What Range This Port Belongs To
Port 2939 sits in the registered ports range, which runs from 1024 to 49151. IANA manages this range — organizations can formally request port assignments for their services, and IANA records the name in the official registry.1
Unlike the well-known ports (0–1023), registered ports don't require elevated privileges to use. Any application can bind to port 2939 without special system access.
The SM-PAS-2 Registration
Port 2939 is registered in the IANA registry under the service name SM-PAS-2, with its sibling SM-PAS-1 occupying port 2938 next door.2 Both TCP and UDP are listed.
That's where the documentation ends.
There is no RFC. No description in the registry. No contact information. No public implementation. No paper trail explaining what "SM-PAS" stands for or what the protocol does. Whoever registered these two ports did so and left nothing behind. The registration is a historical artifact — a label on an empty shelf.
This happens more than you might expect. The IANA port registry spans tens of thousands of entries. Some were registered decades ago by organizations that no longer exist, for internal systems that were never publicly documented, or for products that were abandoned before launch. The name persists; the service does not.
Is Anything Actually Using This Port?
Probably not SM-PAS-2, whatever that was.
If you see traffic on port 2939 on your systems, it's more likely to be:
- An application that picked a random high port for internal communication
- A misconfigured or custom service that didn't register its port
- Scanning traffic probing for open ports
Security tools occasionally flag the port due to its obscurity — unknown ports attract scrutiny precisely because they lack context.
How to Check What's Listening
If you want to see whether anything is using port 2939 on your machine:
Linux / macOS:
Windows:
If something appears, the process ID will tell you what's actually bound there.
Why Unassigned (or Abandoned) Ports Matter
The port registry is a coordination system, not an enforcement mechanism. IANA records assignments but cannot verify that services are still alive, correctly implemented, or even real. Ports like 2939 — registered but undocumented — are reminders that the registry reflects intent, not reality.
For network operators, the practical implication is simple: a registered port name tells you what was supposed to be there, not what is. Always verify.
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