This presentation includes a discussion and results of work remotely mapping DNS-based internet filtering across China, using a GeoIP database to locate DNS servers at the city level and identify variations in filtering.
Of particular interest in this work was correlated redirection of domains to similar IP addresses, or even other domains, across China. This occurred even when the DNS servers in question were not, apparently, related.
This supersedes my earlier work on this topic, due to greatly improved filtering detection methods.
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