Port 2928: REDSTONE-CPSS — Registered, Unexplained

What This Port Is

Port 2928 is registered with IANA under the name REDSTONE-CPSS, assigned for both TCP and UDP. The registrant is listed as Jeff Looman (jeff@looman.org). Beyond that, there is no public documentation — no RFC, no open-source project, no vendor announcement.

This is not unusual. The registered ports range is full of reservations made by individuals or companies for internal or proprietary systems. Many were registered, used privately, and never publicly explained.

The Registered Ports Range

Port 2928 falls in the registered ports range: 1024 to 49151. This range works differently from the well-known ports below 1024.

• Well-known ports (0-1023): Reserved for standard, widely-used protocols — HTTP, HTTPS, SSH, DNS. Binding to them typically requires administrator privileges.
• Registered ports (1024-49151): Anyone can apply to IANA to reserve a port for a service. The assignment doesn't require a public standard or open implementation. It just prevents two organizations from accidentally colliding on the same port number.
• Dynamic/ephemeral ports (49152-65535): Used temporarily by client-side connections, assigned by the OS on the fly.

The registered range exists to reduce chaos. Without it, two separate companies could each ship software that defaults to port 2928 — and every firewall rule, every network scan, every diagnostic would be ambiguous. The reservation system is an act of courtesy to the rest of the Internet.

What CPSS Might Mean

CPSS is unexplained in any public source. Common expansions in networking contexts include:

• Control Plane Support System
• Customer Provisioning Support Service
• Custom Protocol Support Suite

None of these are verifiable for this registration. Without the registrant or source documentation, it's guesswork.

If You See Traffic on Port 2928

If something is actively listening on port 2928 on your system or network, the IANA registration doesn't explain it. Check what's actually running.

On Linux or macOS:

# Show what process is listening on port 2928
sudo lsof -i :2928

# Or with ss (more modern)
ss -tlnp | grep 2928

On Windows:

# Show listening processes
netstat -ano | findstr :2928

# Then look up the PID
tasklist | findstr <PID>

With nmap (from another machine):

nmap -sV -p 2928 <target-ip>

The -sV flag attempts to identify what service is actually responding, regardless of what IANA says the port is registered for.

Why Unresolved Registrations Matter

Port 2928's registration is a reminder that the IANA registry is a coordination tool, not a directory of running services. A registration means "we reserved this number." It does not mean the service is common, public, or even still in use.

When you're auditing a network and see traffic on a registered-but-obscure port, the right question isn't "what does IANA say?" — it's "what is actually running here?" The registry gives you a starting point. The process table gives you the answer.