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Wireshark-users: Re: [Wireshark-users] -d option does not listen to the port I choose

From: Bill Meier <wmeier@xxxxxxxxxxx>
Date: Thu, 02 Sep 2010 23:29:31 -0400
James Hozier wrote:
tshark -i en1 -tad -lnx -d tcp.port==7001,irc -R 'irc'

When I start to see the packets on my screen, they are from port 6667,
not from port 7001. Anything from port 7001 I do not see, but it listens
to port 6667 for some reason? Why does it do this?



-d ...  means decode any traffic on tcp port 7001 as irc;
        (it does *not* mean 'listen on this port)
-R .. means filter on irc packets.

So: I think the above means filter on irc:
    - on port 6667 which is the normal tcp port for irc
      (from looking at the irc dissector code);
    - and on on port 7001;

If you want to just see port 7001 traffic you should use
-R 'tcp.port==7001'