Port 2374: Hydra RPC — Registered, Forgotten

Port 2374/TCP is registered with IANA under the name hydra-rpc, submitted by Jacob Feisley on January 21, 2009.¹ That's essentially everything that's publicly known about it.

There's no RFC. No documentation. No known software that ships using this port. The registration exists, and the service it was meant to describe does not appear to have ever reached any public deployment.

Port 2374/UDP is listed as Reserved — meaning it's held back from assignment, not actively used.

What Range This Port Belongs To

Port 2374 falls in the registered port range: 1024–49151.

Registered ports sit between the well-known ports (0–1023), which are reserved for foundational Internet services like HTTP, DNS, and SSH, and the ephemeral ports (49152–65535), which operating systems hand out temporarily for outbound connections.

The registered range is where applications stake their claim. A developer or company submits a request to IANA, describes what the port will be used for, and IANA records it. The process is largely administrative — IANA doesn't test, certify, or verify that the service ever ships.

This is why the registered range contains thousands of ports like 2374: legitimate registrations for services that were planned, never widely deployed, and eventually forgotten. The name sits in the registry indefinitely, neither released nor used.

Checking What's Actually on This Port

If you see port 2374 open on a system, it's almost certainly not hydra-rpc — it's whatever that system's administrator configured to listen there. The official assignment is advisory, not enforced.

To check what's listening on port 2374:

Linux/macOS:

# Show the process listening on port 2374
ss -tlnp | grep 2374

# Or with lsof
lsof -i :2374

Windows:

netstat -ano | findstr :2374

The process ID in the output can be cross-referenced in Task Manager or tasklist to identify what's running.

Why Unassigned (or Obscure) Ports Matter

Every open port is a question: what's listening here, and should it be?

Ports without well-known assignments are harder to reason about in firewall rules, security audits, and network monitoring. When a well-known port is open — say, port 443 — you have reasonable expectations about what should be there. When an obscure registered port is open, you have almost none.

Security scanners like Nmap flag unexpected open ports specifically because unrecognized services are worth investigating. A port being registered doesn't make it safe. An unknown process listening on 2374 deserves the same scrutiny as any other unexpected open door.