On Configuring BGP Route Reflectors

Abstract

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.