SNI-based blocking

TSG automatically generates recurring weekly "SNI Report of Overseas APP" and companion "Server IP and Location of Overseas APP" reports at what is almost certainly a China-national (not export-customer) scale — single weekly runs process from ~5.7 trillion to over 135 billion rows and up to ~775TB/week — breaking down QUIC.SNI/SSL.SNI/HTTP.Host traffic per named blocked-in-China platform (YouTube, Facebook, Google, Twitter, Instagram, Telegram, WhatsApp, Netflix, BBC, Viber, Line, Snapchat, Gmail, HBO, and more), down to individual CDN edge hostnames (e.g. specific scontent-*.fbcdn.net and rr*---sn-*.googlevideo.com nodes ranked by bytes). The report series recurs weekly from at least Feb 2023 through Mar 2024.

A dedicated internal "运营商前端分析团队" (Carrier Front-end Analysis Team) produces weekly, carrier-specific traffic-analysis reports explicitly titled "新疆移动流量分析报告" (Xinjiang Mobile Traffic Analysis Report) and "新疆联通流量分析报告" (Xinjiang Unicom Traffic Analysis Report), with instances dated from at least July 2022 through March 2024. One instance (Xinjiang Mobile, 2023-05-15) reports total carrier bandwidth of 4.4Tbps (1Tbps access bandwidth), 27.34PB of weekly throughput, 123 distinct identified application-layer protocols, and a section (4.1, pages 17+) explicitly tracking server IP/location for 28 named overseas apps (BBC, Discord, ESPN, Facebook, Gmail, Google, Hulu, Instagram, Netflix, Reddit, Skype, Telegram, Twitter, Uber, WhatsApp, Wikipedia, YouTube, Zoom, etc.).

An internal module spec describes a proxy for authenticated/authorized users to reach overseas ('境外') services: it extracts the true destination domain from the TLS ClientHello SNI, resolves it via a normal public DNS resolver, forwards traffic (L4) to the real IP over a 'dedicated network,' rate-limits by client IP, and dynamically picks the lower-latency of two dedicated-network paths -- a 'VPN leased line' and a 'covert network' (隐蔽网络). Non-SNI TLS connections to the proxy are immediately closed (FIN), and the deployment does not yet support HTTP/3/QUIC.

An internal security-research presentation surveys published CDN-abuse techniques relevant to censorship evasion -- 'Domain Borrowing' (Black Hat Asia '21) and 'Domain Shadowing' (USENIX Security '21, explicitly labeled by the presenter as a 'new-type censorship-evasion technique,' 新型审查绕过技术) -- both exploiting CDNs' failure to verify accelerated-domain or origin ownership so that traffic with SNI==Host==a high-reputation domain reaches an attacker- or circumvention-controlled origin, and closes with concrete CDN-hardening recommendations (verify domain/origin ownership, set a distinct Host header on origin fetch, reject default-site requests with 403).

A MESA Lab monthly-report task list includes the next-step item 'design a scheme to identify forged/spoofed SNI in traffic' ([SNI判别]), alongside a separate active/passive traffic-fingerprinting project ('CAM-TEST') that extracts service banners passively and issues active host/port CGI GET probes.

An internal measurement-study report documents researchers live-testing the public DPYProxy TLS/SNI record-fragmentation tool against the GFW from inside China, against a control run from a German VPS. On a GFW IP-blocklisted Wikipedia IP, SNI fragmentation of any tested size (1/5/10/20 bytes) still ended in a server-side RST (though 1-5 byte fragments reached ServerHello before RST vs. 10-20 byte fragments RSTing right after ClientHello); on a non-blocklisted IP for the same domain, SNI fragmentation fully bypassed SNI-based blocking and returned a normal HTTP 200 response, matching the Germany baseline. The same report notes that testing Psiphon triggered roughly 5-10 minutes of residual censorship that also blocked other, unrelated circumvention tools from the same vantage point.

A design doc for a DNS/proxy gateway hosted at a public IIE-branded DoH endpoint (iie-public-doh.com) force-resolves the domains of ~40 target websites to a non-transparent SNI-routing proxy (which reads the ClientHello SNI without decrypting) while all other domains resolve normally; an 'open target resource discovery' module actively crawls each target site with a headless Chrome driver to map its dependent resource domains and assess their domestic-vs-overseas availability, feeding the allow-list.

