Check if your Left 4 Dead 2 server is online
Left 4 Dead 2 replies to the usual Source query, but because of its lobby system a server that answers is not necessarily one people can join.
The ports Left 4 Dead 2 uses
Queries go over UDP on the game port. The catch is particular to this game: the server can be set to accept players only through Steam lobbies, in which case a direct connection is turned away even though the port is open and this check passes.
Every port a default Left 4 Dead 2 install uses
With the game port left at 27015. If you changed it with -port, the other ports move with it.
| Port | What it is for |
|---|---|
| 27015 UDP | Game trafficRequired Gameplay and queries. |
| 27015 TCP | Steam handshakeRequired The same number over TCP. |
Still offline? Try this
Passing here while direct connects fail points at the lobby-only option, not the router. Switching it off lets people connect directly; you give up the matchmaking integration in exchange.
What a Left 4 Dead 2 server needs to run well
- Memory, 8 players
- 3 GB
- CPU cores
- 2+
- Disk
- 20 GB+
Source engine, one campaign map at a time. State resets between rounds so nothing accumulates.