->modules;
+	for (size_t i = 0; i < mod_list->len; ++i) {
+		struct kr_module *mod = mod_list->at[i];
+		if (strcmp(mod->name, module) == 0) {
+			return callprop(mod, prop, input, ctx);
+		}
+	}
+	return NULL;
+}
+
+static void flags_to_str(char *dst, const knot_pkt_t *pkt, size_t maxlen)
+{
+	int offset = 0;
+	int ret = 0;
+	struct {
+		uint8_t (*get) (const uint8_t *packet);
+		char name[3];
+	} flag[7] = {
+		{knot_wire_get_qr, "qr"},
+		{knot_wire_get_aa, "aa"},
+		{knot_wire_get_rd, "rd"},
+		{knot_wire_get_ra, "ra"},
+		{knot_wire_get_tc, "tc"},
+		{knot_wire_get_ad, "ad"},
+		{knot_wire_get_cd, "cd"}
+	};
+	for (int i = 0; i < 7; ++i) {
+		if (!flag[i].get(pkt->wire)) {
+			continue;
+		}
+		ret = snprintf(dst + offset, maxlen, "%s ", flag[i].name);
+		if (ret <= 0 || ret >= maxlen) {
+			dst[0] = 0;
+			return;
+		}
+		offset += ret;
+		maxlen -= ret;
+	}
+	dst[offset] = 0;
+}
+
+static char *print_section_opt(struct mempool *mp, char *endp, const knot_rrset_t *rr, const uint8_t rcode)
+{
+	uint8_t ercode = knot_edns_get_ext_rcode(rr);
+	uint16_t ext_rcode_id = knot_edns_whole_rcode(ercode, rcode);
+	const char *ext_rcode_str = "Unused";
+	const knot_lookup_t *ext_rcode;
+
+	if (ercode > 0) {
+		ext_rcode = knot_lookup_by_id(knot_rcode_names, ext_rcode_id);
+		if (ext_rcode != NULL) {
+			ext_rcode_str = ext_rcode->name;
+		} else {
+			ext_rcode_str = "Unknown";
+		}
+	}
+
+	return mp_printf_append(mp, endp,
+		";; EDNS PSEUDOSECTION:\n;; "
+		"Version: %u; flags: %s; UDP size: %u B; ext-rcode: %s\n\n",
+		knot_edns_get_version(rr),
+		(knot_edns_do(rr) != 0) ? "do" : "",
+		knot_edns_get_payload(rr),
+		ext_rcode_str);
+
+}
+
+char *kr_pkt_text(const knot_pkt_t *pkt)
+{
+	if (!pkt) {
+		return NULL;
+	}
+
+	struct mempool *mp = mp_new(512);
+
+	static const char * snames[] = {
+		";; ANSWER SECTION", ";; AUTHORITY SECTION", ";; ADDITIONAL SECTION"
+	};
+	char flags[32];
+	uint8_t pkt_rcode = knot_wire_get_rcode(pkt->wire);
+	uint8_t pkt_opcode = knot_wire_get_opcode(pkt->wire);
+	const char *rcode_str = "Unknown";
+	const char *opcode_str = "Unknown";
+	const knot_lookup_t *rcode = knot_lookup_by_id(knot_rcode_names, pkt_rcode);
+	const knot_lookup_t *opcode = knot_lookup_by_id(knot_opcode_names, pkt_opcode);
+	uint16_t qry_id = knot_wire_get_id(pkt->wire);
+	uint16_t qdcount = knot_wire_get_qdcount(pkt->wire);
+
+	if (rcode != NULL) {
+		rcode_str = rcode->name;
+	}
+	if (opcode != NULL) {
+		opcode_str = opcode->name;
+	}
+	flags_to_str(flags, pkt, sizeof(flags));
+
+	char *ptr = mp_printf(mp,
+		";; ->>HEADER<<- opcode: %s; status: %s; id: %hu\n"
+		";; Flags: %s QUERY: %hu; ANSWER: %hu; "
+		"AUTHORITY: %hu; ADDITIONAL: %hu\n\n",
+		opcode_str, rcode_str, qry_id,
+		flags,
+		qdcount,
+		knot_wire_get_ancount(pkt->wire),
+		knot_wire_get_nscount(pkt->wire),
+		knot_wire_get_arcount(pkt->wire));
+
+	if (knot_pkt_has_edns(pkt)) {
+		ptr = print_section_opt(mp, ptr, pkt->opt_rr, knot_wire_get_rcode(pkt->wire));
+	}
+
+	if (qdcount == 1) {
+		KR_DNAME_GET_STR(qname, knot_pkt_qname(pkt));
+		KR_RRTYPE_GET_STR(rrtype, knot_pkt_qtype(pkt));
+		ptr = mp_printf_append(mp, ptr, ";; QUESTION SECTION\n%s\t\t%s\n", qname, rrtype);
+	} else if (qdcount > 1) {
+		ptr = mp_printf_append(mp, ptr, ";; Warning: unsupported QDCOUNT %hu\n", qdcount);
+	}
+
+	for (knot_section_t i = KNOT_ANSWER; i <= KNOT_ADDITIONAL; ++i) {
+		const knot_pktsection_t *sec = knot_pkt_section(pkt, i);
+		if (sec->count == 0 || knot_pkt_rr(sec, 0)->type == KNOT_RRTYPE_OPT) {
+			/* OPT RRs are _supposed_ to be the last ^^, if they appear */
+			continue;
+		}
+
+		ptr = mp_printf_append(mp, ptr, "\n%s\n", snames[i - KNOT_ANSWER]);
+		for (unsigned k = 0; k < sec->count; ++k) {
+			const knot_rrset_t *rr = knot_pkt_rr(sec, k);
+			if (rr->type == KNOT_RRTYPE_OPT) {
+				continue;
+			}
+			auto_free char *rr_text = kr_rrset_text(rr);
+			ptr = mp_printf_append(mp, ptr, "%s", rr_text);
+		}
+	}
+
+	/* Close growing buffer and duplicate result before deleting */
+	char *result = strdup(ptr);
+	mp_delete(mp);
+	return result;
+}
+
+char *kr_rrset_text(const knot_rrset_t *rr)
+{
+	if (!rr) {
+		return NULL;
+	}
+
+	/* Note: knot_rrset_txt_dump will double the size until the rrset fits */
+	size_t bufsize = 128;
+	char *buf = malloc(bufsize);
+	int ret = knot_rrset_txt_dump(rr, &buf, &bufsize, &KNOT_DUMP_STYLE_DEFAULT);
+	if (ret < 0) {
+		free(buf);
+		return NULL;
+	}
+
+	return buf;
+}
+
+uint64_t kr_now()
+{
+	return uv_now(uv_default_loop());
+}
+
+const char *kr_strptime_diff(const char *format, const char *time1_str,
+		             const char *time0_str, double *diff) {
+	assert(format != NULL);
+	assert(time1_str != NULL);
+	assert(time0_str != NULL);
+	assert(diff != NULL);
+
+	struct tm time1_tm;
+	time_t time1_u;
+	struct tm time0_tm;
+	time_t time0_u;
+
+	char *err = strptime(time1_str, format, &time1_tm);
+	if (err == NULL || err != time1_str + strlen(time1_str))
+		return "strptime failed for time1";
+	time1_tm.tm_isdst = -1; /* determine if DST is active or not */
+	time1_u = mktime(&time1_tm);
+	if (time1_u == (time_t)-1)
+		return "mktime failed for time1";
+
+	err = strptime(time0_str, format, &time0_tm);
+	if (err == NULL || err != time0_str + strlen(time0_str))
+		return "strptime failed for time0";
+	time0_tm.tm_isdst = -1; /* determine if DST is active or not */
+	time0_u = mktime(&time0_tm);
+	if (time0_u == (time_t)-1)
+		return "mktime failed for time0";
+	*diff = difftime(time1_u, time0_u);
+
+	return NULL;
+}
+
+int knot_dname_lf2wire(knot_dname_t * const dst, uint8_t len, const uint8_t *lf)
+{
+	knot_dname_t *d = dst; /* moving "cursor" as we write it out */
+	bool ok = d && (len == 0 || lf);
+	if (!ok) {
+		assert(false);
+		return kr_error(EINVAL);
+	}
+	/* we allow the final zero byte to be omitted */
+	if (!len) {
+		goto finish;
+	}
+	if (lf[len - 1]) {
+		++len;
+	}
+	/* convert the name, one label at a time */
+	int label_end = len - 1; /* index of the zero byte after the current label */
+	while (label_end >= 0) {
