also see Explain Port forwarding and DMZ

There are cases when NAT is not good enough to handle your advanced network applications - like game servers and NetMeeting. I don’t know of a single broadband router than handles EVERYTHING perfectly. That does not mean that you should not use a NAT router, it just means that your network requirements are a little heavier than other peoples.

When running a game server or a h.323 server is VERY important to you, I would suggest splitting up your network. Put the majority of your computers behind your router/firewall and put your server directly on the Internet. This of course requires multiple IP address from your ISP but that is usually not a problem.

The configuration of computer (A), we will call it the Game Server, is VERY important. First off, it needs a second network card for file and print sharing with your LAN. That connection is represented in orange. Since the game server is directly on the Internet and more subject to attacks, virus', worms etc I would suggest disabling the LAN network adapter when not in user (orange cable in diagram). The ability to enable and disable network cards without rebooting means making the game server a Windows 2000 or Windows XP computer.

Next, ensure that the only service bound to your Internet network card is TCP/IP. You do not need NetBEUI or Client for Microsoft Networks or File and Print Sharing. You can leave everything bound to your LAN Network card though.

It is important that this computer is kept up to date. Run Windows Update and install all security patches and service packs at least once a week.

Make sure you have all non-essential services SHUT DOWN. Shut down the WEB server, FTP server and SMTP server. If you are running a web server, make sure the administration web site and default web sites deleted or at least shut down. There are so many exploits that utilize problems in these sites it is not funny.