Also known as: Classless inter-domain routing

Classless inter-domain routing (CIDR) is an IP addressing scheme for creating unique identifiers for networks and individual machines. This allows for specificity in configuring routing and firewall rules for a network.

CIDR notation is the notation system for simply communicating and calculating these ranges. A network CIDR looks like (for IPv4 addressing). Each block seperated by a “.” accounts for 8 bits of an IPv4 address, which is 32 bits. In this case, this CIDR range corresponds to the IP range - This is because the /24 indicates that the first 24 bits are fixed.