[ntp:questions] high precision tracking: trying to understand sudden jumps

David Woolley david at ex.djwhome.demon.co.uk.invalid
Mon Mar 31 20:55:35 UTC 2008

Richard B. Gilbert wrote:
> Stratum is taken into account in selecting a time source.
> I can't swear to it but I'd be surprised if three stratum 10 servers 
> could out vote one stratum 2 server.
At least for RFC1305, stratum is not considered (except in as much as 
refid is not checked for stratum 1) until after the intersection 
algorithm has removed false tickers.

I believe there have been cases on the newsgroup in which people have 
peered systems using the local clock and then had the system form a 
clique which rejects real sources of time.

The main thing that would probably mitigate against this if the local 
clocks were in appliances is that the local clock gets a falsely narrow 
error tolerance band.  With the peering configuration, the bands 
overlap, but with multiple appliances, they would have to drift at very 
similar rates to stay compatible.  The narrow tolerance is why local 
clocks that agree make it particularly difficult for a good clock to be 
accepted, as the good clock has to be very close to the clique to not be 

More information about the questions mailing list