Port 726: Unassigned — A quiet address in valuable space

Port 726 exists in a strange position. It sits in the well-known ports range—the addresses from 0 to 1023 that were supposed to represent the essential services of the Internet. And yet, it has never been assigned.¹

What Range This Port Belongs To

Port 726 is part of the well-known ports (also called system ports), which span from 0 to 1023. These ports are controlled by IANA (Internet Assigned Numbers Authority) and are meant to be assigned only to fundamental Internet services.²

This is the most valuable address space in the port system. Port 22 is SSH. Port 80 is HTTP. Port 443 is HTTPS. Every port in this range was supposed to matter.

Port 726 has remained unassigned.

Why Unassigned Ports Exist

Not every well-known port has been claimed. When the port system was designed, 1,024 addresses felt like enough room for every important protocol. But protocols were created more slowly than anticipated, and not every number from 0 to 1023 ended up being needed.

Unassigned ports in this range serve as a reserve. If a new fundamental Internet protocol emerges—something that genuinely needs to operate at the system level—these ports are available. They're held in trust for future infrastructure.

Port 726 is part of that reserve. It belongs to the range where ports are assigned deliberately, carefully, only when the service justifies the privilege of a well-known address.

Checking What's Listening

Even though port 726 has no official assignment, something might be listening on it on your system. To check:

On Linux or macOS:

sudo lsof -i :726
# or
sudo netstat -tulpn | grep :726

On Windows:

netstat -ano | findstr :726

If nothing appears, the port is closed. If something is listening, you've found a service using an unassigned port—likely a custom application or an unofficial use.

What This Port Means

Port 726 is a reminder that the Internet was built with room to grow. Not every address needs to be filled. Not every door needs to be opened.

In a system where most well-known ports were claimed decades ago, the unassigned ones represent possibility. They're the addresses waiting for something important enough to deserve them.

For now, port 726 remains quiet. And that's exactly what an unassigned port should be.

How to Check If Port 726 Is in Use on Your System

If you want to see whether anything on your network is using port 726:

Using nmap:

nmap -p 726 localhost

Using netcat:

nc -zv localhost 726

If the port is closed, you'll see a connection refused message. If it's open, something is listening—and you've found an unofficial use.