Port 2623: LMDP — A Name Without a Protocol

What Port 2623 Is

Port 2623 sits in the registered port range (1024–49151). These are ports that vendors and developers can formally claim through IANA — not for well-known services like HTTP or SSH, but for applications, protocols, and services that need a stable, recognizable address.

IANA's registry shows port 2623 assigned to LMDP on both TCP and UDP, with a contact named Ken Bailey.¹ That's everything the record contains. No RFC. No description beyond the four letters. No link to documentation.

LMDP doesn't appear in any published RFC. It doesn't appear in Wireshark's protocol dissectors. It doesn't appear in any known software documentation. Whatever it stood for — Lightweight Message Delivery Protocol, Licensing Management Data Protocol, something else entirely — it left no public trace.

What This Means in Practice

If you see traffic on port 2623, it isn't LMDP — at least not any version anyone has documented. It's more likely:

• Application-defined traffic: Some software chose this port because it was quiet and available
• Test or internal services: Development tools occasionally bind to obscure registered ports
• Misconfiguration: Something pointed at the wrong port number

The registration doesn't create a protocol. It just reserves a number. LMDP reserved 2623, and then apparently never showed up to use it.

How to Check What's Listening

If port 2623 is active on your system:

On Linux/macOS:

# Show what process is listening on port 2623
ss -tlnp | grep 2623

# Or with lsof
lsof -i :2623

On Windows:

netstat -ano | findstr :2623

The output will show the process ID (PID). Cross-reference that against your running processes to identify what opened the port.

Why Ghost Ports Matter

The registered port range has tens of thousands of entries. Many look like LMDP: a name, a contact, no documentation. Some were registered for products that were never shipped. Some were registered for internal protocols that stayed internal. Some were registered by people who moved on, changed jobs, or simply stopped.

This matters for security. An unrecognized service on any port deserves scrutiny — but an unrecognized service on an obscure, undocumented port deserves more. If port 2623 is open on a machine and you didn't put it there, find out what did.

The IANA registry is a record of intention, not implementation. Port 2623 proves the gap between the two can be infinite.