[time-nuts] Recommendations for NTP server

Geoff Powell geoff at g8kbz.demon.co.uk
Sun Apr 23 17:54:58 EDT 2006


In article <444BF2D0.40603 at cloudview.com>, John Pettitt
<jpp at cloudview.com> writes
>I'll second the soekris box - my box time.no-such-agency.net is a 4801
>running FreeBSD with a GPS18LVC.    You can expect offsets in the +/-
>5us range except when the box is stressed - the standard xtal in the box
>is not temperature compensated so offsets will spike to as much as 250us
>when the system does something compute intensive.  If you don't need the
>HD consider the 4501 as it has the ability to timestamp a PPS using
>internal counters rather than the DCD kludge. - Again see phk's
>excellent work on the subject including the code in FreeBSD to support
>PPS on a 4501.

So you'd recommend a 4501, with FreeBSD in Compact Flash? I wanted to
use CF anyway, since a box running 24/7 is not the best environment in
which to have moving parts. The box will have no more that NTP and MRTG
on it.

Thanks for the accuracy estimate.

>
>Regarding DSL - I now have three stratum one servers here: a GPS18LVC, a
>TrueTime NTS100 and TrueTime GPS XL-DC  (it is addictive isn't it) - my
>ISP just installed a GPS18LVC based server one hop (on gig-e) from my
>DSL concentrator so I can get a very clear picture of the error
>introduced by my DSL asymmetry.  For my line (6000 down 608 up
>backhauled over ATM) it's 1.5ms.  In a perfect world NTP would allow a
>fudge offset to be applied to subnets (in my case 1.5ms on the default
>and 0.0 on the local LAN) which would factor out the know DSL error -
>alas it doesn't do that right now.

My ADSL is 2272 down/256 up, so I'd likely be seeing bigger asymmetry.

Thanks,

-- 
Geoff Powell




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