MBB
A transit or leaf node performs multipoint make-before-break (MBB) when it detects that the upstream node toward the root of the multicast tree has changed.
MBB follows a graceful procedure allowing a MBB transition to the new upstream node.
Support for MBB is optional. If the new upstream node does not support MBB, the downstream node waits for the configured timer before switching over to the new upstream node.