Port 1933 sits in the registered port range — the 1024 to 49151 band where organizations and vendors claim numbers for specific purposes. It is not unassigned. IANA records it under the service name xmapi, registered for IBM's License Manager Management Agent, sometimes called the MT Agent.1
You are almost certainly not running it.
What the Registered Service Is
IBM's License Manager is a software licensing infrastructure — the component that tracks and enforces license compliance across IBM software installations, particularly in mainframe and z/OS environments. The MT Agent is the monitoring piece: it reports license usage back to a central License Manager server.
Port 1933 (TCP and UDP) is the default port for that agent's communication.2
This is a narrow, enterprise-specific use. If you're running IBM z/OS or legacy IBM enterprise software with license management configured, this port may be active. If you're not, it isn't.
What the Registered Port Range Means
Registered ports (1024–49151) are documented with IANA but are not reserved the way well-known ports (0–1023) are. Any process on any system can open a registered port without special privileges — the registration is informational, not enforced.3
This matters for port 1933 specifically: because the registered use is obscure and rare, this port is occasionally repurposed by:
- Custom internal applications that picked a number arbitrarily
- Development servers that happened to bind here
- Malware that chose it precisely because nothing watches it
An open port 1933 on a system that isn't running IBM license management software warrants a look.
How to Check What's Listening
On Linux or macOS:
On Windows:
Match the PID to a process in Task Manager or with tasklist to identify what's actually there.
Why Unassigned-ish Ports Matter
The port registry is not a wall — it's a directory. Registering a port tells you what should be there, not what is. Port 1933 being registered to IBM's licensing agent doesn't mean that's what's running on your machine if you see it open.
The practical lesson: an unfamiliar open port is worth examining regardless of what the registry says. The registry describes intent. lsof describes reality.
Frequently Asked Questions
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