问题 单项选择题

[问题5] 如果防火墙采用NAPT技术,则该单位至少需要申请 (10) 个可用的公网地址。

答案

参考答案:A

解析:这是一道要求掌握网络地址端口转换(NAPT)技术需要最少的公网IP地址数量的理解题。本题的解答思路如下。 网络地址转换(Network Address Translation,NAT)是一个IETF(Internet Engineering Task Force, Internet工程任务组)标准,允许一个整体机构以一个公用IP地址出现在Internet上。换言之,它是一种把内部私有网络地址(IP地址)翻译成合法网络IP地址的技术。 NAT有三种类型:静态NAT、动态NAT、网络地址端口转换(NAPT)。其中,静态NAT设置起来最为简单,内部网络中的每台主机都被永久映射成外部网络中的某个合法的地址。动态NAT则是在外部网络中定义一系列的合法地址,采用动态分配的方法映射到内部网络。网络地址端口转换(Network Address Port Translation,NAPT)则是把内部地址映射到外部网络的一个"地址的不同端口上。 动态NAT只是转换IP地址,它为每个内部的IP地址分配1个临时的外部IP地址,主要应用于拨号,对于频繁的远程连接也可以采用动态NAT。当远程用户连接上之后,动态地址NAT就会分配给他一个IP地址。当该用户断开网络连接时,该IP地址就会被释放并留待以后使用。 NAPT是人们比较熟悉的一种转换方式,普遍应用于接入设备中。它可以将中小型的网络隐藏在 1个合法的IP地址后面。NAPT与动态NAT不同,它将内部连接映射到外部网络中的1个单独的IP地址上,同时在该地址上加上一个由NAT设备选定的TCP端口号。 由以上分析可知,如果防火墙采用NAPT技术,则至少需要向ISP机构申请1个可用的公网地址。

单项选择题

Passage Two

During the last thirty years, the international economy has experienced a basic change. Improvements in the Internet and other communications have had important effects on world markets. Faster methods of transport from one place to another have made the world seem smaller to the businessmen. As a result, the world no longer. consists of a number of separate economies under the control of different nations. Instead, the nations have been integrated into a single economy, and the integration is becoming more and more complete every year. For the first time in history, we can truly speak of a global economy.
The most dramatic example of this integration was the oil crisis of 1973 and 1974. It came as a great surprise to the public in the industrial nations to discover that they depended so heavily on imported oil. However, the best evidence for the growing integration is the rapid expansion in the volume of world trade. It went up by about 7% a year during the decade from 1990 to 2000, and in several quasi-industrial (半工业的) countries the growth was even more rapid. As a result, some imported products have become as common as domestic commodity. Some of them are too common for the public to any more realize they are foreign.
Production has also become international, which is manifested by the large corporations stepping across national borders and established branches and subsidiaries in several different countries. As an example, U.S. companies are building automobiles in Canada, Germany, Britain and Japan. In some cases, components of an automobile are produced abroad and shipped to the United States, where it is then finished with the imported parts. When even the United States has the largest number of such corporations, it is not the only. Other multinationals, for instance, are based in Japan, France, Germany, the UK and Italy.
Labor, too, is much more mobile than in the past. Both skilled and unskilled workers can now readily migrate from one country to another. In Europe, for example, there are large numbers of Turkish workers employed in the Germany Economy. Doctors, lawyers, and other professionals are also finding it easier to work in foreign countries. The labor market has become international, and the number of expatriate workers is continuing to grow.

"Expatriate workers" in the last sentence are those who ______ .

A.can’t find jobs in their own countries

B.leave their countries to live and work abroad

C.have to leave their countries for all their life

D.are professionals in medicine, law and other professions

单项选择题