How to configure a secondary NTP master?

Unanswered Question
May 12th, 2010


Just new to this community hopefully someone will be able to help me out. Then as my knowledge increases hopefully I'll be able to help someone else out!

I'm using a 2821 purely to provide ntp to the network. It is set as ntp master 12. If I configure a secondary 2821 exactly the same will it cause any clocking issues for the devices in my network. I do not want the network continually flipping between ntp masters as this may cause problems with my voip phones. Should I change one of the routers to ntp master 10? If I do this will it become the primary master so to speak? Or will it be ok with both at 12?



I have this problem too.
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Paolo Bevilacqua Wed, 05/12/2010 - 13:51

NTP is designed so that no matter what, clients will never flip between server and is actually a very, very little traffic protocol with unfrequent updates.

The advantage of a client using multiple server is not only for redundancy, but for accuracy also as every little bit of differential information is used in that sense

So in practice, anyway you will set stratum, ir will not make any difference.

tonycraig Wed, 05/12/2010 - 14:10

Thanks for the advice.

So if I set up my remote site routers as follows

ntp server Data centre A
ntp server Data centre B

How will each remote site determine which server to take the ntp info from?

Sorry to ask more questions but if i end up with 1000s of phones with different time on the displays I'll get my ass kicked!


Leo Laohoo Wed, 05/12/2010 - 15:26

Hi Tony,

You can also use the "prefer" option:

ntp server prefer
ntp server

This will tell the appliance to use until is un-reachable.


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