NTP question

Thu May 2 02:30:16 UTC 2019

Hi Keith,

On 5/1/19 6:17 PM, Keith Medcalf wrote:
> 
>> If your network is air gapped from the Internet then sure. If it's
>> not, you can run NTP against a reasonably reliable set of time
>> sources (not random picks from Pool) and be able to say, "my log
>> timestamps are accurate to +/- 10 milliseconds so it must be you who
>> is farked up." While my milliseconds loses the pecking order contest,
>> it's just as good for practical purposes and a whole lot less
>> expensive.
> 
> You mean something like this, which is relatively easy to achieve:
> 
> ==============================================================================
> offset -0.000009, frequency -0.823, time_const 30, watchdog 238
> synchronised to NTP server (192.5.41.40) at stratum 2
>    time correct to within 12 ms
>    polling server every 1024 s
> ==============================================================================
>      remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> +clock.sjc.he.ne .CDMA.           1 u  287 1024  377   64.313    0.337   0.867
> -tock.usnogps.na .IRIG.           1 u    5 1024  377  103.080   -2.097   0.316
> -tick.usnogps.na .IRIG.           1 u  806 1024  377  103.053   -2.328   0.363
> +india.colorado. .NIST.           1 u  270 1024  377   41.214   -0.159   0.113
> +time-b-b.nist.g .NIST.           1 u  984 1024  377   42.609    0.200   0.045
> +time-c-b.nist.g .NIST.           1 u  180 1024  377   42.563    0.201   0.064
> +time-a-b.nist.g .NIST.           1 u  163 1024  377   42.639    0.137   0.032
> *192.5.41.40     .PTP.            1 u  235 1024  377   12.756   -0.388  12.479
> -192.5.41.41     .IRIG.           1 u  312 1024  377   13.575   -1.172   2.425
>  LOCAL(0)        .LOCL.          10 l    -   64    0    0.000    0.000   0.000
> ------------------------------------------------------------------------------
> pll offset:           -8.474e-06 s
> pll frequency:        -0.823 ppm
> maximum error:        0.123149 s
> estimated error:      0.000122 s
> status:               2001  pll nano
> pll time constant:    10
> precision:            1e-09 s
> frequency tolerance:  500 ppm
> ==============================================================================

That all looks great except for the LOCAL clock at S10.  In the event
you lose connectivity to the outside, this system will jump from S2 to
S10.  Depending on the setup of your other systems, groups of them will
go sailing off in their own directions.

http://support.ntp.org/bin/view/Support/OrphanMode is the better solution.

If you cannot do that for some reason, please see the "Dual Time
Servers" case at
http://support.ntp.org/bin/view/Support/UndisciplinedLocalClock .

-- 
Harlan Stenn <stenn at nwtime.org>
http://networktimefoundation.org - be a member!