Port 289 is officially unassigned. According to the IANA Service Name and Transport Protocol Port Number Registry, both TCP and UDP on port 289 have no registered service, no official purpose, and no assigned protocol.1
It's an empty room in a very exclusive building.
What the Well-Known Range Means
Port 289 falls within the System Ports range (0-1023), also called the well-known ports.2 These ports were reserved by the Internet Assigned Numbers Authority for protocols that would become fundamental infrastructure. SSH lives at 22. HTTP at 80. HTTPS at 443.
But not every number got claimed.
The well-known range was designed with space to grow. When the port number system was formalized, IANA reserved the entire range for official assignments through an IETF Review or IESG Approval process. Only protocols that met certain standards of documentation and implementation could claim a well-known port.
Port 289 never met anyone who wanted it.
Why Keep Ports Unassigned?
Unassigned ports exist for future protocols. When someone creates a new standard that needs a well-known port, IANA can assign one of these empty spaces. The alternative would be chaos: people picking their own numbers, services conflicting, network administrators unable to enforce policies because nothing is documented.
Unassigned ports are not free-for-all spaces. RFC 6335 explicitly warns against "port squatting"—using unassigned numbers in deployed software without IANA approval.2 If you build something on port 289 and it spreads, IANA can't track that usage. Later, when they assign 289 to a legitimate protocol, your software breaks.
The emptiness is intentional. It's organizational capacity.
Checking What's Listening
Just because IANA says port 289 is unassigned doesn't mean nothing is using it on your machine. Software can bind to any port. Malware sometimes hides on unassigned ports precisely because they're not monitored.
Check what's actually listening:
On Linux/Mac:
On Windows:
If something responds, investigate what process owns it. Unassigned ports should usually be silent.
The Architecture of Empty Space
There are hundreds of unassigned ports in the well-known range. Port 289 is one of many. They represent something important about how the Internet was designed: with room to grow.
The architects didn't know what would be needed in 2026. They just knew that reserving space was wiser than scrambling to retrofit a system later. The well-known ports weren't fully allocated because no one could predict which protocols would matter.
Port 289 might stay empty forever. Or someone might write an RFC tomorrow proposing a protocol that needs it. Either way, the space exists.
That's not waste. That's architecture.
Related Ports
- Port 0: Reserved, used for dynamic port allocation
- Ports 1-1023: The well-known/system ports range
- Ports 1024-49151: Registered ports, less restrictive assignment process
- Ports 49152-65535: Dynamic/private/ephemeral ports, never assigned
Frequently Asked Questions
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