+		/* find label_start */
+		int i = label_end - 1;
+		while (i >= 0 && lf[i])
+			--i;
+		const int label_start = i + 1; /* index of the first byte of the current label */
+		const int label_len = label_end - label_start;
+		assert(label_len >= 0);
+		if (label_len > 63 || label_len <= 0)
+			return kr_error(EILSEQ);
+		/* write the label */
+		*d = label_len;
+		++d;
+		memcpy(d, lf + label_start, label_len);
+		d += label_len;
+		/* next label */
+		label_end = label_start - 1;
+	}
+finish:
+	*d = 0; /* the final zero */
+	++d;
+	return d - dst;
+}
+
+static void rnd_noerror(void *data, uint size)
+{
+	int ret = gnutls_rnd(GNUTLS_RND_NONCE, data, size);
+	if (ret) {
+		kr_log_error("gnutls_rnd(): %s\n", gnutls_strerror(ret));
+		abort();
+	}
+}
+void kr_rnd_buffered(void *data, uint size)
+{
+	/* static circular buffer, from index _begin (inclusive) to _end (exclusive) */
+	static uint8_t buf[512/8]; /* gnutls_rnd() works on blocks of 512 bits (chacha) */
+	static uint buf_begin = sizeof(buf);
+
+	if (unlikely(size > sizeof(buf))) {
+		rnd_noerror(data, size);
+		return;
+	}
+	/* Start with contiguous chunk, possibly until the end of buffer. */
+	const uint size1 = MIN(size, sizeof(buf) - buf_begin);
+	uint8_t *d = data;
+	memcpy(d, buf + buf_begin, size1);
+	if (size1 == size) {
+		buf_begin += size1;
+		return;
+	}
+	d += size1;
+	size -= size1;
+	/* Refill the whole buffer, and finish by another contiguous chunk. */
+	rnd_noerror(buf, sizeof(buf));
+	memcpy(d, buf, size);
+	buf_begin = size;
+}
+
+void kr_rrset_init(knot_rrset_t *rrset, knot_dname_t *owner,
+			uint16_t type, uint16_t rclass, uint32_t ttl)
+{
+	assert(rrset);
+	knot_rrset_init(rrset, owner, type, rclass, ttl);
+}
+uint16_t kr_pkt_qclass(const knot_pkt_t *pkt)
+{
+	return knot_pkt_qclass(pkt);
+}
+uint16_t kr_pkt_qtype(const knot_pkt_t *pkt)
+{
+	return knot_pkt_qtype(pkt);
+}
+uint32_t kr_rrsig_sig_inception(const knot_rdata_t *rdata)
+{
+	return knot_rrsig_sig_inception(rdata);
+}
+uint32_t kr_rrsig_sig_expiration(const knot_rdata_t *rdata)
+{
+	return knot_rrsig_sig_expiration(rdata);
+}
+uint16_t kr_rrsig_type_covered(const knot_rdata_t *rdata)
+{
+	return knot_rrsig_type_covered(rdata);
+}
+
diff --git a/lib/utils.h b/lib/utils.h
new file mode 100644
index 0000000..21eabac
--- /dev/null
+++ b/lib/utils.h
@@ -0,0 +1,495 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <netinet/in.h>
+
+#include <gnutls/gnutls.h>
+#include <gnutls/crypto.h>
+#include <lua.h>
+
+#include <libknot/libknot.h>
+#include <libknot/packet/pkt.h>
+#include <libknot/rrset.h>
+#include <libknot/rrtype/rrsig.h>
+
+#include "lib/generic/array.h"
+#include "lib/defines.h"
+
+struct kr_query;
+struct kr_request;
+
+/*
+ * Logging and debugging.
+ */
+
+/** @brief Callback for request events. */
+typedef void (*trace_callback_f)(struct kr_request *request);
+/** @brief Callback for request logging handler. */
+typedef void (*trace_log_f)(const struct kr_query *query, const char *source, const char *msg);
+
+#define kr_log_info(...) do { printf(__VA_ARGS__); fflush(stdout); } while(0)
+#define kr_log_error(...) fprintf(stderr, ## __VA_ARGS__)
+
+/* Always export these, but override direct calls by macros conditionally. */
+/** Whether in --verbose mode.  Only use this for reading. */
+KR_EXPORT extern bool kr_verbose_status;
+
+/** Set --verbose mode.  Not available if compiled with -DNOVERBOSELOG. */
+KR_EXPORT bool kr_verbose_set(bool status);
+
+/** Log a message if in --verbose mode. */
+KR_EXPORT KR_PRINTF(1)
+void kr_log_verbose(const char *fmt, ...);
+
+/** Utility for QRVERBOSE - use that instead. */
+KR_EXPORT KR_PRINTF(3)
+void kr_log_qverbose_impl(const struct kr_query *qry, const char *cls, const char *fmt, ...);
+
+/**
+ * @brief Return true if the query has request log handler installed.
+ */
+#define kr_log_trace_enabled(query) (__builtin_expect( \
+	(query) && (query)->request && (query)->request->trace_log, \
+	false))
+
+/**
+ * Log a message through the request log handler.
+ * @param  query current query
+ * @param  source message source
+ * @param  fmt message format
+ * @return true if the message was logged
+ */
+KR_EXPORT KR_PRINTF(3)
+bool kr_log_trace(const struct kr_query *query, const char *source, const char *fmt, ...);
+
+#ifdef NOVERBOSELOG
+/* Efficient compile-time disabling of verbose messages. */
+#define kr_verbose_status false
+#define kr_verbose_set(x)
+#endif
+
+/** Block run in --verbose mode; optimized when not run. */
+#define VERBOSE_STATUS __builtin_expect(kr_verbose_status, false)
+#define WITH_VERBOSE(query) if(__builtin_expect(kr_verbose_status || kr_log_trace_enabled(query), false))
+#define kr_log_verbose if(VERBOSE_STATUS) kr_log_verbose
+
+#define KR_DNAME_GET_STR(dname_str, dname) \
+	char dname_str[KR_DNAME_STR_MAXLEN]; \
+	knot_dname_to_str(dname_str, (dname), sizeof(dname_str)); \
+	dname_str[sizeof(dname_str) - 1] = 0;
+
+#define KR_RRTYPE_GET_STR(rrtype_str, rrtype) \
+	char rrtype_str[KR_RRTYPE_STR_MAXLEN]; \
+	knot_rrtype_to_string((rrtype), rrtype_str, sizeof(rrtype_str)); \
+	rrtype_str[sizeof(rrtype_str) - 1] = 0;
+
+/* C11 compatibility, but without any implementation so far. */
+#ifndef static_assert
+#define static_assert(cond, msg)
+#endif
+
+/** @cond Memory alloc routines */
+static inline void *mm_alloc(knot_mm_t *mm, size_t size)
+{
+	if (mm) return mm->alloc(mm->ctx, size);
+	else return malloc(size);
+}
+static inline void mm_free(knot_mm_t *mm, const void *what)
+{
+	if (mm) {
+		if (mm->free)
+			mm->free((void *)what);
+	}
+	else free((void *)what);
+}
+
+/** Realloc implementation using memory context. */
+KR_EXPORT
+void *mm_realloc(knot_mm_t *mm, void *what, size_t size, size_t prev_size);
+
+/** Trivial malloc() wrapper. */
+void *mm_malloc(void *ctx, size_t n);
+
+/** Initialize mm with standard malloc+free. */
+static inline void mm_ctx_init(knot_mm_t *mm)
+{
+	mm->ctx = NULL;
+	mm->alloc = mm_malloc;
+	mm->free = free;
+}
+/* @endcond */
+
+/** Return time difference in miliseconds.
