Port 1513: Fujitsu-DTC — A ghost in the registry

Port 1513 is officially registered with IANA for a service called fujitsu-dtc, assigned to Fujitsu Systems Business of America, Inc.¹ Both TCP and UDP protocols were reserved for this port.

The problem? Nobody seems to remember what fujitsu-dtc actually did.

The Ghost Service

The IANA registry lists "fujitsu-dtc" as the service name, but there's almost no documentation about what this service was, when it was deployed, or whether anyone actually used it. Fujitsu Systems Business of America no longer exists under that name—the company has gone through multiple reorganizations and rebrandings since the 1990s when this port was likely registered.²

Port 1514, the port immediately after, was also registered to the same company for "fujitsu-dtcns" (Fujitsu DTC Name Service), suggesting there was at least a small ecosystem of related services.³ But like 1513, there's virtually no trace of what these services actually did or who used them.

Why These Ports Matter

Port 1513 represents something important about how the Internet works: once a port is registered, it stays registered. Even when the company changes names, the product disappears, and the last person who understood the protocol retires.

This isn't a flaw—it's intentional. Port assignments are permanent to prevent conflicts. If port 1513 were reassigned to a new service, any ancient Fujitsu equipment still running somewhere in a basement could suddenly start sending packets to the wrong service. Chaos.

So the registry fills up with ghosts. Thousands of ports registered in the 1980s and 1990s for services that vanished decades ago, but their reservations remain forever.

The Registered Port Range

Port 1513 sits in the registered port range (1024-49151). These ports are assigned by IANA to specific services upon request, but unlike well-known ports (0-1023), they don't require root privileges to use.

Any application can technically listen on port 1513—there's no enforcement. But the IANA registration means you shouldn't use it for something else, because somewhere, somehow, there might still be a piece of Fujitsu equipment trying to speak fujitsu-dtc.

Checking What's Listening

If you want to see whether anything is actually using port 1513 on your system:

# On Linux or macOS
sudo lsof -i :1513
sudo netstat -tulpn | grep 1513

# On Windows
netstat -ano | findstr :1513

Chances are: nothing. The port sits empty, reserved for a service that nobody uses anymore.

The Archaeology of the Registry

The IANA port registry is archaeological. Every assignment tells a story—who needed network services in 1991, which protocols mattered in 1995, which companies were important enough to get their own port numbers.

Port 1513 tells the story of Fujitsu Systems Business of America, a company that once built enterprise systems important enough to warrant their own registered ports. The service disappeared. The company reorganized. But the port remains, a permanent marker of something that once existed.

This is how the Internet remembers.