[ntp:questions] Re: Sufficient # servers to sync to

David Schwartz davids at webmaster.com
Sat Mar 19 01:21:25 UTC 2005

"Brad Knowles" <brad at stop.mail-abuse.org> wrote in message 
news:mailman.29.1111192970.588.questions at lists.ntp.isc.org...

> At 3:16 PM -0800 2005-03-18, David Schwartz wrote:

>>      The assumption is that you have three servers, two of which are 
>> working
>>  and one of which is not. If two of them are working, then their 
>> intervals
>>  *must* overlap.

> They can't overlap, since it takes two machines to *define* an interval. 
> If you have three machines, you may have as many as two different 
> intervals.  If one of those machines is insane, then you're back to the 
> well-known two-machine problem.

    A machine reports a time of X and it reports its own accuracy as Y and 
the round trip time is Z. Why does this one machine not define an interval 
X+Y+Z to X-Y-Z?

>>                   Obviously if you have three servers and no two of them 
>> are
>>  reliable, you are screwed.
> You're pretty much screwed if you have just three servers and any one of 
> them is unreliable.

    I don't see why. Common sense say that if you have three servers and 
they report:


    The time is probably 10:11.


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