Hi Maurice
This is expected behavior with OpenNTPd and not a problem with your hardware. With only a local sensor, ntpd can control the clock very tightly so that microsecond offsets are normal but once you add remote servers, their network delay and asymmetry start to influence the clock control as well. Even if the sensor remains selected in ntpctl, the other peers will still affect the filtering and frequency correction, which typically results in millisecond-level variation. Weights don’t fully isolate the sensor, and seeing it selected does not mean the other sources have zero impact. If you want to keep microsecond accuracy, the usual approach is to run the machine as a pure stratum-1 server with only the sensor configured and get redundancy by running multiple such boxes. However, If you need fallback to network time in the same daemon, then OpenNTPd is simply not designed for that use case. Regards, Kihaguru Njenga Gathura On Wed, 31 Dec 2025, 17:28 Maurice Janssen, <[email protected]> wrote: > Hi, > > I have a couple of small machines (Soekris 6501 and 5501) that I use as > NTP server in the NTP pool. > When I use a sensor as the only source of time (Garmin 18lvc on the serial > port or Meinberg PZF180PEX DCF77 receiver card), the offset is quite good: > nearly allways below 20 us, most of the time below 5 us and sometimes even > less than 1 us. > But when I add another server (mainly as backup in case the sensor doen't > work), the offset drifts away to 1 or 2 ms. I tried with 1 sensor and > 1 server, with 1 sensor and multiple servers, I tried adding weight 5 or 10 > to the sensor, but this doesn't seem to have any effect. In all cases ntpd > stays synchronised to the sensor (with poll=15s), but after an hour or so > after starting ntpd the offset starts to increase. And from that moment, > the > offset wanders between roughly -2 and +2 ms. > It almost seems as if ntpd is synchronised with one of the servers (with > much higher polling interval), however ntpctl still shows that it is > synchronised to the sensor (albeit with the wandering offset as described > above). > > I would prefer to have the microsecond offset _and_ some servers as backup, > but can't get it working like that. > > Am I missing something? Or is this a bug in ntpd? > > Thanks for any help. > > >
