Understanding IP class range.

[James Mcphee]

192.168.1.0/25 just means 25 bits in the network portion of the IP
address.  In a 32 bit address, that means you have 7 bit of space left for
the device address part.  with 8 bits apiece in each octet, you can figure
it out pretty quickly.  I've always heard the /## notation referred to as
cisco notation.

On Mon, Aug 31, 2015 at 8:51 AM, Keith Smith <techlists at phpcoderusa.com>
wrote:

>
> Very nice Kenn!!
>
> Ok so if I had 192.168.1.0/25 the range would be 192.168.1.0 -
> 192.168.1.127
>
> /26 would be 192.168.1.0 - 192.168.1.192 ?  or is it 192.168.1.0 -
> 192.168.1.64 ?
>
> Is that correct?
>
> Not sure how to make a net mask out of 192.168.1.0/25 - would it be
> 255.255.255.128?
>
>
> Thanks!!
>
>
>
> On 2015-08-31 02:55, parabellum7 at yahoo.com wrote:
>
>> Hi Keith,
>>
>> If I recall correctly, the /24 part of 192.168.0.0/24 is the subnet
>> specified in CIDR notation (Classless Inter Domain Routing).
>>
>> Think in binary terms, that /24 equals
>> 11111111.11111111.11111111.00000000  (note there's 24 1's) equals
>> 255.255.255.0 so is a class C subnet with the first three octets being
>> the network mask.
>>
>> Likewise if you had an IP addy followed by a /8 that equals
>> 11111111.00000000.00000000.00000000 equals 255.0.0.0 so is a class A
>> subnet.
>>
>> Called octets cuz there's 8 bits hence a decimal max of 255.
>>
>> CIDR is usually seen at ISP's or in enterprise networks that need to
>> subnet further as the network mask does not have to align with the
>> octet boundary as it does in the classfull network addressing we're
>> used to. That's where things get weird and all this because those
>> silly routers only speak binary. :]
>>
>> If you're seeing 192.168.0.0/24 in a zenmap target field it means scan
>> everything from and including 192.168.0.0 to 192.168.0.255.
>>
>>
>> IP network classes or Classfull Network Addressing
>>
>>         - Range -                                               - mask -
>>               # of networks   # of nodes      CIDR mask
>> A       1.1.1.1 -       126.255.255.255         255.0.0.0
>>  126                             16,777,214      /8
>> B       128.0.0.1 - 191.255.255.255             255.255.0.0
>>  16,384                  65,534          /16
>> C       192.0.0.1 - 223.255.255.255             255.255.255.0
>>  2,097,151               254                     /24
>> D       224.0.0.1 - 239.255.255.255
>> E       240.0.0.1 - 255.255.255.255
>>
>>
>>
>> --Kenn
>>
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>
> --
> Keith Smith
>
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-- 
James McPhee
jmcphe at gmail.com
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