[time-nuts] NIST NTP servers way off for anyone else?

[Adam Space]

I'm not sure if anyone else uses the NIST's NTP servers, but I've noticed
that the offsets I'm getting from Gaithersburg servers seem to be
really far off, like 40-50 ms off. This is pretty odd since they usually
have a 2 - 3 ms accuracy at worst.

It is interesting to think about what is going on here. NIST has a secondary
time scale
<https://www.nist.gov/pml/time-and-frequency-division/time-services/utcnist-time-scale/secondary-utcnist-time-scales-and>
at Gaithersburg, maintained by a couple of caesium clocks that are
typically kept within 20ns of UTC(NIST), i.e. their primary time scale in
Boulder. They also host their remote time transfer calibration service and
their Internet Time Service (i.e. NTP servers) out of Gaithersburg.

It seems highly unlikely that their time scale there is that far off. One
thing that immediately comes to mind is asymmetric network delays causing
this. I do think this has to be the reason for the large discrepancy, but
even so, it is an impressive feat of asymmetric path delays. The maximum
error in offset from a client to server due to asymmetric network delays is
one half of the delay. (This corresponds to one path being instantaneous
and the other path taking the entire delay time). When I query their
servers, I am getting about a 45ms offset, and a delay of around 100ms.
This would mean the maximum error due to asymmetric path delays is around
50ms--and less even if we're being realistic (one of the delays can't
literally be zero). Basically, for the offset error to be accounted for
primarily by asymmetric network delays, the delays would have to be *very*
asymmetric.

Is anyone else experiencing the same thing?