Port 2261: CoMotion Master Server — A Name Without a Tenant

Port 2261 is a registered port — meaning it sits in the range from 1024 to 49151, where software vendors and developers can formally register a port number with IANA to associate it with their application. This range exists so that services can claim a consistent, predictable home on the network.

Port 2261's registered name is CoMotion Master Server (service name: comotionmaster). And that's where the trail goes cold.

The Ghost in the Registry

Port databases dutifully list CoMotion Master Server as the official occupant of port 2261. But search for the software itself — documentation, a company, a product page, source code, anything — and you find nothing. The software has vanished. The port reservation remains.

This is more common than you'd expect. The registered port range contains thousands of entries for software that was once active but is no longer maintained, companies that shut down, products that were abandoned mid-development, or internal tools that were registered but never widely distributed. The IANA registry is a historical record as much as it is an active directory.

Port 2261 is not dangerous. It's simply quiet. There are no known exploits associated with it, no malware families that favor it, no active services running on it in typical environments.

What the Registered Range Means

The 1024–49151 range is where the bulk of software services live. Unlike the well-known ports (0–1023), which require elevated privileges to bind on most operating systems, registered ports can be used by ordinary applications. IANA maintains the registry, but registration is voluntary — plenty of software uses ports in this range without ever registering them.

When you see a registered port with a name but no findable software, it usually means one of two things:

• The software existed but is no longer distributed
• The registration was speculative or internal and the software never shipped publicly

How to Check What's Using Port 2261

If you see traffic on port 2261 in your environment, it's not the ghost of CoMotion — it's something specific to your system. Check what's actually listening:

On Linux or macOS:

# Show what process is bound to port 2261
ss -tlnp | grep 2261
# or
lsof -i :2261

On Windows:

# Show listening ports with process IDs
netstat -ano | findstr :2261
# Then look up the PID
tasklist | findstr <PID>

With nmap (from another machine):

nmap -p 2261 <target-ip>

If something is listening on 2261 in your environment, it's an application that chose this port — either because it was assigned here or because it picked an available number. Identify the process before deciding whether to allow or block it.

Why Unassigned and Dormant Ports Matter

The port space has 65,535 numbers. Only a few thousand are actively in use at any given time. The rest — including ports like 2261 that have names but no living software — form a kind of commons. They're available to be claimed, by legitimate software and by malicious software alike.

Firewall rules that default to "block everything not explicitly needed" work precisely because of this. You don't need to know what every port does. You need to know what your systems actually use, and block everything else.

Port 2261 is one of thousands of quiet numbers — registered, named, and empty. If it shows up active in your environment, someone put it there. Find out who.