The answer is to configure a priority queue for DSCP EF traffic within the shaper. This is correct because when a shaper limits traffic to 50 Mbps and the aggregate load exceeds that rate, the output queue fills and drops packets indiscriminately, including VoIP marked with DSCP EF. A priority queue ensures that VoIP packets are serviced before all other traffic, bypassing the default FIFO or CBWFQ behavior, which guarantees low latency and jitter even under congestion. On the ENCOR 350-401 exam, this tests your understanding of the interaction between shaping and queuing—a common trap is thinking that marking alone or simply increasing bandwidth solves voice quality issues, but shaping without a priority queue still causes drops. Remember the key principle: shaping limits the rate, but priority queuing protects real-time traffic within that limit. A useful memory tip is “Shape the pipe, but prioritize the voice”—the shaper sets the speed limit, while the priority queue gives VoIP a police escort through traffic.
350-401 Architecture Practice Question
This 350-401 practice question tests your understanding of 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.
A mid-size enterprise is deploying a new branch office with 50 users. The branch will have its own router, switch, and wireless AP. The WAN link is a 50 Mbps MPLS circuit. The company uses VoIP and requires Quality of Service. The network administrator has configured the router with a QoS policy that marks VoIP traffic with DSCP EF and all other traffic with DSCP 0. The policy also shapes traffic to 50 Mbps. After deployment, users report that voice quality is poor during peak hours. The administrator checks the router and sees that the output queue on the WAN interface is often full and drops are occurring. Which action should the administrator take to improve voice quality?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure a priority queue for DSCP EF traffic within the shaper.
The shaper is limiting traffic to 50 Mbps, but during peak hours, the aggregate traffic exceeds this rate, causing the output queue to fill and drop packets indiscriminately. By configuring a priority queue for DSCP EF (VoIP) traffic within the shaper, the router will service VoIP packets before other traffic, ensuring low latency and jitter even when the link is congested. This is the standard Cisco approach for voice quality on shaped links, as priority queuing bypasses the normal FIFO or CBWFQ behavior for marked traffic.
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.
✗
Increase the shaping rate to 60 Mbps to allow for burst.
Why it's wrong here
The circuit is limited to 50 Mbps; shaping above that will cause drops at the provider edge.
✓
Configure a priority queue for DSCP EF traffic within the shaper.
Why this is correct
A priority queue ensures voice packets are dequeued before other traffic, reducing voice drops.
Related concept
Read the scenario before looking for a memorised answer.
✗
Replace shaping with policing to drop non-voice traffic.
Why it's wrong here
Policing drops excess packets, which may include voice if bursts occur, and does not prioritize voice.
✗
Change the marking to use CoS instead of DSCP for better QoS.
Why it's wrong here
CoS is a Layer 2 marking; the router interface is Layer 3, and DSCP is appropriate. This would not fix the queue drop issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that increasing bandwidth or policing alone solves voice quality issues, but the trap here is that shaping without a priority queue causes all traffic to be treated equally, so VoIP suffers from jitter and delay even if the total rate is within the shaped limit.
Detailed technical explanation
How to think about this question
Under the hood, the shaper uses a token bucket to meter traffic; when the bucket is empty, packets are queued. Without a priority queue, all packets (including VoIP) are treated equally in the shaping queue, leading to tail drops. With a priority queue (LLQ), the shaper allows VoIP packets to bypass the token bucket check up to a configured bandwidth limit, ensuring they are sent immediately. In real-world deployments, the priority queue should be limited to a percentage of the shaping rate (e.g., 30% for voice) to prevent starvation of other traffic.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure a priority queue for DSCP EF traffic within the shaper. — The shaper is limiting traffic to 50 Mbps, but during peak hours, the aggregate traffic exceeds this rate, causing the output queue to fill and drop packets indiscriminately. By configuring a priority queue for DSCP EF (VoIP) traffic within the shaper, the router will service VoIP packets before other traffic, ensuring low latency and jitter even when the link is congested. This is the standard Cisco approach for voice quality on shaped links, as priority queuing bypasses the normal FIFO or CBWFQ behavior for marked traffic.
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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