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

Frederick Bruckman fredb at immanent.net
Mon Jan 19 20:07:46 UTC 2004


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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