[ntp:questions] Polling time backoff

Richard B. Gilbert rgilbert88 at comcast.net
Mon Nov 30 01:22:08 UTC 2009


David Lord wrote:
> shane-dated-2009 at csy.ca wrote:
>>> Dave Hart <davehart at gmail.com> writes:
>>>
>>>> On Nov 28, 11:52=A0pm, shane-dated-2... at csy.ca wrote:
>>>>> Just wondering if there is anything in particular which would keep 
>>>>> ntpd
>>>>> polling its servers every 64s
>>>>>
>>>>> server 127.127.20.0 minpoll 4 prefer
>>>>> fudge 127.127.20.0 flag3 1 flag2 0
>>>> The refclock is holding the poll interval down.  You have to use
>>>> minpoll on the remote server lines to force them to a longer poll
>>>> interval in the presence of a reflock with a smaller poll interval.
>>> Is that really right? I thought that all of the clocks had their poll 
>>> intervals
>>> determined independently. YOu seem to be saying they do not, that the 
>>> poll
>>> intervals are "universal" the smallest poll interval for any server 
>>> is used.
>>> On my system that is certainly not true
>>
>> Hmm, I think Richard Gilbert's post was pretty well spot on, watching the
>> poll last night, it did go as high as 512 at around 2 AM for some of the
>> servers. I just unconfig'd the refclock to see if that's making a 
>> difference
>> but so far, polling is still at 64s. A bit odd, my connection to the net
>> isn't terrible, res. cable connection but delays are decent. It's 
>> asymmetric
>> though which I understand can give ntpd some grief.
> 
> I may be talking rubbish but ntpd here seems to need to get
> within a certain tolerance before poll increases. At 64s
> there may be too much jitter whilst at higher initial polls
> this appears to be smoothed out and poll can increase
> further.
> 
A much oversimplified explanation is that short poll intervals are used 
to correct large errors quickly and long intervals are to correct small 
errors very accurately.




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