300-420 Question #196: Real Exam Question with Answer & Explanation

Question

A customer plans to adopt distributed QoS in their enterprise WAN. The policy must allow for individual packet marking according to the type of treatment required and for forwarding based on hop-by-hop treatment locally defined on each device. Which technology must the customer select?

Options

• ACBWFQ
• BLLQ
• CDiffserv
• DIntServ

Explanation

DiffServ is the appropriate technology for a distributed QoS solution that uses individual packet marking and hop-by-hop forwarding decisions based on local device configurations.

Common mistakes.

• A. Class-Based Weighted Fair Queuing (CBWFQ) is a queuing mechanism, not a comprehensive end-to-end QoS architecture that dictates how packets are marked and handled across an entire WAN.
• B. Low Latency Queuing (LLQ) is a specific queuing feature that combines priority queuing with CBWFQ, but it is not an end-to-end QoS architecture like DiffServ.
• D. Integrated Services (IntServ) provides end-to-end QoS guarantees with per-flow state and signaling (RSVP), which does not scale well in large enterprise WANs due to the overhead of maintaining state for every flow.

Concept tested. DiffServ principles and architecture

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_diffserv/configuration/xe-3s/qos-diffserv-xe-3s-book.html

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