The answer is that the VLAN-to-VNI mapping is missing under the VLAN configuration. When the NVE interface shows up/up, the overlay tunnel is operational, but the VNI not being listed in `show nve vni` means the VNI was never instantiated on that NVE interface. This occurs because the VNI must first be mapped to a VLAN using the `vn-segment` command under the VLAN configuration; without this mapping, the VNI cannot be associated with the NVE and advertised via BGP EVPN. On the Cisco DCCOR 350-601 exam, this scenario tests your understanding of the VXLAN data-plane instantiation process—a common trap is assuming an up/up NVE guarantees VNI presence, but the VLAN-to-VNI mapping is a prerequisite step. Remember the memory tip: "No VN-segment, no VNI in the segment."
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.
A data center engineer is troubleshooting intermittent connectivity between two servers in different VLANs. The servers are connected to different leaf switches in a VXLAN EVPN fabric. When checking the fabric, the engineer notices that the NVE interface on one leaf is up/up but the VNI for the server VLAN is not listed in 'show nve vni'. What is the most likely cause?
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 VLAN-to-VNI mapping is missing under the VLAN configuration
The NVE interface being up/up indicates the overlay tunnel is operational, but the absence of the VNI in 'show nve vni' means the VNI is not instantiated on the NVE. This typically occurs when the VLAN-to-VNI mapping is missing under the VLAN configuration (e.g., 'vlan 100' then 'vn-segment 10100'), which prevents the VNI from being associated with the NVE interface and advertised via BGP EVPN.
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.
✗
MTU mismatch on the underlay network
Why it's wrong here
MTU mismatch would cause packet drops but not the absence of VNI from 'show nve vni'.
✗
Anycast gateway is not configured on the leaf
Why it's wrong here
Anycast gateway is used for first-hop redundancy; its absence does not affect VNI visibility on the NVE.
✗
BGP EVPN peers are not established
Why it's wrong here
BGP EVPN peers not established would affect route exchange, but the VNI would still appear in 'show nve vni' if configured.
✓
The VLAN-to-VNI mapping is missing under the VLAN configuration
Why this is correct
The VNI must be mapped to a VLAN using 'vn-segment vlan-id' under the VLAN configuration; without it, the VNI does not appear in the NVE interface.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between the NVE interface being operational (up/up) and the VNI being properly instantiated via VLAN-to-VNI mapping, leading candidates to incorrectly suspect BGP or underlay issues when the real problem is a missing local configuration step.
Trap categories for this question
Command / output trap
MTU mismatch would cause packet drops but not the absence of VNI from 'show nve vni'.
Detailed technical explanation
How to think about this question
In VXLAN EVPN, the 'vn-segment' command under the VLAN configuration maps the VLAN to a VNI, which then triggers the creation of the VNI on the NVE interface. Without this mapping, the switch does not create the Layer 2 VNI database entry, so 'show nve vni' omits it. This is a common misconfiguration when migrating from traditional VLANs to VXLAN, as the mapping step is easily overlooked in favor of only configuring the NVE interface and BGP EVPN.
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 VLAN-to-VNI mapping is missing under the VLAN configuration — The NVE interface being up/up indicates the overlay tunnel is operational, but the absence of the VNI in 'show nve vni' means the VNI is not instantiated on the NVE. This typically occurs when the VLAN-to-VNI mapping is missing under the VLAN configuration (e.g., 'vlan 100' then 'vn-segment 10100'), which prevents the VNI from being associated with the NVE interface and advertised via BGP EVPN.
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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