[ntp:questions] NTP Polling Explanation

Bill Myers whmyers at gmail.com
Tue Aug 15 13:58:28 UTC 2006

I have System Administrators who insist upon maxpoll=4.  First of all,
thanks to those in this list who I have plagerized!  Second, is the
following explanation accurate and use appropriate terminology.

Q:   Do you recommend any tweaks to the NTP configuration beyond the listing
of the servers, such as maxpoll=4?

A:    Tweaks are not recommended and are discouraged. Forcing a poll
interval that is more frequent than NTP would normally select on its own
hurts accuracy and stability of time on the local system.  NTP polling does
not directly synchronize the local system clock to the server clock; rather,
a complex algorithm calculates an adjustment value for each tick of the
local system clock.  Shorter polling intervals cause NTP to make large but
less accurate calculations that never stabilize, causing the local system
clock to wander.  Longer polling intervals allow NTP to calculate smaller
tick adjustments that stabilizes to a more accurate value, reducing wander
in the local system clock.

NTP dynamically selects the optimal poll interval between the values of
minpoll and maxpoll, which default to 64 and 1024 seconds respectively and
are correct for most environments. Shorter values are used to correct large
errors while longer values are used to refine accuracy. NTP dynamically
varies this value as conditions change and requires several days of
continuous operation to converge on an optimal adjustment value.

Thanks in advance ...

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