Detecting and assessing the hybrid IPv4/IPv6 as relationships

The business relationships between the Autonomous Systems (ASes) play a central role in the BGP routing. The existing relationship inference algorithms are profoundly based on the valley-free rule and generalize their inference heuristics for both the IPv4 and IPv6 planes, introducing unavoidable inference artifacts. To discover and analyze the Type-of-Relationship (ToR) properties of the IPv6 topology we mine the BGP Communities attribute which provides an unexploited wealth of reliable relationship information. We obtain the actual relationships for 72% of the IPv6 AS links that are visible in the RouteViews and RIPE RIS repositories. Our results show that as many as 13% of AS links that serve both IPv4 and IPv6 traffic have different relationships depending on the IP version. Such relationships are characterized as hybrid. We observe that links with hybrid relationships are present in a large number of IPv6 AS paths. Furthermore, an unusually large portion of IPv6 AS paths violate the valley-free rule, indicating that the global reachability in the IPv6 Internet requires the relaxation of the valley-free rule. Our work highlights the importance of correctly inferring the AS relationships and the need to appreciate the distinct characteristics of IPv6 routing policies.