Exam 300-510 topic 1 question 50 discussion

i think correct answer A

Agreed. 'A' is correct answer. A shared tree is built first between receiver and the RP. The receiver is then able to switch to a Source tree as needed.

A is the most correct because the others are totally wrong. The LHR knows about the RP through configuration or other methods. It looks up the RP in the unicast routing table, and sends the PIM join message direction RP. Most PIM messages are link local; they are addressed to the link local multicast group 224.0.0.13 (all PIM routers). Therefore, the PIM join travels router by router toward the RP. Passing each router, the router creates a state for this multicast request: It creates a state for (*.G), since it has not learned anything about sources yet. For (*,G) the router maintains an outgoing interface list (OIL), and the interface on which the PIM join was received is entered in the OIL.

A is correct

D is SSM. Also the source does not "respond by sending all data". Usually, the source is already sending, it's the routers that act by forwarding the traffic to the new receiver

The best answer would be A. This question cannot be answered in a correct way. A receiver never sends traffic to the RP. This is done by the router to which the receiver is connected. The receiver has no knowledge what so ever of an RP

D is not correct as it desicribes PIM-SSM scenario. They ask for PIM-SM so first receiver joins shared tree towards RP using group address (it has no idea what the source is at this point) and only after receiving traffic from source via shared tree it is able to identify source IP and send join to create Source Tree.