On 2014-12-04, Rob <nom...@example.com> wrote: > David Lord <sn...@lordynet.org> wrote: >> Brian Utterback wrote: >>> On 12/2/2014 4:00 AM, Rob wrote: >>>> The whole "have 3 servers to select a majority" thing is absolutely not >>>> required when your servers are accurately synchronized themselves and >>>> your requirements are "only" within-a-second. It is true that when you >>>> have two servers the clients cannot know which one is right, but it is >>>> trivial to keep servers within a millisecond of eachother with GPS and >>>> within 10 milliseconds using only network peering. To that is two >>>> orders of magnitude better than you require. >>> >>> Be careful with this generalization. While it may be "trivial", it isn't >>> "automatic". I deal with customers all the time that have configured >>> exactly two servers on their clients and then are surprised later when >>> all of the clients become unsynchronized and start free drifting. I >>> always recommend against it. I still think that it takes four to >>> guarantee a majority but I don't have proof of that. Someday I will >>> spend some time to either prove or disprove it, but alas, time is >>> something I don't generally have extra to spend. But you are better off >>> with one than two from an operational standpoint. >> >> The ntp html docs on selection state that four are needed to >> guarantee a majority and give an example of this case. > > In practice this problem does not occur when you use only your own > servers that you monitor and trust, and it confuses people that > want to setup NTP on their company network. > > They get sent away with "you need to configure and maintain 4 servers > or better even more". When the servers either are synced correctly > or are down, this is not required.
People love to either read or make rules, no matter how senseless. That way you do not have to think. _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
