[ntp:questions] large dispersion

Dave dave.deconsulting at gmail.com
Wed May 30 19:14:22 UTC 2007


On May 30, 1:05 pm, "Richard B. Gilbert" <rgilber... at comcast.net>
wrote:
> Dave wrote:
> > 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
>
> <snip>
>
> > Do I need to worry about the jitter value from ntpq -p, or does
> > everything look okay?
>
> Looking a little more carefully at your ntpq banner it looks as if the
> delay (round trip delay) to your server is unreasonably large.  You're
> using an RFC-1918 address which is a private network but the delay
> suggests that the server is a couple of thousand miles away or that you
> are using tin cans and string to communicate with it.
>
> The potential error in transmitting the time from server to client is
> one half the round trip delay.  This, in turn, suggests that minimizing
> the round trip delay is a good idea.  I don't know how to account for a
> delay like this in what is presumably a small LAN.  Can you explain it?

Thanks, Steve for explaining that. I tried to condense it when I copy/
pasted it, and it looked fine in the original text window. Sorry about
the confusion. Even so, if you're still wondering, I have a GPS
antenna feed coming into the NTA-100 and ethernet out to a switch
(approx 6 feet of cable).  Thanks for all the help




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