That wouldn't work, as you can't use a hardcoded IP if the software must work on any LAN (you don't know what IPs are used inside the LAN, for server and clients).

I don't know the details, but I think it's possible to broadcast something to every computer on a LAN. So you can use a certain port to send out a message to all computers on the LAN and see which ones respond.

This is not built into 3dgs, so you would have to do plugin programming.