Thanks for your answer, I can't have a step on the clock because that would screw up my applications. However if I keep the load within a certain range I should fine, don't I ? I am synchronising one node to several public NTP servers, and the others nodes are synchronised to the first one. There are 2 to 24 nodes in my sub net. Do you think that should be feasible ?
Maxime On Sat, Apr 19, 2008 at 10:34 AM, David Woolley <[EMAIL PROTECTED]> wrote: > Unruh wrote: > > Harlan Stenn <[EMAIL PROTECTED]> writes: > > > >>>>> In article < > [EMAIL PROTECTED]>, > [EMAIL PROTECTED] (maxime louvel) writes: > > > >> maxime> Hi, I would like to know if NTP (and particularly ntpd) is able > to > >> maxime> synchronise a clock, only playing with the frequency. I want > to > >> maxime> avoid any step in the clock that would probably screw up my > network > >> maxime> appli. > > > >> It's *possible* and it can be a really bad idea. > > > >> For most folks, only steps *backward* are a problem. > > > > Actually, ntp does synchronize the clock by "playing with the frequency > > only" unless the step size is so large (128ms by default but up to > 600sec > > by option) that it will step. > > There are two supported settings for this limit, 128ms and 600,000ms, > but you can set other values, including infinite, with an option that > comes with severe health warnings. If you set a value of more than > 500ms on systems that implement part of the clock discipline in the > kernel, you will force them not to use that mechanism, and therefore get > lower quality time. > > There are also options, unfortunately also with health warnings, that > can effectively eliminate the main legitimate cause of this, which is > high asymmetric traffic loads on medium speed internet connections which > have not been traffic shaped for NTP. If you suffer large steps for > other reasons, you should fix the underlying cause. Fixing asymmetric > load can have commercial implications, as only high value ISP accounts > are likely to support the necessary traffic shaping. > > (Another source of steps is lost clock ticks, but that generally only > gives the, relatively benign, positive steps.) > > Systems which suffer large steps and aren't allowed to step have been > reported to hunt (in the control theory sense) rather badly. > > Note, the subject is a little confusing as it could be read as meaning > that steps are allowed to remain uncorrected. That would be > unacceptable for a protocol where every node is both client and server. > That would be like if you had to drive 30 miles and insisted that you > drove at 30 mph, but you were delayed by a traffic jam, and still > declared the journey complete after exactly one hour. > > _______________________________________________ > questions mailing list > [email protected] > https://lists.ntp.org/mailman/listinfo/questions > -- Maxime Louvel 0044 7964 5555 80 43 Allen road Whitemore reans WV60AW Wolverhampton United Kingdom _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
