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I had originally written this article for xmodulo . The previous tutorials demonstrated how we can  turn a CentOS box into a BGP router  and  filter BGP prefixes  using Quagga. Now that we understand basic BGP configuration, we will examine in this tutorial how to perform more advanced traffic engineering on Quagga. More specifically, we will show how we can influence the routing path of existing traffic by tuning BGP attributes (e.g., local preference). Routing and Path Selection In a typical Internet environment where multiple routing paths exist from a source to a destination, the actual path taken by traffic is the result of diligent traffic engineering which involves multiple factors, including the number of router/AS hops in the path, bandwidth capacity, path reliability, congestion in the path, and so on. To be more specific, a routing path chosen by traffic is shaped by individual routing decisions made by each intermediate router based on its local ...