[ntp:questions] Date Jumped

Danny Mayer mayer at ntp.org
Mon Jan 25 03:23:18 UTC 2010

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> Danny Mayer wrote:
>>> This can happen any time.  pool.ntp.org is a large
>>>  collection of servers that joined a voluntary pool
>>>  of servers.  Any single server in this pool can send
>>>  the wrong date and time if it likes to, or if there
>>>  is an error.
>> Someone with privileges changed the clock, realised his
>>  or her mistake and changed it back.
> ... and if you are using three or more NTP servers,
>  if one gets changed to the wrong date / time, it will
>  get ignored by NTP.

That's not what I said. I said that this *cannot* happen on the local
server after the first time it steps the clock no matter what the remote
servers say, even if all of the remote servers agree on the time. The
step size is too large for it to be processed by ntpd.

>   See all that NTP byzantine generals stuff;
>    NTP minsane & minclock options, ...
>    NTP selection / intersection / mitigation algorithms, ...

Not related.


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