Port 20045: Unassigned — The Unclaimed Ports

Port 20045 has no official assignment in the IANA Service Name and Transport Protocol Port Number Registry.¹ It exists, but nobody owns it. No RFC defines what should run here. No protocol committee decided this port's purpose.

And yet, things use it anyway.

The Registered Ports Range

Port 20045 lives in the registered ports range (1024-49151)—a vast territory of over 48,000 possible port numbers.² IANA maintains this registry, accepting applications from developers who want to officially claim a port for their protocol or service.³

But most ports in this range remain unassigned. They're addresses without residents. Numbers waiting for meaning.

The registered range sits between two extremes:

• Below it: well-known ports (0-1023), reserved for fundamental Internet services
• Above it: dynamic/private ports (49152-65535), the ephemeral addresses assigned temporarily by operating systems

The registered range is where custom services, enterprise applications, and specialized protocols are supposed to live. If you're building a new network protocol and want a permanent address, you apply to IANA for a port in this range.

Port 20045 is not one of them.

What Actually Uses Port 20045

Officially: Nothing.

In practice: Security researchers have observed port 20045 in connection with Linux.Siggen.1830, a Linux malware variant that uses this port for command and control communications.⁴

This is the reality of unassigned ports. Without an official service claiming them, they become whatever someone decides to make them:

• Custom applications that picked a random high port
• Internal enterprise services that needed a consistent address
• Malware looking for a port that won't immediately raise red flags

There's no central registry of these unofficial uses. No documentation. They exist in the shadow space between official protocol and actual network traffic.

Why Unassigned Ports Matter

The existence of thousands of unassigned ports isn't a bug—it's a feature of how the Internet scales.

When you build a custom application that needs network communication, you need a port number. You could use a dynamic port (49152-65535), but those are temporary. Every time your application restarts, the OS might assign a different number.

Or you could pick an unassigned port in the registered range and use it consistently. Your firewall rules work. Your documentation makes sense. Your monitoring tools know what to look for.

Is this "wrong"? Not exactly. IANA's registry is a coordination mechanism, not a permission system. You don't need IANA's approval to use port 20045. You just need to be aware that:

1. Someone else might have picked the same port for their application
2. IANA could assign it officially at any time
3. If malware is using it, security tools might flag your traffic

Checking What's Listening

If you need to know what's actually using port 20045 on a specific system:

On Linux or macOS:

sudo lsof -i :20045
sudo netstat -tulpn | grep 20045
ss -tulpn | grep 20045

On Windows:

netstat -ano | findstr :20045

These commands show you the process ID, program name, and protocol for anything listening on or connected to port 20045.

If you find something unexpected, that's worth investigating.

The Gap Between Official and Real

Port 20045 represents something fundamental about how the Internet actually works versus how we document it.

The official registry—the carefully maintained list at IANA—is a map. But the map is not the territory. Real networks run real services on ports that appear nowhere in the official documentation.

Custom applications. Internal tools. Enterprise software. Malware. They all need port numbers, and most of them never bother applying for official registration.

The registered ports range exists in this strange state: officially unassigned, practically in use. Port 20045 is just one of thousands of addresses living in that gap.

Related Ports

• Ports 1024-49151 — The full registered ports range
• Ports 49152-65535 — Dynamic/ephemeral ports, assigned temporarily by the OS
• Port 20000 — Unassigned, but close to this range where Usermin (20000/tcp) and DNP (20000/tcp) have been observed
• Port 21000 — Another unassigned port occasionally used by custom applications