From Rigs of Rods Wiki
How to Port Forward for a RoR Server
an article by pandabear
If you want to run a Server for RoR, Chances are you already have this figured out in a sense. But If your RoR Server keeps saying "Can't register at Master Server", then chances are you haven't opened a Port properly.
What is Port Forwarding?
Port forwarding allows other peoples computers (a person playing on RoR Multiplayer for example) to connect to a specific computer within a private local area network. Example: Me connecting to your RoR server. I am not connecting to something hosted on a public, internet-facing website or something, but instead connecting directly to your computer to play on your Server.
Port forwarding is super easy. See [www.portforward.com] for instructions for all major routers/modems.
How to Open a port on your Router
I will be using a generic D-Link system for this tutorial. Please check your manual or the link above for your own equipment.
1. Make sure you know your PUBLIC IP Address. You can get this here
2. Connect to your router using your default gateway IP address. Usually 192.168.0.1, but check here for yours.
3. Poke around in your settings/advanced tabs and look for a tab named Port Forwarding or something along those lines.
4. Enter the desired ports you want to open. This is generally a number between 12000 and 12100
5. Enter [b]YOUR PUBLIC[/b] IP address into the IP Column.
6. Press save!
You should have successfully opened a port now!
Didn't enter a correct Port number
port numbers are usually 12000-12500
Server can't register at master server You didn't forward correctly. Try again