“Look, Ma, no probes!” — Characterizing CDNs’ latencies with passive measurement

Cloudflare, a content delivery network (CDN) provider, has developed a method to measure and predict the performance of its network and other CDNs without relying on active probes. The technique involves using passive RTT measurements from Cloudflare's own infrastructure to estimate latency between clients and other CDNs. This approach allows for understanding latency to locations where CDNs have deployed their infrastructure, as well as showing performance improvements in locations where one CDN exists but others do not. The methodology has been validated through a large-scale traceroute and ping measurement campaign, with results indicating that Cloudflare exhibits the lowest median RTT across all observed clients.