The answer is the SSM range being applied while the receiver sends a (*,G) report. This is correct because IGMPv3 snooping on the PE router processes the receiver’s IGMPv3 report to install forwarding entries for multicast traffic. When the SSM range (232.0.0.0/8) is configured, the router expects an (S,G) report specifying the source; however, if the receiver sends a (*,G) report—which is only valid in ASM mode—the snooping function will not install the necessary forwarding entry, causing multicast traffic to be dropped even though the MDT is established. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of how IGMPv3 snooping interacts with MVPN and the critical distinction between SSM and ASM group ranges. A common trap is assuming any IGMPv3 report will work, but the (*,G) report is rejected outside the SSM range. Memory tip: “SSM demands an S,G—a star alone leaves the path unknown.”
350-501 Services Practice Question
This 350-501 practice question tests your understanding of services. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A service provider is deploying IGMPv3 snooping on an MVPN network to optimize multicast forwarding. After configuration, multicast traffic is not reaching receivers. The source is sending to group 239.1.1.1. The PE router has received the IGMP report from the receiver, and the MDT is established. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Why wrong: Incorrect. In MVPN, the MDT is established via PIM SSM or similar; an RP may not be needed for SSM.
B
The IGMP snooping is filtering the multicast traffic because of wrong VLAN configuration
Why wrong: Incorrect. IGMP snooping filtering would prevent reports from reaching the PE, but MDT is established.
C
The source-specific multicast (SSM) range is applied but the receiver sent a (*,G) report
Correct. IGMPv3 allows source-specific reports. If the group falls in SSM range, the receiver must specify the source; otherwise, traffic is not forwarded.
D
The multicast routing is not enabled globally
Why wrong: Incorrect. If multicast routing were disabled, the MDT would not be established.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The source-specific multicast (SSM) range is applied but the receiver sent a (*,G) report
Option C is correct because IGMPv3 snooping on the PE router processes the receiver's IGMPv3 report. If the SSM range (232.0.0.0/8) is applied to group 239.1.1.1, the receiver must send an IGMPv3 (S,G) report to join a specific source. However, if the receiver sends a (*,G) report (which is allowed only in ASM mode), the IGMP snooping will not install the forwarding entry, causing multicast traffic to be dropped even though the MDT is established.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 RP for the group is not configured
Why it's wrong here
Incorrect. In MVPN, the MDT is established via PIM SSM or similar; an RP may not be needed for SSM.
✗
The IGMP snooping is filtering the multicast traffic because of wrong VLAN configuration
Why it's wrong here
Incorrect. IGMP snooping filtering would prevent reports from reaching the PE, but MDT is established.
✓
The source-specific multicast (SSM) range is applied but the receiver sent a (*,G) report
Why this is correct
Correct. IGMPv3 allows source-specific reports. If the group falls in SSM range, the receiver must specify the source; otherwise, traffic is not forwarded.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The multicast routing is not enabled globally
Why it's wrong here
Incorrect. If multicast routing were disabled, the MDT would not be established.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume IGMPv3 snooping always works with any group, forgetting that the SSM range enforces (S,G) reports and that a (*,G) report in that range is silently dropped, not processed.
Trap categories for this question
Similar concept trap
Incorrect. In MVPN, the MDT is established via PIM SSM or similar; an RP may not be needed for SSM.
Detailed technical explanation
How to think about this question
In IGMPv3, the SSM range (232.0.0.0/8 per RFC 4607) requires receivers to send (S,G) membership reports; a (*,G) report in this range is ignored by the IGMP snooping switch. The PE router's IGMP snooping builds forwarding entries based on the group-record type in the report; a (*,G) report for an SSM group results in no (S,G) state, so multicast traffic from the source is not forwarded. In real-world deployments, misconfigured SSM ACLs or legacy receivers sending IGMPv2 reports can cause similar silent failures.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Services — This question tests Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The source-specific multicast (SSM) range is applied but the receiver sent a (*,G) report — Option C is correct because IGMPv3 snooping on the PE router processes the receiver's IGMPv3 report. If the SSM range (232.0.0.0/8) is applied to group 239.1.1.1, the receiver must send an IGMPv3 (S,G) report to join a specific source. However, if the receiver sends a (*,G) report (which is allowed only in ASM mode), the IGMP snooping will not install the forwarding entry, causing multicast traffic to be dropped even though the MDT is established.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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