DiffServ Compliant WRED

Differentiated Services is a multiple service model that can satisfy differing Quality of Service (QoS) requirements. With Differentiated Services, the network tries to deliver a particular kind of service based on the QoS specified by each packet. This specification can occur in different ways. The DiffServ Compliant WRED feature enables WRED to use either the 6-bit differentiated services code point (DSCP) or the IP Precedence setting in IP packets when it calculates the drop probability for a packet. The DSCP value is the first six bits of the IP type of service (ToS) byte.

To configure the DiffServ Compliant WRED feature, first specify the policy map, add the class, and configure the bandwidth or shape for the class. If you want WRED to use the DSCP value when it calculates the drop probability, use the dscp-based argument with the random-detect command to specify the DSCP value and then use the random-detect dscp command to modify the default minimum and maximum thresholds for the DSCP value. If you want WRED to use the IP Precedence value when it calculates the drop probability, use the precedence-based argument with the random-detect command to specify the IP Precedence value. This configuration can then be applied wherever policy maps are attached (for example, at the interface level, the per-VC level, or the shaper level).

Remember the following points when using the commands included with this feature:

• If you use the dscp-based argument, WRED will use the DSCP value to calculate the drop probability.
• If you use the precedence-based argument, WRED will use the IP Precedence value to calculate the drop probability.
• The dscp-based and precedence-based arguments are mutually exclusive.
• If you do not specify either argument, WRED will use the IP Precedence value to calculate the drop probability (the default method).

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number [name-tag]

4.    class-map class-map-name

5.    match match-criterion

6.    policy-map policy-map-name

7.    class {class-name | class-default}

8.    bandwidth {kbps | remaining percentage | percent percentage}

9.    random-detect [dscp-based | precedence-based]

10.    random-detect dscp dscp-value min-threshold max-threshold [ mark-probability-denominator]

11.    exit

12.    exit

13.    interface type number [name-tag]

14.    service-policy output policy-map-name

15.    end

16.    show policy-map interface type number

17.    exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	interface type number [name-tag] Example: Device(config)# interface GigabitEthernet 0/0/0	Configures an interface type and enters interface configuration mode. Enter the interface type and number.
Step 4	class-map class-map-name Example: Device(config-if)# class-map diffservclass	Specifies the name of the class map to be created and enters QoS class-map configuration mode.
Step 5	match match-criterion Example: Device(config-cmap)# match any	Configures the match criteria for a class map.
Step 6	policy-map policy-map-name Example: Device(config-cmap)# policy-map diffservpm	Creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy, and enters QoS policy-map configuration mode.
Step 7	class {class-name | class-default} Example: Device(config-pmap)# class diffservclass	Specifies the name of the class whose policy you want to create or change or specifies the default class (commonly known as the class-default class) before you configure its policy. Enters QoS policy-map class configuration mode.
Step 8	bandwidth {kbps | remaining percentage | percent percentage} Example: Device(config-pmap-c)# bandwidth percent 30	Specifies the bandwidth allocated for a class belonging to a policy map.
Step 9	random-detect [dscp-based | precedence-based] Example: Device(config-pmap-c)# random-detect dscp-based	Configures WRED for a class in a policy map.
Step 10	random-detect dscp dscp-value min-threshold max-threshold [ mark-probability-denominator] Example: Device(config-pmap-c)# random-detect dscp af11 10000 30000 25	Changes the minimum and maximum packet thresholds for the differentiated services code point (DSCP) value.
Step 11	exit Example: Device(config-pmap-c)# exit	Exits QoS policy-map class configuration mode.
Step 12	exit Example: Device(config-pmap)# exit	Exits QoS policy-map configuration mode.
Step 13	interface type number [name-tag] Example: Device(config)# interface GigabitEthernet 0/0/0	Configures an interface type and enters interface configuration mode. Enter the interface type and number.
Step 14	service-policy output policy-map-name Example: Device(config-if)# service-policy output policy1	Attaches a policy map to an output interface. Enter the policy map name. Note    Policy maps can be configured on ingress or egress routers. They can also be attached in the input or output direction of an interface. The direction (input or output) and the router (ingress or egress) to which the policy map should be attached varies according your network configuration. When using the service-policy command to attach the policy map to an interface, be sure to choose the router and the interface direction that are appropriate for your network configuration.
Step 15	end Example: Device(config-if)# end	Returns to privileged EXEC mode.
Step 16	show policy-map interface type number Example: Device# show policy-map interface GigabitEthernet 0/0/0	(Optional) Displays the traffic statistics of all classes that are configured for all service policies either on the specified interface or subinterface or on a specific PVC on the interface. Enter the interface type and number.
Step 17	exit Example: Device# exit	(Optional) Exits privileged EXEC mode.

The following example enables WRED to use the DSCP value 8 for the class c1. The minimum threshold for the DSCP value 8 is 24 and the maximum threshold is 40. The last line attaches the traffic policy to the output interface or VC p1.

Device(config)# interface GigabitEthernet 0/0/0
Device(config-if)# class-map c1
Device(config-cmap)# match ip precedence 1
Device(config-cmap)# policy-map p1
Device(config-pmap)# class c1
Device(config-pmap-c)# bandwidth 48
Device(config-pmap-c)# random-detect dscp-based
Device(config-pmap-c)# random-detect dscp 8 24 40
Device(config-if)# service-policy output p1