+  * @note based on the _BSD_SOURCE timersub() macro */
+static inline long time_diff(struct timeval *begin, struct timeval *end) {
+    struct timeval res = {
+        .tv_sec = end->tv_sec - begin->tv_sec,
+        .tv_usec = end->tv_usec - begin->tv_usec
+    };
+    if (res.tv_usec < 0) {
+        --res.tv_sec;
+        res.tv_usec += 1000000;
+    }
+    return res.tv_sec * 1000 + res.tv_usec / 1000;
+}
+
+/** @cond internal Array types */
+struct kr_context;
+
+typedef array_t(knot_rrset_t *) rr_array_t;
+struct ranked_rr_array_entry {
+	uint32_t qry_uid;
+	uint8_t rank; /**< enum kr_rank */
+	uint8_t revalidation_cnt;
+	bool cached : 1;  /**< Set to true if the entry was written into cache */
+	bool yielded : 1;
+	bool to_wire : 1; /**< whether to be put into the answer */
+	bool expiring : 1; /**< low remaining TTL; see is_expiring; only used in cache ATM */
+	knot_rrset_t *rr;
+};
+typedef struct ranked_rr_array_entry ranked_rr_array_entry_t;
+
+/** Array of RRsets coming from multiple queries; for struct kr_request.
+ *
+ * Notes:
+ *  - RRSIGs are only considered to form an RRset when the types covered match;
+ *    cache-related code relies on that!
+ *  - RRsets from the same packet (qry_uid) get merged.
+ */
+typedef array_t(ranked_rr_array_entry_t *) ranked_rr_array_t;
+/* @endcond */
+
+/** Concatenate N strings. */
+KR_EXPORT
+char* kr_strcatdup(unsigned n, ...);
+
+/** You probably want kr_rand_* convenience functions instead.
+ * This is a buffered version of gnutls_rnd(GNUTLS_RND_NONCE, ..) */
+KR_EXPORT
+void kr_rnd_buffered(void *data, unsigned int size);
+
+/** Return a few random bytes. */
+static inline uint64_t kr_rand_bytes(unsigned int size)
+{
+	uint64_t result;
+	if (size <= 0 || size > sizeof(result)) {
+		kr_log_error("kr_rand_bytes(): EINVAL\n");
+		abort();
+	}
+	uint8_t data[sizeof(result)];
+	kr_rnd_buffered(data, size);
+	/* I would have liked to dump the random data into a size_t directly,
+	 * but that would work well only on little-endian machines,
+	 * so intsead I hope that the compiler will optimize this out.
+	 * (Tested via reading assembly from usual gcc -O2 setup.)
+	 * Alternatively we could waste more rnd bytes, but that seemed worse. */
+	result = 0;
+	for (unsigned int i = 0; i < size; ++ i) {
+		result |= ((size_t)data[i]) << (i * 8);
+	}
+	return result;
+}
+
+/** Throw a pseudo-random coin, succeeding approximately with probability nomin/denomin.
+ * - low precision, only one byte of randomness (or none with extreme parameters)
+ * - tip: use !kr_rand_coin() to get the complementary probability
+ */
+static inline bool kr_rand_coin(unsigned int nomin, unsigned int denomin)
+{
+	/* This function might be called with non-constant values
+	 * so we try to handle odd corner cases instead of crash. */
+	if (nomin >= denomin)
+		return true;
+	else if (nomin <= 0)
+		return false;
+
+	/* threshold = how many parts from 256 are a success */
+	unsigned int threshold = (nomin * 256 + /*rounding*/ denomin / 2) / denomin;
+	if (threshold == 0) threshold = 1;
+	if (threshold == 256) threshold = 255;
+	return (kr_rand_bytes(1) < threshold);
+}
+
+/** Memory reservation routine for knot_mm_t */
+KR_EXPORT
+int kr_memreserve(void *baton, char **mem, size_t elm_size, size_t want, size_t *have);
+
+/** @internal Fast packet reset. */
+KR_EXPORT
+int kr_pkt_recycle(knot_pkt_t *pkt);
+
+/** @internal Clear packet payload. */
+KR_EXPORT
+int kr_pkt_clear_payload(knot_pkt_t *pkt);
+
+/** Construct and put record to packet. */
+KR_EXPORT
+int kr_pkt_put(knot_pkt_t *pkt, const knot_dname_t *name, uint32_t ttl,
+               uint16_t rclass, uint16_t rtype, const uint8_t *rdata, uint16_t rdlen);
+
+/** Set packet header suitable for authoritative answer. (for policy module) */
+KR_EXPORT
+void kr_pkt_make_auth_header(knot_pkt_t *pkt);
+
+/** Simple storage for IPx address or AF_UNSPEC. */
+union inaddr {
+	struct sockaddr ip;
+	struct sockaddr_in ip4;
+	struct sockaddr_in6 ip6;
+};
+
+/** Address bytes for given family. */
+KR_EXPORT KR_PURE
+const char *kr_inaddr(const struct sockaddr *addr);
+/** Address family. */
+KR_EXPORT KR_PURE
+int kr_inaddr_family(const struct sockaddr *addr);
+/** Address length for given family, i.e. sizeof(struct in*_addr). */
+KR_EXPORT KR_PURE
+int kr_inaddr_len(const struct sockaddr *addr);
+/** Sockaddr length for given family, i.e. sizeof(struct sockaddr_in*). */
+KR_EXPORT KR_PURE
+int kr_sockaddr_len(const struct sockaddr *addr);
+/** Compare two given sockaddr.
+ * return 0 - addresses are equal, error code otherwise.
+ */
+KR_EXPORT KR_PURE
+int kr_sockaddr_cmp(const struct sockaddr *left, const struct sockaddr *right);
+/** Port. */
+KR_EXPORT KR_PURE
+uint16_t kr_inaddr_port(const struct sockaddr *addr);
+/** Set port. */
+KR_EXPORT
+void kr_inaddr_set_port(struct sockaddr *addr, uint16_t port);
+
+/** Write string representation for given address as "<addr>#<port>".
+ * \param[in]     addr   the raw address
+ * \param[out]    buf    the buffer for output string
+ * \param[in,out] buflen the available(in) and utilized(out) length, including \0 */
+KR_EXPORT
+int kr_inaddr_str(const struct sockaddr *addr, char *buf, size_t *buflen);
+
+/** Return address type for string. */
+KR_EXPORT KR_PURE
+int kr_straddr_family(const char *addr);
+/** Return address length in given family (struct in*_addr). */
+KR_EXPORT KR_CONST
+int kr_family_len(int family);
+/** Create a sockaddr* from string+port representation (also accepts IPv6 link-local). */
+KR_EXPORT
+struct sockaddr * kr_straddr_socket(const char *addr, int port);
+/** Parse address and return subnet length (bits).
