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(CIDR) /sid*r/ A technique that summarises ablock of Internet addresses in a routing table as anaddress in dotted decimal notation followed by a forwardslash and a two-digit decimal number giving the number ofleading one bits in the subnet mask. For example,123.123.123.0/24 specifies a subnet mask of11111111.11111111.11111111.00000000 (binary), implying theblock of addresses 123.123.123.0 through 123.123.123.255.CIDR is "classless" because it is not limited to the subnetmasks specified by Internet address classes A, B and C.According to RFC 1519, CIDR was implemented to distributeInternet address space more efficiently and to provide amechanism for IP route aggregation. This in turn reducesthe number of entries in IP routing tables, enabling faster,more efficient routing, e.g. using routing protocols suchas OSPF. CIDR is supported by BGP4.See also RFC 1467, RFC 1518, RFC 1520.