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Byte-Based Weighted Random Early Detection
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Byte-Based Weighted Random Early Detection

Last Updated: November 23, 2012

This module explains how to enable byte-based Weighted Random Early Detection (WRED), and set byte-based queue limits and WRED thresholds.

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 Table at the end of this document.

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.

Restrictions for Byte-Based Weighted Random Early Detection

  • WRED is only useful when the bulk of the traffic is TCP/IP traffic. With TCP, dropped packets indicate congestion, so the packet source will reduce its transmission rate. With other protocols, packet sources may not respond or may resend dropped packets at the same rate. Thus, dropping packets does not decrease congestion.
  • You cannot configure byte-based WRED on a class in which the queue-limit is configured in milliseconds or packets.

Information About Byte-Based Weighted Random Early Detection

Changes in functionality of WRED

This feature extends the functionality of WRED. In previous releases, you specified the WRED actions based on the number of packets. With the byte-based WRED, you can specify WRED actions based on the number of bytes.

Changes in Queue Limit and WRED Thresholds

In Cisco IOS XE Release 2.4, the Cisco ASR 1000 Series Aggregation Services Routers support the addition of bytes as a unit of configuration for both queue limits and WRED thresholds. Therefore, as of this release, packet-based and byte-based limits are configurable, with some restrictions.

How to Configure Byte-Based Weighted Random Early Detection

Configuring Byte-Based WRED

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    class-map class-map-name

4.    match ip precedence ip-precedence-value

5.    exit

6.    policy-map policy-name

7.    class class-name

8.    random-detect

9.    random-detect precedence precedence min-threshold bytes max-threshold bytes mark-prob-denominator


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
class-map class-map-name


Example:

Router(config)# class-map c1

 

Specifies the user-defined name of the traffic class.

 
Step 4
match ip precedence ip-precedence-value


Example:

Router(config-cmap)# match ip precedence 1

 

Specifies up to eight IP Precedence values used as match criteria.

 
Step 5
exit

Example:

Router(config-cmap)# exit

 

Exits from class-map configuration mode.

 
Step 6
policy-map policy-name


Example:

Router(config)# policy-map p1

 

Specifies the name of the traffic policy to configure.

 
Step 7
class class-name


Example:

Router(config-pmap)# class c1

 

Specifies the name of a predefined traffic class, which was configured with the class-map command, used to classify traffic to the traffic policy.
 
Step 8
random-detect


Example:

Router(config-pmap-c)# random-detect

 

Enables WRED.

 
Step 9
random-detect precedence precedence min-threshold bytes max-threshold bytes mark-prob-denominator


Example:



Example:

Router(config-pmap-c)# random-detect precedence 1 2000 bytes 3000 bytes 200

 

Configures the parameters for bytes with a specific IP precedence.

 

Configuring the Queue Depth and WRED Thresholds

Before You Begin

Be sure that your configuration satisfies the following conditions when configuring the queue depth and WRED thresholds:

  • When configuring byte-based mode, the queue limit must be configured prior to the WRED threshold and before the service policy is applied.
  • When setting the queue depth and WRED thresholds in an enhanced QoS policies aggregation configuration, the limits are supported only for the default class at a subinterface policy map and for any classes at the main interface policy map.

Note

Consider the following restrictions when you configure the queue depth and WRED thresholds:

  • Do not configure the queue limit unit before you configure a queueing feature for a traffic class.
  • If you do not configure a queue limit, then the default mode is packets.
  • When you configure WRED thresholds, the following restrictions apply:
    • The WRED threshold must use the same unit as the queue limit. For example, if the queue limit is in packets, then the WRED thresholds also must be in packets.
    • If you do not configure a queue limit in bytes, then the default mode is packets and you must also configure the WRED threshold in packets.
    • The queue limit size must be greater than the WRED threshold.
  • The unit modes for either the queue limit or WRED thresholds cannot be changed dynamically after a service policy is applied.
>

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    policy-map policy-map-name

4.    class class-name

5.    qos-queueing-feature

6.    queue-limit queue-limit-size [bytes | packets]

7.    random-detect [dscp-based | prec-based]

8.   Do one of the following:

  • random-detect dscp dscp-value {min-threshold max-threshold | min-threshold bytes max-threshold bytes} [max-probability-denominator]
  • random-detect precedence precedence {min-threshold max-threshold | min-threshold bytes max-threshold bytes} max-probability-denominator


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
policy-map policy-map-name


Example:

Router(config)# policy-map main-interface

 

Specifies the name of the traffic policy that you want to configure or modify and enters policy-map configuration mode.

