With nat router:
forward ports 7777-7778 to the machine that hosts the game
in git:
configuration:
setup udp tunnel to all other players.
TCP/UDP ports: 10777,11777
advanced configuration:
Ethernet II
UDP
Only if broadcast
alter source ip from your lan ip to your online ip
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Just played some alien swarm mod with this setup. Worked perfectly.
Hooray for Ark