350-501 Services Practice Question
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?
⚠ Common exam trap
Many 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.
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
✓
The source-specific multicast (SSM) range is applied but the receiver sent a (*,G) report
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.
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.
- ✗
The multicast routing is not enabled globally
Why it's wrong here
Incorrect. If multicast routing were disabled, the MDT would not be established.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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