CIDR
Definition
Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and for IP routing. It replaced the previous system of addressing based on classes A, B, and C. Its goal was to slow the growth of routing tables on routers across the Internet, and to help slow the rapid exhaustion of IPv4 addresses.
Why It Matters
CIDR provides a much more flexible and efficient way to allocate IP address blocks. It allows network administrators to create subnets of almost any size, which was not possible with the rigid class-based system.
Contextual Example
CIDR notation specifies an IP address and a prefix size, like `192.168.1.0/24`. The `/24` indicates that the first 24 bits are the network portion of the address, and the remaining 8 bits are for host addresses. This block contains 256 addresses, from 192.168.1.0 to 192.168.1.255.
Common Misunderstandings
- CIDR is pronounced "cider".
- It is the standard notation used today for describing IP address blocks and routing rules.