The authors' blockpage-based methodology cannot detect transit censorship implemented via TCP RST injection or packet drops, because distinguishing these from transient network errors requires identifying their location on the routing path. As a result, the 8-country, 6-AS finding is explicitly characterized as a lower bound on the true extent of Russian transit censorship.

AS201776 (Miranda-Media Ltd) is responsible for the largest volume of Russian transit censorship by destination IP count, affecting approximately 16,000 IP addresses in Ukraine from US and Sydney vantage points. AS3216 (PJSC Vimpelcom) has the widest geographic reach—delivering blockpages for traffic destined to 8 countries—but impacts no more than 1,000 IP addresses per country from any single vantage point.

§5 Preliminary Results / Table 1 evaluation

Scanning the IP address spaces of 18 countries surrounding Russia, the authors identify Russian transit censorship affecting at least 8 countries (Afghanistan, Azerbaijan, Kyrgyzstan, Kazakhstan, Lithuania, South Korea, Tajikistan, and Ukraine), attributable to at least 6 Russian ASes. Only 2 of these 8 countries (Kyrgyzstan and Kazakhstan) had been reported in prior work, and the collateral damage is characterized as a lower bound due to the study's blockpage-only methodology.

§5 Preliminary Results evaluation

The study's three vantage points (US university, AWS Sydney, AWS Tokyo) produce substantially different transit censorship observations: the US vantage point detects blockpages in all 8 affected countries, while Sydney and Tokyo detect transit censorship only in Kazakhstan and Ukraine. This variance is attributed to routing path differences across vantage points, confirming that transit censorship coverage is highly path-dependent.

§5 Preliminary Results evaluation

AS60299 (Mezhdugorodnyaya Mezhdunarodnaya Telefonnaya Stanciya Ltd) and AS201776 (Miranda-Media Ltd) deploy commercial DPI technology manufactured by Russian company VAS Experts to perform transit censorship. Ukraine is subject to transit censorship by the most Russian ASes (at least 5: AS3216, AS25227, AS35816, AS47203, AS201776), likely due to post-2022 re-routing of Ukrainian Internet traffic through Russian telecommunications infrastructure.

§5 Preliminary Results deployment

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

The automated probe list generation system discovered 45.79 potentially blocked domains per 1,000 domains crawled, compared to 4.11 for FilteredWeb — over 10× higher efficacy. It uncovered 1,490 potentially blocked domains in crawls of just 71,960 URLs, versus 1,255 blocked domains found by Hounsel et al. in crawls of 1,000,000 URLs, with 1,473 of the 1,490 domains not overlapping with prior work.

2024-tang-automatic §5.5 measurement-platformdns-poisoningip-blocking

VPS-based vantage points in Singapore and India detected censorship patterns similar to 'free' locations, failing to observe blocking known to be enforced by local ISPs following government directives. This occurred because ISP-level censorship is implemented per-carrier rather than centrally, and the VPS provider's ISP did not enforce those blocks — confirmed by re-testing from a residential IP that did observe the expected blocks.

2024-tang-automatic §6.2 measurement-platformip-blocking

DeResistor-generated evasion strategies achieve an overall success rate of up to 98.61% against GFW (across vantage points in Qingdao, Shanghai, and Beijing) for the best strategy, and 100% in both India (Bangalore) and Kazakhstan (Oral) for the top-performing strategy, while standalone Geneva strategies tested in the same environment achieve comparable or slightly lower rates on some censors but are blocked at the IP level before training completes.

2023-amich-deresistor §6.3, Table 2 rst-injectiondns-poisoningip-blocking

Censoring middleboxes' TCP non-compliance — specifically, their willingness to censor bidirectionally without completing the three-way handshake — enables external vantage points outside a censoring country to trigger and measure censorship without any local endpoint participation. The approach requires only a confirmed censored domain per AS, evidence of bidirectional censorship, and minimal residual censorship.

2023-nourin-detecting §2 middlebox-interferencerst-injectionmeasurement-platform