Classless Inter-Domain Routing (CIDR)
CIDR is an abbreviation for Classless Inter-Domain Routing. CIDR is a packet routing methodology used to allocate IP address blocks and route traffic on the Internet. CIDR was developed to help alleviate the problem of IP address exhaustion.
CIDR uses a technique called subnetting to allow one IP address to be used for multiple destinations. Subnetting allows a single IP address to be divided into multiple, smaller networks. This division is accomplished by borrowing bits from the host portion of the IP address and using them as part of the network ID. The number of bits borrowed depends on the size of the network being created.
For example, consider an organization that has been allocated the IP address block 192.168.100.0/24 (192.168.100.0 with a 24-bit netmask). This organization can create two /25 subnets (192.168 168.100/25 and 192 .168 .101/25) or four /26 subnets (192 .168 .100 .64/26, 192 .168 .100 .128/26 , 192 .168 .100 .192/26 , and 192 168 101 0/26).
The advantage of using CIDR is that it allows for more efficient use of IP addresses than traditional Classful addressing methods. CIDR also allows for easier aggregation of routes, which reduces the size of routing tables and improves Scalability Of The Internet Protocol
