Concept Guide

Queue Conguration Service-Pool
Conguration
WRED Threshold
Relationship
Q threshold = Q-T,
Service pool threshold =
SP-T
Expected Functionality
1 0 0 X X Queue based WRED,
No ECN marking
1 X Q-T < SP-T
SP-T < Q-T SP based WRED,
No ECN marking
1 1 0 X X Queue-based ECN marking above queue threshold.
ECN marking to shared buer limits of the service-pool and
then packets are tail dropped.
1 X Q-T < SP-T
SP-T < Q-T Same as above but ECN marking starts above SP-T.
Conguring WRED and ECN Attributes
The functionality to congure a weight factor for the WRED and ECN functionality for backplane ports is supported on the platform.
WRED drops packets when the average queue length exceeds the congured threshold value to signify congestion. Explicit Congestion
Notication (ECN) is a capability that enhances WRED by marking the packets instead of causing WRED to drop them when the threshold
value is exceeded. If you congure ECN for WRED, devices employ this functionality of ECN to mark the packets and reduce the rate of
sending packets in a congested, heavily-loaded network.
To congure the weight factor for WRED and ECN capabilities, global buer pools for multiple queues, and associating a service class with
ECN marking, perform the following:
1 Congure the weight factor for the computation of average-queue size. This weight value applies to front-end ports.
QOS-POLICY-OUT mode
DellEMC(conf-qos-policy-out)#wred—profile weight number
2 Congure a WRED prole, and specify the threshold and maximum drop rate.
WRED mode
DellEMC(conf-wred) #wred—profile thresh-1
DellEMC(conf-wred) #threshold min 100 max 200 max-drop-rate 40
3 Congure another WRED prole, and specify the threshold and maximum drop rate.
WRED mode
DellEMC(conf-wred) #wred—profile thresh-2
DellEMC(conf-wred) #threshold min 300 max 400 max-drop-rate 80
4 Create a global buer pool that is a shared buer pool accessed by multiple queues when the minimum guaranteed buers for the
queue are consumed.
mode
DellEMC(conf) #service-pool wred green pool0 thresh-1 pool1 thresh-2
DellEMC(conf) #service-pool wred yellow pool0 thresh-3 pool1 thresh-4
DellEMC(conf) #service-pool wred weight pool0 11 pool1 4
700
Quality of Service (QoS)