The game displays a message "Strict NAT detected"
The game tries to get around NAT as much as it can, without making you forward ports in your router manually. If you are receiving the "Strict NAT detected" warning, you should still be able to connect to other users who don't get that warning.
However, if both users are behind strict NATs, they will have more trouble connecting to one another. In that case, we do relay messages through the server for you so that you're more likely to be able to play. Not all routers are the same, and there do seem to be connection bugs for some people.
Here are a few things to try:
- Upgrade your router's firmware. I've done a lot of testing with some of the less expensive routers from several brands, and a firmware upgrade fixed the NAT performance on many of them.
- Turn on UPnP in your router, if it has the capability. UPnP support is often flaky in routers that are already strict NAT, but the game does try using UPnP if it's enabled.
- Torchlight uses UDP from a "random" OS-assigned port. If you need to set it to a specific port, you can change the UDPORT :0 line in your local_settings.txt file and set it to a port of your choosing. Just make sure it's over 1024. If you're playing with multiple people on the same LAN, and port forwarding to that port, make sure you choose different ports.
If you're still not able to connect to games, please send us a support ticket.