Port 633 is officially assigned to servstat—Service Status update from Sterling Software. But Sterling Software hasn't existed since 2000. The service is gone. The port remains.
What servstat Was
The official IANA registry lists port 633 as assigned to "servstat" for both TCP and UDP protocols.1 It was a service status update mechanism created by Sterling Software, a major software company in the 1980s and 1990s.
What exactly did servstat do? The historical record is thin. No RFC defines it. No modern documentation explains it. It was proprietary software from an era when companies built their own protocols without publishing specifications.
The Company That Owned It
Sterling Software was founded in Dallas in 1981. By the mid-1990s, it had grown into one of the largest software and computer services firms in the world.2
On February 14, 2000, Computer Associates acquired Sterling Software in a stock transaction worth $4 billion—one of the largest software acquisitions in history.3 Computer Associates absorbed Sterling's products, sold off parts of the business, and the servstat service quietly disappeared.
The port assignment didn't disappear. It's still there in the IANA registry, a permanent reservation for a service that no longer exists.
Why This Port Matters
Port 633 sits in the well-known ports range (0-1023). These ports are controlled by IANA and require special permissions to use on most systems. They're supposed to be reserved for fundamental Internet services.
But many well-known ports are ghosts. They were assigned to companies and protocols in the 1980s and 1990s, when the Internet was smaller and port numbers seemed abundant. The companies vanished. The services died. The ports remain locked.
Port 633 is one of them. It can't be reassigned—IANA doesn't revoke well-known port assignments. So it sits there, unused, a monument to the impermanence of technology.
What Runs on Port 633 Today
Probably nothing. The servstat service is gone. Sterling Software is gone.
If you see traffic on port 633, it's either:
- Legacy software that never got updated
- Something unofficial repurposing the port
- A misconfiguration
- Malware using an obscure port to hide
To check what's listening on port 633 on your system:
If nothing appears, the port is silent—as it probably should be.
The Lesson of Ghost Ports
The Internet is full of these. Ports assigned to protocols no one uses. Services no one remembers. Companies that no longer exist.
Port 633 is a reminder: the infrastructure layer outlasts the applications built on top of it. Sterling Software is gone. Computer Associates absorbed it and moved on. But the port assignment remains, carved into the registry, permanent.
Twenty-five years from now, someone will look at today's well-known ports and wonder what half of them were for. The cycle continues.
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