2-2z Reducing Layer 2 broadcast packets, thus saving network bandwidth.z Enhancing the security of multicast traffic.z Facilitating the implementation of per-host accounting.Basic Concepts in IGMP SnoopingIGMP Snooping related portsAs shown in Figure 2-2, Router A connects to the multicast source, IGMP snooping runs on Switch Aand Switch B, and Host A and Host C are receiver hosts (namely, multicast group members).Figure 2-2 IGMP snooping related portsRouter A Switch ASwitch BGE1/0/1 GE1/0/2GE1/0/3GE1/0/1GE1/0/2ReceiverReceiverHost AHost BHost CHost DSourceMulticast packetsRouter portMember portPorts involved in IGMP snooping, as shown in Figure 2-2, are described as follows:z Router port: A router port is a port on an Ethernet switch that leads the switch towards a Layer 3multicast device (DR or IGMP querier). In the figure, GigabitEthernet 1/0/1 of Switch A andGigabitEthernet 1/0/1 of Switch B are router ports. The switch registers all its local router ports in itsrouter port list.z Member port: A member port is a port on an Ethernet switch that leads the switch towards multicastgroup members. In the figure, GigabitEthernet 1/0/2 and GigabitEthernet 1/0/3 of Switch A andGigabitEthernet 1/0/2 of Switch B are member ports. The switch registers all the member ports onthe local device in its IGMP snooping forwarding table.z Whenever mentioned in this document, a router port is a port on the switch that leads the switch toa Layer 3 multicast device, rather than a port on a router.z Unless otherwise specified, router/member ports mentioned in this document include static anddynamic ports.z An IGMP-snooping-enabled switch deems that all its ports on which IGMP general queries with thesource IP address other than 0.0.0.0 or PIM hello messages are received are dynamic router ports.
