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Cisco IOS XE Quality of Service Solutions Configuration Guide, Release 2
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Quality of Service Overview
- Part 1: Classification
- Part 2: Congestion Management
- Part 3: Congestion Avoidance
- Part 4: Policing and Shaping
- Part 5: Link Efficiency Mechanisms
- Part 6: Quality of Service Solutions
- Part 7: Modular Quality of Service Command-Line Interface
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Table Of Contents
Information About Class-Based Policing
Class-Based Policing Functionality
Benefits of Class-Based Policing
Restrictions for Class-Based Policing
How to Configure Class-Based Policing
Verifying Class-Based Traffic Policing
Monitoring and Maintaining Traffic Policing
Configuration Examples for Class-Based Policing
Configuring a Service Policy That Includes Traffic Policing: Example
Feature Information for 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
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 Class-Based Policing" section.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE Software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
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Information About Class-Based Policing
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Information About Class-Based Policing
Before configuring class-based policing, you should understand the following concepts:
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Class-Based Policing Functionality
The Class-Based Policing feature performs the following functions:
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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. A traffic policy is configured using the Modular Quality of Service Command-Line Interface (MQC). For information on configuring the MQC, see the "Applying QoS Features Using the MQC" module.
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.
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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.
How to Configure Class-Based Policing
See the following sections for configuration tasks for the Class-Based Policing feature. Each task is identified as optional or required.
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Configuring Traffic Policing
To successfully configure the Class-Based Policing feature, a traffic class and a traffic policy must be created, and the traffic policy must be attached to a specified interface. These tasks are performed using the Modular QoS CLI. For information on the Modular QoS CLI, see the "Applying QoS Features Using the MQC" module.
The Class-Based Policing feature is configured in the traffic policy. To configure the Class-Based Policing feature, use the following command in policy-map class configuration mode:
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.
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.
For more information about token bucket mechanisms, see the "Policing and Shaping Overview" module.
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 interfaceFastEthernet1/1/1service-policy output: xclass-map: a (match-all)0 packets, 0 bytes5 minute rate 0 bpsmatch: ip precedence 0police:1000000 bps, 10000 limit, 10000 extended limitconformed 0 packets, 0 bytes; action: transmitexceeded 0 packets, 0 bytes; action: dropconformed 0 bps, exceed 0 bps, violate 0 bpsTroubleshooting Tips
Check the interface type. Verify that class-based policing is supported on your interface. See the "Restrictions for Class-Based Policing" section.
Monitoring and Maintaining Traffic Policing
To monitor and maintain the Class-Based Policing feature, use the following commands in EXEC mode, as needed:
Configuration Examples for Class-Based Policing
This section provides the following configuration example:
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Configuring a Service Policy That Includes Traffic Policing: Example
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.
For additional information on configuring traffic classes and traffic policies, see the "Applying QoS Features Using the MQC" module.
For more information about token bucket mechanisms, see the "Policing and Shaping Overview" module.
class-map access-matchmatch access-group 1exitpolicy-map police-settingclass access-matchpolice 8000 1000 1000 conform-action transmit exceed-action set-qos-transmit 1 violate-action dropexitexitservice-policy output police-settingThe 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:
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(time between packets < which is equal to T - T1 > * policer rate)/8 bytes
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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.
Additional References
The following sections provide references related to class-based policing.
Related Documents
QoS commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples
Traffic marking
"Marking Network Traffic" module
Traffic policing
Traffic policing and shaping concepts and overview information
Modular Quality of Service Command-Line Interface (MQC)
"Applying QoS Features Using the MQC" module
Standards
MIBs
RFCs
Technical Assistance
Feature Information for Class-Based Policing
Table 1 lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE 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 Feature Information for Class-Based Policing
Class-Based Policing
Cisco IOS XE Release 2.1
This feature was introduced on Cisco ASR 1000 Series Routers.
The following sections provide information about this feature:
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The following command was introduced or modified: police.
Glossary
average rate—Maximum long-term average rate of conforming traffic.
conform action—Action to take on packets with a burst size below the rate allowed by the rate limit.
DSCP—differentiated services code point.
exceed action—Action to take on packets that exceed the rate limit.
excess burst size—Bytes allowed in a burst before all packets will exceed the rate limit.
normal burst size—Bytes allowed in a burst before some packets will exceed the rate limit. Larger bursts are more likely to exceed the rate limit.
policing policy—Rate limit, conform actions, and exceed actions that apply to traffic matching a certain criteria.
QoS group—Internal QoS group ID for a packet used to determine weighted fair queuing characteristics for that packet.
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