[ntp:questions] handling falseticker

catia.lavalle at bechtle.com catia.lavalle at bechtle.com
Tue Feb 17 07:51:43 UTC 2009


Hallo,

I have the following configuration Stratum 0 configuration: 

1 x Stratum 0 (DCF "Clock") --> 1 x Stratum 1 (let's give it the IP 
10.1.1.1)
1 x Stratum 0 (GPS "Clock") --> 1 x Stratum 1 (let's give it the IP 
10.1.1.2)
I do not have (for security policy) the possibility to give any other 
alternative (extern) time source to the Stratum 2 Servers.

This means that my Stratum 2 Servers have only 2 servers. Obviously this 
configuration is not "falseticker save". 
I have a monitoring active which warns me if the time offset between the 2 
Stratum 1 server gets bigger than a fixed limit.

In such a situation anyway the NTP daemon on the Stratum 2 servers would 
mark one of the 2 Stratum 1 servers as a falseticker and "ignore" the time 
coming from it.
Since there are only 2 Stratum 1 server to choose from the "voting" 
decision do not really apply, in such a way that the decision that the NTP 
on the Stratum 2 servers take upon "ops! there is a falseticker. Which one 
is falseticker?" is rather casual (I guess). 

Say they mark the server 10.1.1.1 as falseticker. 


     remote           refid
===================
*10.1.1.1          .GPS. 
x10.1.1.2           .DCF. 
  127.127.1.1    .LOCL. 

At this point I will get a warning from my monitoring, I will check 
manually with an external source which time really is and have a look to 
the decision that NTP on the Stratum 2 Server took. Say I realize that the 
decision taken is wrong: the 10.1.1.1 is not the false ticker, the true 
false ticker is 10.1.1.2

What should I do? I mean is there a way to force NTP "on the fly" to 
change it's mind? I have in mind something like a command line saying 
"force to trust server 10.1.1.1" (which simultaneously automatically will 
imply "then ignore  10.1.1.2 since this means it is the true 
falseticker")? ==> to force the following "switch"

     remote           refid
===================
x10.1.1.1          .GPS. 
*10.1.1.2           .DCF. 
  127.127.1.1    .LOCL. 

Sure I could reconfigure ntp.conf with a prefer on the 10.0.0.1 server, 
and restart the daemon (would it work? I guess so), but I do not really 
like it, I find it to "permanent".


thanks




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