Cisco 7609-S Software Configuration Guide - Page 449

Chapter 29 Configuring MLDv2 Snooping for IPv6 Multicast Traffic Understanding How MLDv2 Snooping Works Figure 29-1 Initial MLDv2 Listener Report Router A CPU PFC 0 1 MLDv2 report VLAN 130143 Forwarding table 2 3 4 5 Host 1 Host 2 Host 3 Host 4 Multicast router A sends an MLDv2 general query to the router, which forwards the query to ports 2 through 5 (all members of the same VLAN). Host 1 wants to join an IPv6 multicast group and multicasts an MLDv2 report to the group with the equivalent MAC destination address of 0x0100.5E01.0203. When the router snoops the MLDv2 report multicast by Host 1, the router uses the information in the MLDv2 report to create a forwarding-table entry, as shown in Table 29-1, that includes the port numbers of Host 1, the multicast router, and the router. Table 29-1 MLDv2 Snooping Forwarding Table Destination MAC Address 0100.5exx.xxxx 0100.5e01.0203 Type of Packet MLDv2 !MLDv2 Ports 0 1, 2 The router hardware can distinguish MLDv2 information packets from other packets for the multicast group. The first entry in the table tells the router to send only MLDv2 packets to the CPU. This prevents the router from becoming overloaded with multicast frames. The second entry tells the router to send frames addressed to the 0x0100.5E01.0203 multicast MAC address that are not MLDv2 packets (!MLDv2) 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 29-2), the router snoops that message and adds the port number of Host 4 to the forwarding table as shown in Table 29-2. Because the forwarding table directs MLDv2 messages only to the router, the message is not flooded to other ports. Any known multicast traffic is forwarded to the group and not to the router. OL-4266-08 Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX 29-5