Regulating Packet Flow Using Class-Based Traffic Shaping

First Published: February 25, 2002
Last Updated: March 2, 2009

Packet flow on a network can be regulated using a traffic-shaping mechanism. One such traffic-shaping mechanism is a Cisco feature called class-based traffic shaping. Class-based traffic shaping allows you to regulate the flow of packets (on a per-traffic-class basis) going out an interface, matching the packet flow to the speed of the interface. This module describes the concepts and tasks related to configuring class-based traffic shaping.

Finding Feature Information

For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Class-Based Traffic Shaping" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE Software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for Configuring Class-Based Traffic Shaping

•Restrictions for Configuring Class-Based Traffic Shaping

•Information About Class-Based Traffic Shaping

•How to Configure Class-Based Traffic Shaping

•Configuration Examples for Class-Based Traffic Shaping

•Additional References

•Feature Information for Class-Based Traffic Shaping

Prerequisites for Configuring Class-Based Traffic Shaping

A policy map and a class map must be created first using the Modular Quality of Service (QoS) Command-Line Interface (MQC).

Restrictions for Configuring Class-Based Traffic Shaping

Class-based traffic shaping applies to outbound traffic only.

Class-based traffic shaping does not support the following commands:

•traffic-shape adaptive

•traffic shape fecn-adaptive

•traffic-shape group

•traffic-shape rate

Information About Class-Based Traffic Shaping

Class-Based Traffic-Shaping Functionality

Class-based traffic shaping is a traffic-shaping mechanism (also known as a "traffic shaper"). A traffic shaper typically delays excess traffic using a buffer, or queueing mechanism, to hold packets and shape the flow when the data rate of the source is higher than expected. It holds and shapes traffic to a particular bit rate by using the token bucket mechanism.

Class-based traffic shaping is the Cisco-recommended traffic-shaping mechanism.

Using class-based traffic shaping, you can perform the following tasks:

•Configure traffic shaping on a per-traffic-class basis. It allows you to fine-tune traffic shaping for one or more classes, and it allows you to configure traffic shaping on a more granular level.

•Specify average rate or peak rate traffic shaping. Specifying peak rate shaping allows you to make better use of available bandwidth by allowing more data than the configured traffic shaping rate to be sent if the bandwidth is available.

•Configure traffic shaping in a hierarchical policy map structure. That is, traffic shaping is configured in a primary-level (parent) policy map, and other QoS features (for instance, CBWFQ and traffic policing) can be configured in the secondary-level (child) policy maps.

Benefits of Class-Based Traffic Shaping

All of the benefits associated with traffic shaping also apply to class-based traffic shaping, but on a more granular level.

Hierarchical Policy Map Structure of Class-Based Traffic Shaping

With the class-based traffic shaping mechanism, traffic shaping can be configured in a hierarchical policy map structure; that is, traffic shaping is enabled in a primary-level (parent) policy map and other QoS features used with traffic shaping, such as class-based WFQ (CBWFQ) and traffic policing, can be enabled in a secondary-level (child) policy map. Traffic shaping is enabled by using the shape command (and specifying a rate) in a policy map.

CBWFQ allows you to fine-tune the way traffic is placed in a queue. For instance, you can specify that all voice traffic be placed in a high-priority queue and all traffic from a specific class be placed in a lower-priority queue.

If you want to use CBWFQ with the class-based traffic shaping mechanism a secondary-level (child) policy map must be created. This secondary-level (child) policy map is then used to configure CBWFQ by enabling the bandwidth command.

The following sample configuration illustrates how the class-based traffic shaping mechanism is configured in a hierarchical policy map structure: 

enable

configure terminal

 policy-map policy_parent        ! This is the primary-level policy map.

  class class-default

   shape average 1000000         ! This enables traffic shaping.

   service-policy policy_child   ! This associates the policy maps.

With this configuration, WFQ is used as the default queueing mechanism for placing all the traffic in a queue.

In the following secondary-level (child) policy map, the alternative queueing mechanism CBWFQ is configured: 

enable

configure terminal

 policy-map policy_child     ! This is the secondary-level policy map.

  class class-default

   bandwidth percent 50      ! This enables CBWFQ.

How to Configure Class-Based Traffic Shaping

Traffic shaping is configured in a policy map. Policy maps determine the specific quality of service (QoS) feature that will be applied to traffic on a network. In this module, the QoS feature being applied is traffic shaping.Traffic shaping is configured in the primary-level (parent) policy map in the hierarchy.

In the secondary-level (child) policy map, additional QoS features used with traffic shaping (for example, CBWFQ and traffic policing) are typically configured.

Configuring Class-Based Traffic Shaping in a Primary-Level (Parent) Policy Map

Prerequisites

Before configuring traffic shaping, you must use the MQC to create a policy map and a class map.

SUMMARY STEPS

1. enable

2. configure terminal

3. policy-map policy-map-name

4. class {class-name | class-default}

5. shape [average | peak] mean-rate [[burst-size] [excess-burst-size]]

6. service-policy policy-map-name

7. end

8. show policy-map

9. show policy-map interface type number

10. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

policy-map policy-map-name

Example:

Router(config)# policy-map policy_parent

Specifies the name of the policy map created earlier and enters policy-map configuration mode. See the "Prerequisites" section for more information.

•Enter the policy map name.

Step 4 

class {class-name | class-default}

Example:

Router(config-pmap)# class class-default

Specifies the name of the class whose policy you want to create and enters policy-map class configuration mode.

•Enter the name of the class or enter the class-default keyword.

