2019-hoang-measuring
findings extracted from this paper
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China's GFW poisons DNS responses from major open resolvers (Google 8.8.8.8/8.8.4.4, Cloudflare 1.1.1.1/1.0.0.1, OpenDNS 208.67.222.222/220) for I2P domains, returning public IPs belonging to Facebook, SoftLayer, and other non-Chinese organizations. Blocking is non-uniform: AS9808 (Guangdong Mobile) appended a loopback 127.0.0.1 record alongside falsified IPs—a pattern not seen at other ASes—while the I2P mirror site remained accessible from most Chinese locations despite the homepage being blocked.
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DNS injection from China's GFW leaked into South Korean networks: queries sent from Korean ASes (AS38676, AS9848) to open resolvers returned the same falsified IP addresses observed inside China, because geographic proximity caused transit routing through Chinese infrastructure. This demonstrates that the GFW censors both egress and ingress traffic, producing cross-border poisoning as a side effect. Sporadic rather than consistent injection at these ASes confirmed the leakage hypothesis rather than intentional Korean blocking.
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Oman and Qatar deploy layered blocking: after a TCP handshake to geti2p.net completes normally, a TCP RST is injected immediately after the TLS ClientHello (SNI-based blocking), while HTTP connections to the mirror site receive injected packets redirecting to explicit national block pages. Kuwait applied only the HTTP mirror block, and only at one of six tested ASes (AS47589, Kuwait Telecommunication Company), with all other Kuwaiti networks leaving I2P fully accessible—illustrating significant ISP-level variation within a single country.
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Over one month, 54K measurements from 1.7K ASes in 164 countries detected I2P blocking in exactly five countries: China (DNS poisoning of homepage and 3 of 10 reseed servers), Iran (TCP RST injection with HTTP 403 on mirror site), Oman and Qatar (SNI-based blocking of HTTPS homepage plus TCP injection with block-page redirect on HTTP mirror), and Kuwait (TCP injection on mirror site at AS47589 only). All other tested countries left I2P fully reachable.
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A measurement infrastructure built on VPN Gate's 192K volunteer-operated residential vantage points (3.5K ASes, 181 countries) detected I2P blocking events that were missed entirely by both OONI—which had no test data for four of the five affected countries—and ICLab—which had vantage points in only two of the five countries and obtained only intermittent connections there. Residential vantage points reveal filtering policies invisible from datacenter-hosted probes, with ISP-level granularity confirming partial national blocking (one of six Kuwaiti ASes, heterogeneous Chinese AS behavior) that aggregate measurements would miss.