"reset" a serial number

[Joseph S D Yao]

On Thu, May 25, 2000 at 11:22:15AM -0500, Dave Daniels wrote:
> > See http://www.isc.org/products/BIND/docs/config_hints.html
> >
> > 2999041401 -> 851557752 -> 2000052400
> config_hints.html says addition, but this is subtraction. I don't quite
> understand. What does adding 2147483647 to the serial do?

This is 32-bit arithmetic.  Modulo 4294967296.

If you don't remember "mod" arithmetic from grade school, think of a
clock.  Every time we get to 12, we start over with 1.  This is a form
of modulo arithmetic, mod-12.  Except that mathematicians and computer
folks like to start with 0, so they would have clocks that read 0-11.
Or, better, mod-24 and 0-23.  Oh!  They do!  ;-)

The number 2147483648 is exactly half of 4294967296.  Add the former
number to your existing SN to get a number that "wraps around":
	2999041401
	2147483648
	==========
	5146525049

BUT this number is bigger than 4294967296!  So, subtract that number
from the sum:
	5146525049
	4294967296
	==========
	 851557753

851557753 is the "same" as 5146525049 in mod-4294967296 arithmetic.

If you leave that serial number in for a while, it WILL update your
slaves, since the BIND software realizes that it has wrapped around.
You can then update your serial number, normally, to something greater
than 851557753.  Such as 2000052400.  ;-)

'Salright?

-- 
Joe Yao				jsdy at cospo.osis.gov - Joseph S. D. Yao
COSPO/OSIS Computer Support					EMT-B
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