[ntp:questions] Local time sources

Richard B. Gilbert rgilbert88 at comcast.net
Mon May 10 12:33:54 UTC 2010


Miroslav Lichvar wrote:
> On Sun, May 09, 2010 at 09:33:46PM -0400, Richard B. Gilbert wrote:
>> Not three but four!  If you have only three servers configured and
>> one fails you have the worst possible configuration.  Is it not
>> written that a man with two clocks can never be certain what time it
>> is?
> 
> And to make him even less certain, give him a third clock! :)
> 
> I think in NTP world the saying is just confusing. If you care about
> having accurate time, having two sources is actually better than one.
> If they don't agree, you know something is wrong (ntpd will report
> unsynchronized status) and you can do something about it. With only
> one source you never know.
>  

You know something is wrong but that is all you know!  Clock A may be 
wrong.  Clock B may be wrong.  Both may be wrong.  You lack the 
information necessary to determine what time it is.

The matter is discussed in some detail in the RFC and in more detail in 
"Das Buch"!




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