Dual-end blocking is a user configurable feature to directly conserve bandwidth of the RPL and indirectly conserve processing power of the RPL owner. When you configure a node in a major ring adjacent to the RPL owner to be an RPL node with dual-end blocking enabled, data traffic and R-APS messages will not be forwarded to the blocked port of the RPL owner.
When a failure occurs in the ring and the RPL node (not the RPL owner) receives a R-APS (of type SF, FS, or MS), the RPL node unblocks the configured dual-end blocked port. When the RPL node receives a R-APS (NR, RB), it reblocks the originally configured dual-end blocked port. To configure dual-end blocking you need to configure the RPL and dual-end blocking on both the RPL owner and the adjacent peer (RPL node).