Cisco Catalyst 2000 User Manual (English)

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Chapter 13

Quality of Service

See the following sections to configure and use these features:

■ 13-1: QoS Theory: Discusses the various operations and mechanisms that make up

quality of service (QoS) as a whole

■ 13-2: QoS Configuration: Explains the sequence of steps necessary to configure

and monitor QoS on a Catalyst switch

■ 13-3: QoS Data Export: Presents the configuration steps needed to gather and send

QoS statistics information to external collection devices

13-1: QoS Theory

■ QoS defines policies on how switches and routers deliver different types of traffic. A

QoS domain is the entire collection of network devices that are administered so that

they adhere to the QoS policies.

■ To guarantee that QoS policies are met, QoS must be configured on all switches and

routers end-to-end across the network.

■ Traffic should be classified at the edges of the QoS domain. Where this isn’t possi-

ble, classify traffic as close as possible to the source. Classification can occur at

Layer 2 or Layer 3, depending on the network functions available at the edge.

■ The top portion of Figure 13-1 shows QoS operations on a Catalyst switch, includ-

ing the following:

■ Classification: Selects specific traffic to which a QoS policy can be applied. The

priority values of inbound frames can also be trusted or reclassified.

■ Policing: Limits the bandwidth used by a traffic flow. Policers can control aggre-

gate or individual flows and can also mark or drop traffic.

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