What is CIDR and Supernetting

What is Supernetting ?

Combining several IP network addresses into one IP address.

Supernetting reduces the number of entries in a routing table ( less IP address ,means , less record of the IP inside the routing table , so when router try to search for destination IP address , it take less time to search )

Supernetting, also known as Classless InterDomain Routing (CIDR)

In the following example, a group of networks with contiguous numbers starting with 172.16.8.0 and ending with 172.16.16.0 are supernetted into the subnet mask of 255.255.224.0.

The subnet mask is derived by comparing the binary of the first and last addresses.

The last bit location on the right that is the same in both addresses marks the end of the mask.

The CIDR notation for this is /19, because there are 19 1 bits in the subnet mask.

For example, the IP address 172.16.8.1 would be 172.16.8.1/19.

172.16.8.0 10101100.00010000.00001000.00000000
172.16.16.0 10101100.00010000.00010000.00000000
.
.
Subnet Mask .

255.255.224.0 11111111.11111111.11100000.00000000


What is CIDR ?

Short for Classless Inter-Domain Routing,

It is an IP addressing scheme that replaces the older system based on classes A, B, and C.
( not using class A , B , C )

With CIDR, a single IP address can be used to designate many unique IP addresses.
(combine few IP address to be ONE IP address )

A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number, called the IP network prefix. For example:
172.200.0.0/16

The IP network prefix specifies how many addresses are covered by the CIDR address, with lower numbers covering more addresses.

An IP network prefix of /12, for example, can be used to address 1,048,576 former Class C addresses.

CIDR addresses reduce the size of routing tables and make more IP addresses available within organizations. [ I will explain this point on the whiteboard ]

CIDR is also called supernetting.