[ntp:questions] Syncing to nearby vs. faraway servers

Brian Utterback brian.utterback at sun.com
Tue Jun 16 19:07:26 UTC 2009

Rich Wales wrote:
> Richard B. Gilbert wrote:
>> The "Delay" values for some of the servers you have configured
>> are large enough to suggest that they are poor choices!
> Agreed.  Please note, though, that I didn't explicitly choose
> these particular servers -- they came from pools.
> This does suggest that even servers randomly picked from my own
> country's pool (*.us.pool.ntp.org) might not be good choices.
> When 4.2.6 comes out, will the "pool" command with the "preempt"
> option do a better job of weeding out pool servers that are far
> away, and thus possibly of doubtful reliability?

Hi Rich. Long time (UCLA '82).  The selection algorithm already does 
favor shorter delay servers, all other things being equal. The 
selection algorithm is actually pretty complex, but the delay is taken 
into account at one point. Actually, it happens even earlier, because 
the choice of sample from any given server is made based on the delay. 
  So, of the potential 8 samples from any one server, the one with the 
smallest delay is taken.

As far as the preempt keyword, it does what you want in theory. I 
haven't tried it in a while, but the last time I gave it a shot, I 
thought that it whittled down the list way too fast. YMMV.

My personal vision is to have the NTP network be self-organizing and 
emergent. I am afraid there is a long way to go in that regard.

Brian Utterback

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