A First Look at Anycast CDN Traffic

IP anycast routes packets to the topologically nearest server according to BGP proximity. UDP-based services (e.g., DNS resolvers and multicast rendez-vous points), which are based on a single request-response scheme, have been historically the first to use IP anycast. While there is a common belief in the Internet measurements community that stateful services cannot run on top of anycast due to Internet path instabilities, in this work we shed some light on the usage of anycast by Anycast-enabled Content Delivery Networks (A-CDNs). Indeed, to the best of our knowledge, little is known in the literature about the nature and the dynamics of these new players. In this paper, we provide a first look at the traffic of ACDNs. Our methodology combines active and passive measurements. Building upon our previous work, we use active measurements to detect anycast usage for servers hosting popular websites, and geolocate the A-CDN caches. Next, we characterise the traffic towards A-CDNs in the wild using a month-long dataset collected passively from a European ISP. We find that i) A-CDNs such as CloudFlare and EdgeCast serve popular web content over TCP, ii) A-CDN servers are contacted by users on a daily basis, and ii) routes to A-CDN servers are stable with few changes observed.