India's federated censorship model — each ISP independently enforces government blacklists — produces dramatically inconsistent filtering: Airtel censored only 1 of 50 pornographic sites probed, while MTNL censored 45 of 50; Reliance Jio censored 0 sites across all 540 test URLs. A well-informed user can escape censorship through a judicious choice of ISP.

Only 4 Indian ASes are needed to intercept >90% of AS-level paths from all Indian ASes to censored sites; 10 ASes cover ~95% of paths. Fewer than 5,000 edge routers spread across those ASes would suffice for nationwide IP filtering, with ~70% of those routers belonging to just two private ISPs (Bharti Airtel AS9498 and Tata Comm. AS4755).

§4.1, Table 2, Table 3 evaluation

Any one of five Indian ASes — each needing control of only its BGP-speaking routers — can individually censor traffic for all ~896 Indian ASes via IP prefix hijacking. For example, AS4755 (Tata Comm.) fake advertisements can impact 955 ASes total (896 Indian + 41 foreign); AS9730 (Bharti Telesonic) requires as few as 7 edge routers to execute such an attack.

§4.3, Table 4 evaluation

If India deployed centralized filtering at its key ASes, approximately 121,931 foreign-origin paths (1.15% of all Internet paths to censored sites worldwide) that transit Indian ASes would experience collateral blocking, affecting non-Indian users in Finland, Hong Kong, Singapore, Malaysia, the US, and elsewhere who have no connection to Indian censorship law.

§4.1, §4.4 policy

Eight Indian ASes can collectively intercept 99.14% of AS-level paths connecting all Indian ASes to DNS resolvers, including GoogleDNS and OpenDNS; 4,906 routers across these 8 ASes suffice to launch DNS injection attacks covering the entire country. The same 8 ASes also appear among the 10 key ASes identified for IP filtering.

§4.2 evaluation

IRBlock discovered that 1.7M of 3.3M blocked apex domains (52%) were attributed to blanket suffix-level blocking rules rather than individual domain listings. Examples include regex patterns targeting all Israeli domains (.il TLD), adult content (.porn), and country-coded suffixes (.com.mx, .my.id). Of 87K Tranco-ranked apex domains analyzed, 37% fell into adult content, with entertainment and gambling following. Approximately 1.27M apex domains were jointly censored by both DNS and HTTP filters, while the two filters maintained operationally independent blocklists for a significant fraction of domains.

2025-tai-irblock §5.3 dns-poisoningip-blockingkeyword-filtering

For Tier 2 apps (IP geo-blocking only), using a VPN with a foreign endpoint was sufficient to restore access. For Tier 1 apps (SIM + IP geo-blocking), the authors confirmed that (1) removing the Indian SIM card and accessing via WiFi, or (2) intercepting HTTP traffic with a MITM proxy to suppress or rewrite the carrier_region=IN parameter, fully bypassed server-side censorship. The authors note that Indian users primarily rely on mobile Internet, making SIM removal impractical as a user-facing solution.

2024-gosain-out §4.3, §5 ip-blockingkeyword-filtering

After India imposed a permanent ban in January 2021, seven of the eight previously SIM-only-blocked apps escalated to dual-factor filtering: they continued extracting carrier_region=IN from the SIM card while simultaneously adding IP geo-blocking. Accessing these apps now requires both a VPN (for source IP masking) and SIM removal or carrier_region parameter suppression; MICO Chat remained the sole app using only SIM-based blocking.

2024-gosain-out §4.3 (Permanent ban subsection), Table 2 ip-blockingkeyword-filtering

Seven of the 220 banned apps (Tier 1, including TikTok, Likee, Kwai, UC Browser, FaceU, Hago, and V-Fly) used the Android TelephonyManager.getSimCountryISO() API to read the primary SIM's country code and embed a carrier_region=IN parameter in HTTP requests, enabling server-side identification and blocking of Indian users regardless of source IP or VPN state. A dual-SIM phone with an Indian SIM in the secondary slot only (primary empty or non-Indian) bypassed the check.

2024-gosain-out §4.3 ip-blockingkeyword-filtering

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

The largest measurement study of Turkmenistan censorship to date tested 15.5 million domains and found more than 122,000 domains censored using separate blocklists for DNS, HTTP, and HTTPS. Reverse-engineering the blocking rules revealed approximately 6,000 over-blocking rules that cause incidental filtering of more than 5.4 million additional domains — a 44x collateral damage ratio relative to intentionally blocked domains.

2023-nourin-measuring §Results dns-poisoningdpikeyword-filteringip-blocking