Table Of Contents
First Published: October 15, 2001Last Updated: March 21, 2011
This document describes the Two-Rate Policer feature and how to configure it. Two-Rate Policer allows you to manage traffic rates through an interface; it is especially helpful in managing network bandwidth where large packets are in the same traffic stream.
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 for Two-Rate Policer" section.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for Two-Rate Policer
•Cisco 2600 series
•Cisco 7100 series
•Cisco 7200 series
•Cisco 7500 series (VIP-based platform only)
Note The set-clp-transmit action available with Two-Rate Policer, the Enhanced ATM Port Adapter (PA-A3) is required. The set-clp-transmit action is not supported on any platform that does not support the PA-A3 adapter (such as the Cisco 2600 series router, the Cisco 3620 router, and the 3640 router). For more information, see the documentation for your specific router.
•On a Cisco 7500 series router, Cisco Express Forwarding or Distributed Cisco Express Forwarding must be configured on the interface before you can use the Two-Rate Policer. For additional information on Cisco Express Forwarding or Distributed Cisco Express Forwarding, see the "Cisco Express Forwarding Features Roadmap" module.
•A traffic class and a service policy must be created, and the service policy must be attached to a specified interface. These tasks are performed using the Modular quality of service (QoS) Command-Line Interface (CLI) (MQC). For information on the MQC, see the "Applying QoS Features Using the MQC" module.
Restrictions for Two-Rate Policer
The following restrictions apply to the Two-Rate Policer feature:
•On a Cisco 7500 series router, traffic policing can monitor Cisco Express Forwarding or Distributed Cisco Express Forwarding switching paths only. Cisco Express Forwarding or Distributed Cisco Express Forwarding must be configured on both the interface receiving the packet and the interface sending the packet.
•On a Cisco 7500 series router, traffic policing cannot be applied to packets that originated from or are destined to a router.
•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 the following interfaces:
–Any interface on a Cisco 7500 series router that does not support Cisco Express Forwarding or Distributed Cisco Express Forwarding
Information About Two-Rate Policer
Networks police traffic by limiting the input or output transmission rate of a class of traffic based on user-defined criteria. Policing traffic allows you to control the maximum rate of traffic sent or received on an interface and to partition a network into multiple priority levels or class of service (CoS).
The Two-Rate Policer 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 IP precedence value, IP differentiated services code point (DSCP) value, Multiprotocol Label Switching (MPLS) experimental value, Quality of Service (QoS) group, ATM Cell Loss Priority (CLP) bit, and the Frame Relay Discard Eligibility (DE) bit.
With the Two-Rate Policer, you can enforce traffic policing according to two separate rates—committed information rate (CIR) and peak information rate (PIR). You can specify the use of these two rates, along with their corresponding values, by using two keywords, cir and pir, of the police command.
The Two-Rate Policer manages the maximum rate of traffic through a token bucket algorithm. The token bucket algorithm can use the user-configured values to determine the maximum rate of traffic allowed on an interface at a given moment in time. The token bucket algorithm is affected by all traffic entering or leaving the interface (depending on the location of the interface on which the Two-Rate Policer is configured) and is useful in managing network bandwidth in cases where several large packets are sent in the same traffic stream.
The token bucket algorithm provides users with three actions for each packet: a conform action, an exceed action, and an optional violate action. Traffic coming into the interface with the Two-Rate Policer configured is assigned one of these categories. Within these three categories, users can decide packet treatments. For instance, packets that conform can be configured to be sent, packets that exceed can be configured to be sent with a decreased priority, and packets that violate can be configured to be dropped.
The Two-Rate Policer is often configured on interfaces at the edge of a network to limit the rate of traffic entering or leaving the network. In the most common configurations, traffic that conforms is sent and traffic that exceeds is sent with a decreased priority or is dropped. Users can change these configuration options to suit their network needs.
Note Two-Rate Policer enables you to use Differentiated Services (DiffServ) Assured Forwarding (AF) Per-Hop Behavior (PHB) traffic conditioning. For more information about DiffServ, see the "Implementing DiffServ for End-to-End Quality of Service Overview" module.
Note Starting with Cisco IOS Release 12.1(5)T, you can police traffic by using the Traffic Policing feature (sometimes referred to as the single-rate policer). The Two-Rate Policer (available with Cisco IOS Release 12.2(4)T) is in addition to the Traffic Policing feature, and it provides additional functionality. For more information about the Traffic Policing feature, see the "Traffic Policing" module.
