[ntp:questions] ntp-dev: PPS is a falseticker?

mike cook michael.cook at sfr.fr
Sat Jun 14 16:52:40 UTC 2014


Le 14 juin 2014 à 16:56, Rob a écrit :
> 
>> By the way, you can have more than one server marked prefer.
> 
> So the solution is to mark everything but the PPS server marked prefer?
> What is the value of that?

The documentation, although a bit long in the tooth, does not recommend multiple preferred peers:-
"While the rules do not forbid it, it does not seem useful to designate more than one peer as preferred, since the additional complexities to mitigate among them do not seem justified from on-air experience."

Let's see what happens:-

# muon  stratum1 gps ref
  server 192.168.1.4  iburst minpoll 4 maxpoll 4 prefer

# laurelineA GPS sync'd NTP server
  server 192.168.1.23 iburst minpoll 4 maxpoll 6 prefer

# raspberry pi net sync'd NTP server
  server 192.168.1.15 iburst minpoll 4 maxpoll 6 prefer

restart ntpd and let the dust settle:

Sat Jun 14 18:30:56 CEST 2014
     remote           refid      st t when poll reach   delay   offset  jitter
=========================================================
o127.127.22.1    .PPS1.           0 l   14   16  377    0.000   -0.004   0.008
+192.168.1.4     .PPS1.           1 u   11   16  377    0.874    0.047   0.010
+192.168.1.23    .GPS.            1 u   10   16  377    0.549    0.054   0.051
*192.168.1.15    192.168.1.23     2 u    9   16  377    0.918    0.498   0.056

now pull 192.168.1.15. 

Sat Jun 14 18:36:37 CEST 2014
     remote           refid      st t when poll reach   delay   offset  jitter
=========================================================
o127.127.22.1    .PPS1.           0 l    2   16  377    0.000   -0.006   0.008
*192.168.1.4     .PPS1.           1 u   15   16  377    0.881    0.044   0.017
+192.168.1.23    .GPS.            1 u   15   16  377    0.552    0.053   0.008
 192.168.1.15    192.168.1.23     2 u  158   16    0    0.914    0.422   0.052

192.168.1.4 gets selected and we still have PPS. 

So while not being categoric about it, it looks like assigning multiple prefer peers may have some merit.

Mike



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