How resilient are individual ASes against AS-level link failures?

Most ISPs rely on their upstream providers in achieving global reachability, thus they tend to make backup upstream links for the purpose of improving their own resilience. Yet, the Internet AS topology does not entail as much redundancy as it is widely thought, e.g., in our observation, 23.6% of all ASes only have single provider. Moreover, even though an AS has multiple upstream links, if all its upstream paths share a common link, the failure on the shared link may destroy its global reachability. This raises the question, how resilient are individual ASes against AS-level link failures? In this paper, we investigate the connectivity resilience for individual ASes from a global perspective. We identify the main factor that affects the resilience of individual ASes-the number of edge-disjoint uphill paths to Tier-1 they hold. To this end, we propose algorithms to quantify the resilience for individual ASes against AS-level link failures. We apply our methods on large-scale AS relationships data sets in order to study the resilience properties of the actual Internet. Our findings reveal that a considerable proportion (29.9%) of ASes are vulnerable to even one link failure in their upstream.