Classless Inter-Domain Routing

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Classless Inter-Domain Routing

(CIDR) /sid*r/ A technique that summarises a block of Internet addresses in a routing table as an address in dotted decimal notation followed by a forward slash and a two-digit decimal number giving the number of leading one bits in the subnet mask. For example, specifies a subnet mask of 11111111.11111111.11111111.00000000 (binary), implying the block of addresses through

CIDR is "classless" because it is not limited to the subnet masks specified by Internet address classes A, B and C.

According to RFC 1519, CIDR was implemented to distribute Internet address space more efficiently and to provide a mechanism for IP route aggregation. This in turn reduces the number of entries in IP routing tables, enabling faster, more efficient routing, e.g. using routing protocols such as OSPF. CIDR is supported by BGP4.

See also RFC 1467, RFC 1518, RFC 1520.
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The reference design provides the most robust packet forwarding performance available for high-speed networking applications such as classless inter-domain routing (CIDR), gigabit ethernet, packet over SONET (POS) and virtual private networking (VPN).
In response to the rapid growth of the Internet and router overload, Wellfleet will add support of BGP-4 across its entire line of multiprotocol router/bridges for Classless Inter-Domain Routing (CIDR).