Port 2789: Media Agent — Registered, Forgotten, Available

What Port 2789 Is

Port 2789 sits in the registered ports range (1024–49151). These ports require an application to formally claim them with IANA, unlike the ephemeral ports above 49151, which anyone can use freely.

IANA's registry shows port 2789 assigned to a service called "media-agent", registered to a contact at a domain (brm.com) that no longer resolves. The software this port was reserved for appears to have never shipped, or shipped and disappeared. Either way, it's not something you'll encounter in the wild.

The Registered Range: What It Means

The registered ports range was designed to prevent collisions — software vendors claim a port so their application doesn't step on someone else's. Registration doesn't require payment, open-source code, or continued existence. You file paperwork with IANA, IANA records it, and that's the end of IANA's involvement.

This means the registered range has thousands of ports in exactly port 2789's situation: formally claimed, practically available. No RFC governs them. No active software uses them. They're squatted land.

Known Unofficial Uses

Cisco Unified Communications Manager has historically used port 2789 for JTAPI (Java Telephony API) application server communication in some configurations.¹ This is an internal communication channel between Cisco voice infrastructure components, not something exposed to the public Internet.

The broader 2700–2800 range has also been documented in connection with KnowShowGo, a peer-to-peer application that is itself long defunct.²

Beyond these historical associations, port 2789 has no notable active usage.

How to Check What's Listening

If you see port 2789 active on a system, check:

On Linux/macOS:

# Show what process has port 2789 open
ss -tlnp | grep 2789
# or
lsof -i :2789

On Windows:

netstat -ano | findstr :2789
# Then look up the PID:
tasklist | findstr <PID>

On a standard system, you should see nothing. An active listener warrants investigation — it's either legitimate software you've installed (Cisco UCM, a backup agent, custom tooling) or something that shouldn't be there.

Why These Ports Matter

The registered range exists to give the Internet a shared coordination layer. When a developer registers a port, they're making a promise: "this port means this service, everywhere." That promise only holds when the software survives.

Port 2789 is a small example of what happens when it doesn't. The registration persists in IANA's records indefinitely. The software is gone. Other developers either avoid the port out of caution or use it anyway knowing the registration is effectively abandoned.

This friction — between formal registration and practical reality — is why most modern software prefers dynamic port assignment or user-configurable ports over relying on IANA allocations.