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352-001 · Question #598
352-001 Question #598: Real Exam Question with Answer & Explanation
The correct answer is C: WRED. WRED is the correct congestion avoidance mechanism because it proactively discards lower-priority packets as queues build, preventing the TCP global synchronization caused by tail-drop.
Question
You are redesigning a high-speed transit network due to congestion-related issues. Which congestion avoidance mechanism can you apply to the existing network?
Options
- ANBAR
- BFIFO
- CWRED
- DRate-limit
- EPolicy-Based Routing
Explanation
WRED is the correct congestion avoidance mechanism because it proactively discards lower-priority packets as queues build, preventing the TCP global synchronization caused by tail-drop.
Common mistakes.
- A. NBAR (Network-Based Application Recognition) is a deep-packet inspection classification engine used to identify application traffic for policy application and has no congestion avoidance function.
- B. FIFO queuing is the default, non-intelligent scheduling method that uses tail-drop when full, which worsens congestion by triggering TCP global synchronization rather than avoiding it.
- D. Rate-limiting (traffic policing) enforces a configured bandwidth ceiling by dropping or remarking excess traffic at ingress but does not manage queue depth or provide active congestion avoidance inside the network.
- E. Policy-Based Routing (PBR) redirects packets to alternate next-hops based on match criteria for traffic engineering purposes and has no mechanism for congestion avoidance.
Concept tested. WRED congestion avoidance and TCP global synchronization prevention
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