Hi,
On 2021-12-14 17:26, Steven Sommars wrote:
The Gaithersburg servers are accurate. This plot shows Gaithersburg
time-e-g.nist.gov for the current month.
[image: image.png]
My monitoring client is located near Chicago and is Stratum-1 GPS sync'd.
Typical round-trip time to Gaithersburg is ~27 msec.
On 2021-12-07 a few monitoring polls saw RTT of ~100 msec. This changes
the computed offset from
~0 msec to to ~40 msec ( (100-27)/2. ). Such transient increases are
often called "popcorn spikes"
Many NTP clients including ntpd and chrony contain logic that identifies
and suppresses these outliers
Further, Gaithersburg is subject to fiber-cut outages and other planned &
unplanned network outages.
If you look carefully at the diagram, you can see a brief outage beginning
at about 2021-12-08 03:00 UTC.
I have other monitoring clients and can produce similar diagrams from other
locations. A monitoring client
in Japan saw this for the same Gaithersburg server:
[image: image.png]
The delay spikes occur at different times and have different signs. [The
2021-12-08 outage is still present]
See http://leapsecond.com/ntp/NTP_Paper_Sommars_PTTI2017.pdf for a
discussion of why there are multiple
offset bands. In the same paper there are examples of sustained high
delay, something that
Magnus summarized the situation. Either asymmetric network delay or a
misbehaving NTP server can
cause the computed offset to be non-zero. The former is very common.
NTP servers, even stratum 1's
driven by GPS, are sometimes in error.
For sure. I've seen significant biases and jitter from bad servers. I
just had to save the company from getting a worse situation as the
IT-folks wanted to setup a new server in a virtualized machine. Having
multiple propper machines in house, it was just a few things to fix to
set it up.
Also, I assume that NIST have monitoring, and in fact if you look back I
tossed a link that gave an in depth report from NIST on their current setup.
If actual offsets traceable to the actual machines of NIST is found,
please report it into NIST, and I think that will be Judah Levine.
Cheers,
Magnus
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