Hal,
Hal Murray wrote:
martin.burni...@burnicki.net said:
Please note under Windows you should configure all upstream servers with a
line reading
server aa.bb.cc.dd iburst minpoll 6 maxpoll 6
There are lots of times when reducing maxpoll is reasonable, but I think an
unqualified suggestion is not appropriate.
I don't think my suggestion was unqualified. ;-)
We have already discussed this in the NTP newsgroup/questions mailing list.
Here is a loopstats graph from a Windows XP system running ntpd 4.2.6p5
without limitation of maxpoll:
http://people.ntp.org/burnicki/windows/ntpd-4.2.6p5-WinXP-no_poll_limit.pdf
And if you limit maxpoll to 6 in the same installation the results look
like this:
http://people.ntp.org/burnicki/windows/ntpd-4.2.6p5-WinXP-poll_6.pdf
A loopstats graph from another test with ntp-dev running on Windows 7
without limitation of the polling interval are here:
http://people.ntp.org/burnicki/windows/ntpd-4.2.7-Win7-poll4-max.pdf
And similarly, with limitation of the polling interval to 6:
http://people.ntp.org/burnicki/windows/ntpd-4.2.7-Win7-poll4-6.pdf
In the examples above I had minpoll set to 4, just to see how the fix
for NTP bug 2328 behaves, and you can clearly see that time
synchronization is degraded if the polling interval is *below* 6 since
the workaround doesn't work properly, as mentioned in the bug report.
So I wouldn't suggest anyway to set minpoll below 6.
maxpoll of 6 polls every 64 seconds. The default maxpoll is 10, or 1024
seconds, so that's a 16x[1] increased load on the servers. Some/many people
would consider that to be abusive use of a resource.
If you are using your servers, you can do whatever you want. If you are
using your ISP's servers or a friends, then whatever they agree to is fine.
The NIST servers are already heavily/over loaded. I'm not sure if the pool
could stand a 16x increase in load.
I agree that limiting maxpoll isn't the best choice if you can avoid it.
However, by default ntpd starts at minpoll 6 anyway, it determines
automatically if the polling interval can be increased towards 10, or be
decreased again towards 6.
You can see how the interval is decreased automatically in the loopstats
for 4.2.6/Win XP, if the time discipline becomes too bad.
So public services should anyway account for clients sticking a the
default lowest poll interval, namely 6.
And of course it is generally not a good idea to let each laptop get its
time directly from the primary servers at NIST or PTB, but this is a
different problem.
Martin
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