Alien's Duke Nukem Router Guide
Routers... The essence of protection but pure evil for applications.
Finding out if you have a Router
Well first you must discover if you have a router, here is just 2 of many routers:


If you can see one of these sort of small devices lying about your home you have a router. There are other ways to tell though. On XP go to start, run and type "cmd". On Vista go to start, type cmd in search and press cmd. In both Vista or XP type "ipconfig". This will bring up something along the lines of this:

IP Address = My network identification (internal) for my routers understanding.
Default Gateway = My router's IP address.
If the default gateway is similar to your IP then you have a router.
Accessing your Router
Open your default browser and type in your gateway ip. It should ask for a username and password. If it does not try a different browser. Once a username and password is requested try some combinations such as:
Username: admin
Password:
Username: admin
Password: admin
Username: admin
Password: password
Username: admin
Password: 1234
If none of these work you can contact the person who set your computer up (adminstrator) or reset the router. If you reset the router the internet will still work fine but all router settings will be reset to default (if any was set). To reset the router find the device and look for a small button (you will probably need a pin) or you can try unplugging the router for several minutes. Once this has been done the combinations above will most likely work but you can search around the internet for your router (check the device for model information).
Port Forwarding
Once inside you will have to find a port forwarding sections. This could come anywhere within the router menus so have a look around. I have seen it under NAT, advanced networking and a firewall section. This website has a good list of routers and their models. If you can find your model or a webpage that looks similar to yours you can get a basic idea of where to go from that website using any program as an example.
Once you have the port forwarding section select UDP and have the port 23513 opened to your IP. See my screenshot below (I selected both, does not matter really).

Press add, accept, confirm or whatever the button my be called and make sure port forwarding is enabled. Do the same for 8501 if you wish to host but make sure that is TCP.
Then try run DukesterX, options and test firewall. If passed then congratulations. If it does not pass try hosting a game/joining a game and see whether people can join/run the game or you can join/run their game.
If you want a more detailed and advanced explanation try |if3|355's router guide here.