For the same multicast source, the device can determine the only multicast traffic incoming interface on the device through RPF inspection.

Question

Options

• ATRUE
• BFALSE

• A
  80% (33)
• B
  20% (8)

Explanation

RPF (Reverse Path Forwarding) inspection works by looking up the multicast source address in the unicast routing table to identify which interface the router would use to reach that source. Since a router has exactly one best-path route to any given source address, there is exactly one RPF interface - making the statement TRUE. When a multicast packet arrives, the router checks whether it came in on that RPF interface; if not, the packet is dropped to prevent routing loops.

Why B (FALSE) is wrong: There is no ambiguity here - the RPF check is deterministic. The unicast routing table resolves to a single best-path interface per source, so the incoming interface is always singular and unambiguous for a given source.

Memory tip: Think of RPF as a "return address check." Just as a letter can only come from one direction if you know exactly where the sender lives, multicast traffic from a specific source can only legitimately arrive on one interface - the one your router would use to send traffic back to that source.

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