Port 1621: Unassigned — Available for use

Port 1621 is an unassigned port in the registered range (1024-49151). It has no official service assigned by IANA, which means any application can use it without needing to register or get permission.

What the Registered Range Means

Ports 1024-49151 are the registered range. Unlike well-known ports (0-1023) which require root privileges and official assignment, registered ports are available for applications to claim. If your software needs a consistent port to listen on, you can pick one from this range. Port 1621 is one of thousands in this category—unclaimed, available, waiting.

Known Uses

While port 1621 has no official assignment, it has at least one documented real-world use:

Micro Focus Vulnerability Manager — Unix agents use port 1621 to communicate with Core Services.¹ These agents connect to report security vulnerabilities, missing patches, and configuration issues. If you run netstat -na on a system with Vulnerability Manager installed, you'll see entries for port 1621—sometimes dozens of them, as agents check in and report what they've found.

Some connections may show CLOSE_WAIT status, meaning the communication finished but the connection hasn't been fully released yet. This is normal behavior and typically clears quickly.

Why Unassigned Ports Matter

The Internet needs breathing room. Not every port can have an official assignment. The registered range exists so that applications can pick a port and use it consistently without bureaucracy. Port 1621 might be unassigned by IANA, but it's not unused. Somewhere right now, security agents are connecting through this port, checking systems, reporting vulnerabilities.

This is how the port system works: official assignments for the protocols everyone uses (HTTP, SSH, DNS), and thousands of unassigned ports for everything else.

How to Check What's Using Port 1621

On Linux or macOS:

sudo lsof -i :1621

Or using netstat:

netstat -na | grep 1621

On Windows:

netstat -ano | findstr :1621

If something is listening on port 1621, these commands will show you what.

Protocol Support

Port 1621 works with both TCP and UDP:

• TCP — Connection-oriented, reliable delivery. Most applications using port 1621 (like Vulnerability Manager agents) use TCP for guaranteed communication.
• UDP — Connectionless, faster but no delivery guarantees. Available if an application needs it.

Security Considerations

Since port 1621 has no standard service, seeing unexpected traffic on this port should raise questions:

• If you're not running Vulnerability Manager or another known application, why is something listening here?
• Malware sometimes uses unassigned ports specifically because they're less monitored than well-known ports
• Check what process is bound to the port before assuming it's legitimate

The lack of an official assignment makes port 1621 flexible—but that flexibility cuts both ways.