Deployment Scenarios Commands

This chapter provides commands used for QoS implementation of features that are described in other technology books, such as MPLS, L2VPN.

To use commands of this module, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using any command, contact your AAA administrator for assistance.

For detailed deployment scenarios, see the Modular QoS Configuration Guide for Cisco ASR 9000 Series Routers.

random-detect discard-class

To configure the Weighted Random Early Detection (WRED) thresholds for packets with a specific discard class value, use the random-detect discard-class command in policy map class configuration mode. To return the thresholds to the default for the discard class, use the no form of this command.

random-detect discard-class discard-value min-threshold [units] max-threshold [units]

no random-detect discard-class discard-value min-threshold [units] max-threshold [units]

Syntax Description

discard-value

Discard class value. Valid values are from 0 to 7. Up to eight values can be entered separated by commas.

min-threshold

Minimum threshold in number of packets. The value range of this argument is from 0 to 1073741823 in bytes.

max-threshold

Maximum threshold in number of packets. The value range of this argument is from the value of the min-threshold argument to 1073741823. When the average queue length exceeds the maximum threshold, WRED drops all packets with the specified discard class value.

units

(Optional) Units for the threshold values. Values can be:

  • bytes —bytes
  • gbytes —gigabytes
  • kbytes —kilobytes
  • mbytes —megabytes
  • ms —milliseconds
  • packets —packets (default)
  • us —microseconds

Command Default

Default unit for max-threshold and min-threshold is packets .

Command Modes

Policy map class configuration

Command History

Release

Modification

Release 3.7.2

This command was introduced.

Usage Guidelines

WRED is a congestion avoidance mechanism that slows traffic by randomly dropping packets when congestion exists. WRED is most useful with protocols like TCP that respond to dropped packets by decreasing the transmission rate.

When you configure the random-detect discard-class command on an interface, packets are given preferential treatment based on the discard class of the packet.

When the value of the units argument is packets, packets are assumed to be 256 bytes in size.

Task ID

Task ID

Operations

qos

read, write

Examples

This example shows how to set the discard class values for discard class 3 to a minimum byte threshold of 1000000 and a maximum byte threshold of 2000000: 


RP/0/RSP0/CPU0:router(config)# policy-map policy1
RP/0/RSP0/CPU0:router(config-pmap)# class class1
RP/0/RSP0/CPU0:router(config-pmap-c)# random-detect discard-class 3 1000000 2000000

Related Commands

Command Description

class (policy-map)

Specifies the name of the class whose policy you want to create or change.  

policy-map

Creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy.  

random-detect precedence

Configures the Weighted Random Early Detection (WRED) thresholds for packets with a particular IP precedence.  

show policy-map interface

Displays policy configuration information for all classes configured for all service policies on the specified interface.  

set cos

To set the Layer 2 class of service (CoS) value of an outgoing packet, use the set cos command in policy map class configuration mode. To remove a specific CoS value setting, use the no form of this command.

set cos [inner] cos-value

no set cos [inner] cos-value

Syntax Description

inner

(Optional) Specifies the inner CoS in, for example, a QinQ configuration.

cos-value

Specific IEEE 802.1Q CoS value from 0 to 7.

Command Default

No Layer 2 CoS value of an outgoing packet is set.

Command Modes

Policy map class configuration

Command History

Release

Modification

Release 3.7.2

This command was introduced.

Usage Guidelines

Use the set cos command to mark a packet that is being sent to a switch. Switches can leverage Layer 2 header information, including a CoS value marking.

For Layer 3, the set cos command can be used only in service policies that are attached in the output direction of an interface. Packets entering an interface cannot be set with a CoS value.

Task ID

Task ID

Operations

qos

read, write

Examples

In this example, the policy map called cos-set is created to assign different CoS values for different service classes, and then is attached to the output GigabitEthernet subinterface 0/1/0/9.100 VLAN. 


RP/0/RSP0/CPU0:router(config)# policy-map cos-set
RP/0/RSP0/CPU0:router(config-pmap)# class class1
RP/0/RSP0/CPU0:router(config-pmap-c)# set cos 1
RP/0/RSP0/CPU0:router(config-pmap-c)# exit
RP/0/RSP0/CPU0:router(config-pmap)# class class2
RP/0/RSP0/CPU0:router(config-pmap-c)# set cos 2
RP/0/RSP0/CPU0:router(config-pmap-c)# exit
RP/0/RSP0/CPU0:router(config-pmap)# exit
RP/0/RSP0/CPU0:router(config)# interface gigabitethernet 0/1/0/9.100
RP/0/RSP0/CPU0:router(config-subif)# service-policy output cos-set

Related Commands

Command Description

class-map

Defines a traffic class and the associated rules that match packets to the class.  

policy-map

Creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy.  

service-policy (interface)

Attaches a policy map to an input interface or output interface to be used as the service policy for that interface.