问题 单项选择题

某企业在DMZ区域部署了DNS服务器、Web服务器和E-mail服务器等,这些服务器上配置的是私网地址,由边界路由器实现NAT转换对Internet开放相应的服务。该Web服务器和邮件服务器由本单位的DNS服务器解析,在使用中发现外网无法解析服务器IP地址。网络管理员在外网管理机上使用nslookup得到如图所示的结果。

由以上测试结果可以初步判断,造成该DNS服务器无法对外解析lP地址的可能原因是()。

A.DNS服务器未启动

B.DNS服务器中未设置名称服务器

C.边界路由器的NAT工作异常

D.DNS服务器设置中名称服务器地址使用了内网地址

答案

参考答案:D

解析:

命令nslookup主要用于查询域名对应的IP地址,包括A记录和CNAME记录。如果查到的是CNAME记录还会返回别名记录的设置情况。nslookup命令分交互模式和非交互模式两种工作方式。图使用的是交互工作模式。由于图是在管理机的DOS命令窗口中运行命令。nslookup后系统返回的信息,由图中信息“Default Server:nsl.acc.com”和“Address:61.32.35.17”可知,该管理机的TCP/IP协议参数中的首选DNS服务器的IP地址设为61.32.35.17,该DNS服务器的域名为nsl.acc.com。

交互模式除了能查询单台主机,还可以查询DNS记录的任何类型,并且传输一个域的整个区域信息。图15-5中子命令settype=ns用于设置所要查询的类型为NS(名字服务器)资源记录。其下一行的“test.com”为所要查询的域名。当命令nslookup的系统返回信息“Non-authoritative answer:”,表明此次查询是在本地主机缓存区中查找并找到的数据,即此次查询并没有涉及Internet中的其他DNS服务器。

由图中系统返回的信息“test.com nameserver=nsl.test.com”可知,test.com的NS服务器是nsl.test.com。换而言之,域名为test.com的。DNS服务器已处于开机启动状态且设置了名称服务器。信息“nsl.test.com internet address=192.168.1.3”表明该DNS服务器设置中名称服务器的IP地址使用的是192.168.1.3。地址192.168.1.3是一个C类的私有IP地址。这将导致外网无法正确解析Web服务器和邮件服务器的IP地址等现象。

阅读理解

阅读理解。

     The energy crisis (危机) has made people aware of how the careless use of the earth's energy has brought

the whole world to the edge of disaster. The over-development of motor transport, with its increase of more

cars, more traveling, has contributed to the near-destruction of our cities and the pollution not only of local air

but also of the earth's atmosphere. 

     Our present situation is unlike natural disasters of the past. Worldwide energy use has brought us to a state

where long-range planning is vital. What we need is not a continuation of our present serious state, which

endangers the future of our country, our children, and our earth, but a movement forward in order to work

rapidly and effectively on planetary problems.

     This country has been falling back under the continuing exposures of loss of morality and the revelation (揭

露) that lawbreaking has reached into the highest place in the land. There is a strong demand for morality to

turn for the better and for some devotion that is vast enough and yet personal enough to enlist the devotion of

all. In the past it has been only in a way in defense of their own country and their own benefits that people have

been able to devote themselves wholeheartedly.

     This is the first time that we have been asked to defend ourselves and what we hold dear in cooperation

with all the other people of this planet, who share with us the same endangered air and the same endangered

oceans. There is a common need to reassess our present course, to change that course and to employ new

methods through which the world can survive. This is a priceless opportunity.

     To grasp it, we need a widespread understanding of nature if the crisis we and the world are facing is no

passing inconvenience, no byproduct of the ambitions of the oil-producing countries, no environmentalists'

only fears, no byproduct of any present system of government. What we face is the result of the invention

of the last four hundred years. What we need is a transformed life style. This new life style can flow directly

from science and technology, but its acceptance depends on a sincere devotion to finding a higher quality of

life for the world's children and future generation.

1. Which of the following has nearly destroyed our cities?[ ]

A. The loss of beliefs and ideas. 

B. More of law-breaking.

C. Natural di8asters in many areas.

D. The rapid growth of motors.

2. By comparing past problems with present ones, the author draws our attention to the _____. [ ]

A seriousness of this crisis

B. ineffectiveness of laws

C. similarity of the past to the present

D. hopelessness of the situation

3. Which of the following is used as an example to show the loss of morality? [ ]

A. Disregard for law.

B. Lack of devotion.

C. Lack of understanding.

D. Destruction of cities.

4. The author wrote the passage in order to _____. [ ]

A. make a recommendation for a transformed life style 

B. limit ambitions of the people of the whole world

C. demand devotion to nature and future generation

D. encourage awareness of the decline of morality

名词解释