问题 单项选择题

某中型企业采用单核心层次化网络结构设计,定义了核心层、接入层两个层次结构。该企业分配给产品部的IP地址块为192.168.31.128/27,分配给市场部的IP地址块为192.168.31.160/27,分配给财务部的IP地址块为192.168.31.224/27。这3个部门的计算机分别连接到各自的接入层交换机,然后通过接入层交换机将IP分组转发至三层核心交换机。某网络规划师经过分析计算,得到这3个地址块经过聚合后的地址为192.168.31.128/25。以下说法中,正确的是()。

A.该规划师所计算的CIDR地址块数据有误

B.由于该CIDR地址块会导致路由黑洞,因此该三层核心交换机不能正常转发数据包

C.该CIDR地址块可能会导致路由黑洞,但该三层核心交换机仍能正常转发数据包

D.这是一个合理的设计方案,不会存在潜在的路由问题

答案

参考答案:C

解析:

本试题所给出的3个地址块经路由汇聚后的超网IP地址块为192.168.31.128/25,具体解答思路如表所示。

路由汇聚超网地址解答表
IP地址二进制表示备注
192.168.31.192/271100 0000.1010 1000.0001 1111.1100 0000阴影部分为子网掩

码比特“1”所覆盖的

范围

192.168.31.160/271100 0000.1010 1000.0001 1111.1010 0000
192.168.31.128/271100 0000.1010 1000.0001 1111.1000 0000
三者共同部分为192.168.31.128/251100 0000.1010 10001 0001 1111.1000 0000

在超网划分时,通常要求待汇总的地网络地址块数目是2n,如2个、4个、8个、……。否则,可能会导致路由黑洞(也称为地址孔洞)。例如,对于子网掩码为“/27(即255.255.255.224)”的网段,本试题CIDR地址块192.168.31.128/25包含了实际中并不存在的子网(即192.168.31.224/27)。但幸运的是,当出现路由黑洞时,相关的三层交换机(或路由器)仍可以按最长地址匹配原则,正常转发IP数据包。

阅读理解

The way we do things round here

Some years ago, I was hired by an American bank. I received a letter from the head of the Personnel Department that started, “Dear John, I am quite pleased that you have decided to join us.” That “quite” saddened me. I thought he was saying “We’re kind of pleased you decided to join us although I wish we had hired someone else.” Then I discovered that in American English “quite” sometimes means “very”, while in British English it means “fairly”.

So the first lesson about working in other countries is to learn the language and by that I don’t just mean the words people speak. It is body language, dress, manners, ideas and so on. The way people do things highlights many of the differences we see between cultures.

Some of these differences may be only on the surface--- dress, food and hours of work--- while others may be deeper and take longer to deal with. Mostly, it is just a question of getting used to the differences and accepting them, like the climate (气候), while getting on with business.

Some of the differences may be an improvement. People are more polite; the service is better; you ask for something to be done and it happens without having to ask again. However, other differences can be troubling, like punctuality (准时). If you invite people to a party at 7 o’clock your guests will consider it polite to turn up exactly on time in Germany, five minutes early in the American Midwest, an hour early in Japan, 15 minutes afterwards in the UK, up to an hour afterwards in Italy and some time in the evening in Greece. I prefer not to use the word “late” because there is nothing wrong with the times people arrive. It is simply the accepted thing to do in their own country.

小题1:The author was unhappy as mentioned in Paragraph 1 because he thought _____.

A.the American bank didn’t think much of him

B.the American bank might hire another person

C.it’s difficult to get used to American culture

D.it’s easy to misunderstand Americans小题2:The word “highlights” in Paragraph 2 probably means _______.

A.encourages

B.helps to narrow

C.increases

D.draws attention to小题3:According to the author, what should we do with most cultural differences?

A.Ask the native people for help.

B.Understand and accept them.

C.Do things in our own way.

D.Do in-depth research.小题4:When invited to a party the people who are usually punctual(准时的)are ______.

A.Italians

B.Germans

C.Greeks

D.the British

单项选择题