[ntp:questions] Keeping NTP Honest

Richard B. Gilbert rgilbert88 at comcast.net
Fri Jul 10 21:42:15 UTC 2009

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> Unruh wrote:
>> Evandro Menezes <evandro at mailinator.com> writes:
>>> As I mentioned before, in some cases, NTP relies too
>>>  much on low-stratum servers, even when they're blatantly
>>>  wrong.  For instance, the last leap second event, when
>>>  many pool servers were poorly configured.
>>> Mulling over that, I wondered how I could tip NTP to
>>>  scale down the poll period in such cases.  So I tried
>>>  this trick and it seems to work fairly well when only
>>>  one server is kaput:
>>> server   pool.ntp.org iburst maxpoll 6
>>> server 0.pool.ntp.org
>>> server 1.pool.ntp.org
>>> server 2.pool.ntp.org
>>> server 3.pool.ntp.org
>>> By having one server that remains polled every 64s, NTP
>>>  could realize more quickly that there was something
>>>  rotten in Denmark.  However, if that one server is
>>>  neither selected nor a candidate, this trick doesn't
>>>  work.  I'd hesitate to make it the preferred server
>>>  though.
>>> Thoughts?
>> And you have at least a 1/5 chance that IT is the bad server.
>>  What do you do then?
> Ignore the strat 1s with floor?  e.g.
> tos minclock 5 minsane 4 floor 2
> pool us.pool.ntp.org preempt iburst
> pool pool.ntp.org preempt iburst

If you have one server out of five that has gone astray, ntpd should 
notice it fairly quickly.  It should not need help.  Two bad servers 
that agree with each other are more difficult.

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