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First Published: November 01, 2011
Last Updated: February 02, 2014
DiffServ Compliant WRED
DiffServ Compliant WRED extends the functionality of Weighted Random Early Detection to enable support for DiffServ and Assured Forwarding (AF) per hop behavior (PHB). This feature enables customers to implement AF PHB by coloring packets according to Differentiated Services Code Point (DSCP) values and then assigning preferential drop probabilities to those packets.
NoteThis feature can be used with IP packets only. It is not intended for use with Multiprotocol Label Switching (MPLS)-encapsulated packets.
Information About DiffServ Compliant WRED
Differentiated Services for 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.
Usage Guidelines for DiffServ Compliant WRED
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).
If WRED is configured in microsecond, you need to explicitly configure the Qlimit in microsecond. The units of both the Qlimit and WRED should be same. This changes the threshold value for Min and Max. The same holds true for WRED configuration in bytes.
How to Configure DiffServ Compliant WRED
Configuring DiffServ Compliant WRED
ProcedureConfiguration Examples for DiffServ Compliant WRED
Example: DiffServ compliant WRED
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 (bytes/ms) Device(config-if)# service-policy output p1
Note
Cisco RSP3 Module supports match qos-group at egress match condition.
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