Port 426 sits in the well-known port range (0-1023), officially assigned by IANA to a service called "smartsdp."1 But if you go looking for what smartsdp actually does, you'll find nothing. No protocol specification, no documentation, no active deployments. Just a name in the registry.
What We Know
Port 426 is assigned for both TCP and UDP to "smartsdp," registered by Marie Pierre Belange.2 That's it. That's the entire public record.
Some port databases claim it's used for "Integrated Client Message Service (ICMS)" for "secure client-server communication," but this appears to be speculation or conflation with another service—there's no authoritative source for this claim.3
The Well-Known Range
Port 426 belongs to the well-known port range (0-1023), which requires IANA assignment. These ports are reserved for system services and standardized protocols. Getting a port number in this range used to mean your protocol mattered enough to warrant official recognition.
But not every assignment led to widespread adoption. Some protocols were registered, implemented once or twice, then abandoned. The port number remains, a tombstone in the registry.
Why Unassigned Ports Matter
Even empty ports serve a purpose. The registry prevents collisions—if someone had actually deployed smartsdp in 1995, and someone else tried to use port 426 for a different service in 2000, chaos would follow. The assignment creates a reservation, a claim on namespace even if the service never materializes.
This is the difference between the Internet's design and its reality. The design assumes careful planning, official assignments, documented protocols. The reality is messier: services appear and vanish, protocols die, port numbers become archaeological artifacts.
Checking What's Listening
If you want to see what's actually using port 426 on your system:
On Linux/Mac:
On Windows:
Chances are, nothing is listening. Port 426 is almost certainly silent on your machine, as it is on most machines across the Internet.
The Honest Truth
Port 426 is a ghost. Someone registered it, the paperwork went through, the number was assigned. But the service either never launched, died quietly, or exists in such obscurity that the Internet has forgotten it completely.
This happens more than you'd think. The port registry is full of these ghosts—services that made sense in 1992, protocols that solved problems nobody has anymore, or ideas that never made it past the registration form.
Port 426 is a reminder: not every door leads somewhere. Some are just painted on the wall.
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