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5-1
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 . . . . . . . . . . . 5-33
Default Priority Settings for Selected Codepoints . . . . . . . . . . . . . . . 5-34
Quickly Listing Non-Default Codepoint Settings . . . . . . . . . . . . . 5-34
Notes on Changing a Priority Setting . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36