[ntp:questions] Re: Synchronisation lost with swisstime.ethz.ch

Richard B. Gilbert rgilbert88 at comcast.net
Thu Aug 11 16:50:37 UTC 2005

frank.olsen at steria.com wrote:

>Thanks for your help!
>I did think that there was a problem with the server, but not knowing
>much about NTP I wasn't sure how to be absolutely sure. So, if I get a
>stratum 13 or 16 on a server that us supposed to be 1 or 2 or 3 or
>whatever, I can safely assume that there is something wrong with that
>server, is that correct?
>Another question: if I do use several servers, what happens if one of
>them doesn't respond? (OK, this is probably in the basic documentation
>so I'll read that right away.)
>Best regards,
>Frank Olsen
If one of several servers fails to respond, the client will use the 
servers that do respond.

The minimum number of servers required to survive the failure of one 
server is four.  Two servers constitute the worst possible configuration 
since the client has no way to determine which one is more nearly 
correct when they differ, as they inevitably will.  Seven servers allow 
the client to survive two "false tickers".   More than seven are 
overkill unless the application is extremely critical.

Your client will select the server that appears to be "best" as the 
synchronization source and use the runners up as an "advisory committee".

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