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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 IPv6 address specification 2001:db8:: / 32 is a large address block with 2 96 addresses, having a 32-bit routing prefix. For IPv4, a network may also be characterized by its subnet mask or netmask , which is the bitmask that, when applied by a bitwise AND operation to any IP address in the network, yields the routing prefix.
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:
IPv4 uses 32-bit addresses which limits the address space to 2 32 addresses, i.e. 4 294 967 296 addresses. [108] IPv4 is in the process of replacement by IPv6, its successor, which uses 128-bit addresses, providing 2 128 addresses, i.e. 340 282 366 920 938 463 463 374 607 431 768 211 456, [179] a vastly increased address space. The shift to ...
The slash in an IP address (e.g., 192.0.2.0/29) indicates the prefix size in CIDR notation. The number of addresses of a subnet may be calculated as 2 address size − prefix size, in which the address size is 128 for IPv6 and 32 for IPv4. For example, in IPv4, the prefix size/29 gives: 2 32–29 = 2 3 = 8 addresses.