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@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@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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