Which of the following Quality of Service (QoS) scheduling mechanisms are considered advanced queuing techniques on Cisco routers? (Select all that apply.)
Correct Answer: A,B,C
Detailed Explanation: Quality of Service (QoS) is a critical feature in modern networks that ensures bandwidth is allocated appropriately among different types of traffic, thereby meeting performance requirements for latency-sensitive applications such as voice and video. Cisco routers support several QoS scheduling mechanisms that manage how packets are queued and transmitted. Class-Based Weighted Fair Queuing (CBWFQ): CBWFQ is an extension of Weighted Fair Queuing (WFQ) that allows administrators to classify traffic into different classes and assign a specific amount of bandwidth to each class. This mechanism ensures that each traffic class receives its guaranteed minimum bandwidth while allowing unused bandwidth to be shared among other classes. CBWFQ is considered an advanced queuing mechanism because it provides granular control over traffic prioritization and bandwidth allocation. Low Latency Queueing (LLQ): LLQ builds upon CBWFQ by adding a strict priority queue to support delay-sensitive traffic (such as VoIP). In LLQ, one class is designated as a priority class and is served before any other traffic. However, to prevent this class from monopolizing the link, limits are placed on its usage. LLQ is particularly useful in environments where both high bandwidth and low latency are required for certain traffic flows. Weighted Fair Queuing (WFQ): WFQ is a fair scheduling algorithm that divides available bandwidth among all active flows based on their weight. Each flow gets a share of the bandwidth proportional to its assigned weight, which helps prevent any single flow from dominating the link. WFQ is considered an advanced queuing mechanism because it dynamically adjusts to changing traffic loads and ensures that traffic is transmitted fairly. Priority Queueing (PQ): Priority Queueing (PQ) is a simpler mechanism that always serves the highest-priority queue first. While it is useful for ensuring that critical traffic is transmitted with minimal delay, it lacks the fairness and flexibility of CBWFQ, LLQ, or WFQ. PQ can lead to starvation of lower-priority queues if high-priority traffic is constant, making it less sophisticated compared to the other techniques. For this reason, Option D is not considered an advanced queuing mechanism in the context of modern QoS scheduling on Cisco routers. Practical Implications: Advanced queuing mechanisms like CBWFQ, LLQ, and WFQ are essential for meeting the diverse QoS requirements of modern networks. They enable network administrators to provide differentiated services for various types of traffic, ensuring that latency-sensitive applications receive the priority and bandwidth they require without completely starving other traffic. Conclusion: The advanced QoS scheduling mechanisms on Cisco routers include Class-Based Weighted Fair Queuing (CBWFQ), Low Latency Queueing (LLQ), and Weighted Fair Queuing (WFQ) (Options A, B, and C). Priority Queueing (PQ) is simpler and does not provide the level of control offered by the advanced mechanisms, making Option D incorrect. Mastery of these QoS techniques is vital for designing and managing networks that meet stringent performance requirements.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.