Port 2456: Valheim's Gate — The Registered Port That Vikings Claimed

What Port 2456 Is

Port 2456 sits in the registered port range (1024–49151). These ports are recorded by IANA — the organization that maintains the master list of port assignments — but IANA registration doesn't mean active use. It means someone, at some point, filled out the paperwork.

The official IANA record lists port 2456 under the service name altav-remmgt, supporting both TCP and UDP.¹ What altav-remmgt actually is, or was, is poorly documented. No active software is known to use it. The registration exists as a placeholder from a company or project that has since faded into obscurity.

What the port is actually known for is something else entirely.

The Unofficial Use: Valheim

Valheim — the Norse mythology survival game released in 2021 — uses UDP port 2456 as its dedicated server port by default.² When you run a Valheim server, it listens on:

• UDP 2456 — game traffic (player connections, world state)
• UDP 2457 — Steam query port (how the Steam server browser finds your server)

The game chose this port for no particularly notable reason, but the result is that millions of players have opened port 2456 on their routers to host servers for their friends. For a lot of people, Valheim was their first encounter with port forwarding — the moment they learned that "the Internet" has doors, and some of them need to be unlocked.

What the Range Means

Registered ports (1024–49151) occupy the middle ground of the port space:

• Well-known ports (0–1023): Reserved for foundational protocols — HTTP, HTTPS, SSH, DNS. Binding to these requires elevated privileges on most systems.
• Registered ports (1024–49151): Available for applications to register with IANA. No privilege required to bind, but IANA keeps the list to reduce conflicts.
• Dynamic/ephemeral ports (49152–65535): Unregistered. Used temporarily by clients for outbound connections.

Port 2456's registered status means it's technically "spoken for," but in practice, that reservation means nothing. The original registrant is gone. Valheim moved in without asking.

Checking What's Listening on This Port

If you see port 2456 active on a machine and want to know why:

On Linux/macOS:

# Show what process is using port 2456
ss -tulnp | grep 2456

# Or with lsof
lsof -i :2456

On Windows:

# Show listening ports with process IDs
netstat -ano | findstr :2456

# Then look up the PID
tasklist | findstr <PID>

If you're running a Valheim server, this is expected. If you're not, it's worth investigating — unrecognized open ports are always worth a second look.

Why Unassigned and Dormant Ports Matter

The IANA registry is imperfect by design. Organizations registered ports in eras before the Internet scaled to billions of devices, and many of those registrations are now orphaned — the company dissolved, the product died, the RFC was never written. The registry reflects intent, not reality.

What fills the gap is use. Valheim didn't petition IANA. It picked a port that seemed free, shipped the game, and created a de facto standard through sheer popularity. That's how much of the registered port space actually works: informal conventions that accumulate enough critical mass to become the thing everyone knows.

Port 2456 is a small example of how the port numbering system actually evolves — not through orderly assignment, but through survival of the well-adopted.