一、前言 随着Internet的商业化,大量的企业的内部网络与Internet互联,使现代的企业网的概念发生了根本性的变化。在政府部门之间、跨地区的企业内部网络之间的互连,传统的方式是租用专线实现的。出差人员如果需要访问公司内部的网络,不得个采用长途拨号的方式连接到企业所在地的内部网。这些互联方式价格比较昂贵,一般只有大型的企业可以承担。同时造成网络的重复建设和投资。 I. Preface With the commercialization of the Internet, the interconnection of a large number of enterprises’ internal networks with the Internet has fundamentally changed the concept of modern enterprise networks. In the government departments, inter-regional interconnection between the internal network of enterprises, the traditional way is to leased line to achieve. Business travelers who need to access the company’s internal network, not long-distance dial-up using the way to connect to the enterprise’s intranet. These interconnection methods are more expensive and generally only large enterprises can afford. At the same time create duplication of network construction and investment.