What ports does a Necesse server use?
A player-hosted Necesse server listens on UDP 14159. That is what has to reach the host's PC: the port forward on their router, and what the firewall prompt on first launch is asking for.
UDP 14159— inbound, to the machine running the server.
Or skip the port forward entirely: in Checkpoint64, Checkpoint Connect lets the host share the server running on their PC with their team, and teammates join directly when they can and through a relay when they can't.
Ports are the half of hosting that happens on the router. The other half is on disk — the world itself, which lives in Necesse's save folder on one PC and which nobody else has a copy of. Checkpoint64 doesn't host anything for you; it backs that folder up automatically and keeps every version, so a corrupted or overwritten world is one click from restored. If you'd rather not run a server at all, a small group can pass one world between them instead: the dedicated server alternative guide walks through it.