Port 2718: pn-requester2 — A Ghost in the Registry

Port 2718 is technically assigned. IANA lists it as pn-requester2 — PN REQUESTER 2 — on both TCP and UDP. There is no RFC behind it. No known software claims it. No documentation explains what "PN REQUESTER" was, who asked for the registration, or what problem it was meant to solve.¹

It is a ghost in the registry: named but not explained, claimed but never inhabited.

The Range It Belongs To

Port 2718 falls in the registered ports range (1024–49151). This is the middle tier of the port number system:

• Well-known ports (0–1023) are reserved for core protocols — HTTP at 80, HTTPS at 443, SSH at 22. You need elevated privileges to listen on these.
• Registered ports (1024–49151) are assigned by IANA upon request. Anyone can apply. The bar is low, and the registry reflects that — thousands of entries with no active users, abandoned software, and company names that no longer exist.
• Dynamic/ephemeral ports (49152–65535) are assigned on-the-fly by operating systems for outgoing connections.

The registered range was meant to bring order to the middle of the port space. In practice, it's part library catalog and part archaeological dig.

What "pn-requester2" Might Have Been

The name suggests a pairing — "pn-requester2" implies there was a first, "pn-requester," assigned to port 2717. Both registrations exist. Neither has any surviving documentation.²

"PN" could stand for many things in networking contexts: Packet Network, Private Network, Proprietary Name. Without documentation, we can't know. The registration may date from an era when IANA processed requests with minimal scrutiny and many registrants never followed through with a real implementation.

This is not unusual. Scan the registered port space and you will find hundreds of entries like this — names without stories, claims without software.

The Mathematical Coincidence

The number 2718 is the first four digits of e, Euler's number (≈ 2.71828182845...). It is one of the most important constants in mathematics — the base of the natural logarithm, the rate at which things grow and decay, the number that makes calculus elegant.³

No evidence suggests the port was assigned with this in mind. It is probably a coincidence. But it means that if you are a mathematician running something on a high-numbered port, 2718 has a certain appeal.

What's Actually on This Port

On any given system, almost certainly nothing official. Port 2718 may be used by:

• Custom internal applications that needed a high-numbered port and picked something arbitrary
• Developer tooling or local services running temporarily during development
• Nothing at all — most ports are silent on most machines

To check what is listening on port 2718 on your system:

# macOS / Linux
sudo lsof -i :2718

# Linux alternative
ss -tlnp | grep 2718

# Windows
netstat -ano | findstr :2718

If something appears, the process ID will tell you exactly what software is using it.

Why Unassigned Ports Matter

Every connection your computer makes uses two port numbers: one on your end (ephemeral, chosen by the OS from the dynamic range) and one on the remote end (the service's port). When you see an unfamiliar port number in your network traffic, it tells you something — either a known service is running there, or something has claimed a space in the port system that was meant to be organized.

The registered port range exists because the alternative — every application picking a random number — would be chaos. The registry says "these numbers mean these things." Port 2718 is a reminder that the registry is an imperfect map. The territory does what it wants.