Public DNS Resolvers Meet Content Delivery Networks: A Performance Assessment of the Interplay

2025-02-09

AI Summary

This paper addresses two critical performance issues in public DNS–CDN coordination: (1) CDN hostname resolution latency and (2) end-to-end latency from users to CDN edge nodes. To account for emerging realities—including IPv6 adoption, widespread ECS (EDNS Client Subnet) deployment, and CDN anycast evolution—we conduct large-scale empirical measurements spanning DNS latency analysis, ECS support detection, dual-stack (IPv4/IPv6) performance comparison, CDN node geolocation, and RTT mapping. Our key contributions include: (i) the first systematic demonstration that DNS cache hit rate critically governs CDN geographic mapping accuracy; (ii) identification of measurable yet non-triggering Happy Eyeballs fallback under IPv6, leading to degraded mapping quality in mainstream resolvers; and (iii) quantitative evaluation showing Cloudflare DNS achieves the lowest resolution latency, while Google and OpenDNS deliver mapping quality comparable to ISP resolvers; Quad9, however, incurs significant latency penalties for most CDNs.

Technology Category

• Application Domains: Humanities & Computational Social Science
• Search and Optimization: Distributed Search
• Data Mining & Knowledge Management: Graph Mining, Social Network Analysis & Community

Application Category

• Responsible Web: Measurement, analysis, and circumvention of Web censorship
• Web Mining and Content Analysis: Web measurements
• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization

Abstract

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.

Problem

• Assess latency of DNS queries for CDN hostnames.
• Evaluate latency between users and CDN edge servers.
• Analyze IPv6 impact on CDN-edge-server latency.

Innovation

• Assesses DNS-CDN interplay performance
• Evaluates IPv6 and DNS ECS impact
• Compares resolver latency and cache rates