[time-nuts] June 30 2015 leap second

Martin Burnicki martin.burnicki at burnicki.net
Fri Jan 9 15:44:15 EST 2015

Gregory Maxwell wrote:
> On Fri, Jan 9, 2015 at 3:21 PM, Martin Burnicki
> <martin.burnicki at burnicki.net> wrote:
>> Systems which are simply time clients can receive the leap second warning
>> via the usual protocols like NTP or PTP/IEEE1588.
> Indeed, they can. Even when there hasn't been a leap-second.
> Practically all internet (and otherwise?) time distribution is
> unauthenticated, the leap second itself is unauthenticated.

... and even the time you get via NTP or PTP is usually not 
authenticated. So you can trust the time and leap second warning, or you 
shouldn't trust either.

> It's fragile enough that there have been accidental false leap-second events.

Yes, for example if there have been GPS receivers which decoded the UTC 
parameters incorrectly, and started to announce a leap second when there 
wasn't one (end of September).

That's why, for example, ntpd's leap second handling code has been 
changed in v4.2.6 to accept a leap second warning only if the warning is 
received from a majority of the configured servers.

If you want to be sure you can also provide ntpd with a leap second file 
which is then (in current versions) considered as authentic source for 
leap second information.


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