[ntp:questions] Re: Stratum problem with non-handled clock
david at djwhome.demon.co.uk
Thu Jun 2 06:45:53 UTC 2005
In article <mailman.50.1117683487.91305.questions at lists.ntp.isc.org>,
Christophe Greisberger <greisberger at zenon-media.net> wrote:
> I have an exact clock and set the stratum to 16.
> Is there any ntp.conf tweak to force the stratum to a lower value?
The best solution is to use a clock for which ntpd has a clock driver
so that ntpd knows that the clock is working and can have confidence that,
for example, the time isn't simply being stepped every few minutes, but
is being properly disciplined in both phase and frequency. (You many
want to consult your clock supplier; if they don't have an ntpd driver,
it is likely that they are not seriously in the market.)
As clock drivers are generally better supported on Unix, a good idea
would be to use a cast off machine (can be a 486DX) as the machine
with the clock and run FreeBSD on it. (Such a machine will be much
better as a time server than any NT box.)
Failing that, you can configure a local clock driver. The disadvantage
with this is it doesn't know the true time quality, e.g. time since last
clock sample and maximum drift rate, so it will report falsely optimistic
time quality parameters. It will also not know if the clock has failed.
The workaround is to fudge its stratum to a relatively high value. The
default is around 3, but normally people are advised to use 10, which
makes it very difficult for someone with access to a known valid source
to use it by mistake.
As this is a more legitimate use of local clock than the increasingly
common one of using it to distribute an arbitrary function of time from
an unsynchronised machine, one might tolerate a lower stratum, but the
lack of fault reporting is still an issue.
> Or even a parameter of ntpd so that it accepts high stratum clocks?
There is never going to be a parameter in any official version that
disables this part of the time quality checks. Stratum 16 means
unsynchronised and a server reporting it will normally also send other
indications of this state, e.g. leap indicator = 3.
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