Port 206 sits in the well-known ports range (0–1023) with an official assignment to a protocol that's been dead for two decades. This is what happens when technology moves faster than bureaucracy.
What Runs Here
Port 206 was assigned to AppleTalk Zone Information Service (at-zis), part of Apple's proprietary networking protocol suite.1 The service helped organize AppleTalk networks into logical zones and allowed devices to discover services.
Both TCP and UDP port 206 were designated for this purpose. Neither sees legitimate use today.
The Story
In 1985, Apple released AppleTalk—a complete networking stack for Macintosh computers. Before TCP/IP became universal, different vendors had their own networking languages. Apple's was AppleTalk.
The Zone Information Service was part of AppleTalk's Name Binding Protocol. It let network administrators organize resources into zones (like "Marketing" or "Engineering") and helped devices find printers, file servers, and other services within those zones.
By the early 2000s, Apple abandoned AppleTalk entirely in favor of TCP/IP. Mac OS X made TCP/IP the default. The protocol that ran on port 206 became obsolete.
But the port assignment remains in the IANA registry. Bureaucratic inertia keeps it there—a marker of what used to be.
The Registry Problem
The well-known ports range (0–1023) is finite. Only 1,024 addresses exist. Hundreds are assigned to protocols nobody uses anymore: old file transfer methods, ancient email systems, proprietary networking schemes from the 1980s.
Port 206 is one of many fossils. The assignment prevents reuse, but nothing legitimate listens here anymore. It's a tombstone in a crowded graveyard.
Security Considerations
Empty ports attract attention. Historical records show trojans and malware have used UDP port 206 for command and control.2 When a port has an official assignment but no legitimate traffic, it becomes attractive for malicious use—security tools might not flag it as suspicious.
If you see traffic on port 206, investigate it. No legitimate service should be using it in 2026.
How to Check What's Listening
On Linux or macOS:
On Windows:
If something is listening, it's worth examining. AppleTalk has been gone for twenty years.
Why This Port Matters
Port 206 represents a broader problem: the well-known ports range is full of history nobody uses anymore. IANA assigned ports in the 1980s and 1990s to protocols that seemed important at the time. Many never saw widespread adoption. Others, like AppleTalk, thrived and died.
The registry doesn't forget. Ports remain assigned long after the protocols disappear. This creates friction—valuable port numbers locked to obsolete technology.
Port 206 is a reminder that the Internet's infrastructure carries archaeological layers. Every protocol someone designed, every port someone requested, every standard someone thought would matter—they're all still there in the registry, whether they're used or not.
Related Ports
Ports 201–204: Also assigned to AppleTalk services (Echo, Name Binding, Routing Maintenance) Port 548: Apple Filing Protocol (AFP), another Apple protocol that's been largely replaced
Frequently Asked Questions
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