 
Step 4
class class-name


Example:

Router(config-pmap)# class AF1

 

Specifies the name of the traffic class and enters policy-map class configuration mode.

 
Step 5
qos-queueing-feature


Example:

Router(config-pmap-c)# bandwidth remaining ratio 90

 

Enters a QoS configuration command. Some of the queueing features that are currently supported are bandwidth, priority, and shape.

Note    Multiple QoS queueing commands can be entered at this step. However, due to dependencies between the queue limit and WRED thresholds, you should configure WRED after you configure the queue limit.
 
Step 6
queue-limit queue-limit-size [bytes | packets]


Example:

Router(config-pmap-c)# queue-limit 547500 bytes

 

Specifies the maximum number (from 1 to 8192000) of bytes or packets that the queue can hold for this class.

 
Step 7
random-detect [dscp-based | prec-based]


Example:

Router(config-pmap-c)# random-detect dscp-based

 

Enables WRED in either DSCP-based mode or precedence-based mode.

 
Step 8
Do one of the following:
  • random-detect dscp dscp-value {min-threshold max-threshold | min-threshold bytes max-threshold bytes} [max-probability-denominator]
  • random-detect precedence precedence {min-threshold max-threshold | min-threshold bytes max-threshold bytes} max-probability-denominator


Example:

Router(config-pmap-c)# random-detect precedence 8 750000 bytes 750000 bytes

 

Configures WRED parameters for a particular DSCP value or IP precedence.

Note    Use the min-threshold max-threshold arguments without the bytes keyword to configure packet-based thresholds, when the queue-limit unit is also packets (the default). Alternatively, use these arguments with the bytes keyword when the queue-limit unit is configured in bytes.
 

Examples

The following examples show both correct and invalid configurations to demonstrate some of the restrictions.

The following example shows the correct usage of setting the queue limit in bytes mode after the bandwidth remaining ratio queueing feature has been configured for a traffic class: 

class AF1
	bandwidth remaining ratio 90
		queue-limit 750000 bytes

The following example shows an invalid configuration for the queue limit in bytes mode before the bandwidth remaining ratio queueing feature has been configured for a traffic class: 

class AF1
	queue-limit 750000 bytes
		bandwidth remaining ratio 90

The following example shows the correct usage of setting the queue limit in bytes mode after the bandwidth remaining ratio queueing feature has been configured for a traffic class, followed by the setting of the thresholds for WRED in compatible byte mode: 

class AF1
	bandwidth remaining ratio 90
		queue-limit 750000 bytes
			random-detect dscp-based
				random-detect dscp 8 750000 bytes 750000 bytes

This example shows an invalid configuration of the WRED threshold in bytes without any queue limit configuration, which therefore defaults to a packet-based queue depth. Therefore, the WRED threshold must also be in packets: 

class AF1
	bandwidth remaining ratio 90
	random-detect dscp-based
	random-detect dscp 8 750000 bytes 750000 bytes

Changing the Queue Depth and WRED Threshold Unit Modes

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    no service-policy output policy-map-name

5.    exit

6.    policy-map policy-map-name

7.    class class-name

8.    queue-limit queue-limit-size [bytes | packets]

9.   Do one of the following:

  • no random-detect dscp dscp-value {min-threshold max-threshold | min-threshold bytes max-threshold bytes} [max-probability-denominator]
  • no random-detect precedence precedence {min-threshold max-threshold | min-threshold bytes max-threshold bytes} max-probability-denominator

10.   Do one of the following:

  • random-detect dscp dscp-value {min-threshold max-threshold | min-threshold bytes max-threshold bytes} [max-probability-denominator]
  • random-detect precedence precedence {min-threshold max-threshold| min-threshold bytes max-threshold bytes} max-probability-denominator


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
interface type number


Example:

Router(config)# policy-map main-interface

 

Specifies the interface where you want to remove a service policy, and enters interface configuration mode.

