mediumMultiple Choice
CCNP Practice Question: Given the following policy-map: policy-map…
Given the following policy-map:
policy-map QOS_POLICY
class VOICE
priority percent 30
class VIDEO
bandwidth percent 20 queue-limit 100 packets
class class-default
fair-queue
What is the effect of the 'priority percent 30' command in the VOICE class?
⚠ Common exam trap
Cisco often tests the misconception that 'priority percent' simply limits bandwidth like a policer, but the key trap is that it also provides strict priority queuing, which guarantees low latency for voice traffic, not just a bandwidth cap.
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
✓
Voice traffic is placed in a strict priority queue with a guaranteed bandwidth of 30% of the interface bandwidth.
The 'priority percent 30' command in the VOICE class configures a strict priority queue (LLQ) that guarantees voice traffic up to 30% of the interface bandwidth. During congestion, voice packets are always transmitted before other traffic, but they are policed to ensure they do not exceed the allocated 30%, preventing starvation of other queues.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Voice traffic is placed in a strict priority queue with a guaranteed bandwidth of 30% of the interface bandwidth.
Why this is correct
The priority command in a Cisco MQC policy map creates a strict priority queue (PQ) for the voice class, which is drained by the scheduler before any other queue. The percentage specifies the bandwidth reserved for that queue during congestion, ensuring low latency and jitter for real-time traffic. This guarantee is measured against the interface bandwidth, so voice always has a dedicated share of link capacity even under heavy load.
- ✗
Voice traffic is limited to 30% of the interface bandwidth and will be dropped if exceeded.
Why it's wrong here
This option misinterprets the priority command as a policer that drops voice traffic the moment it exceeds the configured 30% rate. In reality, the priority queue guarantees at least 30% of the interface bandwidth, and voice traffic beyond that percentage is forwarded if the interface has available capacity; it is not automatically dropped. Drops occur only when the queue itself overflows due to sustained congestion, not as an immediate enforcement at the quota boundary.
- ✗
Voice traffic is given a weight of 30 in the weighted fair queueing algorithm.
Why it's wrong here
This statement confuses strict priority queueing with Class-Based Weighted Fair Queueing (CBWFQ). The priority command does not assign a numerical weight to the voice class; instead, it places all voice packets into a dedicated low-latency queue that is emptied before any other queue is serviced. WFQ weights influence fairness among multiple flows, but priority queueing explicitly bypasses that fairness to minimize delay for delay-sensitive traffic.
- ✗
Voice traffic is re-marked with IP precedence 30.
Why it's wrong here
The priority command is a scheduling and queueing mechanism, not a marking or re-marking function. It does not modify the IP precedence or DSCP fields in voice packets; it only determines how those packets are treated by the queueing discipline. Marking voice traffic to a specific IP precedence value would require a separate set command or a policy-map action such as 'set ip precedence', which is not part of the priority command.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 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 350-401 exam.