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

David L. Mills mills at udel.edu
Mon Dec 26 18:49:58 UTC 2005


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.


David J Taylor wrote:
> Richard B. Gilbert wrote:
> []
>>The reference implementation of ntpd contributes to the deluge in a
>>small way!   Running a Motorola Oncore as a reference clock causes my
>>home server to query its internet servers every 16 seconds.  It's
>>nothing I would do by choice; they serve only as a sanity check on my
>>Oncore reference clock   There does not appear to be any way of
>>turning this feature off short of modifying the code.
> Agreed.  I would like to have my client PCs poll their two LAN servers at 
> 64s and one Internet server at 1024s (also as a sanity check), but it 
> seems that if any LAN server is set to 64s the Internet servers are also 
> polled at 64s intervals.
> David 

More information about the questions mailing list