Google Public DNS and Location-Sensitive DNS Responses

Monday, December 15, 2014

Webmaster level: advanced

Recently the Google Public DNS team, in collaboration with Akamai, reached an important milestone: Google Public DNS now propagates client location information to Akamai nameservers. This effort significantly improves the accuracy of approximately 30% of the location-sensitive DNS responses returned by Google Public DNS. In other words, client requests to Akamai hosted content can be routed to closer servers with lower latency and greater data transfer throughput. Overall, Google Public DNS resolvers serve 400 billion responses per day and more than 50% of them are location-sensitive.

DNS is often used by Content Distribution Networks (CDNs) such as Akamai to achieve location-based load balancing by constructing responses based on clients’ IP addresses. However, CDNs usually see the DNS resolvers’ IP address instead of the actual clients’ and are therefore forced to assume that the resolvers are close to the clients. Unfortunately, the assumption is not always true. Many resolvers, especially those open to the Internet at large, are not deployed at every single local network.

To solve this issue, a group of DNS and content providers, including Google, proposed an approach to allow resolvers to forward the client’s subnet to CDN nameservers in an extension field in the DNS request. The subnet is a portion of the client’s IP address, truncated to preserve privacy. The approach is officially named edns-client-subnet or ECS.

This solution requires that both resolvers and CDNs adopt the new DNS extension. Google Public DNS resolvers automatically probe to discover ECS-aware nameservers and have observed the footprint of ECS support from CDNs expanding steadily over the past years. By now, more than 4000 nameservers from approximately 300 content providers support ECS. The Google-Akamai collaboration marks a significant milestone in our ongoing efforts to ensure DNS contributes to keeping the Internet fast. We encourage more CDNs to join us by supporting the ECS option.

For more information about Google Public DNS, please visit our website. For CDN operators, please also visit " A Faster Internet " for more technical details.