Cisco IOS XE Quality of Service Solutions Configuration Guide, Release 2 - Byte-Based Weighted Random Early Detection [Cisco IOS XE Software]

Table Of Contents

Byte-Based Weighted Random Early Detection

Finding Feature Information

Contents

Restrictions for Byte-Based WRED

Information About Byte-Based WRED

Changes in functionality of WRED

Changes in Queue Limit and WRED Thresholds

How to Configure Byte-Based WRED

Configuring Byte-Based WRED

Configuring the Queue Depth and WRED Thresholds

Prerequisites

Restrictions

Examples

Changing the Queue Depth and WRED Threshold Unit Modes

Verifying the Configuration for Byte-Based WRED

Configuration Examples for Byte-Based WRED

Configuring Byte-Based WRED: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Byte-Based Weighted Random Early Detection

Byte-Based Weighted Random Early Detection

First Published: August 26, 2003

Last Updated: June 30, 2009

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

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 Byte-Based Weighted Random Early Detection" 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

•Restrictions for Byte-Based WRED

•Information About Byte-Based WRED

•How to Configure Byte-Based WRED

•Configuration Examples for Byte-Based WRED

•Additional References

•Feature Information for Byte-Based Weighted Random Early Detection

Restrictions for Byte-Based WRED

•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 WRED

To configure Byte-Based WRED you should understand the following concepts:

•Changes in functionality of WRED

•Changes in Queue Limit and WRED Thresholds

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. For more information about WRED, see the Cisco IOS XE Quality of Service Solutions Configuration Guide

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.

For more information, see the "Configuring the Queue Depth and WRED Thresholds" section

How to Configure Byte-Based WRED

The following sections describe how to configure byte-based WRED:

•Configuring Byte-Based WRED

•Configuring the Queue Depth and WRED Thresholds

•Verifying the Configuration for Byte-Based WRED

Configuring Byte-Based WRED

Use the following steps to enable 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 max-probability-denominator

DETAILED STEPS
Command or Action

Purpose

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. Names can be a maximum of 40 alphanumeric characters.
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. Names can be a maximum of 40 alphanumeric characters.
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:

Router(config-pmap-c)# random-detect pecedence 1 2000 bytes 3000 bytes 200
Configures the parameters for bytes with a specific IP precedence.
Configuring the Queue Depth and WRED Thresholds

Beginning in Cisco IOS XE Release 2.4, the Cisco ASR 1000 Series Aggregation Services Routers support configuration of byte-based queue limits and Weighted Random Early Detection (WRED) thresholds. In prior releases, the Cisco ASR 1000 Series Routers were limited to packet-based limits only. However, there are some dependencies when configuring both the queue limit and WRED unit modes for a class.

Prerequisites

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.

Restrictions

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

DETAILED STEPS

Command or Action

Purpose

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

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

random-detect precedence precedence {min-threshold max-threshold | min-threshold bytes max-threshold bytes} max-probability-denominator
Example:

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

Correct Configuration

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
Invalid Configuration

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
Correct Configuration

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
Invalid Configuration

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

You cannot dynamically change the queue depth or WRED threshold configuration for a service policy if that service policy has been applied to an interface or subinterface. However, once you remove a service policy from an interface, you can modify the policy map to change the queue-limit and random-detect precedence by re-entering those commands with new values or units.

To change the queue depth and WRED threshold unit modes after you have applied a service policy, complete the following steps.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type

4. no service-policy number 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. no random-detect dscp dscp-value {min-threshold max-threshold | min-threshold bytes max-threshold bytes} [max-probability-denominator]
or
no random-detect precedence precedence {min-threshold max-threshold | min-threshold bytes max-threshold bytes} max-probability-denominator

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

DETAILED STEPS
Command or Action

Purpose

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

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

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

To verify that byte-based WRED is correctly configured, issue the show policy-map interface or show policy-map command.

SUMMARY STEPS

1. show policy-map interface

2. show policy-map

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.
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.
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 WRED

This section provides the following configuration examples:

•Configuring Byte-Based WRED: Example

Configuring Byte-Based WRED: Example

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

The following sections provide references related to the Byte-Based Weighted Random Early Detection feature.

Related Documents

Related Topic

Document Title

Modular QoS CLI

Modular Quality of Service Command-Line Interface

QoS Commands

Cisco IOS Quality of Service Solutions Command Reference

Standards

Standards

Title

No new or modified standards are supported, and support for existing standards has not been modified.

—

MIBs

MIBs

MIBs Link

No new or modified MIBs are supported, and support for existing MIBs has not been modified.

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

RFCs

Title

No new or modified RFCs are supported, and support for existing RFCs has not been modified.

—

Technical Assistance

Description

Link

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To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport

Feature Information for Byte-Based Weighted Random Early Detection

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 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

Table 1 Feature 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.

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