CIDR (Classless Inter-Domain Routing) is a method of IP addressing and routing that allows for more efficient use of IP address space compared to the older classful IP addressing scheme. CIDR enables flexible subnetting and summarization of IP address blocks, which is essential for the efficient allocation of IP addresses on the internet.
Key points about CIDR include:
- Classless Addressing: CIDR eliminates the rigid class-based system (Class A, B, C) and allows IP addresses to be allocated in a more granular and flexible manner.
- Prefix Length: CIDR notation includes a prefix length in the form of “/X” after the IP address, where X represents the number of bits in the network portion of the address. For example, “/24” indicates that the first 24 bits are used for the network, leaving 8 bits for host addresses in IPv4.
- Subnetting: CIDR makes it easy to create subnets of varying sizes within a larger IP address block. Subnet masks can be represented in CIDR notation as well.
- Routing: CIDR is crucial for efficient routing on the internet. It allows routers to summarize multiple IP address blocks into a single route advertisement, reducing the size of routing tables.
- IP Address Conservation: By allowing for variable-length subnet masks, CIDR helps conserve IP addresses by assigning only the necessary number of addresses to a subnet.
- IPv6: CIDR principles are also applied in IPv6, where address space is vast, and efficient allocation is essential.
CIDR has become the standard for IP addressing and routing on the modern internet. It allows for efficient utilization of IP addresses, which is crucial as the number of devices connected to the internet continues to grow.