Abstract: Use of a centralized control architecture in a network. Policy declaration, routing computation, and permission checks are managed by a logically centralized controller. By default, hosts on the network can only route to the network controller. Hosts and users must first authenticate themselves with the controller before they can request access to the network resources. The controller uses the first packet of each flow for connection setup. When a packet arrives at the controller, the controller decides whether the flow represented by that packet should be allowed. The switches use a simple flow table to forward packets under the direction of the controller. When a packet arrives that is not in the flow table, it is forwarded to the controller, along with information about which port the packet arrived on. When a packet arrives that is in the flow table, it is forwarded according to the controller's directive.