QoS: Policing and Shaping Configuration Guide, Cisco IOS XE Release 3S
Class-Based Policing
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Class-Based Policing

Class-Based Policing

Class-based policing allows you to control the maximum rate of traffic that is transmitted or received on an interface. Class-based policing is often configured on interfaces at the edge of a network to limit traffic into or out of the network.

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.

Information About Class-Based Policing

Class-Based Policing Functionality

The Class-Based 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.

Class-based policing allows you to control the maximum rate of traffic transmitted or received on an interface. The Class-Based Policing feature is applied when you attach a traffic policy that contains the class-based policing configuration to an interface.

The Class-Based 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.

Benefits of Class-Based Policing

Bandwidth Management Through Rate Limiting

Class-based policing allows you to control the maximum rate of traffic transmitted or received on an interface. Class-based policing is often configured on interfaces at the edge of a network to limit traffic into or out of the network. In most class-based 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.

  • Use class-based 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.

  • Use class-based policing to assign packets to a QoS group. The router uses the QoS group to determine how to prioritize packets.

Traffic can be marked without using the Class-Based Policing feature. If you want to mark traffic but do not want to use class-based policing, see the “Marking Network Traffic” module.

Restrictions for Class-Based Policing

Class-based policing can be configured on an interface or a subinterface, but it is not supported on EtherChannel or tunnel interfaces.

Restrictions for the Cisco ASR 903 Router

  • Class-based policing on subinterfaces is not supported.

  • Policing is supported for ingress policy maps only.

  • Hierarchical policing (policing at both parent level and child level) is not supported.

How to Configure Class-Based Policing

Configuring a Traffic Policing Service Policy

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    class-map [match-all | match-any] class-map-name

    4.    match ip precedence precedence-value

    5.    exit

    6.    policy-map policy-map-name

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

    8.    police bps burst-normal burst-max conform-action action exceed-action action violate-action action

    9.    exit

    10.    exit

    11.    interface interface-type interface-number

    12.    service-policy {input | output} policy-map-name

    13.    end


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


    Example:
    Router# configure terminal
     

    Enters global configuration mode.

     
    Step 3 class-map [match-all | match-any] class-map-name


    Example:
    Router(config)# class-map match-any MATCH_PREC 
     

    Specifies the name of the class map to be created and enters QoS class map configuration mode.

    • The class map defines the criteria to use to differentiate the traffic. For example, you can use the class map to differentiate voice traffic from data traffic, based on a series of match criteria defined using the match command.

    Note   

    If the match-all or match-any keyword is not specified, traffic must match all the match criteria to be classified as part of the traffic class.

     
    Step 4 match ip precedence precedence-value


    Example:
    Router(config-cmap)# match ip precedence 0
     

    Enables packet matching on the basis of the IP precedence values you specify.

    Note   

    You can enter up to four matching criteria, as number abbreviation (0 to 7) or criteria names (critical, flash, and so on), in a single match statement.

     
    Step 5 exit


    Example:
    Router(config-cmap)# exit
     

    Returns to global configuration mode.

     
    Step 6 policy-map policy-map-name


    Example:
    Router(config)# policy-map POLICE-SETTING
     

    Creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy, and enters QoS policy-map configuration mode.

     
    Step 7 class {class-name | class-default}


    Example:
    Router(config-pmap)# class MATCH_PREC
     

    Specifies the name of the class whose policy you want to create or change or specifies the default class (commonly known as the class-default class) before you configure its policy, and enters policy-map class configuration mode.

     
    Step 8 police bps burst-normal burst-max conform-action action exceed-action action violate-action action


    Example:
    Router(config-pmap-c)# police 8000 1000 1000 conform-action transmit exceed-action set-qos-transmit 1 violate-action drop
     

    Configures traffic policing according to burst sizes and any optional actions specified.

     
    Step 9 exit


    Example:
    Router(config-pmap-c)# exit 
     

    (Optional) Exits policy-map class configuration mode.

     
    Step 10 exit


    Example:
    Router(config-pmap)# exit 
     

    (Optional) Exits QoS policy-map configuration mode.

     
    Step 11 interface interface-type interface-number


    Example:
    Router(config)# interface GigabitEthernet 0/0/1
     

    Configures an interface type and enters interface configuration mode.

    • Enter the interface type and interface number.

     
    Step 12 service-policy {input | output} policy-map-name


    Example:
    Router(config-if)# service-policy input POLICE-SETTING 
     

    Attaches a policy map to an interface.

    • Enter either the input or output keyword and the policy map name.

     
    Step 13 end


    Example:
    Router(config-if)# end
     

    (Optional) Exits interface configuration mode and returns to privileged EXEC mode.

     

    Monitoring and Maintaining Traffic Policing

    Before You Begin

    Note



    SUMMARY STEPS

      1.    enable

      2.    show policy-map

      3.    show policy-map policy-map-name

      4.    show policy-map interface


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Router> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.

       
      Step 2 show policy-map


      Example:
      Router# show policy-map
       

      Displays all configured policy maps.

