[ntp:questions] Remaining synced on an unsynchronised peer?

Richard B. Gilbert rgilbert88 at comcast.net
Tue Dec 1 01:17:44 UTC 2009


unruh wrote:
> On 2009-11-30, Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
>> Michael Butow wrote:
>>> P.S. Detail that I omitted: we use minpoll=maxpoll=5 (for historic 
>>> reasons in our system).
>> "Historical Reasons" is a pretty feeble excuse.  NTPD will, if permitted 
>> to do so, adjust that polling interval as needed to get the most 
>> accurate time.  By pegging minpoll and maxpoll you are crippling the 
>> ability of NTPD to get the greatest possible accuracy.
> 
> That of course has nothing to do with his question, and if furthermore
> wrong. It depends on what they want to optimize as to what the optimal
> poll level is. The poll6-10 of the stock ntp is a "one sixe fits all"
> which is not necessarily optimal for any particular situation. Whether
> or not they have the ability to figure out what is optimal, or even what
> optimal means is another question, but "historical reasons" could well
> be " sometime in the past someone who really knew what they were doing
> optimised the system at poll level 5". It could mean many other things
> as well, but you have no idea what it means, and your attack is
> misplaced. 
> Note that poll level 11 is almost certainly NOT the ideal poll level to

Where id "poll level 11" sneak in?  I'm sure that I did not mention it
and I don't recall anyone else doing so!

The polling intervals normally used, and self selected by NTPD, are in 
the range 64 seconds to 1024 seconds.  (MINPOLL=6 MAXPOLL=10).  If a 
hardware reference clock is installed, MINPOLL may be forced to 4.

> minize offset from true time while connected to the net. It is also
> level which guarentees that daily temp fluctuations will drive the
> system mad. (poll level 11 means that the ntp system has a time scale for
> responding to changes of about 8 hours, while daily temp fluctuations
> are closer to 1 hr. time scale. )

I run heat in the winter and air conditioning in the summer.  The 
temperature generally stays at 70 degrees F +/- two degrees.  NTPD seems 
to have no problem coping with this environment.  If the environment 
were a commercial data center, the controls of temperature and humidity 
might be a good deal tighter.

> Now perhaps we can get back to answering his question. 
> I suspect but do not know, that part of the problem is the level. The
> machines will always have a level one higher than the system they are
> getting their time from, and they do not like to get time from a system
> at a higher level than they are. Thus the first one to get its time from
> the other will up its level to one higher than the other, and the other
> will then see the first as having too high a level(stratum) to sync to.
> (or the two will walk each other up to the highest level of 15 and see
> each other as unuseable sources)
> 
No NTPD will take time from a Stratum greater than its own.  It's not a 
matter of "not liking", a proper NTP client cannot take time from a 
lower stratum (larger number).  Stratum One gets time from an atomic 
clock.  Stratum Two gets time from Stratum One, Stratum Three gets time 
from Two and so on.  In principle strata range from 1 to 15.  In 
practice anything claiming a stratum between 6 and 15 is probably bogus.

> I might be wrong in that analysis but that is my suspicion.
> 
I disagree.  I too may be wrong but I don't think so.




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