Port forwarding that actually works

Most “it worked yesterday” stories are double NAT, wrong protocol, or a firewall rule that only opens TCP when the game needs UDP. For protocol fundamentals, IETF’s plain-language companion on how the Internet works is still useful background: The Tao of IETF (dense, but honest about why networking is opinionated).

Static maps beat hope

Pick a port range per game instance. Document internal IP, external port, protocol, and which process binds it. UPnP can help labs; production communities deserve explicit maps — see our UPnP vs static note.

Verify from outside your LAN

Testing only from inside the house often hits hairpin NAT quirks. Use a phone on cellular data or a friend’s client to confirm the public path.