+  * @warning 'dst' must be at least `sizeof(struct in6_addr)` long. */
+KR_EXPORT
+int kr_straddr_subnet(void *dst, const char *addr);
+
+/** Splits ip address specified as "addr@port" or "addr#port" into addr and port
+  * and performs validation.
+  * @note if #port part isn't present, then port will be set to 0.
+  *       buf and\or port can be set to NULL.
+  * @return kr_error(EINVAL) - addr part doesn't contains valid ip address or
+  *                            #port part is out-of-range (either < 0 either > UINT16_MAX)
+  *         kr_error(ENOSP)  - buflen is too small
+  */
+KR_EXPORT
+int kr_straddr_split(const char *addr, char *buf, size_t buflen, uint16_t *port);
+/** Formats ip address and port in "addr#port" format.
+  * and performs validation.
+  * @note Port always formatted as five-character string with leading zeros.
+  * @return kr_error(EINVAL) - addr or buf is NULL or buflen is 0 or
+  *                            addr doesn't contain a valid ip address
+  *         kr_error(ENOSP)  - buflen is too small
+  */
+KR_EXPORT
+int kr_straddr_join(const char *addr, uint16_t port, char *buf, size_t *buflen);
+
+/** Compare memory bitwise.  The semantics is "the same" as for memcmp().
+ *  The partial byte is considered with more-significant bits first,
+ *  so this is e.g. suitable for comparing IP prefixes. */
+KR_EXPORT KR_PURE
+int kr_bitcmp(const char *a, const char *b, int bits);
+
+/** @internal RR map flags. */
+static const uint8_t KEY_FLAG_RRSIG = 0x02;
+static inline uint8_t KEY_FLAG_RANK(const char *key)
+	{ return ((uint8_t)(key[0])) >> 2; }
+static inline bool KEY_COVERING_RRSIG(const char *key)
+	{ return ((uint8_t)(key[0])) & KEY_FLAG_RRSIG; }
+
+/* Stash key = {[5] class, [1-255] owner, [5] type, [5] additional, [1] \x00 } */
+#define KR_RRKEY_LEN (16 + KNOT_DNAME_MAXLEN)
+/** Create unique null-terminated string key for RR.
+  * @param key Destination buffer for key size, MUST be KR_RRKEY_LEN or larger.
+  * @param class RR class.
+  * @param owner RR owner name.
+  * @param type RR type.
+  * @param additional flags (for instance can be used for storing covered type
+  *	   when RR type is RRSIG).
+  * @return key length if successful or an error
+  * */
+KR_EXPORT
+int kr_rrkey(char *key, uint16_t class, const knot_dname_t *owner,
+	     uint16_t type, uint16_t additional);
+
+/** @internal Add RRSet copy to ranked RR array. */
+KR_EXPORT
+int kr_ranked_rrarray_add(ranked_rr_array_t *array, const knot_rrset_t *rr,
+			  uint8_t rank, bool to_wire, uint32_t qry_uid, knot_mm_t *pool);
+
+/** @internal Mark the RRSets from particular query as
+ * "have (not) to be recorded in the final answer".
+ * @param array RRSet array.
+ * @param to_wire Records must be\must not be recorded in final answer.
+ * @param qry_uid Query uid.
+ * @param check_dups When to_wire is true, try to avoid duplicate RRSets.
+ * @param extraCheck optional function checking whether to consider the record
+ * @return 0 or an error
+ */
+int kr_ranked_rrarray_set_wire(ranked_rr_array_t *array, bool to_wire,
+			       uint32_t qry_uid, bool check_dups,
+			       bool (*extraCheck)(const ranked_rr_array_entry_t *));
+
+KR_PURE
+char *kr_pkt_text(const knot_pkt_t *pkt);
+
+KR_PURE
+char *kr_rrset_text(const knot_rrset_t *rr);
+
+KR_PURE
+static inline char *kr_dname_text(const knot_dname_t *name) {
+	return knot_dname_to_str_alloc(name);
+}
+
+KR_CONST
+static inline char *kr_rrtype_text(const uint16_t rrtype) {
+	char type_str[32] = {0};
+	knot_rrtype_to_string(rrtype, type_str, sizeof(type_str));
+	return strdup(type_str);
+}
+
+/**
+ * Call module property.
+ */
+KR_EXPORT
+char *kr_module_call(struct kr_context *ctx, const char *module, const char *prop, const char *input);
+
+/** Swap two places.  Note: the parameters need to be without side effects. */
+#define SWAP(x, y) do { /* http://stackoverflow.com/a/3982430/587396 */ \
+	unsigned char swap_temp[sizeof(x) == sizeof(y) ? (ssize_t)sizeof(x) : -1]; \
+	memcpy(swap_temp, &y, sizeof(x)); \
+	memcpy(&y,        &x, sizeof(x)); \
+	memcpy(&x, swap_temp, sizeof(x)); \
+	} while(0)
+
+/** Return the (covered) type of an nonempty RRset. */
+static inline uint16_t kr_rrset_type_maysig(const knot_rrset_t *rr)
+{
+	assert(rr && rr->rrs.count && rr->rrs.rdata);
+	uint16_t type = rr->type;
+	if (type == KNOT_RRTYPE_RRSIG)
+		type = knot_rrsig_type_covered(rr->rrs.rdata);
+	return type;
+}
+
+/** Printf onto the lua stack, avoiding additional copy (thin wrapper). */
+KR_PRINTF(2)
+static inline const char *lua_push_printf(lua_State *L, const char *fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	const char *ret = lua_pushvfstring(L, fmt, args);
+	va_end(args);
+	return ret;
+}
+
+/** @internal Return string representation of addr.
+ *  @note return pointer to static string
+ */
+static inline char *kr_straddr(const struct sockaddr *addr)
+{
+	assert(addr != NULL);
+	/* We are the sinle-threaded application */
+	static char str[INET6_ADDRSTRLEN + 1 + 5 + 1];
+	size_t len = sizeof(str);
+	int ret = kr_inaddr_str(addr, str, &len);
+	return ret != kr_ok() || len == 0 ? NULL : str;
+}
+
+/** The current time in monotonic milliseconds.
+ *
+ * \note it may be outdated in case of long callbacks; see uv_now().
+ */
+KR_EXPORT
+uint64_t kr_now();
+
+/** Convert name from lookup format to wire.  See knot_dname_lf
+ *
+ * \note len bytes are read and len+1 are written with *normal* LF,
+ * 	 but it's also allowed that the final zero byte is omitted in LF.
+ * \return the number of bytes written (>0) or error code (<0)
+ */
+int knot_dname_lf2wire(knot_dname_t *dst, uint8_t len, const uint8_t *lf);
+
+/** Patched knot_dname_lf.  LF for "." has length zero instead of one, for consistency.
+ * (TODO: consistency?)
+ * \param add_wildcard append the wildcard label
+ * \note packet is always NULL
+ */
+static inline int kr_dname_lf(uint8_t *dst, const knot_dname_t *src, bool add_wildcard)
+{
+	knot_dname_storage_t right_aligned_dst;
+	uint8_t *right_aligned_dname_start = knot_dname_lf(src, right_aligned_dst);
+	if (!right_aligned_dname_start) {
+		return kr_error(EINVAL);
+	}
+	int len = right_aligned_dname_start[0];
+	assert(right_aligned_dname_start + 1 + len - KNOT_DNAME_MAXLEN == right_aligned_dst);
+	memcpy(dst + 1, right_aligned_dname_start + 1, len);
+	if (add_wildcard) {
+		if (len + 2 > KNOT_DNAME_MAXLEN)
+			return kr_error(ENOSPC);
+		dst[len + 1] = '*';
+		dst[len + 2] = '\0';
+		len += 2;
+	}
+	dst[0] = len;
+	return KNOT_EOK;
+}
+
+/**
+ * Difference between two calendar times specified as strings.
