The Multicast Subsecond Convergence feature set enhances both enterprise and service provider network backbones by providing
almost instantaneous recovery of multicast paths after unicast routing recovery.
Because PIM relies on the unicast routing table to calculate its RPF when a change in the network topology occurs, unicast
protocols first need to calculate options for the best paths for traffic, and then multicast can determine the best path.
Multicast subsecond convergence allows multicast protocol calculations to finish almost immediately after the unicast calculations
are completed. As a result, multicast traffic forwarding is restored substantially faster after a topology change.