Reference Guide

Explicit congestion notication
When you use explicit congestion notication (ECN) in conjunction with WRED, packets are marked instead of dropping them. Devices on
a network respond to congestion before a queue overows and packets drop, enabling improved queue management. You can congure
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-congurable weight factor is used. Use the
weight value command to congure the weight for the WRED average queue size.
The weight factor is set to zero by default.
Queue management
Queues share buer 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 trac in POLICY-MAP mode. yellow congures a medium drop
precedence, and green congures a low drop precedence (default).
color {yellow | green}
• Congure explicit congestion notication (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
Congure 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
492
Quality of service