“The Great Firewall” Disconnected China from the Global Internet for an Hour
Researchers from the Great Firewall Report team observed an unusual incident on the night of August 20: for 74 minutes, China was effectively cut off from most of the global internet after all traffic on TCP port 443 was blocked.
According to their analysis, the disruption began at 00:34 and lasted until 01:48 Beijing time (UTC+8). During this period, the system known as the “Great Firewall” unconditionally injected fake TCP RST+ACK packets, terminating any connections on port 443—both inbound and outbound.
Impact of the Block
The consequences were immediate. Chinese users were unable to access the vast majority of websites hosted outside the country. Services relying on HTTPS (which runs over port 443) were also disrupted. Companies such as Apple and Tesla, whose overseas servers provide critical functionality, experienced interruptions to their services.
Technical Anomalies
Researchers noted that the device fingerprint responsible for the block did not match any known node or component of the “Great Firewall.” This suggests that either:
- A new device had been introduced into the censorship infrastructure, or
- An existing device was operating in a new or misconfigured state.
Theories and Uncertainty
Specialists put forward two main theories:
- The incident may have been a test of China’s ability to block port 443 traffic nationwide.
- It could have been the result of a configuration error that was quickly identified and reversed.
Because the disruption lasted just over an hour, investigating its root cause remains difficult.
