Port 3124: Beacon Port — A Name Without a Story

What Port 3124 Is

Port 3124 lives in the registered port range (1024–49151). These ports are assigned by IANA to specific services through a formal request process, distinguishing them from the well-known ports (0–1023) reserved for foundational Internet protocols.

IANA lists port 3124 as beacon-port for both TCP and UDP.¹ That's the full extent of its official documentation. There is no RFC, no protocol specification, no known implementation, and no organization that has publicly claimed it. The name exists in the registry the way a placeholder exists in a form — it occupies the space without filling it.

Known Unofficial Uses

Rainbow Six Vegas (UDP, incidental)

Ubisoft's Rainbow Six Vegas uses a wide UDP sweep of ports 3074–3174 for multiplayer gameplay.² Port 3124 falls inside this range, but it isn't specifically targeted — it's just one of 100 ports the game's networking layer may use. If you're seeing UDP traffic on 3124 during a gaming session, Vegas (or Vegas 2) is the likely explanation.

No other widely observed unofficial use has been documented for this port.

What's Listening on Port 3124

If you see activity on port 3124 and want to know why, these commands will tell you what process owns it.

On Linux or macOS:

# Using ss (modern, preferred)
ss -tlnp | grep 3124

# Using lsof
sudo lsof -i :3124

# Using netstat
netstat -tlnp | grep 3124

On Windows:

netstat -ano | findstr :3124
tasklist | findstr <PID>

The PID from netstat maps to a process name in tasklist. On macOS, lsof gives you the process name directly.

Why Unassigned Ports Matter

The registered port range contains over 48,000 port numbers. Many were claimed in IANA's earlier, less rigorous era — sometimes with just a name and no supporting documentation. "Beacon-port" at 3124 is a product of that era: a registration without substance.

These ghost entries matter because:

• They can mislead. A firewall rule written to block "beacon-port" traffic isn't blocking any known protocol — it's blocking a name.
• They're available for squatting. Unimplemented registrations create ambiguity. Any application can use port 3124 and technically conflict with a nominal IANA assignment.
• They record intent without record. Someone, at some point, thought a beacon protocol should exist on this port. That idea never became a specification.

Port 3124 isn't dangerous, deprecated, or interesting in any security sense. It's a label on an empty shelf — a small artifact of how the port registry was built before stricter standards were applied.