Port 2935: QTP — A Registered Port for a Protocol That Never Arrived

What This Port Is

Port 2935 sits in the registered port range (1024–49151). These are ports that applications and services can register with IANA to stake a claim — a way of saying "this is ours, don't step on it." Unlike the well-known ports below 1024, registered ports don't require elevated privileges to open, and registration doesn't require that the protocol actually see wide deployment.

Port 2935 is registered for QTP — the Quick Transaction Protocol — on both TCP and UDP.¹

The Protocol Behind the Name

QTP was designed in 1999 to solve a specific, practical problem: Point-of-Sale terminals and Credit Authorization Terminals needed to communicate with IP-based processing systems, and the existing solutions were all proprietary. If you wanted a third-party Network Access Server to handle your payment terminal traffic, you were at the mercy of whatever gateway your vendor had built.

QTP proposed an open standard. It aimed for fast connection setup, high-volume session handling, fault tolerance, and network independence — working over PSTN, ISDN, X.25, or Frame Relay. The authors were engineers from INETCO Systems, Alcatel Australia, and Ascend Communications.²

The draft expired in November 1999. It was never adopted as an RFC. The IANA registration persists, a nameplate on an empty office.

What's Probably Actually on This Port

Almost nothing. If you see traffic on port 2935 on a machine you control, it's almost certainly an application that chose the port arbitrarily — or something you didn't authorize. One historical footnote: the flight simulator Falcon 4 has been observed using this port,³ which says less about the port and more about how game developers pick numbers.

How to Check What's Listening

If you want to see whether anything is using port 2935 on your system:

macOS / Linux:

sudo lsof -i :2935

or

ss -tlnp | grep 2935

Windows:

netstat -ano | findstr :2935

If something shows up, the process ID in the output will tell you what it is.

Why Unassigned and Ghost Ports Matter

The registered port range exists to prevent collisions — to make sure two applications don't accidentally choose the same port and confuse each other. But registration requires no proof of survival. QTP claimed port 2935, never shipped, and the reservation remained.

This happens more than you'd expect. The registered range contains protocols that were proposed, partially implemented, and then abandoned. Their port numbers are occupied in name, free in practice. For most network operators, these ghost registrations are invisible noise. For anyone scanning ports or configuring firewalls, they're a reminder that the port registry is a historical document as much as a living standard.