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A classful network is an obsolete network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing (CIDR) in 1993. The method divides the IP address space for Internet Protocol version 4 (IPv4) into five address classes based on the leading four address bits.
Classless Inter-Domain Routing (CIDR / ˈ s aɪ d ər, ˈ s ɪ-/) is a method for allocating IP addresses for IP routing.The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous classful network addressing architecture on the Internet.
The 0.0.15.255 wildcard in this example indicates a subnetwork with a maximum of 4094 hosts—it is the bitwise complement of the subnet mask 255.255.240.0. The no auto-summary command prevents automatic route summarization on classful boundaries, which would otherwise result in routing loops in discontiguous networks.
A subnetwork, or subnet, is a logical subdivision of an IP network. [ 1 ] : 1, 16 The practice of dividing a network into two or more networks is called subnetting . Computers that belong to the same subnet are addressed with an identical group of its most-significant bits of their IP addresses .
RIPv1 uses classful routing. The periodic routing updates do not carry subnet information, lacking support for variable length subnet masks (VLSM). This limitation makes it impossible to have different-sized subnets inside of the same network class. In other words, all subnets in a network class must have the same size.
Some large / 8 blocks of IPv4 addresses, the former Class A network blocks, are assigned in whole to single organizations or related groups of organizations, either by the Internet Corporation for Assigned Names and Numbers (ICANN), through the Internet Assigned Numbers Authority (IANA), or a regional Internet registry.
IGRP is considered a classful routing protocol. Because the protocol has no field for a subnet mask , the router assumes that all subnetwork addresses within the same Class A, Class B, or Class C network have the same subnet mask as the subnet mask configured for the interfaces in question.
A wildcard mask is a mask of bits that indicates which parts of an IP address are available for examination. In the Cisco IOS, [1] they are used in several places, for example: To indicate the size of a network or subnet for some routing protocols, such as OSPF. To indicate what IP addresses should be permitted or denied in access control lists ...