diff --git a/doc/man/knot.conf.5in b/doc/man/knot.conf.5in
index c405a6aa2..dd356bae5 100644
--- a/doc/man/knot.conf.5in
+++ b/doc/man/knot.conf.5in
@@ -671,6 +671,14 @@ working TCP.
 .UNINDENT
 .UNINDENT
 .sp
+\fBNOTE:\fP
+.INDENT 0.0
+.INDENT 3.5
+Incoming DDNS over XDP isn\(aqt supported.
+The server always responds with SERVFAIL.
+.UNINDENT
+.UNINDENT
+.sp
 \fIDefault:\fP not set
 .SS udp
 .sp
diff --git a/doc/reference.rst b/doc/reference.rst
index b5f19806c..c73148ec5 100644
--- a/doc/reference.rst
+++ b/doc/reference.rst
@@ -717,6 +717,10 @@ Change of this parameter requires restart of the Knot server to take effect.
    intended to offer the DNS service, at least to fulfil the DNS requirement for
    working TCP.
 
+.. NOTE::
+   Incoming :ref:`DDNS<dynamic updates>` over XDP isn't supported.
+   The server always responds with SERVFAIL.
+
 *Default:* not set
 
 .. _xdp_udp: