Dell M6220 User Configuration Manual page 180

JOIN messages upstream. The control plane updates the driver with
checkpointed unicast routes. The forwarding plane reconciles L3 hardware
tables.
The OSPF graceful restart finishes, and the control plane deletes any stale
unicast routes not relearned at this point. The forwarding plane reconciles L3
multicast hardware tables. Throughout the process, the hosts continue to
receive their multicast streams, possibly with a short interruption as the top
aggregation router learns that one of its LAG members is down. The hosts see
no more than a 50 ms interruption in unicast connectivity.
180
Managing a Switch Stack