[ntp:questions] Re: Question on abusive clients.

David J Taylor david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk.invalid
Mon Dec 26 19:00:25 UTC 2005

David L. Mills wrote:
> David,
> The poll intervals are not managed as you think. The basic
> consideration is for the discipline loop time constant, which
> determines the optimum poll interval. The design goal is to move it
> to the highest value consistent with the anticipated clock frequency
> wander. A secondary consideration is that the loop not be
> undersampled should the timing source change. You have constrained
> the poll interval and time constant when you specify a maxpoll for a
> source that happens to synchronize the client and that forces all the
> others to the same value in case one of them is selected.
> There small gain in performance when forcing the poll interval to
> smaller values as against letting the algorithms optimize for ambient
> conditions. If you are trying to squeeze the optimum performance when
> doing that, the cost is all the sources are constrained as well.
> Dave


Thanks for that.  I recall there was some issue like the one you mentioned 
but, not dealing with these things every day, I was not able to elucidate 
it as well as you!

I have now followed Richard's (I think) suggestion that I set, in my 
client config, the two local LAN servers to maxpoll=6, and the fallback 
Internet servers to minpoll=10.  Is there any danger in doing this?  I am 
presuming that the fallback situation is very unlikely to happen, and that 
if it does happen, I will not have the optimum time keeping for a period.

I have found that the daily drift is less with a poll of 64s rather than 
1024s, and this what I prefer to see.


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