Unreal Tornament Behind a big wall of fire

I want to host UT IP games from behind my firewall. Ok sounds easy (well kind of), I just find out what ports I need to open on the firewall, give the contestants your firewall's ip number and way you go. Hum... so what ports do I need to open on the firewall?<br>
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Does any one know? Or has even got this working?<br>
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I hope this is possible, I think it is as I can host Red Faction games ok, but their website give you the ports to open.<br>
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Oh, I can join other peoples games, not on the internet but by knowing there ip number, which is what I want to do.<br>
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Thanks<br>
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Andy