Step 5 

shape [average | peak] mean-rate [burst-size] [excess-burst-size]

Example:

Router(config-pmap-c)# shape average 1000000

Shapes traffic according to the keyword and rate specified.

•Enter the keyword and rate.

Step 6 

service-policy policy-map-name

Example:

Router(config-pmap-c)# service-policy policy_child

Uses a service policy as a QoS policy within a policy map (called a hierarchical service policy).

•Enter the policy map name.

Step 7 

end

Example:

Router(config-pmap-c)# end

Returns to privileged EXEC mode.

Step 8 

show policy-map

Example:

Router# show policy-map

(Optional) Displays all configured policy maps.

Step 9 

show policy-map interface type number

Example:

Router# show policy-map interface serial4/0/0

(Optional) Displays the packet statistics of all classes that are configured for all service policies either on the specified interface or subinterface or on a specific PVC on the interface.

•Enter the interface type and number.

Step 10 

exit

Example:

Router# exit

(Optional) Exits privileged EXEC mode.

What to Do Next

So far, you have configured class-based Traffic Shaping in a primary-level (parent) policy map. To configure a secondary-level (child) policy map in the hierarchical policy map structure (an optional task), proceed with the instructions in "Configuring the Secondary-Level (Child) Policy Map" section.

Configuring the Secondary-Level (Child) Policy Map

SUMMARY STEPS

1. enable

2. configure terminal

3. policy-map policy-map-name

4. class {class-name | class-default}

5. bandwidth {bandwidth-kbps | remaining percent percentage | percent percentage}

6. end

7. show policy-map

8. show policy-map interface type number

9. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

policy-map policy-map-name

Example:

Router(config)# policy-map policy1

Specifies the name of the policy map created earlier and enters policy-map configuration mode. See the "Prerequisites" section for more information.

•Enter the policy map name.

Step 4 

class {class-name | class-default}

Example:

Router(config-pmap)# class class-default

Specifies the name of the class whose policy you want to create and enters policy-map class configuration mode.

•Enter the name of the class or enter the class-default keyword.

Step 5 

bandwidth {bandwidth-kbps | remaining percent percentage | percent percentage}

Example:

Router(config-pmap-c)# bandwidth percent 50


Specifies or modifies the bandwidth allocated for a class belonging to a policy map.

•Enter the amount of bandwidth as a number of kbps, a relative percentage of bandwidth, or an absolute amount of bandwidth.

Note The bandwidth command used here is only an example of a QoS feature than can be configured. The bandwidth command configures CBWFQ. You could also use the police command to configure traffic policing.

Step 6 

end

Example:

Router(config-pmap-c)# end

Returns to privileged EXEC mode.

Step 7 

show policy-map

Example:

Router# show policy-map

(Optional) Displays all configured policy maps.

Step 8 

show policy-map interface type number

Example:

Router# show policy-map interface serial4/0/0

(Optional) Displays the packet statistics of all classes that are configured for all service policies either on the specified interface or subinterface or on a specific PVC on the interface.

•Enter the interface type and number.

Step 9 

exit

Example:

Router# exit

(Optional) Exits privileged EXEC mode.

Configuration Examples for Class-Based Traffic Shaping

Example: Class-Based Traffic Shaping Configuration

The following is an example of class-based Traffic Shaping configured in a hierarchical policy map structure. In this example, two policy maps have been created; the primary-level (parent) policy map called "policy_parent," and a secondary-level (child) policy map called "policy_child." Traffic shaping is configured in the policy_parent policy map, and CBWFQ has been configured in the policy_child policy map.

The service-policy command associates the two policy maps in the hierarchical policy map structure. 

enable

configure terminal

 policy-map policy_parent 

  class class-default

   shape average 1000000         ! This enables traffic shaping.

   service-policy policy_child   ! This associates the policy maps.

   exit 

  exit 

 policy-map policy_child

  class class-default

   bandwidth percent 50   ! This enables CBWFQ.

   end

Additional References

Related Documents

Related Topic
Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

QoS commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples

Cisco IOS Quality of Service Solutions Command Reference

Packet classification

"Classifying Network Traffic" module

MQC, policy maps, class maps, and hierarchical policy maps

"Applying QoS Features Using the MQC" module

Overview of using traffic shaping to regulate packet flow on a network

"Regulating Packet Flow Using Traffic Shaping" module


Standards

Standard
Title

No new or modified standards are supported, and support for existing standards has not been modified.

—


MIBs

MIB
MIBs Link

No new or modified MIBs are supported, and support for existing MIBs has not been modified.

To locate and download MIBs for selected platforms, Cisco IOS XE Software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFC
Title

No new or modified RFCs are supported, and support for existing RFCs has not been modified.

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Technical Assistance

Description
Link

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http://www.cisco.com/cisco/web/support/index.html


Feature Information for Class-Based Traffic Shaping

Table 1 lists the features in this module.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE Software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS XE Software release that introduced support for a given feature in a given Cisco IOS XE Software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE Software release train also support that feature.

.

Table 1 Feature Information for Class-Based Traffic Shaping

Feature Name
Software Releases
Feature Configuration Information

Class-Based Shaping

Cisco IOS XE Release 2.1

This feature was introduced on Cisco ASR 1000 Series Aggregation Services Routers.

The following sections provide information about this feature:

•Information About Class-Based Traffic Shaping

•How to Configure Class-Based Traffic Shaping

Hierarchical Traffic Shaping

Cisco IOS XE Release 2.1

This feature was introduced on Cisco ASR 1000 Series Aggregation Services Routers.

The following sections provide information about this feature:

•Hierarchical Policy Map Structure of Class-Based Traffic Shaping

•How to Configure Class-Based Traffic Shaping


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