Definition of Prefix RoutingCIDR

Prefix routing is just the means by which the Internet identifies the portion of the 32-bit TCP/IP address that uniquely identifies the organization. In effect, this means that the Internet can allocate a group of class networks, which are represented by a single address. This allows for prefix routing and summarization within the routing tables of the Internet. Prefix masks represent a group of TCP/IP network addresses using the method of address or subnet masks.

This aggregation of Internet addresses defies the old structure of Class A, B, C addressing, or classful addressing. The aggregation of Internet addresses, therefore, is classless and deals with connectivity between organizations through the Internet, referred to as interdomain routing. This technology is called classless interdomain routing (CIDR). Table 3-4 shows the RFCs that outline the use of CIDR in an IP network.

Table 3-4 RFCs on CIDR

RFC Number



Applicability statement for the implementation of CIDR


An architecture for IP address allocation with CIDR


CIDR: an address assignment and aggregation strategy


Exchanging routing information across provider boundaries in a CIDR


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