350-501 Question #339: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. A network engineer is implementing multicast Source-A to send a multicast stream for Receiver-A, and multicast Source-B to send a multicast stream for Receiver-B. Router RC forwards the IGMP host a report and leaves messages to IP address 192.168.10.1. How must the multicast features be implemented to prevent RB from receiving multicast flooding from Source-A?

Options

• AChange the helper-address value to 192.168.10.2 on RC.
• BEnable ip pim neighbor-filter on RC interface Ge0/0.
• CConfigure PIM-SSM on RB and RC interface Ge 0/0.
• DEnable ip pim passive on RB interface Ge0/0.

Explanation

To prevent unwanted multicast flooding from Source-A to Router RB, configure ip pim passive on RB's interface Ge0/0, which disables PIM adjacency formation and routing participation on that interface.

Common mistakes.

• A. helper-address is used for forwarding broadcast-based services like DHCP, not for controlling multicast PIM behavior or preventing multicast flooding.
• B. ip pim neighbor-filter is used to control which PIM neighbors are formed, which is a security feature, but ip pim passive is a more direct way to prevent all PIM operations on an interface to stop unwanted flooding.
• C. While PIM-SSM can help by requiring explicit (S,G) joins, ip pim passive directly addresses the 'flooding' issue by stopping PIM protocol activity on an interface that should not be routing multicast.

Concept tested. PIM passive interface configuration

Reference. https://www.cisco.com/c/en/us/td/docs/ios/ipmulti/command/reference/imc_book/imc_i1.html#wp1077755

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