Configuring Explicit Congestion Notification

Explicit Congestion Notification (ECN) enables the switch/router to signal to endpoints about congestion seen in traffic. This then enables the endpoints to take appropriate actions to mitigate traffic congestion. The advantage of this method is that it reduces the packet drops and jitter encountered when traffic congestion occurs.

  1. Enter configuration mode. 
    device# configure terminal
  2. Create a RED profile identified as profile 1, set the thresholds, set the drop probability, and enable the Explicit Congestion Notification feature. 
    device(config)# qos red-profile 1 min-threshold 30 max-threshold 60 drop-probability 44 ecn on
  3. Verify the ECN configuration. 
    device(config)# do show qos red profiles 1

Red Profile 1
        Minimum Threshold: 30
        Maximum Threshold: 60
        Drop Probability: 44  
        ECN: On

    Activated on the following interfaces:
        Eth 0/1  traffic-class: 0 drop-precedence: 03
  4. Return to privileged exec mode. 
    device(config)# exit
  5. Save the configuration. 
    device# copy running-config startup-config
  6. To view the per port ECN statistics, use the show qos red statistics command. 
    device# show qos red statistics interface eth 0/1

Statistics for interface: Eth 0/1
        Port Statistics:
            Packets Dropped: 147, Queue Full Drops: 222, ECN Marked: 234

This example creates a RED profile and applies it to an interface. 

device# qos red-profile 1 min-threshold 10 max-threshold 50 drop-probability 100 ecn on
device# int eth 0/1
device(conf-if-eth0/1)# qos random-detect traffic-class 0 red-profile-id 1

This example shows how to view the per port ECN statistics using the show qos red statistics command. 

device# show qos red statistics interface eth 0/1

Statistics for interface: Eth 0/1
        Port Statistics:
            Packets Dropped: 147, Queue Full Drops: 222, ECN Marked: 234
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