Port 483 is officially registered with IANA under the service name "ulpnet," assigned to someone named Kevin Mooney. It supports both TCP and UDP. Beyond that, the trail goes cold.
The Mystery of ulpnet
There is no RFC defining ulpnet. No technical documentation. No known implementation. The name might stand for "Upper Layer Protocol Network" (ULP is a common networking acronym), but that's speculation. Nobody seems to know what ulpnet was supposed to do, whether it was ever implemented, or why it needed a well-known port.
Port 483 exists in the IANA registry the way a reservation exists in a restaurant ledger after the party never shows up.
What Is the Well-Known Port Range?
Ports 0-1023 are called well-known ports or system ports. IANA manages this range, assigning ports to protocols that are supposed to be standardized and widely used. Getting a port in this range typically requires an RFC or formal specification.
Port 483 is an anomaly. It has the assignment but not the protocol.
Why This Matters
The well-known port range is finite. There are only 1,024 ports in this range, and hundreds are already assigned. Every port reserved for a protocol that doesn't exist is a port unavailable for protocols that do.
Ulpnet is a reminder that the Internet's infrastructure was built by humans making requests, assigning numbers, and sometimes walking away. Not every port assignment became a living protocol. Some are just names in a registry, archaeological artifacts of projects abandoned or never started.
Checking Port 483 on Your System
You can see if anything is listening on port 483:
Linux/macOS:
Windows:
If something is using port 483, it's almost certainly not ulpnet. It's probably a custom application that picked an obscure port number to avoid conflicts.
The Honest Truth
Port 483 is assigned but effectively unassigned. It has a name but no known protocol. It occupies space in the well-known range without a known purpose. Whether ulpnet was a real project that died quietly or a placeholder that was never filled, the result is the same: a port number waiting for a protocol that will probably never arrive.
The Internet is full of these small mysteries. Ports reserved for services that faded into obscurity. Names in registries with no corresponding documentation. Port 483 is one of them—a ghost protocol haunting the well-known port range.
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