Businesses today are faced with supporting a broader variety of communications among a wider range of sites even as they seek to reduce the cost of their communications infrastructure. Employees are looking to access the resources of their corporate intranets as they take to the road, telecommute, or dial in from customer sites. Plus business partners are joining together in extranets to share business information, either for a joint project of a few months' duration or for long-term strategic advantage.

At the same time, businesses are finding that past solutions to wide-area networking between the main corporate network and branch offices, such as dedicated leased lines or frame-relay circuits, do not provide the flexibility required for quickly creating new partner links or supporting project teams in the field. Meanwhile, the growth of the number of telecommuters and an increasingly mobile sales force is eating up resources as more money is spent on modem banks, remote-access servers, and phone charges. The trend toward mobile connectivity shows no sign of abating; Forrester Research estimated that more than 80 percent of the corporate workforce would have at least one mobile computing device by 1999.

VPNs using the Internet have the potential to solve many of these business networking problems. VPNs allow network managers to connect remote branch offices and project teams to the main corporate network economically and provide remote access to employees while reducing the in-house requirements for equipment and support.

Rather than depend on dedicated leased lines or frame relay's permanent virtual circuits (PVCs), an Internet-based VPN uses the open, distributed infrastructure of the Internet to transmit data between corporate sites. Companies using an Internet VPN set up connections to the local connection points (called points-of-presence [POPs]) of their Internet service provider (ISP) and let the ISP ensure that the data is transmitted to the appropriate destinations via the Internet, leaving the rest of the connectivity details to the ISP's network and the Internet infrastructure. Because the Internet is a public network with open transmission of most data, Internet-based VPNs include measures for encrypting data passed between VPN sites, which protects the data against eavesdropping and tampering by unauthorized parties.

In addition, VPNs are not limited to corporate sites and branch offices. As an added advantage, a VPN can provide secure connectivity for mobile workers. These workers can connect to their company's VPN by dialing into the POP of a local ISP, which reduces the need for long-distance charges and outlays for installing and maintaining large banks of modems at corporate sites.