问题 单项选择题

VPN主要采用了4项技术用以保障安全,它们是加/解密技术、密钥管理技术、身份认证技术和______。

A.交换技术
B.路由技术
C.隔离技术
D.隧道技术

答案

参考答案:D

解析:目前VPN主要采用4项技术来保证安全,这4项技术分别是隧道技术(Tunneling)、加/解密技术(Encryption & Decryption)、密钥管理技术(Key Management)、使用者与设备身份认证技术(Authentication)。
(1)隧道技术。隧道技术是VPN的基本技术,类似于点对点连接技术,它在公用网建立一条数据通道(隧道),让数据包通过这条隧道传输。隧道是由隧道协议形成的,分为第二、三层隧道协议。第二层隧道协议是先把各种网络协议封装到PPP中,再把整个数据包装入隧道协议中。这种双层封装方法形成的数据包依靠第二层协议进行传输。第二层隧道协议有L2F、PPTP、L2TP等。L2TP协议是目前IETF的标准,由IETF融合PPTP与L2F而形成。第三层隧道协议是把各种网络协议直接装入隧道协议中,形成的数据包依靠第三层协议进行传输。第三层隧道协议有VTP、IPSec等。IPSec(IP Security)由一组RFC文档组成,定义了一个系统来提供安全协议选择、安全算法,确定服务所使用密钥等服务,从而在IP层提供安全保障。
(2)加/解密技术。加/解密技术是数据通信中一项比较成熟的技术,VPN可直接利用现有技术。
(3)密钥管理技术。密钥管理技术的主要任务是如何在公用数据网上安全地传递密钥而不被窃取。
(4)使用者与设备身份认证技术。使用者与设备身份认证技术最常用的是使用者名称与密码或卡片式认证等方式。

阅读理解

From the beginning of human history, wild animals provided food, clothing and sometimes medicine. We may not depend so much on wild animals now. But we hear about them every day. Americans use the names of animals in many ways. Automobile manufacturers (制造商) and gasoline companies especially like to use big cats to sell their products. They like lions, tigers and wildcats. When Americans say wildcat, they usually mean a lynx, an ocelot or a bobcat. All these cats attack quickly and fiercely. So wildcats represent something fast and fierce.

An early American use of the word wildcat was quite different. It was used to describe members of Congress who declared war on Britain in 1812. A magazine of that year said the wildcat congressmen went home. It said they were unable to face the responsibility of having involved their country in an unnecessary war.

Wildcat also has been used as a name for money. At that time, some states permitted banks to make their own money. One bank in the state of Michigan offered paper money with a picture of a wildcat on it. Some banks, however, did not have enough gold to support all the paper money they offered. So the money had little or no value. It was called a wildcat bill or a wildcat bank note.

The banks which offered this money were called wildcat banks. A newspaper of the time said those were the days of wildcat money. It said a man might be rich in the morning and poor by night.

Wildcat then was used for an oil well or gold mine that had almost no oil or gold in it. Dishonest developers would buy such property. Then they would sell it and leave town with the money. The buyers were left with worthless holes in the ground. Today, wildcat oil wells are in areas that are not known to have oil.

小题1:What is the main idea of the passage?

A.Wildcats and their stories.

B.Wildcats and their characters.

C.Varieties of animal species.

D.Relationship between animals and humans.小题2:From the passage we can know that ______.

A.wildcats represent the state of Michigan.

B.the use of wildcats was not always the same

C.wildcats are the best friend of human beings

D.honest developers never buy wildcat oil wells小题3:The underlined words “a lynx, an ocelot or a bobcat”in Paragraph 1 may refer to ______.

A.gasoline companies

B.automobile manufacturers

C.names of wildcats

D.brands of automobile小题4:It can be inferred that during the days of wildcat money ______.

A.people couldn’t buy anything with the money

B.people didn’t know how to save money

C.the rich invested too much on oil wells

D.people complained and suffered a lot

选择题