>Hello,
>
>On Fri, Oct 5, 2001, 15:55:02 GMT
> Stefan Jeglinski, <[EMAIL PROTECTED]> wrote:
>
>>There doesn't appear to be any way to use the IP/n notation to
>>describe certain small blocks of IPs.
>>
>>For example, to denote the BellSouth adsl block
>>216.77.224.1-216.77.254.254, I can conveniently use (AFAICT)
>>
>>216.77.224.0/19
>>
>>OTOH, if I want to denote another BellSouth block
>>216.77.200.1-216.77.223.254 (about the same size), there appears to
>>be no convenient IP/n description.
>>
>>
>>Am I right here?
>
>First, it helps to include the network and broadcast addresses into the range:
>
>216.77.200.0-216.77.223.255
>
>In binary:
>200 = 0xC8 = 0b11001000
>223 = 0xDF = 0b11011111
> ^ because of this bit we need more than one range
>Two ranges: 0b11001000 -> 0b11001111 == 0xC8 -> 0xCF == 200 -> 207
> 0b11010000 -> 0b11011111 == 0xD0 -> 0xDF == 208 -> 223
>
>
>216.77.200.0-216.77.223.255 ==
>{ 216.77.200.0-216.77.207.255, 216.77.208.0-216.77.223.255 } ==
>{ 216.77.200.0/20, 216.77.208.0/19 }
>
I agree that these results correctly represent the end-point of each
address range, but I disagree that your start-points are different,
or even correct.
IIRC, the /n means that all bits in a mask after bit n are zero. Therefore:
/20 -> netmask = 255.255.240.0
/19 -> netmask = 255.255.224.0
For -each- of these, although the end-points of the usable address
ranges are different, the start-point of each must be 216.77.192.1.
To show this by example, let us take 3 different addresses and
appropriate netmasks:
216.77.200.x AND 255.255.240.0 = 216.77.192.0
216.77.208.x AND 255.255.224.0 = 216.77.192.0
216.77.192.x AND 255.255.240.0 = 216.77.192.0
216.77.192.x AND 255.255.224.0 = 216.77.192.0
IOW:
216.77.200.0/20 = 216.77.192.0-216.77.207.255
216.77.208.0/19 = 216.77.192.0-216.77.223.255
IOW:
They each have the desired end-point, but neither has the desired
start-point. In fact, they have the -same- start point.
Or am I missing something?
Stefan Jeglinski
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