Port 478: SPSC — The Assigned But Unknown

Port 478 sits in the well-known ports range (0-1023), officially assigned by IANA to a service called "spsc." But here's the strange part: nobody seems to know what spsc actually is.

The Ghost Assignment

The Internet Assigned Numbers Authority maintains the authoritative registry of port assignments.¹ Port 478 appears in that registry, marked for both TCP and UDP, assigned to "spsc." The entry exists. The assignment is real. But the protocol itself has vanished into obscurity.

Unlike neighboring ports with clear purposes and documented protocols, port 478 has no RFC, no specification, no community of users, no stack overflow questions, no GitHub projects. It's a name in a directory with no forwarding address.

What We Know (And Don't Know)

Official Assignment: Port 478, TCP and UDP, service name "spsc"²

Documentation: None found

Active Use: No evidence of deployment

Protocol Specification: Unknown

Some port databases incorrectly associate port 478 with the Simple Network Paging Protocol (SNPP),³ but SNPP's actual assigned port is 444, with implementations commonly using 7777 as an alternative.⁴ The confusion might stem from proximity in the port range or database errors that propagated across the web.

The Well-Known Ports Range

Port 478 belongs to the well-known ports (0-1023), also called system ports.⁵ This range is reserved for services fundamental enough to warrant IANA assignment and privileged access. Binding to these ports typically requires root or administrator privileges on Unix-like systems.

The presence of port 478 in this privileged range suggests it was intended for something significant, assigned by IANA through their formal process. But whatever that something was, it left no trace beyond the registry entry itself.

Why This Matters

The Internet's port system works because of coordination. IANA assigns ports to prevent conflicts, to create shared understanding, to let software find software across the network. Port 478 represents the flip side: an assignment made, a number reserved, but no protocol that anyone remembers using it.

It's possible spsc was:

• A protocol proposed but never deployed
• An internal service that never saw public use
• A name collision or administrative artifact
• Something so niche it left no digital footprint

We don't know. The assignment exists without the story.

Checking Port 478

To see if anything is listening on port 478 on your system:

Linux/macOS:

sudo lsof -i :478
sudo netstat -tulpn | grep :478

Windows:

netstat -ano | findstr :478

If something appears, you've found either a system with historical context or a security issue (malware has been known to use unassigned or obscure ports to avoid detection).⁶

The Unassigned Majority

Most ports in the well-known range have clear assignments and active use. But scattered throughout the registry are entries like port 478—names without narratives, assignments without evidence of purpose.

These ghost entries serve as reminders that the Internet's infrastructure isn't just the protocols we use every day. It's also the protocols we thought we'd need, the services that never materialized, the plans that changed direction before deployment.

Port 478 was assigned to spsc. Whether spsc ever carried a single packet, we may never know.