[ntp:questions] different Ntp servers...

Andy andyy1234 at gmail.com
Tue May 26 16:51:04 UTC 2009

On May 26, 4:14 pm, "Richard B. Gilbert" <rgilber... at comcast.net>
> Terje Mathisen wrote:
> > Andy wrote:
> >> About 10 years ago we used to have 2 seperate GPS receivers feeding
> >> into two Sparc servers via their serial port. I can't remember the
> >> version of NTP we ran however these were our stratum one servers, One
> >> of the Sparcs developed a fault on it's serial interface which delayed
> >> the input meaning the two stratum one servers started showing
> >> different time so all the statum 2 servers stopped trusting both
> >> stratum 1 servers as they could not determine which server, if any,
> >> was telling the  truth. Ever since then we have always used at least 3
> >> stratum one servers with seperate stratum zero sources to form a
> >> quorum so that startum 2 can differentiate the good from the bad. I
> >> believe this is set down as best practise in the ntp.org FAQ - this is
> >> a practical example of why this is wise.
> > The "best practice" is in fact to use at least _four_ sources, that way
> > you can lose one and still have a voting group.
> > Terje
> The magic numbers are 4, 5 and 7 protecting from the failure of one,
> two, or three servers respectively.  If you can't do it with seven
> servers you have more serious problems!- Hide quoted text -
> - Show quoted text -

We use 4 at the moment, we had 5 but we've decommissioned a building
that housed one recently. Interestingly I'm having difficulty
convincing some new colleagues that we need more than two!.........

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