easyMultiple ChoiceObjective-mapped
CCNP Practice Question: Which QoS mechanism is used to prevent congestion…
Which QoS mechanism is used to prevent congestion by dropping packets before a queue becomes full?
⚠ Common exam trap
Cisco often tests the distinction between congestion management (queuing/scheduling) and congestion avoidance (drop policy), so the trap here is that candidates confuse mechanisms like CBWFQ or PQ (which manage queues after they form) with WRED (which prevents queues from filling up in the first place).
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
✓
Weighted Random Early Detection (WRED)
Weighted Random Early Detection (WRED) is a congestion avoidance mechanism that proactively drops packets before a queue becomes full. By monitoring the average queue depth and dropping packets with a probability that increases as the queue depth grows, WRED signals TCP senders to reduce their transmission rate, thereby preventing tail drop and global synchronization. This differs from congestion management mechanisms like PQ or CBWFQ, which only act on packets after the queue is full.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Weighted Random Early Detection (WRED)
Why this is correct
WRED proactively drops packets to avoid tail drop and global synchronization.
- ✗
Priority Queuing (PQ)
Why it's wrong here
PQ is a scheduling mechanism, not a congestion avoidance mechanism.
- ✗
Class-Based Weighted Fair Queuing (CBWFQ)
Why it's wrong here
CBWFQ is a scheduling mechanism that guarantees bandwidth.
- ✗
Tail Drop
Why it's wrong here
Tail drop drops packets only when the queue is full, not before.
Visual reference
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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.