[ntp:questions] Optimal config

David L. Mills mills at udel.edu
Tue May 6 04:10:11 UTC 2008


Richard,

It's a little more complicated than that. If the server is unreachable 
when a poll is scheduled, a single poll is sent. If no reply is heard, 
the cleint tries again in 64 s and repeats for a total of three times 
and returns to the original poll interval. If not heard after that, it 
backs off. This behavior is designed to protect busy servers while 
minimizing the time to resume after a length outage.

If a reply is heard for the first poll, the client completes the iburst 
sequence for a total of six polls. This is almost always enough for 
initial synchroniztion. The same behavior is used for the burst mode, 
ehich is recommended when the poll interval is much greater than 1024 s.

Dave

Richard B. Gilbert wrote:
> Dennis Hilberg, Jr. wrote:
> 
>> Richard B. Gilbert wrote:
>>
>>> Iburst simply causes ntpd to send eight requests to a server at 
>>> intervals of two seconds when it initializes.  The eight replies that 
>>> will normally result allow ntpd to fill its filter pipeline and make 
>>> a pretty good guess at what time it is.  Subsequent requests are sent 
>>> at the normal poll intervals, ranging from 64 to 1024 seconds.
>>
>>
>> Unless the specified peer becomes unreachable, in which case the 
>> eight-packet burst will resume until the peer is reachable. For 
>> ntp-4.2.4p4 anyway.
>>
>> Dennis
>>
> 
> It seems as if the code might be improved a little.  There's no point in 
> whipping a dead horse!  If no reply is received in response to any of 
> the eight initial request packets, it would seem reasonable to do the 
> "exponential back off"; wait one minute and try again, wait two minutes 
> and try again, wait four minutes and try again. . . .




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