  A common approach when setting up a website is to utilize third party Web
hosting and content delivery networks. Without taking this trend into account,
any measurement study inspecting the deployment and operation of websites can
be heavily skewed. Unfortunately, the research community lacks generalizable
tools that can be used to identify how and where a given website is hosted.
Instead, a number of ad hoc techniques have emerged, e.g., using Autonomous
System databases, domain prefixes for CNAME records. In this work we propose
Pythia, a novel lightweight approach for identifying Web content hosted on
third-party infrastructures, including both traditional Web hosts and content
delivery networks. Our framework identifies the organization to which a given
Web page belongs, and it detects which Web servers are self-hosted and which
ones leverage third-party services to provide contents. To test our framework
we run it on 40,000 URLs and evaluate its accuracy, both by comparing the
results with similar services and with a manually validated groundtruth. Our
tool achieves an accuracy of 90% and detects that under 11% of popular domains
are self-hosted. We publicly release our tool to allow other researchers to
reproduce our findings, and to apply it to their own studies.

Networking and Internet Architecture