It is a network that uses public telecommunication infrastructure, e.g. Internet, to provide individual users or remote offices with secure access to their organization’s network. VPN can be contrasted with an expensive system of leased or owned lines that can only be used by one organization. VPN main target is to provide the organization with the same features but at a much lower cost.
VPN works by connecting to the shared public infrastructure and maintaining privacy through tunnelling protocols (e.g. L2TP) and security procedures. Effectively, the protocols, by encrypting data at the one end and decrypting data at the other end, send the data through a “tunnel” which is not available to “enter” by data that is not properly encrypted. A supplementary level of security involves not only encrypting data but also receiving and originating network addresses.