Anycast-based DNS in Mobile Networks

Abstract

Anycast offers a method for making a service IP address available to a routing system from several locations at once. It is used today to provide important services, such as naming and content delivery, in an economic, scalable, and simple to operate manner. The appeal and clear benefits of anycast to service providers have motivated a number of recent experimental studies on its potential performance impact. All studies have, to the best of our knowledge, focused on wired networks, despite the growing dominance of mobile as the most common and sometimes only form of Internet access. In this paper, we present the first study of anycast performance for mobile users. In particular, our evaluation focuses on three distinct anycast services, K- and F-Root, each providing part the DNS root zone, and Google DNS.

Our research revolves around three axes. First, we show that mobile clients are frequently routed to suboptimal replicas in terms of latency and that this issue is not limited to specific regions or ASes of the world. Second, we find that clients are often redirected to a DNS server hosted very far away from her. This happens more frequently while on a cellular connection than on WiFi, with a significant impact on performance. Our study reveals that this is not simply an issue of not having better alternatives, and that the problem is not localised to particular geographic areas or particular ASes. We investigate root causes of this phenomenon and describe three of the major detected classes of anycast anomalies. Third and finally, we explore IP assignment dynamics of mobile clients and find that recurrent IP changes on the client side lead to significant perceived variations of anycast latency.