Port 2303: Arma Steam Query — The Server's Listening Ear

Port 2303 sits in the registered port range (1024–49151). These are ports IANA tracks and assigns to specific services, but 2303 has never received an official assignment. On paper, it's unclaimed territory.

In practice, it has a clear owner.

The Unofficial Use: Arma Steam Query

Bohemia Interactive, the studio behind the Arma series, uses port 2303 as the Steam query port for their dedicated game servers. When you open a server browser in Arma 3, your client sends UDP packets to this port asking: "How many players? What map? What mods?" The server answers here.

The logic behind 2303 is simple arithmetic. Arma dedicated servers run on port 2302 by default (UDP, game traffic and VoIP combined). Bohemia incremented by one for Steam query.¹

The full Arma 3 port family:

If you're running multiple Arma instances on the same machine, Bohemia recommends spacing them by at least 100 ports — so a second server would claim 2402, 2403, 2404, and so on.¹

What the Registered Range Means

The registered port range (1024–49151) is where services stake claims with IANA. Anyone can submit an application. Once registered, other services are expected to stay off that number to avoid conflicts.

But registration isn't enforcement. There's no technical mechanism preventing software from using any port in this range. Port 2303's unassigned status means Bohemia never formally registered it — they just used it, and the community followed. Millions of Arma servers have been configured this way for over a decade.

What to Do If You See Port 2303 Open

If you spot 2303 open on a machine:

It's probably Arma. Check if an Arma dedicated server is running.

Check what's listening:

# Linux / macOS
sudo ss -tulnp | grep 2303
# or
sudo lsof -i :2303

# Windows (Command Prompt, run as Administrator)
netstat -ano | findstr :2303

The output will show the process ID. On Linux/macOS, lsof will show the process name directly. On Windows, take the PID to Task Manager to identify the process.

If no game server is running and you see 2303 open, investigate. Unassigned ports occasionally get squatted by malware using obscure numbers to avoid detection — though 2303 is not specifically associated with any known malicious software.

Why Unassigned Ports Matter

The port system works on coordination, not enforcement. When Bohemia uses 2303 without registering it, they're betting no assigned service will ever conflict. That bet has held for Arma. But it also means 2303 could someday receive an official IANA assignment — and anyone running an Arma server would suddenly be in conflict with a legitimate service.

This is why the registered range exists: not to prevent informal use, but to give the Internet a shared map of who lives where. When you skip registration, you're building on unmarked land.