"Supernetting" what's this stuff?

Supernetting or Classless Inter-Domain Routing (CIDR)

Supernetting, also called Classless Inter-Domain Routing (CIDR), is a way to aggregate multiple Internet addresses of the same class. The original Internet Protocol (IP) defines IP addresses in four major classes of address structure, Classes A through D. Each class allocates one portion of the 32-bit Internet address format to a network address and the remaining portion to the specific host machines within the network.

EXAMPLE:-

For example, suppose you want to supernet the 16 Class C networks

201.168.0.0 through 201.168.15.0 into a single Supernetted Address Range.

You would find the number 16 in the column labeled # of Networks and discover you need to supernet on 4 bits. This really means borrowing 2 bits from the bits normally reserved for the network portion of the address.

Since 201.168.0.0 is a Class C address with a Standard Subnet Mask of 255.255.255.0 we know we will be modifying the 3^rd octet (the last range normally reserved for network addresses) and using the first 4 bits for our network mask.

In binary, our 3^rd octet becomes 11110000 which is equivalent to 240 decimal. Therefore our subnet mask is 255.255.240.0.

If you look at the entire subnet mask in binary you can see how many addresses are reserved for the hosts:

 11111111.11111111.11110000.00000000

 nnnnnnnn.nnnnnnnn.nnnnHHHH.HHHHHHHH

All the positions where 0s or Hs are present represent the Host address portion. There are 12 H’s present, so 2¹²=4096 which is the same as 256*16 (the number of networks we were originally trying to combine).

For more accurate information see the following VIDEO:-