+ * \param format[in] format for strptime
+ * \param diff[out] result from C difftime(time1, time0)
+ */
+KR_EXPORT
+const char *kr_strptime_diff(const char *format, const char *time1_str,
+		             const char *time0_str, double *diff);
+
+/* Trivial non-inline wrappers, to be used in lua. */
+KR_EXPORT void kr_rrset_init(knot_rrset_t *rrset, knot_dname_t *owner,
+				uint16_t type, uint16_t rclass, uint32_t ttl);
+KR_EXPORT uint16_t kr_pkt_qclass(const knot_pkt_t *pkt);
+KR_EXPORT uint16_t kr_pkt_qtype(const knot_pkt_t *pkt);
+KR_EXPORT uint32_t kr_rrsig_sig_inception(const knot_rdata_t *rdata);
+KR_EXPORT uint32_t kr_rrsig_sig_expiration(const knot_rdata_t *rdata);
+KR_EXPORT uint16_t kr_rrsig_type_covered(const knot_rdata_t *rdata);
diff --git a/lib/zonecut.c b/lib/zonecut.c
new file mode 100644
index 0000000..5e54d97
--- /dev/null
+++ b/lib/zonecut.c
@@ -0,0 +1,597 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "lib/zonecut.h"
+
+#include "contrib/cleanup.h"
+#include "lib/defines.h"
+#include "lib/generic/pack.h"
+#include "lib/layer.h"
+#include "lib/resolve.h"
+#include "lib/rplan.h"
+
+#include <libknot/descriptor.h>
+#include <libknot/packet/wire.h>
+#include <libknot/rrtype/rdname.h>
+
+#define VERBOSE_MSG(qry, ...) QRVERBOSE(qry, "zcut", __VA_ARGS__)
+
+/** Information for one NS name + address type. */
+typedef enum {
+	AI_UNINITED = 0,
+	AI_REPUT,	/**< Don't use this addrset, due to: cache_rep, NO_IPV6, ...
+			 * cache_rep approximates various problems when fetching the RRset. */
+	AI_CYCLED,	/**< Skipped due to cycle detection; see implementation for details. */
+	AI_LAST_BAD = AI_CYCLED, /** bad states: <= AI_LAST_BAD */
+	AI_UNKNOWN,	/**< Don't know status of this RRset; various reasons. */
+	AI_EMPTY,	/**< No usable address (may mean e.g. just NODATA). */
+	AI_OK,		/**< At least one usable address.
+			 * LATER: we might be interested whether it's only glue. */
+} addrset_info_t;
+
+
+static void update_cut_name(struct kr_zonecut *cut, const knot_dname_t *name)
+{
+	if (knot_dname_is_equal(name, cut->name)) {
+		return;
+	}
+	knot_dname_t *next_name = knot_dname_copy(name, cut->pool);
+	mm_free(cut->pool, cut->name);
+	cut->name = next_name;
+}
+
+int kr_zonecut_init(struct kr_zonecut *cut, const knot_dname_t *name, knot_mm_t *pool)
+{
+	if (!cut || !name) {
+		return kr_error(EINVAL);
+	}
+
+	memset(cut, 0, sizeof(*cut));
+	cut->name = knot_dname_copy(name, pool);
+	cut->pool = pool;
+	cut->nsset = trie_create(pool);
+	return cut->name && cut->nsset ? kr_ok() : kr_error(ENOMEM);
+}
+
+/** Completely free a pack_t. */
+static inline void free_addr_set(pack_t *pack, knot_mm_t *pool)
+{
+	if (unlikely(!pack)) {
+		/* promised we don't store NULL packs */
+		assert(false);
+		return;
+	}
+	pack_clear_mm(*pack, mm_free, pool);
+	mm_free(pool, pack);
+}
+/** Trivial wrapper for use in trie_apply, due to ugly casting. */
+static int free_addr_set_cb(trie_val_t *v, void *pool)
+{
+	free_addr_set(*v, pool);
+	return kr_ok();
+}
+
+void kr_zonecut_deinit(struct kr_zonecut *cut)
+{
+	if (!cut) {
+		return;
+	}
+	mm_free(cut->pool, cut->name);
+	if (cut->nsset) {
+		trie_apply(cut->nsset, free_addr_set_cb, cut->pool);
+		trie_free(cut->nsset);
+	}
+	knot_rrset_free(cut->key, cut->pool);
+	knot_rrset_free(cut->trust_anchor, cut->pool);
+}
+
+void kr_zonecut_move(struct kr_zonecut *to, const struct kr_zonecut *from)
+{
+	if (!to || !from) abort();
+	kr_zonecut_deinit(to);
+	memcpy(to, from, sizeof(*to));
+}
+
+void kr_zonecut_set(struct kr_zonecut *cut, const knot_dname_t *name)
+{
+	if (!cut || !name) {
+		return;
+	}
+	knot_rrset_t *key, *ta;
+	key = cut->key; cut->key = NULL;
+	ta = cut->trust_anchor; cut->trust_anchor = NULL;
+	kr_zonecut_deinit(cut);
+	kr_zonecut_init(cut, name, cut->pool);
+	cut->key = key;
+	cut->trust_anchor = ta;
+}
+
+int kr_zonecut_copy(struct kr_zonecut *dst, const struct kr_zonecut *src)
+{
+	if (!dst || !src) {
+		return kr_error(EINVAL);
+	}
+	if (!dst->nsset) {
+		dst->nsset = trie_create(dst->pool);
+	}
+	/* Copy the contents, one by one. */
+	int ret = kr_ok();
+	trie_it_t *it;
+	for (it = trie_it_begin(src->nsset); !trie_it_finished(it); trie_it_next(it)) {
+		size_t klen;
+		const char * const k = trie_it_key(it, &klen);
+		pack_t **new_pack = (pack_t **)trie_get_ins(dst->nsset, k, klen);
+		if (!new_pack) {
+			ret = kr_error(ENOMEM);
+			break;
+		}
+		const pack_t *old_pack = *trie_it_val(it);
+		ret = pack_clone(new_pack, old_pack, dst->pool);
+		if (ret) break;
+	}
+	trie_it_free(it);
+	return ret;
+}
+
+int kr_zonecut_copy_trust(struct kr_zonecut *dst, const struct kr_zonecut *src)
+{
+	knot_rrset_t *key_copy = NULL;
+	knot_rrset_t *ta_copy = NULL;
+
+	if (src->key) {
+		key_copy = knot_rrset_copy(src->key, dst->pool);
+		if (!key_copy) {
+			return kr_error(ENOMEM);
+		}
+	}
+
+	if (src->trust_anchor) {
+		ta_copy = knot_rrset_copy(src->trust_anchor, dst->pool);
+		if (!ta_copy) {
+			knot_rrset_free(key_copy, dst->pool);
+			return kr_error(ENOMEM);
+		}
+	}
+
+	knot_rrset_free(dst->key, dst->pool);
+	dst->key = key_copy;
+	knot_rrset_free(dst->trust_anchor, dst->pool);
+	dst->trust_anchor = ta_copy;
+
+	return kr_ok();
+}
+
+int kr_zonecut_add(struct kr_zonecut *cut, const knot_dname_t *ns, const void *data, int len)
+{
+	if (!cut || !ns || !cut->nsset || (data && len <= 0)) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+	/* Disabled; add_reverse_pair() misuses this for domain name in rdata. */
+	if (false && data && len != sizeof(struct in_addr)
+		  && len != sizeof(struct in6_addr)) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+
