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+.. SPDX-License-Identifier: GPL-3.0-or-later
+
+.. _mod-dnstap:
+
+Dnstap (traffic collection)
+===========================
+
+The ``dnstap`` module supports logging DNS requests and responses to a unix
+socket in `dnstap format <https://dnstap.info>`_ using fstrm framing library.
+This logging is useful if you need effectively log all DNS traffic.
+
+The unix socket and the socket reader must be present before starting resolver instances.
+Also it needs appropriate filesystem permissions;
+the typical user and group of the daemon are called ``knot-resolver``.
+
+Tunables:
+
+* ``socket_path``: the unix socket file where dnstap messages will be sent
+* ``identity``: identity string as typically returned by an "NSID" (RFC 5001) query, empty by default
+* ``version``: version string of the resolver, defaulting to "Knot Resolver major.minor.patch"
+* ``client.log_queries``: if ``true`` queries from downstream in wire format will be logged
+* ``client.log_responses``: if ``true`` responses to downstream in wire format will be logged
+
+.. Very non-standard and it seems unlikely that others want to collect the RTT.
+.. * ``client.log_tcp_rtt``: if ``true`` and on Linux,
+        add "extra" field with "rtt=12345\n",
+        signifying kernel's current estimate of RTT micro-seconds for the non-UDP connection
+        (alongside every arrived DNS message).
+
+.. code-block:: lua
+
+    modules = {
+        dnstap = {
+            socket_path = "/tmp/dnstap.sock",
+            identity = nsid.name() or "",
+            version = "My Custom Knot Resolver " .. package_version(),
+            client = {
+                log_queries = true,
+                log_responses = true,
+            },
+        }
+    }