Since August 2023, Henan Province has operated its own TLS SNI-based and HTTP Host-based censorship middleboxes that inspect and block traffic exiting the province—a second filtering layer on top of the national GFW. The Henan Firewall is fingerprinted by a unique TCP RST+ACK injection carrying a fixed 10-byte payload (0x01 02 03 04 05 06 07 08 09 00), IP ID 0x0001, and an observed TTL of 58. Unlike the GFW, it injects resets only toward the client, performs no residual censorship, and requires no TCP handshake to trigger. Longitudinal testing (Nov 2023–Mar 2025, Tranco top 1M daily + 227M CZDS domains weekly) found the Henan Firewall blocked a cumulative 4.2 million domains—more than five times the GFW's cumulative blocklist—and at peak blocked ten times more domains than the GFW.

The Henan Firewall only inspects traffic leaving Henan Province toward the rest of the world—it does not inspect domestic intra-China traffic nor inbound traffic entering the province. This contrasts with the GFW, which operates bidirectionally at China's national border. Measurement across seven CN cities (Beijing, Shanghai, Chongqing, Guangzhou, Nanjing, Chengdu, Zhengzhou) found no evidence of comparable provincial firewalls in the other six locations, making Henan the only documented province with an autonomous censorship layer as of March 2025. The Henan Firewall also uses the same blocklist for both HTTP Host-based and TLS SNI-based censorship, whereas the GFW maintains separate domain lists per protocol.

§3 / §4.2 / §5.1 detection

The Henan Firewall is stateless in two exploitable ways: (1) it requires the TCP header to be exactly 20 bytes—enabling any TCP option (e.g., TCP Timestamps, which Windows disables by default) to bypass it entirely; (2) it does not perform TCP reassembly, so splitting a TLS ClientHello across two TCP segments such that the SNI extension straddles the boundary bypasses the censor. Both bypasses require only client-side changes and have already been implemented in Xray, GoodbyeDPI, and Shadowrocket. TLS record fragmentation (splitting the ClientHello across multiple TLS records within one TCP segment) also defeats both the Henan Firewall and the GFW, since neither performs TLS reassembly.

§4.3 / §6 defense

Analyzing over 3 million OONI network measurements (2016–2020) from 17 ASes covering 98.45% of broadband and 90.94% of mobile subscribers in Spain, the study detected 16 unique blockpages, 2 DPI vendors (Fortinet/Fortigate in Telefonica; Allot in Vodafone), and 78 blocked websites across copyright, political, civil-rights, and referendum categories.

2021-ververis-understanding §3, §4 dpidns-poisoningpacket-injectionsni-blockingmeasurement-platform

The paper identifies a fundamental architectural vulnerability in single-IP circumvention designs: a relay must generate new observable flows (via DNS or TLS SNI) to reach end services after receiving client connections, creating a detectable server-and-client behavioral contrast. A relay accessing user-facing domains (news, social media) scores high on a Relay Suspicion Score (w=0.9) versus infrastructure domains (w=0.1). The paper argues this host-level signal is censorship-invariant and cannot be concealed by link obfuscation.

2026-almutairi-server §2.4, §4 traffic-shapedpisni-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

The report maps specific Belt and Road Initiative Digital Silk Road projects through which Chinese technology vendors have transferred censorship and surveillance infrastructure to Iran, including fiber backbone investments, data-center co-location agreements, and equipment supply chains. Specific vendors named include Huawei and ZTE as network infrastructure providers, with the report noting that equipment exports include filtering-capable hardware that Iran's ISPs have deployed at network choke points.

2026-article19-tightening-the-net §4, §5 dpisni-blockingthrottling

QUICstep successfully circumvents the GFW's QUIC SNI censorship (active since April 2024) in live testing. Using an Alibaba VM in mainland China as client and an AWS instance in North Virginia as server, a native QUIC client was blocked after several fetches of youtube.com SNI, while QUICstep consistently succeeded across 50 consecutive fetches. 7 tiktokcdn.com subdomains that were QUIC-SNI blocked were also reliably accessible via QUICstep. The approach routes only QUIC long-header (handshake) packets through a WireGuard tunnel; all subsequent short-header (data) packets travel the native path.

2026-lee-quicstep §4.3.2, §3.2.3 http3-quic-blocksni-blockingdpi

The largest single source of censored domains in the GNL is MESA lab's SNI monitoring dataset (E21-SNI-Top200w.txt) containing 57,362 censored domains, and E21-SNI-Top120W-20221020.txt with 36,467 domains—totaling over 93K domains from network tap data alone for a single country (E21 = Ethiopia per InterSecLab attribution). A separate Xinjiang dataset (XJ-CUCC-SNI-Top200w.txt) contains 13,604 domains. These datasets "do not seem to come from popular domain lists, and instead appear to be gathered from network taps," confirming that Geedge builds censorship target lists directly from passive traffic observation.

2026-sheffey-geedge §4.2, Table 3 dpisni-blockingmeasurement-platform