Operation Manual – MulticastH3C S7500 Series Ethernet Switches Chapter 6 IGMP Configuration6-4z The data from the multicast source reaches the IGMP router over the multicastroutes. If there are receivers in the network connected to the IGMP router, the datawill be forwarded to this network segment and the receiver hosts receive the data.IGMP leave messages are not defined in IGMPv1. When a host leaves a multicastgroup, the multicast router knows that a host has left the group only when the querymessage times out.When all the hosts in a network segment have left the multicast group, the branchcorresponding to the related network segment is pruned from the multicast tree.6.1.4 IGMP ProxyA lot of leaf networks (leaf domains) are involved in the application of a multicast routingprotocol (PIM-DM for example) over a large-scaled network. It is a hard work toconfigure and manage these leaf networks.To reduce the workload of configuration and management without affecting themulticast connection of leaf networks, you can configure an IGMP Proxy in a Layer 3switch in the leaf network (Switch B in the figure). The Layer 3 switch will then forwardIGMP join or IGMP leave messages sent by the connected hosts. After theconfiguration of IGMP Proxy, the leaf switch is no longer a PIM neighbor but a host forthe external network. Only when the Layer 3 switch has directly connected members,can it receive the multicast data of corresponding groups.IGMP join/leavemessageVLAN -int 222.22.22 .1VLAN -int133.33.33.1VLAN -int 133.33.33.2Switch ASwitch BGeneral/group-specificqueryExteriornetworkStubnetworkHostIGMP join/leave messageGeneral / group-specific query/Figure 6-2 Diagram for IGMP ProxyFigure 6-2 is an IGMP Proxy diagram for a leaf network.Configure Switch B as follows:z Enable multicast routing on VLAN interface 1 and VLAN interface 2, and thenconfigure the PIM protocol on it. And configure the IGMP protocol onVLAN-interface 1 at the same time.
