Scotch: Elastically Scaling up SDN Control-Plane using vSwitch based Overlay

Software Defined Networks use logically centralized control due to its benefits in maintaining a global network view and in simplifying programmability. However, the use of centralized controllers can affect network performance if the control path between the switches and their associated controllers becomes a bottleneck. We find from measurements that the software control agents on some of the switches have very limited throughput. This can cause performance degradation if the switch has to handle a high traffic load, as for instance due to flash crowds or DDoS attacks. This degradation can occur even when the data plane capacity is under-utilized. The goal of our paper is to design new mechanisms to enable the network to scale up its ability to handle high control traffic loads. For this purpose, we design, implement, and experimentally evaluate Scotch, a solution that elastically scales up the control plane capacity by using a vSwitch based overlay. Scotch takes advantage of both the high control plane capacity of a large number of vSwitches and the high data plane capacity of commodity physical switches to increase the SDN network scalability and resiliency under normal (e.g., flash crowds) or abnormal (e.g., DDoS attacks) traffic surge.