Combination of simulation and formal methods to analyse network survivability

Modern computer networks are complex and their topology can dynamically change when links go down. It is difficult to predict behaviour of a large network with dynamic routing protocols. To automatically prove survivability and reliability of an end-to-end connection, formal analysis combined with simulation can be exploited. In this paper, an approach based on detection of critical elements using formal analysis and subsequent simulation of time related properties is introduced. Our network model is automatically extracted from configurations of network devices. Then, critical network elements are detected using graph search algorithms. After that, several simulation scenarios are executed over a model in order to detect time dependencies. Modelling and simulation is done in OMNeT++ simulator, formal analysis is computed using scripting. The first results of this combined analysis show feasibility of this approach and help to reveal both qualitative parameters (status of links and nodes), and quantitative parameters (timers, routing protocols) that influence reliability and survivability of the network. The approach is demonstrated on a simplified topology of Czech Academic Network (CESNET).