Configuring Overhead Accounting
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Overhead Accounting

Last Updated: May 17, 2012

Overhead accounting enables the router to account for packet overhead when shaping traffic to a specific rate. This accounting ensures that the router executes quality of service (QoS) features on the actual bandwidth used by subscriber traffic.


Note
Overhead Accounting is not the same as Traffic Shaping Overhead Accounting for ATM, documented here: http://www.cisco.com/en/US/docs/ios/12_2sb/feature/guide/ovrhactg.html

Finding Feature Information

Your software release may not support all the features documented in this module. 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 Table at the end of this document.

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

Restrictions for Overhead Accounting

  • Overhead Accounting values are in bytes.
  • You can set one Overhead Accounting value per policy.
  • Overhead Accounting is supported only for the shape and bandwidth commands.
  • Overhead Accountingis supported only on LAN and WAN interfaces.
  • You can enable overhead accounting for shaping and bandwidth on top-level parent policies, middle-level child policies, and bottom-level child policies.
  • When you enter the show policy-map interface command, the resulting classification byte counts and the queuing feature byte counts do not match. This mismatch occurs because the classification byte count does not consider overhead, whereas the queuing features do consider overhead.

Information About Overhead Accounting

Overhead Accounting factors in packet datagram sizes. The following features use packet datagram size to make decisions in data plane operation; they use Overhead Accounting:

  • Rate-limited priority queue (conditional policer)
  • WRED (random drop)
  • Qlimit (tail drop)
  • Shaping
  • Bandwidth operations

How to Use Overhead Accounting

Overhead Accounting is disabled by default. You set the Overhead Accounting value. Configuring Overhead Accounting on a queue does not change queueing parameters you have already configured.

Enabling Overhead Accounting

SUMMARY STEPS

1.    enable

2.    configure {terminal | memory | network}

3.    policy-map policy-name

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

5.   bandwidth{bandwidth-kbps |percentpercentage|remaining percentpercentage}[account{subscriber-encap} | {user-definedoffset}]

6.    exit

7.    policy-map policy-name

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

9.   shape[average|peak]mean-rate [burst-size] [excess-burst-size]account{subscriber-encapsulation |user-definedoffset}

10.   service-policypolicy-map-name

11.    exit


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Router> enable

 

Enables higher privilege levels, such as privileged EXEC mode.

Enter your password if prompted.

 
Step 2
configure {terminal | memory | network}


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
policy-map policy-name


Example:

Router(config)# policy-map policy1

 

Specifies the name of the policy map created earlier.

Enter policy map name.

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

Example:

Router(config-pmap)# class class1

 

Enters policy-map configuration mode.

 
Step 5
bandwidth{bandwidth-kbps |percentpercentage|remaining percentpercentage}[account{subscriber-encap} | {user-definedoffset}]

Example:

Router(config-pmap-c)# bandwidth percent 20

 

Enables class-based fair queuing and overhead accounting.

 
Step 6
exit


Example:

Router(config-pmap-c)# exit

 

Exits the policy-map class configuration mode.

 
Step 7
policy-map policy-name


Example:

Router(config)# policy-map policy1

 

Specifies the name of the policy map created earlier.

Enter policy map name.

 
Step 8
class{class-name | class-default}

Example:

Router(config-pmap)# class class1

 

Enters policy-map configuration mode.

 
Step 9
shape[average|peak]mean-rate [burst-size] [excess-burst-size]account{subscriber-encapsulation |user-definedoffset}

Example:

Router(config-pmap-c)# shape average 1000000 account user-defined 33

 

Shapes traffic to the indicated bit rate according to the algorithm specified or to enable overhead accounting.

 
Step 10
service-policypolicy-map-name


Example:

Router(config-pmap-c)# service-policy oh-child-bw

 

Applies a child policy to the parent class-default class. Do not specify the input or output keywords when applying a child policy to a parent class-default class.

 
Step 11
exit


Example:

Router(config-pmap-c)# exit

 

Exits the policy-map class configuration mode.

 

Verifying Overhead Accounting

SUMMARY STEPS

1.    enable

  • Enter your password if prompted.

2.   show policy-map[policy-map-name]

  • (Optional) Enter the policy map name. The name can be a maximum of 40 alphanumeric characters.

3.   show policy-map interface

4.   show running-config

5.    exit


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable
  • Enter your password if prompted.


Example:

Router> enable

 

Enables higher privilege levels, such as privileged EXEC mode.

 
Step 2
show policy-map[policy-map-name]
  • (Optional) Enter the policy map name. The name can be a maximum of 40 alphanumeric characters.


Example:

Router# show policy-map unit-test

 

(Optional) Displays the configuration of all classes for a specified policy map or of all classes for all existing policy maps.

 
Step 3
show policy-map interface


Example:

Router# show policy-map serial2/0

 
 (Optional) Displays the statistics and the configurations of the input and output policies that are attached to an interface.  
Step 4
show running-config


Example:

Router# show running-config

 
 (Optional) Displays the contents of the currently running configuration file.  
Step 5
exit


Example:

Router(config-pmap-c)# exit

 

Exits the policy-map class configuration mode.

 

Configuration Examples for Overhead Accounting

This example shows a two-level policy with Overhead Accounting on the parent shaper and a child that has bandwidth configured: 

policy-map oh-child-bw
class oh-child
bandwidth percent 20

policy-map oh1
class class-default
shape average 1000000 account user-defined 33
service-policy oh-child-bw

Additional References

Related Documents

Related Topic Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

Standards and RFCs

Standard/RFC Title

MIBs

MIB MIBs Link

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

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

Technical Assistance

Description Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

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

Feature Information for Overhead Accounting

Feature Name Releases Feature Information
Overhead Accounting 15.2(1)T

Overhead accounting enables the router to account for packet overhead when shaping traffic to a specific rate. This accounting ensures that the router executes quality of service (QoS) features on the actual bandwidth used by subscriber traffic.

The following commands were introduced or modified: shape and bandwidth.

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