What Runs Here
Port 525 (UDP) is officially assigned to Timed, also known as the Timeserver protocol.1 Timed was a Unix daemon that synchronized system clocks across local networks by exchanging time information between machines and electing the most accurate clock as the reference.2
This is legacy infrastructure. Timed predates the Network Time Protocol (NTP) and represents an entire generation of time synchronization that has been obsolete for decades.
How Timed Worked
The protocol was straightforward: multiple Unix systems running the Timed daemon would communicate over UDP port 525, broadcasting or unicasting time information to detect discrepancies between their system clocks.3
Timed used an election algorithm—democracy for clocks. The connected machines would collectively determine which system had the most accurate time, appoint it as the server, and the others would synchronize to it.4 The algorithm aimed to keep all participating clocks aligned within an acceptable margin of error.
There was no sophisticated data analysis. No clock disciplining. Just a group of machines asking each other "what time do you have?" and voting on who was probably right.
Why It Disappeared
NTP happened.
The Network Time Protocol (RFC 5905) runs on port 123 and does everything Timed did, but better—hierarchical time sources, cryptographic authentication, sub-millisecond accuracy, compensation for network delay, and algorithms that actually discipline the system clock rather than just setting it.5
Timed was designed for local networks where all the machines could see each other. NTP was designed for the Internet, where time needs to flow from atomic clocks through layers of servers to billions of devices. The moment NTP became stable, Timed became archaeology.
Current Status
The port is still officially assigned by IANA. You won't find Timed running on modern systems. It exists in the well-known ports range (0-1023) as a historical marker—this is where time synchronization lived before we figured out how to do it properly.
If you see traffic on port 525 today, it's either:
- A museum piece (an ancient Unix box still running)
- Misconfiguration (something accidentally using this port)
- Research (someone studying old protocols)
- Malware (using an abandoned port for cover)
Related Ports
- Port 123 (UDP) — NTP, the protocol that replaced Timed
- Port 37 (TCP/UDP) — Time Protocol (RFC 868), an even simpler time service
- Port 13 (TCP/UDP) — Daytime Protocol, returns human-readable time
Checking What's Listening
To see if anything is actually using port 525 on your system:
Linux/macOS:
Windows:
You shouldn't find anything. If you do, you've either discovered a time capsule or a problem.
Why This Port Matters
Port 525 is a reminder that infrastructure evolves. The Timed daemon kept Unix networks synchronized in the 1980s and early 1990s—it solved a real problem with the tools available at the time. Every packet it sent mattered to the systems depending on it.
Then better tools arrived, and Timed became unnecessary. The protocol faded. The daemons stopped running. The port number remains in the registry, officially assigned to a service that no longer exists in practice.
This is what obsolescence looks like in the port system. Not deleted—just quietly reserved for something that used to matter.
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