Administrator Guide

Conguring a Weight for WRED and ECN Operation
You can congure a WRED weight to customize WRED and ECN operation on a front-end or backplane interface. In the conguration
procedure, you must also congure the global service-pools of shared buer memory that can be accessed by multiple queues when the
minimum guaranteed buers for a queue are consumed.
1 Congure 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 Congure one or more WRED proles, 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 prole, and assign the WRED prole to specic 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 buer pool that serves as a shared buer accessed by multiple queues when the minimum guaranteed buers 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 specic queues on backplane ports with a service class.
CONFIGURATION mode
Dell(conf)#service-class wred ecn 0, 3-5, 7 backplane
Pre-Calculating Available QoS CAM Space
Pre-calculating available QoS CAM space allows you to measure the number of CAM entries a policy-map consumes.
This feature allows you to avoid applying a policy-map on an interface that requires more CAM entries than are available and receive a CAM
full error message (shown in the following example). The partial policy-map conguration might cause unintentional system behavior.
%EX2YD:12 %DIFFSERV-2-DSA_QOS_CAM_INSTALL_FAILED: Not enough space in L3
Cam(PolicyQos) for class 2 (Te 12/20) entries on portpipe 1 for linecard 12
%EX2YD:12 %DIFFSERV-2-
DSA_QOS_CAM_INSTALL_FAILED: Not enough space in L3 Cam(PolicyQos) for class 5 (Te 12/
22) entries on portpipe 1 for linecard 12
Quality of Service (QoS)
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