The answer is that VLAN 100 is not defined on the fabric interconnects. Even when both vNICs show as up and the MAC pool is correctly assigned, the server cannot reach the default gateway if the VLAN is missing from the fabric interconnect’s VLAN database; the fabric interconnect must have the VLAN created and assigned to the appropriate uplink ports or port-channels for Layer 2 forwarding to occur. This scenario is a classic trap on the Cisco DCCOR / CCNP Data Center Core 350-601 exam, testing your understanding that UCS Manager profiles define vNICs at the server side, but the fabric interconnect acts as the network switch—without the VLAN defined there, traffic is dropped silently. A common mistake is to blame the vNIC configuration or the MAC pool, but the real issue is the missing VLAN on the fabric interconnect itself. Memory tip: “vNICs up, VLAN missing—check the FI, not the server.”
350-601 Compute Practice Question
This 350-601 practice question tests your understanding of compute. 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.
Refer to the exhibit. A UCS manager profile is configured with two vNICs on separate fabrics. The server is failing to communicate with the default gateway on VLAN 100. Both vNICs are up. What is the most likely issue?
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 100 is not defined on the fabric interconnects
The most likely issue is that VLAN 100 is not defined on the fabric interconnects. In UCS Manager, even if the vNICs are up and the MAC pool is available, the server cannot communicate with the default gateway if the VLAN is not present on the fabric interconnect's VLAN database. The fabric interconnect must have VLAN 100 created and assigned to the appropriate uplink ports or port-channels for traffic to be forwarded.
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 MAC pool is exhausted
Why it's wrong here
MAC pool exhaustion would prevent MAC assignment, not connectivity of already assigned MACs.
✓
The VLAN 100 is not defined on the fabric interconnects
Why this is correct
If VLAN 100 is absent on the FIs, traffic cannot be forwarded to the gateway.
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 boot policy is missing
Why it's wrong here
Boot policy affects boot sequence, not IP connectivity.
✗
The server is using active-standby NIC teaming and the active vNIC is on a fabric that does not have the VLAN
Why it's wrong here
Both vNICs are up, and the exhibit doesn't indicate teaming; misconfigured VLAN is more fundamental.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a vNIC being 'up' implies full Layer 2 connectivity, when in fact the VLAN must be defined on the fabric interconnect for traffic to be switched.
Detailed technical explanation
How to think about this question
Under the hood, UCS fabric interconnects operate as a distributed Layer 2 switching platform. VLANs must be explicitly created in the VLAN manager and assigned to the appropriate fabric (A or B) and uplink interfaces. If VLAN 100 is missing, the fabric interconnect will drop frames destined for that VLAN at the ingress port, even if the vNIC is up and has a valid MAC. In real-world scenarios, this often occurs after a VLAN is added to a service profile but not propagated to the fabric interconnect's VLAN database, causing silent packet drops.
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.
Compute — This question tests Compute — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The VLAN 100 is not defined on the fabric interconnects — The most likely issue is that VLAN 100 is not defined on the fabric interconnects. In UCS Manager, even if the vNICs are up and the MAC pool is available, the server cannot communicate with the default gateway if the VLAN is not present on the fabric interconnect's VLAN database. The fabric interconnect must have VLAN 100 created and assigned to the appropriate uplink ports or port-channels for traffic to be forwarded.
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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