IPV4 Multicast Address

IPV4 Multicast (multicast) mechanism refers to: the mechanism of sending and receiving IP multicast traffic. IP multicast traffic is sent to a single destination IP address, but is received and processed by multiple IP hosts, regardless of where the host is located on the IP internetwork. A host listens on a specific IP multicast address and receives all packets sent to that IP address.

IP multicasting is more efficient than IP unicast and broadcast. Unlike unicast, multicast sends only one copy of the data. Unlike broadcasts, multicast traffic is only received and processed by the computer on which it is being listened.

IP multicast address (multicast, also known as group address): Class D Address: In 224.0.0.0 to 239.255.255.255, this is defined by setting the top four high-order bits to 1110来. In the network prefix or CIDR (classless inter-domain Routing) notation, the IP multicast address is abbreviated to 224.0.0.0/4. Multicast addresses from 224.0.0.0 to 224.0.0.255 (224.0.0.0/24) are reserved for local subnets, while lifetimes in the IP header (time to Live,ttl) are ignored and are not forwarded by IP routers.

In the host and server environments, basically only 224.0.0.0/4 are used as multicast addresses.

224.0.0.1– all hosts on this subnet.

224.0.0.2– all routers on this subnet.

224.0.0.5– Open Shortest Path First (Open Shortest path FIRST,OSPF) algorithm version 2nd, designed to reach all OSPF routers on a network.

224.0.0.6– Open Shortest Path First algorithm version 2nd, designed to reach all OSPF-specified routers on a network.

224.0.0.9– Routing Information Protocol (Routing information Protocol,rip) 2nd edition.

224.0.1.1– Network Time Protocol (network Times Protocol).

ZZ from:http://hi.baidu.com/chinakite/blog/item/a51831ad228f9d0a4a36d635.html IP Multicast traffic must depend on the IP multicast address, which is a class D IP address in IPv4 , ranging from 224.0.0.0 to 239.255.255.255, and divided into three categories of local link multicast addresses, reserved multicast addresses, and administrative rights multicast addresses. where the local link multicast address range is 224.0.0.0~224.0.0.255, which is reserved for routing protocols and other purposes, routers do not forward IP packets belonging to this range; The multicast address is reserved for 224.0.1.0~ 238.255.255.255, can be used for global scope (such as Internet) or network protocol; Administrative rights multicast addresses are 239.0.0.0~239.255.255.255 for internal use, similar to private IP addresses, not for the internet, You can limit the multicast scope.

The ZZ from:http://book.51cto.com/art/200904/120471.htm multicast IP address also requires the corresponding multicast MAC address to actually transfer frames on the local network. The multicast MAC address starts with the hexadecimal value 01-00-5e, and the remaining 6 hexadecimal digits are based on the last 23-bit conversion of the IP multicast group address.

All hosts that receive multicast packets using the same IP multicast address form a host group, also known as a multicast set. The members of a multicast group are subject to change, a host can join or leave the multicast group at any time, the number of members of the multicast group and the geographic location are unrestricted, and a host can belong to several multicast groups. In addition, a host that is not part of a multicast group can send packets to that multicast group.