Port 20023: Unassigned — A Number in the Registered Range

Port 20023 is officially unassigned. It has no registered service, no RFC defining its purpose, no protocol that calls it home. It's one of thousands of ports in the registered range that exist as possibilities rather than certainties.

What Range This Port Belongs To

Port 20023 sits in the registered ports range (1024-49151).¹ These ports are managed by the Internet Assigned Numbers Authority (IANA), which assigns them to specific services upon application by a requesting entity.

Unlike well-known ports (0-1023) which require IETF review and are reserved for common protocols, registered ports can be requested by organizations or developers who need a standardized port number for their application. The process is documented in RFC 6335.²

But not every port in this range gets assigned. Port 20023 is one of the gaps — officially marked as "Unassigned" in the IANA registry.³

Why Unassigned Ports Matter

The existence of unassigned ports is what makes the port system flexible. When you run a development server on your laptop, it needs a port. When a new protocol gets designed, it needs a number. When an application wants to communicate without conflicting with well-known services, it needs somewhere to listen.

Unassigned ports are that somewhere. They're the breathing room in a system that would otherwise run out of numbers.

Most applications that use unassigned ports do so temporarily or locally — a database running on your machine, a game server among friends, a microservice in a container that only talks to other containers. They don't need IANA registration because they're not trying to become Internet-wide standards.

Known Unofficial Uses

Port 20023 has been referenced in some network security databases as potentially associated with malware or trojans.⁴ This doesn't mean the port itself is dangerous — it means that at some point, malicious software used this port for communication.

This is common with unassigned ports. Because they have no official owner, malware authors sometimes choose them for command-and-control traffic or data exfiltration. But any port can be used this way. The number itself is neutral.

Some references mention "VPControl" as a service name for this port,⁵ but this does not appear in the official IANA registry and may represent an unofficial or obsolete assignment.

How to Check What's Listening on This Port

If you want to know whether anything on your system is using port 20023, you can check with standard networking tools.

On Linux or macOS:

# Using lsof to check what's listening on port 20023
sudo lsof -i:20023

# Using netstat to see all listening ports
netstat -tulpn | grep 20023

# Using ss (modern replacement for netstat)
ss -tulpn | grep 20023

On Windows:

# Using netstat to check port 20023
netstat -ano | findstr :20023

These commands will show you if any process is listening on or connected to port 20023, along with the process ID (PID) so you can identify what program is using it.⁶

The Architecture of Absence

Port 20023 has no story because it was never given one. It sits between port 20022 and port 20024, both also unassigned, in a stretch of unclaimed numbers that runs for thousands of ports.

This absence is structural. The port system works because there are 65,535 possible port numbers and only a fraction of them are spoken for. The unassigned ports aren't failed assignments or forgotten protocols — they're the system working as designed.

When you see "Unassigned" in the registry, you're seeing the space that makes the Internet flexible enough to accommodate whatever comes next.