Software Defined Networking (SDN) is a powerful approach that enhances network control and management, and provides a flexible way to develop network applications. However, scalability of SDN networks is an important concern for many network operators. The main peculiarities of SDN when applied to an Internet Service Provider (ISP) network are the large geographical extension and the need of in-band transmission of control traffic. Therefore, the control traffic exchanged between the SDN controller and the network nodes must be carefully evaluated for the network design and dimensioning. We consider an ISP network controlled by the recently ONOS (Open Network Operating System) controller developed by ON.Lab. We devise a quantitative model to compute the exact number of exchanged OpenFlow messages and the corresponding bandwidth needed to install a traffic flow when running the default ONOS layer-2 forwarding applications. We compute also the exact number of flow rules installed in each switch. We show the general applicability of our models for a Point Of Presence (POP) network and for a large set of real nationwide and worldwide ISP networks. Our quantitative models can be used for a safe network planning also when the network applications are not fully reactive.

In distributed SDN architectures, the network is controlled by a cluster of multiple controllers. This distributed approach permits to meet the scalability and reliability requirements of large operational networks. Despite that, a logical centralized view of the network state should be guaranteed, enabling the simple development of network applications. Achieving a consistent network state requires a consensus protocol, which generates control traffic among the controllers whose timely delivery is crucial for network performance. We focus on the state-of-art ONOS controller, designed to scale to large networks, based on a cluster of self-coordinating controllers, and concentrate on the inter-controller control traffic. Based on real traffic measurements, we develop a model to quantify the traffic exchanged among the controllers, which depends on the topology of the controlled network. This model is useful to design and dimension the control network interconnecting the controllers.

We consider a distributed Software Defined Networking (SDN) architecture adopting a cluster of multiple controllers to improve network performance and reliability. Besides the Openflow control traffic exchanged between controllers and switches, we focus on the control traffic exchanged among the controllers in the cluster, needed to run coordination and consensus algorithms to keep the controllers synchronized. We estimate the effect of the inter-controller communications on the reaction time perceived by the switches depending on the dataownership model adopted in the cluster. The model is accurately validated in an operational Software Defined WAN (SDWAN). We advocate a careful placement of the controllers, that should take into account both the above kinds of control traffic. We evaluate, for some real ISP network topologies, the delay tradeoffs for the controllers placement problem and we propose a novel evolutionary algorithm to find the corresponding Pareto frontier.Our work provides novel quantitative tools to optimize the planning and the design of the network supporting the control plane of SDN networks, especially when the network is very large and in-band control plane is adopted. We also show that for operational distributed controllers (e.g. OpenDaylight and ONOS), the location of the controller which acts as a leader in the consensus algorithm has a strong impact on the reactivity perceived by switches.

No abstract

In distributed SDN architectures, the network is controlled by a cluster of multiple controllers. This distributed approach permits to meet the scalability and reliability requirements of large operational networks. Despite that, a logical centralized view of the network state should be guaranteed, enabling the simple development of network applications. Achieving a consistent network state requires a consensus protocol, which generates control traffic among the controllers whose timely delivery is crucial for network performance. We focus on the state-of-art ONOS controller, designed to scale to large networks, based on a cluster of self-coordinating controllers. In particular, we study the inter-controller control traffic due to the adopted consistency protocols. Based on real traffic measurements and the analysis of the adopted consistency protocols, we develop some empirical models to quantify the traffic exchanged among the controllers, depending on the considered shared data structures, the current network state (e.g. topology) and the occurring network events (e.g. flow or host addition). Our models provide a formal tool to be integrated into the design and dimension the control network interconnecting the controllers. Our results are of paramount importance for the proper design of large SDN networks, in which the control plane is implemented in-band and cannot exploit dedicated network resources. Index Terms-Software Defined Networking, ONOS controller, consistency protocols, inter-controller traffic measurements.