[LEAPSECS] stale leap second information

Tony Finch dot at dotat.at
Mon Jan 19 04:54:49 EST 2015

Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> However, I think it is a loosing strategy to send an ever longer
> list of addresses, it's only a matter of time before some random
> piece of DNS software does something stupid (again).

Yes, the basic response size is 776 bytes so it is likely to have all
sorts of interesting problems on end-user devices behind dodgy CPE
gateways. But I thought it might amuse :-)

> But my idea was to encode it more tight and add a CRC to detect
> DNS-spoofing (hotels free wifi etc.):
> 	8 bit unsigned year (2015...2270)
> 	4 bit unsigned month (1...12)
> 	8 bit signed int before count
> 	2 bit signed int (after - before) count
>        10 bit CRC-10
> Obviously the IPv6 mapping can be even more robust.

If you are only broadcasting the next or just recently occurred leap
second, you can perhaps leave out the year and just give a month number,
which is understood to be in a -2 .. +10 window around the current month.
e.g. if I read a month number of 12 now I would understand that to mean
there was a leap second at the end of last year, but if I read the same
value in March I would understand there is a leap second at the end of
this year.

f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
Northwest Fitzroy, Sole, Lundy, Fastnet, Irish Sea: Mainly northerly 4 or 5 at
first except in west Sole and far northwest Fitzroy, otherwise southwesterly
becoming cyclonic 5 to 7, increasing gale 8 at times in northwest Fitzroy,
Sole and Fastnet. Slight or moderate in Irish Sea, otherwise moderate or
rough, becoming very rough or high in northwest Fitzroy and west Sole. Mainly
fair, then rain or showers. Good, occasionally poor.

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