A subsystem design doc describes an outbound proxy gateway for identity-authenticated users that performs IP access control, extracts the destination domain from the ClientHello SNI (without decrypting), resolves it via an overseas DNS server, and rewrites the destination IP to route traffic abroad through a 'dedicated network' — defaulting to a WireGuard VPN interface (wg0) and falling back to a 'covert network line' via a SOCKS5 proxy when the VPN line's bandwidth cap is exceeded.

An internal risk memo, "Signal审查规避模式阻断风险说明" (Signal circumvention-mode blocking risk explanation), documents that after the operator pushed a "Deny Signal APP" policy, users with Signal's censorship-circumvention (domain fronting via Google infrastructure) enabled could still send messages/files; packet capture showed the fronted traffic used Google SNIs (clients3/4.google.com, inbox.google.com, android.clients.google.com, www.google.com), and the team built a targeted FQDN+JA3+payload signature specifically to block this fronted traffic while flagging a residual risk of false-positive blocking of legitimate Google services.

Recurring automated "Tiangou Secure Gateway — SNI Report of Overseas APP" documents (weekly, multiple recurrences across 2023-2024) enumerate every distinct QUIC.SNI/SSL.SNI/HTTP.Host value observed per major foreign platform (Netflix, WhatsApp, Telegram, Twitter, YouTube, Signal- adjacent services, etc.) with packet/byte counts, processing runs at up to ~6.3 trillion rows per report. QUIC SNI is tracked as a distinct column from TLS SNI, showing the pipeline separately fingerprints HTTP/3 traffic.

TSG's blocking of YouTube/Facebook/Twitter/Tencent at Ethiopia's IGW nodes fails for a large fraction of sessions because those sessions structurally never traverse the inspection point — quantified per-site traffic-completeness rates ranged from 0% to 40% (vs. ~100% completeness at the upstream PE node), with roughly half of sampled YouTube/Facebook sessions missing entirely from IGW-side logs. Root cause was traffic-splitting/mirroring architecture, not a detection failure of the DPI engine itself.

A recurring weekly 'Tiangou Secure Gateway / Server IP and Location of Overseas APP' report series tracks per-app server-IP geolocation for Instagram, Snapchat, Telegram, and Likee traffic, with entries repeatedly geolocated to Almaty, Pavlodar, and Nur-Sultan, Kazakhstan across late 2023-early 2024 -- consistent with (though not conclusive proof of on its own, given ambiguity over whether the geolocated IPs are CDN edge nodes or another artifact) an operating Kazakhstan TSG deployment continuously monitoring named social/messaging platforms.

A hands-on MESA lab experiment testing TLS-record/TCP fragmentation (via the DPYProxy tool, replicating the public "Circumventing the GFW with TLS Record Fragmentation" technique) against live GFW found SNI fragmentation reliably bypasses GFW's SNI-based blocking of a non-blocklisted wikipedia.org IP, but has zero effect on GFW's separate IP blocklist: for an already-blocklisted IP, every fragment size tested still failed, with GFW tearing down the connection via <RST,ACK> immediately after ClientHello for larger fragments, or after the server's Hello for very small (1-5 byte) fragments.

An internal "网站/应用资源测绘" (website/app resource-mapping) presentation describes active EDNS-Client-Subnet DNS probing from many simulated geographic vantage points to map Google's and Facebook's global service-IP distribution by country/province, a mobile-app pipeline combining UI automation with MITM-proxy/ SSL-pinning-bypass to extract button-to-URL mappings from decrypted app traffic, and a "网站指纹审查" section that explicitly documents domain fronting as an effective evasion of its own DNS/SNI/Host-based website-fingerprint detection, alongside literature-based behavioral/ML website-fingerprinting intended to survive the QUIC/ECH/DoH transition.

The tango/kni (Kernel Network Interface) repo shows TSG's SNI/TLS-ClientHello-based interception logic (kni_entry.cpp) receiving dedicated 2024 fixes for handling TLS ClientHello fragmented across multiple packets ("ssl chello frag") and a "chello first packet hit intercept policy" bug, on top of a long-standing (2020) "dynamic bypass" feature that replaced raw-ClientHello matching with JA3 TLS fingerprints, plus counters for SSL certificate-pinning detection.

