On 30 Jul 2004 at 12:54, John Keown wrote:
I did not make the rule for the notation. That are part of the binary number
system. The total space is the 32 bit octal address space. Therefore there
are certain mathematical restrictions imposed by both the binary and octal
notation. The /xx defines that as some power of 2 a /24 is 2 to 8 power. or
256. a / 25 is 2 the 7 and etc.
I don't see where this is defined, neither had I heard about this
"definition". My known definition for y.y.y.y/xx was that the /xx part
defines the network mask for a specific y.y.y.y IP address. I don't know
of any definition that restricts the y.y.y.y-part to the first IP in the
range.
The range is calculated by the mathematical operators or, and, xor and the
nor operators. the number must be represented in binary format of 0 and 1.
Calculations with the netmask is done with an boolean AND and not XOR.
You can easily calculate the range borders from any CIDR notation even
if the given IP-Adress is not the first in the range (as it was the case
in your example).
Any IP-handling library does that, SPF does it, and I don't really see
where the problem is.
It does appear that the rfc implies that a /24 on a non boundary is
acceptable and from that I say it is doomed.
I haven't really found out an RFC about it, but I would think that
restricting the CIDR-notation to using just the BORDER-IP as you
suggest would doom its usefulness.
--
Ernesto Baschny <ernst(_at_)baschny(_dot_)de>
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