Unveil the Hidden Presence: Characterizing the Backend Interface of Content Delivery Networks

Abstract

Content Delivery Networks (CDNs) are critical to today’s Internet ecosystem for delivering rich content to end-users. CDNs augment the Internet infrastructure by deploying geographically distributed edge servers, which play a dual role in CDNs: one as frontend interface to facilitate end-user’s proximal access and the other as backend interface to fetch content from origin servers. Previous research has well studied the frontend interface of CDNs, but no active approach has yet been provided to investigate the backend interface. In this paper, we first propose an active approach to measuring the backend interface of CDNs. Then, we present a large-scale measurement study to characterize the backend interface for three CDN platforms, so as to understand the CDN’s globally distributed infrastructure, which is essential to its performance and security. In particular, we discover the address space and operation patterns of the backend interface of CDNs. Then, by analyzing the backend addresses and their associated frontend addresses, we study their geolocation association. Furthermore, we issue traceroutes from origin servers to the backend addresses of the CDNs to analyze their performance implications, and perform port scanning on the backend addresses to investigate their security implications.