Analysis of a June 2025 dataset using DBSCAN clustering confirmed a heterogeneous injector deployment: individual source ports are routed to processes that are either ~100% cyclic or ~100% random-order, with an estimated ratio of approximately 6 cyclic processes to 1 non-linear process. Despite the difference in IP-selection logic, the cyclic and non-linear injectors show virtually identical DNS answer TTL distributions, indicating shared codebase with diverged IP-selection modules rather than entirely separate systems.

One type of GFW DNS injector (identified by response flags 0x8400 when query RD=0) uses ordered, cyclic IP address pools. By probing at approximately 100–500 queries per second with a fixed UDP 4-tuple, the complete ordered pool can be recovered: for torproject.org this yields 592 IPv4 addresses and 30 IPv6 addresses. The same pool is documented in Appendix A of the Wallbleed (NDSS 2025) paper for the domain 4.tt.

§Collect DNS responses / §Infer the IP address ordering deployment

The GFW DNS injector runs as multiple parallel processes that share the same IP address pool but each maintain an independent incrementing counter. Load balancing to these processes is 4-tuple hash-based (src IP, dst IP, src port, dst port), so a fixed source port is routed deterministically to one process. Probing with variable source ports revealed 3 distinct linear sequences in March 2025, growing to 5 or more by June 2025.

§Visualization (variable source ports) / wkrp comment 2025-06-03 deployment

Between March 26 and June 3, 2025, the GFW cyclic injector's IPv4 pool for torproject.org shrank from 592 to 591 addresses (the IP 162.125.82.7 was removed), and the observable number of load-balanced process sequences increased from 3 to 5. These changes occurred without altering the fundamental cyclic structure or pool membership of the remaining addresses, demonstrating that the injector infrastructure undergoes incremental updates while preserving its core mechanism.

wkrp comment 2025-06-03 (pool diff and process count) evaluation

Two distinct GFW DNS injector types respond to blocked domains simultaneously, returning duplicate responses per query. They are distinguishable by DNS response flags: the cyclic-ordering injector sets flags 0x8400 (AA bit) when query RD=0, while the second injector sets 0x8180. They also differ in DNS parser behavior: the 0x8180 injector responds to queries using an embedded literal dot (0x2e label separator), while the cyclic injector does not—reversing a behavior documented in the Wallbleed paper.

§Filter DNS responses / wkrp comment on two injector types 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

TSG's DNS parser enforces a hard limit of exactly 17 compression-pointer jumps per query; a query with 18 jumps causes domain name extraction to fail and suppresses the injection response. Only China's GFW Injector 2 shares the full combination of DNS flags 0x8180, compression-pointer encoding in injected answers, and the 17-pointer capability boundary, confirming it runs TSG's DNS injection code.

2026-ablove-technical-analysis-geedge §6.1, Table 5 dns-poisoningdpi

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