Introduction to VPN

World without VPN
In the 1960s' and 70s', when the use of computer was just a bit fancy to most of the people, the so-called "Network" would only mean a connection between two computers using telephone line communicating by command line(fig. 1.1).

Fig 1.1 so-called "Network" with two computers

As time and technologies advances, networks with several computers (called terminals or workstations), servers and other resources (printers, scanners, etc.) in organizations were formed. This kind of network (called LAN nowadays) is set up to share data and resources among computers within the network (fig.1.2). At this moment, most networks were physically separated from each other, and no equipment was set up to connect external network.

Fig 1.2 Early LAN with 4 workstations and a hub

In the late1980s', the time that the term "internet" had started to be popular for every computer users and organizations, routers were always installed in the LAN to connect the internal network with internet (fig. 1.3).

Fig 1.3 Typical LAN with router for internet access

During 1990s', internet is so popular that everyone and every businesses are both talking about advertising on it for good. But the concern of internet security has also become so acute. Firewalls are therefore installed in many networks to provide some degree of security (Fig 1.4).

Fig 1.4 LAN with router and firewall to control external access

Every computer in the LAN can access resource in the network freely, while computers outside the LAN have only limited access through gateways to LAN resource, like mail service and HTTP service. There should be no problem when the organization is small, and the demand for external access is low.