+	/* Get a pack_t for the ns. */
+	pack_t **pack = (pack_t **)trie_get_ins(cut->nsset, (const char *)ns, knot_dname_size(ns));
+	if (!pack) return kr_error(ENOMEM);
+	if (*pack == NULL) {
+		*pack = mm_alloc(cut->pool, sizeof(pack_t));
+		if (*pack == NULL) return kr_error(ENOMEM);
+		pack_init(**pack);
+	}
+	/* Insert data (if has any) */
+	if (data == NULL) {
+		return kr_ok();
+	}
+	/* Check for duplicates */
+	if (pack_obj_find(*pack, data, len)) {
+		return kr_ok();
+	}
+	/* Push new address */
+	int ret = pack_reserve_mm(**pack, 1, len, kr_memreserve, cut->pool);
+	if (ret != 0) {
+		return kr_error(ENOMEM);
+	}
+	return pack_obj_push(*pack, data, len);
+}
+
+int kr_zonecut_del(struct kr_zonecut *cut, const knot_dname_t *ns, const void *data, int len)
+{
+	if (!cut || !ns || (data && len <= 0)) {
+		return kr_error(EINVAL);
+	}
+
+	/* Find the address list. */
+	int ret = kr_ok();
+	pack_t *pack = kr_zonecut_find(cut, ns);
+	if (pack == NULL) {
+		return kr_error(ENOENT);
+	}
+	/* Remove address from the pack. */
+	if (data) {
+		ret = pack_obj_del(pack, data, len);
+	}
+	/* No servers left, remove NS from the set. */
+	if (pack->len == 0) {
+		free_addr_set(pack, cut->pool);
+		ret = trie_del(cut->nsset, (const char *)ns, knot_dname_size(ns), NULL);
+		assert(ret == 0); /* only KNOT_ENOENT and that *can't* happen */
+		return (ret == 0) ? kr_ok() : kr_error(ret);
+	}
+
+	return ret;
+}
+
+int kr_zonecut_del_all(struct kr_zonecut *cut, const knot_dname_t *ns)
+{
+	if (!cut || !ns) {
+		return kr_error(EINVAL);
+	}
+
+	/* Find the address list; then free and remove it. */
+	pack_t *pack;
+	int ret = trie_del(cut->nsset, (const char *)ns, knot_dname_size(ns),
+			   (trie_val_t *)&pack);
+	if (ret) { /* deletion failed */
+		assert(ret == KNOT_ENOENT);
+		return kr_error(ENOENT);
+	}
+	free_addr_set(pack, cut->pool);
+	return kr_ok();
+}
+
+pack_t *kr_zonecut_find(struct kr_zonecut *cut, const knot_dname_t *ns)
+{
+	if (!cut || !ns) {
+		return NULL;
+	}
+	trie_val_t *val = trie_get_try(cut->nsset, (const char *)ns, knot_dname_size(ns));
+	/* we get pointer to the pack_t pointer */
+	return val ? (pack_t *)*val : NULL;
+}
+
+static int has_address(trie_val_t *v, void *baton_)
+{
+	const pack_t *pack = *v;
+	const bool found = pack != NULL && pack->len != 0;
+	return found;
+}
+
+bool kr_zonecut_is_empty(struct kr_zonecut *cut)
+{
+	if (!cut || !cut->nsset) {
+		assert(false);
+		return true;
+	}
+	return !trie_apply(cut->nsset, has_address, NULL);
+}
+
+int kr_zonecut_set_sbelt(struct kr_context *ctx, struct kr_zonecut *cut)
+{
+	if (!ctx || !cut || !ctx->root_hints.nsset) {
+		return kr_error(EINVAL);
+	}
+
+	trie_apply(cut->nsset, free_addr_set_cb, cut->pool);
+	trie_clear(cut->nsset);
+
+	const uint8_t *const dname_root = (const uint8_t *)/*sign-cast*/("");
+	update_cut_name(cut, dname_root);
+	/* Copy root hints from resolution context. */
+	return kr_zonecut_copy(cut, &ctx->root_hints);
+}
+
+/** Fetch address for zone cut.  Any rank is accepted (i.e. glue as well). */
+static addrset_info_t fetch_addr(pack_t *addrs, const knot_dname_t *ns, uint16_t rrtype,
+				 knot_mm_t *mm_pool, const struct kr_query *qry)
+// LATER(optim.): excessive data copying
+{
+	int rdlen;
+	switch (rrtype) {
+	case KNOT_RRTYPE_A:
+		rdlen = 4;
+		break;
+	case KNOT_RRTYPE_AAAA:
+		rdlen = 16;
+		break;
+	default:
+		assert(!EINVAL);
+		return AI_UNKNOWN;
+	}
+
+	struct kr_context *ctx = qry->request->ctx;
+	struct kr_cache_p peek;
+	if (kr_cache_peek_exact(&ctx->cache, ns, rrtype, &peek) != 0) {
+		return AI_UNKNOWN;
+	}
+	int32_t new_ttl = kr_cache_ttl(&peek, qry, ns, rrtype);
+	if (new_ttl < 0) {
+		return AI_UNKNOWN;
+	}
+
+	knot_rrset_t cached_rr;
+	knot_rrset_init(&cached_rr, /*const-cast*/(knot_dname_t *)ns, rrtype,
+			KNOT_CLASS_IN, new_ttl);
+	if (kr_cache_materialize(&cached_rr.rrs, &peek, mm_pool) < 0) {
+		return AI_UNKNOWN;
+	}
+
+	/* Reserve memory in *addrs.  Implementation detail:
+	 * pack_t cares for lengths, so we don't store those in the data. */
+	const size_t pack_extra_size = knot_rdataset_size(&cached_rr.rrs)
+		- cached_rr.rrs.count * offsetof(knot_rdata_t, len);
+	int ret = pack_reserve_mm(*addrs, cached_rr.rrs.count, pack_extra_size,
+				  kr_memreserve, mm_pool);
+	if (ret) abort(); /* ENOMEM "probably" */
+
+	int usable_cnt = 0;
+	addrset_info_t result = AI_EMPTY;
+	knot_rdata_t *rd = cached_rr.rrs.rdata;
+	for (uint16_t i = 0; i < cached_rr.rrs.count; ++i, rd = knot_rdataset_next(rd)) {
+		if (unlikely(rd->len != rdlen)) {
+			VERBOSE_MSG(qry, "bad NS address length %d for rrtype %d, skipping\n",
+					(int)rd->len, (int)rrtype);
+			continue;
+		}
+		/* Check RTT cache - whether the IP is usable or not. */
+		kr_nsrep_rtt_lru_entry_t *rtt_e = ctx->cache_rtt
+			? lru_get_try(ctx->cache_rtt, (const char *)rd->data, rd->len)
+			: NULL;
+		const bool unusable = rtt_e && rtt_e->score >= KR_NS_TIMEOUT
+			&& qry->creation_time_mono
+			   < rtt_e->tout_timestamp + ctx->cache_rtt_tout_retry_interval;
+		if (!unusable) {
+			result = AI_OK;
+			++usable_cnt;
+		}
+
+		ret = pack_obj_push(addrs, rd->data, rd->len);
+		assert(!ret); /* didn't fit because of incorrectly reserved memory */
+		/* LATER: for now we lose quite some information here,
+		 * as keeping it would need substantial changes on other places,
+		 * and it turned out to be premature optimization (most likely).
+		 * We might e.g. skip adding unusable addresses,
+		 * and either keep some rtt information associated
+		 * or even finish up choosing the set to send packets to.
+		 * Overall there's some overlap with nsrep.c functionality.
