Port Configuration and Firewall Rules

Required Ports

The minimum required set for a public server is:

• UDP 27015 inbound — players cannot connect without this
• UDP 26901 and 1200 outbound — server will not appear in the server browser without these

Setting the Game Port

The port is set at launch with -port:

-port 27015

This binds both the UDP game port and the TCP RCON port to 27015. The IP binding is controlled separately with +ip:

+ip 0.0.0.0     # Listen on all interfaces
+ip 10.0.0.5    # Listen on a specific interface only

For Pterodactyl, the panel configures port allocation for you. The 27015 default can be overridden in the panel's port settings.

RCON Port

RCON uses TCP on the same port as the game (default 27015). It does not use a separate port. When configuring your firewall, ensure both UDP and TCP are open on 27015.

Steam Master Server Registration

For your server to appear in the Steam server browser and in-game server list, outbound UDP traffic must be allowed to Steam's master servers:

UDP 26901 outbound     # Primary Steam master server
UDP 1200 outbound      # Secondary/legacy Steam master server

These are outbound connections initiated by your server. If your host's firewall blocks all outbound traffic by default, you must explicitly allow these. If your server does not appear in the browser after 5–10 minutes with a valid GSLT token, blocked outbound ports are the most likely cause.

SourceTV

SourceTV allows external spectating and demo recording. It is disabled by default. If you enable it:

tv_enable 1
tv_port 27020       // Default SourceTV port
tv_name "My Server SourceTV"

Open UDP 27020 inbound if you enable SourceTV.

Running Multiple Servers

When running more than one server on the same machine or node, each server must bind to a unique port. The convention is to increment by 10:

In Pterodactyl, allocate a new port for each server instance. Set the -port launch flag in each server's startup command accordingly, or use the panel's port variable if the egg supports it.

Each server also needs its own GSLT token. Tokens are per-server, not per-account.

Recommended Firewall Rules (inbound)

# Minimum public server
UDP 27015 ALLOW
TCP 27015 ALLOW

# Broader range (covers default port and some variants)
UDP 27000:27015 ALLOW
TCP 27015 ALLOW

Verifying Ports Are Open

From an external machine, test that the game port is reachable:

# Test UDP connectivity (requires nmap)
nmap -sU -p 27015 <your-server-ip>

# Test TCP (RCON)
nc -zv <your-server-ip> 27015

From within the server container, verify the process is listening:

ss -ulnp | grep 27015    # UDP
ss -tlnp | grep 27015    # TCP

If ss shows the port is bound but external connections fail, the block is at the host's firewall or network layer, not the server process.

Related

• Installing Your Garry's Mod Dedicated Server
• Using RCON to Remotely Manage Your Server
• Troubleshooting Common Garry's Mod Server Errors
• Configuring Your Server with server.cfg