350-501 Automation and Quality of Service Practice Question
A network engineer notices that voice traffic is being dropped during congestion. The traffic is marked with DSCP EF. After reviewing the QoS policy, it is discovered that the voice traffic is not being placed into a priority queue. Which configuration change would ensure voice traffic receives priority treatment?
⚠ Common exam trap
Cisco often tests the misconception that bandwidth guarantees or queue tuning alone can provide priority treatment, when in fact only the 'priority' command creates the strict priority queue required for real-time traffic like voice.
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
✓
Add the 'priority' command under the voice class in the policy map
DSCP EF (Expedited Forwarding, per RFC 3246) requires strict priority queuing to guarantee low latency and jitter for voice traffic. The 'priority' command under the voice class in a policy map places the traffic into a strict priority queue (LLQ), ensuring it is serviced before any other queue during congestion. Without this command, the voice traffic is treated as a regular class, subject to bandwidth constraints and potential drops.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the queue limit to 1000 packets
Why it's wrong here
Queue limit only sets the maximum queue depth; it does not provide priority treatment.
- ✗
Increase the bandwidth percentage for the voice class
Why it's wrong here
Increasing bandwidth reserves more capacity but does not provide low-latency priority; voice may still experience jitter.
- ✗
Enable WRED on the voice class
Why it's wrong here
WRED is a congestion avoidance mechanism, not a priority queueing strategy.
- ✓
Add the 'priority' command under the voice class in the policy map
Why this is correct
The 'priority' command places traffic into a low-latency queue, which is essential for real-time traffic like voice.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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