Publication date: Sep, 2009Revision A8653-9. MulticastThe function, is used to establish the multicast groups to forward themulticast packet to the member ports, and, in nature, avoids wasting the bandwidthwhile IP multicast packets are running over the network. This is because a switchthat does not support IGMP or IGMP Snooping can not tell the multicast packet fromthe broadcast packet, so it can only treat them all as the broadcast packet. WithoutIGMP Snooping, the multicast packet forwarding function is plain and nothing isdifferent from broadcast packet.A switch supported IGMP Snooping with the functions of query, report andleave, a type of packet exchanged between IP Multicast Router/Switch and IPMulticast Host, can update the information of the Multicast table when a member(port) joins or leaves an IP Multicast Destination Address. With this function, once aswitch receives an IP multicast packet, it will forward the packet to the memberswho joined in a specified IP multicast group before.The packets will be discarded by the IGMP Snooping if the user transmitsmulticast packets to the multicast group that had not been built up in advance.3-9-1. IGMP SettingFunction name:IGMP SettingFunction description:IGMP is used to snoop the status of IP multicast groups and display itsassociated information in both tagged VLAN and non-tagged VLAN networks.Enabling IGMP with either passive or active mode, you can monitor the IGMPsnooping information, which contains the multicast member list with themulticast groups, VID and member port.Fig. 3-21
