controllers in a software defined network automatically discover and authenticate each other as part of the control plane operations , without any need for manual configuration of other controllers . the new capability of such controllers is based on controller - advertisement messages transferred between controllers in the same or different sdns . in doing so , multiple controllers can be used for load sharing , improved reliability under failure of a controller by enabling seamless take over and recovery . moreover , controllers can cooperate to enable end - to - end services to work across multiple sdns . controller - advertisement messages are also used to check the health statuses of discovered controllers in the same or different sdns .