VPN (virtual private network) is a “worm hole” that allows a VPN client connect to a remote network segment. VPN has many applications. For example, let’s say a company has a local area network that is not Internet visible. Various resources, such as network printers, network storage and a database server may live in this network segment. An employee typically has to be on site to connect to this LAN.
Two VPN interfaces connect via the Internet in a secure way. An employee can, then, use a VPN interface on his/her computer anywhere on the Internet and connect to another VPN interface that is bridged to the office LAN. He/she can, then, use the company LAN as if it is local to the employee’s location. Because VPN uses secure authentication methods, it is quite safe when properly configured.
A VPN is a “tunneling” technique. This means that although a VPN client can open any number of connections to any number of ports to any number of interfaces in a VPN, all traffic goes through a single connection between two VPN interfaces. To the public network, there is only one secure connection between two VPN interfaces. However, to the private network, there can be any arbitrary number of connections.