662 PowerConnect B-Series FCX Configuration Guide53-1002266-01Configuring IGMP snooping22Every group on a physical port keeps its own tracking record. However, it can only track groupmembership; it cannot track by (source, group). For example, Client A and Client B belong to group1but each receives traffic streams from different sources. Client A receives a stream from (source_1,group1) and Client B receives a stream from (source_2, group1). The device still waits for theconfigured leave-wait-time before it stops the traffic because these two clients are in the samegroup. If the clients are in different groups, then the waiting period is not applied and traffic isstopped immediately.To enable the tracking and fast leave feature for VLAN 20, enter the following commands.PowerConnect(config)# vlan 20PowerConnect(config-vlan-20)# multicast trackingSyntax: [no] multicast trackingThe membership tracking and fast leave features are supported for IGMPv3 only. If any port or anyclient is not configured for IGMPv3, then the multicast tracking command is ignored.Configuring fast leave for IGMPv2When a device receives an IGMPv2 leave message, it sends out multiple group-specific queries. Ifno other client replies within the waiting period, the device stops forwarding traffic. Whenfast-leave-v2 is configured, and when the device receives a leave message, it immediately stopsforwarding to that port. The device does not send group specific-queries. You must ensure that nosnooping-enabled ports have multiple clients. When two devices connect together, the queriermust not be configured for fast-leave-v2, because the port might have multiple clients through thenon-querier. The number of queries, and the waiting period (in seconds) can be configured usingthe ip multicast leave-wait-time command. The default is 2 seconds.To configure fast leave for IGMPv2, enter the following commands.PowerConnect(config)# vlan 20PowerConnect(config-vlan-20)# multicast fast-leave-v2Syntax: [no] multicast fast-leave-v2Enabling fast convergenceIn addition to sending periodic general queries, an active device sends general queries when itdetects a new port. However, because the device does not recognize the other device's port upevent, multicast traffic might still require up to the query-interval time to resume after a topologychange. Fast convergence allows the device to listen to topology change events in Layer 2 protocolssuch as spanning tree, and then send general queries to shorten the convergence time.If the Layer 2 protocol cannot detect a topology change, fast convergence may not work in somecases. For example, if the direct connection between two devices switches from one interface toanother, the rapid spanning tree protocol (802.1w) considers this optimization, rather than atopology change. In this example, other devices will not receive topology change notifications, andwill be unable to send queries to speed up the convergence. Fast convergence works well with theregular spanning tree protocol in this case.To enable fast-convergency, enter the following commands.PowerConnect(config)# vlan 70PowerConnect(config-vlan-70)# multicast fast-convergenceSyntax: multicast fast-convergence
