Hello Lucas
In PIM Sparse Mode (PIM-SM), the traffic flow is unidirectional - from the Rendezvous Point (RP) towards the receivers. The RP acts as a central point for multicast group registration and request processing. The multicast traffic is initially sent to the RP, which then forwards the traffic down the multicast distribution tree to the receivers. This is why it’s often said that “PIM Sparse mode can only go downstream”.
For the most part yes. Bidirectional PIM (Bidir-PIM) does not have a concept of a source-specific tree. It uses a shared tree that is rooted at the RP for both sending and receiving multicast traffic. Hence, it’s ‘bidirectional’. The RPF interface in Bidir-PIM is used for both sending and receiving multicast traffic to and from the RP.
So, to sum up: Yes, the Bidir-PIM is bidirectional because the RPF interface is used to both send and receive traffic to and from the RP. While in PIM-SM, this interface can only receive traffic from the RP to that given tree.
It states in the diagram that the 1.1.1.1 IP address on the E0/0 interface of the router on the left (core1) is the RP. You can also see it in the output shown on core1.
Auto-RP does provide a level of redundancy. If the RP fails, another RP is automatically chosen. Take a look at this lesson to learn more about Auto-RP:
Yes, as long as it is routable, and the address is not being used elsewhere.
Multicast can be difficult to get your head around. I believe that labbing these topologies will be the most beneficial, so that you can see first hand the behavior of the protocol.
I hope this has been helpful!
Laz