Port 3657: ImmediaNet Beacon — A Ghost in the Registry

What Port 3657 Is

Port 3657 sits in the registered port range (1024–49151). These ports are allocated by IANA to specific services upon request — not as freely as the well-known ports below 1024, but not as chaotic as the ephemeral ports above 49151.

IANA's registry lists port 3657 as immedianet-bcn — the ImmediaNet Beacon — registered in January 2003 for both TCP and UDP. ¹

That's essentially where the trail ends.

The Orphaned Registration

ImmediaNet registered this port in 2003, at the height of the broadband and VoIP boom when companies were staking out port numbers the way gold rush settlers staked out land claims. Whatever the "Beacon" protocol was supposed to do, ImmediaNet left no public documentation, no RFC, no open-source implementation — and the company itself has no meaningful presence on the web today.

This is more common than you might expect. The IANA registry contains hundreds of ports registered by companies that have since dissolved, pivoted, or been acquired, leaving behind orphaned registrations with no living steward. Port 3657 is one of them: officially claimed, practically abandoned.

No Known Unofficial Uses

There are no widely documented unofficial uses of port 3657. No major application or protocol has adopted it as a default. If you're seeing traffic on this port, it's worth investigating — it's not expected noise from a common service.

What's Actually on This Port

If you want to know what's listening on port 3657 on your machine:

macOS / Linux:

# Show what process is listening on port 3657
lsof -i :3657

# Or with ss (Linux):
ss -tlnp | grep 3657

Windows:

netstat -ano | findstr :3657

The output will show the process ID. On Linux and macOS, lsof will show the process name directly.

If something unexpected shows up on this port, cross-reference the process name against what you know is running. Unassigned or orphaned ports occasionally get used by malware precisely because they're unlikely to be firewalled and their traffic blends into the noise.

Why Orphaned Ports Matter

When a company registers a port and then disappears, the registration doesn't go away. IANA doesn't actively reclaim ports from defunct organizations, which means the registered range has accumulated decades of ghost entries. This matters because:

• Firewall rules may reference port names from the registry that correspond to nothing running
• Security scanners flag traffic on registered ports as potentially anomalous — which is useful precisely because it usually is
• New services sometimes take over orphaned ports informally, creating confusion between the registered name and the actual use

Port 3657 is uncontested territory. Whatever ImmediaNet built, it never shipped widely enough to leave a mark. The port is yours to use — but document it if you do.