[ntp:questions] Varying Offset Values

Danny Mayer mayer at ntp.isc.org
Mon Aug 21 02:18:42 UTC 2006

David Russell wrote:
> Hi,
> I have been observing the values that a stratum 2 server has for its
> clock offset from multiple stratum 1 GPS based time servers using
> ntpq -p.
> Two of the three time servers show an offset agreement in the 50-200 
> microsecond range.  But the offset for third, which is at the same
> site as one of the first two, has been off as much as 10 milliseconds
> from the other two but now is down to 800 microseconds.
> The first two timer servers are installed at different sites and the
> third is installed on an adjacent subnet to one of the servers in the
> first group. I am showing a consistent offset for two stratum 1
> servers at different sites but a significant difference between two
> stratum 1 servers that have a nearly identical path to/from the
> stratum 2 server.
> It seems to me that the data is telling me that the third stratum 1
> server is drifting all over the place and should be taken out of
> service and fixed.
> My question is: if I had three stratum 1 servers installed side by
> side that were perfect time keepers, shouldn't my stratum 2's clock
> offset from the each of stratum 1 servers be nearly the same?

I'd add several additional stratum 1 servers and see what falls out. If
the additional servers confirm that it's bad, either take it out of
service and get it fixed if you own it or just drop it and use different

> Thanks,
> David
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