Port 3561: BMC-OneKey — A Ghost in the Registry

What Port 3561 Is

Port 3561 sits in the registered port range — the band from 1024 to 49151 where organizations can formally claim a number for their software through IANA, the Internet Assigned Numbers Authority.

It's officially assigned to BMC-OneKey, registered by BMC Software in August 2002 for both TCP and UDP. ¹

That's where the clean answers end.

The Ghost in the Registry

BMC Software is a real company — one of the larger enterprise IT management vendors, known for products like BMC Helix, server automation tools, and mainframe operations software. They've been around since 1980.

But "BMC-OneKey"? That product has effectively disappeared. No public documentation. No product pages. No archived announcements. A 2002 IANA registration is the clearest evidence it ever existed.

This happens more than you'd expect. A product gets registered, then it's discontinued, renamed, absorbed into something else, or simply never widely deployed. The port number stays reserved in the IANA registry regardless — there's no formal process to reclaim it. The registered port space is full of these fossils: numbers officially spoken for by products that no longer speak.

Port 3561 is one of them.

What the Registered Port Range Means

Anyone can request a registered port from IANA. The process is lightweight — fill out a form, provide a contact, describe the service. IANA records the assignment. There's no verification that the software actually gets built, ships, or survives.

This is by design. The system prioritizes coordination over gatekeeping. The goal is preventing two applications from accidentally claiming the same number and colliding. Whether the product thrives afterward is not IANA's concern.

The registered range has over 48,000 possible ports. Thousands are assigned to products that are obscure, defunct, or enterprise-only software most people will never encounter.

What Might Actually Be Using Port 3561 on Your System

If you see traffic on port 3561, it almost certainly isn't BMC-OneKey. It's more likely:

• Custom application behavior — developers pick available ports for internal services, APIs, or inter-process communication without checking the registry
• Dynamic assignment — operating systems sometimes pull from the upper registered range when allocating ephemeral ports for outbound connections, depending on system configuration
• Something specific to your environment — enterprise software often uses non-standard ports internally

To see exactly what's listening:

macOS / Linux:

# Show what process is bound to port 3561
sudo lsof -i :3561

# Alternative with ss (Linux)
ss -tlnp | grep 3561

Windows:

# Show listening ports with process IDs
netstat -ano | findstr :3561

# Then find the process by PID
tasklist | findstr <PID>

Why Unassigned and Ghost Ports Matter

Port numbers are a coordination mechanism, not a lock. When a port is unassigned or registered to a dormant product, it's available territory — and software routinely uses available territory. Firewalls and security tools that block traffic based on port numbers need to account for this: the number tells you less than you might hope about what's actually flowing through it.

The only way to know what's using a port is to look at the process behind it.