350-501 Architecture Practice Question
A service provider wants to prioritize voice traffic over data traffic on a PE-CE link. Which QoS mechanism should be applied at the PE ingress to classify packets?
⚠ Common exam trap
Cisco often tests the misconception that policing or shaping can classify traffic, when in reality they are actions applied after classification, not mechanisms for identifying packet types.
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
✓
Class-based marking based on NBAR
Class-based marking using NBAR (Network-Based Application Recognition) is the correct mechanism because it can inspect packets at the application layer to distinguish voice traffic (e.g., RTP, SIP) from data traffic. On a PE-CE link, marking at ingress allows the service provider to set the appropriate DSCP or IP precedence value, which downstream QoS policies can then trust and act upon. This classification step is essential before any policing, shaping, or queuing can be applied.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Policer
Why it's wrong here
Policing is an action that drops or marks packets; it does not classify.
- ✓
Class-based marking based on NBAR
Why this is correct
NBAR performs deep packet inspection to classify traffic by application.
- ✗
WRED
Why it's wrong here
WRED is a congestion avoidance mechanism that drops packets based on probability; it does not classify.
- ✗
Shaper
Why it's wrong here
Shaping buffers packets to enforce a rate; it does not classify.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 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 350-501 exam.