A port is nothing more than the final portion of the destination address for any piece of Internet traffic. Imagine an IP address as a house address, the port would tell you who in this house it belongs too.

Most people have a modem/router/firewall, that doesn't allow servers to directly connect to the computers unless the computer starts it. That is great for most things like surfing the web and chatting online. However a lot of computer games you will need to open ports.

Ports used by various on-line games, services, and APIs:

¹These games may require you to open/forward the ports listed under "Microsoft Zone.com" if you are playing on the Zone.

²You will also have to open the ports required for a specific game as well.

³These ports are only required if you are hosting a game. You should be able to join a game without any special setup.

⁴These games may require you to open the ports listed under "Blizzard Battle.net" if you are playing on Battle.net.

Colors are used to signify if the game has been tested or untested by me personally. The other information is included for completeness and is correct to the best of my knowledge. Of course, if anyone wants to send a game or hardware for me to test, I'm willing.

I still can't find the ports for insert game here

DirectPlay Applications

If the game in question uses DirectX's DirectPlay you can open the ports listed under the correct version of direct X. To find the version of DirectPlay This may not be the latest version that is installed nor the the version that is required by the game. that is being used by the game:

1. On the Windows Start menu, click Run.
2. In the Open box, type dxdiag, and then click OK.
3. Click the Save All Information button to save a Dxdiag.txt report.
4. Click Desktop, and then click Save.
5. Open the DxDiag.txt file on your desktop and find the section marked DirectPlay Lobbyable Apps . Note that each game listed here will report either "(DX7)" or "(DX8)" which corresponds to its DirectPlay connection method.

Then forward/unblock the ports listed in the above table under "Microsoft DirectPlay"

Other Methods

Netstat

You can run a program which will display the currently used ports by typing netstat -an at a command line prompt. For more information on the command type netstat /? or see Microsoft KB article.

The method I use is to run netstat, then start the game, then run netstat again and compare the two results. Be aware that not all ports used by a game are used all the time. For example DirectPlay games will only have a few of the hundred or so possible ports open at any one time.

References

Microsoft Knowledge Base Q159031

Zone: Network Ports Required to Play

Microsoft Knowledge Base Q240429

DirectX: Ports Required to Play on a Network

Microsoft Knowledge Base Q320020

Dungeon Siege: Network Ports Required for Multiplayer Games

Blizzard Entertainment: Technical Support Site

Port Information for Firewalls, Proxies, and Routers

WWII Online Customer Service -- Connection Issues

I am behind a firewall; which ports do I need to have open? And how do I set up my firewall software?