300-420 Question #132: Real Exam Question with Answer & Explanation

The correct answer is A: It allows for a loop-free distribution tree from the source to receivers.. The multicast Reverse Path Forwarding (RPF) check is a fundamental IP multicast mechanism that ensures a loop-free distribution tree from the source to receivers by verifying that incoming multicast packets arrive on the interface leading back to the source.

Advanced Addressing and Routing Solutions

Question

What is the function of the multicast Reverse Path Forwarding check?

Options

AIt allows for a loop-free distribution tree from the source to receivers.
BIt serves as an Auto RP Mapping agent.
CIt prevents bootstrap messages from reaching all routers.
DIt is used to discover and announce RP-set information.

Explanation

The multicast Reverse Path Forwarding (RPF) check is a fundamental IP multicast mechanism that ensures a loop-free distribution tree from the source to receivers by verifying that incoming multicast packets arrive on the interface leading back to the source.

Common mistakes.

B. Serving as an Auto RP Mapping agent is a role in PIM for Rendezvous Point (RP) discovery, distinct from the RPF check's primary function.
C. Preventing bootstrap messages from reaching all routers is not the function of the RPF check; bootstrap messages are part of PIM's RP discovery process.
D. Discovering and announcing RP-set information is performed by mechanisms like the Bootstrap Router (BSR) or Auto-RP, not by the RPF check itself.

Concept tested. Multicast RPF check function

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-3s/imc_pim_xe_3s_book/imc_pim_rpf.html

Topics

#Multicast RPF#Reverse Path Forwarding#Multicast Routing#Loop Prevention

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