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.

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

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.

Issue body — The Issue 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

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

GFWeb tested 1.02 billion domains against the GFW over 20 months and discovered 943,000 pay-level domains blocked by HTTP filters and 55,000 by HTTPS filters — the largest GFW blocklist dataset ever published. The HTTP-to-HTTPS ratio (17:1) confirms that the GFW's HTTPS keyword-based and SNI-based blocking covers far fewer domains than its HTTP host-header blocking, likely because HTTPS blocks carry higher collateral-damage risk.

2024-hoang-gfweb Abstract, §5.1 dpidns-poisoningip-blockingkeyword-filteringsni-blocking

OONI data shows anomaly rates in Russia's top five ASes (including Rostelecom AS12389, Vimpelcom AS8402) rose from roughly 7–11% in January and early February 2022 to 12–21% in mid-March 2022, with social-media and news domains such as Facebook, Twitter, Instagram, and BBC going from available to near-completely blocked after the invasion.

2023-ramesh-network §4.1 dpirst-injectionip-blockingdns-poisoning

Domain shadowing makes all three traffic indicators — connecting URL, SNI, and Host header — appear to belong to an allowed shadow domain while fetching content from a blocked back-end domain via CDN. Unlike domain fronting, it exploits a legitimate CDN feature (arbitrary back-end binding) rather than a SNI/Host mismatch quirk, so CDNs cannot disable it by enforcing header consistency without breaking legitimate use cases such as third-party service outsourcing via CNAME. The technique was demonstrated successfully accessing www.facebook.com from a heavily censored country.

2021-wei-domain §3.3, §6.2 sni-blockingdpiip-blockingdns-poisoning

Table 1 of the survey documents that by 2013–2014 censors were deploying simultaneous blocking across BGP, DNS, IP/port filtering, TCP disruption, TLS, and application-layer keyword filtering. No single detection tool in the survey covers all six layers; the most comprehensive, OONI (2012), covers DNS, IP/port, TCP, TLS, keyword, and HTTP but notes only partial BGP coverage.

2015-aceto-internet Table 1 bgp-hijackdns-poisoningport-blockingip-blockingrst-injectiontls-fingerprintkeyword-filteringdpi

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