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

From: James Hozier <guitarscn1@xxxxxxxxx>
Date: Thu, 2 Sep 2010 20:10:27 -0700 (PDT)
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?