What is CIDR Notation?

CIDR Explained

CIDR, or Classless Inter-Domain Routing, is a technique employed for IP address allocation and routing across both IPv4 and IPv6 networks.

IPv4 Networks

In the realm of IPv4 networks, IP addresses consist of 32-bit figures showcased in dotted decimal notation, like 192.0.2.0. Using CIDR notation, such an IPv4 address is paired with a forward slash and a subsequent number. This number pinpoints the quantity of initial bits in the IP address signifying the network segment. For instance, the CIDR notation 192.0.2.0/24 reveals that the starting 24 bits of the IP address denote the network, with the latter 8 bits indicating the host. This approach enables a more streamlined utilisation of IP addresses and refined routing in expansive networks.

IPv6 Networks

For IPv6 networks, IP addresses comprise 128-bit figures displayed in hexadecimal format, an example being 2001:0db8:85a3:0000:0000:8a2e:0370:7334. In the context of CIDR, an IPv6 address comes with a forward slash and a number that signifies the initial bits of the IP address defining the network segment. Take for instance the CIDR notation 2001:0db8::/32. Here, the initial 32 bits of the IPv6 address pinpoint the network, whilst the subsequent 96 bits designate the host. This structure facilitates efficient IPv6 address allocation and enhances routing precision within IPv6 networks.

Benefits of CIDR Notation

Thanks to CIDR notation, networks can be partitioned into tinier subnets. This allows for the effective allocation of IP addresses and grants increased adaptability in shaping networks. Additionally, it permits routing protocols, like the Border Gateway Protocol (BGP), to share routing data more productively by broadcasting CIDR blocks instead of individual IP addresses.

To sum it up, CIDR is a strategy for IP address distribution and routing, optimising the efficiency of IP address usage and refining routing in extensive networks. It's applicable in both IPv4 and IPv6 networks, and it empowers networks to be fragmented into smaller subnets, ensuring optimal IP address allocation and heightened network design flexibility.