+		 */
+	}
+	if (usable_cnt != cached_rr.rrs.count) {
+		VERBOSE_MSG(qry, "usable NS addresses: %d/%d\n",
+				usable_cnt, cached_rr.rrs.count);
+	}
+	return result;
+}
+
+/** Fetch best NS for zone cut. */
+static int fetch_ns(struct kr_context *ctx, struct kr_zonecut *cut,
+		    const knot_dname_t *name, const struct kr_query *qry,
+		    uint8_t * restrict rank)
+{
+	struct kr_cache_p peek;
+	int ret = kr_cache_peek_exact(&ctx->cache, name, KNOT_RRTYPE_NS, &peek);
+	if (ret != 0) {
+		return ret;
+	}
+	/* Note: we accept *any* rank from the cache.  We assume that nothing
+	 * completely untrustworthy could get into the cache, e.g out-of-bailiwick
+	 * records that weren't validated.
+	 */
+	*rank = peek.rank;
+
+	int32_t new_ttl = kr_cache_ttl(&peek, qry, name, KNOT_RRTYPE_NS);
+	if (new_ttl < 0) {
+		return kr_error(ESTALE);
+	}
+	/* Materialize the rdataset temporarily, for simplicity. */
+	knot_rdataset_t ns_rds = { 0, NULL };
+	ret = kr_cache_materialize(&ns_rds, &peek, cut->pool);
+	if (ret < 0) {
+		return ret;
+	}
+
+	/* Insert name servers for this zone cut, addresses will be looked up
+	 * on-demand (either from cache or iteratively) */
+	bool all_bad = true; /**< All NSs (seen so far) are in a bad state. */
+	knot_rdata_t *rdata_i = ns_rds.rdata;
+	for (unsigned i = 0; i < ns_rds.count;
+			++i, rdata_i = knot_rdataset_next(rdata_i)) {
+		const knot_dname_t *ns_name = knot_ns_name(rdata_i);
+		const size_t ns_size = knot_dname_size(ns_name);
+
+		/* Get a new pack within the nsset. */
+		pack_t **pack = (pack_t **)trie_get_ins(cut->nsset,
+					(const char *)ns_name, ns_size);
+		if (!pack) return kr_error(ENOMEM);
+		assert(!*pack); /* not critical, really */
+		*pack = mm_alloc(cut->pool, sizeof(pack_t));
+		if (!*pack) return kr_error(ENOMEM);
+		pack_init(**pack);
+
+		addrset_info_t infos[2];
+		/* Fetch NS reputation and decide whether to prefetch A/AAAA records. */
+		unsigned *cached = lru_get_try(ctx->cache_rep,
+					(const char *)ns_name, ns_size);
+		unsigned reputation = (cached) ? *cached : 0;
+		infos[0] = (reputation & KR_NS_NOIP4) || qry->flags.NO_IPV4
+			? AI_REPUT
+			: fetch_addr(*pack, ns_name, KNOT_RRTYPE_A, cut->pool, qry);
+		infos[1] = (reputation & KR_NS_NOIP6) || qry->flags.NO_IPV6
+			? AI_REPUT
+			: fetch_addr(*pack, ns_name, KNOT_RRTYPE_AAAA, cut->pool, qry);
+
+		#if 0 /* rather unlikely to be useful unless changing some zcut code */
+		WITH_VERBOSE(qry) {
+			auto_free char *ns_name_txt = kr_dname_text(ns_name);
+			VERBOSE_MSG(qry, "NS %s infos: %d, %d\n",
+					ns_name_txt, (int)infos[0], (int)infos[1]);
+		}
+		#endif
+
+		/* AI_CYCLED checks.
+		 * If an ancestor query has its zone cut in the state that
+		 * it's looking for name or address(es) of some NS(s),
+		 * we want to avoid doing so with a NS that lies under its cut.
+		 * Instead we need to consider such names unusable in the cut (for now). */
+		if (infos[0] != AI_UNKNOWN && infos[1] != AI_UNKNOWN) {
+			/* Optimization: the following loop would be pointless. */
+			all_bad = false;
+			continue;
+		}
+		for (const struct kr_query *aq = qry; aq->parent; aq = aq->parent) {
+			const struct kr_qflags *aqpf = &aq->parent->flags;
+			if (   (aqpf->AWAIT_CUT  && aq->stype == KNOT_RRTYPE_NS)
+			    || (aqpf->AWAIT_IPV4 && aq->stype == KNOT_RRTYPE_A)
+			    || (aqpf->AWAIT_IPV6 && aq->stype == KNOT_RRTYPE_AAAA)) {
+				if (knot_dname_in_bailiwick(ns_name,
+							aq->parent->zone_cut.name)) {
+					for (int j = 0; j < 2; ++j)
+						if (infos[j] == AI_UNKNOWN)
+							infos[j] = AI_CYCLED;
+					break;
+				}
+			} else {
+				/* This ancestor waits for other reason that
+				 * NS name or address, so we're out of a direct cycle. */
+				break;
+			}
+		}
+		all_bad = all_bad && infos[0] <= AI_LAST_BAD && infos[1] <= AI_LAST_BAD;
+	}
+
+	if (all_bad) { WITH_VERBOSE(qry) {
+		auto_free char *name_txt = kr_dname_text(name);
+		VERBOSE_MSG(qry, "cut %s: all NSs bad, count = %d\n",
+				name_txt, (int)ns_rds.count);
+	} }
+	knot_rdataset_clear(&ns_rds, cut->pool);
+	return all_bad ? ELOOP : kr_ok();
+}
+
+/**
+ * Fetch secure RRSet of given type.
+ */
+static int fetch_secure_rrset(knot_rrset_t **rr, struct kr_cache *cache,
+	const knot_dname_t *owner, uint16_t type, knot_mm_t *pool,
+	const struct kr_query *qry)
+{
+	if (!rr) {
+		assert(!EINVAL);
+		return kr_error(EINVAL);
+	}
+	/* peek, check rank and TTL */
+	struct kr_cache_p peek;
+	int ret = kr_cache_peek_exact(cache, owner, type, &peek);
+	if (ret != 0) {
+		return ret;
+	}
+	if (!kr_rank_test(peek.rank, KR_RANK_SECURE)) {
+		return kr_error(ENOENT);
+	}
+	int32_t new_ttl = kr_cache_ttl(&peek, qry, owner, type);
+	if (new_ttl < 0) {
+		return kr_error(ESTALE);
+	}
+	/* materialize a new RRset */
+	knot_rrset_free(*rr, pool);
+	*rr = mm_alloc(pool, sizeof(knot_rrset_t));
+	if (*rr == NULL) {
+		return kr_error(ENOMEM);
+	}
+	owner = knot_dname_copy(/*const-cast*/(knot_dname_t *)owner, pool);
+	if (!owner) {
+		mm_free(pool, *rr);
+		*rr = NULL;
+		return kr_error(ENOMEM);
+	}
+	knot_rrset_init(*rr, /*const-cast*/(knot_dname_t *)owner, type,
+			KNOT_CLASS_IN, new_ttl);
+	ret = kr_cache_materialize(&(*rr)->rrs, &peek, pool);
+	if (ret < 0) {
+		knot_rrset_free(*rr, pool);
+		*rr = NULL;
+		return ret;
+	}
+
+	return kr_ok();
+}
+
+int kr_zonecut_find_cached(struct kr_context *ctx, struct kr_zonecut *cut,
+			   const knot_dname_t *name, const struct kr_query *qry,
+			   bool * restrict secured)
+{
+	if (!ctx || !cut || !name) {
+		//assert(false);
+		return kr_error(EINVAL);
+	}
+	/* I'm not sure whether the caller always passes a clean state;
+	 * mixing doesn't seem to make sense in any case, so let's clear it.
