REMINDER: LEAP SECOND

Majdi S. Abbas msa at latt.net
Fri Jun 19 18:51:44 UTC 2015


On Fri, Jun 19, 2015 at 06:29:34PM +0000, Mel Beckman wrote:
> The universal workaround is to simply disable NTP on your devices sometime 
> on Leap-Second eave. This will let the clocks free-run over the one-second 
> push, an event of which they will be blissfully ignorant. When you re-enable 
> NTP after The Leap, normal, non-destructive, NTP convergence will occur.

	<randy>I encourage all my competitors to use this
approach.</randy>

	If you're more than 128 ms off when NTP is flipped back on, it
will still probably step the clock, then start slewing it.  So you've
skipped the leap per se, but your clocks will still jump forward quite
a bit.

	This might isolate you from any leap second related failures,
but it does not protect you against the system clock being stepped.
If the leap pending information data persists, you might not even be
isolated from any leap second failures.  You could manage to upset
the system clock even more.

	Are your time servers correctly armed for the leap?

> Better, if you have a master NTP site clock, you need only disable it’s 
> upstream NTP feed to isolate all the subsidiary devices. If you don’t 
> have such a master clock, this is an excellent time to set one up one. 
> I have found the Time Machines TM1000A GPS time server very inexpensive 
> and super reliable:
> 
> http://www.newegg.com/Product/Product.aspx?Item=0N6-001Y-00007 

	$20 says that doesn't leap correctly.  A lot of the inexpensive
units appear to be using NMEA speaking GPS modules, and there's no real way 
to get leap information out of them.  Many of them may ignore the
timestamps and just use the PPS, in which case they may persist a second
behind the world for quite some time.
	
	--msa



More information about the NANOG mailing list