Clock on NTP Master Always Falls Behind

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Jun 7th, 2010
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Dear All,


We have configured our Core Router 7206 as NTP master which provides clocking to all the network devices (around 3000 devices ) in our Network.


NTP Source IP on the router is the GiG Interface, but we are facing a problem on it that the router always falls behind 5 to 10 mins of the current time.


We always have to correct it after 3 to 4 days.


when we check the NTP status it shows syncronized but it still falls behind.


Kindly suggest any workaround so that the router clock does not fall behind.


Regards,

Ranjit.

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Leo Laohoo Tue, 06/08/2010 - 03:12
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Firstly I will never recommend anyone to make an appliance as an NTP master.  I've never used this command.


Secondly, where is the router getting an authoritative NTP source from?

ranjit123 Tue, 06/08/2010 - 03:17
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Router takes the Authorative clock from its self clock.


Also what is the solution when reference clock is not allowed to be taken from external NTP servers???


Regards,

Ranjit

Richard Burts Tue, 06/08/2010 - 09:18
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Ranjit


The built in clock of a Cisco router is not particularly accurate. That is one reason why it is not usually recommended to set a router as NTP master. I am not clear why your router can not learn NTP from an external NTP server. If there is some policy reason that prevents Internet access for NTP then you may be able to install something that would provide accurate time locally. This link might be a place to start:

http://www.symmetricom.com/products/ntp-servers/ntp-network-appliances/


HTH


Rick

Leo Laohoo Tue, 06/08/2010 - 14:41
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Router takes the Authorative clock from its self clock.

I'm with Rick.  This is the reason why I don't use "NTP master" command.  The components of a router is like a stand-alone computer.  The clock mechanism is software driven and therefore prone to inaccurate readings in the short-to-medium term.


Look for a GPS server which can be used as an authoritative NTP server if your network is not allowed to go out to the internet.   There are a significant number of vendors that can do this.  You can get one that's the size of your palm to one that you can rack mount (usually 1 RU).


Hope this helps.

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