Maybe this helps (found it in the tutorial workshop 25 mp):

Quote:

Hosting an online game
How can we set up our home PC so that people can play our online game over the internet? There are two problems. First, your PC is probably not directly connected to the Internet, but sits behind a router and a firewall. Second, the internet IP address of your PC will probably change all the time, dependent on your service provider. The solution to the first problem is Port Forwarding, to the second a DynDNS service. Here's a brief step by step instruction to set up an online game server.

Port forwarding directs all Internet data packets with a certain port address to a certain PC in your local network. Open the control panel of your router, and use the Port Forwarding function to assign your port address (set up with dplay_port or the -port command line option) to the local IP of your server. By default, the engine uses port 2300. Your local server IP can be read from the server_ip string, or found with the ipconfig utility. It normally starts with 192.168... Make sure to set up your network so that the local IP of your server is always the same.
Additionally to port forwarding, you need to open the same port in the Windows firewall of your server. Otherwise the traffic will pass the router, but will be blocked by your PC.
Once you've did that, and started the game in server mode, people can connect to your Internet address. They have to start the game in client mode and give your Internet IP address with the -ip command line option. Your Internet IP is assigned by your service provider - it's not the same as your local server IP. You can find your Internet IP through websites like www.whatismyip.com. Note that you can probably not connect to your own Internet IP unless your router supports NAT loopback. So you need to ask other people to test the connection.
Now people can join your game, but they need always to call you before and ask for your current Internet IP. For preventing this, get a persistent domain from a free DynDNS service like www.dyndns.org. If your router supports DynDNS domains, it can be set up to automatically connect to the service and submit the new Internet IP whenever it has changed. Otherwise you need to install a DynDNS client on your PC.