A critical view of the sensitivity of transit ASs to internal failures

Recent work on hot-potato routing [1] has uncovered that large transit ASs can be sensitive to hot-potato disruptions. Designing a robust network is felt as overly important by transit providers as paths crossed by the traffic have both to be optimal and reliable. However, equipment failures and maintenance make this robustness non-trivial to achieve. To help understanding the robustness of large networks to internal failures, [2] proposed metrics aimed at capturing the sensitivity of ASs to internal failures. In this paper, we discuss the strengths and weaknesses of this approach to understand the robustness of the control plane of large networks, having carried this analysis on a large tier-1 ISP and smaller transit ASs. We argue that this sensitivity model is mainly useful for intradomain topology design, not for the design the whole routing plane of an AS. We claim that additional effort is required to understand the propagation of BGP routes inside large ASs. Complex iBGP structures, in particular route-reflection hierarchies [3], affect route diversity and optimality but it an unclear way.