IP-level blocking causes severe over-blocking because more than 87% of all domains deploy name-based virtual hosting on shared IP addresses (per Edelman's 2003 survey of .com/.net/.org). A single blocked IP can deny access to thousands of unrelated sites; when xs4all.nl was blocked in 1996/1997, between 3,000 and 6,000 separate websites were collaterally blocked.

The paper evaluates all major circumvention techniques available in 2003 and concludes that only application-layer proxies (HTTP, SOCKS, JAP, peek-a-booty) and IP tunneling can defeat all three blocking layers (IP filtering, DNS tampering, filtering proxies) simultaneously. Encryption alone cannot circumvent IP or DNS blocking; HTTPS hides URL paths but not the destination host; DNS-over-HTTPS/DNSSEC can detect but not defeat DNS tampering without a third-party resolver.

§2.4 defense

An empirical DNS survey of North Rhine-Westphalia providers (May 2003) found that kids.stormfront.org — not named in the blocking order — was returned with obscure errors by 56% of surveyed servers, while rotten.com (also not in the order) was erroneously blocked by 11% of providers. www.stormfront.org itself was blocked by 12 providers with 0% still accessible, demonstrating that real-world DNS-tampering deployments systematically over-block non-targeted names at high rates.

§4.2, Table 1 evaluation

Survey of NRW provider DNS implementations revealed at least five distinct tampering strategies in the wild: name hijacking to a government redirect server, NXDOMAIN for entire zones, name astrayment to 127.0.0.1 (user's own machine) or to unallocated IPs such as 1.1.1.1, silence (no reply), and provoked SERVERFAIL. One provider (tops.net) additionally set tracking cookies on users redirected to its block-notification page, demonstrating that name hijacking creates a surveillance vector beyond the blocking itself.

§4.2 evaluation

DNS zone architecture prevents providers from blocking individual hostnames without also disrupting all other services (email, chat, file transfer) for every name in the same DNS zone. A provider blocking www.bad.example.com must create a synthetic zone for bad.example.com, requiring continuous re-synchronization with authoritative servers at 3–24 hour intervals; failing to replicate MX records blocks email to non-targeted addresses in the zone.

§2.2.3 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