The paper identifies 47 Cloudflare IP addresses that are already blocked by the GFW despite being shared by at least 85 websites, contradicting the prior assumption that censors avoid blocking shared CDN IPs due to collateral damage. This suggests censors will accept significant collateral damage to block CDN-hosted content when the set of co-hosted non-forbidden pages is deemed manageable.

As of July 2019, approximately 10.93% of the Alexa top 1 million websites support ESNI (all via Cloudflare CDN, which enabled ESNI across all its platforms in September 2018), with 92.56% of Cloudflare-hosted sites using encrypted SNI over TLS 1.3. However, fewer than 0.01% of observed TLS ClientHello messages in the wild contained an ESNI extension, revealing a severe gap between server-side readiness and client-side adoption.

§4.2, §5.1 evaluation

Of the Alexa top 1 million websites censored in China, 84.5% are blocked by IP address, meaning that even if both DNS hijacking and SNI filtering are fully circumvented, the vast majority of blocked sites remain inaccessible. Only 66 currently censored sites can be unblocked by ESNI alone (combined with an encrypted DNS channel), while 101,049 ESNI-supported sites remain blocked by IP.

§4.1, §4.3 evaluation

Monitoring ESNI-related censorship across 14 geographic regions — including Mainland China, Iran, UAE, South Korea, and 10 others — found no blocking of ESNI traffic or interference with ESNIKey retrieval via DNS TXT records as of mid-2019, contradicting a widely circulated report claiming South Korea had already blocked ESNI. Additionally, the GFW's residual censorship window after a triggered RST was measured at 60 seconds (down from the previously reported 90 seconds).

§4.4, §6 evaluation

In China's Great Firewall, SNI filtering is almost never the sole blocking mechanism: only 70 of the 21,446 SNI-filtered sites are exclusively censored via SNI. The GFW uses SNI filtering as a 'third gatekeeper' — applied after DNS hijacking and IP blocking — and maintains separate blacklists for SNI filtering and DNS hijacking, evidenced by 2,764 sites under DNS injection but not SNI filtering.

§4.1 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

Brussee measures a systematic pattern of Chinese government websites actively blocking access from outside China (the "reverse Great Firewall"), publishing a CSV dataset of affected domains (available at zenodo.org/records/18172145). The paper frames this outbound geo-blocking as a cybersecurity-motivated practice — Chinese authorities classify foreign access to domestic government infrastructure as an attack surface — distinct from the inbound information control goal of the GFW.

2026-brussee-reverse-great-firewall §3, §5 ip-blockingasn-blackholing

Brussee develops a conceptual framework distinguishing two logics of government geo-blocking: (1) information control (blocking inbound foreign content from domestic users) and (2) data sovereignty / attack-surface reduction (blocking outbound access by foreign actors to domestic systems). Chinese government site blocking of external IPs is motivated primarily by the second logic, creating an asymmetric internet topology where CN citizens cannot reach the outside world, and outside actors cannot probe CN government infrastructure.

2026-brussee-reverse-great-firewall §2, §4 ip-blockingasn-blackholing

ShieldShare demonstrates that an Android application can route all hotspot-client traffic through a VPN tunnel without root access by using a SOCKS5/HTTP/HTTPS proxy layer between the hotspot and the VPN, with per-client traffic accounting and quota management. The system works because Android's native hotspot does not forward VPN routing tables to connected clients; ShieldShare interposes a proxy that handles this. Released as open-source.

2026-edorh-shieldshare §Abstract ip-blocking