| Re: [chrony-users] Dealing with SNTP sources |
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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.
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?
Nice greetings,
Harald
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