A MAAT/rulescan crash-debugging log shows the engine's getCfgId() lookup called with domain=".twitter.com", table_id=12, type="SNI", confirming MAAT performs SNI-field domain matching against a configured blocklist table (table_id 12 = SSL/SNI domain tables DF_SSL_REGION/DJ_SSL_REGION; table_id 22 = HTTP URL tables DF_HTTP_URL/DJ_HTTP_URL seen in the same crash series), and that the underlying librulescan.so string-scan library is prone to native crashes (SIGABRT) under real traffic.

A MESA-affiliated researcher's experiment log documents live testing of Psiphon and a TLS-fragmentation SNI-evasion tool (DPYProxy) against the real Great Firewall from inside mainland China. Fragmenting the TLS ClientHello/TCP stream into very small (1-5 byte) segments bypassed GFW SNI-based blocking of a non-blocklisted Wikipedia IP, while larger fragments (10-20 bytes) did not; a separately IP-blocklisted Wikipedia IP still failed regardless of fragmentation. Testing Psiphon also appeared to trigger a ~5-10 minute window in which the researcher's own unrelated circumvention tool stopped working.

A raw production SSL/TLS session log from sapp's monitoring pipeline (timestamps dated 2021-08-23, client IPs in domestic Chinese carrier ranges) shows the per-connection logging schema includes dedicated fields for a captured certificate chain (INDIVIDUAL_CERT_FILE, MIDDLE_CERT_FILE, ROOT_CERT_FILE, CHAIN_CERT_FILE) and for any injected packet (INJECTED_PKT_FILE), alongside SNI and TLS version -- confirming sapp's live SNI-logging and MITM-cert-capture instrumentation was operating against real user traffic to services including huobi.com, steamcommunity.com, and dropbox.com.

TSG's SSL parsing plugin (MESA_Platform/ssl) explicitly detects and 'detains' TCP-fragmented TLS ClientHello packets, buffering/reassembling them before running SNI/certificate inspection (tickets TSG-16297, TSG-19861), with dedicated per-session detain-timeout metrics added in 2024 -- meaning ClientHello fragmentation is a defeated, not just untested, SNI-blocking evasion technique against this DPI engine.

MESA_Platform's "quic" module (built and packaged as stellar-on-sapp/sapp RPMs) implements SNI/User-Agent extraction from both cleartext GQUIC (versions 23-59) and encrypted IETF QUIC RFC9000 ClientHello payloads, and supports a QUIC SNI whitelist -- i.e. the DPI pipeline decrypts/parses encrypted QUIC handshakes to recover the destination domain rather than being blocked by QUIC's encryption.

Standard workflow (recurring across AdGuard, JumpJump, Hula, BigMama, and Ace VPN tickets) for adding a new VPN app to TSG's blocklist: capture traffic on iOS/Android/Windows in a dedicated test environment, extract SNI first, fall back to enumerating server IPs when SNI proves ineffective or the app rotates it, then re-verify weekly/periodically with automated 'dial testing' (拨测) that checks whether newly discovered IPs still connect ('未穿透' = not yet penetrated/blocked).

TSG's Psiphon3 blocking (Ethiopia/E21 site) uses a dynamically-learned "Top SNI" / "Top Server IP" allowlist meant to avoid collaterally blocking shared infrastructure Psiphon3 also rides on (e.g. Google); a bug in the learning pipeline (SNI values under 3 bytes rolled back the whole DB write transaction) let the allowlist silently go stale, causing Google traffic to be misidentified and blocked as Psiphon3.

TSG23.07 added support for FQDN substring matching (vs. exact/wildcard only) for the P19 deployment, a detection-capability upgrade.

Geedge's TSG self-check test suite (run against firewall version v23.07.18-591aed7) enumerates the product's full interference capability set: SSL bypass/intercept (including handling of expired, self-signed, and untrusted-root certificates), HTTP/SSL proxy actions (redirect, block, replace, hijack, insert), three distinct firewall deny modes (silent drop, TCP RST, blockpage), and DNS deny modes (silent drop, A-record redirect, AAAA-record redirect, including TTL-range variants).

