[87649] in North American Network Operators' Group
Re: Leap second reminder - Check your NTP
daemon@ATHENA.MIT.EDU (Roy)
Sat Dec 31 20:07:48 2005
Date: Sat, 31 Dec 2005 17:06:59 -0800
From: Roy <garlic@garlic.com>
To: Kevin Day <toasty@dragondata.com>
Cc: nanog@nanog.org
In-Reply-To: <1EDC3E40-8788-43A6-A266-CAD29A50C87F@dragondata.com>
Errors-To: owner-nanog@merit.edu
Kevin Day wrote:
>
> Last NTP spam:
>
>
> I'm by no means an NTP expert, if anyone else is, please pipe up.
>
> About 30 minutes before the leap second should have occurred, several
> of our systems reported "xntpd[13742]: time reset 0.958385 s", which
> was really strange. They moved the wrong direction, and they did it
> early. Shortly after, those systems lost ntp association and began
> drifting. About 10 minutes after midnight all have regained sync. I
> wasn't checking things that early to see why, it's possible some of
> our NTP sources started disagreeing on what the correct time was, and
> would also match what other people have reported off-list, going back
> as far as 18 hours before midnight.
>
> Several public NTP sources are now indicating a "leap second alarm"
> (setting the leap bits to 11), which will cause most NTP clients to
> rule them out as a source. ntp-2.gw.uiuc.edu is an example:
>
> 130.126.24.44: Server dropped: Leap not in sync
> server 130.126.24.44, port 123
> stratum 2, precision -19, leap 11, trust 000
> refid [128.174.38.133], delay 0.03357, dispersion 0.00049
>
> According to ntpdate, its clock seems to have stopped about 5 minutes
> before midnight, and hasn't yet recovered.
>
> Other NTP servers haven't cleared their "today is a leap second day"
> bit, which they should have by now. Some NTP implementations rule out
> servers that don't agree with what their "master" server thinks the
> leap second bits should be. My reading of the NTP spec says that at
> 00:00:00 the leap bits should have been returned to zero. Attempting
> to sync from one of these servers will produce a "Next leap second
> occurs at 00:00:00.000 UTC Sun Jan 01 2006" message, but that should
> be harmless as long as they correct themselves a while before midnight.
>
> Still others have their clocks off by a significant amount(10+
> minutes) and think they're still in sync, but since I started typing
> this email, they all have corrected themselves.
>
>
> While I can't say anything broke on our network as a result of the
> leap second, a good percentage of our gear lost NTP sync or had some
> kind of NTP problem around midnight UTC. You may want to check your
> NTP status at some point, in case something drifted quite a way off
> and won't step itself back now because the difference is too great.
>
> -- Kevin
>
There is at least one stratum-1 server here on the West coast that my
NTP says is now off by 1 second. Several stratum-2 are synced to it and
are now off also. So checking servers might be a good idea
Roy Engehausen
