350-601 Storage Network Practice Question
An engineer notices that a Fibre Channel link between two Cisco MDS 9000 series switches is flapping every few minutes. The interface counters show a high number of CRC errors. What is the most likely cause of this issue?
⚠ Common exam trap
Cisco often tests the distinction between physical-layer issues (CRC errors, flapping) and logical/configuration issues (VSAN mismatch, zoning, NPV), tempting candidates to select a configuration-based answer when the symptoms clearly point to a hardware fault.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Faulty SFP or optical cable
CRC errors on a Fibre Channel link indicate physical-layer corruption of frames, typically caused by faulty optics, dirty or damaged fiber cables, or marginal signal integrity. Flapping occurs because the link repeatedly fails to maintain proper synchronization due to excessive bit errors, triggering port reset or re-initialization. A faulty SFP or optical cable directly introduces noise or attenuation that corrupts the data stream, leading to CRC errors and link instability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
NPV mode enabled on the switch
Why it's wrong here
NPV mode does not cause CRC errors.
- ✗
Incorrect zoning configuration
Why it's wrong here
Zoning affects access control, not physical errors.
- ✓
Faulty SFP or optical cable
Why this is correct
CRC errors point to physical layer problems.
- ✗
VSAN mismatch between switches
Why it's wrong here
VSAN mismatch causes login failures, not CRC errors.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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