Software-defined networking (SDN) renovates traditional networking systems by replacing a distributed, per-switch control plane with a (logically) centralized one. To design a scalable, highly available SDN control plane, it is inevitable to disseminate the network state to multiple instances horizontally by using measures like replication and partitioning. However, some recent studies reported that it is not sufficient to cover a large scale network in a purely horizontal manner.

In this paper, we propose FRACTAL, a framework for recursive abstraction of SDN control-plane, to address this problem. In FRACTAL, a large network is divided into multiple small networks, each of which is abstracted as a single virtual switch. This “divide-and-abstract” process is recursively iterated until a divided network can be handled by a single controller. A virtual switch is controlled by the higher level controller over OpenFlow, so that FRACTAL can coexist with other SDN mechanisms.