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Date: Thu, 10 May 2007 22:56:43 -0600 (MDT)
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To: peterjeremy@optushome.com.au
From: "M. Warner Losh" <imp@bsdimp.com>
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Cc: freebsd-stable@freebsd.org, martin.dieringer@gmx.de
Subject: Re: clock problem
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In message: <20070508191617.GH838@turion.vk2pj.dyndns.org>
            Peter Jeremy <peterjeremy@optushome.com.au> writes:
: There seems to be a bug in ntpd where the PLL can saturate at
: +/-500ppm and will not recover.  This problem seems too occur mostly
: where the reference servers have lots of jitter (ie a fairly congested
: link to them).

Yes.  This is a rather interesting misfeature of ntpd.  Its rails are
at +/- 500ppm, and when it hits the rail it assumes that things are
too bad to continue and it stops.

Most PC clocks have a frequency error on the order of 10-150ppm, so it
doesn't take a whole lot of jitter from a conjectsted remote network
to exceed the limits...

Warner