| Re: [chrony-users] Dealing with SNTP sources |
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Am 2011-05-04 20:04, schrieb Bill Unruh:
> On Wed, 4 May 2011, Harald Krammer wrote:
>
>> Hello,
>> I have a question about dealing with SNTP sources.
>>
>> when I interact with two SNTP servers (also named as NTP server),
>
> An sntp server must, AFAIK be a stratum 0 server.
>
Really? My opinion is, that the stratum behavior is equal. SNTP means a
usage of simple algorithm. e.g. only hard time set after a query
Some SNTP implementation are extremely inaccurate. In my area NTP is
also used over GPRS connections ( round trip delay till 100 ms - 2 s).
Accuracy does not play a major role in some applications.
>> then it's hard to find a solution to prevent the case of 'no majority'.
>> The most (S)NTP devices solved this problem with selecting of one
>> primary time source and one backup time source . More cannot be
>> adjusted.
>>
>> I did it with following setting:
>> server <server-1-ip> iburst minpoll 6 maxpoll 8 prefered
>> server <server-2-ip> iburst minpoll 6 maxpoll 8 minstratum 8
>>
>> The option 'prefered' didn't help, but lowering of stratum was
>> a solution to prevent the case of 'no majority'.
>>
>> With following settings:
>> server <server-1-ip> iburst minpoll 6 maxpoll 8 prefered
>> server <server-2-ip> iburst minpoll 6 maxpoll 8
>>
>> I got 'Can't synchronise: no majority' and here is my traces:
>
> Recall that 2 servers is a worst case situation. If they disagree, noone
> can
> say which is correct. You need three at least.
>
>
>>
>> sources.c:324:(SRC_SetSelectable)[04-14:40:35] 10.126.9.246
>> sources.c:302:(SRC_AccumulateSample)[04-14:40:35] ip=[10.126.9.246] t=Wed
>> 05/04/11 14:40:35.145764 ofs=-0.003653 del=0.000741 disp=0.000629 str=2
>> sourcestats.c:574:(SST_GetSelectionData)[04-14:40:35] n=4 off=0.000498
>> del=0.000897 dis=0.001328 var=0.000000 pdist=0.001318 avoff=-0.000005
>> avok=1 selok=1
>> sourcestats.c:574:(SST_GetSelectionData)[04-14:40:35] n=4 off=-0.003653
>> del=0.000741 dis=0.000632 var=0.000000 pdist=0.001000 avoff=-0.004032
>> avok=1 selok=1
>> sources.c:624:(SRC_SelectSource)[04-14:40:35] Can't synchronise: no
>> majority
>>
>> 210 Number of sources = 2
>> MS Name/IP address Stratum Poll LastRx Last sample
>> =================================================================
>> ^x 10.126.9.245 2 6 33 +20ns[-1669us] +/- 398us
>> ^x 10.126.9.246 2 6 33 -4332us[-4332us] +/- 857us
>
> The intervals do not overlap. It cannot figure out which is best. Trying to
> force something is silly, since you cannot figure out what the right one to
> force is. Use three servers.
>
>
>>
>> After a while is again synchronized
>> 210 Number of sources = 2
>> MS Name/IP address Stratum Poll LastRx Last sample
>> ===============================================================
>> ^* 10.126.9.245 2 6 50 -111us[ -278us] +/- 378us
>> ^+ 10.126.9.246 2 6 49 +737us[ +737us] +/- 521us
>
> Now they overlap (just barely) .
>
>>
>> After 2..3 min again: Can't synchronise: no majority
>> 210 Number of sources = 2
>> MS Name/IP address Stratum Poll LastRx Last sample
>> ================================================================
>> ^x 10.126.9.245 2 6 4 -403us[ -403us] +/- 529us
>> ^x 10.126.9.246 2 6 2 +2207us[+2207us] +/- 353us
>
> And now they do not. Get a third source so you and it can figure out
> which is the bad source.
>
>
>>
>> and so on
>>
>> =======================================================================
>> Date (UTC) Time IP Address St Freq ppm Skew ppm Offset
>> =======================================================================
>> 2011-05-04 14:40:28 0.0.0.0 0 19.521 42.166 0.000e+00
>> 2011-05-04 14:40:33 10.126.9.246 3 19.521 42.166 -2.127e-03
>> 2011-05-04 14:40:34 10.126.9.245 3 19.521 42.166 4.087e-03
>> 2011-05-04 14:40:35 0.0.0.0 0 19.521 42.166 0.000e+00
>> 2011-05-04 14:41:39 10.126.9.245 3 -0.505 50.104 -1.669e-03
>> 2011-05-04 14:41:40 0.0.0.0 0 -0.505 50.104 0.000e+00
>> 2011-05-04 14:42:43 10.126.9.245 3 -9.630 15.559 -8.059e-04
>> 2011-05-04 14:42:45 0.0.0.0 0 -9.630 15.559 0.000e+00
>> 2011-05-04 14:43:49 10.126.9.245 3 -11.892 9.416 -3.936e-04
>> 2011-05-04 14:44:53 10.126.9.245 3 -12.749 5.457 -1.671e-04
>> 2011-05-04 14:45:57 0.0.0.0 0 -12.749 5.457 0.000e+00
>> 2011-05-04 14:49:11 10.126.9.246 3 -12.434 8.937 5.796e-03
>> 2011-05-04 14:50:16 10.126.9.246 3 -11.686 15.050 6.131e-04
>> 2011-05-04 14:51:19 10.126.9.245 3 -1.017 27.162 1.354e-04
>> 2011-05-04 14:52:20 0.0.0.0 0 -1.017 27.162 0.000e+00
>> 2011-05-04 14:52:25 10.126.9.245 3 -1.017 27.162 2.711e-04
>>
>>
>> The solution 'minstratum 8' is fine for me. The behavior
>> without setting of minstratum was unclear for me.
>> Is it explainable?
>
>>
Thank you for your explanation.
Nice greetings,
Harald
--
Harald Krammer
Mobil +43.(0) 664. 130 59 58
Mail: Harald.Krammer (at) hkr.at
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