350-501 Networking Practice Question
A service provider is experiencing intermittent multicast issues in their core network. They use PIM-SM with a static RP at 10.1.1.1. The multicast traffic originates from a source connected to PE1 and is received by customers connected to PE2. Recently, after a firewall upgrade between the PE routers and the core, some multicast streams stopped working, while others continue. The network team notices that 'show ip mroute' on PE2 shows the (*, G) entry but not the (S, G) entry for the affected groups. The RP is reachable via OSPF. The firewall logs show no dropped packets for known multicast addresses. Which action should the engineer take to restore full multicast forwarding?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure a static RP at the customer site (PE2) to bypass the firewall for registration traffic
The firewall upgrade likely blocked PIM register messages from PE1 to the RP, preventing the RP from learning about the source. By configuring a static RP on the customer-facing interface or using a different RP that can receive registration, the (S,G) state can be built. Option A is wrong because PIM-SM is correct for sparse-mode groups. Option C is wrong because adjusting timers would not fix the absence of (S,G). Option D is wrong because Auto-RP would add complexity and might be blocked by the firewall as well.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the PIM register suppression interval on the source's first-hop router
Why it's wrong here
This would only delay re-registration, not solve the root cause of the register not reaching the RP.
- ✓
Configure a static RP at the customer site (PE2) to bypass the firewall for registration traffic
Why this is correct
A static RP on PE2 ensures that the source's registration reaches the RP even if the firewall blocks unicast PIM register messages. This allows the (S,G) to be formed.
- ✗
Change the multicast mode from PIM-SM to PIM-DM on all interfaces
Why it's wrong here
PIM-DM uses flood-and-prune and would not solve the RP registration issue; it would also be inefficient for a sparse group.
- ✗
Enable Auto-RP on the network to dynamically learn the RP
Why it's wrong here
Auto-RP uses multicast advertisements that may also be blocked by the firewall, and it does not address the immediate issue of lost registrations.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.