350-601 Network Practice Question
A network engineer is implementing QoS on a Nexus 9000 switch. The requirement is to prioritize storage traffic (iSCSI) and ensure lossless behavior. Which queuing strategy should be applied to the egress interface?
⚠ Common exam trap
Cisco often tests the misconception that any queuing or scheduling algorithm (like WRR or tail drop) can provide lossless behavior, but the trap here is that only PFC with a dedicated no-drop queue satisfies the strict no-loss requirement for storage traffic like iSCSI or FCoE.
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) with a no-drop queue for iSCSI.
Priority Flow Control (PFC) is the IEEE 802.1Qbb mechanism designed to provide lossless behavior for specific traffic classes, such as iSCSI storage traffic, on Nexus 9000 switches. By creating a no-drop queue for iSCSI, PFC uses pause frames on a per-priority basis to prevent buffer overflow, ensuring zero packet loss required by storage protocols.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Tail drop with DSCP-based classification.
Why it's wrong here
Tail drop can cause packet loss, which is unacceptable for iSCSI.
- ✗
Weighted Round Robin (WRR) with three queues.
Why it's wrong here
WRR does not provide lossless behavior.
- ✓
Priority Flow Control (PFC) with a no-drop queue for iSCSI.
Why this is correct
PFC enables lossless Ethernet by pausing traffic when buffers are full.
- ✗
Policing at the ingress and marking at the egress.
Why it's wrong here
Policing drops packets, which can cause retransmissions.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-601 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-601 exam.