Port 476 sits in the well-known ports range (0-1023), officially assigned by IANA to a service called "tn-tl-fd1."1 The registration lists Ed Kress of ThinkNet as the contact. That's where the trail goes cold.
What We Know (and Don't Know)
The port is assigned to both TCP and UDP protocols. The service name "tn-tl-fd1" follows a naming pattern that suggests ThinkNet Transport Layer Field Device 1—but that's speculation. No RFC documents this protocol. No manual explains what it does. Forum posts from 2007 show confused users asking "what is this?" with no answers.2
This is a ghost port. Officially registered, but functionally unknown.
The Well-Known Ports Range
Port 476 belongs to the well-known ports range (0-1023), reserved by IANA for system services and widely-used protocols. Getting a port assigned in this range used to require demonstrating that your protocol would be widely deployed and standardized. Port 476 was assigned, which means at some point IANA believed tn-tl-fd1 would matter.
But it didn't. Or it did briefly, and then vanished. Or it still runs somewhere, and no one talks about it.
Why Ghost Ports Matter
The IANA port registry is supposed to be the authoritative map of the Internet's nervous system. But it's full of entries like this—services that were registered decades ago, companies that no longer exist, protocols that never took off or were replaced by something better.
Port 476 is a reminder that the Internet isn't just the protocols that won. It's also the ones that lost, the experiments that failed, the startups that folded before their documentation made it online. The registry preserves their names, but not their stories.
Checking What's Listening
If you want to see if anything is actually using port 476 on your system:
On Linux/Mac:
On Windows:
If something is listening on port 476, it's almost certainly not the original tn-tl-fd1 service. It's more likely malware, a misconfigured application, or a developer who picked an "unused" port without checking the registry.
The Honest Truth
Port 476 teaches us something uncomfortable about the Internet: documentation rots faster than code. Companies disappear. Engineers move on. Email addresses go dead. The registry preserves the registration, but not the reason.
Somewhere, maybe on an old server in a closet, tn-tl-fd1 might still be running. Or maybe it never ran anywhere at all. Maybe someone at ThinkNet reserved the port "just in case" and then the company pivoted, or shut down, or the project got canceled.
We'll probably never know. Port 476 is a ghost—present in the registry, absent from the Internet, haunting the well-known ports range with a name that means nothing anymore.
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