IRC connection behind ISA

Hi all,
        I would like to know as how IRC can be allowed for the clients
behind ISA(integrated mode). I have a secure NAT client and would like to
connect to IRC server. I have already opened TCP port 6667 for both inbound
and outbound but still no luck. Please advice as what other configuration is
required for IRC to work behind ISA.
 
Regards,
Vinay.

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