Port 1656 is registered to dec-mbadmin-h, a management service from Digital Equipment Corporation (DEC). Both TCP and UDP variants are registered with IANA.1
The company no longer exists. The protocol is forgotten. The port number remains in the registry.
What Is DEC-MBAdmin-H?
Nobody really knows anymore.
The name suggests "DEC Mailbox Administration" (the "h" likely denotes a variant or specific implementation). Digital Equipment Corporation was one of the pioneering computer companies of the 1960s through 1990s, creating the PDP and VAX series of minicomputers that shaped early computing and networking.2
DEC developed numerous management protocols for their systems. dec-mbadmin-h was apparently one of them. The documentation has been lost to time. The engineers who built it have moved on. The systems that used it have been decommissioned.
The Registered Port Range
Port 1656 falls in the registered port range (1024-49151). This range is maintained by IANA for services that aren't quite universal enough to warrant a well-known port (0-1023), but are official enough to deserve registration.3
To get a port in this range, someone had to submit an application to IANA. Someone at DEC filled out the paperwork. Someone at IANA approved it. The port was assigned. And then the world moved on.
What Happened to DEC?
Digital Equipment Corporation was acquired by Compaq in 1998 for $9.6 billion—at the time, the largest acquisition in the computer industry.4 Compaq itself was acquired by HP in 2002. The DEC brand disappeared. The technology was absorbed, retired, or abandoned.
Many DEC protocols went with it. Port 1656 is one of the artifacts.
Why This Port Matters
Port 1656 is a reminder that the Internet has a long memory.
The IANA registry doesn't automatically delete entries when companies disappear or protocols become obsolete. The port numbers remain, officially assigned, even when nobody uses them anymore. This creates a kind of archaeological record—layers of old assignments that tell the history of networking.
There are hundreds of ports like 1656. Registered to companies that no longer exist. Protocols that nobody runs. Services that vanished when the last server was shut down.
They're ghosts in the registry. But they're honest ghosts—they actually existed once.
Is Anything Actually Using Port 1656?
Probably not for dec-mbadmin-h.
In theory, any application can listen on port 1656. The registration doesn't prevent other software from using it—it's just a notation in a database. If you find something listening on 1656, it's more likely to be:
- Custom application software that picked the port arbitrarily
- Malware that chose an obscure port to avoid detection
- A legacy DEC system that actually is still running (unlikely, but possible)
How to Check What's Listening
On Linux or macOS:
On Windows:
If nothing returns, nothing is listening. That's the expected result for most systems.
Related Ports
Port 1655 is registered to dec-mbadmin (without the "-h")—the parent or sibling protocol.5 It's equally obscure. Equally forgotten.
Together they occupy two consecutive port numbers in the registry, artifacts of a management system that once mattered to someone.
Frequently Asked Questions About Port 1656
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