TCP fragmentation before the SNI extension circumvents the GFW, but TCP fragmentation placing the SNI in the first TCP segment does not. The paper notes the GFW is showing 'the first signs of successfully handling TCP fragmentation,' indicating active hardening of TCP-layer circumvention that makes TLS-layer techniques increasingly necessary.

The GFW's SNI inspection is a stateless single-record parser: it cannot detect the SNI extension when the ClientHello is split across multiple TLS records, even when all records are contained within the same TCP segment. In contrast, the GFW does detect SNI when it appears fully within the first TCP segment despite TCP fragmentation, indicating the reassembly gap is specific to the TLS record layer.

§3 detection

TLS record fragmentation is implementable entirely in userspace at the application layer and requires no elevated privileges, unlike TCP segmentation which requires raw socket access. The authors' DPYProxy tool demonstrates a MITM approach that wraps TLS messages into smaller records before transmission without breaking the TLS handshake, since TLS records are unprotected during the handshake phase.

§2, §5 defense

96.21% of CitizenLab-tracked censored domains (1,092 of 1,135 scanned) and 92.36% of Tranco Top 1M domains (766,909 of 830,357 scanned) already support TLS record fragmentation, with support exceeding 90% across all Tranco rank ranges. This broad server-side compatibility makes TLS record fragmentation deployable without any server-side changes.

§4, Table 2 evaluation

TLS record fragmentation successfully circumvents the GFW in all tested configurations: splitting the ClientHello across multiple TLS records — whether the split falls before or after the SNI extension — bypasses GFW SNI-based blocking in every case (Table 1). TCP fragmentation after the SNI extension fails, but any TLS-layer fragmentation succeeds.

§3, Table 1 defense

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

Of 6,915,266 domains extracted from the 572 GiB Geedge Networks Leak (GNL), 298,955 censored domains (93.7% of all GNL-censored domains) appear in neither Tranco top-1M nor CitizenLab test lists. Measurements across China (Guangzhou/Nanjing), Myanmar, Pakistan, and Algeria confirmed censorship via DNS injection and SNI-based TLS connection termination. The GNL covers 25–62% of Tranco-censored domains across countries, showing substantial but incomplete overlap. This vendor-side ground truth reveals a censorship surface roughly two orders of magnitude larger than curated academic test lists.

2026-sheffey-geedge §4.1, Table 2 dpisni-blockingdns-poisoningmeasurement-platform