Oman and Qatar deploy layered blocking: after a TCP handshake to geti2p.net completes normally, a TCP RST is injected immediately after the TLS ClientHello (SNI-based blocking), while HTTP connections to the mirror site receive injected packets redirecting to explicit national block pages. Kuwait applied only the HTTP mirror block, and only at one of six tested ASes (AS47589, Kuwait Telecommunication Company), with all other Kuwaiti networks leaving I2P fully accessible—illustrating significant ISP-level variation within a single country.

China's GFW poisons DNS responses from major open resolvers (Google 8.8.8.8/8.8.4.4, Cloudflare 1.1.1.1/1.0.0.1, OpenDNS 208.67.222.222/220) for I2P domains, returning public IPs belonging to Facebook, SoftLayer, and other non-Chinese organizations. Blocking is non-uniform: AS9808 (Guangdong Mobile) appended a loopback 127.0.0.1 record alongside falsified IPs—a pattern not seen at other ASes—while the I2P mirror site remained accessible from most Chinese locations despite the homepage being blocked.

§5.1 detection

DNS injection from China's GFW leaked into South Korean networks: queries sent from Korean ASes (AS38676, AS9848) to open resolvers returned the same falsified IP addresses observed inside China, because geographic proximity caused transit routing through Chinese infrastructure. This demonstrates that the GFW censors both egress and ingress traffic, producing cross-border poisoning as a side effect. Sporadic rather than consistent injection at these ASes confirmed the leakage hypothesis rather than intentional Korean blocking.

§5.1 detection

Over one month, 54K measurements from 1.7K ASes in 164 countries detected I2P blocking in exactly five countries: China (DNS poisoning of homepage and 3 of 10 reseed servers), Iran (TCP RST injection with HTTP 403 on mirror site), Oman and Qatar (SNI-based blocking of HTTPS homepage plus TCP injection with block-page redirect on HTTP mirror), and Kuwait (TCP injection on mirror site at AS47589 only). All other tested countries left I2P fully reachable.

§5, Table 2 evaluation

A measurement infrastructure built on VPN Gate's 192K volunteer-operated residential vantage points (3.5K ASes, 181 countries) detected I2P blocking events that were missed entirely by both OONI—which had no test data for four of the five affected countries—and ICLab—which had vantage points in only two of the five countries and obtained only intermittent connections there. Residential vantage points reveal filtering policies invisible from datacenter-hosted probes, with ISP-level granularity confirming partial national blocking (one of six Kuwaiti ASes, heterogeneous Chinese AS behavior) that aggregate measurements would miss.

§5.4, §7 evaluation

An internet-wide scan of 500k IP addresses from an in-country VPS vantage point found TCP establishment-interception injections on 43,479 addresses (8.7% of scanned), with over 70% concentrated in two Akamai ASes (AS16625 and AS20940). The injection pattern — triggered by the first packet sent to these addresses — is consistent with targeted blocking of domain-fronting proxies hosted on Akamai CDN.

2025-alaraj-iran-refraction §4.1.2 packet-injectionrst-injectionip-blocking

Iran's censorship of refraction-networking proxies (Conjure via Psiphon) is not monolithic: different ISPs independently deploy different techniques and timelines. Over 800 million logged Conjure connections from July 2023–February 2025 across 10+ Iranian ASes show TCI (AS58224, ~33% of traffic) uses packet injection, while MCCI/Hamrah-e Avval (AS197207, ~22%) applies IP-based blocking, and some ASes (Parsonline AS16322, Shatel AS31549) show no proxy blocking at all.

2025-alaraj-iran-refraction §4 rst-injectionip-blockingpacket-injectiondpi

TLS connections to blocked services (instagram.com, telegram.org) were terminated by TCP RST immediately after the client's ClientHello, before any certificate exchange, confirming SNI-based DPI that reads the plaintext SNI extension and aborts the handshake. HTTP filtering additionally matched Host headers and URL keywords case-sensitively, with injected HTTP 403 pages or TCP RST responses, and case-change evasions were sometimes effective.

2025-aryapour-stealth-blackout §4.2, §4.3 sni-blockingdpirst-injectionkeyword-filtering

Iran's DNS censor now injects two distinct block-page IPs: 10.10.34.36 (≈87% of 47,633 censored domains) and 10.10.34.34 (≈13%). Both originate from the same network node at Iran's border. Prior research (Aryan et al. 2013) described only 10.10.34.34. The IP injected correlates strongly with the HTTP censorship method applied: domains with 10.10.34.34 in DNS receive TCP RST via HTTP (86.8% of RST cases), while domains with 10.10.34.36 in DNS receive HTTP block pages (84.6% of block-page cases).

2025-lange-i-ra-nconsistencies §3.1, Table 2 dns-poisoningrst-injectionpacket-injection

Neither China nor Iran directly block ECH ClientHello messages; instead both effectively prevent ECH by censoring encrypted DNS resolvers. China blocks Cloudflare's DoH/DoT resolver (mozilla.cloudflare-dns.com) via SNI-based blocking in TLS and QUIC, causing residual censorship of up to 360 and 180 seconds respectively. Iran blocks both Cloudflare and NextDNS DoH hostnames via DNS block-page injection, TLS TCP RST, and HTTP block pages. Iran cannot analyze QUIC, so DoQ is uncensored and enables ECH in Iran. China's NextDNS IP blackholing affected only one of two resolved IPs, leaving an uncensored path.

2025-niere-encrypted §5, Table 1, Figure 5 dns-poisoningsni-blockingrst-injectionhttp3-quic-block

The GFI's HTTP and HTTPS filters are now stateful (requiring initial SYN packet with matching sequence numbers) and have been activated on all TCP ports—not only standard ports 80 and 443 as reported by prior studies. This is a significant departure from previous work that found stateless HTTP/HTTPS blocking limited to standard ports. The HTTP filter injects a 403 Forbidden blockpage (not RST packets as used by the GFW), while HTTPS injects a single RST+ACK packet. The GFI also exhibits TCP non-compliance (not requiring a full three-way handshake to trigger filtering), enabling outside-in measurement without in-country servers.

2025-tai-irblock §2.1, §3.2 dpirst-injectionpacket-injectionmiddlebox-interference