[ntp:questions] Thoughts on KOD

Miroslav Lichvar mlichvar at redhat.com
Tue Jul 8 09:19:36 UTC 2014

On Mon, Jul 07, 2014 at 07:04:01PM +0200, Jan Ceuleers wrote:
> I'm not sure why sending the requester's timestamp back to him is better
> than an immutable timestamp.
> The effect of the former is slow drift, the effect of the latter is (I
> suspect) no lock at all due to the lack of passage of time. So I think
> that the latter is more likely to catch the admin's eye. If there is an
> admin.

I think most clients check at least one of the stratum/leap fields
and don't use the time stamps from a KOD response to actually update
their clock.

If the KOD response was modified to set the leap and stratum bits as
synchronized, the client would drift slowly away, but ntpd would need
to stick to it and never send the client correct time.

I agree that purposely serving bad time might be the best way how to
get an attention of the user and get the NTP implementation fixed if
it can be identified reliably and no innocent clients behind that IP
adress are harmed.

The identification could be improved, for example by monitoring the
distribution of the client's polling interval as simple clients use a
fixed interval, but I'm not sure if it's possible to make it so
reliable that ntpd could be allowed to send a reponse with purposely
bad time.

Miroslav Lichvar

More information about the questions mailing list