doc: add note about big endian for icmp_seq match

diff --git a/doc/userguide/rules/header-keywords.rst b/doc/userguide/rules/header-keywords.rst
index e28b14e28315306c3f8c325d6c94f112aeacbb2e..a6837d73cf5e0124577a5e8aeb17f8bb34605f12 100644 (file)
--- a/doc/userguide/rules/header-keywords.rst
+++ b/doc/userguide/rules/header-keywords.rst
@@ -711,6 +711,12 @@ Example of icmp_seq in a rule:
 
     alert icmp $EXTERNAL_NET any -> $HOME_NET any (msg:"GPL SCAN Broadscan Smurf Scanner"; dsize:4; icmp_id:0; :example-rule-emphasis:`icmp_seq:0;` itype:8; classtype:attempted-recon; sid:2100478; rev:4;)
 
+.. note:: Some pcap analysis tools, like wireshark, may give both a little
+  endian and big endian value for ``icmp_seq``. The ``icmp_seq`` keyword
+  matches on the big endian value, this is due to Suricata using the network
+  byte order (big endian) to perform the match comparison.
+
+
 icmpv4.hdr
 ^^^^^^^^^^