352-001 Question #62: Real Exam Question with Answer & Explanation

Question

Options

• Athe router handles the overflow of traffic by using FIFO
• Bthe router handles the possible buildup of congestion by using WRED
• Cthe router forces inbound and outbound traffic to stay within a defined profile by using rate limiting
• Dthe router separates packets based on certain characteristics by using NBAR
• Ethe router marks packets based on certain characteristics by using PBR

Explanation

Congestion avoidance in QoS proactively drops packets before queues fill completely, and WRED is the standard Cisco mechanism that implements this behavior.

Common mistakes.

• A. FIFO (First In First Out) is a basic queuing strategy with no intelligence about traffic priority or queue depth; it does not perform any congestion avoidance and simply drops all packets when the queue is full (tail-drop).
• C. Rate limiting (traffic policing) enforces a defined bandwidth contract by dropping or remarking traffic that exceeds a configured rate; this is a traffic conditioning mechanism, not a congestion avoidance mechanism.
• D. NBAR (Network-Based Application Recognition) is a deep packet inspection classification tool used to identify application traffic, not a mechanism that manages or avoids congestion.
• E. PBR (Policy-Based Routing) directs packets to specific next hops based on defined criteria; it is a routing mechanism and does not mark packets for QoS treatment in the context of congestion avoidance.

Concept tested. QoS congestion avoidance using WRED

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_conavd/configuration/xe-16/qos-conavd-xe-16-book/qos-conavd-wred-cfg.html

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