[ntp:questions] ntp server specs

Richard B. Gilbert rgilbert88 at comcast.net
Thu Apr 21 01:11:05 UTC 2011

On 4/20/2011 7:43 PM, Chris Albertson wrote:
> On Wed, Apr 20, 2011 at 2:07 PM, C BlacK<rblak at non.net>  wrote:
>> If I am setting up an ntp server for a lot machines, I have some questions.
> Then you almost certainly want two NTP servers.  Ho9w else to do
> scheduled maintenance, handle unscheduled down times or even know that
> your NTP server is working correctly.   If NTP is important you need
> at least two.  But no big deal as PC hardware is dirt cheap and used
> re-purposed)  PC hardware works fine for this

Two NTP servers does not constitute a solution to the problem.  If the 
two servers disagree, which one do you believe?

Four servers are required for a robust configuration.  One server can 
fail, either not responding or responding with an incorrect time and be 
"voted out" by the remaining servers.

If you *must* have the correct time to satisfy either legal or 
operational requirements you use at least four servers.  To survive the 
failure of two servers, you need five and to survive the failure of 
three you need seven.  In this context "failure" can mean either not 
responding or responding with incorrect time.

And yes, it has happened that systems have responded with grossly 
incorrect time.  The last NTP Survey found one system that responded 
with the wrong year!!!!!!!

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