IP VPN

A virtual private network (VPN) is the use of a secure data transfer protocol to connect computing resources over a shared orpublic infrastructure.By configuring a VPN, computers or networks can share data just the same as if they were connected via cable in a point-to-pointL ocal area network (LAN). The security of the VPN is assured either by establishing virtual circuits, or by using tunnelling techniques which hide the source and destination addresses and encrypt the data. This prevents both the systems and the data from being accessed by third parties that also use the public or shared infrastructure. The benefit of a VPN is it allows an organisation to have secureconnections to geographically separated offices by using existing connection (ADSL, ISDN, cabel Ethernet). There are several different protocols that support PPTP,IPsec,L2F, L2TP.

Motivations for bulding VPNs

There are several motivations for building VPNs, but a common thread is that they all share the requirement to "virtualize" some portion of an organization's communications—in other words, make some portion (or perhaps all) the communications essentially "invisible" to external observers, while taking advantage of the efficiencies of a common communications infrastructure. The base motivation for VPNs lies in the economics of communications. Communications systems today typically exhibit the characteristic of a high fixed-cost component, and smaller variable-cost components that vary with the transport capacity, or bandwidth, of the system. Within this economic environment, it is generally financially attractive to bundle numerous discrete communications services onto a common, high-capacity communications platform, allowing the high fixed-cost components associated with the platform to be amortized over a larger number of clients. Accordingly, a collection of virtual networks implemented on a single common physical communications plant is cheaper to operate than the equivalent collection of smaller, physically discrete communications plants, each servicing a single network client.

USES OF VPNs

External Office Networking

A VPN can be used wherever a secure point-to-point connection is required between office locations. For example, a large hospital may have its central computer system in an administration building, while its patient facilities and laboratory are in other buildings – perhaps across the street or across town, or even interstate. Rather than using conventional leased-line services to connect the computer systems in each building, a VPN can be created at alow cost and data can be exchanged securely. A VPN device (switch, router or server) is placed between the departmentcomputers and the main network backbone.

External Office Networking

A company may have a small branch or remote employee that depends heavily on data from its main office, or it may have vendors or customers that it wants to give restricted data access.