CIDR Calculator

Classless Inter Domain Routing (CIDR) provides a flexible method to allocate and specify IP addresses used in inter-domain routing compared to the original system of classful IP address assignment. As a result, the number of available addresses has been greatly increased. CIDR is now the routing system used by virtually all gateway hosts on the backbone network of the Internet. Many small companies also benefit from CIDR in that four class Cs can be grouped into one subnet to provide over 1,000 IP addresses.