How is RPF used in multicast routing?

Question

Options

• Ato prevent multicast packets from looping
• Bto prevent PIM packets from looping
• Cto instruct PIM where to send a (*,G) or (S,G) join message
• Dto prevent multicast packets from looping and to instruct PIM where to send a (*,G) or (S,G) join message

• A
  3% (1)
• B
  8% (3)
• C
  3% (1)
• D
  86% (32)

Explanation

Reverse Path Forwarding (RPF) serves two distinct but related roles in multicast routing. First, it prevents multicast packet looping: when a multicast packet arrives on an interface, the router checks whether that interface is the one used to reach the packet's source via unicast. If not, the packet is discarded, preventing it from being forwarded in loops. Second, RPF determines PIM join direction: the RPF interface toward the source (for (S,G) joins) or toward the RP (for (*,G) joins) is the interface on which a router sends PIM Join messages to build the multicast distribution tree. Both functions are fundamental to how PIM-SM and PIM-DM operate.

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