the role of multicast and IGMP---------------------------------The so-called multicast, as opposed to unicast and broadcast, refers to the network host will send the data at once to multiple target hosts belonging to the same group. The main use of the IGMP protocol. IGMP is the meaning of Internet Group Management protocol. The protocol is used toThe multicast group membership is established and maintained between the IP host and the multicast router directly adjacent to it, but does not include the propagation and maintenance of the group member relationship information between the multicast routers, which is completed by the multicast routing protocol. All hosts participating in the multicast must implement IGMP.
Multicast Messages----------------------------------Multicast uses the Class D IP address, the classification of IP addresses is shown below, and the Class D address range is 224.0.0.0 to 239.255.255.255.
Note that the multicast address 224.0.0.1 is referred to as all host group addresses, that is, all hosts with multicast capability will join the group.
IGMP is a third-tier TCP/IP protocol that is encapsulated in an IP packet for transmission. The message format for IGMP is fixed, with a total of 8 bytes, as shown in.
There are two types of IGMP: 1 means that the packet is a multicast router query message, 2 is the report issued by the IP host. The following 4 bytes are the multicast address.
the process of multicast-----------------------------------A typical process is this: 1. An IP host process can join and leave a multicast group on the host interface at any time, and the host needs to maintain a table of interfaces that contains the groups and the number of processes in those groups. At this point the host needs to send an IGMP report 2. The router periodically sends IGMP query packets, at which point the group address in the message is 03. The IP host responds to the router's IGMP query message, and for a host, if it joins more than one group, it needs to return an IGMP report for each group. 4. Based on this information, the router maintains a table for each interface, which describes the group of the interface. The message in this process is visible
Multicast and IGMP protocol detailed
