What is the adhoc base port?

[AdamN]

As what i posted before 27312 is used by AdhocServer, while the game may have varies of ports (most of them are below 1024 which are privileged ports on most system), so you will also need to forwards those specific ports used by specific games.

You can set Port Offset to higher than 1024 to prevent games using privileged ports.

For compatibility (and less trouble ) it's better to use VPN/tunneling service than directly forward the ports on your router (if you don't want to enable DMZ due to security reason), since VPN/tunneling software usually using a consistent port.