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CIDR is the standard that specifies the details of both classless addressing and an associated routing scheme. Accordingly, the name is slightly inaccurate designation because CIDR specifies addressing as well as routing. The original IPv4 model built on network classes was a useful mechanism for allocating identifiers (netid and hostid) when the primary users of the Internet were academic and research organisations. But, this mode proved insufficiently flexible and inefficient as the Internet grew rapidly to include gateways into corporate enterprises with complex networks. By September 1993, it was clear that the growth in Internet users would require an interim solution while the details of IPv6 were being finalised. The resulting proposal
was submitted as RFC 1519 titled ‘Classless Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Strategy.’ CIDR is classless, representing a move away fromthe original IPv4 network class model. CIDR is concerned with interdomain routing rather
than host identification. CIDR has a strategy for the allocation and use of IPv4 addresses,
rather than a new proposal.