Which two statements about PIM-DM are true? (Choose two.)
A.
It forwards data packets on the shared distribution tree.
B.
It delivers multicast traffic only when the data is explicitly requested.
C.
It uses a unicast routing table to perform the RPF check.
D.
It is most efficient when the network uses active receivers on every subnet.
E.
It requires a rendezvous point.
Explanation:
PIM DM
Dense mode: we forward multicast traffic on all interfaces until a downstream router requests us to stop fowarding.
PIM dense mode is a push method where we use source based trees.
https://networklessons.com/multicast/multicast-pim-dense-mode/
PIM dense mode doesn’t use RPs so there is no reason at all for our routers to listen to
the 224.0.1.40 group address. For whatever reason, as soon as you enable PIM then autoRP is also enabled and the router will listen to this group address. You can ignore this
entry completely when you are working with PIM dense mode.
http://www.cisco.com/c/en/us/td/docs/ios/solutions_docs/ip_multicast/White_papers/rps.html#wp1030914
A rendezvous point (RP) is required only in networks running Protocol Independent Multicast sparse mode (PIM-SM).
http://www.cisco.com/c/en/us/td/docs/ios/solutions_docs/ip_multicast/White_papers/mcst_ovr.html#wp1009036
RPF Check
When a multicast packet arrives at a router, the router performs an RPF check on the
packet. If the RPF check succeeds, the packet is forwarded. Otherwise, it is dropped.
For traffic flowing down a source tree, the RPF check procedure works as follows:
1. The router looks up the source address in the unicast routing table to determine if the
packet has arrived on the interface that is on the reverse path back to the source.
2. If the packet has arrived on the interface leading back to the source, the RPF check
succeeds and the packet is forwarded.
3. If the RPF check in Step 2 fails, the packet is dropped.