In a VPN, there are security exposures everywhere along an end-to-end path: on the dial-up link, in an ISP's access box, in the Internet, in the firewall or router, and even in the corporate intranet. 在VPN中,整个通信路径上到处都有可能受到安全攻击的地方:在拨号链路上,在ISP的接入服务器中,在Internet中,在防火墙或路由器中,甚至在企业内部网中。
The Point-to-Point Protocol, an IETF standard, which manage the dial-up link. IETF的一种标准,用来管理拨号连接。