The answer is that the 'Primary Fabric' setting is not defined in the vNIC template. When you enable fabric failover on a UCS vNIC, the system requires an explicit primary fabric assignment—either FI-A or FI-B—to know which interconnect should handle traffic under normal conditions. Without this definition, the vNIC cannot determine the active path, so it stays pinned to the original Fabric Interconnect even when that link fails, which is why UCS vNIC fabric failover not working is often traced to this missing configuration. On the Cisco DCCOR 350-601 exam, this scenario tests your understanding of UCS service profile and vNIC template behavior, and it’s a common trap because many candidates assume the failover checkbox alone is sufficient. Remember: fabric failover tells the system *that* it can fail over, but the primary fabric tells it *where* to fail over from—think of it as needing both the “go” signal and the “starting line.”
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.
A UCS administrator notices that a service profile associated with a vNIC template that uses 'fabric failover' is not failing over to the secondary Fabric Interconnect when the primary link goes down. The vNIC template is set to 'fabric failover' enabled, and both Fabric Interconnects are in the same VLAN. 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.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'Primary Fabric' setting is not defined in the vNIC template.
When 'fabric failover' is enabled on a vNIC template, the UCS Manager requires the 'Primary Fabric' setting to be explicitly defined to determine which Fabric Interconnect (FI-A or FI-B) should be the active path. Without this setting, the system cannot properly orchestrate the failover behavior, causing the vNIC to remain pinned to the primary FI even when its link goes down. This is a common misconfiguration because the 'fabric failover' checkbox alone does not imply a primary fabric assignment.
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 'Primary Fabric' setting is not defined in the vNIC template.
Why this is correct
The primary fabric must be selected in the vNIC template for failover to function correctly.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The server is pinned to the primary Fabric Interconnect via a pin group.
Why it's wrong here
Pin groups control uplink selection, not vNIC failover.
✗
The MTU size on the secondary Fabric Interconnect is set to 1500 instead of 9000.
Why it's wrong here
MTU mismatch would cause connectivity issues but not prevent failover.
✗
The 'MAC Address' policy is set to 'pool-based' instead of 'static'.
Why it's wrong here
MAC address policy does not affect failover behavior.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that enabling 'fabric failover' alone is sufficient for automatic failover, when in fact the 'Primary Fabric' field must also be explicitly configured to define the active path.
Detailed technical explanation
How to think about this question
Under the hood, UCS uses the 'Primary Fabric' setting to program the fabric selector in the VIC (Virtual Interface Card) firmware, which determines the active uplink path. If this field is left undefined, the VIC defaults to using the first discovered fabric (usually FI-A) and will not respond to link-down events on that fabric because the failover logic is not initialized. In a real-world scenario, an administrator might enable 'fabric failover' but forget to set 'Primary Fabric' to 'A' or 'B', leading to silent failover failures that are only discovered during a maintenance window.
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 'Primary Fabric' setting is not defined in the vNIC template. — When 'fabric failover' is enabled on a vNIC template, the UCS Manager requires the 'Primary Fabric' setting to be explicitly defined to determine which Fabric Interconnect (FI-A or FI-B) should be the active path. Without this setting, the system cannot properly orchestrate the failover behavior, causing the vNIC to remain pinned to the primary FI even when its link goes down. This is a common misconfiguration because the 'fabric failover' checkbox alone does not imply a primary fabric assignment.
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", "primary". 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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