Overview
ISPs usually have most of their routers running BGP, with some leaf nodes running IGP. On the other hand, most customers have few routers running BGP and the majority of their internal IGP routers running defaults toward the BGP routers. In these scenarios, it is important to have the BGP policies go hand-in-hand with routing inside the AS. Conflicting policies might result in routing loops if the AS's physical layout does not complement the logical layout. This chapter discusses the interaction of BGP routes with IGPs inside the AS and presents the options of controlling routes via policy routing.