Dell S4820T, Configuration Manual

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Queue
Configuration
Service-Pool
Configuration
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 buffer 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.
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 Z9000 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
Dell(conf-qos-policy-out)#wred—profile weight number
2. Configure a WRED profile, and specify the threshold and maximum drop rate.
WRED mode
Dell(conf-wred) #wred—profile thresh-1
Dell(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
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Quality of Service (QoS)