[VoiceOps] DST handling

James Hess mysidia at gmail.com
Fri Nov 6 00:28:30 EST 2009

The NTP protocol uses UTC as reference time;  UTC  is a time zone that
has no DST changes.      If the real-time clock on a device is kept in
a local time, the NTP implementation on the device has to translate
to UTC  and back.
There should be no difference in the calculated UTC time before, or
after time change  caused by DST.

On Thu, Nov 5, 2009 at 4:34 PM, Jonathan Thurman
<jonathan at thurmantech.com> wrote:
> On Thu, Nov 5, 2009 at 3:16 PM, David Hiers <hiersd at gmail.com> wrote:
>[...] It is the responsibility of the operator to get the clock in
> sync to start with, then NTP will adjust for the natural drift.

Adjusting clocks by large amounts by default can be dangerous.. there
might be an accident on another NTP server.    An evil hacker who can
forge NTP packets may have cracked an expired  Kerberos TGT,   or  may
desire that a server execute a certain cron job over and over

If the time is off by less than 128ms,  NTP will slew.  If it's off by
more than that NTP will often step  (make a large error correction)
But there is a "panic"  limit  to the error corrections. If the clock
is too far off,  NTP will simply exit.   You can change the number of
seconds, or set it to be unlimited  [at own risk]:

tinker panic 0

In certain *ix distros, you also get stepping at NTP startup according to
entries made in an  /etc/ntp/step-tickers


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