Virtual Private Network Protocols

Virtual Private Networks have evolved from intranets, which are password protected sites designed for use only by company employees. But instead of created protected sites, a Virtual Private Network is a private network that uses a public network (usually the internet) to connect remote sites or users together. Instead of using a dedicated, real world connections such as leased line (like ISDN or OC3), a Virtual Private Network uses "virtual" connections routed through the internet from the company's private network to the remote site or employee. There are two common Virtual Private Network types. The first is "Remote access, also known as virtual private dial-up network (VPDN), this is a user-to-LAN connection used by a company that has employees who need to connect to the private network from various remote locations. Typically, a corporation that wishes to set up a large virtual private network will outsource to an enterprise service provider (ESP). The ESP sets up a network access server (NAS) and provides the remote users with desktop client software for their computers. The telecommuters can then dial a toll-free number to reach the NAS and use their virtual private network client software to access the corporate network". The other type of VPN is site-to-site, which through the use of dedicated equipment and large scale encryption, a company can connect multiple fixed sites over a public network (Internet). There are two types of site-to-site intranet-based (If a company has one or more remote locations that they wish to join in a single private network, they can create an intranet VPN to connect LAN to LAN) and extranet-based (When a company has a close relationship with another company (for example, a partner, supplier or customer), they can build an extranet virtual private network that connects LAN to LAN, and allows all of the various companies to work in a shared environment). A virtual private network can grow to accommodate more users and different locations much easier than a leased line; it's a fact that scalability is a major advantage that virtual private networks have over typical leased lines. Because unlike leased lines, where the cost increases in proportion to the distances involved, the geographic locations of each office matter little in the creation of a virtual private network

Most virtual private networks rely on tunneling to create a private network that reaches across the internet. Essentially, tunneling is thew process of placing an entire packet within another packet and sending it over a network. The protocol of the outer pakcket is understood by the network and both points, called tunnel interfaces, where the packet enters and exits the networks. Tunneling requires three different protocols Carrier protocol (The protocol used by the network that the information is traveling over), Encapsulating protocol (The protocol (GRE, IPec, L2F, PPTP, L2tp) that is wrapped around the original

data), and Passenger protocol (The original

data (IPX, NetBeui,