Two-Rate Policer

This module describes the Two-Rate Policer feature and explains how to configure it.

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Feature Overview

When configured, an ATM switch at the network side of a user-to-network (UNI) interface polices the flow of cells in the forward (into the network) direction of a virtual connection. These traffic policing mechanisms are known as usage parameter control (UPC). With UPC, the switch determines whether received cells comply with the negotiated traffic management values and takes one of the following actions on violating cells:

  • Pass the cell without changing the cell loss priority (CLP) bit in the cell header.

  • Tag the cell with a CLP bit value of 1.

  • Drop (discard) the cell.

The SVC/SoftPVC feature enables you to specify which traffic to police, based on service category, on switched virtual circuits (SVCs) or terminating VCs on the destination end of a soft VC.

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.

Restrictions for Two-Rate Policing

The following restrictions apply to the Two-Rate Policer:

  • Two-rate policing can be configured on an interface, a subinterface, a Frame Relay data-link connection identifier (DLCI), and an ATM permanent virtual circuit (PVC).

  • Two-rate policing is not supported on EtherChannel or tunnel interfaces.

Prerequisites for Two-Rate Traffic Policing

To configure the Two-Rate Policer, a traffic class and a service policy must be created, and the service policy must be attached to a specified interface.

Configuration Tasks

See the following sections for configuration tasks for the Two-Rate Policer feature.

Configuring the Two-Rate Policer

Command

Purpose 


Router(config-pmap-c)# 
police cir  
cir [bc conform-burst
] pir  pir
 
[be peak-burst
] 
[conform-action  action  
[exceed-action  action  
[violate-action   action ]]]

Specifies that both the CIR and the PIR are to be used for two-rate traffic policing, and specifies multiple actions applied to packets marked as conforming to, exceeding, or violating a specific rate. Use one line per action that you want to specify. Enters policy-map class police configuration mode.

The bc and be keywords and their associated arguments (conform-burst and peak-burst , respectively) are optional.

Although not required for configuring the Two-Rate Policer, the command syntax of the police command also allows you to specify the action to be taken on a packet when you enable an optional action argument. The resulting action corresponding to the keyword choices are listed in Table 1 .

Table 1. police Command Action Keywords

Keyword

Resulting Action

drop

Drops the packet.

set-clp-transmit

Sets the ATM CLP bit from 0 to 1 on the ATM cell and sends the packet with the ATM CLP bit set to 1.

set-dscp-transmit new-dscp

Sets the IP DSCP value and sends the packet with the new IP DSCP value setting.

set-frde-transmit

Sets the Frame Relay DE bit from 0 to 1 on the Frame Relay frame and sends the packet with the DE bit set to 1.

set-mpls-exp-transmit

Sets the MPLS experimental bits from 0 to 7 and sends the packet with the new MPLS experimental bit value setting.

set-prec-transmit new-prec

Sets the IP precedence and sends the packet with the new IP precedence value setting.

set-qos-transmit new-qos

Sets the QoS group value and sends the packet with the new QoS group value setting.

transmit

Sends the packet with no alteration.

Verifying the Two-Rate Policer Configuration

Command

Purpose 


Router#
 
show   policy-map interface

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

Troubleshooting Tips

Monitoring and Maintaining the Two-Rate Policer

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

Example Limiting the Traffic Using a Policer Class

In this example, the Two-Rate Policer is configured on a class to limit traffic to an average committed rate of 500 kbps and a peak rate of 1 Mbps. 


Router(config)# class-map police
Router(config-cmap)# match access-group 101
Router(config-cmap)# policy-map policy1
Router(config-pmap)# class police
Router(config-pmap-c)# police cir 500000 bc 10000 pir 1000000 be 10000 conform-action
 transmit exceed-action set-prec-transmit 2 violate-action drop
Router(config)# interface serial3/0/0
Router(config-if)# service-policy output policy1
Router(config-if)# end
Router# show policy-map policy1
 Policy Map policy1
  Class police
   police cir 500000 conform-burst 10000 pir 1000000 peak-burst 10000 conform-action transmit exceed-action set-prec-transmit 2 violate-action drop

Traffic marked as conforming to the average committed rate (500 kbps) will be sent as is. Traffic marked as exceeding 500 kbps, but not exceeding 1 Mbps, will be marked with IP Precedence 2 and then sent. All traffic exceeding 1 Mbps will be dropped. The burst parameters are set to 10,000 bytes.

In the following example, 1.25 Mbps of traffic is sent ("offered") to a policer class. 


Router# show policy-map interface serial3/0/0
 Serial3/0/0
  Service-policy output: policy1
   Class-map: police (match all)
    148803 packets, 36605538 bytes
    30 second offered rate 1249000 bps, drop rate 249000 bps
    Match: access-group 101
    police:
     cir 500000 bps, conform-burst 10000, pir 1000000, peak-burst 100000
     conformed 59538 packets, 14646348 bytes; action: transmit
     exceeded 59538 packets, 14646348 bytes; action: set-prec-transmit 2
     violated 29731 packets, 7313826 bytes; action: drop
     conformed 499000 bps, exceed 500000 bps violate 249000 bps
   Class-map: class-default (match-any)
    19 packets, 1990 bytes
    30 seconds offered rate 0 bps, drop rate 0 bps
    Match: any

The Two-Rate Policer marks 500 kbps of traffic as conforming, 500 kbps of traffic as exceeding, and 250 kbps of traffic as violating the specified rate. Packets marked as conforming will be sent as is, and packets marked as exceeding will be marked with IP Precedence 2 and then sent. Packets marked as violating the specified rate are dropped.

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

Token bucket mechanisms

"Policing and Shaping Overview" module

MQC

"Applying QoS Features Using the MQC" module

QoS features such traffic marking, and traffic policing

  • "Marking Network Traffic" module

  • "Traffic Policing" module

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 2698

A Two Rate Three Color Marker

Technical Assistance

Description

Link

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

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Feature Information for Two-Rate Policer

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 2. Feature Information for Two-Rate Policer