This 350-501 practice question tests your understanding of automation and quality of service. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which congestion avoidance technique drops packets probabilistically before the queue becomes full?
FIFO
Why wrong: FIFO drops only when queue is full.
Priority Queuing
Why wrong: Priority Queuing is a scheduling mechanism.
WRED
WRED proactively drops packets to avoid congestion.
Custom Queuing
Why wrong: Custom Queuing is a scheduling mechanism.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
WRED
WRED (Weighted Random Early Detection) is a congestion avoidance mechanism that monitors the average queue depth and, when it exceeds a configured threshold, begins dropping packets probabilistically before the queue becomes completely full. This proactive dropping signals TCP senders to reduce their transmission rates, thereby preventing tail drop and global synchronization.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
FIFO
Why it's wrong here
FIFO drops only when queue is full.
Priority Queuing
Why it's wrong here
Priority Queuing is a scheduling mechanism.
WRED
Why this is correct
WRED proactively drops packets to avoid congestion.
Related concept
Read the scenario before looking for a memorised answer.
Custom Queuing
Why it's wrong here
Custom Queuing is a scheduling mechanism.
Common exam traps
The trap here is that candidates often confuse congestion avoidance (WRED) with congestion management (queuing algorithms like PQ, CQ, or FIFO), mistakenly thinking that any queuing mechanism that drops packets qualifies as congestion avoidance.
Detailed technical explanation
WRED uses an exponentially weighted moving average (EWMA) to calculate the average queue size, which smooths out transient bursts and prevents premature drops. It supports up to eight Differentiated Services Code Point (DSCP) or IP Precedence values, allowing different drop probabilities for different traffic classes. In a real-world scenario, WRED is critical on WAN links where TCP global synchronization would otherwise cause severe performance degradation after a tail drop event.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Automation and Quality of Service — This question tests Automation and Quality of Service — Read the scenario before looking for a memorised answer..
The correct answer is: WRED — WRED (Weighted Random Early Detection) is a congestion avoidance mechanism that monitors the average queue depth and, when it exceeds a configured threshold, begins dropping packets probabilistically before the queue becomes completely full. This proactive dropping signals TCP senders to reduce their transmission rates, thereby preventing tail drop and global synchronization.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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.
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