[ntp:questions] Keeping NTP Honest
Richard B. Gilbert
rgilbert88 at comcast.net
Sun Jul 12 19:39:07 UTC 2009
Evandro Menezes wrote:
> On Jul 10, 2:40 pm, Unruh <unruh-s... at physics.ubc.ca> wrote:
>> And you have at least a 1/5 chance that IT is the bad server. What do
>> you do then?
> Well, bar a false ticker, when it's ignored, it would keep NTP in
> shorter poll periods. IOW, "honest".
> I wonder though if the right thing would be to configure 6 servers
> with half of them limited to 64s polling...
Four, five, or seven are the "magic" numbers which allow you to survive
the failure of one, two, or three servers respectively. I suppose these
numbers could be extended to cover the failures of still more servers
but at some point you've got to say "this is ridiculous" and stop.
Failure, in this context, can mean anything from not responding to
responding with the wrong year; e.g. suddenly it's 2023. Such things
should not happen but they do; the last NTP Survey found a server
responding with the wrong year!
Tinkering with MINPOLL and MAXPOLL is generally a bad idea. Ntpd will
adjust its polling interval to the optimum value for the conditions then
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