[ntp:questions] flipping between stratum 1 clocks regularily

Unruh unruh-spam at physics.ubc.ca
Tue Feb 19 21:24:34 UTC 2008

"mmoore0011 at hotmail.com" <mmoore0011 at hotmail.com> writes:


>I've recently been provided with 4 "highly accurate" ntp servers that
>are using GPS as their primary synchronization source.  Well, 2 of the
>hosts are using GPS (stratum 1) and the other two are syncing to those
>(stratum 2).  I've been going around configuring all 4 hosts in my
>ntp.conf and am starting to notice that my machines are flipping back
>and forth between the two stratum 1s.  I don't think this is

A The accuracy is not limited by teh clock. It is limited by the ability of
the computer to respond to the interrupt and read the system time. That is
about 3usec. Even if the clock signal is better than 1usec, the computer
cannot achieve that accuracy. 

>Some of the documentation from the clock vendors suggests that their
>clocks are "so accurate" that ntp has a hard time determining which is
>more so and this affect can occur.  I was thinking of dropping one of
>the ST1 clocks from the config and going with 1 ST1 and 2 ST2s....
>that seems more stable in a test.  I wanted to see if anyone else has
>dealt with something similar and how you fixed it.

So make one the preferred and the other a backup.


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