In Iran (AS62442), HTTPS connections fail at 34.4% (mostly TLS-hs-to, consistent with SNI filtering), while HTTP/3 over QUIC fails at only 16.2%. SNI spoofing reduces TCP failure from 60.1% to 10.2% but has zero effect on QUIC (20.1% both with real and spoofed SNI), indicating Iranian censors apply separate UDP endpoint blocking to QUIC rather than SNI-based identification.

In China (AS45090), HTTP/3 over QUIC has a lower overall failure rate (27.1%) than HTTPS over TCP (37.3%), but hosts that time out during the TCP handshake (TCP-hs-to, indicating IP blocking) always also fail over QUIC — while hosts blocked via TLS-hs-to or conn-reset (SNI-based methods) nearly always succeed over QUIC.

§5.1, Table 1, Figure 3a evaluation

In India (AS55836), TCP and QUIC failure rates closely track each other (15.0% vs 12.0%), with every TCP-hs-to and route-err failure matched by a corresponding QUIC failure, confirming IP-based blocking affects both protocols equally. In contrast, India AS14061 (VPS) shows 16.3% TCP failure entirely from route-err but only 0.1% QUIC failure, suggesting the VPS vantage point sits outside the censored path.

§5.1, Table 1, Figure 3b detection

Only approximately 5% of domains from the combined Citizen Lab and Tranco Top-4000 test lists supported QUIC in early 2021, heavily skewing the measurable set toward large global .com domains (e.g., Google properties). This bias means the study predominantly captures censorship of internationally targeted sites rather than country-specific domains.

§4.3 evaluation

Across all four studied countries (China, Iran, India, Kazakhstan), HTTP/3 over QUIC had consistently lower failure rates than HTTPS over TCP: 27.1% vs 37.3% in China, 16.2% vs 34.4% in Iran, and 12.0% vs 15.0% in India (AS55836). The only QUIC-specific interference method observed was black-holing during the QUIC handshake (QUIC-hs-to); no RST injection or SNI-based QUIC filtering was detected.

§5, Table 1 evaluation

QUICstep successfully circumvents the GFW's QUIC SNI censorship (active since April 2024) in live testing. Using an Alibaba VM in mainland China as client and an AWS instance in North Virginia as server, a native QUIC client was blocked after several fetches of youtube.com SNI, while QUICstep consistently succeeded across 50 consecutive fetches. 7 tiktokcdn.com subdomains that were QUIC-SNI blocked were also reliably accessible via QUICstep. The approach routes only QUIC long-header (handshake) packets through a WireGuard tunnel; all subsequent short-header (data) packets travel the native path.

2026-lee-quicstep §4.3.2, §3.2.3 http3-quic-blocksni-blockingdpi

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

During the June 2025 blackout, virtually all UDP-based protocols were blocked across major Iranian networks — WireGuard, AmneziaWG, QUIC, WebRTC, and OpenVPN — with the sole deliberate exception of UDP port 53 (DNS), preserved to avoid cascading failures in internal infrastructure.

2025-piotrowska-nym-iran-blackout Protocol-level blocking port-blockingdpihttp3-quic-block

Since April 7, 2024, the GFW decrypts every QUIC client Initial packet at China's national border and blocks connections whose TLS ClientHello SNI matches a QUIC-specific blocklist. Blocking takes the form of dropping all subsequent UDP packets sharing the same (src-IP, dst-IP, dst-port) 3-tuple for 180 seconds—with no RST injection. The GFW applies a source-port heuristic: packets with src-port ≤ dst-port are not inspected, capturing >92% of real QUIC client Initials while processing only ~30% of all UDP traffic. The QUIC blocklist contains 58,207 unique FQDNs (Tranco, Oct 2024– Jan 2025), approximately 60% of the DNS blocklist in size; 33% of blocked FQDNs do not actually support QUIC, suggesting the list was derived from an existing domain-name blocklist rather than live QUIC service discovery.

2025-zohaib-quic-sni §3 / §3.1 / §3.3 / §4 http3-quic-blockdpisni-blocking

Russia's TSPU ("Средства противодействия угрозам") system is deployed inline at individual ISP edges rather than at centralized internet exchange points, producing substantial per-ISP heterogeneity: some providers apply layer-7 SNI/Host filtering while others rely primarily on IP-prefix blocklists, and QUIC/HTTP3 is blocked at several major providers. Rollout timing and enforcement depth vary measurably across autonomous systems, meaning a single "Russia passes/fails" test fixture systematically underestimates blocking coverage.

2024-xue-tspu-russia §4–§5 sni-blockingdpihttp3-quic-blockip-blocking

Winter and Lindskog [157] (2012) documented that the GFW used TLS SNI inspection in combination with IP/port filtering and TCP disruption to block Tor, as recorded in the survey's Table 1. This is one of the earliest published accounts of the GFW applying SNI-based blocking specifically to a circumvention protocol, demonstrating that the GFW correlated multiple detection signals rather than relying on any single technique.

2015-aceto-internet Table 1 sni-blockingip-blockingport-blockingrst-injection