[ntp:questions] NTP servers redundancy

Brian Utterback brian.utterback at sun.com
Wed Jan 20 21:37:42 UTC 2010

Rob wrote:

> This is not relevant when the two servers return the same time within
> the margin that one considers acceptable.

You are incorrect. It is relevant. In practice, no two servers EVER
have exactly the same time. And each time NTP decides to switch to the
other server, it is also going to adjust the clock frequency to
compensate for the perceived drift, even though the clock frequency
may have already be correct.  It is thus likely for clock hopping to
cause a feedback loop that will take the system clock outside of the
interval between the two clocks. With the correct timing on the
hopping, it can go very far outside the interval.

Brian Utterback

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