Which two commands are required to enable multicast on a router, knowing that the receivers only
support IGMPv2? (Choose two.)

A.
ip pim rp-address

B.
ip pim ssm

C.
ip pim sparse-mode

D.
ip pim passive

Explanation:
Sparse mode logic (pull mode) is the opposite of Dense mode logic (push mode), in Dense mode
it is supposed that in every network there is someone who is requesting the multicast traffic so
PIM-DM routers begin by flooding the multicast traffic out of all their interfaces except those from

where a prune message is received to eliminate the “leaf” from the multicasting tree (SPT), the
Source-Based Tree (S, G); as opposed to Sparse mode that send the traffic only if someone
explicitly requested it.
Not like Dense mode, which build a separated source-based tree (S, G) between the source and
the requester of the traffic, Sparse mode mechanism is based on a fixed point in the network
named Rendez-Vous point.
All sources will have to register with the RP to which they send their traffic and thereby build a
source-based tree (S, G) between them and the RP (not with the final multicast receiver like in
PIM-DM) and all PIM-SM routers, “whatever” multicast traffic they are requesting, have to register
with the RP and build a shared-tree (*. G)

http://tools.ietf.org/html/rfc2236
http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00800b0871.
shtml
http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094821.shtml#sparse
mode