Reference Guide

Table 55. Scenarios for WRED and ECN Configuration (continued)
Queue Configuration Service-Pool
Configuration
WRED Threshold Relationship
Q threshold = Q-T
Service-pool threshold = SP-T
Expected Functionality
Disabled Disabled N/A N/A N/A WRED/ECN not applicable
Enabled Disabled Disabled N/A N/A Queue-based WRED;
No ECN marking
Enabled N/A Q-T < SP-T
SP-T < Q-T Service-pool-based WRED;
No ECN marking
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.
mode
Dell(conf)#service-pool wred green pool0 thresh-1 pool1 thresh-2
Dell(conf)#service-pool wred yellow pool0 thresh-3 pool1 thresh-4
Dell(conf)#service-pool wred weight pool0 11 pool1 4
5. Enable ECN marking on specific queues on backplane ports with a service class.
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Quality of Service (QoS)