- Policing and Shaping Overview
- IPv6 QoS: MQC Traffic Policing
- Configuring Traffic Policing
- IPv6 QoS: MQC Traffic Shaping
- MQC Traffic Shaping Overhead Accounting for ATM
- Two-Rate Policer
- Control Plane Policing
- Class-Based Policing
- QoS Percentage-Based Policing
- Port-Level Shaping and Minimum Bandwidth Guarantee
Contents
- Class-Based Policing
- Finding Feature Information
- Feature Overview
- Benefits
- Restrictions
- Prerequisites
- Configuration Tasks
- Configuring Traffic Policing
- Verifying Traffic Policing
- Troubleshooting Tips
- Monitoring and Maintaining Traffic Policing
- Configuration Examples
- Example Configuring a Service Policy that Includes Traffic Policing
- Additional References
Class-Based Policing
Feature History
|
Release |
Modification |
|
12.1(5)T |
This command was introduced for Cisco IOS Release 12.1 T. A new Class-Based Policing algorithm was introduced. The violate-action option became available. This feature became available on Cisco 2600, 3600, 4500, 7200, and 7500 series routers. |
|
12.2(2)T |
The set-clp-transmit option for the action argument was added to the police command. The set-frde-transmit option for the action argument was added to the police command. The set-mpls-exp-transmit option for the action argument was added to the police command. |
|
12.0(26)S |
This feature was integrated into Cisco IOS Release 12.0(26)S for the Cisco 7200 and 7500 series routers. The name of the feature changed from Traffic Policing to Class-Based Policing. |
- Finding Feature Information
- Feature Overview
- Prerequisites
- Configuration Tasks
- Monitoring and Maintaining Traffic Policing
- Configuration Examples
- Additional References
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.
Feature Overview
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 contain the Class-Based Policing configuration to an interface.
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.
Benefits
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. 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 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. 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 Class-Based 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 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.
Packet Prioritization for Frame Relay Frames
The Class-Based 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 Class-Based 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
- To use the set-clp-transmitaction available with this feature, the Enhanced ATM Port Adapter (PA-A3) is required. Therefore, 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 3640 router, and the 4500 series router). For more information, see the documentation for your specific device.
- On a Cisco 7500 series router, Class-Based Policing can monitor Cisco Express Forwarding (CEF) switching paths only. In order to use the Class-Based Policing feature, 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, Class-Based Policing cannot be applied to packets that originated from or are destined to a device.
- Class-Based Policing can be configured on an interface or a subinterface.
Class-Based Policing is not supported on the following interfaces:
 Note | Class-Based Policing is supported on tunnels that are using the Cisco generic routing encapsulation (GRE) tunneling protocol. |
Prerequisites
On a Cisco 7500 series router, Cisco Express Forwarding (CEF) must be configured on the interface before Class-Based Policing can be used.
Configuration Tasks
Configuring Traffic Policing
Verifying Traffic Policing
Use the show policy-map interface EXEC 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:
Device# show policy-map interface
Ethernet1/7
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 your interface is not mentioned in the nonsupported interface description in the Restrictions section of this module.
- For input Class-Based Policing on a Cisco 7500 series router, verify that CEF is configured on the interface where Class-Based Policing is configured.
- For output Class-Based Policing on a Cisco 7500 series router, ensure that the incoming traffic is CEF-switched. Class-Based Policing cannot be used on the switching path unless CEF switching is enabled.
Monitoring and Maintaining Traffic Policing
|
Command |
Purpose |
|---|---|
|
Device# show policy-map |
Displays all configured policy maps. |
|
Device# show policy-map policy-map-name |
Displays the user-specified policy map. |
|
Device# show policy-map interface |
Displays statistics and configurations of all input and output policies that are attached to an interface. |
|
Device# show policy-map interface service instance |
Displays the policy map information for a given service instance under a port channel. |
Configuration Examples
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 Fast Ethernet interface 0/0.
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 Fast Ethernet interface 0/0 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 B is greater than or equal to 0, the packet conforms and the conform action is taken on the packet. 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 B is less than 0, the excess token bucket is checked for bytes by the packet. If the number of bytes in the exceed bucket B is greater than or equal to 0, the exceed action is taken and B bytes are removed from the exceed token bucket. No bytes are removed from the conform bucket in this scenario.
- 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 it 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
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 |
|
Modular Quality of Service (QoS) Command-Line Interface (CLI) (MQC), hierarchical policies, policy maps |
"Applying QoS Features Using the MQC" module |
|
Policing and shaping traffic |
"Policing and Shaping Overview" module |
Standards
|
Standard |
Title |
|---|---|
|
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
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MIBs
|
MIB |
MIBs Link |
|---|---|
|
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature. |
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: |
RFCs
|
RFC |
Title |
|---|---|
|
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
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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. |