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2013 Latest Cisco 350-001 Exam Section 4: PIM-SM Mechanics (3 Questions)

QUESTION NO: 1
Which of the following is used to calculate the upstream neighbor interface for a multicast route entry in a PIMv2 Sparse Mode network?
A. The address of the Mapping Agent.
B. The address of a directly connected member of the multicast group.
C. The address of the currently active Rendezvous Point for the multicast group.
D. The address of the PIM neighbor that sent the PIM Join message.
E. The address of the PIM neighbor that sent the PIM Hello message.
Answer: C
Explanation:
The address of the upstream neighbor in any PIMv2 Sparse Mode network is always calculated via the neighbor closest to the Rendezvous Point (RP).
Incorrect Answers:
A. The upstream neighbor for a multicast group is calculated from the RP, not the
mapping agent.

B. The directly connected multicast neighbor would only be used if it were the nearest
upstream neighbor toward the RP, which will not always be the case.
D, E. The neighbor that sends the PIM messages is not necessarily going to be the same
neighbor that is upstream toward the RP, so these choices are also incorrect.

Reference:
CCIE Professional Development Routing TCP/IP Volume II by Jeff Doyle and Jennifer De Haven Carroll, Page 492.

QUESTION NO: 2
What single choice listed below best describes PIM functionality?

A.
PIM uses the multicast routing information to perform the multicast forwarding function. PIM is a multicast routing protocol, and uses the multicast routing table to perform the RFP check. Like other routing protocols, PIM sends and receives routing updates between routers.
B. PIM uses unicast routing protocol information that populates the unicast routing table, including EIGRP, OSPF, BGP, and static routes.
C. PIM uses the multicast and unicast routing information to perform the multicast forwarding function. PIM uses the multicast routing table to perform the RPF check. Like other routing protocols, PIM does not send and receive routing updates between routers.
D. PIM uses multicast routing protocols to populate the multicast routing table, including
E. PIM uses the unicast routing information to perform the multicast forwarding function. Although PIM is called a multicast routing protocol, it actually uses the unicast routing table to perform the RPF check function instead of building up a completely independent multicast routing table. Unlike other routing protocols, PIM does not send and receive routing updates between routers.
Answer: E
Explanation:
Protocol-independent multicast (PIM) gets its name from the fact that it is IP routing protocol-independent. PIM can leverage whichever unicast routing protocols are used to populate the unicast routing table, including EIGRP, OSPF, BGP, or static routes. PIM uses this unicast routing information to perform the multicast forwarding function, so it is IP protocol-independent. Although PIM is called a multicast routing protocol, it actually uses the unicast routing table to perform the reverse path forwarding (RPF) check function instead of building up a completely independent multicast routing table. PIM does not send and receive multicast routing updates between routers like other routing protocols do.

QUESTION NO: 3
The TestKing IP multicast network is shown below:

Which routers will multicast stream (239.1.2.3)?
Note: Switch TestKingA is a catalyst running IGMP snooping. (Choose two)

A. TestKing1
B. TestKing2
C. TestKing3
D. IGMP snooping does not know receiver in vlan 33, so switch D will drop the multicast stream.
E. Router TestKing2 only after PC joins group 239.1.2.3
Answer: A, C
Explanation:
Based on the configuration examples shown in the diagram the Ethernet interfaces on
router TestKing1 and TestKing3 are configured for sparse-dense mode. A description of
this mode is below:
Sparse-Dense Mode:
An alternative to choosing just dense mode or just sparse mode is to run PIM in a single
region in sparse mode for some groups and dense mode for other groups.

In sparse-dense mode, if the group is in dense mode, the interface will be treated as dense
mode. If the group is in sparse mode, the interface will be treated in sparse mode. The
group is “sparse” if the router knows about an RP for that group.
When an interface is treated in dense mode, it is populated in the outgoing interface list of
the multicast routing table when either of the following conditions is true:

Members or DVMRP neighbors are on the interface.

Any of the PIM neighbors on the interface have not pruned for the group.
When an interface is treated in sparse mode, it is populated in the outgoing interface list
of the multicast routing table when either of the following conditions is true:

Members or DVMRP neighbors are on the interface.

A PIM neighbor on the interface has received an explicit join message.
Since there is no information regarding the use of a RP we can safely assume that the
interfaces would operate in Dense mode, therefore both TestKing1 and TestKing3 would
stream these multicast messages.

Reference:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_command_reference_chapter09186a00800c
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