Explicit Congestion Notification (ECN) allows a TCP sender to reduce the transmission rate to avoid packet drops. ECN is specified in RFC 3168. vSphere 7.0 and later supports ECN and it is enabled by default.

You can get the ECN status of any netstack using esxcli command.

Procedure

  1. In the ESXi Shell on the host, use the following command.
    esxcli network ip netstack set -N <NetStack-Name> --ecn=<str>
  2. You can set the status of ECN. The setting has the following possible values in ESXi. 
    ...
  --ecn=<str>           The status of ECN (Explicit Congestion Notification).
                            disabled: Completely disable ECN functionality
                            echo-only: Only echoing ECN, won't initiate
                            enabled: Fully enable ECN functionality
    The default value of this parameter is enabled. ESXi is likely to use ECN if the value of this parameter is enabled. If a router or a network appliance in the environment cannot handle IP packets with ECN bits accurately, then the ECN capability can be set to disabled.