On Configuring BGP Route Reflectors

The Border Gateway Protocol (BGP) is the standard protocol for exchanging routing information between border routers of Autonomous Systems (ASes) in today´s Internet. Within an AS, border routers exchange externally-learned BGP route advertisements via Internal-BGP (I-BGP) peerings. Naive solutions for these I-BGP peering sessions (e.g., based on full-mesh topologies) simply cannot scale to the sizes of modern AS networks. Carefully designed route-reflector configurations can drastically reduce the total number and connection cost of the required I-BGP sessions. Nevertheless, no principled algorithmic approaches exist for designing such configurations, and current practice relies on manual reflector selection using simple, ad-hoc rules. In this paper, we address the novel and challenging optimization problems involved in designing effective BGP route-reflector configurations for AS networks. More specifically, we consider the problems of selecting route reflectors in an AS topology to minimize: (1) the total connection cost of all I-BGP peering sessions, and (2) the average distance traversed by route advertisements within the AS. We present NP-hardness results that establish the intractability of these problems, and propose several polynomial-time approximation algorithms (based on LP-rounding and combinatorial techniques) with guaranteed (constant-factor or logarithmic) bounds on the quality of the approximate solution. Our simulation results validate our approach, demonstrating the effectiveness of our configuration algorithms over a wide range of network topologies.