Port 456: macon-udp & scohelp — The Forgotten Assignment

Port 456 is assigned. Officially. By IANA. To two services: macon-udp on UDP and scohelp on TCP.¹

But if you search for what these protocols actually do, you'll find almost nothing. A few port database entries. A mention that scohelp was part of SCO UnixWare 7's default HTTP server installation.² And that's it.

This is what happens to protocols that fade from use but never get unassigned.

What the Well-Known Ports Range Means

Port 456 sits in the well-known ports range (0-1023), the most restricted and prestigious section of the port number space.³ These ports are assigned by IANA through rigorous review processes—"IETF Review" or "IESG Approval"—because this range is both the smallest and the most densely allocated.⁴

As of RFC 6335, approximately 76% of well-known ports were assigned.⁴ Getting a well-known port requires documenting why the registered ports range (1024-49151) won't work. The bar is high.

Port 456 cleared that bar. Twice. Once for macon-udp, once for scohelp.

What We Know About These Protocols

macon-udp: Assigned to UDP port 456. Purpose unknown. No widely recognized software uses it.¹ The name suggests it might be related to some network management or communication system, but no documentation survives in public archives.

scohelp: Assigned to TCP port 456. Part of SCO's Unix systems, specifically UnixWare 7, where it ran an HTTP server for help documentation.² SCO faded from relevance decades ago. The protocol remains assigned.

Neither protocol has known security vulnerabilities. Not because they're secure—because they're not used enough to attack.⁵

Why This Matters

The well-known ports range is finite. There are exactly 1,024 ports in this space. Once assigned, ports rarely get reclaimed, even when their protocols die.

Port 456 is a perfect example: two official assignments for protocols that have effectively disappeared, occupying space that could theoretically be used for something else. But IANA doesn't reassign ports lightly. Backward compatibility matters, even for forgotten services.

This is the Internet's version of legacy code. The registry keeps growing, assignments accumulate, and even dead protocols leave permanent marks.

How to Check What's Listening on Port 456

If you want to see whether anything is actually using port 456 on your system:

On Linux or macOS:

sudo lsof -i :456
sudo netstat -tuln | grep 456

On Windows:

netstat -an | findstr :456

Chances are, you'll find nothing. Port 456 is assigned, but it's not used.

The Unassigned Port Problem

Not every port in the well-known range is assigned. Some are officially "Unassigned"—available for allocation if someone requests them and can justify the need.³ Others are "Reserved"—held by IANA for special purposes.⁴

Port 456 is neither. It's assigned. But to protocols that barely exist anymore.

This creates a strange situation: the port is taken, but it's also effectively empty. It's Schrödinger's port assignment—simultaneously occupied and abandoned.

Related Ports

Port 456 sits in a neighborhood of equally obscure assignments:

• Port 457 — scohelp (UDP)⁶
• Port 450 — tserver (Computer Supported Telecommunication Applications)
• Port 464 — kpasswd (Kerberos password changing)

Some of these ports still serve active protocols. Port 456 does not.

Port 456 is a monument to protocols that once mattered enough to get official assignments but didn't matter enough to survive. The Internet remembers everything, even the things it's forgotten.