CIDR

Classless Inter-Domain Routing is a way to allocate and specify the Internet addresses used in interdomain routing more flexibly than with the original system of IP address classes. This address aggregation scheme uses supernet addresses to represent multiple IP destinations. Rather than advertise a separate route for each destination, a router uses a supernet address to advertise a single route representing all destinations. RIP (Routing Information Protocol) does not support CIDR; backbone area and OSPF (Open Shortest Path First) support CIDR.