[ntp:questions] Regarding NTP configuration ntp.conf

Brian Utterback brian.utterback at sun.com
Tue Dec 22 18:27:06 UTC 2009

Richard B. Gilbert wrote:
> Three is not a good number of servers.  If any one of the three fails
> either by not responding or by serving incorrect time you are reduced to
> two servers; back to the worst case.  The magic numbers are four, five,
> or seven, protecting you from the failure of one, two, or three,
> respectively, of the configured servers.

Even without a failure, three servers do not always allow two servers
to out vote a bad third one. Usually yes, but not always, depending on
the different dispersions and offsets. Four will always allow three to
out vote a bad fourth.

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