In one embodiment, a method comprises: determining, by a network device that is configured for joining a local directed acyclic graph (DAG) instance in a data network, an unreachability by the network device to any member of the local DAG instance; generating and broadcasting, by the network device, a request message that identifies the network device requesting to join the local DAG instance, the request message causing a neighboring network device in a global DAG instance of the data network to rebroadcast the request message for reception by a member of the local DAG instance, the neighboring network device a non-member of the local DAG instance; and receiving, by the network device, a reply message indicating a member of the local DAG instance is reachable via the neighboring network device in the global DAG instance.