IPV6 White Paper (5)

Multicast Technology1IntroductionMulticast technology provides an effective way for a sender to transmit data to a group of recipients. 1. During Multicast Transmission, data is sent to the receiver's multicast address, instead of the unicast address of each receiver. The sender only sends one copy of data, copy the data from the source node to the target node. Figure 1 Multicast. multicasting has many practical applications. For example, commanders in different regions can use the multicasting system to participate in planning meetings, and then use the multicast protocol to transmit the plan to lower-level commanders; modify the data of the geographically distributed logical database, such as on-demand video, remote instruction, and online TV. 2. the multicast address is the sending IP multicast data, and the sender needs to determine a suitable multicast address, which represents a group. IPv4 multicast addresses use Class d ip addresses to determine multicast groups. In the Internet, the multicast address ranges from 224.0.0.0 to 234.255.255.255. Among them, the important addresses are: 224.0.0.1-All multicast hosts in the CIDR block.
224.0.0.2-All vrouters supporting multicast in the CIDR Block
224.0.0.4-All DVMRP routers in the CIDR Block
224.0.0.5-All OSPF Routers
224.0.0.6-All OSPF assigned Routers
224.0.0.9-All r00002 Routers
224.0.0.13-1/256 of the IPV6 address space of all PIM routers is allocated to multicast addresses. An FF11111111 value indicates that the address is a multicast address. The identifier segment is always set to 0 and retained. When the fourth t id is set to 0, it indicates a permanent multicast address. When the t id is set to 1, it indicates a non-permanent multicast address, which acts as a temporary multicast address. 3. The Group Management Protocol host uses the Group Management Protocol IGMP to notify the local multicast router that it wants to receive multicast traffic from the host group address. If the host supports IGMPv2, it can also notify multicast router to exit a host group. The multicast router maintains a host group member table for each port through the IGMP protocol, and regularly queries the Host group members in the table to determine whether the host group is alive. 4. to achieve multicast communication, the multicast routing protocol must be established, currently, common multicast routing protocols include the distance vector Multicast Routing Protocol DVMRP, protocol-independent intensive mode multicast protocol, and Protocol-independent decentralized mode multicast protocol. DVMRP is an Internal Gateway Protocol applicable to a single independent system. It is a multicast routing protocol based on distance vector algorithms. Based on RIP, it uses its own dynamic routing protocol for Route switching and route table construction. Currently, it is basically replaced by PIM. The PIM Protocol aims to provide a sufficient number of Inter-Domain multicast routes on the Internet. PIM has two compatible operation modes: intensive mode and divergent mode. The dense mode adopts the same mode as DVMRP to establish a resource-based multicast tree built in the PIM-DM environment. The PIM-DM is named "protocol-Independent Multicast" because it is independent of the IP routing protocol. The PIM-DM is suitable for situations where the sender and receiver are very close, and only a small number of senders and a large number of receivers or multicast traffic continues to be very large. The PIM-SM is similar to the PIM-DM, which is based on Multicast Routing Protocol to determine the RPF interface protocol. The PIM-SM Protocol assumes that the number of recipients in the network is sparse or multicast groups are separated by the WAN, which is suitable for the scenarios where the number of recipients in multicast groups is small and the intermittent multicast traffic is used. Unlike the broadcast mode of the PIM-DM, The PIM-SM defines a set point (RP) where all receivers are registered in the RP and multicast groups are forwarded to the receiver by the RP.