SDN is the concept to decouple the control plane from the Specific device (router, Switches etc) and given the authority of control plan to the Controller and left the devices is only for data plane. Controller also monitor the whole data traffic view of network and install the forwarding rules on switches according to the data traffic and topology of the network. It is essential to limiting the broadcast and avoids loops with OpenFlow devices. Therefore, on the data layer if one SDN domain egress switches can only have exactly one connection to any other ingress domain switch, which will limit the scalabiltity when deploying SDN networks.There is at least two inter-domain connection necessary to improve scalability for end-to-end services
