[ntp:questions] Re: Windows timekeeping - sudden degradation - why?

David J Taylor david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk.invalid
Sat Dec 10 07:36:04 UTC 2005


John Allen wrote:
> This thread has intrigued me because I think I may have a similar
> problem.
> My Windows XP system ran Terje's NTP 4.2.0a happily from May 2004
> until sometime in the last month - I can't be as precise as David
> Taylor. My PC was synchronizing to my server running Linux also with NTP
> 4.2.0. Using NTPMonitor occasionally, I was seeing offsets typically 
> 20-50
> ms from reliable low-stratum servers - more than satisfactory for me
> and I paid very little attention to it. The SP2 upgrade went smoothly
> some months ago.
> Sometime in the last few weeks NTP on the PC has completely lost the
> ability to synchronize with the server. I'm seeing offsets increasing
> by several seconds an hour - they are consistent across my server and
> distant stratum 1-3 servers. The offsets are alway negative which
> means (I think) that the PC's time is running faster than the server.
>
> I've tried all the obvious things - installing later and earlier
> versions of ntpd, removing applications running in the
> background...none of these seems to affect the behaviour of NTP in
> the slightest. I've made some fairly major changes to the PC in the
> last 2 months, some of which I'm not keen to reverse - like
> installing Visual Studio C++ Express Edition, .NET 2.0 runtime,
> Windows SDK, BIOS upgrade, so there are plenty of things which could
> have clobbered NTP.
> Here is the output from
> ntpq -c "rv 0" deeley
> assID=0 status=c074 sync_alarm, sync_unspec, 7 events,
> event_peer/strat_chg, version="ntpd  2004 May 07 8:37:39  (1)"?,
> processor="unknown", system="WINDOWS/NT", leap=11, stratum=16,
> precision=-20, rootdelay=0.000, rootdispersion=32.160, peer=0, 
> refid=STEP,
> reftime=00000000.00000000  Thu, Feb  7 2036  7:28:16.000, poll=4,
> clock=0xc7449871.72e5796b, state=3, offset=0.000, frequency=0.000,
> noise=2299.254, jitter=870.642, stability=0.000
>
> (only 45 minutes after restarting the NTP service)
>
> Some of this looks a bit strange so maybe I'm out of my depth here,
> but I'm curious to know if this could be a similar issue to David
> Taylor's.
> John

John,

I'm not an expert in reading those "rv" outputs, but if you are on stratum 
16 it means you aren't synchronised.  Try the command:  ntpq -p deeley. 
The "reach" column should show 377 for each server  - octal for a bit 
field of 8 ones meaning 8 good connections.

My guess is that you may have a TCP/IP problem, like a firewall blocking 
access from your NTP client to its servers.

BTW: I've now written a program to force the MM timer to have a resolution 
of 1ms permanently, and this seems to have fixed the problem I had.

David 





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