Concept Guide

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
Guidelines for Conguring ECN for Classifying and
Color-Marking Packets
Keep the following points in mind while conguring the marking and mapping of incoming packets using ECN elds in IPv4 headers:
• Currently Dell EMC Networking OS supports matching only the following TCP ags:
– ACK
– FIN
– SYN
– PSH
– RST
– URG
In the existing software, ECE/CWR TCP ag qualiers are not supported.
Quality of Service (QoS)
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