[ntp:questions] Re: HOWTO prepare ntpd to the leap of a second
Richard B. Gilbert
rgilbert88 at comcast.net
Thu Dec 29 23:58:05 UTC 2005
David L. Mills wrote:
> You really should read the commentary in the NIST leapsecond file,
> which explains the rationale for when the file is issued, the epoch of
> insertion and the current TAI offset. The file does not expire when
> the leap is inserted; it remains valid as a record of past TAI offsets
> until the next edition is issued.
> It could be that some sites have an old edition and others a newer
> one. The Autokey protocol compares the leapsecond tables for itself
> and its upstream servers and uses only the newest one. If the client
> has dependent clients, it passes only the newest table to them.
> When multiple valid sources display conflicting leap bits, the logical
> OR of these bits is used. While a more sophisticated decision algorthm
> could be used, the most common error is when an upstream server does
> not implement or recognize the leap condition. Thus if a server sets
> the bits, it probably knows what it is doing.
> Serge Bets wrote:
>> On Thursday, December 29, 2005 at 14:16:09 +0000, David L. Mills wrote:
>>> Serge Bets wrote:
>>>> The NIST file is absolutely true until expiration. This fact is not
>>>> exploited by the NTP daemon, but could perhaps be.
>>> I don't understand your concern.
>> The NTP daemon will not assert leap=00 against any bogus source wrongly
>> saying leap=01 during June 2006.
>> The authority of the soon updated NIST leapseconds file, expiring only
>> later on 29 December 2006, thus valid, and showing no leap event on
>> 30 June 2006, could perhaps be used to force correct leap=00.
>> Effectively overruling the less sure leap bits of other sources.
Does ntpd maintain a copy of this leap second file somewhere? Where?
I'd always assumed that NIST servers set the leap second bits when it
was time to set them; that they propagated downward and the leap second
happened automagically, everywhere. Does GPS propagate the leap second
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