Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 399

Chapter 26 Configuring MLDv2 Snooping for IPv6 Multicast Traffic Understanding How MLDv2 Snooping Works When the switch snoops the MLDv2 report multicast by Host 1, the switch uses the information in the MLDv2 report to create a forwarding-table entry, as shown in Table 26-1, that includes the port numbers of Host 1, the multicast router, and the switch. Table 26-1 MLDv2 Snooping Forwarding Table Destination MAC Address 0100.5exx.xxxx 0100.5e01.0203 Type of Packet MLDv2 !MLDv2 Ports 0 1, 2 The switch hardware can distinguish MLDv2 information packets from other packets for the multicast group. The first entry in the table indicates that only MLDv2 packets should be sent to the CPU, which prevents the switch from becoming overloaded with multicast frames. The second entry indicates that frames addressed to the 0x0100.5E01.0203 multicast MAC address that are not MLDv2 packets (!MLDv2) should be sent to the multicast router and to the host that has joined the group. If another host (for example, Host 4) sends an unsolicited MLDv2 report for the same group (Figure 26-2), the switch snoops that message and adds the port number of Host 4 to the forwarding table as shown in Table 26-2. Because the forwarding table directs MLDv2 messages only to the switch, the message is not flooded to other ports. Any known multicast traffic is forwarded to the group and not to the switch. Figure 26-2 Second Host Joining a Multicast Group Router A 1 CPU PFC 0 VLAN 45751 Forwarding table 2 3 4 5 Host 1 Host 2 Host 3 Host 4 Table 26-2 Updated MLDv2 Snooping Forwarding Table Destination MAC Address 0100.5exx.xxxx 0100.5e01.0203 Type of Packet MLDv2 !MLDv2 Ports 0 1, 2, 5 OL-11439-03 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY 26-5