Evaluating the SDN control traffic in large ISP networks

Scalability of Software Defined Networking (SDN) approach is one of the key issues that many network operators are willing to address and understand. Indeed, the promised programmability and flexibility of a SDN network is paid with a non-negligible control traffic exchanged between the network nodes and the SDN controllers. We consider a network controlled by a real OpenFlow-enabled controller, i.e. OpenDaylight. We evaluate analytically the number of OpenFlow messages for installing a new traffic flow, assuming the default reactive forwarding application available in OpenDaylight. We apply these results to the specific case of a large ISP network, comprising a backbone interconnecting many POPs. By evaluating exactly the amount of generated control traffic, we are able to assess the scalability of the reactive forwarding application in a practical relevant scenario for ISPs.