Port 281 sits in the well-known range (0-1023), officially assigned to something called "personal-link" by IANA. But if you see traffic on port 281 today, it's probably not Personal Link—whatever that was. It's more likely a Honda talking to a service center.
What Lives Here
Official assignment: personal-link (Personal Link)1
Actual observed use: Honda Automobile Customer Service application
Protocols: TCP and UDP
Range: Well-known ports (0-1023)
IANA assigned this port to Dan Cummings for something called "Personal Link." No RFC. No detailed documentation. No clear explanation of what Personal Link was supposed to do. Just a name in the registry and a port number reserved in the well-known range.
Then Honda started using it.
The Honda Connection
Port 281 is commonly observed carrying traffic for Honda's automotive customer service systems.2 When your Honda sends diagnostic data back to the dealership, when the telematics system reports your vehicle's location, when the onboard computer says something needs attention—port 281 might be the channel.
TCP port 281 handles remote diagnostics: error codes, performance data, maintenance requirements flowing from the car to the service center.
UDP port 281 carries real-time telemetry: location updates, status pings, non-critical information where speed matters more than guaranteed delivery.
This is what happens to abandoned well-known ports. If nobody's using them, someone else moves in.
What Well-Known Means
Ports 0-1023 are the well-known range. These require elevated privileges to bind to on Unix-like systems. They're supposed to be assigned by IANA through a formal process, documented in RFCs, reserved for protocols that matter to the Internet's infrastructure.
Port 281 got the assignment but not the documentation. It's a well-known port in name only—technically privileged, practically obscure.
The Security Angle
Port 281 has been flagged in the past as a vector for malware.3 A Trojan or virus used this port to communicate, which isn't surprising. Obscure assigned ports with little legitimate traffic make excellent cover for malicious communication. If port 281 isn't supposed to be active on your network, and suddenly it is, that's worth investigating.
If you're running Honda's legitimate automotive services, port 281 is expected. If you're not, it shouldn't be open.
Checking What's Listening
On Linux or macOS:
On Windows:
If something's listening and you don't know why, find out. Well-known ports don't open themselves.
Why Unassigned Ports Matter
Port 281 isn't technically unassigned—it has an official service name. But it might as well be. "Personal Link" is a name without a protocol, a reservation without documentation, a well-known port that nobody knows.
This happens more than you'd think. IANA's registry is full of ports assigned to services that never shipped, protocols that never caught on, companies that no longer exist. The well-known range is littered with abandoned addresses.
And then someone like Honda comes along and uses one. Because the port is there, because it's available in practice if not in theory, because sometimes it's easier to squat on an obscure assignment than to register a new port in the registered range (1024-49151).
The result is a port that means two different things: officially "Personal Link," practically "Honda diagnostics." The Internet is full of these gaps between what the registry says and what actually runs on the wire.
Related Ports
- Port 280: http-mgmt (though also rarely used for its official purpose)
- Port 282: Another unassigned well-known port
- Port 443: HTTPS—an example of a well-known port that actually lives up to its assignment
Frequently Asked Questions
The Truth About Port 281
Port 281 is a door with two nameplates. One says "Personal Link" in faded letters—the official assignment that never quite happened. The other says "Honda" in fresh paint—the actual use that nobody officially documented.
This is what the Internet looks like up close. The registry says one thing. The wire says another. And somewhere, a Honda is sending diagnostic codes through a port that was supposed to be for "Personal Link," whatever that was.
The Internet works anyway.
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