[ntp:questions] different Ntp servers...
Richard B. Gilbert
rgilbert88 at comcast.net
Tue May 26 15:14:52 UTC 2009
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.
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!
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