Port 429: OCS_AMU — A Ghost in the Registry

Port 429 sits in the well-known port range (0-1023), officially assigned to a service called OCS_AMU. The service is marked as "historic" in IANA records.¹ What that means in practice: something once ran here that mattered enough to get an official port number, but has since faded into obscurity.

Nobody can tell you what OCS_AMU actually did.

What We Know

Port 429 is assigned to both TCP and UDP protocols for the OCS_AMU service.² The assignment appears in the official IANA Service Name and Transport Protocol Port Number Registry—the authoritative list of what port numbers are supposed to be used for.

The "historic" designation means the service is no longer in active use and isn't compatible with many modern service discovery mechanisms. It's a fossil in the registry.

The Well-Known Port Range

Port 429 belongs to the well-known ports (0-1023), also called system ports. These are assigned by IANA and historically required root/administrator privileges to bind to on Unix-like systems. They represent the oldest and most fundamental services of the Internet—plus a few like OCS_AMU that didn't survive the journey.

Getting a well-known port number assigned was once a significant event. It meant your protocol mattered. Port 429 has that assignment, but the service it was assigned to has vanished from active use.

Why Historic Ports Matter

The Internet doesn't delete its history. Once a port number is assigned, it generally stays assigned—even when the service dies. This creates archaeological layers in the port registry: services from the 1980s and 1990s that once seemed essential, now marked historic, their purpose lost to time.

These historic assignments serve a purpose: they prevent new services from accidentally conflicting with old implementations that might still exist somewhere. Port 429 might be marked historic, but somewhere, on some ancient server in some forgotten data center, OCS_AMU might still be running.

The Internet assumes immortality for everything it touches.

Checking What's Using Port 429

Even though OCS_AMU is historic, something could be listening on port 429. Here's how to check:

On Linux/macOS:

# See what's listening on port 429
sudo lsof -i :429

# Or using netstat
sudo netstat -tulpn | grep :429

# Check if the port is open on a remote system
nmap -p 429 hostname

On Windows:

# Check what's using port 429
netstat -ano | findstr :429

If you find something listening on port 429, it's either a very old implementation of OCS_AMU, or—more likely—a modern application repurposing an abandoned port number.

The Honest Truth

Port 429 is a placeholder for something forgotten. The IANA registry lists the name (OCS_AMU) but provides no description, no RFC reference, no documentation of what it was supposed to do. The service disappeared, but its port number remains—a gravestone with a name but no epitaph.

This is common in the well-known port range. Of the 1,024 possible well-known ports, many are assigned to services that nobody uses anymore. They represent decisions made decades ago, protocols that seemed important at the time, infrastructure that has since been replaced or abandoned.

Port 429 is one of these ghosts. It got a number. It got registered. Then it faded away, leaving only the assignment behind.