Hi Joachim, Thank you for looking into this! On Thu, 17 Jul 2025 15:30:35 +0200 Joachim Kroß wrote:

It seems the explicitly misbehaving server has been replaced by a more sane one (albeit apparently not synchronized)

Oh, yes that's correct - sorry for that. I started doing some tests with an NTPv5 enabled Chrony server. The NTP simulator is still available on another server though, albeit IPv6 only (because such VM's are so much cheaper): ntp1.testdns.nl. For those interested; my simple NTP simulator is here: https://github.com/mdavids/ntptools/tree/main/go/fake-ntp-server A version that allows to simulate jitter and clock drift is here: https://github.com/mdavids/ntptools/tree/main/go/fake-ntp-server-2 Just a few simple experiments, mostly the result of a bit of vibe coding. -- Marco