Ganesh Hariharan Thu, 02/04/2010 - 09:21
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Does anyone know how often NTP updates on Cat switches? I believe you
can set it on routers but can you set the frequency on switches?


An NTP client makes a transaction with its server over its polling interval (from 64 to 1024 seconds) which dynamically changes over time depending on the network conditions between the NTP server and the client.The router also increases the poll interval when router polls a bad ntp server,No more than one NTP transaction per minute is needed to synchronize two machines. It is not possible to adjust the NTP poll interval on a router.

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Martin Ermel Tue, 05/04/2010 - 13:50
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The offset is the difference between 2 clocks (e.g. offset from UTC)
The drift is the divergence of the frequency of 2 clocks. So if you know the drift over time of the frequency of your local clock (e.g. compared to the frequency of an NTP server) you can use this value (drift) as a correcting factor in calculations.
i.e. if you lost connectivity to your NTP server you can use the local clock and its frequency to calculate the correct time. And if you know the drift of you local clock you can make these calculations more accurate (because you know the factor of the inaccuracy of your local frequency)

So, there is no relation between offset and drift. The drift is a correcting factor and the offset is a "static" value - just the difference between 2 clocks.

(if anybody thinks I am wrong, please correct me...)

Have a look at these presentations of Emmanuel Tychon (he is talking of the "clock skew" instead of "drift"):

here are 2 other very interesting presentations:


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