time.cloudflare.com suddenly 5-10 ms off the real time in the eastern US.

[mnordhoff@infosec.exchange]

time.cloudflare.com suddenly 5-10 ms off the real time in the eastern US.

I'd guess probably something boring, like network asymmetry near the top of the tree (bottom of the tree?).

(When the service was new, the accuracy was routinely worse than this.)

[mnordhoff@infosec.exchange]

RE: https://infosec.exchange/@mnordhoff/115675202677067879

https://groups.google.com/a/list.nist.gov/g/internet-time-service/c/Zd7VaR-vqV4

On Saturday, 6 December 2025 at approximately 21:13 UTC, the atomic time source (a single cesium beam atomic clock) for all the internet time servers at the NIST Gaithersburg campus failed and exhibited a time step of approximately -10 ms.

Oh.

[mnordhoff@infosec.exchange]

This is, by the way, less than a month after the time servers hosted at JILA/University of Colorado were turned off due to failure of the atomic clock there.

https://groups.google.com/a/list.nist.gov/g/internet-time-service/c/y0smqm7W1J4

So NIST is down to 2 sites at the moment, also in Colorado.

USNO (the military) also has public stratum 1 NTP servers in two other locations (one of which is in Colorado because everyone loves Colorado), and of course there are many other stratum 1 time servers in the United States (probably mostly using GPS/GNSS).