Time sync of RIPE probes

1

I’ve been looking at NTP measurements from RIPE probes.

For a number of the probes, the time seems to drift by two seconds, then reset (see plot).

says " And v3 probes currently use OpenNTPD but will switch to ntpd in the near future."

It also details a backup mechanism: “Basically, the probe checks whether its local clock is within two seconds of the controller’s clock. If not, and the entire HTTP request took less than one second, the probe updates its local clock.”.

My suspicion therefore is that they only get time via NTP if the DHCP server provides one - if not they use the fall back mechanism (rather than pool ntp servers). Is that correct?

RipeAtlas-ntp
RipeAtlas-ntp581×493 80.4 KB

Chris

2

As the linked article explains, doing NTP on such small (battery-less) devices is not easy! As long as this behavior is observed only on a handful of probes, it is fair to assume these just don’t get tim sync from their NTP servers and therefore use the fallback mechanism. The sawtooth pattern suggests these just drift continuously and adjusted back to the two second window periodically. I’m not 100% sure that’s really the case, but IMO it’s plausible.