The answer is a Priority Flow Control (PFC) mismatch between the upstream switch and the storage array. The 'no buffer space' drops on FCoE interfaces occur because PFC, defined by IEEE 802.1Qbb, is essential for maintaining lossless transport; when one device sends pause frames that the other does not honor, or when the PFC priorities are misaligned, receive buffers overflow and frames are dropped. On the Cisco DCCOR 350-601 exam, this scenario tests your understanding of DCB convergence and FIP snooping—common traps include blaming buffer size or link speed, but the root cause is always PFC misconfiguration. Remember the memory tip: “PFC mismatch drops buffer—align priorities to stop the slaughter.”
350-601 Storage Network Practice Question
This 350-601 practice question tests your understanding of storage 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 storage administrator is troubleshooting FCoE performance issues between a Cisco UCS FI and a storage array. The fabric is configured with FIP snooping and DCB. The administrator checks the FCoE interface counters and sees many dropped frames due to 'no buffer space'. What is the most likely root 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
✓
Priority flow control settings are mismatched between the upstream switch and the storage array
The 'no buffer space' drops on FCoE interfaces indicate that the receive buffers are being exhausted, which is a classic symptom of Priority Flow Control (PFC) being misconfigured or mismatched between the upstream switch and the storage array. PFC (IEEE 802.1Qbb) is essential for lossless FCoE transport; if one side sends pause frames that the other does not honor, or if the PFC priorities are not aligned, buffers overflow and frames are dropped. This directly explains the observed counter behavior.
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.
✗
Jumbo frames are disabled on the switch ports
Why it's wrong here
Jumbo frames are required for FCoE, but disabling them would cause different errors.
✗
The FCoE VLAN is not trunked to the storage array
Why it's wrong here
Missing VLAN trunking would cause no connectivity, not buffer drops.
✗
FIP snooping is not enabled on the FCoE VLAN
Why it's wrong here
FIP snooping prevents unauthorized FCoE devices, doesn't cause buffer drops.
✓
Priority flow control settings are mismatched between the upstream switch and the storage array
Why this is correct
PFC mismatch can cause buffer exhaustion and drops.
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 'no buffer space' drops (caused by PFC/flow control mismatches) and other drop types like 'output drops' or 'CRC errors', leading candidates to incorrectly blame jumbo frames or VLAN issues.
Detailed technical explanation
How to think about this question
PFC works by pausing individual traffic classes (CoS values) on a per-priority basis to prevent frame loss. When PFC settings are mismatched—for example, one device uses CoS 3 for FCoE while the other uses CoS 4—the pause frames are ignored, leading to buffer overflow on the receiving interface. The 'no buffer space' counter increments when the hardware buffer pool is exhausted, which is a direct result of the lossless class not being properly flow-controlled.
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.
Storage Network — This question tests Storage Network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Priority flow control settings are mismatched between the upstream switch and the storage array — The 'no buffer space' drops on FCoE interfaces indicate that the receive buffers are being exhausted, which is a classic symptom of Priority Flow Control (PFC) being misconfigured or mismatched between the upstream switch and the storage array. PFC (IEEE 802.1Qbb) is essential for lossless FCoE transport; if one side sends pause frames that the other does not honor, or if the PFC priorities are not aligned, buffers overflow and frames are dropped. This directly explains the observed counter behavior.
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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