Traffic Policing

This feature module describes the Traffic Policing feature. The Traffic Policing feature performs the following functions:

  • Limits the input or output transmission rate of a class of traffic based on user-defined criteria.

  • Marks packets by setting the ATM Cell Loss Priority (CLP) bit, Frame Relay Discard Eligibility (DE) bit, IP precedence value, IP differentiated services code point (DSCP) value, MPLS experimental value, and Quality of Service (QoS) group.

Traffic policing allows you to control the maximum rate of traffic that is transmitted or received on an interface. The Traffic Policing feature is applied when a service-policy containing the feature is attached to an interface. A service-policy (traffic policy) is configured using the Modular Quality of Service (QoS) Command-Line Interface (CLI) (MQC).

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 module.

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 Traffic Policing

  • Traffic policing can be configured on an interface or a subinterface.

  • Traffic policing is not supported on the EtherChannel interfaces.

Benefits

Bandwidth Management Through Rate Limiting

Traffic policing allows you to control the maximum rate of traffic transmitted or received on an interface. Traffic policing is often configured on interfaces at the edge of a network to limit traffic into or out of the network. In most Traffic Policing configurations, traffic that falls within the rate parameters is transmitted, whereas traffic that exceeds the parameters is dropped or transmitted with a different priority.

Packet Marking

Packet marking allows you to partition your network into multiple priority levels or classes of service (CoS). A packet is marked and these markings can be used to identify and classify traffic for downstream devices. In some cases, such as ATM Cell Loss Priority (CLP) marking or Frame Relay Discard Eligibility (DE) marking, the marking is used to classify traffic.

  • Use traffic policing to set the IP precedence or DSCP values for packets entering the network. Networking devices within your network can then use the adjusted IP precedence values to determine how the traffic should be treated. For example, the Weighted Random Early Detection (WRED) feature uses the IP precedence values to determine the probability that a packet will be dropped.

  • Use traffic policing to assign packets to a QoS group. The router uses the QoS group to determine how to prioritize packets within the router.

Traffic can be marked without using the Traffic Policing feature. If you want to mark traffic but do not want to use Traffic Policing, see the "Marking Network Traffic" module.

Packet Prioritization for Frame Relay Frames

The Traffic Policing feature allows users to mark the Frame Relay DE bit of the Frame Relay frame. The Frame Relay DE bit is one bit and, therefore, can be set to either 0 or 1. In congested environments, frames with the DE bit set to 1 are discarded before frames with the DE bit set to 0.

Packet Prioritization for ATM Cells

The Traffic Policing feature allows users to mark the ATM CLP bit in ATM cells. The ATM CLP bit is used to prioritize packets in ATM networks. The ATM CLP bit is one bit and, therefore, can be set to either 0 or 1. In congested environments, cells with the ATM CLP bit set to 1 are discarded before cells with the ATM CLP bit set to 0.

How to Configure Traffic Policing

Configuring Traffic Policing

Command

Purpose

Router(config-pmap-c)# police bps burst-normal burst-max conform-action action exceed-action action violate-action action

Specifies a maximum bandwidth usage by a traffic class.

Note 

The Traffic Policing feature works with a token bucket mechanism. There are currently two types of token bucket algorithms: a single token bucket algorithm and a two token bucket algorithm. A single token bucket system is used when the violate-action option is not specified, and a two token bucket system is used when the violate-action option is specified.

Monitoring and Maintaining Traffic Policing

Command

Purpose

Router# show policy-map

Displays all configured policy maps.

Router# show policy-map policy-map-name

Displays the user-specified policy map.

Router# show policy-map interface

Displays statistics and configurations of all input and output policies that are attached to an interface.

Configuration Examples for Traffic Policing

Example Configuring a Service Policy That Includes Traffic Policing

The following configuration shows how to define a traffic class (with the class-map command) and associate that traffic class with a traffic policy (with the policy-map command). Traffic policing is applied in the traffic policy. The service-policy command is then used to attach the traffic policy to the interface.

In this particular example, traffic policing is configured with the Committed Information Rate (CIR) at 8000 bits per second, the normal burst size at 2000 bytes, and the excess burst size at 4000 bytes. Packets coming into FastEthernet interface 1/1/1 are evaluated by the token bucket algorithm to analyze whether packets conform exceed, or violate the specified parameters. Packets that conform are transmitted, packets that exceed are assigned a QoS group value of 4 and are transmitted, and packets that violate are dropped. 


Router(config)# class-map acgroup2
Router(config-cmap)# match access-group 2
Router(config-cmap)# exit
Router(config)# policy-map police
Router(config-pmap)# class acgroup2
Router(config-pmap-c)# police 8000 2000 4000 conform-action transmit exceed-action set-qos-transmit 4 violate-action drop
Router(config-pmap-c)# exit
Router(config-pmap)# exit
Router(config)# interface fastethernet1/1/1
Router(config-if)# service-policy input police
Router(config-if)# end

Additional References

Related Documents

Related Topic

Document Title

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

Cisco IOS Quality of Service Solutions Command Reference

Conceptual information about policing and shaping

"Policing and Shaping Overview" module

MQC

"Applying QoS Features Using the MQC" module

Marking network traffic

"Marking Network Traffic" module

IPv6 Traffic Policing

“IPv6 QoS: MQC Traffic Policing” module in the QoS: Policing and Shaping Configuration Guide.

Standards

Standard

Title

None

--

MIBs

MIB

MIBs Link

  • CISCO-CLASS-BASED-QOS-MIB

  • CISCO-CLASS-BASED-QOS-CAPABILITY-MIB

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

RFC 2697

A Single Rate Three Color Marker

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 Traffic Policing

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

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.
Table 1. Feature Information for Traffic Policing

Feature Name

Releases

Feature Information

Traffic Policing

Cisco IOS XE Release 2.1

This feature was introduced on Cisco ASR 1000 Series Routers.

The following commands were modified: police , show policy-map , show policy-map interface .