The Understanding and Forecast of AS-Level Anycast Path Inflation

Anycast, as a network layer solution for providing faster and stabler services to end-users, is actively deployed on the Internet today. A common argument is that the underpinning routing system will automatically direct users to the closest site among the set of anycast sites. However, anycast path inflations are observed, where users are unexpectedly directed to a site farther away. In this paper, we study a specific kind of anycast path inflation called AS-level Anycast Path Inflation (AAPI). AAPI means, after the deployment of an anycast site in a different Autonomous System (AS), the number of ASes that traffic passes through is larger than that before, so that users may experience increased latencies or be exposed to higher inter-domain security risks. We discuss AAPI’s causes, analyse its characteristics, and propose deployment guidance. In particular, we classify AAPI in two basic forms, i.e. Route Suppression (RS) and Route Promotion (RP), and present their various characteristics as well as their possible coupling. We propose Conflict Point (CP), a topological feature which represents the intrinsic conflict between routing policies and AS path length at these nodes, to further study the necessary and sufficient conditions for AAPI. And based on the properties of CP, we give some suggestions on anycast deployment strategy to avoid AAPI and verify them by simulation.