Peering Only? Analyzing the Reachability Benefits of Joining Large IXPs Today

Internet Exchange Points (IXPs) became a fundamental building block of inter-domain routing throughout the last decade. Today, they offer their members access to hundreds-if not thousands-of possible networks to peer. In this paper, we pose the question: How far can peering at those large IXPs get us in terms of reachable prefixes and services? To approach this question, we first analyze and compare Route Server snapshots obtained from eight of the world's largest IXPs. Afterwards, we perform an in-depth analysis of bi-lateral and private peering at a single IXP based on its peering LAN traffic and queries to carefully selected, nearby looking glasses. To assess the relevance of the prefixes available via each peering type, we utilize two orthogonal metrics: the number of domains served from the prefix and the traffic volume that a large eyeball network egress towards it. Our results show that multi-lateral peering can cover (similar to)20% and (similar to)40% of the routed IPv4 and IPv6 address space, respectively. We observe that many of those routes lead to out-of-continent locations reachable only via three or more AS hops. Yet, most IXP members only utilize "local" (i.e., single hop) routes. We further infer that IXP members can reach more than half of all routed IPv4 and more than one-third of all routed IPv6 address space via bi-lateral peering. These routes contain almost all of the top 10K egress prefixes of our eyeball network, and hence they would satisfy the reachability requirements of most end users. Still, they miss up to 20% of the top 10K prefixes that serve the most domains. We observe that these missing prefixes often belong to large transit and Tier 1 providers.