What ports does a Valheim dedicated server use?

UDP 2456 and 2457 by default: the -port value and the port above it.

Do I need to port forward for a Valheim server?

Only on the Steam backend. With the -crossplay launch option the server goes through a relay and needs no port forwarding, which also works behind CGNAT.

Why is my Valheim server not showing up in the server list?

Check -public 1, wait 5 to 10 minutes after start, and remember the list is unreliable. Join with Join IP and IP:2456, or with the join code on crossplay servers.

Why doesn't my Valheim join code work?

It changes every time the server restarts. Copy the current code from the server log or the pause menu.

Why can't Xbox or PS5 friends join my Valheim server?

The server needs -crossplay, and crossplay must be enabled in each player's game. Without it only Steam players can see or join.

What does "Incompatible version" mean in Valheim?

The server and player are on different game versions. Dedicated servers don't update on restart, so update the server with SteamCMD.

Valheim server not showing up or friends can't join?

Quick answer

Valheim dedicated servers use UDP ports 2456 and 2457 (the -port value and the next one up). On the Steam backend (no -crossplay) you must forward both. With -crossplay the server uses a relay, so no port forwarding is needed, but LAN and loopback IPs don't work. If the server isn't showing up in the list, the list can take 5 to 10 minutes and needs -public 1; join directly with IP:2456 instead.

Ports

2456 UDP: Game port (-port), used by in-game Join IP
2457 UDP: Game port + 1, Steam query / server browser

How to fix it, step by step

Wait for "Game server connected". The world takes a minute or two to load. Connecting before the log says Game server connected fails.
Check the password rules. The password is case-sensitive, at least 5 characters, and must not be contained in the world name or seed. Otherwise the server logs Error bad password: and doesn't start.
Pick the backend that fits your group. Everyone on Steam: leave out -crossplay and forward the ports. Anyone on Xbox, PS5, Switch 2 or Game Pass: add -crossplay; no port forwarding is needed. Edit a copy of the start script, because Steam overwrites the original on update.
Forward UDP 2456-2457 (Steam backend). Forward the UDP range 2456-2457 to the server PC's reserved local IP, and allow the server through the firewall (tick every box in the Windows Firewall pop-up).
Join by IP, not the list. In Valheim: Join Game, Join IP, then public-ip:2456. In Steam's server browser favourites, use the query port (public-ip:2457). Hosted servers rarely use 2456, so use the exact address you were given.
Match versions. A dedicated server doesn't update itself on restart. Update it with SteamCMD (app_update 896660 validate) and make sure players are on the same version.
Crossplay: use the current join code. The 6-digit join code changes every time the server restarts. Read the current one from the log or pause menu. Crossplay must be enabled on both the server and each player's game.

Why the server isn't showing up in the list

-public 0 hides it on purpose. Use -public 1.
New servers can take 5 to 10 minutes to appear.
The list is unreliable either way: join by IP or join code.

Mods and console players

Everyone needs the same mods at the same versions (r2modman helps), and mods must be updated for 1.0. Console players can't install mods, so a server with client-side mods excludes them. Adding anyone to permittedlist.txt blocks everyone who isn't on it.

Test it from the outside

Your own Wi-Fi can't tell you whether friends can reach the server. The free Server Doctor check contacts your server once from the internet, the way the game does, and tells you the most likely cause. The same check runs in Discord with /fix.

No PC to host 24/7?

Valheim worlds only exist while the server runs, so friends can't play when your PC is off. A hosted Valheim server stays online, and crossplay mode or a host means nobody has to touch a router.

Valheim server not showing up, or friends can't join?