Port 1689 has no officially assigned service. IANA lists it as unassigned in the registered port range. There is no RFC, no protocol, no standard that claims it.
What Range It Belongs To
Port 1689 falls in the registered port range (1024-49151). This range is where IANA formally assigns ports to specific applications and protocols — SSH at 22, HTTP at 80, HTTPS at 443, and thousands of others. Registered ports require an application to submit a request and receive an official assignment.
Port 1689 never received one.
That said, "unassigned" doesn't mean unused. The registered port range has over 48,000 ports, and IANA's registry has gaps. Software vendors, internal tools, and network administrators reach into those gaps all the time.
Known Unofficial Uses
Port 1689 occasionally appears in two contexts:
Microsoft KMS (neighbor port): Microsoft's Key Management Service — the system that handles volume license activation for Windows and Office in corporate environments — runs on port 1688 by default.1 Some configurations, scripts, and firewall rules reference 1689, likely due to manual port changes, off-by-one configuration errors, or organizational customization. It is not a standard KMS port, but the proximity matters when reading firewall logs.
Java Management Extensions: Some sources list port 1689 in relation to Java Management Extensions (JMX) monitoring setups, though this is informal and non-standard.
Neither use is official. If you see traffic on port 1689, it warrants investigation rather than assumption.
How to Check What's Listening
To see if anything is using port 1689 on your machine:
macOS/Linux:
or
Windows:
The process ID in the output can be cross-referenced with Task Manager or Get-Process to identify the owning application.
Why Unassigned Ports Matter
The registered port range is not fully allocated. Unassigned ports are a normal part of the ecosystem — they represent space the Internet has not yet committed to a particular purpose.
This matters for security: software that squats on unassigned ports can be harder to detect and block, because no baseline expectation exists for what should be there. Unexpected traffic on an unassigned port like 1689 is worth examining. It might be legitimate internal software. It might be something else.
The presence of traffic tells you something is running. The absence of an assignment tells you nothing is supposed to be.
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