350-401 Practice Question: Given this configuration: interface…

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  The router uses 172.16.1.1 as the RP for all multicast groups, and PIM sparse-mode is enabled on both interfaces.

  Why this is correct

  This configuration is correct because the command 'ip pim rp-address 172.16.1.1' statically designates 172.16.1.1 as the rendezvous point for all multicast groups, and the accompanying 'ip pim sparse-mode' statements on both interfaces ensure PIM operates in sparse mode, which is required for RP-based multicast forwarding. Static RP assignment takes precedence over dynamic mechanisms like Auto-RP or BSR, and it applies globally to all groups unless a group-list qualifier is specified. With sparse-mode enabled, receivers explicitly join via the RP, and senders register with the RP, establishing the shared tree before potentially switching to the shortest path tree.

• ✗

  The router will automatically elect an RP using BSR because no RP is configured.

  Why it's wrong here

  This is incorrect because an RP is explicitly configured with 'ip pim rp-address 172.16.1.1'; therefore, the router does not rely on or automatically elect an RP via BSR. BSR (Bootstrap Router) is a dynamic RP election mechanism that only operates when explicitly enabled with 'ip pim bsr-candidate' and 'ip pim rp-candidate' commands, and it does not override a static RP assignment. Since the static RP is present, BSR would be ignored for groups covered by the static configuration, so the claim that 'no RP is configured' is factually false.

• ✗

  PIM dense-mode is used because sparse-mode is not fully configured.

  Why it's wrong here

  This is incorrect because PIM sparse-mode is explicitly configured on both interfaces through the 'ip pim sparse-mode' command, which fully enables sparse-mode operation on those interfaces. PIM dense-mode is a separate mode that would require the 'ip pim dense-mode' command instead, and it is never automatically invoked merely because sparse-mode is 'not fully configured.' The configuration is complete for sparse mode: the RP is statically defined, interfaces are enabled, and no additional sparse-mode parameters are mandatory for basic operation, so the inference of dense mode is unfounded.

• ✗

  The configuration is invalid because the RP address must be a loopback interface.

  Why it's wrong here

  This is incorrect because the RP address specified in 'ip pim rp-address' can be any routable interface address on the router that acts as the RP; there is no requirement that it be a loopback interface. While loopback interfaces are strongly recommended for stability and reachability—because they are not subject to link failures—the configuration remains valid even if the RP address is a physical interface IP. Cisco IOS accepts any IP address in the 'rp-address' command, and the RP must simply be reachable by all PIM routers; loopback is a best practice, not a mandatory condition for validity.

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