[ntp:questions] "good enough" ntp configuration

Richard B. Gilbert rgilbert88 at comcast.net
Fri Jun 8 21:03:53 UTC 2007

Mark Boolootian wrote:
> Folks,
> I'm a simple-minded dweeb looking to provide campus systems with
> reasonably accurate clocks.  If campus system clocks are within, say,
> two seconds of one another, they'll probably let me keep my job.
> I've rummaged through the docs and mailing list, but I haven't really
> found an answer to this "good enough" kind of question.  At the moment,
> I have a pair of NTP stratum 1 appliances, one GPS, the other CDMA.  
> These appliances claim to be able to handle approximately 200,000 clients:
>   http://www.endruntechnologies.com/time_server_clients.htm
> We'd probably be fine with a factor of ten less.
> What I'd like to know is, given my desire for sub-two seconds of accuracy 
> (am i using the correct term for what i want?) am I good enough to just 
> point clients at the stratum 1 pair?  
> I don't see any value in building a hierarchical stratum infrastructure.
> I've seen several things that have me wondering if it might be wise to
> add a third server, but I can't really tell how useful that would be.
> Any advice would be much appreciated. Thanks in advance.
> mark
> ---
> Mark Boolootian
> UC Santa Cruz

You're probably okay just pointing the whole campus to your two servers.
Best practice, when using internet servers, is to use a minimum of four.
In your situation, with two high quality reference clocks, it's probably 

Assuming that the clients have no internal problems, you can probably 
keep the herd within ten milliseconds.  Some Windows and Linux systems 
have been known to lose clock interrupts during periods of high disk 
activity.  The symptom is that ntpd will step the clock forward 
periodically.  Even with this sort of misbehavior, you should be able to 
maintain synchronization within two seconds.

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