Guidelines for interdomain traffic engineering

Network operators must have control over the flow of traffic into, out of, and across their networks. However, the Border Gateway Protocol (BGP) does not facilitate common traffic engineering tasks, such as balancing load across multiple links to a neighboring AS or directing traffic to a different neighbor. Solving these problems is difficult because the number of possible changes to routing policies is too large to exhaustively test all possibilities, some changes in routing policy can have an unpredictable effect on the flow of traffic, and the BGP decision process implemented by router vendors limits an operator's control over path selection.We propose fundamental objectives for interdomain traffic engineering and specific guidelines for achieving these objectives within the context of BGP. Using routing and traffic data from the AT&T backbone we show how certain BGP policy changes can move traffic in a predictable fashion, despite limited knowledge about the routing policies in neighboring AS's. Then, we show how operators can gain greater flexibility by relaxing some steps in the BGP decision process and ensuring that neighboring AS's send consistent advertisements at each peering location. Finally, we show that an operator can manipulate traffic efficiently by changing the routes for a small number of prefixes (or groups of related prefixes) that consistently receive a large amount of traffic.