This paper investigates two key performance aspects of the interplay between public DNS resolution services and content delivery networks -- the latency of DNS queries for resolving CDN-accelerated hostnames and the latency between the end-user and the CDN's edge server obtained by the user through a given resolution service. While these important issues have been considered in the past, significant developments, such as the IPv6 finally getting traction, the adoption of the ECS extension to DNS by major DNS resolution services, and the embracing of anycast by some CDNs warrant a reassessment under these new realities. Among the resolution services we consider, We find Google DNS and OpenDNS to lag behind the Cloudflare resolver and, for some CDNs, Quad9 in terms of DNS latency, and trace the cause to drastically lower cache hit rates. At the same time, we find that Google and OpenDNS have largely closed the gap with ISP resolvers in the quality of CDNs'client-to-edge-server mappings as measured by latency, while the Cloudflare resolver still shows some penalty with Akamai, and Quad9 exhibits a noticeable penalty with three of the four CDNs in the study, keeping up only for Cloudflare CDN that does not use DNS to map clients to servers. Finally, in several locations, we observe IPv6 penalty in the latency of client-to-CDN-edge-server mappings produced by the resolvers. Moreover, this penalty does not rise above typical thresholds employed by the Happy Eyeballs algorithm for falling back to IPv4 communication. Thus, dual-stacked clients in these locations may experience suboptimal performance.

翻译：本文研究了公共DNS解析服务与内容分发网络交互的两个关键性能方面——解析CDN加速主机名的DNS查询延迟，以及用户通过特定解析服务获取的终端用户与CDN边缘服务器之间的延迟。尽管这些重要问题在过去已被探讨，但IPv6的最终普及、主流DNS解析服务对DNS ECS扩展的采用，以及部分CDN对任播技术的接纳等重大发展，使得在新现实条件下重新评估变得必要。在我们考察的解析服务中，我们发现Google DNS和OpenDNS在DNS延迟方面落后于Cloudflare解析器，且对于某些CDN而言也落后于Quad9，并通过追踪发现其根源在于显著较低的缓存命中率。同时，我们发现Google和OpenDNS在CDN客户端到边缘服务器映射质量（以延迟衡量）方面已基本追平ISP解析器，而Cloudflare解析器在Akamai CDN中仍存在性能损失，Quad9则在研究涉及的四家CDN中有三家表现出明显性能损失，仅在未使用DNS进行客户端到服务器映射的Cloudflare CDN中保持相当性能。最后，在多个地理位置我们观察到解析器生成的客户端到CDN边缘服务器映射存在IPv6延迟损失。值得注意的是，这种延迟损失并未超过Happy Eyeballs算法用于回退至IPv4通信的典型阈值。因此，这些地区的双栈客户端可能会经历次优性能。