On Mon, Jul 13, 2015 at 01:17:01PM +0000, Matthew Huff <mhuff@ox.com> wrote a message of 14 lines which said:
We have 5 NTP server: 2 x stratum 1 rubidium oscillator time servers with GPS sync, and 3 servers running NTP 4.2.6p5-3 synced to external internet based NTP stratum 1 servers. We monitor our NTP environment closely, and over the last 10+ years, normally all of our NTP servers are sync'ed within +/- 2 msec. Starting last Friday, we started seeing some remote NTP servers with GPS reference consistently offset by 10 msec.
I have no idea but I just wanted to remind people that, for a few months, RIPE Atlas probes have been able to do NTP queries <https://atlas.ripe.net/docs/data_struct/#v4660_ntp> so it may be a cool way to monitor NTP servers from many points.