[ntp:questions] ***SPAM*** Client doesn't drop failed source

Michael Moroney moroney at world.std.spaamtrap.com
Fri Jan 8 20:45:04 UTC 2010

We were trying to see how NTP failover worked before implementing an
accurate time system on an isolated network.  Situation: Two NTP GPS
clocks are defined as the primary source, two others (belonging to a
different organization) are secondary sources.  To test we set up a client
that synchronizes with the four clocks, and ntpq> peers shows one of the
primaries with a "*" in the first column meaning it was synchronized to as
time source, the other 3 show "+" as expected, meaning they are usable
sources.  We disconnect the antenna of the selected clock.  As expected
the clock (Spectracom) changes its stratum from 1 to 16 after a delay, and
on the next poll (interval is 1024 seconds) ntpq shows its stratum as 16
and the clock is not considered a source (first column shows blank), and
the second primary has the "*".  We reconnect the antenna and disconnect
the other primary antenna.  It selects the first primary as expected.  We
disconnect both antennas and it selects one of the backup clocks as source
as expected.  We connect the antennas and it goes back to one of the

Now the question: For the next test, we disconnect the LAN cable of the
selected primary clock, and we expect the next poll to fail and the client
to give up on it and to select the other primary clock.  No, we just see 
the time from the last poll incrementing well beyond the poll interval
(1024 seconds) but the disconnected clock still selected as primary!
When we connect the cable it fails over to the other primary.

How do we get the system to fail over to another clock if the one it was
using fails?  The system isn't a Unix (OpenVMS) it does use Unix type NTP
commands/programs (ntpq, ntpdate, ntpdc)

More information about the questions mailing list