[ntp:questions] Re: Behavior when one server is erroneous

David L. Mills mills at udel.edu
Tue Jan 20 01:40:34 UTC 2004


Frederick,

You will find comfort, not to mention wealth and happiness, from Slide 9
and the slides around it in the architecture briefing at the NTP project
page. The thing you are missing is the synchronization distance, which
depends on delay and dispersion and which must be very large for the
half-second suckers to be believed. If it is and they are, the dirty
rotten chimers really are that bad and ntpd is doing the best it can.

The combining algorithm, also detailed in the slides, does a average
weighted by inverse distance, so if the distance is very large, the
influence of the bad chimers should be dimished.

Why are you messing with these bums in the first place? Fix the problem.
I would suspect massive frequency error at the root of the problem.

Dave

Frederick Bruckman wrote:
> 
> In article <mailman.35.1074288033.1757.questions at ntp.org>,
>         "Christopher J. Burian" <cburian at ll.mit.edu> writes:
> >
> > What I wanted to bring to the attention of ntpd developers is
> > that the daemon appears to do some sort of weighted averaging
> > of the three mostly correct servers and the one bad server.
> > Shouldn't the algorithm perhaps vote to reject servers notably
> > different from consensus?
> 
> Mostly it does, except in the 4th report below, the refclock
> is marked authoritative, even though it's at odds with all the
> others. It seems like what you want is to add "tos minsane 2"
> (or 3) to the top of "/etc/ntp.conf". That should cause the
> refclock to be rejected if it doesn't agree with at least 1
> (or 2) others. An alternative design would be to simply let
> your stratum 1 server faithfully report the bad time received
> from the refclock, and smooth it all out at stratum 2.
> 
> > ntpq> pe
> >      remote           refid      st t when poll reach   delay   offset  jitter
> > ==============================================================================
> > *127.127.29.1    .CDMA.           0 l    7   16  377    0.000  -26.916 116.099
> > +155.34.100.67   .GPS.            1 u  184  512   37    3.277  450.174  80.107
> > +155.34.3.123    .GPS.            1 u  185  512   37    5.223  450.440  79.103
> > +155.34.3.8      155.34.3.123     2 u   23   64  377    0.002  574.188  25.114
> > ntpq> pe
> >      remote           refid      st t when poll reach   delay   offset  jitter
> > ==============================================================================
> > x127.127.29.1    .CDMA.           0 l   10   16  377    0.000  -226.84  99.691
> > x155.34.100.67   .GPS.            1 u  331  512   37    3.277  450.174  80.107
> > x155.34.3.123    .GPS.            1 u  332  512   37    5.223  450.440  79.103
> > *155.34.3.8      155.34.3.123     2 u    5   64  377    0.002  583.724  14.496
> > ntpq> pe
> >      remote           refid      st t when poll reach   delay   offset  jitter
> > ==============================================================================
> > *127.127.29.1    .CDMA.           0 l   16   16  377    0.000  -671.47 141.500
> > x155.34.100.67   .GPS.            1 u   22  256   17    3.357  -74.293  46.467
> >  155.34.3.123    .GPS.            1 u   21  256   17    5.096  -19.350  72.238
> >  155.34.3.8      155.34.3.123     2 u   56   64   76    0.919  -21.359 177.973
> > ntpq> pe
> >      remote           refid      st t when poll reach   delay   offset  jitter
> > ==============================================================================
> > *127.127.29.1    .CDMA.           0 l    5   16   37    0.000  -75.688  41.494
> >  155.34.100.67   .GPS.            1 u   20   64    1    9.419  750.087   0.002
> >  155.34.3.123    .GPS.            1 u   21   64    1    5.276  746.882   0.002
> >  155.34.3.8      155.34.3.123     2 u   20   64    3    0.002  288.527 457.307
> > ntpq> pe
> >      remote           refid      st t when poll reach   delay   offset  jitter
> > ==============================================================================
> > *127.127.29.1    .CDMA.           0 l   11   16  377    0.000  295.474  70.632
> > +155.34.100.67   .GPS.            1 u  183  512   37    3.707  784.915 144.207
> > +155.34.3.123    .GPS.            1 u  183  512   37    5.202  897.152 125.242
> > +155.34.3.8      155.34.3.123     2 u   25   64  377    0.002  1129.50 168.278
> 
> --
> Frederick



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