If you don't know what Port Forwarding is yet, you might want to start by reading our What is Port Forwarding guide.
You might also be interested in our huge collection of Router Screenshots where you can see every page of every router that we know of.
To setup port forwarding on the Apple AirPortExtreme router your computer needs to have a static IP address. You should complete one of the following steps first:
Now that you have setup a Static IP Address on your computer, please enter the IP address that you assigned to your computer here:
Open up the finder on your Mac.
Click the Applications button near the left of the page.
Click the Utilities button near the right of the page.
Click the AirPort Admin Utility button near the right of the page.
Select Apple Base Station from the Select Base Station list.
Click the Port Mapping button near the top of the page.
Click the Add button near the right of the page.
We will list a series of lines here that will show you exactly how to forward the ports you need to forward. MultiTheftAuto requires you to forward the 2003 ports. Go ahead and enter the settings shown above into the Port Mapping Add menu and then click Ok.
When you're finished, click Update near the bottom of the screen to save your changes.
And that's it! You're done!
Now that you have forwarded ports for MultiTheftAuto on the Apple AirPortExtreme you should test to see if your ports are forwarded correctly.