I have already posted this information to several other forums including the World in Conflict forums where it has received much attention and helped many people with posts such as "I can't connect to servers" , "I can't see all the servers" , "my friends can't see/connect to my server" etc. I have decided to post it again and hopefully it'll be made into a sticky!
I work in IT (design complex NAT/network structures for coporate clients) so that's how I know what I'm talking about. Second, I've had my server the Monk's [PROVING GROUNDS] running a dedicated server for most multiplayer games released since HW1/Operation Flashpoint, so anyone with game hosting issues, ask away! NAT and the misconceptions/inability to configure it are the single largest cause for people not being able to see/connect to/host internet servers today!
A quick lesson on NAT:
NAT (Strict) - Port AND Address-restricted NAT (the router/firewall insists that the packet return from both the same IP Address AND Port the packet was originally sent out to)
NAT (Moderate) - Port-restricted NAT (the router/firewall insists that the packet return from the same Port the packet was originally sent out to but doesn't care if the IP Address isn't the same)
NAT (OPEN) - Port AND Address independent NAT (the router/firewall doesn't care which Port OR IP Address the return packet comes from and simply forwards the data packet on to the internal IP you will have specified in your "port-forwarding") Obviously OPEN-NAT is the least secure and also by extension the most flexible for hosting/connecting-to games.
MOST games will work having TCP set to STRICT and UDP set to MODERATE. ALL games will work setting both TCP and UDP NAT filtering to OPEN. (your routers may or may not even let you modify NAT filtering, many SOHO routers do not!) I have "real" routers/firewalls (very expensive also ) so I have granular control over many things that many SOHO routers don't even reference such as the above.
If your router DOES allow NAT control then my suggestions above willwork! Plain and simple. NAT, when not implemented with any sort of controls (like on many SOHO routers, and crappy retail anti-malware/firewall software) is the single biggest reason for sour gamers!
Happy gaming/hosting, monk out!
EDIT: here is a link a "networking guide for the gamer" I wrote which may also come in handy the "[url=http://www.themonk.ca/Monk/Networking_for_the_Gamer_by_the_Monk.pdf]Networking for the Gamer[/url]" guide I compiled of all the "generic" networking information I posted to various forums.
Here is the link to my SINS-specific guide "Networking and SINS" (version 1.0 written Feb 14/2008) which contains all information necessary in order to play/host SINS!