I'm trying to set up a server for Dungeon Siege

I have no idea what I am doing. I set up a tunnel, I set the thing to TCP, I did as much as I could given that I have no idea what I am doing.

How do I know I set up the server correctly? I can tell the tunneling…stuff works, but I can’t seem to get it to work with Dungeon Siege. How do I set up servers for abandonware games?

I am using the Steam version of Dungeon siege for additional context. No mods and no fan patches.