Port 2457: Unassigned — The Steam Query Port Valheim Claimed

What Range This Port Belongs To

Port 2457 falls in the registered port range (1024–49151). These ports are managed by IANA, which maintains a registry of officially assigned services. Port 2457 appears in that registry as unassigned — meaning no organization has claimed it for an official protocol.¹

Unassigned doesn't mean unused. It means no one has formally reserved it. In practice, applications pick ports from this range all the time without registering them, creating an informal layer of de facto assignments that exists entirely outside the official record.

Observed Unofficial Uses

Valheim Dedicated Servers (most common)

The game Valheim, developed by Iron Gate Studio, defaults its dedicated servers to a three-port cluster:

• 2456 — game traffic (the port players connect to)
• 2457 — Steam server browser query (A2S protocol)
• 2458 — Steam communication

Port 2457 is the one Steam uses to ask "are you alive, and how many players are connected?" It's what makes a server show up in the server browser. If you run a Valheim server and port 2457 is blocked, the server becomes invisible to Steam's matchmaking — players can still connect directly by IP, but discovery fails.²

This isn't an official Steam assignment either. It's just the default the Valheim developers chose, and enough servers are running it that 2457 is now strongly associated with this purpose.

Historical Malware Associations

Security databases flag port 2457 as having been used by malware in the past. This is a weak signal — dozens of ports carry similar warnings, and the presence of a port in a trojan database from the early 2000s says little about current risk. If you see unexpected traffic on 2457 and you're not running a game server, investigate. But the warning alone is not cause for alarm.³

Checking What's Listening on This Port

If port 2457 is open on a machine and you're not sure why, these commands tell you what process owns it:

Linux/macOS:

# Show process listening on 2457
sudo ss -tlnp sport = :2457
# or
sudo lsof -i :2457

Windows (PowerShell):

# Show process ID and port
netstat -ano | findstr :2457
# Then look up the PID
Get-Process -Id <PID>

A Valheim server process will typically show as valheim_server or valheim_server.x86_64. Anything else warrants a closer look.

Why Unassigned Ports Matter

The port registry exists to prevent collisions — two applications fighting over the same door. When a port goes unassigned, that coordination breaks down. Applications that need a port just... pick one, and hope nothing else is using it.

In the registered range, this creates a shadow economy of informal assignments. Port 2457 is a small example: no RFC governs it, no standards body blessed it, but thousands of Valheim servers worldwide agree on what it means. The Internet frequently works this way — convention filling the gaps that formal standards leave open.