Operation Manual – MulticastH3C S5600 Series Ethernet Switches Chapter 3 IGMP Configuration3-41) This host sends a Leave Group message (often referred to as leave message) toall routers (the destination address is 224.0.0.2) on the local subnet.2) Upon receiving the leave message, the querier sends a configurable number ofgroup-specific queries to the group being left. The destination address field andgroup address field of message are both filled with the address of the multicastgroup being queried.3) One of the remaining members, if any on the subnet, of the group being queriedshould send a membership report within the maximum response time set in thequery messages.4) If the querier receives a membership report for the group within the maximumresponse time, it will maintain the memberships of the group; otherwise, thequerier will assume that no hosts on the subnet are still interested in multicasttraffic to that group and will stop maintaining the memberships of the group.3.1.4 IGMP ProxyA lot of stub networks (stub domains) are involved in the application of a multicastrouting protocol (PIM-DM for example) over a large-scaled network. It is a hard work toconfigure and manage these stub networks.To reduce the workload of configuration and management without affecting themulticast connection of leaf networks, you can configure an IGMP Proxy on a Layer 3switch in the stub network (Switch B shown in Figure 3-2). The Layer 3 switch will thenforward IGMP join or IGMP leave messages sent by the connected hosts. After IGMPProxy is configured, the stub switch is no longer a PIM neighbor but a host for theexterior network. The Layer 3 switch receives the multicast data of correspondinggroups only when it has directly attached multicast members.Figure 3-2 Diagram for IGMP proxy