A confirmed bypass — TSG failed to extract SNI from TLS ClientHello when the SNI extension appeared later than expected in the extension list, letting those flows through unblocked (and incidentally TLS 1.3 flows generally, since clients fell back to 1.3 after 1.2 was blocked); fixed on-site via a patch to the "ssl.so" detection plugin.

A Deny policy using an SNI "Negate" condition fails to block after a page is refreshed multiple times, a duplicate of a prior known bug (TSG-18234) — indicating a reliability gap for negated-SNI-condition policies under repeated/retried connections.

TSG has a Lua-scriptable custom-classifier engine: operators upload a Lua script defining a custom traffic "Attribute", then build custom "App" rules matching on it. A 2024-05 ticket references a script literally named cdn_tunnel_finder.lua -- an operator-authored detector targeting CDN/domain-fronting-style tunneling.

TSG's application-fingerprinting engine matches 'FlyVPN' via a combination of IP-address and FQDN/port feature objects (each independently versioned/timestamped); a false-positive bug investigation confirms the live traffic-classification component is called 'sapp' and that restarting it is a standard troubleshooting step for signature drift.

TSG's SSL interception engine matches wildcard SNI patterns (e.g. "*tumblr.com") to decide whether to intercept (certificate-replace) a connection, but a separately-maintained "SSL Decryption Exclusions" allowlist takes priority over interception policy -- a domain on that list is never intercepted even if it matches an active policy.

Root-caused an Ethiopia SNI-block-failure incident to the detection mechanism itself: APP_SKETCH's FQDN-scanning module -- which exists specifically to identify Psiphon3 and Freegate via top-N SNI matching -- was CPU-expensive enough to saturate cores, triggering sapp's fail-open DDoS bypass and letting some target connections through uninspected. A signature-structure fix roughly doubled throughput (33K/s to 73K/s new connections) and disabling the fail-open bypass restored reliable blocking.

Project "E21" tested SNI-FQDN-wildcard block policies against international news/media/academic domains -- opride.com (Oromo news), ethiotube.net, Reuters, NYT, Bloomberg, GitHub, ResearchGate, NIH.gov -- from an Ethio-Telecom-range office IP. Most blocks silently failed (shared root cause with OMPUB-466); britannica.com needed a separate deny-quic policy since QUIC bypassed SNI blocking.

TSG maintains a traffic-volume-ranked "Top SNI" / "Top Server IP" allowlist (Galaxy component, learned from live traffic, capped at top ~2000 SNIs / ~40000 server IPs per Nacos config) that is checked before a VPN/circumvention-tool deny policy (including a Psiphon3-specific policy) is enforced. Confirmed empirically: Psiphon3 client traffic whose destination SNI was in the Top SNI list passed through undenied, while traffic to the same client IPs with an SNI not yet in the list was blocked. A 2022-06 incident over-blocked TikTok/BBC/CNN/NYTimes because their SNIs were not yet in the learned allowlist at the time.

Multi-week TSG engineering investigation of iTOP VPN (requested by an Ethiopia deployment, cross-tested in a Myanmar environment) found blocking only takes effect for VPN sessions established AFTER a detection policy is pushed; a VPN already connected before the policy loads is never blocked or logged, regardless of signature type (SNI or server-IP).

The Fujian (domestic China) deployment uses a punycode/IDN-aware keyword-filtering policy object named '中文涉诈域名' (Chinese fraud-related domains) with wildcard item matching; a bug ticket shows the policy engine failing to match an IDN punycode domain correctly against this object, revealing the underlying components: a 'verify-policy' microservice, and libraries 'libmaatframe' and 'librulescan' handling rule evaluation.

As of TSG v23.07, FQDN matching supports left-anchored prefix/wildcard matching (e.g. 'voice-group-80x-api.*'), added specifically so a Fujian domestic deployment could detect domains with a fixed subdomain prefix but rotating remainder. Earlier versions only supported exact FQDN match.

