CIDR, or Classless Inter-Domain Routing, is a method used to assign and manage IP addresses on Internet networks.

Before the implementation of CIDR, IP addresses were divided into classes, such as Class A, Class B, and Class C, resulting in inefficient use of IP addresses and address exhaustion issues.

With CIDR, IP addresses are allocated and managed more efficiently by grouping addresses into contiguous blocks, allowing for greater flexibility in address allocation and better utilization of available address space. Here are several key aspects of CIDR worth highlighting:

CIDR Notation

In CIDR, IP addresses are represented using a special notation that combines the IP address and the subnet length prefix, separated by a slash (“/”). For example, “192.168.1.0/24” indicates a network with base IP address “192.168.1.0” and a subnet length prefix of 24 bits.

Subnet length prefix

The subnet length prefix specifies how many bits of the IP address make up the network portion of the address. For example, in the notation “192.168.1.0/24”, the first 24 bits are used to identify the network, and the last 8 bits are reserved to identify individual hosts on the network.

Address block division

CIDR allows blocks of IP addresses to be divided into smaller subnets as necessary to fit the needs of the network. This allows for more efficient address allocation and prevents wasted IP addresses.

Route summary

CIDR also facilitates the aggregation of multiple network paths into a single, more general path, which reduces the load on routing tables and improves the efficiency of routing on the Internet.

In summary, CIDR is a fundamental method for the efficient allocation and management of IP addresses on the Internet, allowing greater flexibility, efficiency and scalability in IP address management and network routing.