Classless Inter-Domain Routing (CIDR) is a method of IP address allocation and routing that allows for more efficient use of IP addresses and better routing. It was introduced in 1993 to replace the previous classful network addressing architecture.
CIDR allows for the allocation of variable-sized blocks of IP addresses, improving address space utilization and reducing the growth of routing tables on routers across the Internet. It is based on the idea that IP addresses can be allocated and routed based on their network prefix rather than their class, which was the traditional way of IP address allocation. CIDR addresses are represented using a slash notation, which specifies the number of bits in the network prefix.
For example, an IP address of 192.168.1.0 with a prefix length of 24 would be represented as 192.168.1.0/24.CIDR supports Variable-Length Subnet Masking (VLSM), thus supporting more precise network prefix specifications and grants users flexibility by offering support for prefixes of any length.