[ntp:questions] Remaining synced on an unsynchronised peer?

Brian Utterback brian.utterback at sun.com
Tue Dec 1 17:45:29 UTC 2009

Dave Hart wrote:

> distrusted by downstream ntpds.  Assuming no orphan-mode
> configuration, it is not clear to me if the stratum is supposed to go
> the maximum and the synchronization (leap bits) to 11, or if they are
> expected to remain at the last values with only the root dispersion to
> indicate the problem.

This has been discussed before. With ntpd, once an association gets
out of leap-11, it never goes back. That is not true of xntpd.

> I pick a nit about calling a ntpd unsynchronized as soon as its
> sources are severed.  A "freewheeling" ntpd simply maintaining the
> last known frequency compensation is initially still a good source of
> time, decreasingly so over time.  NTP 4 maintains an error budget
> along those lines, resulting in the root dispersion value that's part
> of every NTP response.

Which is exactly the reason an association never goes
"unsynchronized". I think the key milestones are:

1. Reach goes to 0.
2. Root dispersion goes to greater than 1 second.
3. Ref time goes to greater than one day.

As I recall, these milestones can trigger different behaviors, but I
don't remember just what they are.

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