Port 686 sits in the well-known port range (0-1023), officially assigned by IANA to a service called HCP-Wismar (Hardware Control Protocol Wismar). Both TCP and UDP versions exist in the registry.1
But here's the strange part: nobody seems to remember what it was for.
The Ghost Protocol
Search the Internet for HCP-Wismar and you'll find the same thing repeated across dozens of port databases: "Hardware Control Protocol Wismar, port 686." That's it. No RFC. No documentation. No company website. No user forums discussing configuration issues. No GitHub repositories implementing the protocol.
It exists in IANA's registry. It has a name. It has a port number. But the actual protocol—what it controlled, who built it, why Wismar (a city in Germany) is in the name—has vanished.2
What We Know
Port number: 686
Transport protocols: TCP and UDP
Range: Well-known ports (0-1023)
Official assignment: HCP-Wismar
Status: Assigned but essentially unused
The well-known port range is supposed to be reserved for fundamental Internet services—protocols important enough to claim a number below 1024. Port 686 got that designation. And then it disappeared.
The Other Tenant
Some sources mention that port 686 has also been used by ipcserver, a component of macOS's now-deprecated NetInfo system.3 NetInfo was Apple's directory service in the pre-OS X days, used for managing network configuration and user accounts.
This is one of those situations where an assigned port got quietly repurposed. HCP-Wismar existed on paper. Apple needed a port for internal RPC services. Port 686 was available in practice, if not in theory. So it got used.
NetInfo itself is now obsolete—replaced by Open Directory in modern macOS. Which means port 686 might be serving neither its original purpose nor its borrowed one.
Why Unassigned Ports Matter
Port 686 isn't technically unassigned—it has HCP-Wismar in the registry. But it's functionally orphaned, which raises an interesting question: what happens to ports that were assigned but never used, or used and then abandoned?
The port number system has 65,535 addresses. The well-known range has only 1,024. That's valuable space. Port 686 occupies one of those slots for a protocol that either never took off or faded into obscurity so completely that the Internet forgot it existed.
There's no mechanism for reclaiming these ghost ports. Once assigned, they stay assigned. The registry is permanent. So port 686 will likely carry the name HCP-Wismar forever, even if nobody alive remembers what that means.
Checking What's Listening
If you want to see whether anything is actually using port 686 on your system:
On Linux or macOS:
On Windows:
Most systems will return nothing. Port 686 is assigned, but silent.
The Quiet Corners
The port system has hundreds of assignments like this. Protocols that were registered in the 1990s or early 2000s, used by a single organization or a piece of hardware that's long since obsolete. They're not dangerous. They're not broken. They're just... there.
Port 686 is a reminder that the Internet has a long memory and no delete function. Once something goes into the registry, it stays. Even if the protocol dies. Even if the company vanishes. Even if the purpose is forgotten.
Somewhere in IANA's records, HCP-Wismar is still listed as the official tenant of port 686. And somewhere—maybe—there's a piece of hardware in a forgotten server room still listening on that port, waiting for a protocol that the rest of the world has moved on from.
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