Port 2223: Registered but Unclaimed

What Range This Port Belongs To

Port 2223 lives in the registered port range (1024–49151). These ports are assigned by IANA to specific services and applications, but not every number in that range has been claimed. Port 2223 hasn't been — IANA lists it as unassigned for both TCP and UDP. ¹

The registered range exists between the well-known ports (0–1023), which are reserved for foundational protocols like HTTP, SSH, and DNS, and the ephemeral ports (49152–65535), which operating systems assign dynamically to outbound connections. Registered ports are the middle tier: open for applications to claim, but requiring registration to be official.

An unassigned port in this range isn't broken or forbidden. It's just unclaimed real estate.

Known Unofficial Uses

Microsoft Office for Mac Anti-Piracy Monitor (UDP, circa 2002)

The most documented use of port 2223 is a UDP service Microsoft built into early versions of Office for Mac OS X. The application would broadcast on this port as part of a license-checking mechanism — looking for other copies of Office running on the same network segment to detect unlicensed installations.

The feature didn't work well. It caused problems for legitimate users and generated unexpected network traffic that confused administrators. ² Microsoft quietly abandoned the approach as licensing infrastructure moved to activation servers and, eventually, cloud-based validation. You won't encounter this in any modern Office installation.

SSH on Non-Standard Ports

Administrators sometimes move SSH off port 22 to reduce automated scanning. Port 2222 is the most common alternate; port 2223 occasionally appears as a secondary choice or when 2222 is already occupied. There's nothing special about 2223 for this purpose — it's proximity to a popular alternate that earns it occasional use.

Rockwell Automation

Some Rockwell Automation industrial control documentation references ports in the 2220s range for CSP (Common Serial Protocol) communication between their software and programmable logic controllers. Port 2223 appears in some configurations, though the primary documented port for this purpose is 2222. If you find port 2223 open on an industrial network, Rockwell software is a plausible explanation. ³

How to Check What's Listening

On any Unix-like system:

# Show what process owns port 2223
sudo lsof -i :2223

# Or with ss (modern Linux)
sudo ss -tlnp | grep 2223

# Or with netstat
sudo netstat -tlnp | grep 2223

On Windows:

netstat -ano | findstr :2223
# Then look up the PID in Task Manager

If nothing is listening, the port is simply closed. That's the normal state for most unassigned ports.

Why Unassigned Ports Matter

The port numbering system only works because there's an authority (IANA) keeping the registry and because software respects the assignments. Unassigned ports are proof that the system is working — they're slots held in reserve, available for future protocols to claim through proper registration.

They're also where informal conventions live. SSH on 2222, alternate HTTP on 8080, development servers on 3000 and 8000 — none of these are IANA-assigned, but the community uses them consistently enough that they function like assignments. Port 2223 hasn't attracted that kind of informal consensus. It remains genuinely open.