Port 506 sits in the well-known ports range (0-1023), officially assigned by the Internet Assigned Numbers Authority to a service called ohimsrv. Both TCP and UDP protocols are registered. The contact is Scott Powell at openhorizon.com. That's where the trail goes cold.
What We Know
According to IANA's official registry1, port 506 belongs to ohimsrv—presumably "Open Horizon Image Server" or something similar. The scattered references that exist suggest it was used for medical imaging: remote access and control for diagnostic imaging software, allowing healthcare professionals to view and manage medical images from various machines2.
That's the extent of what the Internet remembers.
What We Don't Know
When was ohimsrv created? Who built it? Which hospitals used it? Is it still running somewhere, quietly doing its job behind a firewall where search engines can't see? Or did the software die, leaving only its port number behind?
The company appears to be gone. The service has no documentation we can find. The contact email is attached to a domain that still exists but tells us nothing.
Port 506 is a ghost in the registry.
The Well-Known Ports Range
Port 506 sits in the well-known ports range (0-1023), which means someone had to apply to IANA for this assignment. These ports are reserved for system services—the foundational protocols and applications that needed coordination to avoid conflicts.
Getting a well-known port number meant your service mattered enough to need global recognition. Someone thought ohimsrv was important enough to register. Someone at IANA agreed.
Now it's effectively abandoned, but the port number remains assigned. That's how the registry works: ports don't get recycled just because the service disappears. The number 506 belongs to ohimsrv, even if ohimsrv belongs to history.
Why This Matters
The Internet is built on ports that still work. Port 80 for HTTP. Port 443 for HTTPS. Port 22 for SSH. These are the ports that carry the weight of the living Internet.
But scattered throughout the registry are ports like 506—assignments that made sense once, services that solved real problems, and then vanished. Medical imaging systems that were replaced. Protocols that lost to competitors. Software that couldn't survive the transition from one decade to the next.
Port 506 reminds us that the Internet has a history we're already losing. Not every protocol gets remembered. Not every service leaves enough of a trace for future engineers to understand what it did or why it mattered.
Checking What's on Port 506
If you want to see what's actually listening on port 506 on your system:
Linux/macOS:
Windows:
Chances are, nothing is listening. Port 506 is probably quiet on your machine, just like it's quiet across most of the Internet.
But somewhere—maybe in a hospital basement, maybe on a legacy system nobody's touched in years—ohimsrv might still be running, still serving medical images, still using port 506 exactly as intended.
We just can't see it anymore.
The Honest Truth
Port 506 is assigned, but barely used. It exists in the registry but not in practice. It's a reminder that the Internet's official records preserve assignments long after the services themselves have disappeared.
Not every port has a rich story. Some ports are just numbers in a database, attached to services we can no longer find. Port 506 is one of those. It existed. Someone used it. That's all we can say for certain.
The Internet remembers the port number. It doesn't remember the story.
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