Multi-engineer forensic investigation (pcap, JA3 hashing, TSG session-log correlation) at an Ethiopia site into tv.cctv.com being intermittently unreachable concluded the blocking was NOT done by TSG itself but by a separate, more-client-proximate network censorship system. That system dropped ClientHello-stage TLS1.2 sessions matching cctv.com's SNI, had degraded filtering ability once the client renegotiated to TLS1.3, and at one point misclassified cctv.com traffic as TikTok.

Extensive engineering effort to extend TSG's built-in 'APP Sketch DB' fingerprint database with signatures for major domestic Chinese apps (Douyin, Kuaishou, Mango TV, JD, Tencent Cloud, etc.), primarily via SSL SNI matching, with iterative per-feature test/fail/patch cycles against specific in-app actions (e.g. certain Douyin menu items stayed unblocked after the main signature succeeded).

A debugging ticket for sites "Old Airport-PE" and "Bole-IGW" (naming consistent with Addis Ababa, Ethiopia) confirms the customer verified Psiphon3, YouTube, Facebook, and Telegram blocking as working well during independent testing, and reveals the operational session-correlation method used when packet captures and system logs must be cross-referenced across NAT: JA3_HASH + server IP + client public IP + SSL SNI.

For Hotspot Shield's IKEv2 mode, SNI-only blocking failed because logged SNI hits corresponded to the VPN's own domain/CDN traffic while tunnel-negotiation domains (journalissue.us, middle-island.us) went unlogged; switching the rule to match DNS query name (qname) for those specific domains successfully blocked the connection.

Documents Geedge's standard operating procedure for building a new app-detection signature: collect a target's server IPs and FQDNs, create IP-match and SNI-match (ssl.handshake.extensions_server_name) feature objects, combine them via OR logic into a named custom "application", then validate via session-log reports filtered on that application label.

Signature extraction for named circumvention tools (Freegate, Psiphon, Ultrasurf, Tor Browser) explicitly captures QUIC SNI alongside TLS SNI and HTTP Host header, confirming TSG's fingerprinting pipeline covers QUIC transport, not just TCP/TLS.

M22's extraction against "VPN Hero" (OpenVPN-based) recovered 13 FQDN + 13 IP indicators; FQDNs follow a "zampakuto...shop" template. Post-signature testing in the Myanmar demo environment found no successful connections on Android/iOS.

Documents the exact methodology used to derive a block signature for 'Giti VPN': TLS interception (fiddler) to decrypt the app's traffic, identifying its control/initialization domain and a second per-session domain pattern, then blocking by those two domain-name features rather than deep packet content.

Geedge fingerprinted several V2Ray-based VPN apps by their fixed API/bootstrap domains rather than protocol characteristics — blocking "V2 Pro" via pro.mucacherry.org, "V2 VPN" via v2.mucacherry.org, and "V2Net VPN" via api.v2net.live plus 5 rotating free-node domains (free1-5.v2n3t2.online / v2n3t.online) the app uses to fetch node lists.

TSG's SSL/IPD logging schema records a hit_pos field on every SSL-blocking log entry (NTC_SSL_LOG, IPD_SSL_IP_LOG) whose value is explicitly one of SNI, SAN, or CN -- confirming TSG's TLS-blocking decision can be attributed to, and therefore driven by, the certificate's SAN or CN fields, not only the ClientHello SNI extension.

For a domestic Fujian deployment, Geedge validated SNI-wildcard blocking (*.sohucs.com, *.sns.sohu.com) as technically effective against a specific Chinese social app ('Huyou'), but rejected it for production because the domain is shared with a third-party SDK platform and would cause false-positive blocking of unrelated services -- falling back to destination server-IP blocking, deployed inline via TCP RST injection.

A DPI session-plugin ("stellar" framework) SSL/TLS decoder fully parses live ClientHello/ServerHello handshakes, computing JA3/JA3S fingerprints (MD5 over version+cipher-suites+extensions with GREASE values stripped per the standard JA3 spec), extracting plaintext SNI, explicitly flagging whether a ClientHello carries ESNI (extension type 0xFFCE) or ECH (extension type 0xFE0D), and decoding full X.509 certificate chains (issuer/subject RDN sequences, SAN, validity window, serial, pubkey, signature algorithm) in real time. It also recognizes TLCP 1.0 (China's national "国密"/GmSSL TLS variant) as a distinct protocol version alongside SSLv2 through TLS1.3.

