Port 197 sits in the well-known ports range (0-1023), officially assigned by IANA to something called the Directory Location Service (DLS). Both TCP and UDP. Registered, documented, technically valid.
And almost completely unused.
What DLS Was Supposed to Do
Directory Location Service was documented by Douglas E. Comer around 19901—part of the early wave of protocols designed to help computers find services on networks without manual configuration. The idea: clients could query a directory service to locate resources dynamically.
It sounded useful. It got a port number. And then the world moved on.
What Actually Happened
DLS never achieved meaningful adoption. Other directory service protocols—LDAP, DNS, later Service Location Protocol—became the standards that actually mattered2. They solved similar problems with better designs, stronger backing, or just better timing.
Port 197 remains officially assigned to DLS. The reservation stands. But finding an actual implementation listening on port 197 in the wild? Nearly impossible.
What This Port Represents
Port 197 is a ghost. Not quite abandoned—IANA hasn't reassigned it—but not alive either. It represents something important about how the Internet works:
Not every registered service survives. The port number registry is full of protocols that seemed important enough to warrant official assignment but never gained traction. Some protocols die quickly. Others linger as registered names that nobody uses.
Port 197 got its number in the well-known range, the prestigious block reserved for fundamental services. And then it became a footnote.
The Well-Known Range
Ports 0-1023 are the well-known ports, assigned by IANA for standardized services3. This is the Internet's reserved seating—ports in this range require root/administrator privileges to bind to on most systems.
The theory: important, stable services get low port numbers. HTTP gets 80. HTTPS gets 443. SSH gets 22. These are the foundations.
But not every port in this range lives up to that importance. Port 197 is proof: just because a port is "well-known" doesn't mean it's well-used.
Why Unassigned and Unused Ports Matter
The Internet's port system works because of discipline. Ports get assigned to prevent conflicts. Even if DLS never became popular, reserving port 197 means no other service can claim it and cause confusion.
This is registry hygiene. Some ports become legendary (port 22 for SSH, port 443 for HTTPS). Others become historical curiosities (port 197 for DLS). Both serve a purpose: the registry prevents chaos.
Checking What's Listening on Port 197
Want to see if anything is actually using port 197 on your system?
On Linux/Mac:
On Windows:
Chances are you'll find nothing. Port 197 is assigned but dormant—reserved for a service that barely exists anymore.
The Honest Reality
Port 197 is assigned to Directory Location Service. You can look it up in the IANA registry. You can read about it in old protocol documentation. You can verify it's technically valid.
But you'll almost never see it in use.
This is the Internet's long tail: thousands of port assignments, hundreds of forgotten protocols, decades of ideas that didn't quite work out. Port 197 is one of them—not broken, not reassigned, just quietly waiting for a purpose that never came.
The door is there. It's labeled. Nobody's home.
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