[ntp:questions] ntpd wedged again

unruh unruh at invalid.ca
Wed Feb 15 04:22:23 UTC 2012


On 2012-02-15, Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
> On 2/14/2012 1:43 AM, David J Taylor wrote:
>> "A C" <agcarver+ntp at acarver.net> wrote in message
>> news:4F398579.9060201 at acarver.net...
>> []
>>> I'm not sure it's a good idea either but I would really like to
>>> understand why a refclock clamps the polling interval at such a low
>>> value when nearly every bit of documentation says we should be kind to
>>> NTP servers and make sure the polling period is allowed to reach 1024.
>>
>> If you look back in the archives of this newsgroup you will find that I
>> asked David Mills a similar question, and he gave an answer. I'm not
>> sure that I completely understood the answer, though.
>>
>> I now have lines like the following in my ntp.conf file for my stratum-1
>> PCs:
>>
>> server 0.uk.pool.ntp.org minpoll 10
>> server 1.uk.pool.ntp.org minpoll 10
>> server 0.nl.pool.ntp.org minpoll 10
>>
>> As I have three PCs peered fed from different GPS receivers I'm hoping
>> that the Internet servers are never needed. <G>
>>
>> Cheers,
>> David
>
> The problem with THREE GPS receivers, or just about any other clock, is 
> that it it can too easily degenerate to the two server case.  It is well 
> known that "a man with two clocks can never be certain what time it is."

And the problem with 976 receivers is all it takes is 974 failures and you are
down to the two receiver case. 

>
> Four, five, and seven are the magic numbers for a robust configuration.
> Most sites will settle for four.  The very paranoid or the very rich 
> might go for seven.

Four is horrible, in that two to two is a tie.

>
>



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