Port 2257: simple-tx-rx — A Registered Port That Never Took Off

What Port 2257 Is

Port 2257 sits in the registered ports range (1024–49151), the middle tier of the port numbering system. These ports don't require root or administrator privileges to use, and they're managed by IANA — the Internet Assigned Numbers Authority — which maintains a registry of what's supposed to run on each one.

According to that registry, port 2257 belongs to simple-tx-rx: a "simple text/file transfer" service registered in August 2006 by a private individual named Daniel Kilsdonk.¹ It's registered for both TCP and UDP.

That's where the trail ends.

The Registered-but-Unused Problem

The IANA registry contains thousands of ports like this. Someone had an idea, submitted a registration (the process is open and relatively straightforward), and then — nothing. No RFC. No open-source implementation anyone uses. No mentions in networking literature beyond automated port databases copying from each other.

Simple-tx-rx appears to have been a private or niche project that never got beyond the registration stage. This is common. Registering a port number doesn't require shipping a working protocol. It just requires filling out a form.²

The result: port 2257 is technically "taken" but effectively unclaimed in practice. You're unlikely to encounter it unless something specific on your system or your network has chosen to use it for its own purposes — which would be a local convention, not a standard.

What Might Actually Be Using It

If you see traffic on port 2257, it's probably one of three things:

1. A custom application that needed a port and picked this one arbitrarily
2. A scanner or probe checking for open ports across a range
3. Something specific to your environment — a game, a monitoring tool, or internal software that chose this port for its own reasons

None of these would have anything to do with simple-tx-rx.

How to Check What's Listening

If port 2257 is open on your machine and you want to know why:

Linux / macOS:

# Show what process is bound to port 2257
ss -tlnp | grep 2257

# Or with lsof
lsof -i :2257

Windows:

netstat -ano | findstr :2257

The output will show you the process ID. Cross-reference it with Task Manager or Get-Process -Id <pid> in PowerShell to find out what program opened it.

Why Unassigned (and Under-Used) Ports Matter

The registered ports range exists as a middle ground: not the privileged system ports (0–1023) that require elevated access, and not the ephemeral ports (49152–65535) that operating systems hand out dynamically for outbound connections. Registered ports are meant to give services a stable, predictable address.

In practice, the registry is a mix of heavily-used ports (3306 for MySQL, 5432 for PostgreSQL, 6379 for Redis) and thousands of others like 2257 that represent abandoned ideas, one-off tools, and protocols that never found an audience. The registry doesn't expire or clean itself up. A port registered in 2006 by someone who never shipped a protocol will remain "assigned" indefinitely.

This matters for security: an open port in this range isn't inherently dangerous, but it's worth knowing what's behind it. An unexpected listener on any port — registered or not — is worth investigating.