The port-forwarding keep-alive enable command enables the keeping alive function of the port-forwarding.
The undo port-forwarding keep-alive enable command disables the keeping alive function of the port-forwarding.
By default, the keeping alive function is disabled.
When the keeping alive function of the port-forwarding is enabled, the client periodically sends messages to the gateway, therefore, the port-forwarding connection between the client and the server cannot be terminated due to the SSL session timeout.