The remote connection between two devices, has long been in the game even long before the Internet took over. Yet, with major drawback among others, was remote connection was freaking expensive to establish. If you are on the one side of the continent and another one on the other side of the continent, only way the connection could be established was via telephone line. Another one was if you needed two of the LANs across the continent you would have had to have a thick wallet for private connection.
The purpose of VPN
With the coming of Internet, like lot of other stuff, things got way easier. People could connect with each other, not only in the same continent but across the globe from the comfort of their home and places. This is no stranger to us. We all are very well familiar with this piece of information. But, with cheap connection comes with other risk factors, which is the Internet is open to public.
People soon started to realise the potential risk factors involves in the open public Internet. Even before this was realised by the general non-tech people, tech people, network engineers to be precise, already dived into it and took care of this issue. They addressed this issue by creating a standard, where the computers are connected via tunnels are encrypted or a remote network which creates the private network. This is what is known as Virtual Private Network (VPN).
Architecture of VPN
These encrypted tunnels require endpoints or the end of the tunnel. So that the VPN knows when to encrypt and when to decrypt a network. As for the SSH tunnel, the client and the server sits on their end. The way VPN works is the same. For this to work properly, either some software should be running on the computer or a dedicated Internet appliance such as an endpoint management server should act as an endpoint, in some cases, for a VPN to work completely. Internet appliance is some sort of dedicated box, which serves a specific function or purpose. Internet was quite popular in 1990s but it is not as widely used as of that time.
In order for VPN to work, it needs a protocol which itself uses one of the tunnelling protocols out there. This adds up the ability to ask local DHCP server for an IP address to give the tunnel an IP address which matches the subnet of the local LAN. Then the connection of the IP address is kept which enables to connect to the Internet but under the condition that the endpoints must act like one those NICs (Network Interface Card).