I've been getting a message on Game Ranger saying I have a symmetric nat and cant connect to other players. So I forwarded ports 16000, 6100-6200, 6073 and it worked I didn't get the message anymore. Sometimes though it doesn't work and I'm a little confused.
If I can figure out this first issue I have another question.
I don't know if I'm saying this right but, I have two computers in my lan hooked up by a Ethernet cables to my modem/router zyxel pk5000z we were using theses computers to play together using Game Ranger. When the port forwarding did work it would only let me open ports for one ip adress 1 computer it seemed how do you open ports for all computers on your lan.
Are you on a school or other private network? These ports could be blocked. This is from gamerangers support page: "If you are at work on a company network or at a university, you may not be able to fix the problem yourself. Instead you may have to ask the network administrator to how to port-forward UDP port 16000 to your computer."
If the port is blocked, they must be unblocked for you to do what you want.