A Virtual Private Network (VPN), which is the most common solution for network tunneling, is a way to channel all or, in some cases, part of the network traffic via a different middle node. Technically, it is a private network and provides inter-connectivity to exchange information between various entities that belong to the VPN.
In most cases, VPNs are used to access internal networks such as a company’s intranet resources. Since VPN traffic is encrypted and can be used as a proxy, it is another way to bypass internet censorship. Using VPN to connect to a computer that does not reside within a restricted environment and then accessing desired resources on the internet circumvents the censorship.
A VPN has some advantages over proxy solutions. It uses Internet Protocol Security (IPSec) or SSL, which provides secure communication. Confidentiality, integrity, and authentication tenants of security are available in a VPN so that, even if the network traffic is sniffed, attackers would only see encrypted data and not plain text. The integrity of communication is also provided so that tampering would be detected and discarded from the network.
Although the content of the network channel cannot be observed under normal circumstances, using a VPN to circumvent internet censorship has a downside. Suppose the IP address of the VPN server can be detected, and simply blocking that IP address is enough to prevent the circumvention. It is also easy to profile people if they run a VPN connection back to their offices from public internet spots. Although VPNs are mostly used as a mechanism for accessing corporate environments, they are also widely used for bypassing censorship.