"Blocked" means the GFW has blacklisted the domain: reachable overseas, dead or flaky from mainland China. For China-facing businesses this is close to a traffic death sentence, so testing before buying a used domain is essential.
DNS Poisoning vs Connection Reset
- DNS poisoning: resolvers return forged IPs. Switching to a trusted DNS (223.5.5.5 / 8.8.8.8) or DoH helps locally, but on-path injection on port 53 cannot be fully fixed client-side.
- Connection blocking (RST injection / IP blackhole): DNS resolves fine, but TCP handshakes are killed — true "blocking".
How We Detect It
- Blacklist match against community-maintained gfwlist data (4,300+ domains, refreshed weekly).
- Outbound probing from our overseas servers to ports 80/443, catching blocks the list hasn't recorded yet.
See a live example on the bbc.com record page.
Mitigation Options
- Mostly DNS poisoning: enable DNSSEC, move DNS to an overseas provider, enable HTTPS + ECH for partial relief.
- Blocked by neighboring IPs: move to a new server IP or put a CDN in front to hide the origin.
- The domain itself is blocked and you need China traffic: switching domains is usually unavoidable. Always run a block check before buying a used domain — many "cheap" aged domains have a history.
Note: any service claiming it can "unblock" a GFW-blocked domain for a fee is a scam. The blocklist cannot be paid off.