350-601 Storage Network Practice Question
A network engineer is deploying FCoE in a top-of-rack design. Which statement about the required lossless Ethernet fabric is correct?
⚠ Common exam trap
Cisco often tests the misconception that DCBX automatically enables PFC when FCoE is configured, but in reality, DCBX only negotiates capabilities, and PFC must be manually enabled on the interfaces (e.g., using the 'priority-flow-control' command).
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
✓
Priority Flow Control (PFC) must be enabled to create lossless CoS
FCoE requires a lossless Ethernet fabric to prevent frame drops, which would corrupt Fibre Channel traffic. Priority Flow Control (PFC), defined in IEEE 802.1Qbb, provides per-priority pause mechanisms to create lossless CoS (Class of Service) queues, ensuring no frames are lost due to congestion. Without PFC, standard Ethernet's best-effort delivery would cause frame drops, breaking FCoE's reliability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Data Center Bridging Exchange (DCBX) automatically enables PFC when FCoE is configured
Why it's wrong here
DCBX advertises and negotiates PFC, but PFC must be explicitly enabled.
- ✗
FCoE uses VLAN 1002 by default for all traffic
Why it's wrong here
VLAN assignment is configurable, though default VSANs map to VLAN 1002-1003.
- ✗
FCoE frames are limited to 1500 bytes to avoid fragmentation
Why it's wrong here
FCoE requires jumbo frames up to 2500 bytes typically.
- ✓
Priority Flow Control (PFC) must be enabled to create lossless CoS
Why this is correct
PFC ensures lossless behavior for FCoE frames.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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