A Cloud Provider’s View of EDNS Client-Subnet Adoption

Abstract

Directing users to a nearby, high-performing front-end is core to the business of content delivery networks (CDNs). CDNs which use DNS to direct users to servers face the challenge of making decisions based at the LDNS-level, not based on the client’s IP address, and, in many cases, an LDNS is not representative of the clients it serves. The EDNS Client Subnet specification provides a solution by embedding a portion of the client’s IP address in the DNS query to help CDNs make better redirection decisions, but both the LDNS and authoritative resolver (CDN side) must support the standard. While there has been well-publicized adoption of Client Subnet by authoritative CDN resolvers, adoption rates across LDNSes are unknown.In this work, we examine Client Subnet adoption in LDNSes. We analyze DNS queries captured over one month from Mi-crosoft’s Azure Cloud platform. We find that adoption on the Internet is very low across ISPs but query volume is relatively high due to the popularity of public DNS services. We discover high network adoption rates in China and reveal that Chinese public DNS services deploy LDNSes deep into end-user networks.