[ntp:questions] Re: What went wrong with the leap second

David J Taylor david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk.invalid
Thu Jan 5 08:36:38 UTC 2006

David L. Mills wrote:
> In all the testing with this thing, I never got unexpected behavior,
> but since lots of others did experience pinball machine behavior,
> some wee thing must have been overlooked. Workin' on it.
> Dave


My observation is that the single system seems to work OK.

The problem comes when about half the systems don't step at the same time, 
leaving the client without a reference clock (or sometimes with one) 
having two clusters about one second apart.  As the leap-second propagated 
through, the population of these clusters changed, leaving clients 
confused as to the correct time.

The one thing which stands out as making things much worse was the 
willingness of ntpd to discard a drift value which had been built up over 
many days too quickly - within an hour of the leap seconds drift values 
had shot to the limits (+/- 500) on some of my systems, and it was the 
recovery (in two cases failure to recover in a reasonable time), which was 
the major issue.

I'd suggest that drift should not be changed by a large value, unless 
there is a good reason.  No, I'm not an ntp expert!


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