DNS Keywords
============

There are some more content modifiers (If you are unfamiliar with
content modifiers, please visit the page :doc:`payload-keywords` These
ones make sure the signature checks a specific part of the
network-traffic.


dns_query
---------

With **dns_query** the DNS request queries are inspected. The dns_query
keyword works a bit different from the normal content modifiers. When
used in a rule all contents following it are affected by it.  Example:

  alert dns any any -> any any (msg:"Test dns_query option";
  dns_query; content:"google"; nocase; sid:1;)

.. image:: dns-keywords/dns_query.png

The dns_query keyword affects all following contents, until pkt_data
is used or it reaches the end of the rule.

Normalized Buffer
~~~~~~~~~~~~~~~~~

Buffer contains literal domain name

-  <length> values (as seen in a raw DNS request)
   are literal '.' characters
-  no leading <length> value
-  No terminating NULL (0x00) byte (use a negated relative ``isdataat``
   to match the end)

Example DNS request for "mail.google.com" (for readability, hex
values are encoded between pipes):

DNS query on the wire (snippet)::

    |04|mail|06|google|03|com|00|

``dns_query`` buffer::

    mail.google.com