Documentation

Great Firewall of China

The Great Firewall of China is a collection of technologies, legislated and enforced by the People's Republic of China, to regulate the Internet within China. It is designed to block access to selected foreign websites and to slow down cross-border internet traffic.

The Great Firewall checks transmission control protocol (TCP) packets for prohibited keywords and prohibited content. If the keywords or content appear in the TCP packets, access will be denied. If a connection is blocked, subsequent connections from the same machine will also be blocked by the Great Firewall. The Great Firewall will analyze, filter, and manipulate the internet traffic that crosses China's borders.

File Transfers Issues

File transfers are only blocked when prohibited keywords or content are found in the data, including any references to prohibited third-party sites and services. The People's Republic of China also blocks all cross-border internet traffic at times, usually during censored events such as the weeks before and after June 4th, the anniversary of the Tiananmen Square Massacre.

Transmission Encryption

Encrypted file transfers can also be blocked depending on the transmission protocol (FTP(S), SFTP, HTTP(S), WebDAV, etc.), the encryption type (TLS, SSL, SSH, etc.), and the encryption ciphers being used. The Great Firewall is constantly adjusting to internet traffic so it's impossible to determine exactly why a connection could be blocked. We recommend you test various transmission protocols and ciphers to determine which best meets your needs.