[181421] in North American Network Operators' Group
Re: REMINDER: LEAP SECOND
daemon@ATHENA.MIT.EDU (Matthew Huff)
Tue Jun 23 21:06:44 2015
X-Original-To: nanog@nanog.org
From: Matthew Huff <mhuff@ox.com>
To: Harlan Stenn <stenn@ntp.org>
Date: Wed, 24 Jun 2015 01:06:40 +0000
In-Reply-To: <E1Z7YhL-000NRN-WD@stenn.ntp.org>
Cc: nanog2 <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
A backward step is a known issue and something that people are more comfort=
able dealing with as it can happen on any machine with a noisy clock crysta=
l.
Having 61 seconds in a minute or 86401 seconds in a day is a different stor=
y.
> On Jun 23, 2015, at 8:37 PM, Harlan Stenn <stenn@ntp.org> wrote:
>=20
> shawn wilson writes:
>> On Jun 23, 2015 6:26 AM, "Nick Hilliard" <nick@foobar.org> wrote:
>>>=20
>>=20
>>>=20
>>> Blocking NTP at the NTP edge will probably work fine for most situation=
s.
>>> Bear in mind that your NTP edge is not necessarily the same as your
>> network
>>> edge. E.g. you might have internal GPS / radio sources which could
>>> unexpectedly inject the leap second. The larger the network, the more
>>> likely this is to happen. Most organisations have network fossils and =
ntp
>>> is an excellent source of these. I.e. systems which work away for year=
s
>>> without any problems before one day accidentally triggering meltdown
>>> because some developer didn't understand the subtleties of clock
>> monotonicity.
>>>=20
>>=20
>> NTP causes jumps - not skews, right?
>=20
> Left to its default condition, ntp will step/jump a change in excess of
> 128msec.
>=20
> If you want to slew the clock instead, a 1 second correction will take a
> little over 33 minutes' time to apply.
>=20
> I don't understand why people believe that stopping ntpd for a few
> minutes while the leap second is applied will help. If the system clock
> keeps good time, it will *still* be about 1 second ahead when ntpd is
> restarted, and that will trigger a backward step which is fatal to a
> number of applications.
>=20
> H
