What is CIDR Notation?

CIDR, or Classless Inter-Domain Routing, is a method used for IP address allocation and routing in both IPv4 and IPv6 networks.

In IPv4 networks, IP addresses are 32-bit numbers represented in dotted decimal notation, such as 192.0.2.0. In CIDR notation, an IPv4 address is followed by a forward slash and a number that indicates the number of leading bits in the IP address that represent the network portion. For example, the CIDR notation 192.0.2.0/24 indicates that the first 24 bits of the IP address represent the network, while the remaining 8 bits represent the host. This allows for more efficient use of IP addresses and more precise routing in large networks.

In IPv6 networks, IP addresses are 128-bit numbers represented in hexadecimal notation, such as 2001:0db8:85a3:0000:0000:8a2e:0370:7334. In CIDR notation, an IPv6 address is followed by a forward slash and a number that indicates the number of leading bits in the IP address that represent the network portion. For example, the CIDR notation 2001:0db8::/32 indicates that the first 32 bits of the IPv6 address represent the network, while the remaining 96 bits represent the host. This allows for efficient allocation of IPv6 addresses and more precise routing in IPv6 networks.

CIDR notation enables networks to be divided into smaller subnets, which can be used to allocate IP addresses more efficiently and provide more flexibility in network design. It also enables routing protocols, such as Border Gateway Protocol (BGP), to exchange routing information more efficiently by advertising CIDR blocks rather than individual IP addresses.

In summary, CIDR is a method of IP address allocation and routing that allows for more efficient use of IP addresses and more precise routing in large networks. It is used in both IPv4 and IPv6 networks and enables networks to be divided into smaller subnets for more efficient allocation of IP addresses and greater flexibility in network design.