 
Step 4
no service-policy output policy-map-name


Example:

Router(config-if)# no service-policy output main-interface-policy

 

Removes a service policy applied to the specified interface.

 
Step 5
exit


Example:

Router(config-if)# exit

 

Exits interface configuration mode and returns you to global configuration mode.

 
Step 6
policy-map policy-map-name


Example:

Router(config)# policy-map main-interface-policy

 

Specifies the name of the Traffic policy that you want to modify and enters policy-map configuration mode.

 
Step 7
class class-name


Example:

Router(config-pmap)# class AF1

 

Specifies the name of the traffic class and enters policy-map class configuration mode.

 
Step 8
queue-limit queue-limit-size [bytes | packets]


Example:

Router(config-pmap-c)# queue-limit 5000 packets

 

Specifies the maximum number (from 1 to 8192000) of bytes or packets that the queue can hold for this class.

 
Step 9
Do one of the following:
  • no random-detect dscp dscp-value {min-threshold max-threshold | min-threshold bytes max-threshold bytes} [max-probability-denominator]
  • no random-detect precedence precedence {min-threshold max-threshold | min-threshold bytes max-threshold bytes} max-probability-denominator


Example:

Router(config-pmap-c)# no random-detect dscp 8 750000 bytes 750000 bytes

 

Removes the previously configured WRED parameters for a particular DSCP value or IP precedence.

 
Step 10
Do one of the following:
  • random-detect dscp dscp-value {min-threshold max-threshold | min-threshold bytes max-threshold bytes} [max-probability-denominator]
  • random-detect precedence precedence {min-threshold max-threshold| min-threshold bytes max-threshold bytes} max-probability-denominator


Example:

Router(config-pmap-c)# random-detect dscp 8 4000 4000

 

Configures WRED parameters for a particular DSCP value or IP precedence.

Note    Use the min-threshold max-threshold arguments without the bytes keyword to configure packet-based thresholds, when the queue-limit unit is also packets (the default). Alternatively, use these arguments with the bytes keyword when the queue-limit unit is configured in bytes.
 

Examples

The following example shows how to change the queue depth and WRED thresholds to packet-based values once a service policy has been applied to an interface: 

interface GigabitEthernet1/2/0
no service-policy output main-interface-policy
end
policy-map main-interface-policy
class AF1
	queue-limit 5000 packets
	no random-detect dscp 8 750000 bytes 750000 bytes
	random-detect dscp 8 4000 4000

Verifying the Configuration for Byte-Based WRED

SUMMARY STEPS

1.    show policy-map

2.    The show policy-map interface command shows output for an interface that is configured for byte-based WRED.


DETAILED STEPS
Step 1   show policy-map

The show policy-map command shows the output for a service policy called pol1 that is configured for byte-based WRED.



Example: 
Router# show policy-map
Policy Map pol1
  Class class c1
Bandwidth 10 (%)
exponential weight 9
        class   min-threshold(bytes)   max-threshold(bytes)  mark-probability
        -------------------------------------------------------------------
 
        0       -                       -                      1/10
        1       20000                   30000                  1/10
        2       -                       -                      1/10
        3       -                       -                      1/10
        4       -                       -                      1/10
        5       -                       -                      1/10
        6       -                       -                      1/10
        7       -                       -                      1/10
        rsvp    -                       -                      1/10
Step 2   The show policy-map interface command shows output for an interface that is configured for byte-based WRED.

