3Com Switch 8800 Family IPsec Module Configuration and Command reference Guide

98 CHAPTER 7: VPN OVERVIEW
■ Add or delete users through software configuration rather than changing
hardware facilities, thus delivering great flexibility.
■ Support mobile access of VPN users at any time in any place, thus meeting
growing mobile service demands.
Structure of VPN
Network
VPN comprises a group of sites. A site might join one or more VPNs, but any two
sites are IP reachable only if they belong to the same VPN. According to its
standard definition, VPN with all its Sites coming from a single enterprise is called
Intranet, and cross-enterprise VPN is by contrast called Extranet.
Figure 19 The composition of VPN
The above chart demonstrates the relationship between five sites and three VPNs.
■ VPN1---Site2, Site4
■ VPN2---Site1, Site3, Site4
■ VPN3---Site1, Site5
Fundamental
Technology of VPN
Basic Networking
Application of VPN
Take an enterprise as an example. Its intranet through VPN is shown in following
figure.
Site 1
VPN 1
VPN 3
VPN 2
Site 5
Site 3
Site 4
Site 2