Port 1687: nsjtp-ctrl — A Name Without a Story

What This Port Is

Port 1687 sits in the registered ports range (1024–49151). These ports are technically reserved through IANA — the Internet Assigned Numbers Authority — the body that hands out port numbers the way a city hands out street addresses.

The IANA registry lists port 1687 as nsjtp-ctrl, registered by an individual named Orazio Granato. Port 1688 is registered to the same person as nsjtp-data — suggesting a control/data pair, a common pattern where one port handles commands and another handles the actual transfer.¹

What does nsjtp stand for? The registry doesn't say. There's no description. No RFC. No linked documentation. Just a name, a contact, and silence.

What We Can Infer

The "ctrl/data" naming pattern appears in protocols like FTP (ports 21 and 20) — a separate channel for commands and another for the payload. Whatever nsjtp was designed to do, it followed this established pattern.

Some port databases have speculatively connected port 1687 to "Network ScanJet Transfer Protocol" — a potential HP scanner-related protocol — but this appears to be an inference from the initials, not documentation. HP's actual Jetdirect scanner ports are well-documented elsewhere and do not include 1687.²

In the absence of documentation, port 1687 in the wild is most likely used by whatever application happens to need it — custom software, local services, or development tools that grabbed an available registered port without caring about the nominal reservation.

How to Check What's Listening

If you see port 1687 active on a machine you manage, here's how to investigate:

On Linux or macOS:

ss -tlnp | grep 1687
# or
lsof -i :1687

On Windows:

netstat -ano | findstr :1687
# Then look up the PID:
Get-Process -Id <PID>

The process name will tell you far more than the port number ever could.

Why These Gaps Exist

The registered ports range contains over 48,000 slots. IANA has filled most of them over decades, but many registrations are sparse — a name and a contact with no accompanying documentation. This isn't unusual. The registry was never designed to be a technical specification; it's closer to a land registry than a building code. You can stake a claim without ever breaking ground.

Port 1687 is one of thousands of ports where someone registered a name, and the world moved on without noticing.