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Configuring QoS
Understanding QoS
Packet classification organizes traffic on the basis of whether or not the traffic matches a specific criteria. When a
packet is received, the switch identifies all key packet fields: class of service (CoS), Differentiated Services Code
Point (DSCP), or IP precedence. The switch classifies the packet based on this content or based on an
access-control list lookup. For more information, see
Packet policing determines whether a packet is in or out of profile by comparing the rate of the incoming traffic to
the configured policer. You can control the traffic flow for packets that conform to or exceed the configured policer.
You can configure a committed information rate (CIR) and peak information rate (PIR) and set actions to perform on
packets that conform to the CIR and PIR (conform-action), packets that conform to the PIR, but not the CIR
(exceed-action), and packets that exceed the PIR value (violate-action). For more information, see
page
584.
Packet prioritization or marking evaluates the classification and policer information to determine the action to take.
All packets that belong to a classification can be remarked. When you configure a policer, packets that meet or
exceed the permitted bandwidth requirements (bits per second) can be conditionally passed through, dropped, or
reclassified. For more information, see
Congestion management uses queuing and scheduling algorithms to queue and sort traffic that is leaving a port. The
switch supports these scheduling and traffic-limiting features: class-based weighted fair queuing (CBWFQ),
class-based traffic shaping, port shaping, and class-based priority queuing. You can provide guaranteed bandwidth
to a particular class of traffic while still servicing other traffic queues. For more information, see
Management and Scheduling, page
Queuing on the switch is enhanced with the weighted tail-drop (WTD) algorithm, a congestion-avoidance
mechanism. WTD differentiates traffic classes and regulates the queue size (in number of packets) based on the
classification. For more information, see
This section includes information about these topics:
Modular QoS CLI, page 572
Input and Output Policies, page 573
Classification, page 575
Table Maps, page 583
Policing, page 584
Marking, page 589
Congestion Management and Scheduling, page 593
Congestion Avoidance and Queuing, page 597
Modular QoS CLI
Modular QoS CLI (MQC) allows users to create traffic policies and attach these policies to interfaces. A traffic policy
contains a traffic class and one or more QoS features. You use a traffic class to classify traffic, and the QoS features in
the traffic policy determine how to treat the classified traffic.
Modular QoS CLI configuration includes these steps:
1.
Define a traffic class.
Use the class-map [match-all | match-any] class-map-name global configuration command to define a traffic class
and to enter class-map configuration mode. A traffic class contains three elements: a name, an instruction on how to
evaluate the configured match commands (if more than one match command is configured in the class map), and a
series of match commands
You name the traffic class in the class-map command line to enter class-map configuration mode.
Classification, page
Marking, page
589.
593.
Congestion Avoidance and Queuing, page
572
575.
Policing,
Congestion
597.
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