CloudFlare platform policy creates outsized blocking: 80% of CloudFlare-hosted websites discriminate against at least 60% of studied Tor exits, while Amazon- and Akamai-hosted sites show high policy diversity. Social networking and shopping sites are the most aggressive discriminators — 50% block over 60% of studied exits — while search engines are least aggressive, with 83% blocking fewer than 20% of exits.

Conservative exit policies (Reduced-Reduced, which additionally blocks SSH, Telnet, and IRC ports beyond the default) have no statistically significant correlation with IP blacklisting rates or abuse complaint volume. Web-traffic accounts for 98.88% of all connections on Reduced-Reduced exits, confirming that ports 80/443 are the primary abuse vector and that port-restriction does not meaningfully reduce exposure.

§5.5 evaluation

7% of 84 commercial IP blacklists proactively blacklist Tor exit relay IPs as a matter of policy: the Snort IP and Paid Aggregator blacklists listed newly deployed relay IPs within 3 hours of their first appearance in the Tor consensus and maintained the listing for the entire relay lifetime. In total, 88% of all Tor exits appear on at least one commercial blacklist, compared to 9% of VPNGate and 69% of HMA VPN endpoints.

§5.2, §5.3, §5.6 detection

Real Tor users browsing the Alexa Top 1M websites via deployed exit relays experience failed HTTP requests at rates of 15.8–33.4% and failed HTTPS handshakes at rates of 35.0–49.6%, representing severe service degradation compared to non-Tor browsing (Table 8).

§7, Table 8 evaluation

20.03% of Alexa Top 500 website front-page loads showed discrimination against Tor exit users. Exercising search functionality on compatible sites raised discrimination by 3.89% (to 21.33%), while exercising login functionality raised it by 7.48% (to 24.56%), demonstrating that headless front-page-only crawlers significantly underestimate the true blocking rate Tor users face.

§6.4, Table 6 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

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