[ntp:questions] Re: Leap bits, when to set?

David L. Mills mills at udel.edu
Thu Dec 22 19:10:49 UTC 2005


The leap bits are set when the timing source, either modem, radio or 
server, set them. However, they are provided to the kernel only on the 
day of the leap.


Tapio Sokura wrote:

> There has been some discussion on the NTP pool mailing list about leap 
> bits, specifically when to set them. Reading RFCs 1305 and 2030 leads me 
> to believe that the correct behavior is to set the leap bit not earlier 
> than 24 hours before the actual leap second occurs. I.e. the bit should 
> be set on Dec 31st sometime after 00:00:00 UTC and cleared immediately 
> after the leap second is over.
> If the above is the correct way to time it, there seems to be a number 
> of NTP servers that are out of spec as they already have the leap bit 
> set. Can someone who knows the protocol and its history better shed some 
> light on this? Have the leap bits been set more than 24h before the leap 
> second insertion in previous years, when leap seconds have been inserted?
> I just did a quick poll (Dec 22nd around 08:00 UTC) on the startum one 
> and two time servers listed at the NTP wiki. Of 112 startum one servers 
> that responded, 7 had the leap bit set and 2 reported clock 
> unsynchronized. Of the 173 startum two servers that responded, 36 had 
> the leap bit set.
>   Tapio

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