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Routing & Switching · Advanced

Hierarchical QoS (HQoS)

A nested QoS policy where a parent policy shapes aggregate traffic and a child policy queues classes within the shaped rate.

Definition

HQoS is required when the physical interface is faster than the contracted service rate, because queuing only engages when the interface itself is congested. The parent shaper creates artificial congestion, and the child LLQ/CBWFQ policy allocates bandwidth within it.

Example

policy-map PARENT / class class-default / shape average 50m / service-policy CHILD

Exam tip

Without the parent shaper, a child queuing policy on a 1 Gbps port toward a 50 Mbps service never activates.

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