[ntp:questions] client configuration: it's sufficient 3 servers ?

David Taylor david-taylor at blueyonder.co.uk.invalid
Fri May 24 13:43:05 UTC 2013

On 24/05/2013 09:12, Riccardo Castellani wrote:
> If I have 3 internal NTP servers, what do you think if my clients have all
> these 3 servers in their configuration ?
> According to '5.3.2. Why should I have
> more than one clock?' in 'http://www.ntp.org/ntpfaq/NTP-s-algo-real.htm#Q-NTP-ALGO
> I read 2 servers, it's worst case, but also 3...

Riccardo, to cover the case where both remaining servers would be reject 
were one out of three to fail, I would suggest that you should have four 
internal servers minimum.  However, if your clients are also allowed to 
use the pool directive, seeing external servers where many more servers 
will be allocated to each client, then three internal likely would 
suffice, depending on what OS and what timekeeping requirements you have.

So I would have all three internal servers, plus a pool directive in the 
client configuration file, something like:

server 	iburst
server 	iburst
server	iburst
pool	uk.pool.ntp.org

I hope that each internal server is stratum-1, and has a separate 
GPS/PPS reference or other source.
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