5

Quality of Service (QoS): Managing

Bandwidth More Effectively

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 Classifiers for Prioritizing Outbound Packets . . . . . . . . . . . . . . . . . . . 5-10 Packet Classifiers and Evaluation Order . . . . . . . . . . . . . . . . . . . 5-10

Preparation for Configuring QoS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11 Preserving 802.1p Priority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11 Steps for Configuring QoS on the Switch . . . . . . . . . . . . . . . . . . . . . . . 5-11 Viewing the QoS Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 No Override . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13

Using QoS Classifiers to Configure

Quality of Service for Outbound Traffic . . . . . . . . . . . . . . . . . . . . . . . 5-14 QoS IP Type-of-Service (ToS) Policy and Priority . . . . . . . . . . . . . . . 5-15

Assigning an 802.1p Priority to IPv4 Packets on the Basis

of the ToS Precedence Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16

Assigning an 802.1p Priority to IPv4 Packets on the

Basis of Incoming DSCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17

Assigning a DSCP Policy on the Basis of the DSCP in IPv4

Packets Received from Upstream Devices . . . . . . . . . . . . . . . . . . 5-21

Details of QoS IP Type-of-Service . . . . . . . . . . . . . . . . . . . . . . . . .5-24

QoS Source-Port Priority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27

Assigning a Priority Based on Source-Port . . . . . . . . . . . . . . . . . .5-27

Assigning a DSCP Policy Based on the Source-Port . . . . . . . . . .5-29

Differentiated Services Codepoint (DSCP) Mapping . . . . . . . . . . . 5-33Default Priority Settings for Selected Codepoints . . . . . . . . . . . . . . . 5-34 Quickly Listing Non-Default Codepoint Settings . . . . . . . . . . . . . 5-34 Notes on Changing a Priority Setting . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36

5-1