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350-401 Practice Question: Which three statements about the Differentiated…
Which three statements about the Differentiated Services (DiffServ) QoS model are true? (Choose three.)
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
✓
DiffServ uses the 6-bit DSCP field in the IP header to mark packets, allowing up to 64 different classes of service.
DiffServ is a class-based model that uses the DSCP field in the IP header to classify traffic. It provides per-hop behavior (PHB) and is scalable because core routers only need to inspect the DSCP field. The model does not guarantee end-to-end bandwidth reservation like IntServ does; instead, it relies on traffic conditioning at the edge.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
DiffServ uses the 6-bit DSCP field in the IP header to mark packets, allowing up to 64 different classes of service.
Why this is correct
Correct. DSCP is 6 bits, providing 64 possible codepoints.
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In DiffServ, core routers perform complex classification and marking based on deep packet inspection.
Why it's wrong here
Incorrect. In DiffServ, classification and marking are typically done at the edge; core routers use the DSCP value to apply PHB, reducing complexity.
- ✓
The Assured Forwarding (AF) PHB group provides four classes, each with three drop precedence levels.
Why this is correct
Correct. AF defines four classes (AF1x–AF4x) and three drop precedences (low, medium, high) per class.
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DiffServ requires end-to-end signaling using RSVP to reserve bandwidth along the path.
Why it's wrong here
Incorrect. RSVP is used with the IntServ model, not DiffServ. DiffServ does not use signaling.
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The Expedited Forwarding (EF) PHB is designed for low-loss, low-latency traffic such as voice.
Why this is correct
Correct. EF provides a virtual leased line service with low delay, jitter, and loss, ideal for real-time traffic.
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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.