What is a VPN? A simple definition of Virtual Private Network, or VPN, as it is commonly known, is the use of a public network - mainly the Internet, to create private, secure wide area networks. A more formal definition of a VPN: a combination of tunneling, encryption, authentication, and access control technologies and services used to carry traffic over the Internet, a managed IP network or a provider's backbone. The traffic reaches these backbones using any combination of access technologies, including T1, frame relay, ISDN, ATM or simple dial-up access. VPN Technologies As stated above, there's one thing all virtual private networks have in common: They all share the same core set of technologies, which consists of tunneling, encryption, authentication and access control. Tunneling. Tunneling is at the core of all VPN implementations. There are basic classes of tunnels: end-to-end tunneling and node-to- node tunneling. With end-to-end the tunnel extends from a remote user!
             's PC to the server that the user is connecting to. In this type of scenario, the devices at each end of the connection must handle the establishment of tunnels, and also encrypt and then decrypt the data that's being passed between the two points. The second type, node-to-node tunneling, is where the tunnel terminates at the edge of the network. This type of tunnel could be used to connect LAN's at different sites. In this type of configuration, all the traffic on each LAN is unchanged. Once the traffic passes through a VPN device on the edge of the LAN, it is encrypted and tunneled to a similar device at the second point where it is then decrypted. In addition to the classes of tunnels, there are currently three tunneling protocols that are used in the majority of VPNs: Point-to-Point Tunneling Protocol (PPTP), IP Security (IPSec), and the Layer 2 Tunneling Protocol (L2TP). Of the three PPTP is most widely used, a major reason could be due to the fact that M...