The GFW uses substring-matching regular expressions rather than exact domain matching, causing 41K of 311K censored domains to be overblocked — unrelated domains that happen to contain a censored domain string. The three base domains causing the most overblocking (919.com, jetos.com, 33a.com) collectively caused 15K unrelated domains to be inadvertently censored.

GFWatch tested 534M distinct domains over 9 months (averaging 411M/day) and detected 311K censored domains, the largest such measurement in the literature. Of 138.7K base domains, only 1.3% appear in the top 100K most popular domains, confirming the GFW targets large numbers of obscure and unpopular domains far beyond well-known sites like Facebook or Twitter.

§4, Figure 3 evaluation

A circumvention strategy of holding DNS responses and filtering those matching the known forged-IP pool achieves 99.8% accuracy, correctly classifying 1,005,444,476 of 1,007,002,451 poisoned resolutions. From inside China, 99% of forged responses arrive within 364ms before the legitimate response, establishing 364ms as the recommended hold-on duration; from outside China, 11% of forged responses arrive after the legitimate one, making the IP-blocklist check necessary to avoid misclassifying genuine responses as poisoned.

§7.1, §7.2, Figure 11 defense

The GFW's bidirectional DNS filtering — which poisons DNS queries regardless of whether they originate inside or outside China — has polluted the caches of major public DNS resolvers worldwide: Google (74,715 censored domains), Cloudflare (71,560), OpenNIC (65,567), and OpenDNS (63,295), with 77K censored domains found polluted in total. This is compounded by the fact that 38% of base censored domains (53K) have at least one authoritative name server inside China, ensuring systematic external pollution for those domains.

§6.1, §6.2, Table 2 evaluation

GFWatch discovered 1,781 unique forged IPv4 addresses used in GFW DNS poisoning, yet injection is non-random: only 600 (33.6%) account for 99% of all censored responses, with the remainder in a long tail responsible for just 1%. The forged IPv4 pool is dominated by addresses belonging to Facebook (783 IPs, 44%), WZ Communications (277, 15.6%), Twitter (200, 11.2%), and Dropbox (180, 10.1%); all forged IPv6 responses use the bogus Teredo prefix 2001::/32.

§5.1, §5.2, Figure 8 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

Encrypted DNS protocols (DNS-over-HTTPS and DNS-over-TLS via Cloudflare 1.1.1.1, Google 8.8.8.8, AdGuard, or NextDNS) prevent DNS injection by encrypting the resolver query, making it opaque to in-path GFW middleboxes. The blog recommends these as a lightweight defense that avoids the maintenance overhead of static hosts entries.

2026-anon-6-github-dns §2 使用加密 DNS 服务 dns-poisoning

The GFW blocks GitHub by hijacking DNS resolution to incorrect IP addresses, causing browser timeouts ('github.com 响应时间太长'). The poisoning can be confirmed by comparing nslookup results against a clean resolver (8.8.8.8) versus the local ISP resolver — divergent results confirm injection.

2026-anon-6-github-dns §5 验证 DNS 污染 dns-poisoning

Static /etc/hosts bindings that hardcode correct IPs (e.g. 140.82.113.3 for github.com, 185.199.108.153 for assets-cdn.github.com) bypass DNS-injection blocking entirely, but the blog warns that GitHub IP addresses change and the file must be updated periodically to remain effective.

2026-anon-6-github-dns §1 手动修改 Hosts 文件 dns-poisoning

Chinese users treat full proxy/VPN (Shadowsocks, V2Ray/Clash, commercial VPNs) as the '终极大杀器' (ultimate solution) for bypassing GitHub DNS poisoning, implying that lighter-weight DNS-only fixes fail in some network environments where the censor adds firewall-layer blocking beyond DNS.

2026-anon-6-github-dns §3 使用代理或 VPN dns-poisoningip-blocking

Rule-based proxy tools (Clash, Shadowsocks, V2Ray) are documented as the most reliable solution for accessing GitHub from China, with split-tunneling rules routing only GitHub traffic through the proxy while keeping domestic traffic on the direct path. Git command-line tools require explicit proxy configuration (git config --global http.proxy http://127.0.0.1:7890) to route clone/push operations, as they do not inherit system proxy settings automatically.

2026-anon-github-2026-6-dns §方法二 dns-poisoningip-blocking