Example: 
Router# show policy-map interface 
serial3/1
Service-policy output: pol
Class-map: silver (match-all)
366 packets, 87840 bytes
30 second offered rate 15000 bps, drop rate 300 bps
Match: ip precedence 1 
Queueing
Output Queue: Conversation 266 
Bandwidth 10 (%)
(pkts matched/bytes matched) 363/87120
depth/total drops/no-buffer drops) 147/38/0
exponential weight: 9
mean queue depth: 25920
class     Transmitted       Random drop      Tail drop     Minimum Maximum Mark
          pkts/bytes        pkts/bytes       pkts/bytes    thresh  thresh  prob
                                                           (bytes)  (bytes)
0             0/0               0/0               0/0      20000    40000  1/10
1           328/78720          38/9120            0/0      22000    40000  1/10
2             0/0               0/0               0/0      24000    40000  1/10
3             0/0               0/0               0/0      26000    40000  1/10
4             0/0               0/0               0/0      28000    40000  1/10

Configuration Examples for Byte-Based Weighted Random Early Detection

Example Configuring Byte-Based WRED

The following example shows a service policy called wred-policy that sets up byte-based WRED for a class called prec2 and for the default class. The policy is then applied to Fast Ethernet interface 0/0/1.

policy wred-policy
 class prec2
   bandwidth 1000
   random-detect
   random-detect precedence 2 100 bytes 200 bytes 10
class class-default
   random-detect
   random-detect precedence 4 150 bytes 300 bytes 15
   random-detect precedence 6 200 bytes 400 bytes 5
interface fastethernet0/0/1
  service-policy output wred-policy

The following example shows the byte-based WRED results for the service policy attached to Ethernet interface 0/0/1.

Router# show policy-map interface
 Ethernet0/0/1
Service-policy output: wred-policy (1177)
Class-map: prec2 (match-all) (1178/10)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 2  (1179)
Queueing
queue limit 62500 bytes
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts queued/bytes queued) 0/0
bandwidth 1000 (kbps)
Exp-weight-constant: 9 (1/512)
Mean queue depth: 0 bytes
class     Transmitted       Random drop      Tail drop Minimum        Maximum     Mark
          pkts/bytes        pkts/bytes       pkts/bytes thresh         thresh     prob
                                                         bytes         bytes
0             0/0               0/0              0/0     15625         31250     1/10
1             0/0               0/0              0/0     17578         31250     1/10
2             0/0               0/0              0/0       100           200     1/10
3             0/0               0/0              0/0     21484         31250     1/10
4             0/0               0/0              0/0     23437         31250     1/10
5             0/0               0/0              0/0     25390         31250     1/10
6             0/0               0/0              0/0     27343         31250     1/10
7             0/0               0/0              0/0     29296         31250     1/10
Class-map: class-default (match-any) (1182/0)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any  (1183)
0 packets, 0 bytes
5 minute rate 0 bps
queue limit 562500 bytes
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts queued/bytes queued) 0/0
Exp-weight-constant: 9 (1/512)
Mean queue depth: 0 bytes
class     Transmitted       Random drop      Tail drop Minimum        Maximum     Mark
          pkts/bytes        pkts/bytes       pkts/bytes thresh         thresh     prob
                                                         bytes         bytes
0             0/0               0/0              0/0     140625        281250     1/10
1             0/0               0/0              0/0     158203        281250     1/10
2             0/0               0/0              0/0     175781        281250     1/10
3             0/0               0/0              0/0     193359        281250     1/10
4             0/0               0/0              0/0        150           300     1/15
5             0/0               0/0              0/0     228515        281250     1/10
6             0/0               0/0              0/0        200           400     1/5
7             0/0               0/0              0/0     263671        281250     1/10

Additional References

Related Documents

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Cisco IOS commands

Cisco IOS Master Commands List, All Releases

QoS Commands

Cisco IOS Quality of Service Solutions Command Reference

Modular QoS CLI

Modular Quality of Service Command-Line Interface module

Standards

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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:

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RFC

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Feature Information for Byte-Based Weighted Random Early Detection

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 1Feature Information for Byte-Based Weighted Random Early Detection

Feature Name

Releases

Feature Information

Byte-Based Weighted Random Early Detection

Cisco IOS XE Release 2.4

The Byte-Based Weighted Random Early Detection feature extends the functionality of WRED. In previous releases, you specified the WRED actions based on the number of packets. With the byte-based WRED, you can specify WRED actions based on the number of bytes.

This feature was introduced on Cisco ASR 1000 Series Routers.

The following commands were introduced or modified: random-detect, random-detect precedence, show policy-map, show policy-map interface.

Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2012 Cisco Systems, Inc. All rights reserved.