Network designers perform challenging tasks with so many configuration options that it is often hard or even impossible for a human to predict all potentially dangerous situations. In this paper, we introduce a formal method approach for verification of security constraints on networks with dynamic routing protocols in use. A unifying model based on packet-filters is employed for modelling of network behaviour. Over this graph model augmented with filtering rules over edges verification of reachability properties can be made. In our approach we also consider topology changes caused by dynamic routing protocols.