The Internet Engineering Task Force introduced Classless Inter-Domain Routing (CIDR) in 1993 to replace the previous classful network addressing architecture. Its goals were to slow the growth of routing tables on routers across the Internet and to help slow the rapid exhaustion of IPv4 addresses. IP addresses are described as consisting of two groups of bits in the address: the most significant bits are the network prefix, which identifies a whole network or subnet, and the least significant set forms the host identifier, which specifies a particular interface of a host on that network. This division is used as the basis of traffic routing between IP networks and for address allocation policies.
CIDR Notation
CIDR uses a compact representation of IP addresses and prefixes, allowing for more efficient routing of IP packets. In CIDR notation, an IP address is represented as a string of numbers separated by a slash (/) followed by the prefix length, which specifies the number of bits used for the network address and the host address.
- Example 1: 192.168.0.0/24 – This notation represents a range of 256 IP addresses starting from 192.168.0.0 to 192.168.0.255. The "/24" represents the number of bits used for the network address, in this case 24 bits.
- Example 2: 10.0.0.0/16 – This notation represents a range of 65,536 IP addresses starting from 10.0.0.0 to 10.255.255.255. The "/16" represents the number of bits used for the network address, in this case 16 bits.
Benefits of CIDR
CIDR offers several advantages over the previous classful network addressing architecture.
- Efficient routing: CIDR allows for more efficient routing of IP packets by using a compact representation of IP addresses and prefixes.
- Slower growth of routing tables: By introducing a more flexible addressing scheme, CIDR helps to slow the growth of routing tables on routers across the Internet.
- Conservation of IPv4 addresses: CIDR helps to conserve IPv4 addresses by allowing for more precise allocation of addresses to networks and subnets.
