Hello,
On Mon, Oct 8, 2001, 15:17:43 GMT
Stefan Jeglinski, <[EMAIL PROTECTED]> wrote:
>>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
So, that was my mistake. Shame on my Saturday math... :( The "+/-1" syndrome...
The correct masks are 216.77.200.0/21, 216.77.208.0/20:
/21 -> netmask = 255.255.248.0
/20 -> netmask = 255.255.240.0
>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?
Sorry.
216.77.200.0/21 = 216.77.200.0-216.77.207.255
216.77.208.0/20 = 216.77.208.0-216.77.223.255
Best regards,
Dmitry Akindinov
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