[ntp:questions] large dispersion

Dave dave.deconsulting at gmail.com
Wed May 30 14:55:17 UTC 2007


On May 25, 9:28 am, Dave <dave.deconsult... at gmail.com> wrote:
> On May 24, 8:09 pm, "Richard B. Gilbert" <rgilber... at comcast.net>
> wrote:
>
>
>
> > Dave wrote:
> > > On May 23, 1:16 pm, "Richard B. Gilbert" <rgilber... at comcast.net>
> > > wrote:
>
> > >>Dave wrote:
>
> > >>>I'm experiencing large values of dispersion when I use 'ntpq -p':
>
> > >>>3:22pm:ntp>ntpq -p
> > >>>     remote           refid      st t when poll reach   delay
> > >>>offset    disp
> > >>>==============================================================================
> > >>>*10.2.100.10     .GPS.            1 u   25   64  377     0.46
> > >>>943.557  439.36
> > >>>3:22pm:ntp>
>
> > >>> but when I look at the peerstats log file, my dispersion is low:
>
> > >>>3:22pm:ntp>tail /var/ntp/ntpstats/peerstats.log
> > >>>54243 54804.018 10.2.100.10 9634 0.617563 0.00046 0.31154
> > >>>54243 54868.013 10.2.100.10 9634 0.813226 0.00043 0.32210
> > >>>54243 54932.018 10.2.100.10 9634 0.099169 0.00046 0.55225
> > >>>54243 54996.010 10.2.100.10 9634 0.300057 0.00047 0.28690
> > >>>54243 55060.014 10.2.100.10 9634 0.584358 0.00044 0.31111
> > >>>54243 55124.009 10.2.100.10 9634 0.781632 0.00047 0.32353
> > >>>54243 55188.014 10.2.100.10 9634 0.065932 0.00043 0.55287
> > >>>54243 55252.013 10.2.100.10 9634 0.657674 0.00044 0.37859
> > >>>54243 55316.018 10.2.100.10 9634 0.943557 0.00046 0.43936
> > >>>54243 55380.013 10.2.100.10 9634 0.139388 0.00044 0.59772
> > >>>3:23pm:ntp>
>
> > >>> I'm also concerned with the large amount of maximum/estimated error
> > >>>when I use the xntpdc command 'kerninfo':
>
> > >>>xntpdc> kerninfo
> > >>>pll offset:           0 us
> > >>>pll frequency:        -391.137 ppm
> > >>>maximum error:        524704 us
> > >>>estimated error:      408368 us
> > >>>status:               0089
> > >>>pll time constant:    2
> > >>>precision:            1 us
> > >>>frequency tolerance:  512 ppm
> > >>>pps frequency:        0.000 ppm
> > >>>pps stability:        512.000 ppm
> > >>>pps jitter:           200 us
> > >>>calibration interval: 4 s
> > >>>calibration cycles:   0
> > >>>jitter exceeded:      0
> > >>>stability exceeded:   0
> > >>>calibration errors:   0
> > >>>xntpdc>
>
> > >>>Here is the output of the pstats command:
>
> > >>>xntpdc> pstats 10.2.100.10
> > >>>remote host:          10.2.100.10
> > >>>local interface:      10.2.100.5
> > >>>time last received:   3s
> > >>>time until next send: 61s
> > >>>reachability change:  2947s
> > >>>packets sent:         59
> > >>>packets received:     59
> > >>>bad authentication:   0
> > >>>bogus origin:         0
> > >>>duplicate:            0
> > >>>bad dispersion:       15
> > >>>bad reference time:   0
> > >>>candidate order:      1
> > >>>xntpdc>
>
> > >>>And lastly, my ntp.conf file:
>
> > >>>3:25pm:inet>more ntp.conf
> > >>>server 10.2.100.10             # NTP server
>
> > >>>driftfile /etc/ntp.drift          # Drift available for next restart
> > >>>logfile /var/ntp/ntp.log       # NTP logging
>
> > >>>statsdir /var/ntp/ntpstats/
> > >>>statistics loopstats peerstats clockstats
> > >>>filegen loopstats file loopstats.log type day link enable
> > >>>filegen peerstats file peerstats.log type day link enable
> > >>>filegen clockstats file clockstats.log type day link enable
> > >>>3:25pm:inet>
>
> > >>>Anyone have any ideas? I have a GPS signal coming in to a Brandywine
> > >>>NTA-100, which is configured at 10.2.100.10. Thanks in advance!
>
> > >>If you are using "X"ntpdc you would appear to be using a version that
> > >>may be as much as ten years old!   Just what are you using and what are
> > >>  you running it on?
>
> > > Wow you're right. Heres the version printout:
> > > xntpdc 3-5.93e Mon Sep 20 15:47:24 PDT 1999 (1)
>
> > > I'm running this on a Sun Fire 4200, Solaris 10. Something this old
> > > comes installed on Solaris 10?
>
> > Yup!
>
> > I think it has something to do with the fact that there is, as yet, no
> > RFC for NTP V4.  There is a committee, God help us, working on one.  I
> > think it has been about a year now with no visible results!
>
> > I'd suggest grabbing a more recent version of the code from somewhere.
> > Sun Freeware and Blastwave sites should both have Solaris versions more
> > recent than what Sun ships.  There have been quite a few fixes and
> > enhancements since 3-5.93e.
>
> > If you want/are able to build your own, try the ntp.org web site; there
> > are links there to download the source to the stable and development
> > versions which are, I believe, at 4.2.something.
>
> I just downloaded ntp v4.2.4 from sunfreeware.com and I'll give that a
> try. I'll let you know how it goes!


Ok so I have the new version loaded and its been running for about 24
hours now. I still have a large amount of jitter (reported on by ntpq -
p):
2:50pm:freadd_user>ntpq -p
     remote           refid            st t when poll   reach
delay    offset     jitter
========================================================
*10.2.100.10     .GPS.            1 u    3    64     377     0.461
91.914   385.406


But using ntpdc, I see the correlation in the offset values (msec vs.
sec), but are jitter and dispersion supposed to mean the same thing/
have anything to do with each other?

2:51pm:freadd_user>ntpdc
ntpdc> peers
     remote           local            st  poll reach    delay
offset       disp
==============================================================
*10.2.100.10     10.2.100.5       1   64   377    0.00046  0.091914
0.06059



My kerninfo and sysinfo output looks a lot better with this newer
version:

ntpdc> kerninfo
pll offset:           0.01215 s
pll frequency:        -241.451 ppm
maximum error:        1.14442 s
estimated error:      0.076886 s
status:               0001  pll
pll time constant:    2
precision:            1e-06 s
frequency tolerance:  512 ppm
pps frequency:        0.000 ppm
pps stability:        512.000 ppm
pps jitter:           0.0002 s
calibration interval: 4 s
calibration cycles:   0
jitter exceeded:      0
stability exceeded:   0
calibration errors:   0
ntpdc>
ntpdc>
ntpdc> sysinfo
system peer:          10.2.100.10
system peer mode:     client
leap indicator:       00
stratum:              2
precision:            -22
root distance:        0.00046 s
root dispersion:      0.63643 s
reference ID:         [10.2.100.10]
reference time:       ca080c6d.f68b1c0b  Wed, May 30 2007 14:45:01.963
system flags:         auth monitor ntp kernel stats
jitter:               0.366226 s
stability:            0.000 ppm
broadcastdelay:       0.003998 s
authdelay:            0.000000 s



Do I need to worry about the jitter value from ntpq -p, or does
everything look okay?






More information about the questions mailing list