352-001 Question #151: Real Exam Question with Answer & Explanation

The correct answer is B: CB-WFQ. The 'cyclical' degradation is the key clue - this describes TCP global synchronization, a classic problem with FIFO and tail-drop. When a FIFO queue fills up, the router drops packets from all TCP flows simultaneously. Every TCP session detects loss at the same time, backs off si

Question

FIFO queuing is being used on all routers in a network. The primary application running on the network is data backup using FTP. At certain times, users experience cyclical performance degradation. What two things might mitigate this problem and help ensure bandwidth is used effectively in the network? (Choose two.)

Options

Atraffic shaping
BCB-WFQ
Ctraffic policing
DWRED
EMDRR

Explanation

The 'cyclical' degradation is the key clue - this describes TCP global synchronization, a classic problem with FIFO and tail-drop. When a FIFO queue fills up, the router drops packets from all TCP flows simultaneously. Every TCP session detects loss at the same time, backs off simultaneously, then ramps back up together, creating waves of congestion. WRED (Weighted Random Early Detection) directly solves this: it begins randomly dropping packets from individual flows before the queue is completely full. By staggering drops across flows rather than tail-dropping everything at once, TCP sessions desynchronize and back off at different times, eliminating the cyclical waves and making better use of available bandwidth. CB-WFQ (Class-Based Weighted Fair Queuing) replaces FIFO with a fair, class-aware scheduling policy. It allocates bandwidth by traffic class, prevents any single flow from monopolizing the queue, and ensures all traffic classes get their guaranteed share - making overall bandwidth use more effective. Traffic shaping (A) and policing (C) limit rates but do not address queue management or TCP synchronization. MDRR (E) is a valid queuing mechanism but is not specifically designed to address TCP global synchronization.

Community Discussion

No community discussion yet for this question.

Full 352-001 Practice