Port 831 is unassigned. It used to belong to something—NETCONF over BEEP—but that protocol never shipped, so the IETF gave the port number back.
What Was It Assigned To?
In 2006, port 831 was officially assigned to NETCONF over BEEP (Blocks Extensible Exchange Protocol), a network management protocol defined in RFC 4744.1 The idea was sound: use BEEP as a transport layer for the Network Configuration Protocol, enabling network administrators to manage routers, switches, and other devices remotely.
The protocol supported strong authentication via SASL (Simple Authentication and Security Layer) and encryption through TLS. Devices would connect on TCP port 831, exchange BEEP greetings, negotiate security, and then send NETCONF commands back and forth.
It looked good in the RFC. It never happened in production.
Why It Failed
RFC 4744 was marked "Historic" because the protocol was never deployed.2 Network administrators chose other NETCONF transports—primarily NETCONF over SSH (port 830), which became the de facto standard. BEEP added complexity without enough benefit. SSH was already everywhere, already trusted, already understood.
So port 831 sat empty. For 19 years.
The Release
In December 2025, RFC 9900 officially released port 831 back to IANA.3 The document cleaned up the registry, removing assignments for NETCONF transports that never saw real-world use. Port 831 was returned alongside ports 832 and 833, which were assigned to NETCONF over SOAP—another good idea that nobody wanted.
The registry now shows port 831 as unassigned. Available. Waiting for something that might actually ship this time.
What This Port Teaches
Port 831 is evidence that not every protocol succeeds. The IETF can publish an RFC, IANA can assign a port number, vendors can implement the spec—and it still might go nowhere. The Internet doesn't run on what's standardized. It runs on what gets deployed.
NETCONF over SSH won because it used infrastructure that already existed. BEEP required new stack, new libraries, new understanding. The technical merits didn't matter. The deployment friction did.
The Well-Known Range
Port 831 lives in the well-known port range (0-1023), which is managed by IANA and reserved for system services. Getting a port number in this range used to mean something—it signaled that a protocol was important enough to warrant permanent assignment.
But importance at standardization time doesn't guarantee importance at deployment time. The registry is full of well-known ports that nobody knows.
Checking What's Listening
Even though port 831 is officially unassigned, something could be using it on your system. To check:
On Linux or macOS:
On Windows:
If you see something listening, it's either leftover configuration from when NETCONF over BEEP was briefly implemented, or an application using the port unofficially. Most likely, you'll see nothing.
Why Unassigned Ports Matter
Unassigned ports aren't wasted space. They're options. Every released port is a number that can be reassigned to something new, something that might actually succeed where the previous occupant failed.
Port 831 waited 19 years for traffic that never came. Now it's free. Maybe the next protocol to claim it will actually ship.
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