doc/userguide: document dns.response

Feature: 7012

doc/userguide/rules/dns-keywords.rst

@@ -176,3 +176,24 @@ resource name, for example "www.suricata.io".
 ``dns.query.name`` supports :doc:`multi-buffer-matching`.
 
 ``dns.query.name`` was introduced in Suricata 8.0.0.
+
+dns.response
+------------
+
+``dns.response`` is a sticky buffer that is used to look at all name and 
+rdata fields of DNS response (answer) resource records. It supports 
+inspecting all DNS response sections. Example::
+
+  alert dns any any -> any any (msg:"Test dns.response option"; dns.response; content:"google"; nocase; sid:1;)
+
+rdata field matching supports a subset of types that contain 
+domain name structured data, for example: "www.suricata.io". 
+The list of types inspected is: 
+CNAME, PTR, MX, NS, SOA (mname data: primary name server).  
+
+The buffer being matched on contains the complete re-assembled
+resource name, for example "www.suricata.io".
+
+``dns.response`` supports :doc:`multi-buffer-matching`.
+
+``dns.response`` was introduced in Suricata 8.0.0.