Your router is blocking the incomming connection of your friend because of NAT.

You need to forward all traffic from the port you are using (glob_port = 2300) to the computer you have the server running on. For doing this, you need the local LAN-IP of that computer and have access to your router webinterface.

Unfortunately I can't give you a step-to-step guide as nearly every routers menu is different. Try this page, it has instructions for nearly every model:

http://portforward.com/