| Abstract | 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 traf-
fic, and the BGP decision process implemented by router vendors
limits an operator’s control over path selection. We analyze routing
and traffic data from the AT&T backbone to identify ways to use
BGP policy for traffic engineering tasks. First, we show how cer-
tain 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. These results can help operators accomplish common
traffic engineering tasks using existing BGP features.
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