[ntp:questions] ARRGH!!! I woke up to a 50 SECOND clock error.
Ron Frazier (NTP)
timekeepingntplist at c3energy.com
Sat Mar 17 21:21:49 UTC 2012
On 3/17/2012 3:20 PM, David J Taylor wrote:
> "Ron Frazier (NTP)" <timekeepingntplist at c3energy.com> wrote in message
> news:4F64D793.9010708 at c3energy.com...
>> Hi David,
>> I'm not sure what will happen if you simultaneously prefer and
>> noselect the local server. Assuming the local stratum 1 server is
>> the most stable time source, you'll get a much better picture of what
>> the internet servers are doing relative to it if you allow it to be
>> selectable as well as being preferred. When you graph it, if the
>> local server is the active clock, all the lines for the internet
>> servers will be gathered around and relative to the local server.
>> When I tried to do things the other way around, with an internet
>> server preferred, the graph looked awful because there was so much
>> variation. Also, if your local server starts reporting time that
>> looks too far from the internet servers, regardless of who's fault it
>> is, ntp will clock hop over to the internet servers.
>> I don't THINK your internet servers will ever poll above their
>> default minpoll value of 6, or 64 seconds.
>> I realize you don't have a gps attached to this pc, but the iburst
>> lines reminded me of something. I read somewhere that having iburst
>> on internet server lines, if a local gps is attached, could prevent
>> the PC from synchronizing to the gps before it synchronizes to the
>> internet. On my pc with the gps attached, I don't use the iburst
> The local stratum-1 server shows without a tally code against it in
> the ntpq -p output, so it's being recorded in the peerstats, but not
> used for syncing. The noselect msut override the prefer.
> After about three hours running, the Internet servers are all at 512
> seconds poll interval. The averaged jitter has been below 1
> millisecond for the last couple of hours. The offset is reporting
> between -0.7 and -1.8 milliseconds, and the frequency is stabilising
> very nicely (because of the long poll interval). I'll leave this
> running overnight and tomorrow to see how it handles temperature
> changes and any Internet access changes, and to get a few more points
> on the graph.
Come to think of it, my comment about the polling interval not
increasing may only apply to a local refclock, not a local server.
> One caveat is that I am using the most recent NTP (ntpd 4.2.7p263 from
> Dave Hart's download page), and that with Windows-8, it may be using
> the new precision time system call. From my own tests, this is
> similar, on earlier versions of NTP, to setting the environment
> variable NTPD_USE_INTERP_DANGEROUS, thus forcing the NTP time
> interpolation to be used.
Can you elaborate more about what NTPD_USE_INTERP_DANGEROUS does?
> The configuration I have is:
> - cable modem (with built-in router, but working as a bridge by
> putting my own router in a device in the DMZ).
> - Samknows network monitor (modified WRT54GL router)
> - WRT54GL router running DD-WRT firmware
> - Netgear 8-port consumer 1 Gb/s switch (G5108)
> - wired connection to ~2 year old laptop PC
> I only mention this to show that (a) it's not a direct connection and
> (b) there's no wireless involved. My aim here is simply to see what
> performance may be had with just Internet servers. The PC is only
> running NTP and monitoring software - no user programs and no
> interactive work, so it is a best-case scenario.
(PS - If you email me and don't get a quick response, don't be concerned.
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timekeepingdude AT c3energy.com
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