[ntp:questions] Polling interval in FreeBSD vs. Windows

Mike S mikes at flatsurface.com
Wed Jan 19 05:05:58 UTC 2011


At 10:35 PM 1/18/2011, Dave Hart wrote...
>On Wed, Jan 19, 2011 at 02:47 UTC, Mike S <mikes at flatsurface.com> 
>wrote:
> > At 02:18 PM 1/18/2011, unruh wrote...
> >> Especially as ntpd uses only one of every 8 polls,
> >
> > Is this relatively recent behavior?
>
>No.  See the "Clock filter algorithm" slide 13 in:
>
>http://www.eecis.udel.edu/~mills/database/brief/arch/arch.pdf

That's dated Jul2007. My point of reference is whatever version of NTP 
was used in Debian "Lenny" (4.2.4p4, from Aug2007, it seems) which is 
what I was running before changing to Squeeze (4.2.6p2) a couple of 
months ago. Perhaps a change was made about that time? Maybe I'm just 
getting old and feeble, but I swear "ntpq -p" used to update the offset 
with almost every poll - I would watch it after making a change to get 
a feel for how the offset and drift were adjusting (watch "ntpq -p; 
ntptime"). Or, perhaps, NTP used to report the most recently _measured_ 
offset/jitter, and was changed to reporting the most recently _used_?

Another change I've noticed with very recent versions (maybe a 
4.2.7p?), I didn't keep track) is that the polling interval seems to 
add a random time to what's expected. If watching "ntpq -p", I will 
often see "when" count significantly beyond the current "poll" value. 
It doesn't indicate a missing response when it finally does seem to 
poll.




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