Port 3729: fksp-audit — A Registered Port with a Forgotten Past

What Port 3729 Is

Port 3729 sits in the registered port range (1024–49151). These are ports that software vendors, protocol designers, and organizations can formally claim through IANA — the Internet Assigned Numbers Authority — so their applications have a predictable, consistent port number.

Unlike well-known ports (0–1023), registered ports don't require special operating system privileges to bind. Any application can use them. But registration signals intent: this port, for this purpose, for this product.

The Official Record

IANA lists port 3729 as:

• Service name: fksp-audit
• Description: Fireking Audit Port
• Protocols: TCP and UDP
• Registration date: April 2003¹

That's the entirety of the public record.

Fireking: A Ghost in the Registry

"Fireking" appears to have been a software product or company that built some kind of network audit tool in the early 2000s. They registered port 3729, named their service fksp-audit, and then disappeared.

No public documentation of the Fireking protocol exists. No RFC was written. No technical specification was published. Whatever audit traffic once flowed through this port, it did so privately — and the product (or company) has since ceased to have any public presence.

This is more common than you'd think. The registered port range has hundreds of entries like this: ports claimed during software's active life, then orphaned when the product was discontinued, the company was acquired, or the developer simply moved on. IANA keeps the record. The Internet forgot everything else.

What's Actually on Port 3729 Today

If you see traffic on port 3729, it almost certainly isn't Fireking software. More likely candidates:

• Dynamic or ephemeral port assignment — operating systems pick ports from this range for outgoing connections
• Custom internal applications — developers choose available registered ports for their own services
• Port scanners or security tools — probing during a network audit

To see what's actually listening on this port on your system:

# Linux / macOS
sudo ss -tlnp | grep 3729
# or
sudo lsof -i :3729

# Windows (Command Prompt, run as Administrator)
netstat -ano | findstr :3729

If nothing is listening, the port is idle. If something is, the tool will show you the process name and PID.

Why Unassigned and Orphaned Ports Matter

The registered port range is a shared resource with over 48,000 slots. When products disappear without releasing their registered ports, those slots stay claimed in the registry indefinitely. It's a minor form of namespace pollution — not harmful, but a quiet record of software that didn't outlast its registration.

For practical purposes, port 3729 is available. Just check with IANA first¹ if you're building something you intend to distribute — the paperwork exists so two applications don't collide on the same port number by accident.