mediumMultiple Choice
350-401 Practice Question: An architect is designing a QoS policy for a…
An architect is designing a QoS policy for a campus LAN that must support real-time voice and video traffic alongside mission-critical data. The design must use the DiffServ model with consistent per-hop behavior across all switches. Which approach should the architect choose to ensure that voice traffic receives priority queuing while video traffic is guaranteed bandwidth without starving other classes?
⚠ Common exam trap
Cisco often tests the misconception that strict priority queuing can be applied broadly to multiple traffic classes without starvation risks, but the trap here is that only EF (voice) should use priority queuing, while AF (video) requires a bandwidth guarantee to avoid starving other classes.
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
✓
Use the MQC framework to classify traffic based on DSCP markings, apply a priority queue for EF traffic, and allocate a minimum bandwidth guarantee for AF41 traffic.
It uses the Modular QoS CLI (MQC) framework to classify traffic by DSCP markings, which aligns with the DiffServ model's per-hop behavior consistency. By applying a strict priority queue for EF (Expedited Forwarding, DSCP 46) traffic, voice gets low-latency treatment, while a minimum bandwidth guarantee for AF41 (Assured Forwarding, DSCP 34) ensures video traffic receives a guaranteed share without starving other classes, as AF uses weighted fair queuing with bandwidth allocation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use the MQC framework to classify traffic based on DSCP markings, apply a priority queue for EF traffic, and allocate a minimum bandwidth guarantee for AF41 traffic.
Why this is correct
The MQC framework is the standard Cisco DiffServ implementation: a class-map matches traffic by DSCP (EF for voice, AF41 for video), and a policy-map assigns an explicit priority queue to EF while reserving a minimum bandwidth portion for AF41. Priority for EF ensures low-latency treatment for voice, while the bandwidth guarantee protects video from starvation during congestion, aligning with the EF and AF PHBs defined in RFC 3246 and RFC 2597. This provides the required differentiated treatment in a scalable, class-based manner.
- ✗
Implement a single FIFO queue on all interfaces and rely on the default CoS-to-queue mapping to prioritize voice.
Why it's wrong here
FIFO delivers packets in arrival order without any classification, so voice and video are interleaved with bulk data, causing variable delay and jitter; relying on default CoS-to-queue mappings is irrelevant if there is only a single FIFO queue. Even if multiple queues are physically present, a single FIFO configuration on the interface means no scheduler distinguishes traffic classes, so no queue is given priority or bandwidth protection. This fails to meet the need for a distinct priority service for EF and a guaranteed minimum for AF41.
- ✗
Configure strict priority queuing for all traffic marked with DSCP values greater than 0.
Why it's wrong here
Strict priority queuing for every DSCP value above zero indiscriminately funnels all marked traffic—including low-priority classes like AF11 or CS1—into the high-priority queue, allowing bulk transfers to consume the priority queue and starve other queues. Since the priority queue is served until empty, voice EF packets may still be delayed behind large data packets with a positive DSCP, and AF41 video receives no bandwidth guarantee, only competition. Proper design restricts priority to EF and uses policing or shaping on the priority queue to protect lower-priority classes from starvation.
- ✗
Use the IntServ model with RSVP to reserve bandwidth for each voice and video flow.
Why it's wrong here
IntServ with RSVP requires per-flow signaling and state in every router along the path, reserving bandwidth for each voice and video call; this does not scale in a large campus network with thousands of flows. The scenario already specifies DSCP markings, which is a DiffServ approach—not an IntServ architecture—so RSVP reservations are unnecessary and would add significant overhead and complexity. While RSVP can provide hard guarantees, it conflicts with the class-based QoS model the network should use for converged traffic.
Go deeper
Related to this question
About these practice questions
This 350-401 question is part of Courseiva's 1,923-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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.