Domains on VLESS+WebSocket behind Cloudflare are blocked in Iran even when they have no configured DNS A record and the root domain was never used — indicating Iran blocklists domain names extracted from SNI in reassembled TCP streams rather than requiring prior DNS query evidence.

As of June 2026, Iranian DPI blocking timescales are: CDN-fronted VLESS+WebSocket domains blocked within 24 hours; SSH dynamic port forwarding server IPs blocked within 8 hours; Reality and WireGuard connections blocked immediately (seconds) after handshake completion. This graduated timeline suggests separate fast-path (handshake-pattern) and slow-path (domain reputation / traffic accumulation) detection pipelines operating in parallel.

Issue body — combined observations evaluation

Iran's DPI blocks VLESS/WS traffic routed through Cloudflare CDN in full-strict TLS mode with regularly rotated clean Cloudflare IPs, demonstrating that CDN-fronted traffic is not opaque to the censor and that IP-layer evasion (using clean CDN IPs) is insufficient when the SNI is fingerprinted.

Description detection

Iran's DPI infrastructure performs full TCP reassembly and stateful inspection on the fly, nullifying TCP fragmentation (10–30 byte fragments with 10–20ms delays) applied to VLESS+WebSocket behind Cloudflare CDN in full-strict mode. Domains are blocked within 24 hours despite the CDN layer and rotation of clean Cloudflare IPs. Fragmentation was applied to the first 5 packets and verified correct on the client side with tcpdump; the setup used port 443 with a randomized WebSocket path.

Issue body — Description / The Issue detection

Iran's censor deploys a two-stage blocking response within 24 hours of domain exposure: DNS hijacking that resolves blocked domains to 10.10.34.34, combined with RST floods when clients connect directly to Cloudflare IPs using the blocked SNI. Both mechanisms activate independently, so DNS-resistant clients are still terminated at the TCP layer.

Issue body — The Issue detection

The Reality protocol triggers immediate RST flood responses from Iranian ISP infrastructure at the completion of the TLS handshake, suggesting Iranian DPI has developed a fingerprint or active-probe response specifically targeting Reality's TLS handshake forwarding mechanism as of June 2026.

Issue body — Other Observations §2 detection

Iranian DPI exhibits stateful connection tracking with 'cooling-off' enforcement periods on flagged flows and is synchronized across multiple ISPs, suggesting centralized or coordinated blocking infrastructure. Port 443 receives particularly aggressive inspection, and the DPI performs behavioral analysis of upload/download traffic ratios to identify proxy usage, enabling SSH-based proxy server IPs to be fully blocked within 8 hours.

Issue body and thread summary (Jun 10, 2026) detection

Community members propose a two-hop architecture as a potential mitigation for Iran's current DPI upgrade: a first-hop server inside Iran's whitelisted datacenter ranges (where outbound traffic faces lighter inspection) proxying to a foreign exit node, with Reality masquerading as a legitimate Iranian organization's domain. The architecture's effectiveness under active TCP reassembly and handshake probing is explicitly unverified.

Issue body — Description defense

WireGuard connections are blackholed by Iranian infrastructure immediately after the initial WireGuard handshake completes — clients stop receiving server packets — indicating the Iranian DPI identifies WireGuard by its distinct UDP handshake pattern and applies IP-level blocking at that point.

Issue body — Other Observations §3 detection

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

Testing the Tranco Top 100k domain list from Russian vantage points shows that all 2,644 domains blocked over TLS SNI are also blocked over QUIC SNI, and domains accessible via TLS are accessible via QUIC—indicating the TSPU maintains a unified SNI blocklist across protocols. Additionally, 31 domain patterns including discord.com exhibit 'residual clearance': QUIC connections to those domains are not censored when immediately preceded by non-censored data on the same 4-tuple; 22 domains are only blocked on port 443.

2026-heitmann-russia-s-early-introduction §3, Table 3 sni-blockinghttp3-quic-blockdpi

Reproducing Zohaib et al.'s 10-payload QUIC parser test suite against Russian TSPU devices reveals that the Russian QUIC parser differs meaningfully from the GFW: payload 8 (PING and PADDING frames inserted before the Crypto frame), which circumvents the GFW, does not bypass Russian censorship. Payload 10 (QUICv2) bypasses both censors. Payload 9 (ECH with outer SNI cloudflare-ech.com) is blocked by Russia; payload 3 (version bytes 0x00000002 with invalid MAC) is blocked by both.

2026-heitmann-russia-s-early-introduction Appendix B, Table 2 http3-quic-blockdpisni-blocking

As measured from three Russian vantage points in March–April 2026, TSPU devices decrypt QUIC Initial packets, locate the SNI extension in the embedded TLS handshake, and drop packets with forbidden domains plus all subsequent packets on the 4-tuple for 420 seconds (timer resets on each packet). Censorship is unidirectional (outgoing only), covers all destination ports up to 65535 at Saint Petersburg and Novosibirsk (Moscow exempts 22% of system ports 1–1023), and targets only QUICv1—QUICv2 passes uncensored at all vantage points.

2026-heitmann-russia-s-early-introduction §3 sni-blockinghttp3-quic-blockdpi