350-501 Architecture Practice Question
In a multicast environment, a PE router is not receiving multicast traffic from a source behind a CE. The PIM neighbors are established. The RP is reachable. What is the most likely issue?
⚠ Common exam trap
Cisco often tests the subtle distinction between having PIM neighbors established (which only requires PIM configuration on the interface) versus having multicast routing enabled globally for the VRF, leading candidates to overlook the mandatory 'ip multicast-routing vrf' command.
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 PE does not have the multicast VRF enabled
The most likely issue is that the PE router does not have the multicast VRF enabled. In a multicast VPN (MVPN) environment, even if PIM neighbors are established and the RP is reachable, the PE must have multicast routing explicitly enabled within the VRF using the 'ip multicast-routing vrf <name>' command. Without this, the PE will not process multicast traffic for that VRF, causing it to drop or ignore multicast packets from the source behind the CE.
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 CE is not sending IGMP joins
Why it's wrong here
IGMP joins are sent by hosts, not the CE router.
- ✗
The source address is not in the VRF
Why it's wrong here
The source address is behind the CE, so it is in the VRF. This is not a typical issue.
- ✓
The PE does not have the multicast VRF enabled
Why this is correct
Without multicast VRF, the PE cannot forward multicast traffic in the VRF.
- ✗
The RP is not configured in the VRF
Why it's wrong here
The stem states the RP is reachable, so it is likely configured.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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