What ports does a Project Zomboid server use?
A player-hosted Project Zomboid server listens on UDP 16261-16262. 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 16261-16262(2 ports) — 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 Project Zomboid'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.