PIM Sparse Mode with BSR for Automatic RP Discovery

350-601 By islever Editorial Last updated

Apply routing protocols

Short answer

D Ip pim sparse-mode with BSR provides on-demand shared-tree delivery and automatic RP-set discovery, with each router electing the RP.

Question

A customer deploys a media server to distribute streaming videos to network clients. The requirement is to allow the video feed to reach only requesting clients. The shared trees must not propagate the video feed if no clients from that tree request it. To reduce configuration touchpoints, the solution must support the automatic discovery and announcement of RP-set information. Each router in the network is responsible for selecting the RP. Which configuration set meets these requirements?
  1. router(config-if)# ip pim bidir-enable
  2. router(config-if)# ip pim dense-mode
  3. router(config-if)# ip pim sparse-sense mode
  4. router(config-if)# ip pim sparse mode Correct Answer

Key Takeaways

PIM sparse mode builds shared trees only where receivers exist, and the Bootstrap Router (BSR) discovers and announces the RP-set per prefix so every router can select its RP.

For multicast that reaches only requesting clients with automatic RP-set discovery, enable PIM sparse mode and BSR; dense mode floods and incomplete commands break RP discovery.

Common mistake: Choosing dense-mode (floods to all) or the malformed 'ip pim sparse-sense mode' instead of the valid 'ip pim sparse-mode' with BSR/Auto-RP commands.

Expert Analysis

Why the Answer Is Correct

The requirements map exactly to PIM sparse mode: traffic reaches only requesting clients (shared trees, no dense-mode flooding), and the Bootstrap Router (BSR) mechanism automatically discovers and announces the RP-set for each group prefix so every router can select its RP. ip pim sparse-mode on the interface enables sparse-mode operation, and ip pim bsr participates in BSR elections.

Why the Other Options Are Wrong

B. ip pim dense-mode floods multicast to all interfaces and ignores RP discovery, violating "only requesting clients." A. ip pim bidir-enable enables bidirectional PIM but is not the standard sparse-mode command the question asks for. C. ip pim sparse-sense mode is malformed; the valid syntax is ip pim sparse-mode, and C is also missing the BSR/auto-RP commands needed for RP-set discovery.

Community Comment Notes

Votes D 75 / C 25. Arch_Angel (3 likes) explains BSR discovers and announces RP-set per prefix and interoperates with Auto-RP; SysAd and joncursio note C is incomplete (missing ip pim send-rp-discovery).

Official Reference

https://www.cisco.com/c/en/us/td/docs/dcn/nx-os/nexus9000/105x/configuration/multicast/cisco-nexus-9000-series-nx-os-multicast-routing-configuration-guide-105x/m-configuring-pim-and-pimm6.html

This link opens the official vendor documentation in a new tab.

Community Votes

D
75%
C
25%

75% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 6 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 6

  1. Arch_Angel 👍 3
    D is correct BSR Election and Functionality PIM uses the BSR to discover and announce RP-set information for each group prefix to all the routers in a PIM domain. This is the same function performed by Auto-RP, but the BSR is part of the PIM Version 2 specification. The BSR mechanism interoperates with Auto-RP on Cisco routers. https://www.cisco.com/en/US/docs/ios/12_4t/ip_mcast/configuration/guide/mctbasic.html .|.
  2. Rollizo 👍 2 Answered D
    it is D because of the RP discovery and sparse-mode. Dense-mode is less efective and more endpoints receive no solicited multicast traffic
  3. SysAd 👍 2
    answer is D, using boot strap router. C is incomplete command
  4. asd248402 👍 1 Answered C
    see https://www.cisco.com/en/US/docs/ios/12_4t/ip_mcast/configuration/guide/mctbasic.html#wp1058990
  5. joncursio 👍 1 Answered D
    C does not have all commands required so must be D
Show 1 more comment
  1. crooks_1988 👍 1
    Option C is missing: ip pim send-rp-discovery

Reader comments & corrections

No reader corrections yet — spotted an error or have a note? Share it below.

Log in to comment, report an error, or add a note about this question.

NX-OS Software Downgrade Impact Check

S-grade

Terraform ACI Provider Authentication and APIC DOS Threshold Counting

S-grade

MDS 9000 TE Port Channel for Multi-VSAN Trunking with Mismatch Suspension

S-grade

FCoE FC-Map Configuration to Prevent Cross-Fabric Talk

S-grade

← Back to 350-601 Study Guide