Classless Inter-Domain Routing, commonly referred to as CIDR, is a method used in computer networking to allocate and manage IP addresses. CIDR replaces the older classful network addressing scheme, which was based on fixed and hierarchical address blocks. With CIDR, IP addresses are allocated based on their variable length subnet mask (VLSM), allowing for more efficient and flexible utilization of address space.
Overview
CIDR was introduced in the early 1990s as a response to the rapid growth of the Internet and the depletion of available IPv4 addresses. The original classful network addressing scheme divided IP addresses into three classes: A, B, and C. Each class had a fixed number of bits for the network portion and the host portion of the IP address. This approach resulted in a significant waste of address space as organizations were assigned large blocks of IP addresses, regardless of their actual needs.
CIDR introduced a more efficient way to allocate IP addresses by allowing for variable length subnetting. Instead of rigidly dividing IP addresses into classes, CIDR allows the creation of subnets with varying sizes. The subnet mask, expressed in CIDR notation, indicates the number of significant bits in the network portion of the IP address. For example, a CIDR notation of /24 means that the first 24 bits of the IP address represent the network, while the remaining 8 bits are used for hosts.
Advantages
The adoption of CIDR brought several advantages to the networking industry. Firstly, it enabled more efficient utilization of the limited IPv4 address space. By allowing for variable length subnet masking, CIDR reduced address wastage and allowed service providers to allocate IP addresses more precisely according to their customer’s needs.
Secondly, CIDR simplified routing table management. In the classful addressing scheme, routing tables had to store the information of individual network addresses, resulting in large and cumbersome tables. CIDR simplified this process by enabling aggregation of IP addresses from different subnets into a single entry within the routing table, reducing the size and complexity of routing tables.
Applications
CIDR found widespread application in various networking scenariOS . It became an essential component in the internet backbone, where routers rely on CIDR to efficiently route packets across different networks. It also played a significant role in the growth of internet service providers (ISPs), as CIDR allowed them to manage IP address allocation more effectively and efficiently.
Moreover, CIDR facilitated the implementation of Network Address Translation (NAT), a technique that enabled the sharing of a single public IP address among multiple private IP addresses. NAT became critical in enabling the explosion of home networks and small business networks by overcoming the limitation of available public IP addresses.
Conclusion
CIDR, or Classless Inter-Domain Routing, revolutionized the allocation and management of IP addresses in computer networking. By introducing the concept of variable length subnet masking, CIDR enabled more efficient utilization of IPv4 address space, simplified routing table management, and facilitated the growth of internet service providers. Today, CIDR continues to be a fundamental building block of the modern internet, ensuring effective and scalable network communication.