[ntp:questions] Is it possible to confuse ntpd's freq error measurement procedure?

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Thu Jun 7 01:29:04 UTC 2012


Paul Malishev wrote:
> I have two ntpd peers which exchange time between
>  themselves and also receive time from external server.
> I believe that at some moment connection to external
>  server was lost and time on these two peers drifted a bit.
>
> When connection to external server was restored both ntpd
>  on both peers logged something like:
> Jun  5 13:21:09 peer0 ntpd[5052]:
>  frequency error 18158 PPM exceeds tolerance 500 PPM
>
> After that there were a lot of messages with not so big freq error:
> Jun  5 13:23:18 DIG ntpd[5052]:
>  frequency error 608 PPM exceeds tolerance 500 PPM
...
> When an operator saw time difference with external server about 30sec
...

 They must have been unable to reach the external server,
  for a really long time?


> server 127.127.1.0 noselect
> fudge  127.127.1.0 stratum 10


 If it looses the all other servers, it will likely continue
   to run away at whatever frequency was last set;
  If it can still contact the internal peer,
   they should run off together (or one would chase the other).

 You might try orphan mode instead; e.g.

tos cohort 1 orphan 10

 <http://www.eecis.udel.edu/~mills/ntp/html/orphan.html>
  {Although I'm not certain it would have any significant value,
    when only one other server can be reached.}


> restrict 192.168.0.240 mask 255.255.255.240

 If you ever use a server by host name,
  especially when the name may return multiple A records,
  (e.g. pool servers) you may need to add a restrict source
  line; e.g.

restrict source nomodify


> tinker step 0

 Remove that if you want it to step, instead of slew always.
 BTW, step 0 also disables kernel discipline!


> tos minclock 1 minsane 1

MinSane defaults to 1 ?


> peer 192.168.0.241 burst iburst minpoll 4 maxpoll 6 prefer true
> server **external-server-ip** burst iburst minpoll 4 maxpoll 6 true

 You should not do "burst" on servers that are not your own.
  {I have no idea who **external-server-ip** belongs to.}
   {"iburst" is fine}

  The docs also seem to say to not use burst or iburst with "peer" ?
  <http://www.eecis.udel.edu/~mills/ntp/html/assoc.html>
  <http://www.eecis.udel.edu/~mills/ntp/html/confopt.html>


 Are you really intentionally saying to treat both
  the other internal server and the external server
  as if they always have valid time, with the true option?
   {Even if some day they may not be even close.}

   Are you treating them both as true chimers
    because you only have two servers to reference?


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