20+ practice questions focused on QoS — one of the most tested topics on the ENCOR 350-401 exam. Each question includes a detailed explanation so you learn why the right answer is correct.
Start QoS PracticeA network engineer is configuring QoS on a Cisco Catalyst 3850 switch to prioritize voice traffic. The switch is connected to an IP phone and a PC using a single access port. The engineer applies a service policy on the access port that marks CoS 5 for voice and CoS 0 for data. However, the IP phone is not receiving any voice packets. What is the most likely cause?
Explanation: The correct answer identifies that the switchport must be configured to trust the CoS markings from the IP phone. If the port is set to untrusted, the switch will re-mark all incoming CoS values to 0, overriding the phone's markings.
An engineer is deploying QoS on a WAN link between two sites using a Cisco ISR 4451 router. The link is a 10 Mbps MPLS circuit. The engineer wants to ensure that voice traffic (EF) is never dropped, even during congestion. The current policy uses a single class map for voice with a policer that drops excess traffic. During peak hours, users report choppy voice calls. What change should the engineer make?
Explanation: The correct answer is to replace the policer with a shaper or use a low-latency queue (LLQ) to provide strict priority queuing. A policer drops excess traffic, which can cause voice packet loss. Using LLQ ensures voice gets priority without dropping.
A network engineer is troubleshooting QoS on a Cisco Nexus 9000 switch. The switch is configured with a policy map that uses a class-default with a bandwidth remaining percent of 100. However, during congestion, traffic in a priority queue (class-map for EF) is experiencing drops even though the priority queue is not fully utilized. What is the most likely cause?
Explanation: The correct answer is that the priority queue is policed by default on Nexus switches to prevent starvation of other queues. The priority queue has a policer that drops traffic if it exceeds a certain rate, even if the queue is not congested.
An engineer is configuring QoS on a Cisco ASR 1000 router to support three traffic classes: voice (EF), video (AF41), and data (default). The link is a 50 Mbps Ethernet circuit. The engineer wants to guarantee 10 Mbps for voice, 20 Mbps for video, and the remaining for data. The current policy uses bandwidth percent statements. During congestion, voice traffic is not receiving its guaranteed bandwidth. What is the most likely cause?
Explanation: The correct answer is that bandwidth percent is based on the interface bandwidth, which may not match the actual link speed if the interface bandwidth is not set correctly. The engineer should use bandwidth remaining percent or shape the traffic.
A network engineer is troubleshooting voice quality issues on a Cisco Catalyst 9300 switch. The switch is configured with auto QoS for voice, which enabled trust on the access ports. However, voice packets are being marked with DSCP EF but are still experiencing jitter. The engineer checks the interface queue statistics and sees that the priority queue is not being used. What is the most likely reason?
Explanation: The correct answer is that auto QoS for voice enables trust but does not automatically create a priority queue on the switch; the engineer must also configure a service policy that includes a priority queue for EF traffic.
+15 more QoS questions available
Practice all QoS questions1. Baseline your knowledge
Start with 10 questions to gauge your current understanding of QoS. This tells you whether you need a concept refresher or just practice.
2. Review every explanation
For each question — right or wrong — read the full explanation. Understanding why an answer is correct is more valuable than knowing the answer itself.
3. Focus on exam traps
QoS questions on the 350-401 frequently use trap wording. Look for subtle differences in answers that test your precision, not just general knowledge.
4. Reach 80% consistently
Do repeated sessions until you score 80%+ three times in a row. Then move to mixed-mode practice to test cross-topic recall under realistic conditions.
The exact number varies per candidate. QoS is tested as part of the ENCOR 350-401 blueprint. Practicing with targeted QoS questions ensures you can handle any format or difficulty that appears.
Yes. Courseiva provides free 350-401 practice questions across all exam topics and domains. The platform includes topic-based practice, mock exams, missed-question review, bookmarked questions, and readiness tracking — no account required.
Difficulty is subjective, but QoS is a high-priority exam concept tested in multiple ways — direct recall, scenario analysis, and command-output interpretation. Consistent practice is the best way to build confidence.
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