The answer is that the vNIC without a QoS policy defaults to 1500 MTU, causing jumbo frame drops. When a vNIC is not mapped to any QoS policy, it automatically inherits the default best-effort system class, which enforces a standard Ethernet MTU of 1500 bytes. Since the server is sending jumbo frames with an MTU of 9000 on VLAN 100, these oversized packets exceed the default MTU and are dropped at the interface, regardless of the higher MTU (9216) configured on the unrelated 'Class-Platinum' system class. On the Cisco DCCOR 350-601 exam, this scenario tests your understanding of how QoS policy assignment governs per-vNIC MTU behavior—a common trap is assuming a system class with a larger MTU applies globally. Remember: no QoS policy means the vNIC falls into the best-effort bucket, which caps MTU at 1500. Memory tip: “No policy, no jumbo—1500 is the default sumo.”
350-601 Compute Practice Question
This 350-601 practice question tests your understanding of compute. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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
UCS Manager > Service Profile > vNIC List
vNIC Name: eth0
Fabric ID: A
Adapter Policy: Windows
MTU: 9000
VLAN: 100 (Native)
UCS Manager > LAN > LAN Cloud > QoS System Class
Class-FC: No Drop, MTU 9216, Weight 10
Class-Platinum: Drop, MTU 9216, Weight 30
Class-Gold: Drop, MTU 1500, Weight 20
Class-Silver: Drop, MTU 1500, Weight 10
Class-Bronze: Drop, MTU 1500, Weight 5
Refer to the exhibit. A server with vNIC eth0 is experiencing packet drops on its Ethernet interface. The server is sending jumbo frames (MTU 9000) on VLAN 100. The QoS system class 'Class-Platinum' has an MTU of 9216 and is configured with 'Drop'. The vNIC is not assigned to any QoS policy. What is the most likely reason for the drops?
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.
UCS Manager > Service Profile > vNIC List
vNIC Name: eth0
Fabric ID: A
Adapter Policy: Windows
MTU: 9000
VLAN: 100 (Native)
UCS Manager > LAN > LAN Cloud > QoS System Class
Class-FC: No Drop, MTU 9216, Weight 10
Class-Platinum: Drop, MTU 9216, Weight 30
Class-Gold: Drop, MTU 1500, Weight 20
Class-Silver: Drop, MTU 1500, Weight 10
Class-Bronze: Drop, MTU 1500, Weight 5
A
The vNIC is not mapped to a QoS policy, so it uses the default best-effort class which has an MTU of 1500 and drops jumbo frames.
Without a QoS policy, the default class (often Bronze) applies, which has MTU 1500.
B
The QoS system class for jumbo frames requires a 'No Drop' policy to avoid drops.
Why wrong: Drop policy is not the issue; MTU mismatch is.
C
The server is sending frames larger than 9216 bytes.
Why wrong: The server is sending MTU 9000, which is within 9216.
D
The native VLAN setting on the vNIC causes the QoS system class to be ignored.
Why wrong: Native VLAN does not affect QoS classification.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The vNIC is not mapped to a QoS policy, so it uses the default best-effort class which has an MTU of 1500 and drops jumbo frames.
When a vNIC is not assigned to a QoS policy, it defaults to the best-effair class, which typically has an MTU of 1500 bytes. Since the server is sending jumbo frames (MTU 9000) on VLAN 100, these frames exceed the default MTU and are dropped at the Ethernet interface. The 'Class-Platinum' system class with MTU 9216 is irrelevant because the vNIC is not mapped to it.
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 vNIC is not mapped to a QoS policy, so it uses the default best-effort class which has an MTU of 1500 and drops jumbo frames.
Why this is correct
Without a QoS policy, the default class (often Bronze) applies, which has MTU 1500.
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 QoS system class for jumbo frames requires a 'No Drop' policy to avoid drops.
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a system class with a higher MTU (like Class-Platinum) automatically applies to all traffic, when in fact the vNIC must be explicitly mapped to that QoS policy to use it.
Detailed technical explanation
How to think about this question
In Cisco ACI, each vNIC inherits the QoS policy from its EPG or VMM domain; if none is assigned, the system applies the default best-effort class with an MTU of 1500 bytes. Jumbo frames require a custom QoS policy with a higher MTU (e.g., 9000) to avoid drops. This behavior is defined in the Cisco ACI QoS configuration, where the system class MTU must match or exceed the frame size to prevent fragmentation or discard.
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 vNIC is not mapped to a QoS policy, so it uses the default best-effort class which has an MTU of 1500 and drops jumbo frames. — When a vNIC is not assigned to a QoS policy, it defaults to the best-effair class, which typically has an MTU of 1500 bytes. Since the server is sending jumbo frames (MTU 9000) on VLAN 100, these frames exceed the default MTU and are dropped at the Ethernet interface. The 'Class-Platinum' system class with MTU 9216 is irrelevant because the vNIC is not mapped to it.
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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