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A multicast address is a logical identifier for a group of hosts in a computer network, that are available to process datagrams or frames intended to be multicast for a designated network service. Multicast addressing can be used in the Link Layer (Layer 2 in the OSI model), such as Ethernet multicast, and at the Internet Layer (Layer 3 for OSI) for Internet Protocol Version 4 (IPv4) or Version 6 (IPv6) multicast. ==IPv4== IPv4 multicast addresses are defined by the leading address bits of ''1110'', originating from the classful network design of the early Internet when this group of addresses was designated as ''Class D''. The Classless Inter-Domain Routing (CIDR) prefix of this group is 224.0.0.0/4. The group includes the addresses from 224.0.0.0 to 239.255.255.255. Address assignments from within this range are specified in RFC 5771, an Internet Engineering Task Force (IETF) ''Best Current Practice'' document (BCP 51).The following table is a list of notable well-known IPv4 addresses that are reserved for IP multicasting and that are registered with the Internet Assigned Numbers Authority (IANA).〔(IANA IP multicast addresses assignments ). Internet Assigned Numbers Authority .〕 ===Local subnetwork=== Addresses in the range of 224.0.0.0 to 224.0.0.255 are individually assigned by IANA and designated for multicasting on the local subnetwork only. For example, the Routing Information Protocol (RIPv2) uses 224.0.0.9, Open Shortest Path First (OSPF) uses 224.0.0.5 and 224.0.0.6, and Zeroconf mDNS uses 224.0.0.251. Routers must not forward these messages outside the subnet in which they originate. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「A multicast address is a logical identifier for a group of hosts in a computer network, that are available to process datagrams or frames intended to be multicast for a designated network service. Multicast addressing can be used in the Link Layer (Layer 2 in the OSI model), such as Ethernet multicast, and at the Internet Layer (Layer 3 for OSI) for Internet Protocol Version 4 (IPv4) or Version 6 (IPv6) multicast.==IPv4==IPv4 multicast address redirects here-->IPv4 multicast addresses are defined by the leading address bits of ''1110'', originating from the classful network design of the early Internet when this group of addresses was designated as ''Class D''. The Classless Inter-Domain Routing (CIDR) prefix of this group is 224.0.0.0/4. The group includes the addresses from 224.0.0.0 to 239.255.255.255. Address assignments from within this range are specified in RFC 5771, an Internet Engineering Task Force (IETF) ''Best Current Practice'' document (BCP 51).The following table is a list of notable well-known IPv4 addresses that are reserved for IP multicasting and that are registered with the Internet Assigned Numbers Authority (IANA).(IANA IP multicast addresses assignments ). Internet Assigned Numbers Authority .===Local subnetwork===Addresses in the range of 224.0.0.0 to 224.0.0.255 are individually assigned by IANA and designated for multicasting on the local subnetwork only. For example, the Routing Information Protocol (RIPv2) uses 224.0.0.9, Open Shortest Path First (OSPF) uses 224.0.0.5 and 224.0.0.6, and Zeroconf mDNS uses 224.0.0.251. Routers must not forward these messages outside the subnet in which they originate.」の詳細全文を読む スポンサード リンク
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