Port 428: OCS_CMU — A Well-Known Port Nobody Remembers

Port 428 sits in the well-known range (0-1023), the ports assigned by IANA for foundational Internet services. These are the ports that require root privileges to bind on Unix systems, the ports reserved for protocols important enough to merit global coordination.

Port 428 is officially assigned. But to what, exactly, nobody seems to remember.

The Official Assignment

According to IANA's registry, port 428 is assigned to OCS_CMU (also written as ocs-cmu).¹ The assignment exists for both TCP and UDP, but with a critical notation: the TCP assignment is marked as "historic" and "not usable with many common service discovery mechanisms."²

The CMU suffix suggests Carnegie Mellon University. The service name appears in official registries. But what OCS_CMU actually was—what protocol it spoke, what problem it solved, who created it, when it ran—this knowledge appears to have vanished.

The port number remains. The institutional memory is gone.

What "Historic" Means

When IANA marks an assignment as "historic," it means the assignment exists for backward compatibility, but the service is no longer in active use. The TCP variant of port 428 carries an additional warning: it's not usable with modern service discovery mechanisms.

This is a port that officially belongs to something, but that something has effectively ceased to exist.

The Unofficial Use: IBM ServeRAID Manager

Port 428 also appears in documentation for IBM ServeRAID Manager, server management software for monitoring and configuring ServeRAID RAID controllers.³ This represents an unofficial use—ServeRAID Manager's primary ports are 34570-34580, but port 428 shows up in some contexts.

When official assignments become historic, unofficial uses sometimes fill the void.

Well-Known But Forgotten

Port 428 occupies the well-known range, which means:

• Ports 0-1023: Assigned by IANA for foundational services
• Assignment requires IETF review: Getting a well-known port assigned requires formal standardization
• Root privileges required: Binding to these ports requires elevated permissions on Unix systems

Approximately 76% of well-known ports are assigned.⁴ Port 428 is among them. But unlike port 22 (SSH) or port 80 (HTTP), this one leads to a dead end—an assignment to a service lost to time.

Checking What's Listening

To see if anything is using port 428 on your system:

Linux/Mac:

sudo lsof -i :428
# or
sudo netstat -tlnp | grep :428

Windows:

netstat -ano | findstr :428

Most systems will return nothing. The official assignment exists, but the service is gone.

Why Abandoned Ports Matter

Port 428 is a reminder that the Internet has a history, and history has gaps. Services were created, standardized, assigned port numbers, and then disappeared. The infrastructure outlived the institutional memory.

The port registry is archaeological. Every assigned number represents a decision someone made, a service someone built, a problem someone tried to solve. Port 428 exists because someone at Carnegie Mellon needed a port number for OCS_CMU. The assignment went through IANA's process, was added to the official registry, and remains there today.

But what OCS_CMU was, we no longer know.

This is the genuine strangeness of the well-known ports: they're meant to be permanent, but the knowledge of why they exist is not.

Related Ports

• Port 22: SSH - Still very much in use, institutional memory intact
• Port 80: HTTP - The foundation of the web, thoroughly documented
• Port 427: Assigned to SLP (Service Location Protocol) - Also historic but better documented