try to use hamachi, create a server, copy your ip, send to your firends your ip and create a lan lobby, your friends need to go in console and write this: connect 27.94.34.678:28960 (example)
(the host needs to send the hamachi ip) and the port about mw3
ps.
i dont know if this works but for world at war works very good, so try it 🙂 and sorry for my bad english