Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 
ON THIS PAGE
 

ECN Packets per Queue

Overview

Explicit congestion notification (ECN) enables two endpoint devices on TCP/IP-based networks to send end-to-end congestion notifications to each other. Without ECN, devices respond to network congestion by dropping TCP/IP packets. The dropped packets signal the occurrence of network congestion. In contrast, ECN marks packets to signal network congestion without dropping the packets. ECN reduces packet loss by making the sending device decrease the transmission rate until the congestion clears.

Packets may be delayed as the device decreases the transmission rate until congestion clears. To account for how many packets are delayed, you can use the show interfaces queue command to view the amount of ECN congestion experienced (CE) traffic in the queue.

Benefits

  • Identify the packets that have experienced congestion.

  • Helps in identifying if traffic is going to reach the queue buffer limits.

  • Enables quick troubleshooting of network congestion points.

Configuration

  1. Configure ECN.

    ECN is disabled by default. For how to configure ECN, see Example: Configuring ECN.

  2. Enable ECN on both endpoints and on all of the intermediate devices between the endpoints.

    ECN must be enabled this way for ECN to work properly. Any device in the transmission path that does not support ECN breaks the end-to-end ECN functionality.

  3. Use the show interfaces queue command to view the amount of traffic that has experienced congestion.

    The ECN-CE packets field shows the number of packets that have experienced congestion, while the ECN-CE bytes field shows the number of total bytes in those packets.

    The per-queue ECN counters ECN-CE packets and ECN-CE bytes only count packets that experienced congestion on the local switch.

    For example:

Platform Support

See Feature Explorer for platform and release support.