I run a moderate NAT. The only thing that often interferes with dedi server games in that configuration is that some routers have Port Scan and DOS attack protection. I found that unless this is disabled, the routers drop many game packets, especially if they were sent in a burst. Of course you will need to allow the game outbound connections through any firewall software/hardware you have as well.
Technically though, I don't think you are suppose to need to do port forwarding for MW2 to work, for two reasons. 1. It supposedly has uPnP support, which most routers bought in the last two years have good support for. 2. If connections can't be made to your machine, the game should not pick you to be host in the selection process, you don't need forwarded ports unless you are the host. If you are having problems, then clearly the above is not working correctly.
Originally Posted by Blackhand
