I've never been able to host a public multiplayer game in Halo PC – whenever I try to, it never appears in the games list and other players can't connect to my game, even by inputting a direct IP. I think this is related to my network and port forwarding.
When I start a public internet game, I see a local IP in the IP box. This tells me that some ports aren't being forwarded. What ports do I need to forward to be able to host such games?
Also, the IP box isn't modifyable. After I forward the necessary ports, how do I change the local IP that is currently in the box to my public IP?
Best Answer
You need ports:
I'm not sure about the IP forwarding issue, but try opening these ports and providing your external IP to your friends. Check out setting your machine as the DMZ host a la this question. DMZ host settings can solve the problem by making your machine the first machine to get information from a shared ip address if the router can't figure out where to send the packets.
EDIT: From the Halo multiplayer support site