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+.. SPDX-License-Identifier: GPL-3.0-or-later
+
+.. _mod-nsid:
+
+Name Server Identifier (NSID)
+=============================
+
+Module ``nsid`` provides server-side support for :rfc:`5001`
+which allows DNS clients to request resolver to send back its NSID
+along with the reply to a DNS request.
+This is useful for debugging larger resolver farms
+(e.g. when using :ref:`systemd-multiple-instances`, anycast or load balancers).
+
+NSID value can be configured in the resolver's configuration file:
+
+.. code-block:: lua
+
+   modules.load('nsid')
+   nsid.name('instance 1')
+
+.. tip:: When dealing with Knot Resolver running in `multiple instances`
+        managed with systemd see :ref:`instance-specific-configuration`.
+
+You can also obtain configured NSID value:
+
+.. code-block:: lua
+
+   > nsid.name()
+   'instance 1'
+
+The module can be disabled at run-time:
+
+.. code-block:: lua
+
+   modules.unload('nsid')