Many companies have offices and plants scattered over many cities, sometimes over multiple countries. In the olden days, before public data networks, it was common for such companies to lease lines from the telephone company between some or all pairs of locations.
Private networks work fine and are very secure. If the only lines available are the leased lines, no traffic can leak out of company locations and intruders have to physically wiretap the lines to break in, which is not easy to do. The problem with private networks is that leasing a dedicated line between two is too expensive.
This demand soon led to the innovation of VPNs (Virtual Private Networks), which are overlay networks on top of public networks but with most of the properties of private networks. They are called ‘‘virtual’’ because they are merely an illusion, just as virtual.
Many organizations use Virtual Private Networks (VPNs) to establish secure intranets and extranets. A VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together.
The VPN uses "virtual” connections routed through the Internet from the business's private network to the remote site or employee. By using a VPN, businesses ensure security - anyone intercepting the encrypted data can't read it.
VPN is a secure network that uses the Internet as its main backbone network, but relies on the firewalls and other security features of the Internet and Intranet connections and those of participating organizations.