[ntp:questions] Accept high root dispersion from Windows NTP server

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Sat Jul 11 06:14:15 UTC 2015


Flash 0400 is distance threshold exceeded - try tos maxdist 15 (default is 1.5s) and see if selection works.
Other adjustments may be required to get sync.

If NTP sources are not good, or Windows is not running ntpd, only the SNTP time service, do not even try to use those as NTP sources.
Your Windows DCs may only stay within a few seconds of each other, according to MS articles, and only require time to agree within 5 MINUTES.
Windows VMs may have time which jumps about, even running ntpd against good sources.

You may want to change (some of) your lightly loaded Linux (non-VM) hardware servers running NTP clients to NTP servers, peered with each other, and a DNS RR list to allow those to provide sync to your Windows DCs.
NTP servers should be able to stay within microseconds of each other, even on Windows, and keep clients on a LAN within milliseconds.
Your network should already allow NTP traffic thru, but extra holes can be made to allow your Linux servers to see good external sources.
-- 
Take care. Thanks, Brian Inglis


On 2015-07-10 07:09, Lucas van Braam van Vloten wrote:
> Hi list,
>
> I am running ~30 Linux servers (RHEL6) which synchronize their time
> against the NTP server on two Windows 2008 Domain Controllers.
>
> My Linux clients can see the time servers, but association is rejected.
> I believe that this is due to a very high root dispersion on these
> servers, namely around 10s.
>
> I have talked to the Windows administrator, and according to him this
> high root dispersion has something to do with the server running on a VM
> (VMWare). He says that it does not make the server a less reliable time
> source, and that it cannot be solved on the Windows server. "We just
> have to live with it" (his words)
>
> However, my Linux NTP clients keep rejecting the association.
>
> Is there a way in the NTP client configuration to ignore the root
> dispersion value of the server in the decision whether to associate?
> Or, alternatively, can I adjust the threshold for what is accepted, for
> example to 15 seconds or so?
>
> This is the output on my Linux machine:
>
> ntpq> associations
>
> ind assid status  conf reach auth condition  last_event cnt
> ===========================================================
>    1 61931  9024   yes   yes  none    reject   reachable  2
>    2 61932  9024   yes   yes  none    reject   reachable  2
>
> ntpq> rv 61931
> associd=61931 status=9024 conf, reach, sel_reject, 2 events, reachable,
> srcadr=puhtdc0001.piaddot.prorail.nl, srcport=123, dstadr=172.24.75.21,
> dstport=123, leap=00, stratum=2, precision=-6, rootdelay=31.250,
> rootdisp=11071.594, refid=172.24.70.105,
> reftime=d94a40a7.f1dcccf5  Fri, Jul 10 2015 15:01:27.944,
> rec=d94a4115.dcbd0077  Fri, Jul 10 2015 15:03:17.862, reach=377,
> unreach=0, hmode=3, pmode=4, hpoll=6, ppoll=6, headway=56,
> flash=400 peer_dist, keyid=0, offset=16.847, delay=0.662,
> dispersion=16.516, jitter=8.528, xleave=0.043,
> filtdelay=     0.66    0.72    0.45    0.72    0.41    0.56    0.63
> 0.43,
> filtoffset=   16.85   28.33   19.69   27.05   31.19   22.19   22.18
> 15.32,
> filtdisp=     15.63   16.62   17.61   18.58   19.54   20.55   21.52
> 22.50
> ntpq> rv 61932
> associd=61932 status=9024 conf, reach, sel_reject, 2 events, reachable,
> srcadr=puhtdc0002.piaddot.prorail.nl, srcport=123, dstadr=172.24.75.21,
> dstport=123, leap=00, stratum=3, precision=-6, rootdelay=62.500,
> rootdisp=11128.265, refid=172.24.75.30,
> reftime=d94a404a.0c65965c  Fri, Jul 10 2015 14:59:54.048,
> rec=d94a4114.de3c9281  Fri, Jul 10 2015 15:03:16.868, reach=377,
> unreach=0, hmode=3, pmode=4, hpoll=6, ppoll=6, headway=54,
> flash=400 peer_dist, keyid=0, offset=12.680, delay=0.733,
> dispersion=16.513, jitter=9.014, xleave=0.025,
> filtdelay=     0.73    0.80    0.67    0.63    0.66    1.17    7.34
> 0.68,
> filtoffset=   12.68   17.04   14.66   13.59   19.40   19.83   28.60
> 26.65,
> filtdisp=     15.63   16.62   17.59   18.55   19.56   20.55   21.54
> 22.51
>
> Any help would be greatly appreciated!


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