Port 1680 lives in the registered port range — numbers 1024 through 49151, where applications and services stake their claims with IANA. But IANA's official registry lists port 1680 as unassigned. No service. No protocol. No owner.
The Ghost in the Database
Search the web and you'll find older port databases listing 1680 as "microcom-sbp" — Microcom's Serial Bridge Protocol. Microcom was a real company: a modem manufacturer founded in 1980 that created the Microcom Networking Protocol (MNP), the error-correction standard that most 1980s modems used before V.42 took over.1
Compaq acquired Microcom in 1997.2 The company dissolved. Whatever "SBP" was — a serial bridge protocol, likely for connecting serial terminal hardware to networked software — no public RFC or specification exists. The protocol has no documentation anyone can find. The company that would know is gone.
So port 1680 is an orphan. Some databases inherited the "microcom-sbp" label from older records. IANA never officially assigned it, or the assignment lapsed when the company ceased to exist.
What This Port Range Means
Registered ports (1024–49151) require applications to register with IANA, but registration isn't mandatory the way well-known ports (0–1023) are governed. Organizations can use these ports informally. Over time, some registered entries become abandoned as companies close and products die.
Port 1680 is one of thousands of gaps in the registered range — numbers that were once claimed or considered but now sit empty.
What Might Actually Be on Port 1680
If you see traffic on port 1680, it's almost certainly a local application that chose this port for its own purposes. Common candidates include custom internal software, development servers, or gaming clients looking for an uncrowded port.
Some security scanners flag port 1680 as historically associated with malware that squatted on obscure unassigned ports to avoid detection — a common technique, not a specific threat tied to this number.3
How to Check What's Listening
On Linux or macOS:
On Windows:
The process ID in the output will tell you exactly what's using the port.
Why Unassigned Ports Matter
The port space is finite: 65,535 numbers, divided among well-known services, registered applications, and the ephemeral range your OS uses for outbound connections. Unassigned ports like 1680 are the unclaimed territory — available for new services, temporary use, and the occasional historical mystery.
They also matter for security: an unexpected listener on an unassigned port is worth investigating. Nothing should be there unless you put it there.
Frequently Asked Questions
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