Classless Inter-Domain Routing

Classless Inter-Domain Routing (CIDR) is an internet address assignment and aggregation strategy. CIDR, pronounced "cider" or "cedar", is a refinement to the way IP addresses are interpreted that replaces the previous generation of IP address syntax (the Class A, B, and C addressing scheme). It allows greater flexibility when dividing ranges of IP addresses into separate networks, thus providing more efficient use of increasingly scarce IPv4 addresses. The CIDR strategy is described in RFC 1519.