Classless Inter-Domain Routing (CIDR)

Classless Inter-Domain Routing, or CIDR, is a method for efficiently managing and dividing IP address ranges. It was introduced to replace the rigid class-based structure of IPv4 addressing and improve the utilisation of available addresses. With CIDR, the size of a network is defined by a prefix length, for example 192.168.1.0/24. The number following the slash specifies how many bits of the IP address represent the network portion. This allows networks of different sizes to be created and IP address ranges to be allocated according to specific requirements. CIDR also supports route aggregation, allowing multiple networks to be combined into larger address blocks and helping reduce routing table sizes. It is therefore a fundamental concept in IP addressing, subnetting and efficient network routing.