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Thus, a /20 block is a CIDR block with an unspecified 20-bit prefix. An IP address is part of a CIDR block and is said to match the CIDR prefix if the initial n bits of the address and the CIDR prefix are the same. An IPv4 address is 32 bits so an n-bit CIDR prefix leaves 32 − n bits unmatched, meaning that 2 32−n IPv4 addresses match a ...
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:
In the past, the recommended allocation for an IPv6 customer site was an address space with a 48-bit (/ 48) prefix. [20] However, this recommendation was revised to encourage smaller blocks, for example using 56-bit prefixes. [21] Another common allocation size for residential customer networks has a 64-bit prefix.
Internet Group Management Protocol (IGMP) version 3 [22]: §4.2.14 No 224.0.0.102 Hot Standby Router Protocol version 2 (HSRPv2) / Gateway Load Balancing Protocol (GLBP) No 224.0.0.107 Precision Time Protocol (PTP) version 2 peer delay measurement messaging No 224.0.0.251 Multicast DNS (mDNS) address No 224.0.0.252
Internet Protocol version 4 (IPv4) defines an IP address as a 32-bit number. [77] IPv4 is the initial version used on the first generation of the Internet and is still in dominant use. It was designed in 1981 to address up to ≈4.3 billion (10 9 ) hosts.
IS-IS, another LSR-based protocol, is more common in large service provider networks. Originally designed in the 1980s, OSPF version 2 is defined in RFC 2328 (1998). [1] The updates for IPv6 are specified as OSPF version 3 in RFC 5340 (2008). [2] OSPF supports the Classless Inter-Domain Routing (CIDR) addressing model.