Supernetting / Classless Inter-Domain Routing (CIDR) Example

If I needed about 1000 addresses, I could supernet 4 Class C networks together:
192.60.128.0   (11000000.00111100.10000000.00000000)  Class C subnet address
192.60.129.0   (11000000.00111100.10000001.00000000)  Class C subnet address
192.60.130.0   (11000000.00111100.10000010.00000000)  Class C subnet address
192.60.131.0   (11000000.00111100.10000011.00000000)  Class C subnet address
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192.60.128.0   (11000000.00111100.10000000.00000000)  Supernetted Subnet address
255.255.252.0  (11111111.11111111.11111100.00000000)  Subnet Mask
192.60.131.255 (11000000.00111100.10000011.11111111)  Broadcast address

In this example, the subnet 192.60.128.0 includes all the addresses from 192.60.128.0 to 192.60.131.255. As you can see in the binary representation of the subnet mask, the Network portion of the address is 22 bits long, and the host portion is 10 bits long.

Under CIDR, the subnet mask notation is reduced to a simplified shorthand. Instead of spelling out the bits of the subnet mask, it is simply listed as the number of contiguous 1s bits. In the above example, instead of writing the address and subnet mask as
192.60.128.0, Subnet Mask 255.255.252.0
the network address would be written simply as:
192.60.128.0/22
which indicates the length of network portion of the address is 22. If you look at the subnet mask in binary (11111111.11111111.11111100.00000000), you can easily see how this notation works.

The use of a CIDR notated address is the same as for a Classful address. Classful addresses can easily be written in CIDR notation (Class A = /8, Class B = /16, and Class C = /24)