Exam 350-401 topic 1 question 975 discussion

Here's the key difference between sparse and dense mode: Dense mode: we forward multicast traffic on all interfaces until a downstream router requests us to stop fowarding. Sparse mode: we don't forward multicast traffic on any interface until a downstream router requests us to forward it.

C. PIM sparse mode Explanation: In PIM sparse mode, when there are no connected members or downstream neighbors for a multicast group, the router sends a prune message to the source. This mechanism helps to prevent unnecessary traffic from being forwarded to areas of the network that do not have interested receivers, thus optimizing bandwidth usage.

PIM Sparse Mode -> pull mechanism PIM Dense Mode -> push mechanism

B is correct

PIM dense mode (push mechanism) send multicast traffic to all interfaces until receivers ask to stop forward and then prune unwanted traffic, while PIM sparse mode (pull mechanism) start forwarding multicast traffic if requested to do it. PIM sparse mode is required RP (rendezvous point) from where downstream routers pulling traffics.

In dense mode, a router assumes that all other routers want to forward multicast packets for a group. If a router receives a multicast packet and has no directly connected members or PIM neighbors present, a prune message is sent back to the source. Subsequent multicast packets are not flooded to this router on this pruned branch. PIM builds source-based multicast distribution trees.

PIM (Protocol Independent Multicast) dense mode operates by flooding multicast traffic to all parts of the network, and routers prune back branches of the distribution tree where there are no active receivers. When there are no connected members or downstream neighbors, routers send prune messages upstream toward the source, informing it to stop sending traffic down the pruned branches.