[ntp:questions] Using two NTP Server: Bad?

Richard B. Gilbert rgilbert88 at comcast.net
Fri Apr 22 15:30:08 UTC 2011

On 4/22/2011 5:48 AM, Roger wrote:
> On Thu, 21 Apr 2011 09:32:21 -0400, "Richard B. Gilbert"
> <rgilbert88 at comcast.net>  wrote:
>> One server: if it fails you have nothing!
>> Two servers: If the two differ, which one do you believe?
>> Three servers: degenerates too easily to the two server case.
>> Four servers: Allows the failure of one server.
>> Five servers: Allows the failure of two.
>> Seven servers: Allows the failure of three.
> I've seen these number quoted before and I don't understand
> the last one. Why doesn't 6 allow for the failure of 3? Why
> doesn't 7 allow for the failure of 4? Assuming that this
> wasn't a mistake in the dim and distant past which keeps
> on being repeated what am I missing?

You might try Professor Mills' book on NTP

"Computer Network Time Synchronization: The Network Time Protocol on 
Earth and in Space, Second Edition [Hardcover]"
David L. Mills
David L. Mills (Author)
› Visit Amazon's David L. Mills Page
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I suspect that the math is a little heavy for most people.  The price
may also be a little heavy for most people but if you want to get it
"from the horse's mouth" it's the authoritative source.

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