Forwarding deflection in multi-area OSPF
Stefano Iasi, Pierre François, Steve Uhlig · 2005
Multiple areas in OSPF have been introduced to improve the scalability of IGP routing in large networks. The principle is to partition the links of the network into areas, each link belonging to a single area. In this paper, we show that the way OSPF routers compute their routes makes it possible for deflection to arise, i.e. the forwarding path followed by IP packets differs from the routing path computed by the routing protocol. We give a necessary and sufficient condition for deflection to arise in a domain, and describe how to detect it. The goal is to provide a tool to decide where to establish OSPF virtual links to remove the deflection. The detection of deflection will be implemented in C-BGP [1], an open-source routing solver.