My server has problems :0

[Wraithrider]

Hi all, am relitively new to srcds and have came across a problem with making my server online. I can create my server and my pc and all others in the house can join it, however when my mate from another house tries to join he cannot see me on the list nor can he join via me, I am pretty sure this is due to the fact tht the ip that the server is using is a local ip adress, how can i change this so my freind can join through online? Please help, as It is a truly brilliant game Gmod!

I used this video to install it if it helps
http://www.youtube.com/watch?v=8HHk2rOa-JM&feature=plcp&context=C43a6307VDvjVQa1PpcFMAUnBTcnIiEHE3btuQyQ6nbAY9609T3ZM%3D

[PAL-18]

Through a long process of trial and error i found the following list to be the absolute bare minimum for your server to work without compromising security.

TCP: 27015 (Change this to whatever port you specified +port parameter)
UDP: 26900 to 26901, 27014 to 27017, 27030 to 27039