Bandwidth Management Through Rate Limiting
Two-Rate Policer provides improved bandwidth management through rate limiting. Before this feature was available, you could police traffic with the single-rate Traffic Policing feature. The Traffic Policing feature provided a certain amount of bandwidth management by allowing you to set the peak burst size (be). The Two-Rate Policer supports a higher level of bandwidth management and supports a sustained excess rate. With the Two-Rate Policer, you can enforce traffic policing according to two separate rates—CIR and PIR—specified in bits per second (bps).
Packet Marking Through IP Precedence, DSCP Value, MPLS Experimental Value, and the QoS Group Setting
In addition to rate-limiting, the Two-Rate Policer allows you to independently mark the packet according to whether the packet conforms, exceeds, or violates a specified rate. Packet marking also allows you to partition your network into multiple priority levels or CoSs.
•Use the Two-Rate Policer to set the IP precedence value, the IP DSCP value, or the MPLS experimental value for packets that enter the network. Then networking devices within your network can use this setting to determine how the traffic should be treated. For example, the Weighted Random Early Detection (WRED) feature uses the IP precedence value to determine the probability that a packet will be dropped.
•Use the Two-Rate Policer to assign packets to a QoS group. The router uses the QoS group to determine how to prioritize packets within the router.
If you want to mark traffic but do not want to use the Two-Rate Policer, see the "Marking Network Traffic" module.
Packet Marking for Frame Relay Frames
The Two-Rate Policer 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 that have the DE bit set to 1 are discarded before frames that have the DE bit set to 0.
Packet Marking for ATM Cells
The Two-Rate Policer 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 that have the ATM CLP bit set to 1 are discarded before cells that have the ATM CLP bit set to 0.
How to Use the Two-Rate Policer
See the following sections for tasks using the Two-Rate Policer feature:
•Configuring the Two-Rate Policer (required)
•Verifying the Two-Rate Policer Configuration (optional)
Configuring the Two-Rate Policer
Verifying the Two-Rate Policer Configuration
Router# show policy-map interface
Displays statistics and configurations of all input and output policies attached to an interface.
•Check the interface type. Verify that your interface is not listed as a nonsupported interface in the Restrictions for Two-Rate Policer section of this module.
•For input traffic policing on a Cisco 7500 series router, verify that Cisco Express Forwarding or Distributed Cisco Express Forwarding is configured on the interface on which traffic policing is configured.
•For output traffic policing on a Cisco 7500 series router, ensure that the incoming traffic is Cisco Express Forwarding-switched or Distributed Cisco Express Forwarding-switched. Traffic policing cannot be used on the switching path unless Cisco Express Forwarding or Distributed Cisco Express Forwarding switching is enabled.
Monitoring and Maintaining the Two-Rate Policer
This section provides the following configuration example:
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 policeRouter(config-cmap)# match access-group 101Router(config-cmap)# policy-map policy1Router(config-pmap)# class policeRouter(config-pmap-c)# police cir 500000 bc 10000 pir 1000000 be 10000 conform-action transmit exceed-action set-prec-transmit 2 violate-action dropRouter(config)# interface serial3/0Router(config-if)# service-policy output policy1Router(config-if)# endRouter# show policy-map policy1Policy Map policy1Class policepolice 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.Router# show policy-map interface serial3/0Serial3/0Service-policy output: policy1Class-map: police (match all)148803 packets, 36605538 bytes30 second offered rate 1249000 bps, drop rate 249000 bpsMatch: access-group 101police:cir 500000 bps, conform-burst 10000, pir 1000000, peak-burst 100000conformed 59538 packets, 14646348 bytes; action: transmitexceeded 59538 packets, 14646348 bytes; action: set-prec-transmit 2violated 29731 packets, 7313826 bytes; action: dropconformed 499000 bps, exceed 500000 bps violate 249000 bpsClass-map: class-default (match-any)19 packets, 1990 bytes30 seconds offered rate 0 bps, drop rate 0 bpsMatch: any
The following sections provide references related to the Two-Rate Policer feature.
Related Topic Document Title
QoS features such as class-based weighted fair queueing (CBWFQ), traffic marking, and traffic policing
•"Marking Network Traffic" module
•"Traffic Policing" module
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
MIB MIBs Link
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
Feature Information for Two-Rate Policer
Table 1 lists the features in this module and provides links to specific configuration information.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which 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 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.
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