quiz6key - Quiz 6 Key CNT 5106C 5 April 2011 1 Compare...

Quiz 6 Key
CNT 5106C
5 April 2011
1. Compare sparse and dense mode in PIM. Why is it desirable to have both modes?
2. What does ARP do? Why is it needed? How does ARP work?
KEY
1. PIM is used for multicast routing to a set of multicast group members. Dense mode
assumes that the multicast group members are near each other and are plentiful (locally
anyway), whereas sparse mode assumes that the group members are few and far
between, and bandwidth may be scarce.
In dense mode, PIM assumes that neighboring routers will have group members and will
therefore want to receive multicast messages. If a router does not have any downstream group
members, it sends a prune message to its parent in the multicast tree, causing messages to
stop coming. The multicast tree is built using reverse path forwarding.
In sparse mode, PIM does not assume any node wants to receive multicast messages unless
they explicitly join. Join messages are sent toward a rendevous point for a multicast group, to
make a center-based tree.