GFW DNS AAAA responses for censored domains return 622 IPv6 addresses: 30 from Facebook's 2a03:2880::/32 network (all sharing interface identifier face:b00c:0:25de), and 592 malformed Teredo addresses in the 2001::/32 range that directly hex-encode entries from the IPv4 pool in the lower 32 bits rather than following RFC 4380 Teredo structure. The Teredo addresses' server IPv4 (0.0.0.0) and port (0) fields are nonsensical.

Two of the 8 handshake-accepting injected IPv4 addresses host active services reachable both inside and outside China: 103.230.123.190 runs OpenSSH 8.2p1 on port 22, and 103.246.246.144 redirects 0.164% of all censored-domain requests to a website serving forbidden adult content.

§2.2.1 evaluation

The authors recommend that users encrypt DNS queries (DoT or DoH) to prevent the GFW's on-path injectors from intercepting and poisoning them, and additionally block all outgoing traffic to the known pool of GFW-injected IP addresses to avoid silently connecting to potentially surveillance-oriented infrastructure.

§4 defense

Of 1922 IPv4 addresses collected from GFW-injected DNS A responses to 5,000 queries for censored domains, 8 (0.4%) actually accepted TCP handshakes when probed from within China. The other 1914 addresses were either silent or unreachable.

§2.2 evaluation

Six injected IPv4 addresses (8.7.198.46, 39.109.122.128, 46.82.174.69, 59.24.3.174, 93.46.8.90, 103.97.3.19) accept TCP SYN→SYN+ACK from within China but immediately reply RST when the client sends application data (PSH flag). These hosts mirror IPID values from probe packets, show no response from outside China, and appear to operate statelessly — suggesting GFW-controlled surveillance infrastructure that collects connection metadata without revealing itself.

§2.2.2 detection

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