 variations from "on demand" to repeated scheduling of the excess capacity. 6.8.2 FLOW REDIRECTION Flow redirection is the general capability to specify a packet N-tuple match criteria and action behavior. The basic approach is the simple idea of policy-based targeted route distribution SO that different policies are sent to different source nodes in the network via route reflectors. By varying the match conditions and action behaviors, multiple services are possible. If the match criteria is on destination IP address for a subset of source routers and the action is to drop the packets, then the service can be used for distributed denial of service (DDOS) protec- tion. If the same match criteria is used but the action behavior is to set an alternative next hop then the result could be URL blocking and traffic scrubbing. Additional detail is provided in Chapter 9. SDN controllers can create and distribute policies for the matching action through multiple types Software-Defined Networking of adapters: NetConf or CLI, BGP, or even OpenFlow. The particular adapter is less important that the fact that the SDN controller can manage the data, translate the requested service into a network and device configuration or signaling change, and monitor the service during operation. 6.9 CHOICE OF OPEN SOURCE SDN CONTROLLERS There are multiple open source SDN controllers available in the industry that range from research experiments to hardened and scalable production controllers. Three controllers merit closer inspec- tion when it comes to choosing an SDN controller for a service provider. As is to be expected they have some overlapping capabilities and any one of them is likely to be an acceptable choice. However, based on the specific needs of global control, local control or embedded device control, a specific open source SDN controller could be the proper choice. OpenDaylight [5] is used in AT&T as a global controller. It has most of the attributes for a flexible controller needed for a mature service provider. It also supp