Administrator Guide

Configuring WRED and ECN Attributes
The functionality to configure 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 configured threshold value to signify congestion. Explicit
Congestion Notification (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 configure 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 configure the weight factor for WRED and ECN capabilities, global buffer pools for multiple queues, and associating a service
class with ECN marking, perform the following:
1. Configure 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. Configure a WRED profile, 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. Configure another WRED profile, 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 buffer pool that is a shared buffer pool accessed by multiple queues when the minimum guaranteed buffers
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 Configuring ECN for Classifying and
Color-Marking Packets
Keep the following points in mind while configuring the marking and mapping of incoming packets using ECN fields in IPv4
headers:
● Currently Dell EMC Networking OS supports matching only the following TCP flags:
○ ACK
○ FIN
○ SYN
○ PSH
○ RST
○ URG
In the existing software, ECE/CWR TCP flag qualifiers are not supported.
● Because this functionality forcibly marks all the packets matching the specific match criteria as ‘yellow’, Dell EMC
Networking OS does not support Policer based coloring and this feature concurrently.
● If single rate two color policer is configured along with this feature, then by default all packets less than PIR would be
considered as “Green” But ‘Green’ packets matching the specific match criteria for which ‘color-marking’ is configured will
be over-written and marked as “Yellow”.
Quality of Service (QoS)
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