Enabling Fast Convergence

In addition to periodically sending general queries, an active (querier) device sends out general queries when it detects a new port. However, since it does not recognize the other device port-up event, the multicast traffic might still use the query-interval time to resume after a topology change. Configuring fast-convergence allows the device to listen to topology change events in Layer 2 protocols, such as spanning tree, and send general queries to shorten the convergence time.

If the Layer 2 protocol is unable to detect a topology change, the fast-convergence feature may not work. For example, if the direct connection between two devices switches from one interface to another, the rapid spanning tree protocol (802.1w) considers this an optimization action, rather than a topology change. In this case, other devices will not receive topology change notifications and will be unable to send queries to speed up the convergence. The original spanning tree protocol does not recognize optimization actions, and fast-convergence works in all cases.

The following configuration example enables fast-convergence.

device(config)# vlan 70
device(config-vlan-70)# multicast6 fast-convergence