Port 568 belongs to the well-known ports range (0-1023), the tier reserved for services assigned by the Internet Assigned Numbers Authority (IANA). Getting a well-known port means your protocol is officially recognized. But recognition doesn't guarantee remembrance.
What Is Microsoft Shuttle?
According to the IANA registry, port 568 is assigned to ms-shuttle ("microsoft shuttle"), registered by Rudolph Balaz of Microsoft for both TCP and UDP.1
That's where the trail goes cold.
There's no RFC documenting the protocol. No Microsoft documentation explaining what it does. No technical specifications, no implementation guides, no evidence that anyone outside Microsoft ever used it. The registration exists, but the protocol itself has vanished into history.
The Ghost Protocol
This is the genuinely strange thing about port assignments: they're permanent records of intentions that may no longer exist. Someone at Microsoft—decades ago, based on the registration style—needed a port for something called "Shuttle." They followed the process, got the assignment, and then... silence.
Was it an internal tool that never shipped publicly? An experiment that got abandoned? A service so deeply embedded in Microsoft's infrastructure that it never needed public documentation? We don't know.
What we know: port 568 is officially assigned. What we don't know: whether anything is still listening.
Well-Known but Unknown
The well-known ports range (0-1023) carries an assumption: these are services everyone recognizes. Port 80 is HTTP. Port 443 is HTTPS. Port 22 is SSH. These are the foundational services of the Internet.
Port 568 sits among them, officially recognized but practically forgotten. It's a reminder that IANA assignments are historical records—they tell you what someone once intended to build, not what necessarily still exists.
Security Considerations
Because there's no public documentation of what ms-shuttle actually does, there's no public knowledge of its security characteristics. If you find something listening on port 568:
- It's likely not the original Microsoft Shuttle (unless you're on a very old Microsoft internal network)
- It could be malware using an obscure port to hide
- It could be a modern application that chose an "available" port without knowing it was assigned
The obscurity doesn't make it safe. It makes it suspicious.
How to Check What's Listening
On Linux or macOS:
On Windows:
If something is listening on port 568, you should know what it is and why it's there.
Why This Matters
Unassigned ports are straightforward—nobody officially owns them. But officially assigned ports with no living documentation are something stranger. They're archaeological artifacts in a registry that's supposed to be a living document.
Port 568 tells a story about how the Internet's nervous system works: assignments are forever, but protocols are mortal. The registry remembers what we've forgotten.
Every well-known port represents someone's belief that this service matters enough to claim a permanent spot in the Internet's address space. Most of the time, they were right. Port 568 is what happens when they weren't—or when the world changed and left the protocol behind.
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