现有的VPN根据所起不同的作用分为了三类:在公司远程分支机构的LAN和公司总部LAN之间的VPN、在远程用户或移动雇员和公司内部网之间的VPN(VPDN),以及在供应商、商业合作伙伴的LAN和公司的LAN之间的VPN。显然VPN的关键在于数据通过公用网络时,如何保证它的安全性。实际上它不同于一般互联网络的地方正在于此,它在数据包进入公用网络之前,会先建立起一条隧道,经 Existing VPNs are divided into three categories based on their respective roles: VPNs between a company’s remote branch office’s LAN and corporate headquarters LANs, VPNs (VPDNs) between remote users or mobile employees and the corporate intranet, and VPN between vendor, business partner’s LAN and corporate LAN. Obviously the key of VPN lies in how to ensure the security of data when it passes through the public network. In fact, it is different from the general Internet where is it, before the packet into the public network, will first establish a tunnel, the