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Definition of CIDR

CIDR is a protocol used in IP networking for IP address allocation and routing. It is denoted as a slash at the end of an IP address, followed by a number—like—which indicates how many bits are used for the network prefix. In this example, the ‘24’ indicates that the first 24 bits are the network portion of the address, leaving the remaining bits for host addresses. This method allows for a precise, subnet-based allocation of addresses, reducing waste of IP space.

Origin of CIDR

CIDR was introduced in 1993, at a time when the Internet was experiencing explosive growth, leading to concerns about the potential exhaustion of available IP addresses. This technique was proposed to delay the depletion of addresses by allowing one IP address to be efficiently split across multiple hosts. CIDR also simplified the routing process by decreasing the size of routing tables, making the Internet more scalable and manageable.

Practical Application of CIDR

A practical application of CIDR is found in the management of IP addresses for a company's network. By using CIDR, a network administrator can divide the IP address space into subnets of various sizes appropriate for the number of devices in different departments. This not only conserves addresses but also helps organize the internal network, enhances security, and optimizes traffic flow.

Benefits of CIDR

The benefits of CIDR are multifold. It greatly extends the life of the IPv4 address space by enabling more efficient allocation of addresses. It also reduces the size of routing tables, leading to increased performance and speed in data routing. CIDR’s flexible subnetting capability helps to reduce network congestion and improves the security and management of network infrastructure.


CIDR allows for more efficient use of IP addresses by varying the size of the block of addresses allocated to an organization. This flexibility saves a significant amount of address space that would otherwise go unused.

CIDR simplifies the routing process by aggregating routes into CIDR blocks, reducing the number of entries in routing tables. This leads to more efficient and faster routing of Internet traffic.

Yes, CIDR is used in both IPv4 and IPv6 addressing. While it was initially introduced to extend the longevity of IPv4, it is also inherent to IPv6, providing a solution to address exhaustion and simplifying routing in the expansive address space of IPv6.


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