Administrator Guide

Queue Configuration Service-Pool Configuration WRED Threshold
Relationship
Q threshold = Q-T
Service-pool
threshold = SP-T
Expected
Functionality
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 switch 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.
CONFIGURATION mode
762
Quality of Service (QoS)