Bugs fixed
VPN (eng. Virtual Private Network "virtual private network") is a generalized name for technologies that allow you to provide one or more network connections over another network, such as the Internet. Despite the fact that networks with a lower or unknown level of trust are used for communication (for example, public networks), the level of trust in the constructed logical network does not depend on the level of trust in the underlying networks due to the use of cryptographic tools (encryption, authentication, public key infrastructure, tools protection against repetitions and changes of messages transmitted over the logical network).
Depending on the protocols used and the destination, a VPN can provide three types of connections: host-to-host, host-to-network, and network-to-network.
Implementation levels
Typically, VPNs are deployed at levels no higher than the network, since the use of cryptography at these levels allows the use of transport protocols (such as TCP, UDP) unchanged.
Microsoft Windows users use the term VPN to refer to one of the virtual network implementations - PPTP, which is often not used to create private networks.
Most often, to create a virtual network, encapsulation of the PPP protocol into some other protocol is used - IP (this method uses the implementation of PPTP - Point-to-Point Tunneling Protocol) or Ethernet (PPPoE) (although they also have differences).
VPN technology has recently been used not only to create private networks themselves, but also by some "last mile" providers in the post-Soviet space to provide Internet access.
With the proper level of implementation and the use of special software, a VPN network can provide a high level of encryption of transmitted information.
VPN Structure
A VPN consists of two parts: an "internal" (controlled) network, of which there may be several, and an "external" network through which the encapsulated connection passes (usually the Internet is used).
It is also possible to connect a single computer to a virtual network.
A remote user is connected to the VPN through an access server that is connected to both the internal and external (public) networks. When connecting a remote user (or when establishing a connection to another secure network), the access server requires the identification process to go through, and then the authentication process. After the successful completion of both processes, the remote user (remote network) is empowered to work on the network, that is, the authorization process takes place.
VPN Examples
IPSec (IP security) - often used over IPv4.
PPTP (point-to-point tunneling protocol) - developed jointly by several companies, including Microsoft.
PPPoE (PPP (Point-to-Point Protocol) over Ethernet)
L2TP (Layer 2 Tunnelling Protocol) is used in Microsoft and Cisco products.
L2TPv3 (Layer 2 Tunneling Protocol version 3).
OpenVPN SSL - Open source VPN, supports PPP, bridge, point-to-point, multi-client server modes.
freelan SSL P2P is an open source VPN.
Hamachi is a program for creating a peer-to-peer VPN network.
NeoRouter is a zeroconf (no-configuration) program for providing direct connection of computers behind NAT, it is possible to choose your own server.
Many major providers offer their VPN services for business customers.
