Cisco IE-3000-8TC Software Configuration Guide - Page 449

Chapter 22 Configuring Flex Links and the MAC Address-Table Move Update Feature Understanding Flex Links and the MAC Address-Table Move Update Figure 22-2 VLAN Flex Links Load Balancing Configuration Example Uplink switch B Uplink switch C Forwarding (1-50) gi2/0/6 Forwarding (51-100) gi2/0/8 Switch A 201398 Flex Link Multicast Fast Convergence Flex Link Multicast Fast Convergence reduces the multicast traffic convergence time after a Flex Link failure. This is implemented by a combination of these solutions: • Learning the Other Flex Link Port as the mrouter Port, page 22-3 • Generating IGMP Reports, page 22-3 • Leaking IGMP Reports, page 22-4 • Configuration Examples, page 22-4 Learning the Other Flex Link Port as the mrouter Port In a typical multicast network, there is a querier for each VLAN. A switch deployed at the edge of a network has one of its Flex Link ports receiving queries. Flex Link ports are also always forwarding at any given time. A port that receives queries is added as an mrouter port on the switch. An mrouter port is part of all the multicast groups learned by the switch. After a changeover, queries are received by the other Flex Link port. The other Flex Link port is then learned as the mrouter port. After changeover, multicast traffic then flows through the other Flex Link port. To achieve faster convergence of traffic, both Flex Link ports are learned as mrouter ports whenever either Flex Link port is learned as the mrouter port. Both Flex Link ports are always part of multicast groups. Though both Flex Link ports are part of the groups in normal operation mode, all traffic on the backup port is blocked. So the normal multicast data flow is not affected by the addition of the backup port as an mrouter port. When the changeover happens, the backup port is unblocked, allowing the traffic to flow. In this case, the upstream multicast data flows as soon as the backup port is unblocked. Generating IGMP Reports When the backup link comes up after the changeover, the upstream new distribution switch does not start forwarding multicast data, because the port on the upstream router, which is connected to the blocked Flex Link port, is not part of any multicast group. The reports for the multicast groups were not forwarded by the downstream switch because the backup link is blocked. The data does not flow on this port, until it learns the multicast groups, which occurs only after it receives reports. The reports are sent by hosts when a general query is received, and a general query is sent within 60 seconds in normal scenarios. When the backup link starts forwarding, to achieve faster convergence of multicast data, the downstream switch immediately sends proxy reports for all the learned groups on this port without waiting for a general query. OL-13018-03 Cisco IE 3000 Switch Software Configuration Guide 22-3