6

Quality of Service (QoS): Managing

Bandwidth More Effectively

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

QoS Types for Prioritizing Outbound Packets . . . . . . . . . . . . . . . . . . .

6-8

Packet Types and Evaluation Order . . . . . . . . . . . . . . . . . . . . . . . .

6-9

Preparation for Configuring QoS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11 Steps for Configuring QoS on the Switch . . . . . . . . . . . . . . . . . . . 6-11

Planning a QoS Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13 Prioritizing and Monitoring QoS Configuration Options . . . . . . 6-13

Using QoS Types To Configure QoS for Outbound Traffic . . . . . . . . . . . . 6-14

Viewing the QoS Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14 No Override . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15

QoS IP Type-of-Service (ToS) Policy and Priority . . . . . . . . . . . . . . . 6-16 Assigning an 802.1p Priority to IPv4 Packets on the Basis

of the ToS Precedence Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17 Assigning an 802.1p Priority to IPv4 Packets on the Basis

of Incoming DSCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18 Assigning a DSCP Policy on the Basis of the DSCP in IPv4 Packets Received from Upstream Devices . . . . . . . . . . . . . . . . . . 6-22 Details of QoS IP Type-of-Service . . . . . . . . . . . . . . . . . . . . . . . . .6-26

QoS Interface (Source-Port) Priority . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29 Assigning a Priority Based on Source-Port . . . . . . . . . . . . . . . . . .6-29

Differentiated Services Codepoint (DSCP) Mapping . . . . . . . . . . . . . 6-32 Default Priority Settings for Selected Codepoints . . . . . . . . . . . . 6-33 Quickly Listing Non-Default Codepoint Settings . . . . . . . . . . . . . 6-34

Note On Changing a Priority Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-35 IP Multicast (IGMP) Interaction with QoS . . . . . . . . . . . . . . . . . . . . . . . . . 6-36 QoS Messages in the CLI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-36 QoS Operating Notes and Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-37

6-1