Hi
> On Feb 14, 2017, at 9:23 PM, Chris Albertson <[email protected]> > wrote: > > On Tue, Feb 14, 2017 at 7:31 AM, MLewis <[email protected]> wrote: > >> >> >> - a dedicated machine/box for unencumbered acceptance of PPS, and >> - for systems with a business need, a dedicated NTP server/box disciplined >> by the PPS source (with dedicated communication), while maintaining >> internet NTP sources as backup for when the PPS source fails? >> Is there a better way? >> Other considerations? > > > Don't ever think about "backup servers". NTP will always select the "best" > reference clocks. The best ones are defined as the subset of references > that track each other. > > Best practice today is to have two independent NTP servers and two GPS > receivers. I would argue that you need at least three servers (and more like five). When given only two servers NTP simply dithers back and forth between them. It does not have a way to figure out which of two clocks is wrong. It will detect a missing clock, but not one that is simply off time by a bit. Bob > It is best if these are independent as you can make them, > different buildings if you can. I would even use different brands of > hardware to protect against a bug. Then throughout your company all your > PCs are configured to look at both NTP servers > > Each server is configured to use the GPS reference clock, the other "twin" > NTP server as well as about five Internet "pool" servers. > > If your location does not have an Internet connection. ( YES this can > happen. I've worked on computers that process classified information and > these computers never have Internet access.) You can configure them so > they run in "orphan mode" that is they all use each other as reference > clocks. Then when GPS is lost thenoormal NTP clock selection algorithm > will select the subset of PCs that all agree on what the time is. The > outliers tent to get ignored. When GPS comes back up the system makes a > gradual and graceful recovery. > > > > > > Chris Albertson > Redondo Beach, California > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
