Port 1558 sits in the registered ports range (1024-49151)—the middle territory where organizations can request port assignments from IANA for their specific applications. Unlike well-known ports below 1024, these registrations are more like suggestions than universal standards.
What Registered Ports Mean
The Internet has 65,535 possible port numbers. The first 1,024 are well-known ports, reserved for fundamental services like HTTP and SSH. Ports 49,152 through 65,535 are ephemeral—temporary ports your computer assigns automatically for outbound connections.
Everything in between—ports 1,024 through 49,151—are registered ports. Organizations can apply to IANA to register a port for their software, but this doesn't mean:
- Every installation uses that port
- Other software won't use it
- The registration is enforced in any way
It's a claim, not a lock.
Known Associations
Port databases list 1558 with two historical associations:
IBM Informix databases — Various sources mention port 1558 as a port used by Informix Dynamic Server for client communication. But here's the reality: Informix doesn't have a single default port. Database administrators configure whatever port they want. Some use 1526, others use 9088, others use something entirely different. Port 1558 might have been used in examples or early documentation, but it's not baked into the software.1
Xing StreamWorks — Older port databases reference "Xing Stream Works" for streaming video on port 1558. Xing was a 1990s company that built early Internet streaming technology, long before YouTube existed. The technology is obsolete, and the company was acquired and disappeared decades ago.2
What This Actually Means
If you find port 1558 open on a system, you can't assume what's using it without checking. The registration doesn't tell you. It might be:
- An Informix database configured to use this port
- Some other database or application using an available port
- Malware that picked a random registered port
- Nothing—just noise from a port scan
The only way to know is to check.
Checking What's Listening
On Linux or macOS:
On Windows:
This shows you the actual process using the port, not what the registration claims.
Why Unassigned Ports Matter
The vast majority of the 48,128 registered ports are either unassigned or assigned to software almost nobody runs. This is actually useful. When your database, custom application, or internal service needs a port, you want to pick one that's unlikely to collide with something else.
The registered range provides thousands of options. You can pick an unassigned port or one assigned to software you're definitely not running. The registration system helps prevent conflicts between major applications, but it's not a reservation system—it's more like a phone book for port numbers.
Port 1558 is one of thousands in this middle ground. Not special enough to be well-known, not random enough to be ephemeral. Just a number waiting for software to give it meaning.
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