[ntp:questions] peers with high offset on Intel Quad Core running Windows 2003
Richard B. Gilbert
rgilbert88 at comcast.net
Wed Aug 20 12:23:35 UTC 2008
Jimmy ntp wrote:
> Hi,
> I'm consistently seeing offsets between +- 6 ms on my Windows servers.
> For the same hardware running Linux, NTP behaves great (+- 500 us offset)
> but on Windows it is bad. Also the same version of Windows on AMD procs is
> behaves great.
>
> Hardware:
> HP ProLiant DL360 G5
> * 2 Quad-Core Intel(R) Xeon(R) Processor E5450
> * 8 GB of memory
>
> Software:
> * Windows 2003
> * ntp-4.2.0a
>
> Here is ntp.conf:
> ========================
> server 192.168.10.5 burst iburst minpoll 4 maxpoll 6
> server 192.168.10.6 burst iburst minpoll 4 maxpoll 6
> server 10.10.10.10 burst iburst minpoll 4 maxpoll 6
> server 10.10.10.11 burst iburst minpoll 4 maxpoll 6
> server 10.10.10.12 burst iburst minpoll 4 maxpoll 6
> server 10.10.10.13 burst iburst minpoll 4 maxpoll 6
> server 10.10.10.14 burst iburst minpoll 4 maxpoll 6
> server 10.10.10.15 burst iburst minpoll 4 maxpoll 6
> ========================
>
> % ntpq -np
> remote refid st t when poll reach delay offset
> jitter
> ==============================================================================
> *192.168.10.5 .GPS. 1 u 44 64 377 0.905 -4.274
> 0.656
> +192.168.10.6 .CDMA. 1 u 1 64 377 18.731 -6.324
> 1.915
> +10.10.10.10 192.168.10.5 2 u 29 64 377 0.399 -5.357
> 0.535
> -10.10.10.11 192.168.10.5 2 u 4 64 377 0.352 -6.036
> 0.175
> -10.10.10.12 192.168.10.5 2 u 34 64 377 0.397 -5.200
> 0.642
> -10.10.10.13 192.168.10.5 2 u 1 64 377 0.498 -5.910
> 1.410
> -10.10.10.14 192.168.10.5 2 u 2 64 377 0.376 -6.069
> 1.450
> -10.10.10.15 192.168.10.5 2 u 1 64 377 0.335 -5.132
> 1.465
>
>
> Have any one seen this issue? Any advice? Thanks in advance.
Remove the "burst" and "minpoll 4 maxpoll 6" from all your server
statements! Restart ntpd and be sure to use the -g switch.
Burst is a special purpose keyword intended for situations in which your
system makes a dial-up telephone connection to a server three or four
times a day. Using the burst keyword in any other situation is
considered abusive!
The default values of MINPOLL and MAXPOLL (six and ten) are correct for
virtually all situations and should be left intact! My non-mathematical
explanation is that the shorter poll intervals allow large errors to be
corrected quickly and the longer intervals allow small errors to be
corrected very accurately. NTPD adjusts the polling interval within the
range defined by MINPOLL and MAXPOLL as needed. See RFC-1305 for the math.
If you are good at advanced math and control systems theory, you may
find RFC-1305 enlightening!
Also note that Windows is a difficult environment! The clock ticks at
something like 17 millisecond intervals. If you really need/want time
to the nearest microsecond, Windows is a poor choice of O/S. There is
some way to interpolate between ticks which has been mentioned here from
time to time but I don't recall what it is. I have no need for time to
the nearest microsecond on my Windows systems and have not tried to
memorize the details!
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