Port 225: Reserved — A Placeholder in the Internet's Blueprint

Port 225 is Reserved. It has no assigned service, no protocol, no purpose except to exist in a protected state.

What "Reserved" Means

Port 225 is part of the well-known ports range (0-1023), the most privileged section of the Internet's port system. But unlike ports 22 (SSH) or 443 (HTTPS), port 225 was never assigned to anything. It belongs to a reserved block spanning ports 224-241, set aside in RFC 1060 by Jon Postel in 1990.¹²

Reserved ports are held by IANA for future use or special purposes. They're not available for assignment. They're placeholders—deliberate gaps in the addressing system, kept empty just in case.

The Jon Postel Connection

Jon Postel was the original keeper of the Internet's numbers. He created IANA (Internet Assigned Numbers Authority) and manually managed protocol numbers, port assignments, and domain registrations from his office at USC's Information Sciences Institute. When you see "Reserved [JBP]" in RFC 1060, those are his initials: Jonathan B. Postel.³

He died in 1998, but his reservations remain. Port 225 is part of his legacy—a small administrative decision that became permanent infrastructure.

Why Reserve Ports?

The Internet's architects were planning for unknowns. In 1990, they couldn't predict every protocol that would need a port. So they reserved blocks for:

• Future protocol extensions
• Experimental services
• Potential expansion of existing ranges
• Administrative flexibility

Port 225 is one of these insurance policies. It costs nothing to keep it reserved. It provides flexibility if future standards require well-known port assignments.

The Reality of Unassigned Well-Known Ports

Port 225 lives in valuable addressing space. Well-known ports require root privileges to bind on Unix systems. They're the prime real estate of the port system. And port 225 sits empty.

Most reserved ports stay reserved forever. The Internet moves slowly when changing foundational infrastructure. The chance of port 225 ever being officially assigned is vanishingly small.

How to Check What's Using Port 225

Even though port 225 is officially reserved, something could be listening on it on your system. Here's how to check:

On Linux/Mac:

# Check if anything is listening
sudo lsof -i :225

# Or use netstat
netstat -an | grep :225

On Windows:

# Check listening ports
netstat -an | findstr :225

If you see something bound to port 225, it's either:

• A misconfigured service using an unusual port
• Malware hiding in reserved space
• A custom application using port 225 unofficially

The Honest Truth

Port 225 exists because someone in 1990 thought it might be needed someday. That day never came. It's been sitting empty for over 30 years.

The Internet is built on decisions like this—small administrative choices that become permanent because changing them is harder than leaving them alone. Port 225 is a fossil in the protocol layer. Reserved, protected, and unused.

It will probably stay that way forever.

Related Ports

• Ports 224-241: The entire reserved block that includes port 225
• Port 222-223: Unassigned ports just below the reserved range
• Port 242: Beginning of another assigned range

Last Updated: 2026-02-03