iptables: How to read this OPT string?

Posted by alex on Server Fault See other posts from Server Fault or by alex
Published on 2012-11-30T09:08:38Z Indexed on 2012/12/07 5:08 UTC
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iptables

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logging

I have a simple INPUT rule for iptables that logs any new connections to a logfile. --log-tcp-options and --log-ip-options flags are both set and I get the appropriate OPT output.

One line of my log looks something like this:

Nov 29 17:00:00 IN=venet0 OUT= MAC= SRC=x.x.x.x DST=x.x.x.x LEN=64 TOS=0x00 PREC=0x00 TTL=53 ID=37898 DF PROTO=TCP SPT=57755 DPT=8888 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (0204057D010303010101080A3E521D4D0000000004020000)

I would like to understand how to interpret the OPT string (bold).

Is there some documentation available on what it actually means?
How could I make it human-readable?

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