Port 1563: Cadabra License Manager — The ghost in the registry

Port 1563 is officially registered with IANA for both TCP and UDP, assigned to a service called cadabra-lm (Cadabra License Manager).¹² It sits in the registered ports range—ports 1024 through 49151—where IANA assigns numbers to specific services upon request.

But here's what makes this port strange: the software it was registered for has vanished.

What is the Cadabra License Manager?

Good question. The port databases all list "Cadabra License Manager" as the official service for port 1563.³⁴ But if you search for information about this software, you'll find almost nothing. No company website. No documentation. No download links. No user communities.

What you will find is Cadabra—a computer algebra system for field theory calculations.⁵ It's open-source, actively maintained, and has nothing to do with license management. Different software entirely. Just happens to share part of the name.

The Cadabra License Manager appears to be abandoned. Or it was proprietary software for a company that no longer exists. Or it was renamed and the port registration was never updated. The port remains reserved, officially assigned, while the software itself has faded into obscurity.

What the registered ports range means

Port 1563 lives in the registered ports range (1024-49151). These ports are assigned by IANA when someone submits an application saying "we're building this service and we need a port number."⁶

Unlike well-known ports (0-1023) which require privileged access and are tightly controlled, registered ports are available to any service that bothers to apply. IANA doesn't verify that the software still exists or that anyone actually uses it. Once registered, the port stays registered.

This is how you end up with ports like 1563—officially assigned to software that may no longer exist, or exists but is so niche that the Internet has forgotten it.

What might be listening on port 1563

Just because a port is registered to a specific service doesn't mean that's what you'll find using it. Unassigned or obscure registered ports are often repurposed:

• Malware sometimes uses registered ports with obscure assignments, betting that network administrators won't recognize unusual traffic
• Custom applications might choose port 1563 specifically because it's registered (so it won't conflict with dynamic ports) but unused (so it won't conflict with actual services)
• Nothing at all—most ports on most machines are closed, listening for no one

To check what's actually listening on port 1563 on your system:

# On Linux or macOS
sudo lsof -i :1563
netstat -an | grep 1563

# On Windows
netstat -ano | findstr :1563

If you find something listening on port 1563, it might be the Cadabra License Manager. Or it might be something else entirely that borrowed an abandoned port number.

Why forgotten ports matter

Port 1563 is a reminder that the port registry is not just technical infrastructure—it's archaeological. Every registered port is evidence that someone built something. Most of those things still exist. Some have become essential Internet services. Others, like cadabra-lm, have vanished.

The port number remains. A forwarding address to a building that no one occupies anymore. Officially reserved, technically available, practically forgotten.

This is how the Internet accumulates history. Not by preserving software, but by preserving the numbers that software once used.