From Newsgroup: comp.protocols.time.ntp

On Wed, Jul 02, 2025 at 09:23:12AM +0000, Windl, Ulrich wrote:

Actually, I had completely forgotten about that issue. Reading it again, it seems stratum should be 16 if all sources are unreachable (lost).

Why should it do that?

The idea in NTPv4 is that the decision if a source is acceptable
should be made on the client side. If a server loses all time sources,
its root dispersion will grow (15 ppm by default). If a client of that
server has other sources, it can reselect when the distance becomes
larger than that of the other sources.

If the server quickly switches to the unsynchronized state (as recent
ntpd versions seem to be doing), the client can no longer synchronize
to it, even if it has no other sources available. If there are
multiple clients of that server, their clocks will not stay in sync,
each will be drifting on its own.
--
Miroslav Lichvar

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