       
      Step 3 show policy-map policy-map-name


      Example:
      Router# show policy-map pmap
       

      Displays the user-specified policy map.

       
      Step 4 show policy-map interface


      Example:
      Router# show policy-map interface
       
      Verifies that the Class-Based Policing feature is configured on your interface. If the feature is configured on your interface.
      • The command output displays policing statistics.

       

      Verifying Class-Based Traffic Policing

      Use the show policy-map interface command to verify that the Class-Based Policing feature is configured on your interface. If the feature is configured on your interface, the show policy-map interface command output displays policing statistics.

      SUMMARY STEPS

        1.    enable

        2.    show policy-map interface

        3.    show policy-map interface type interface

        4.    show policy-map interface type interface service instance service-instance number

        5.    exit


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Router> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.

         
        Step 2 show policy-map interface


        Example:
        Router# show policy-map interface
         
        Verifies that the Class-Based Policing feature is configured on your interface. If the feature is configured on your interface.
        • The command output displays policing statistics.

         
        Step 3 show policy-map interface type interface


        Example:
        Router# show policy-map interface GigabitEthernet 0/0/1
         

        Displays traffic statistics for policies applied to a specific interface.

         
        Step 4 show policy-map interface type interface service instance service-instance number


        Example:
        Router# show policy-map interface GigabitEthernet 0/0/1 service instance 1
        
         

        Displays the policy map information for a given service instance under a port channel.

         
        Step 5 exit


        Example:
        Router# exit
         

        (Optional) Exits privileged EXEC mode.

         

        Example: Verifying Class-Based Traffic Policing

        Router# show policy-map interface
          FastEthernet1/1/1
          service-policy output: x
            class-map: a (match-all)
              0 packets, 0 bytes
              5 minute rate 0 bps
              match: ip precedence 0
              police:
                1000000 bps, 10000 limit, 10000 extended limit
                conformed 0 packets, 0 bytes; action: transmit
                exceeded 0 packets, 0 bytes; action: drop
                conformed 0 bps, exceed 0 bps, violate 0 bps

        Troubleshooting Tips

        Check the interface type. Verify that class-based policing is supported on your interface. See the Restrictions for Class-Based Policing.

        Configuration Examples for Class-Based Policing

        Example Configuring a Service Policy That Includes Traffic Policing

        In the following example, class-based policing is configured with the average rate at 8000 bits per second, the normal burst size at 1000 bytes, and the excess burst size at 1000 bytes for all packets leaving the interface.

        class-map access-match
         match access-group 1
         exit
        policy-map police-setting
         class access-match
          police 8000 1000 1000 conform-action transmit exceed-action set-qos-transmit 1   violate-action drop
          exit
         exit
         service-policy output police-setting
        

        The treatment of a series of packets leaving FastEthernet interface 1/1/1 depends on the size of the packet and the number of bytes remaining in the conform and exceed token buckets. The series of packets are policed based on the following rules:

        • If the previous arrival of the packet was at T1 and the current arrival of the packet is at T, the bucket is updated with T - T1 worth of bits based on the token arrival rate. The refill tokens are placed in the conform bucket. If the tokens overflow the conform bucket, the overflow tokens are placed in the exceed bucket. The token arrival rate is calculated as follows:

        (time between packets < which is equal to T - T1 > * policer rate)/8 bytes

        • If the number of bytes in the conform bucket is greater than the length of the packet (for example, B), then the packet conforms and B bytes should be removed from the bucket. If the packet conforms, B bytes are removed from the conform bucket and the conform action is taken. The exceed bucket is unaffected in this scenario.

        • If the number of bytes in the conform bucket is less than the length of the packet, but the number of bytes in the exceed bucket is greater than the length of the packet (for example, B), the packet exceeds and B bytes are removed from the bucket.

        • If the number bytes in the exceed bucket B is fewer than 0, the packet violates the rate and the violate action is taken. The action is complete for the packet.

        In this example, the initial token buckets starts full at 1000 bytes. If a 450-byte packet arrives, the packet conforms because enough bytes are available in the conform token bucket. The conform action (send) is taken by the packet, and 450 bytes are removed from the conform token bucket (leaving 550 bytes).

        If the next packet arrives 0.25 seconds later, 250 bytes are added to the conform token bucket ((0.25 * 8000)/8), leaving 800 bytes in the conform token bucket. If the next packet is 900 bytes, the packet does not conform because only 800 bytes are available in the conform token bucket.

        The exceed token bucket, which starts full at 1000 bytes (as specified by the excess burst size, is then checked for available bytes. Because enough bytes are available in the exceed token bucket, the exceed action (set the QoS transmit value of 1) is taken, and 900 bytes are taken from the exceed bucket (leaving 100 bytes in the exceed token bucket).

