[ntp:questions] Ntp looses sync

David Woolley david at ex.djwhome.demon.co.uk.invalid
Thu Apr 2 07:45:40 UTC 2009


Heiko Gerstung wrote:

> 
> I know NTP appliances that allow you to configure the stratum level of 
> the unit when it is in holdover/free running mode. There is a good 
> chance that the Gude box allows for the same. Did you check that with 
> their technical support?

Setting the local clock stratum to a lower number than one gets from 
real network is considered bad practice, because it risks accidentally 
serving time to something that doesn't realise it is getting time from 
an unsynchronised source.

I'm actually of the opinion that providing a "local clock" pseudo source 
should always be an opt in, but, unfortunately, it tends to set up as an 
opt out when people package ntpd.

Also, it is very rare to have a real stratum 5 server, so I wonder if 
this is also a case of inappropriate enabling of a local clock driver; I 
think that stratum 5 is the default local clock driver stratum, which is 
probably based on the assumption that there is some, reliable, non-NTP, 
discipline for the machine's clock.  The appliance is using a 
recommended local clock stratum for a free running oscillator.

If the 5 is the result of a local clock driver, that should be removed 
from the relevant configuration.  Serious consideration should be given 
to removing the local clock driver from the appliance configuration, as 
its clients will coast at the last known frequency, so shouldn't diverge 
too quickly.




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