Port 2397: NCL — Reserved, Forgotten, and Occasionally Gamed

What Port 2397 Is

Port 2397 sits in the registered ports range (1024–49151), the middle tier of the port numbering system. IANA lists it as assigned to a service named "NCL" on both TCP and UDP — but what NCL stands for, who registered it, and whether anything ever ran on it in production are questions the historical record doesn't answer.¹

This is more common than it sounds. During the 1990s and early 2000s, companies and projects registered port assignments the way startups claimed domain names — speculatively, optimistically, and sometimes with no follow-through. Port 2397's NCL entry is one of hundreds of registrations that outlived whatever they were meant to reserve.

The Gaming Footnote

Port 2397 falls within the 2300–2400 block that Microsoft-era multiplayer games used for DirectX and GameSpy lobby traffic. Age of Empires II, Flight Simulator 2000, and a generation of zone-based online games scattered connections across this range rather than pinning to a single port.² Port 2397 may have occasionally carried game traffic as part of that sweep — not by design, but by proximity.

This is old enough that it's mostly a historical curiosity now. Modern games use different infrastructure.

Is It Assigned or Available?

Technically assigned. Practically vacant.

"Registered" in the IANA sense means IANA recorded the name. It doesn't mean the service is active, maintained, or that anything today will refuse to use the port because of it. Operating systems don't enforce IANA registrations — they're advisory, not access control.

If something is listening on port 2397 on your system, it's not NCL.

How to Check What's Using This Port

Linux / macOS:

# Show what process is bound to port 2397
ss -tlnp | grep 2397

# Or with lsof
lsof -i :2397

Windows:

netstat -ano | findstr :2397

Then match the PID to a process name in Task Manager or with:

tasklist | findstr <PID>

If nothing returns, the port is idle on your system — which is the most likely outcome.

Why This Matters

The registered range contains roughly 48,000 ports. Most modern applications need to pick a home somewhere in it, and the criteria is often "nothing important appears to be here." Port 2397 — obscure, unverifiable, with a ghost registration — is exactly the kind of port a developer picks when they need something quiet and out of the way.

If you're building something and considering this port: it's clean, but verify against your specific environment. The only reliable check is the one you run yourself.