The June 2025 Iran shutdown achieved approximately 90% reduction in international traffic without BGP withdrawal by combining DNS poisoning, protocol whitelisting, and DPI at the national border — maintaining an outward appearance of normal connectivity for traditional monitoring tools while severing the population's access to the global Internet. Unlike the 2019 shutdown, which was implemented per-provider over 24+ hours, the 2025 operation was centralized and covert.

Ceno Browser's decentralized peer-to-peer network grew from approximately 600 active peers on June 13 to nearly 8,000 by July 11, 2025 — a 13× increase in under 30 days — with some Ceno connections remaining online throughout the full blackout, indicating that P2P architectures without fixed enumerable infrastructure can survive centralized application-layer shutdowns.

Executive Summary — Resilient Response evaluation

The Iranian government blocked international One-Time Passwords (OTPs) during the June 2025 shutdown, forcing citizens to abandon secure international platforms and migrate to government-approved domestic services with known security and privacy vulnerabilities — using authentication infrastructure as a deliberate chokepoint to coerce adoption of surveilled platforms at scale.

Executive Summary — Human Rights Implications detection

Lantern's proxyless protocol accounted for approximately 40% of its traffic during the June 2025 Iran shutdown, demonstrating that a direct-server / proxyless transport mode provided a significant load-bearing fallback when conventional proxy infrastructure was blocked by centralized DPI enforcement.

Executive Summary — Resilient Response evaluation

Psiphon's multi-protocol design maintained access for approximately 1.5 million users during the June 2025 Iran shutdown — roughly one-third of its normal user base — while traffic throttling rendered many single-protocol circumvention tools functionally useless for anything beyond basic text communication.

Executive Summary — Resilient Response evaluation

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

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

During the June 2025 shutdown, Iranian authorities blocked international One-Time Password (OTP) SMS delivery, preventing new sign-ins to foreign secure-messaging platforms and VPN services. This forced users toward government-approved domestic platforms that lack security and privacy protections. The blockade of OTPs effectively weaponized account-recovery flows as a secondary shutdown layer, disproportionately affecting users who needed to activate new circumvention tools during the crisis.

2025-iran-shutdown-measurement §Human Rights Implications port-blockingdpikeyword-filtering

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

TCP segmentation (splitting a DNS message into 20-byte TCP fragments) successfully circumvented DNS censorship in China for nearly all resolvers that support TCP. In Iran, TCP segmentation was only partially effective due to the censor's ability to reassemble TCP fragments when system load permits—some runs succeeded completely, others failed entirely across all resolvers. The "Last Response" mode (wait 3 seconds for the final UDP reply) was highly effective against China's on-path GFW injector for all resolvers except the fully IP-blocked Cloudflare 1.1.1.1 resolver.

2026-lange-towards §4.1, §6.2.1, §6.2.2 dns-poisoningdpi

TCP segmentation — splitting DNS-over-TCP messages into 20-byte fragments — successfully circumvented DNS censorship for 40 of 41 tested resolvers in China. In Iran, TCP segmentation is inconsistently effective: it succeeds in some scan runs and fails entirely in others, suggesting the Iranian censor can reassemble TCP fragments when processing capacity permits.

2026-niere-dpyproxy-dns §6.2.1, §6.2.2 dpidns-poisoning