Fixing Valheim server lag with Better Networking (server-side only)

My friends complained about lag on our Valheim server: mobs rubber-banding, items popping around. The obvious suspects looked fine:

• Server CPU: ~16 % of one core, 1.4 GB RAM
• Upload: 20 Mbit/s, of which Valheim used under 2
• Ping to the internet: 14 ms, 0 % loss

The server and the connection had plenty of headroom. The problem was inside Valheim itself.

Why Valheim lags even with good hardware

Two things about Valheim’s networking:

1. Valheim caps how much it sends per player. By default about 150 KB/s. A big base has hundreds of thousands of objects (our world: ~270,000), and syncing them hits that cap. Updates arrive late, and mobs jump around.
2. Areas are simulated by a player’s PC, not the server. Whoever arrives in an area first “owns” it and simulates its mobs and physics for everyone. If that player has a weak PC or bad Wi-Fi, everyone nearby suffers.

Better hardware can’t fix #1, because it’s a software limit.

Better Networking

Better Networking is a BepInEx mod that:

• raises Steam’s send-rate limits (this is the big one, and it works server-side only)
• enlarges the send queue
• adds compression, which only works between two machines that both have the mod

Players without the mod can still join normally.

Installing it on the Docker server

With the lloesche/valheim-server image, mods are easy:

1. Stop the server, which saves the world: docker compose stop
2. Enable BepInEx in the compose environment:

   - BEPINEX=true

3. Drop the mod’s DLL into the plugins folder:

   ./config/bepinex/plugins/CW_Jesse.BetterNetworking.dll

4. docker compose up -d

The log confirms it:

[BepInEx] Loading [Better Networking 2.3.2]
[BepInEx] Chainloader startup complete (1 loaded, 0 skipped, 0 failed)
[Better Networking] Steamworks: k_ESteamNetworkingConfig_SendRateMin: 153600 -> 262144
[Better Networking] Steamworks: k_ESteamNetworkingConfig_SendRateMax: 153600 -> 1048576

That’s the per-player limit going from 150 KB/s to between 256 KB/s and 1 MB/s. The last release is from 2023, but it loaded cleanly on the current server. Always check the log for errors after adding an older mod.

Tuning

Defaults are fine for most servers. The config lives in ./config/bepinex/CW_Jesse.BetterNetworking.cfg:

• Good upload (10+ Mbit/s for a few players): you can raise the queue size.
• Weak upload: lower the update rate to 75 % or 50%. Movement gets slightly less smooth, but it stops overloading the line.

Things only players can fix

• Quit through the menu, not Alt+F4. Hard quits cause sync issues even in vanilla.
• Best connection goes first. Since the first player in an area simulates it, the one with the best PC and connection should lead through portals and into new areas.
• Press F2 in-game to see each player’s ping and data rate. That points at the friend whose connection is the problem.
• Players who install Better Networking themselves get compression too.

Does it disable achievements?

No. Steam achievements are tracked by each player’s game, and a server-side mod can’t touch them.