Port 3376: CD Broker — A Registered Ghost

What This Port Is

Port 3376 sits in the registered port range (1024-49151). These ports are managed by IANA, and anyone could historically request a reservation by submitting an assignment application. Thousands of companies and developers did exactly that in the 1990s and early 2000s, claiming port numbers for products they were building.

Port 3376 was claimed. IANA lists it as "cdbroker" — a service called CD Broker, registered by an individual named Moon Ho Chung. Both TCP and UDP are registered.

That's essentially all that's known.

What CD Broker Was

No documentation survives explaining what CD Broker did. The name suggests something plausible from its era: CD-ROM drives were expensive, and network-based CD sharing was a real category of software in the 1990s. A "broker" for CDs could have been a service that pooled CD-ROM drives across a local network, letting multiple machines access the same physical disc. This was a legitimate enterprise problem before ISOs and digital distribution made it irrelevant.

But this is speculation. The product left no manuals, no forum posts, no archived websites. Whatever CD Broker was, it didn't survive into the searchable era of the Internet. The only trace is a single row in the IANA port registry. ¹

What the Registered Range Means

When you see a port in the 1024-49151 range, it means:

• The port is not reserved for OS-level services (that's ports 0-1023)
• It may have an IANA-registered purpose, or it may be unassigned entirely
• Applications can use these ports without special OS privileges
• On Windows, macOS, and Linux, software routinely binds to registered ports for its own network communication

A registered port doesn't mean the software is still running anywhere. It means someone once filled out a form.

What Might Be Running on This Port Today

If you see traffic on port 3376 on a modern network, it isn't CD Broker. It's almost certainly one of:

• A custom internal application that chose this port arbitrarily
• A game server, development service, or tool that uses it as a default
• Something you installed that picked an available port

If something unexpected is listening on this port, check it.

How to Check What's Listening

Linux / macOS:

# Show what process is listening on port 3376
ss -tlnp | grep 3376

# Or with lsof
lsof -i :3376

# Check for both TCP and UDP
ss -tulnp | grep 3376

Windows:

netstat -ano | findstr :3376

Then match the PID to a process name:

tasklist | findstr <PID>

Why Registered Ports Like This Matter

The registered port system is, in practice, a historical record of software that existed. Most of the 48,000+ ports in the registered range were claimed by applications that are now defunct, abandoned, or simply never widely deployed. They sit in the IANA table indefinitely, reserved for software that no longer runs.

This matters for one reason: collision avoidance. When a developer needs a port for a new application, they check what's registered to avoid accidentally using a port that something else is already using — or once used. An old CD-sharing tool from the late 1990s still holds its reservation, which is a small but real service to anyone building network software today.

Port 3376 is not a security risk. It's not commonly exploited. It's just a number that was claimed, and then forgotten.