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CIDR provides fine-grained routing prefix aggregation. For example, if the first 20 bits of their network prefixes match, sixteen contiguous / 24 networks can be aggregated and advertised to a larger network as a single / 20 routing table entry.
An example of route aggregation as a part of CIDR. A supernetwork, or supernet, is an Internet Protocol (IP) network that is formed by aggregation of multiple networks (or subnets) into a larger network. The new routing prefix for the aggregate network represents the constituent networks in a single routing table entry.
RFC 4271 corrected errors, clarified ambiguities and updated the specification with common industry practices. The major enhancement of BGP4 was the support for Classless Inter-Domain Routing (CIDR) and use of route aggregation to decrease the size of routing tables. RFC 4271 allows BGP4 to carry a wide range of IPv4 and IPv6 "address families".
For example, consider this IPv4 forwarding table (CIDR notation is used): 192.168.20.16/28 192.168.0.0/16 When the address 192.168.20.19 needs to be looked up, both entries in the forwarding table "match". That is, both entries contain the looked up address.
Since the introduction of CIDR, however, the assignment of an IP address to a network interface requires two parameters, the address and a subnet mask. Given an IPv4 source address, its associated subnet mask, and the destination address, a router can determine whether the destination is on a locally connected network or a remote network.
Under "CIDR notation" the following is simply confusing, "The IP address is expressed according to the standards of IPv4 or IPv6. The address may denote a single, distinct interface address or the beginning address of an entire network. The aggregation of these bits is often called the host identifier."
The need to record routes to large numbers of devices using limited storage space represents a major challenge in routing table construction. In the Internet, the currently dominant address aggregation technology is a bitwise prefix matching scheme called Classless Inter-Domain Routing (CIDR).
The CIDR notation for this group is 224.0.0.0 / 4. [1] The group includes the addresses from 224.0.0.0 to 239.255.255.255 . The address range is divided into blocks each assigned a specific purpose or behavior.