Port 3375: VSNM Agent — Registered, Forgotten

What Range This Port Belongs To

Port 3375 is a registered port, in the range 1024-49151. This range sits between the well-known system ports (0-1023, reserved for protocols like HTTP and SSH) and the ephemeral ports (49152-65535, used temporarily for outgoing connections).

Registered ports were designed to give applications a stable, predictable home. A developer registers their service with IANA, gets a port number, and theoretically the world can find them there. In practice, the registry is full of entries like this one.

The Official Assignment: VSNM Agent

IANA lists port 3375 as assigned to vsnm-agent (both TCP and UDP). ¹

That's almost all that's publicly documented. "VSNM Agent" doesn't correspond to any widely deployed software, any active open-source project using this port, or any protocol specification with an RFC. It was registered, but whatever system it was meant for never became part of the common fabric of the Internet.

This happens more than you'd expect. Organizations register ports for internal tools, proprietary systems, or projects that never shipped. The IANA registry accepts the assignment, the port gets a name, and then nothing follows.

What You'll Actually See on Port 3375

If port 3375 is open on a machine you're looking at, it isn't vsnm-agent. It's almost certainly something else entirely: a development server, a local application that picked an available port, or misconfiguration.

If it's open on a machine exposed to the Internet and you don't know why, that's worth investigating.

How to Check What's Listening

On Linux or macOS:

# Show what process is listening on port 3375
sudo ss -tlnp | grep 3375

# Or with lsof
sudo lsof -i :3375

On Windows:

netstat -ano | findstr :3375

The output will include the process ID (PID). Match it to a process name in Task Manager or with ps aux | grep <PID> on Unix systems.

Why Unassigned (or Forgotten) Ports Matter

The registered port range contains thousands of entries like this one: claimed, documented minimally, never widely deployed. They matter for a few reasons:

They're available. An application can safely use port 3375 knowing it won't collide with HTTP (80), HTTPS (443), or SSH (22). The registry, even with its ghost entries, reduces accidental conflicts.

They're not truly empty. Security scanners flag open ports in this range because, while the official service is unknown, something is listening. That something deserves scrutiny.

They illustrate how the Internet evolves. Every obscure port number is a small artifact of a decision someone made, software that was built or planned, a company that once had a different idea about how things would work. The registry is as much history as it is infrastructure.