[ntp:questions] How should an NTP server fail?

Kasper Pedersen spam at kasperkp.dk
Fri Jun 11 17:43:51 UTC 2010


On 06/11/2010 04:47 PM, David L. Mills wrote:
> My scenario did include the condition of eight valid sample before
> pulling the plug The first missed poll response did result in one
> MAXDISPERSE sample in the filter, but that is completely irrelevant. The
> point is the poll routine calls clock_select() for every poll sent when
> the last four samples in the reach register are missing, so it is
> guaranteed that the server be marked down after that.

For entertainment value, 'ntpq cartoons' with 4 samples, and 8 samples:

At 2 minutes after pulling the plug, there is a difference.

4:
  10.5.5.254  10.5.5.16   2 u    1    8    1    0.284   -0.294   0.000
  10.5.5.254  10.5.5.16   2 u    1    8    3    0.340   -0.217   0.078
  10.5.5.254  10.5.5.16   2 u    8    8    7    0.285   -0.121   0.140
*10.5.5.254  10.5.5.16   2 u    3    8   17    0.286    0.044   0.265
*10.5.5.254  10.5.5.16   2 u    9    8   36    0.286    0.044   0.265
*10.5.5.254  10.5.5.16   2 u   17    8   74    0.286    0.044   0.265
*10.5.5.254  10.5.5.16   2 u   24    8  170    0.286    0.044   0.265
*10.5.5.254  10.5.5.16   2 u   33    8  360    0.284   -0.294   0.224
*10.5.5.254  10.5.5.16   2 u   43    8  340    0.284   -0.294   0.224
*10.5.5.254  10.5.5.16   2 u   49    8  300    0.284   -0.294   0.224
*10.5.5.254  10.5.5.16   2 u   61    8  200    0.284   -0.294   0.224
*10.5.5.254  10.5.5.16   2 u   64    8    0    0.285   -0.121   0.135
*10.5.5.254  10.5.5.16   2 u  158    8    0    0.286    0.044   0.000
*10.5.5.254  10.5.5.16   2 u  337    8    0    0.286    0.044   0.000

8:
  10.5.5.254  10.5.5.16   2 u    3    8    1    0.294    2.971   0.000
  10.5.5.254  10.5.5.16   2 u    1    8    3    0.295    3.434   0.463
  10.5.5.254  10.5.5.16   2 u    1    8    7    0.288    3.092   0.256
*10.5.5.254  10.5.5.16   2 u    2    8   17    0.277    3.141   0.198
*10.5.5.254  10.5.5.16   2 u    2    8   37    0.277    3.141   0.200
*10.5.5.254  10.5.5.16   2 u    4    8   77    0.277    3.141   0.186
*10.5.5.254  10.5.5.16   2 u    3    8  177    0.277    3.141   0.182
*10.5.5.254  10.5.5.16   2 u    1    8  377    0.277    3.141   0.224
*10.5.5.254  10.5.5.16   2 u   11    8  376    0.277    3.141   0.304
*10.5.5.254  10.5.5.16   2 u   18    8  374    0.277    3.141   0.304
*10.5.5.254  10.5.5.16   2 u   27    8  370    0.277    3.141   0.304
*10.5.5.254  10.5.5.16   2 u   36    8  360    0.277    3.141   0.306
*10.5.5.254  10.5.5.16   2 u   43    8  340    0.277    3.141   0.334
*10.5.5.254  10.5.5.16   2 u   49    8  300    0.278    2.932   0.317
*10.5.5.254  10.5.5.16   2 u   58    8  200    0.283    2.750   0.443
*10.5.5.254  10.5.5.16   2 u   67    8    0    0.283    2.750   0.409
*10.5.5.254  10.5.5.16   2 u   73    8    0    0.283    2.750   0.178
  10.5.5.254  10.5.5.16   2 u   82    8    0    0.283    2.572   0.000
  10.5.5.254  10.5.5.16   2 u   88    8    0    0.283    2.572   0.000
  10.5.5.254  10.5.5.16   2 u   94    8    0    0.283    2.572   0.000
  10.5.5.254  10.5.5.16   2 u  104    8    0    0.283    2.572   0.000

As to whether this difference means anything, I will let others decide.

The above is 4.2.7p34. Also tested on 4.2.4p7. Spaces were shortened
to fit.


/Kasper Pedresen




More information about the questions mailing list