The study located 495 router interfaces with attached IDS filtering devices across China, with CHINANET holding 79.4% and CNCGROUP 17.4%. The two ISPs use fundamentally different placement strategies: CHINANET distributes filtering across provincial networks (80% of its 21 served provinces operate their own filtering devices, Guangdong alone hosting 84 of 374 CHINANET interfaces), while 90% of CNCGROUP's 82 filtering interfaces concentrate in its backbone.

CNCGROUP's filtering interface count has grown to three times its 2007 level, now accounting for 17.4% of all 495 filtering interfaces found, while CHINANET's count has remained stable since 2007. This divergence indicates CNCGROUP is actively expanding its censorship infrastructure while CHINANET's filtering capacity has matured.

§4.4 evaluation

China's AS-level topology is shallow and concentrated: CHINANET and CNCGROUP together account for 63.9% of 133 unique foreign peerings, 87% of internal ASes are within one hop of a border AS, and just 24 border/backbone ASes serve as effective choke points for all international traffic. The TTL of GFW RST packets is now crafted to prevent IDS localization by TTL inspection, requiring TTL-incrementing probe packets to identify filtering device positions.

§3.2, §3.3, §2 evaluation

The GFW is fully stateful as of 2010: probing all 11,824 Chinese IP prefixes with single TCP packets containing the keyword 'falun' produced no RST responses, confirming that a complete TCP handshake must precede any filtering trigger. Earlier measurements (2006, 2007) reported contradictory results; this study finds statefulness is now universal across all probed prefixes.

§4.1 detection

14 of 495 filtering interfaces (2.9%) are located in non-border internal ASes, all but two belonging to CHINANET provincial subsidiaries. The paper notes that CHINANET's provincial filtering architecture creates infrastructure capable of inspecting inter-provincial domestic traffic, even though there is no current evidence it is being used for that purpose.

§4.4, Table 2 detection

TLS connections to blocked services (instagram.com, telegram.org) were terminated by TCP RST immediately after the client's ClientHello, before any certificate exchange, confirming SNI-based DPI that reads the plaintext SNI extension and aborts the handshake. HTTP filtering additionally matched Host headers and URL keywords case-sensitively, with injected HTTP 403 pages or TCP RST responses, and case-change evasions were sometimes effective.

2025-aryapour-stealth-blackout §4.2, §4.3 sni-blockingdpirst-injectionkeyword-filtering

Iran's HTTP censor exhibits several parsing inconsistencies exploitable for evasion: (1) it is case-sensitive and ignores lowercase method variant "gET"; (2) it does not censor the Host header for HTTP version strings "HTTP", "1.1", and "example" (suggests a version regex of HTTP/.*); (3) when the Host header is absent, the path is not censored for versions "HTTP" and "HTTP/1"; (4) the body is never analyzed regardless of version. All HTTP and DNS censorship occurs at the same last-hop border node, suggesting centralized architecture.

2025-lange-i-ra-nconsistencies §3.2, Table 1 dpikeyword-filteringrst-injection

China's Great Firewall showed anomalous inconsistency: 13 test vectors produced mixed outcomes—TCP RST injection on some executions and a clean server response on others—with circumvention rates between 10% and 35% across 100 executions per vector. The authors attribute this to heterogeneous GFW infrastructure components applying different HTTP parsing logic, a departure from the GFW's usual consistency.

2024-m-ller-turning §5.2 dpirst-injectionkeyword-filteringmiddlebox-interference

China's GFW exhibited unusually inconsistent HTTP censorship behavior: 13 of the evaluated HRS test vectors circumvented the GFW in some executions but not others, with per-vector success rates between 10% and 35% across 100 executions per domain. The authors attribute this to two distinct parts of GFW infrastructure employing different HTTP censorship mechanisms, a departure from the GFW's typical consistency.

2024-niere-http-smuggling §5.2 (China paragraph), §5 intro dpirst-injectionkeyword-filtering

Extending Geneva's genetic algorithm to the application layer automatically discovered 77 unique HTTP evasion strategies and 9 DNS evasion strategies against censors in China, India, and Kazakhstan — all requiring only unprivileged usermode modifications with no TCP/IP header access. Against India's Airtel censor, 56 of the 77 strategies succeeded; 29 worked against Kazakhstan; 22 evaded China's keyword-based HTTP censorship and 27 evaded its Host-header censorship.

2022-harrity-get §5.1, §6 dpikeyword-filteringrst-injectiondns-poisoning

The GFW only inspects two locations within an HTTP request for censored keywords: the path component of the request line and the Host header, in UTF-8 and GB 18030 encodings (with %-decoding applied). Cookie headers, custom headers (e.g., X-Tension), and POST body fields are not monitored. Even in monitored positions, only approximately 75% of requests containing censored keywords actually trigger a TCP RST disconnection.

2021-rambert-chinese §4.4 keyword-filteringdpirst-injection