Port 855: Unassigned — A door that was built but never opened

Port 855 is officially unassigned. IANA—the organization that maintains the authoritative registry of port numbers—has kept ports 855-859 in reserve but has never allocated them to any protocol or service.

What "Unassigned" Means

The port number system divides the 65,536 available ports into three ranges:

• Well-known ports (0-1023) — Reserved for system services and widely-used protocols. Requires administrative privileges to bind to these ports.
• Registered ports (1024-49151) — Available for applications to register with IANA for specific services.
• Dynamic/ephemeral ports (49152-65535) — Available for temporary use by client applications.

Port 855 falls in the well-known range. This means it was set aside decades ago when the port system was designed, reserved for protocols that were important enough to need privileged access. But that protocol never came.

Why Unassigned Ports Matter

Not every port needs to be filled. The gaps in the registry tell a story about how the Internet evolved differently than its architects expected.

When the port system was designed in the early 1980s, the well-known range (0-1023) was sized generously—room for 1,024 fundamental protocols. But the Internet didn't need 1,024 fundamental protocols. It needed a few dozen core services (DNS, HTTP, SMTP, SSH) and then thousands of specialized applications that could live in the registered range.

Port 855 sitting empty isn't a failure. It's proof that the designers built margin into the system. They planned for a future they couldn't predict and left space for protocols that might never arrive.

Checking What's Listening

Even though port 855 has no official assignment, something could still be listening on it. Applications can bind to any port they want, regardless of IANA assignments. To check what's actually using port 855 on your system:

On Linux/macOS:

sudo lsof -i :855
# or
sudo netstat -tulpn | grep :855

On Windows:

netstat -ano | findstr :855

If you see something listening on port 855, it's either:

• A misconfigured application that chose an arbitrary port
• Custom software that deliberately picked an unassigned port to avoid conflicts
• Potentially malicious software trying to hide in an unexpected place

The Quiet Gaps

In a registry where port 22 carries SSH sessions at 3am, where port 443 handles every encrypted web page you visit, where port 25 has been delivering email since 1982—port 855 remains silent.

Not every door needs to be opened. Not every address needs to be claimed. Sometimes the empty spaces in a system are just as important as the filled ones.

Port 855 is available. It's been available for over forty years. And it might stay available forever.

• Port 855 (tcp/udp) :: SpeedGuide¹
• Service Name and Transport Protocol Port Number Registry²
• List of TCP and UDP port numbers - Wikipedia³