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Configuration
Service-Pool
Configuration
WRED Threshold
Relationship
Q threshold = Q-T
Service-pool threshold =
SP-T
Expected Functionality
Enabled Enabled Disabled N/A N/A Queue-based ECN marking above
queue threshold.
ECN marking up to shared buffer
limits of the service-pool and then
packets are tail dropped.
Enabled N/A Q-T < SP-T
SP-T < Q-T Same as above but ECN marking
starts above SP-T.
Configuring a Weight for WRED and ECN Operation
You can configure a WRED weight to customize WRED and ECN operation on a front-end or backplane
interface. In the configuration procedure, you must also configure the global service-pools of shared
buffer memory that can be accessed by multiple queues when the minimum guaranteed buffers for a
queue are consumed.
1. Configure the weight factor for computation of average-queue size. This weight value applies to
front-end and backplane ports.
QOS-POLICY-OUT mode
Dell(conf-qos-policy-out)#wred weight number
2. Configure one or more WRED profiles, and specify the threshold and maximum drop rate
WRED mode
Dell(conf-wred)#wred thresh-1
Dell(conf-wred)#threshold min 100 max 200 max-drop-rate 40
Dell(conf-wred)#wred thresh-2
Dell(conf-wred)#threshold min 300 max 400 max-drop-rate 80
3. Associate a service class for each WRED profile, and assign the WRED profile to specific queues on
backplane ports.
CONFIGURATION mode
Dell(conf)#service-class wred green queue5 thresh-1 queue7 thresh-2
backplane
Dell(conf)#service-class wred yellow queue1 thresh-2 queue3 thresh-1
backplane
Dell(conf)#service-class wred weight queue0 11 queue6 4 queue7 9 backplane
4. Create a global buffer pool that serves as a shared buffer accessed by multiple queues when the
minimum guaranteed buffers for a queue are consumed. The Z9500 supports four global service-
pools in the egress direction.
746
Quality of Service (QoS)