Configuring QoS in Cisco IOS

This article explains how to configure QoS in a cisco IOS using MQC. MQC stands for Modular Quality of Service (QoS) Command-Line Interface (CLI).

How MQC Works

• Define a traffic class by using the class-map command. A traffic class is used to classify traffic.
• Create a traffic policy (policy map) by using the policy-map command. A traffic policy (policy map) contains a traffic class and one or more QoS features that will be applied to the traffic class. The QoS features in the traffic policy determine how to process traffic for the given traffic class.
• Attach the traffic policy (policy map) to the interface by using the service-policy command.

Step-1 Defining a Traffic Class

• a traffic class name
• a series of match commands to classifying packets into a traffic class. Available match commands vary for each Cisco IOS release and platform.
• if more than one match command is used in the traffic class, instructions on how to evaluate these match commands, using match-any or match-all. If not specified match-all is default value.

All packets that fail to meet the matching criteria are classified as members of the default traffic class.

class-map [match-all | match-any] class-map-name
match cos cos-number
Enter additional match commands, if applicable; otherwise,issue:
end

 Example configuration:

class-map match-any class1
match cos 2
match destination-address aaaa.bbbb.cccc
end

Step-2 Creating a Traffic Policy

A traffic policy contains three elements:

• a traffic policy name
• a traffic class, specified with the class command
• a command used to enable the QoS feature. QoS feature commands vary by Cisco IOS release and platform. Most used commands include police and shape.

Example configuration:

policy-map policy-map-name
class {class-name | class-default}
bandwidth {bandwidth-kbps | percent percent}
additional QoS feature commands you want to enable, otherwise issue:
end

Example configuration:

policy-map policy1
class class1
bandwidth 3000
end

Remember that traffic policy (policy map) applies the enabled QoS feature to the traffic class only, when you attach the policy map to the interface.

Step-3 Attaching a Traffic Policy to an Interface

The traffic policy (policy map) applies the enabled QoS feature to the traffic class once you attach the policy map to the interface using the service-policy command.
The QoS feature configured in the traffic policy can be applied to packets entering the interface (input) or to packets leaving the interface (output).

interface interface-type interface-number
service-policy {input | output} policy-map-name
end

Example Configuration:

interface serial0
service-policy input policy1
end

MQC Configuration Example

Create two traffic classes:

Router(config)# class-map class1
Router(config-cmap)# match access-group 101
Router(config-cmap)# exit

Router(config)# class-map class2
Router(config-cmap)# match access-group 102
Router(config-cmap)# exit

Create a traffic policy, by appling seperate QoS features on each traffic class:

Router(config)# policy-map policy1
Router(config-pmap)# class class1
Router(config-pmap-c)# bandwidth 3000
Router(config-pmap-c)# queue-limit 30
Router(config-pmap-c)# exit

Router(config-pmap)# class class2
Router(config-pmap-c)# bandwidth 2000
Router(config-pmap-c)# exit

Attaching one traffic policy to multiple interfaces for outgoing and incoming traffic:

Router(config)# interface fastethernet1/1
Router(config-if)# service-policy output policy1
Router(config-if)# exit

Router(config)# interface fastethernet1/0/0
Router(config-if)# service-policy input policy1
Router(config-if)# exit