        If the next packet arrives 0.40 seconds later, 400 bytes are added to the token buckets ((.40 * 8000)/8). Therefore, the conform token bucket now has 1000 bytes (the maximum number of tokens available in the conform bucket, and 200 bytes overflow the conform token bucket (because only 200 bytes were needed to fill the conform token bucket to capacity). These overflow bytes are placed in the exceed token bucket, giving the exceed token bucket 300 bytes.

        If the arriving packet is 1000 bytes, the packet conforms because enough bytes are available in the conform token bucket. The conform action (transmit) is taken by the packet, and 1000 bytes are removed from the conform token bucket (leaving 0 bytes).

        If the next packet arrives 0.20 seconds later, 200 bytes are added to the token bucket ((.20 * 8000)/8). Therefore, the conform bucket now has 200 bytes. If the arriving packet is 400 bytes, the packet does not conform because only 200 bytes are available in the conform bucket. Similarly, the packet does not exceed because only 300 bytes are available in the exceed bucket. Therefore, the packet violates and the violate action (drop) is taken.

        Verifying Class-Based Traffic Policing

        Use the show policy-map interface command to verify that the Class-Based Policing feature is configured on your interface. If the feature is configured on your interface, the show policy-map interface command output displays policing statistics:

        Router# show policy-map interface
          FastEthernet1/1/1
          service-policy output: x
            class-map: a (match-all)
              0 packets, 0 bytes
              5 minute rate 0 bps
              match: ip precedence 0
              police:
                1000000 bps, 10000 limit, 10000 extended limit
                conformed 0 packets, 0 bytes; action: transmit
                exceeded 0 packets, 0 bytes; action: drop
                conformed 0 bps, exceed 0 bps, violate 0 bps

        Use the show policy-map interface type nummber command to view the traffic statistics for policies applied to that specific interface:

        Router# show policy-map interface gigabitethernet 0/0/1
         GigabitEthernet0/0/1
        
          Service-policy input: TUNNEL_MARKING
        
            Class-map: MATCH_PREC (match-any)
              72417 packets, 25418367 bytes
              5 minute offered rate 0000 bps, drop rate 0000 bps
              Match: ip precedence 0
              QoS Set
                ip precedence tunnel 3
                  Marker statistics: Disabled
        
            Class-map: MATCH_DSCP (match-any)
              0 packets, 0 bytes
              5 minute offered rate 0000 bps, drop rate 0000 bps
              Match: ip dscp default (0)
              QoS Set
                ip dscp tunnel 3
                  Marker statistics: Disabled
        
            Class-map: class-default (match-any)
              346462 packets, 28014400 bytes
              5 minute offered rate 0000 bps, drop rate 0000 bps
              Match: any
        
          Service-policy output: POLICE-SETTING
        
            Class-map: MATCH_PREC (match-any)
              0 packets, 0 bytes
              5 minute offered rate 0000 bps, drop rate 0000 bps
              Match: ip precedence 0
              police:
                  cir 8000 bps, bc 1000 bytes, be 1000 bytes
                conformed 0 packets, 0 bytes; actions:
                  transmit
                exceeded 0 packets, 0 bytes; actions:
                  set-qos-transmit 1
                violated 0 packets, 0 bytes; actions:
                  drop
                conformed 0000 bps, exceed 0000 bps, violate 0000 bps
        
            Class-map: class-default (match-any)
              31 packets, 2019 bytes
              5 minute offered rate 0000 bps, drop rate 0000 bps
              Match: any

        Use the show policy-map interface service instance command to view the traffic statistics for policies applied to that specific interface:

        Router# show policy-map interface gigabitethernet 0/0/1 service instance 1
        	Service-policy input: p
        	
        	Class-map: prec1 (match-all) 
        			0 packets, 0 bytes
        			5 minute offered rate 0000 bps, drop rate 0000 bps
        			Match: ip precedence 1 
        			police:
        							cir 10000000 bps, bc 312500 bytes
        					conformed 0 packets, 0 bytes; actions:
        							transmit 
        					exceeded 0 packets, 0 bytes; actions:
        							drop 
        					conformed 0000 bps, exceeded 0000 bps
        	
        	Class-map: class-default (match-any) 
        			0 packets, 0 bytes
        			5 minute offered rate 0000 bps, drop rate 0000 bps
        			Match: any 
        

        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

        Traffic marking

        “Marking Network Traffic” module

        Traffic policing

        “Traffic Policing” module

        Traffic policing and shaping concepts and overview information

        “Policing and Shaping Overview”

        Modular Quality of Service Command-Line Interface (MQC)

        “Applying QoS Features Using the MQC” module

        Standards

        Standard

        Title

        None

        --

        MIBs

        MIB

        MIBs Link

        Class-Based Quality of Service MIB

        • 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 Class-Based 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 Class-Based Policing

        Feature Name

        Releases

        Feature Information

        Class-Based Policing

        Cisco IOS XE Release 2.1

        Cisco IOS XE Release 3.5S

        This feature was introduced on Cisco ASR 1000 Series Routers.

        In Cisco IOS XE Release 3.5S, support was added for the Cisco ASR 903 Router.

        The following command was introduced or modified: police.