[ntp:hackers] Does ntpd need to whine more ?

Martin Burnicki martin.burnicki at meinberg.de
Tue Oct 4 11:06:29 UTC 2005


Dave,

sorry for the late response, we've had a holiday here in Germany on Monday.

David L. Mills wrote:
> Martin,
> 
> I say again, an intermediate server cannot directly determine for a
> downstream client whether an upstream server has or has not "lost"
> synchronization; it can only reveal in the root distance how much the
> maximum error has accumulated. Only the dependent client can judge from
> this statistic whether or not to believe the time.
> 
> The present behavior is not a bug; it is at the definitive core of the
> design. It is necessary in order to support very long poll intervals as
> with the modem driver.

I'm afraid there's again some misunderstanding here. You always mention
that this is necessary in order to support very long poll intervals.

What I mean, however, has nothing to do with poll intervals. If ntpd
polls an upstream server or refclock and does not get a good response
back, then it should indicate this to its clients, and also to the users
who check the ntpd status to see if their time sync network really is in
sync.

No matter whether ntpd polls its upstream source after a long or short
interval: if it does not receive any response at all (e.g. because the
server is down), or the response packet has the leap bits set (e.g.
because the refclock is not synchronized) then ntpd should not pretend
that everything is OK.

Should the normal user compare the root dispersion to some limit do find
out that his timesync is broken and the upstream server needs interaction?

BTW, the root dispersion is initialized to 0 if ntpd starts up, then
switches to higher values during initial synchronization with an
upstream source, and then converges to a smaller value as the PLL
converges. If root dispersion is a quality/selection criteria, shouldn't
it be initialized to a large value in order to reflect that time is not
very accurate while the leap bits are initially set?

Anyway, here's a quote from your own email to hackers at 1st of October,
concerning ghetto mode (of which I've never heard before that):

> If all base servers or there sources fail, all machies enter ghetto
> mode. The stratum is forced to the ghetto stratum ...

This is exatly what I mean: at least drop the stratum to indicate that
something is wrong. This should be the default behaviour for any ntpd node.


Best regards,

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany


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