Port 417: Onmux — The Ghost Protocol

What Port 417 Is

Port 417 is a well-known port (range 0-1023) officially assigned by IANA to a protocol called "Onmux."¹ It's registered for both TCP and UDP.

That's where the certainty ends.

The Mystery of Onmux

Onmux was registered by Stephen Hanna and appears in RFC 1700 (Assigned Numbers, published in 1994).² The registration includes a name, a port number, and a contact email address from the early Internet era.

What it doesn't include:

• An RFC defining the protocol
• Documentation of what Onmux does
• Evidence of actual implementation or usage
• Any mention in modern network infrastructure

The name suggests multiplexing ("mux" is a common abbreviation), but no technical specification exists to confirm this.

Well-Known Ports Range

Port 417 sits in the well-known ports range (0-1023), which IANA reserves for system-level services.³ These ports typically require elevated privileges to bind to on Unix-like systems. They represent the Internet's core services: HTTP, SMTP, DNS, SSH.

And apparently, Onmux.

The Reality

Onmux is what happens when someone reserves a port number but the protocol either:

• Never got implemented beyond an experimental stage
• Was used internally and never documented publicly
• Existed briefly and was abandoned
• Got registered optimistically and never materialized

Port 417 remains assigned to Onmux in IANA's registry, but in practice, it's unused. A ghost entry. A name without a body.

What This Means for the Port System

Not every assigned port carries traffic. Some are historical artifacts. Some are abandoned experiments. Some are corporate reservations that never went anywhere.

Port 417 is a reminder that the port registry isn't just a technical document—it's also an archaeological record of the Internet's development. Every entry tells a story, even when that story is "we don't know what happened here."

Checking What's on Port 417

To see if anything is actually listening on port 417:

# Check if port 417 is listening
sudo lsof -i :417

# Or with netstat
sudo netstat -tulpn | grep :417

# Scan with nmap
nmap -p 417 localhost

Most likely result: nothing. Port 417 is assigned but empty.