What does CIDR stand for, and why is it significant?

CIDR stands for Classless Inter-Domain Routing, and its significance stems from its ability to allow for more efficient usage of IP address space. Before CIDR was introduced, the hierarchical class-based system (with classes A, B, and C) led to a significant waste of IP addresses. Large organizations might obtain entire Class A blocks even if they did not require that many addresses, leading to vast numbers of IP addresses going unused.

CIDR introduced a more flexible and efficient way of allocating IP addresses. It enables the use of variable-length subnet masking (VLSM), meaning that networks can be allocated IP address ranges that more closely match their actual needs. This not only conserves IP address space but also improves routing efficiency and reduces the size of routing tables. As a result, CIDR has played a crucial role in the management and growth of the internet, allowing for better utilization of the available address space.