In China, an IP blacklist is injected via BGP using null routing. Equipped with a blacklist of undesirable IP addresses, routers drop all packets destined to blocked IPs, which could include the address of a sensitive site like the New York Times, or of a public DNS resolver like Google’s. The method of blocking IP addresses is generally very low cost and easy to deploy. In this section, we’ll dive into the technology behind the major technical elements that comprise the Great Firewall. However, it’s a bit of a misnomer since not all filtering occurs strictly at China’s borders, nor does all traffic flow through a firewall, as we’ll soon see. Built in 1999, the Great Firewall is the blanket term for the collection of techniques used to filter traffic in China. A limited number of international entry points, coupled with the fact that all Internet service providers in China are licensed and controlled by the Ministry of Industry and Information Technology, mean that Chinese authorities can analyze and manipulate Internet traffic much more easily than, say, the United States. Virtually all Internet traffic between China and the rest of the world travels through a small number of fiber-optic cables that enter the country at one of ten different backbone access points, seven of which had only been added in January 2015. In China, the Internet developed with choke points built into it.
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