In Censored Planet DNS measurements of 75 .gov and .mil domains on April 11, 2021, only 36.06% of measurements from China resolved correctly. Of the failures, 19.06% returned SERVFAIL codes caused by US-based nameservers geoblocking Chinese recursive resolvers—server-side access control, not GFW censorship—causing prior studies that did not account for geoblocking to systematically over-estimate DNS blocking in China.

Censored Planet measurements of psiphon.ca in AS6697 (Belarus) around the August 2020 Internet shutdown showed that Psiphon was initially blocked via connection timeouts during the shutdown itself, and then—several weeks after the shutdown ended—the censorship mechanism shifted to TCP RST injection. Outcome-typed measurement data made this two-phase mechanism change immediately visible without re-collecting any raw data.

§4.3 detection

During the Belarus Internet shutdown of August 9, 2020, Censored Planet Echo measurements showed an increase of two orders of magnitude in test measurements failing at the TCP connection stage on the first day of the shutdown, alongside an order of magnitude increase in failed control measurements on the same day. Without comparing test measurements against control measurements that are expected to succeed regardless of content, these failures are indistinguishable from targeted website-level censorship.

§4.2 evaluation

The Censored Planet data analysis pipeline matched more than 60.89% of all HTTP-response data across four years of measurements to either a known blockpage fingerprint or a confirmed non-censorship fingerprint. Over 60 million individual measurements were specifically classified as expected Akamai CDN behavior—responses that previous work had routinely misclassified as censorship because Akamai's edge configuration returns connection timeouts or HTTP 301 redirects when the test domain and vantage-point server are both Akamai-hosted.

§4.2 evaluation

Previous work reported that Myanmar ISPs selectively applied DNS blocking versus TCP/IP blocking, but analysis of the underlying data revealed they applied both concurrently. The apparent difference arose because some OONI volunteers bypassed DNS tampering by using public DNS resolvers (Cloudflare, Google Public DNS) and subsequently experienced IP-level blocking instead, making measurements appear selective when they were not.

§3.1 evaluation

The June 2025 Iran shutdown—carried out during the Iran-Israel war beginning ~June 19—did not use BGP route withdrawals as in 2019. Instead, authorities applied service-level restrictions at the national border: DNS poisoning of foreign destinations, protocol whitelisting permitting only pre-approved domestic services, and DPI to block circumvention-tool traffic. Iran's international traffic fell roughly 90% while the country's BGP routes remained advertised, making the shutdown invisible to BGP-based monitoring systems. OONI measurement volume, which totalled 121,333 in June 2025, collapsed to under 200 submissions on June 19-20.

2025-iran-shutdown-measurement Executive Summary / §2 dpidns-poisoningport-blockingip-blocking

Article 19 documents that Iran's National Information Network (NIN / SHOMA) was designed with explicit reference to China's Great Firewall as a model, with institutional mirroring: Iran's Supreme Council of Cyberspace parallels China's Cyberspace Administration of China, and both governments share a "cyber sovereignty" doctrine used to justify domestic content controls and cross-border technology transfer. The report frames Iran's filtering infrastructure as deliberately architected to replicate GFW capabilities, not as an independently developed system.

2026-article19-tightening-the-net §2, §3 dpisni-blockingdns-poisoningip-blockingbgp-hijackthrottling

Article 19 documents that Iran combines technical filtering with formal coercion of major foreign platforms (including Telegram, Instagram, and WhatsApp) to comply with content removal orders under threat of full blocking. The report notes that Iran's 2022 Women Life Freedom protests accelerated platform blocking when foreign operators refused compliance, demonstrating that the censorship system operates in two modes: coerce-and-allow for compliant platforms, block for non-compliant ones. Domain fronting via these platforms is therefore subject to sudden revocation if political conditions change.

2026-article19-tightening-the-net §6 ip-blockingdns-poisoningthrottling

Both Firefox and Chromium leak cleartext DNS before establishing encrypted DNS connections: they first send an unencrypted UDP DNS query to resolve the DoH server's domain (e.g., doh.opendns.com). An in-path censor can intercept and poison this initial query, making encrypted DNS in browsers completely ineffective without additional circumvention of the resolver-lookup step. Additionally, Chromium always includes the SNI extension in the encrypted DNS TLS handshake (e.g., "doh.opendns.com"), leaking the resolver identity even after the initial lookup. No resolver requires SNI to be present for certificate validation when the resolver's IP certificate is configured.

2026-lange-towards §2.4, §7, §10 dns-poisoningsni-blocking

DNS censorship of encrypted protocols is inconsistent in both China and Iran. In China, Yandex resolvers are censored only when the SNI extension is present; omitting SNI bypasses censorship for these resolvers. In Iran, DoH requires SNI omission for Quad9, Google, Adguard, CleanBrowsing, and NextDNS resolvers, but works with SNI for Yandex and Cisco resolvers. These inconsistencies suggest resolvers have been accidentally missed by censors, highlighting the value of automated tools that trial all resolver-mode combinations rather than hard-coding a single strategy. The support evaluation found 47 resolvers supporting DoH, 16 supporting DoH3, and only 8 supporting DoQ out of ~65 tested.

2026-lange-towards §6.2, Table 2 dns-poisoningsni-blockingip-blocking

DPYProxy-DNS tested 8 circumvention modes against DNS censorship from vantage points in Iran (AS201295, Mashhad) and China (AS4837, China Unicom). In Iran, DoQ was entirely uncensored even with the SNI extension present; DoH3 worked for all Cloudflare and NextDNS resolvers. Iran's censor operates in-path (not on-path like the GFW), making the "Last Response" mode (wait 3s for the last UDP reply) ineffective in Iran but highly effective in China. Auto-mode averaged 12.32s (median 8.28s) in Iran and 13.78s (median 12.90s) in China to discover a working combination.

2026-lange-towards §6.2, §6.3 dns-poisoningsni-blockingip-blocking