TSG's SSL decoder could not parse TLCP (China's national TLS variant) SNI as of v24.02, classifying such flows as generic BASE traffic and defeating server-name blocking; TLCP parsing was added in v24.08/24.09 per a tracked MESA_Platform/ssl commit.

chongming/traffic_replay is a Flask/tcpreplay-based QA harness that replays curated pcaps against a TSG instance to exercise its decoders, including SSL fixtures specifically named ssl_ech_false.pcap, ssl_no_sni.pcap and ssl_tls13.pcap alongside esni.pcap, openvpn.pcap, and major-platform captures (facebook/google/twitter/ youtube). A companion update_tsg_ca.py/tsg_ca.txt installs a TSG-issued CA cert on the test client, confirming the QA environment exercises TLS interception as part of routine detection testing.

TSG ships a built-in periodic-report feature ("Tiangou Secure Gateway" branded PDF exports) that breaks down traffic per major global platform — observed for YouTube, Facebook, Instagram, Netflix, Snapchat, BBC, and Bigo across six independent report exports — via "SNI Report of Overseas APP" and "Server IP and Location of Overseas APP" tables, giving operators granular, per-platform SNI- and IP-geolocation-based usage visibility as a standard dashboard capability, not just blocking.

Dozens of weekly "Tiangou Secure Gateway" auto-generated reports ("SNI Report of Overseas APP" / "Server IP and Location of Overseas APP") in this batch break out per-application SNI and server-IP/geolocation tables for Facebook, YouTube, Twitter, Instagram, Telegram, WhatsApp, Viber, Snapchat, Signal-adjacent messaging apps, and others, at up to 828 TB/week and 12+ Tbps peak processed traffic -- direct operational evidence of continuous, automated, per-app SNI-based classification of outbound "overseas app" traffic at production scale.

TSG runs a recurring, fully-automated weekly analytics job -- literally titled 'Tiangou Secure Gateway SNI Report of Overseas APP' and a companion 'Tiangou Secure Gateway Server IP and Location of Overseas APP' report -- that processes roughly 300 billion to 10 trillion traffic rows per week and produces per-platform SNI and server-IP/location breakdowns (Top10/Top50) for YouTube, Facebook, Google, Twitter, Instagram, Telegram, WhatsApp, Viber, Line, Messenger, Snapchat, Gmail, HBO, Netflix, Discord, BBC, Bigo, ESPN, and Hulu, plus a dedicated Top-100 SNI table for QUIC-protocol traffic.

A confidentiality-marked ("内部资料 注意保密", 架构组/Architecture Group) MESA Lab research report systematically profiles 11 video-conferencing/collaboration platforms (DingTalk, Zoom, Feishu/Lark, WeCom, Tencent Meeting, WebEx, Huawei WeLink, Slack, Teambition, 科技云会, 小鱼易连) with SNI lists, TLS certificate fingerprints, DNS/whois infrastructure, and an explicit "passive traffic analysis feasibility" (被动流量分析可行性) verdict per app — direct precursor engineering work for per-app DPI detection signatures.

An internal methodology memo for the '新疆省口项目' (Xinjiang provincial-gateway project) and '联通IDC项目' (Unicom IDC project) states both rely on 现有的系统（TSG与CN） (the existing TSG and CN [CyberNarrator] systems) to Block/Monitor/identify mainstream apps, and describes a largely manual signature-engineering workflow -- download the target app, capture traffic with 科莱(Colasoft Capsa)/Wireshark, extract fingerprint fields (http.host, http.user_agent, quic.sni, ssl.handshake.extensions_server_name) by hand, and register a per-app signature -- extending CyberNarrator's documented role beyond Psiphon-IP-harvesting/Pakistan subscriber correlation into general domestic app-blocking alongside TSG.

China's Xinjiang mobile-network deployment layers an unnamed third-party DPI engine (distinct from TSG's own app-ID) for app classification; when it misidentifies short-video CDN traffic (Douyin/Kuaishou domains) as 'Unknown', Geedge's on-site fix was configuring custom SNI-based app signatures directly in TSG rather than waiting on the third-party vendor.