The correct answer is that the 'priority percent 30' command places voice traffic into a strict priority queue with a guaranteed bandwidth of 30% of the interface bandwidth, a mechanism known as Low Latency Queuing (LLQ). This command ensures that during congestion, voice packets are always transmitted before any other traffic class, providing the low jitter and delay required for real-time applications. However, the 30% also acts as a policer; if voice traffic exceeds that limit, excess packets are dropped to prevent starvation of other queues, which is a critical distinction from the older 'priority' command without a percent. On the ENCOR 350-401 exam, this tests your understanding of LLQ behavior under congestion versus non-congestion scenarios—a common trap is assuming priority queues are unlimited. Remember the memory tip: "Priority percent is a strict cop, not a free pass—it guarantees the lane but enforces the speed limit."
CCNP SD-Access Architecture Practice Question
This 350-401 practice question tests your understanding of sd-access architecture. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 provides a low-latency queue with a bandwidth guarantee.
Related concept
Read the scenario before looking for a memorised answer.
✗
Voice traffic is limited to 30% of the interface bandwidth and will be dropped if exceeded.
Why it's wrong here
While it limits bandwidth, the priority queue is not a policer; it shapes but does not drop within the limit.
✗
Voice traffic is given a weight of 30 in the weighted fair queueing algorithm.
Why it's wrong here
Priority is not weighted fair queueing; it uses a strict priority queue.
✗
Voice traffic is re-marked with IP precedence 30.
Why it's wrong here
The priority command does not mark packets; it only provides QoS treatment.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Trap categories for this question
Command / output trap
The priority command does not mark packets; it only provides QoS treatment.
Detailed technical explanation
How to think about this question
Under the hood, the 'priority percent' command in Cisco IOS implements Low Latency Queuing (LLQ), which combines a strict priority queue with a policer. The policer uses a token bucket to enforce the bandwidth limit; if the voice traffic exceeds 30% over a time interval, packets are dropped (or optionally, can be configured to be re-marked and queued elsewhere). In real-world VoIP deployments, this ensures jitter-sensitive voice traffic is served first, while preventing a single flow from monopolizing the link.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 350-401 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
SD-Access Architecture — This question tests SD-Access Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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