[ntp:questions] which servers should be peers?

David Taylor david-taylor at blueyonder.co.uk.invalid
Thu Sep 19 07:26:04 UTC 2013

On 18/09/2013 23:09, unruh wrote:
> Well, there is a problem. You said that  you had seen all of your S1
> servers suddenly declare that the time was 1982 and presumably that the
> times were very close (to less than a second). They would then form a
> group of servers which could well outvote the S2s that are delivering
> the correct time. If you really have a failute mode like that, then you
> will be screwed and you will need to include some outsiders to break the
> potential tie.
> Such a unified crazyness really needs to be looked into. Why in the
> world did they all go nuts at the same time?

A good reason to have /different/ devices as the stratum-1 servers.  My 
feeling was that the OP was looking at a very unlikely scenario, until I 
remembered about leap-seconds.  That's the one area where you do need to 
be careful in choosing stratum-1 server components - so that they react 
correctly and automatically to leap-second time adjustments.

I've refrained from suggesting configuration as my experience of large 
installations may well now be out of date, but I would be inclined to:

- peer the four stratum-1 servers, plus allow them access with to the 
pool and to one or two local known good external servers

- configure the stratum-2 servers to point to the four stratum-1 servers 
and to both pool and one or two local known good servers.

Using the "pool" directive for all servers will allow NTP to select the 
appropriate number of extra servers, and automatically drop ones with 
become offline or whatever.
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