+	 * We don't bother freeing the packs, as they're on mempool. */
+	trie_clear(cut->nsset);
+	/* Copy name as it may overlap with cut name that is to be replaced. */
+	knot_dname_t *qname = knot_dname_copy(name, cut->pool);
+	if (!qname) {
+		return kr_error(ENOMEM);
+	}
+	/* Start at QNAME. */
+	int ret;
+	const knot_dname_t *label = qname;
+	while (true) {
+		/* Fetch NS first and see if it's insecure. */
+		uint8_t rank = 0;
+		const bool is_root = (label[0] == '\0');
+		ret = fetch_ns(ctx, cut, label, qry, &rank);
+		if (ret == 0) {
+			/* Flag as insecure if cached as this */
+			if (kr_rank_test(rank, KR_RANK_INSECURE)) {
+				*secured = false;
+			}
+			/* Fetch DS and DNSKEY if caller wants secure zone cut */
+			int ret_ds = 1, ret_dnskey = 1;
+			if (*secured || is_root) {
+				ret_ds = fetch_secure_rrset(&cut->trust_anchor, &ctx->cache,
+						label, KNOT_RRTYPE_DS, cut->pool, qry);
+				ret_dnskey = fetch_secure_rrset(&cut->key, &ctx->cache,
+						label, KNOT_RRTYPE_DNSKEY, cut->pool, qry);
+			}
+			update_cut_name(cut, label);
+			WITH_VERBOSE(qry) {
+				auto_free char *label_str = kr_dname_text(label);
+				VERBOSE_MSG(qry,
+					"found cut: %s (rank 0%.2o return codes: DS %d, DNSKEY %d)\n",
+					label_str, rank, ret_ds, ret_dnskey);
+			}
+			ret = kr_ok();
+			break;
+		} /* else */
+
+		trie_clear(cut->nsset);
+		/* Subtract label from QNAME. */
+		if (!is_root) {
+			label = knot_wire_next_label(label, NULL);
+		} else {
+			ret = kr_error(ENOENT);
+			break;
+		}
+	}
+
+	kr_cache_sync(&ctx->cache);
+	mm_free(cut->pool, qname);
+	return ret;
+}
diff --git a/lib/zonecut.h b/lib/zonecut.h
new file mode 100644
index 0000000..2808c66
--- /dev/null
+++ b/lib/zonecut.h
@@ -0,0 +1,173 @@
+/*  Copyright (C) 2014-2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "lib/cache/api.h"
+#include "lib/defines.h"
+#include "lib/generic/pack.h"
+#include "lib/generic/trie.h"
+
+struct kr_rplan;
+struct kr_context;
+
+/**
+ * Current zone cut representation.
+*/
+struct kr_zonecut {
+	knot_dname_t *name; /**< Zone cut name. */
+	knot_rrset_t* key;  /**< Zone cut DNSKEY. */
+	knot_rrset_t* trust_anchor; /**< Current trust anchor. */
+	struct kr_zonecut *parent; /**< Parent zone cut. */
+	trie_t *nsset;        /**< Map of nameserver => address_set (pack_t). */
+	knot_mm_t *pool;     /**< Memory pool. */
+};
+
+/**
+ * Populate root zone cut with SBELT.
+ * @param cut zone cut
+ * @param name
+ * @param pool
+ * @return 0 or error code
+ */
+KR_EXPORT
+int kr_zonecut_init(struct kr_zonecut *cut, const knot_dname_t *name, knot_mm_t *pool);
+
+/**
+ * Clear the structure and free the address set.
+ * @param cut zone cut
+ */
+KR_EXPORT
+void kr_zonecut_deinit(struct kr_zonecut *cut);
+
+/**
+ * Move a zonecut, transferring ownership of any pointed-to memory.
+ * @param to the target - it gets deinit-ed
+ * @param from the source - not modified, but shouldn't be used afterward
+ */
+KR_EXPORT
+void kr_zonecut_move(struct kr_zonecut *to, const struct kr_zonecut *from);
+
+/**
+ * Reset zone cut to given name and clear address list.
+ * @note This clears the address list even if the name doesn't change. TA and DNSKEY don't change.
+ * @param cut  zone cut to be set
+ * @param name new zone cut name
+ */
+KR_EXPORT
+void kr_zonecut_set(struct kr_zonecut *cut, const knot_dname_t *name);
+
+/**
+ * Copy zone cut, including all data. Does not copy keys and trust anchor.
+ * @param dst destination zone cut
+ * @param src source zone cut
+ * @return 0 or an error code; If it fails with kr_error(ENOMEM),
+ * it may be in a half-filled state, but it's safe to deinit...
+ * @note addresses for names in `src` get replaced and others are left as they were.
+ */
+KR_EXPORT
+int kr_zonecut_copy(struct kr_zonecut *dst, const struct kr_zonecut *src);
+
+/**
+ * Copy zone trust anchor and keys.
+ * @param dst destination zone cut
+ * @param src source zone cut
+ * @return 0 or an error code
+ */
+KR_EXPORT
+int kr_zonecut_copy_trust(struct kr_zonecut *dst, const struct kr_zonecut *src);
+
+/**
+ * Add address record to the zone cut.
+ *
+ * The record will be merged with existing data,
+ * it may be either A/AAAA type.
+ *
+ * @param cut    zone cut to be populated
+ * @param ns     nameserver name
+ * @param data   typically knot_rdata_t::data
+ * @param len    typically knot_rdata_t::len
+ * @return 0 or error code
+ */
+KR_EXPORT
+int kr_zonecut_add(struct kr_zonecut *cut, const knot_dname_t *ns, const void *data, int len);
+
+/**
+ * Delete nameserver/address pair from the zone cut.
+ * @param  cut
+ * @param  ns    name server name
+ * @param  data  typically knot_rdata_t::data
+ * @param  len   typically knot_rdata_t::len
+ * @return       0 or error code
+ */
+KR_EXPORT
+int kr_zonecut_del(struct kr_zonecut *cut, const knot_dname_t *ns, const void *data, int len);
+
+/**
+ * Delete all addresses associated with the given name.
+ * @param  cut
+ * @param  ns    name server name
+ * @return       0 or error code
+ */
+KR_EXPORT
+int kr_zonecut_del_all(struct kr_zonecut *cut, const knot_dname_t *ns);
+
+/**
+ * Find nameserver address list in the zone cut.
+ *
+ * @note This can be used for membership test, a non-null pack is returned
+ *       if the nameserver name exists.
+ * 
+ * @param  cut
+ * @param  ns    name server name
+ * @return       pack of addresses or NULL
+ */
+KR_EXPORT KR_PURE
+pack_t *kr_zonecut_find(struct kr_zonecut *cut, const knot_dname_t *ns);
+
+/**
+ * Populate zone cut with a root zone using SBELT :rfc:`1034`
+ *
+ * @param ctx resolution context (to fetch root hints)
+ * @param cut zone cut to be populated
+ * @return 0 or error code
+ */
+KR_EXPORT
+int kr_zonecut_set_sbelt(struct kr_context *ctx, struct kr_zonecut *cut);
+
+/**
+ * Populate zone cut address set from cache.
+ *
+ * @param ctx       resolution context (to fetch data from LRU caches)
+ * @param cut       zone cut to be populated
+ * @param name      QNAME to start finding zone cut for
+ * @param qry       query for timestamp and stale-serving decisions
+ * @param secured   set to true if want secured zone cut, will return false if it is provably insecure
+ * @return 0 or error code (ENOENT if it doesn't find anything)
+ */
+KR_EXPORT
+int kr_zonecut_find_cached(struct kr_context *ctx, struct kr_zonecut *cut,
+			   const knot_dname_t *name, const struct kr_query *qry,
+			   bool * restrict secured);
+/**
+ * Check if any address is present in the zone cut.
+ *
+ * @param cut zone cut to check
+ * @return true/false
+ */
+KR_EXPORT
+bool kr_zonecut_is_empty(struct kr_zonecut *cut);
+