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).

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

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