[ntp:questions] Re: Setting Up NTP Subnet

Richard B. Gilbert rgilbert88 at comcast.net
Tue Mar 7 22:23:43 UTC 2006

Bill Myers wrote:
>  I have questions regarding best practices on architecture of NTP subnets.
> I've thoroughly read "Notes on Setting up a NTP subnet" from the NTP sites.
> Is there a need for multiple external time source TECHNOLOGIES.  That is, is
> it sufficient to use multiple (8) GPS receivers with ACTS dial backup
> and Rubidium clocks?   This is a sizeable investment for the infrastructure,
> but is it the right way?  Is it necessary or desirable to have other sources
> such as radio and/or Internet?
> In case you have not picked up on it, I'm talking about an appliance here.
> I find it odd that one cannot NTP peer these appliances.  This suggests to
> me that we should create a stratum 2 tier peer layer a stratum 3 tier that
> peers and serves time to the endpoints.
> More dysfunction?  The plan is for the stratum 2 tier, which is also the
> time distribution tier, to be the cache DNS for some high-volume data center
> environments.
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It depends strongly on your needs for correct time and reliability.  You 
have not really specified your requirements. Are you serving a single 
site or multiple sites?  How far can your time deviate from UTC?   How 
much money are your willing and able to spend?

If you absolutely must have sub millisecond accuracy and 100 percent 
reliability then you need to allow for:
1. Failure of a reference clock (GPS receiver)
2. Failure of the GPS System (insane satellites, jamming of GPS 
frequencies, etc.)
3. Failure of one or more of your lowest stratum servers.
4. Things neither you nor I have thought of or can think of!

So tell us more and maybe we can give you better advice.

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