Considerable human and technical resources have been applied to filtering the Internet in China by the Chinese government. These filters are updated constantly, as evidenced by “high-profile sites” (like CNN) that are not always blocked. Furthermore, blocking is achieved primarily at the “router level, and on the basis of IP address”, which can cause a whole site to be blocked, even though Chinese officials might feel that most of the site’s information is not harmful.
Combined with filters to suppress information that contains forbidden keywords or phrases, this blocking method is “technology-intensive.” But the most interesting part of this report, for me, is that it’s apparently hard for Internet users in China to know whether or not a site has been blocked by the Chinese government, or if a computer glitch has occurred, because there is no message or warning displayed about blocked sites!
Source at Harvard Law School’s Berkman Center for Internet and Society