The answer is that the NVE interface is down because the source interface is missing from the configuration. In VXLAN, the NVE (Network Virtualization Edge) interface acts as the tunnel endpoint, and it requires a valid source interface—typically a loopback—to encapsulate and decapsulate VXLAN traffic. Without this source interface configured under the NVE, the interface cannot form overlay adjacencies or establish VXLAN tunnels, leaving it in a permanent down state. On the Cisco DCCOR and CCNP Data Center Core 350-601 exam, this scenario tests your understanding of VXLAN control-plane fundamentals and the mandatory "source-interface" command under the NVE configuration. A common trap is assuming the issue is a routing problem or a physical interface failure, but the root cause is almost always the missing source-interface line. To remember: No source, no tunnel—think of the NVE as a door that needs a hinge (the source interface) to open.
350-601 Network Practice Question
This 350-601 practice question tests your understanding of network. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Exhibit
switch# show interface nve 1
Interface: nve1, state: Down
Description: VXLAN Overlay
Encapsulation: VXLAN
Source Interface: not configured
VRF: default
Refer to the exhibit. What is the most likely cause of the NVE interface being down?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The source interface is not configured.
The NVE (Network Virtualization Edge) interface requires a valid source interface (typically a loopback) to establish VXLAN tunnels. If the source interface is not configured under the NVE interface, the interface remains in a down state because it cannot form VXLAN overlay adjacencies. This is the most common cause of an NVE interface being down in Cisco NX-OS.
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 VXLAN destination UDP port is incorrect.
Why it's wrong here
UDP port configuration is not shown and does not cause NVE to be down.
✗
The overlay VLAN is not configured.
Why it's wrong here
Overlay VLANs are separate from NVE interface state.
✓
The source interface is not configured.
Why this is correct
The output shows 'Source Interface: not configured', which prevents NVE from coming up.
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 VNI list is empty.
Why it's wrong here
VNI list configuration does not affect NVE state; it determines the VXLAN segments.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the specific requirement that the NVE interface must have a source interface configured to come up, and candidates mistakenly think an empty VNI list or incorrect UDP port would cause the interface to be down, but those affect traffic forwarding, not the interface state.
Trap categories for this question
Command / output trap
UDP port configuration is not shown and does not cause NVE to be down.
Detailed technical explanation
How to think about this question
The NVE interface in NX-OS uses the 'source-interface' command to specify the loopback or physical interface whose IP address is used as the source for VXLAN tunnels. Without this, the NVE cannot generate VXLAN packets because it lacks a valid source IP for the outer UDP header. In a real-world scenario, misconfiguring the source interface (e.g., using a down interface) also causes the NVE to remain down, which is a common troubleshooting step when VXLAN overlay connectivity fails.
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.
Network — This question tests Network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The source interface is not configured. — The NVE (Network Virtualization Edge) interface requires a valid source interface (typically a loopback) to establish VXLAN tunnels. If the source interface is not configured under the NVE interface, the interface remains in a down state because it cannot form VXLAN overlay adjacencies. This is the most common cause of an NVE interface being down in Cisco NX-OS.
What should I do if I get this 350-601 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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Question Discussion
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