Reference Guide
Explicit congestion notication
When you use explicit congestion notication (ECN) in conjunction with WRED, packets are marked instead of dropping them. Devices on
a network respond to congestion before a queue overows and packets drop, enabling improved queue management. You can congure
ECN using the ecn command.
When a packet reaches the device with ECN enabled for WRED, the average queue size is computed. To measure the average queue size,
a user-congurable weight factor is used. Use the
weight value command to congure the weight for the WRED average queue size.
The weight factor is set to zero by default.
Queue management
Queues share buer memory space.
All packets in a queue are transmitted, until the queue size reaches a minimum threshold. When the queue size reaches that minimum
threshold, the system starts discarding packets with a certain probability. The probability of discard increases until the queue depth reaches
the maximum threshold. After a queue depth exceeds the maximum threshold, all other packets that attempt to enter the queue are
discarded.
1 Enter the policy-map name and type in CONFIGURATION mode.
policy-map policy-map-name [type {qos | queuing | control-plane}]
2 Enter WRED parameters for a queue and enter a minimum and maximum threshold drop rate in POLICY-MAP mode (1 to 12480 kbps).
random-detect minimum-threshold threshold-value maximum-threshold threshold-value
• Enter the drop probability and enter the maximum drop rate in POLICY-MAP mode (1 to 100).
drop probability percent
• Assign a yellow or green color drop precedence to the trac in POLICY-MAP mode. yellow congures a medium drop
precedence, and green congures a low drop precedence (default).
color {yellow | green}
• Congure explicit congestion notication (ECN) in POLICY-MAP mode.
ecn
• Enter the weight factor to compute average-queue size in POLICY-MAP mode (1 to 15, default 0).
weight value
Congure WRED queue management
OS10(config)# policy-map type queuing gold
OS10(conf-pmap-queuing)# class silver
OS10(conf-pmap-c-que)# random-detect minimum-threshold 10 maximum-threshold 100 drop-
probability 50 color yellow ecn weight 10
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