This is the great firewall of China. It blocks access to Twitter, Facebook, Google, and much more. So the country's 730 million internet users aren't exactly surfing the world wide web. But corporations, foreign residents, and curious Chinese citizens have long been able to tunnel under the wall using a virtual private network.
VPNs mask your computer's address and encrypts your internet traffic, protecting against snooping and censorship. However, the Chinese government has been cracking down. Its what they call cleaning up the internet.
They've been pushing multinationals to switch to expensive state-approved VPNs, which are subject to government scrutiny. And access to commercial and custom-built VPNs is being squeezed. But how?
An encrypted packet of data is effectively sealed. But it still has a visible destination marker. If that destination, or IP address, matches a known VPN server, sensors can step in and destroy the packet.
Providers are constantly building more server locations with new addresses. And sensors are constantly trying to sniff them out. It's tunnel warfare and makes it even harder for businesses in China to connect to the outside world.