350-601 Network Practice Question
A network engineer is configuring Cisco Nexus VXLAN with BGP EVPN. The VTEPs are using loopback0 as the NVE source. The physical interfaces are up, but the NVE interface remains down. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the dependency of the NVE interface on underlay IP reachability, tricking candidates into focusing on NVE-specific configuration errors (like missing source-interface) rather than verifying the underlay routing for the loopback address.
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 loopback0 interface is not reachable via the underlay network.
The NVE interface requires the specified source interface (loopback0) to have IP reachability via the underlay network to establish VXLAN tunnels. If loopback0 is not reachable (e.g., due to missing OSPF/IS-IS routes or incorrect underlay configuration), the NVE interface will remain in a down state even if the physical interfaces are up. This is because the NVE interface depends on the underlay routing to encapsulate and forward VXLAN traffic.
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 loopback0 interface is not reachable via the underlay network.
Why this is correct
The NVE source must be routable in the underlay. If loopback0 is not advertised by IGP, the NVE interface stays down.
- ✗
The NVE interface is not configured with source-interface.
Why it's wrong here
If source-interface were not configured, the NVE interface would not come up. But the scenario states the configuration is in place.
- ✗
The VLAN 1 is not associated with the NVE interface.
Why it's wrong here
VLAN association is for VNI mapping, not for NVE interface state. The NVE interface state depends on source-interface reachability.
- ✗
The loopback0 interface is not created.
Why it's wrong here
If loopback0 were not created, the switch would not accept 'source-interface loopback0' in the NVE configuration; it would be a config error, not just NVE down.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-601 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 350-601 exam.