After taking a nice lunch break from a multiplayer game that's hosted behind an NAT, you'll find that it won't connect when you try to re-join.
However, if you browse to the same game and join from the browse public menu, it joins up with no issues.
The reason, is that when re-joining, no NAT punching is requested from the pingpong servers.
Here's a Wireshark capture of me attempting to re-join (last attempt highlighted) followed by me successfully joining from the browse menu.
- wireshark capture
- Image 402.png (47.32 KiB) Viewed 760 times
From my testing, it appears that this lack of hole punching also applies to connect to address, whether it's through the game menu, or through the command line. This means that if you synchronize mods with a server behind a NAT, then it won't be able to connect after restarting, you'll have to go through the browse menu again.
I think it would make sense to always attempt NAT punching (maybe after a short timeout?) rather than only doing it when games are joined through the public browse function. Alternatively, you could add a NAT punch command-line switch and a NAT punch flag in player-data->last-played->server to allow for joining after mod syncs and re-joining respectively.
