352-001 · Question #95
What statement is true about designing a policy in which more than one class share a queue?
The correct answer is C. It requires consideration of the performance targets of classes sharing the queue. When multiple traffic classes share a single queue, the scheduler applies one policy to all of them without distinction, requiring careful evaluation of each class's performance targets.
Question
What statement is true about designing a policy in which more than one class share a queue?
Options
- AIt must be avoided under all circumstances.
- BIt will result in a negative class.
- CIt requires consideration of the performance targets of classes sharing the queue.
- DIt should be deployed throughout the network to simplify the design.
How the community answered
(37 responses)- A11% (4)
- B5% (2)
- C81% (30)
- D3% (1)
Why each option
When multiple traffic classes share a single queue, the scheduler applies one policy to all of them without distinction, requiring careful evaluation of each class's performance targets.
Sharing a queue is not unconditionally prohibited - it is an acceptable design choice when the sharing classes have compatible performance requirements.
A 'negative class' is a CBWFQ concept related to bandwidth allocation oversubscription, not an automatic consequence of multiple classes sharing a queue.
When classes share a queue, the queuing mechanism cannot differentiate between them, so the designer must verify that the combined scheduling behavior still satisfies each class's individual delay, jitter, and throughput requirements - one class's burst can directly degrade another's service level.
Deploying shared queues throughout the network solely to simplify design is not a recommended practice because it can violate per-class SLAs where traffic profiles differ.
Concept tested: QoS queue sharing and class performance design considerations
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_conmgt/configuration/xe-16/qos-conmgt-xe-16-book/qos-conmgt-oview.html
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