Port 3109: Personnel Protocol — Registered, but Nobody's Home

What Range This Port Belongs To

Port 3109 sits in the registered port range (1024-49151), sometimes called "user ports." This range is where applications request official assignments from IANA — the Internet Assigned Numbers Authority — to stake a claim on a port number and avoid collisions with other software.¹

Registered ports don't require elevated privileges to bind on Linux and macOS (unlike well-known ports below 1024, which need root). Any application can open port 3109. The IANA registration is a courtesy reservation, not a lock.

The Official Registration

IANA lists port 3109 as assigned to "Personnel protocol" on both TCP and UDP, registered by one William Randolph Royere III.¹

That's where the trail ends. There is no RFC defining what "Personnel protocol" does, no open-source implementation, no vendor documentation, and no observable traffic in any network research database. The registration exists. The protocol, in any practical sense, does not.

This is genuinely common. The registered port range accumulated thousands of assignments through the 1990s and early 2000s when IANA's process was less rigorous. Someone had an idea, filed the paperwork, and then the project never shipped — or shipped on a different port, or was abandoned entirely. Port 3109 is one of hundreds of ghost registrations: named, claimed, and empty.

Any Observed Unofficial Uses

Nothing documented. Port 3109 doesn't appear in firewall ruleset databases, malware reports, or network traffic analyses with any consistency. If software uses it on your system, it's almost certainly application-specific — a development server, a local tool, or something vendor-defined that happened to land on this number.

The port range 3074-3174 UDP was historically associated with Ubisoft's Rainbow Six Vegas for peer-to-peer game traffic, but that's a broad range sweep, not a specific assignment to 3109.²

How to Check What's Listening

If you see activity on port 3109 and want to know what's using it:

macOS / Linux:

# Show process listening on port 3109
sudo lsof -i :3109

# Or with ss (Linux)
sudo ss -tlnp sport = :3109

Windows:

# Show process ID bound to port 3109
netstat -ano | findstr :3109

# Then look up the PID
tasklist /FI "PID eq <PID>"

If nothing is listening, you'll get empty output. That's the expected result for most machines — port 3109 is unoccupied.

Why Ghost Registrations Matter

The registered port range is a shared namespace. When thousands of ports carry abandoned registrations, new applications have to navigate around them — or ignore them entirely and just pick something that works. IANA has tightened its process over the years, now requiring contact information, a description of the protocol, and evidence that the registration will actually be used.³

Port 3109 is a small artifact of the earlier, more optimistic era of Internet infrastructure: when reserving a port number felt like staking a claim, and the Internet was small enough that someone thought a "Personnel protocol" might become standard.

It didn't. But the registration remains.