[ntp:questions] Re: NTP, no external time source, peering "Undisciplined Local Clocks" ?
David L. Mills
mills at udel.edu
Wed Oct 19 20:52:09 UTC 2005
As confirmed by experiment, having each client average all the others is
not a good idea. The ensemble tends to do a random walk and display very
poor statility. Better to pick one of them and let it time the rest.
However, folks have tended to extend this idea to provide a multiple
backup capability. This is a bad idea, as evil timing loops can form
that take a long time to count to infinity.
There is a new wrinkle designed for isolated configurations with
multiple backup requirements. It is called orphan mode and works best
with broadcast/multicast networks or networks with multiple
symmetric-mode networks. The networks self-organize, elect a leader and
pecking order depending on the particular failure topology. It's been
tested here in the ntp-dev version, but should still be considered
experimental. See the documentation on the authentication options and
miscellaneous commands pages in the online documentation.
> On Tue, 18 Oct 2005 14:19:11 GMT, mmolteni at cisco.com (Marco Molteni)
> wrote for the entire planet to see:
>>Say I don't know if a clock is better than the other, so by configuring
>>B and C to use A as server I risk to have a not so good time if A is
>>Can I configure A,B,C to peer with each other in a meshed fashion, so
>>to have each clock influenced by all the others?
> The general feeling on this ng is that this is not a good application
> for NTP.
> I would go further, and say it is a poor design using any type of
> software. Sure, you may get some weird approximation of the average
> clock errors around your network, but it will still drift, by an
> unknown amount.
> Three PCs, all of which don't know the time, can't really help each
> other find it.
> - Eric
More information about the questions