问题 单项选择题

目前,某机构网络是一个共有36个子网的A类网络,随着应用业务的不断增长,预计3年后该网络将增至85个子网。若要求每个子网至少支持600台主机,且考虑网络应用业务的未来增长情况,则网络规划设计师应选用的子网掩码是______。CIDR地址块172.16.10.0/20中的最小地址、最大地址分别是______。

A.172.16.0.0、172.16.10.255
B.172.16.0.0、172.16.15.255
C.172.16.10.0、172.16.10.255
D.172.16.10.0、172.16.15.255

答案

参考答案:D

解析: A类IP地址的网络号为8位,主机号为24位。对于子网掩码,A类网络的默认值(即在不划分子网的情况下)是255.0.0.0。由于26=64<85<27=128,因此子网号位数至少为7,即子网号需要向主机号借用7个比特位。另一方面,29-2=510<600<210-2=1022,所以主机号位数至少为10。7+10=17<24,即子网号位数与主机号位数之和小于原A类网络的主机号位数。网络规划设计师可能选用的最小子网掩码的二进制表示是:1111 1111.1111 1110.0000 0000.00000000,即255.254.0.0;可能选用的最大子网掩码的二进制表示是:1111 1111.1111 1111.11111100.0000 0000,即255.255.252.0。
CIDR地址块172.16.1.0/20的网络前缀的长度为20位,主机号为12位,因此172.16.10.0/20地址块中的地址数为212个。其中,当主机号为全0时,该CIDR地址块的最小地址为172.16.10.0;当主机号全为1时,该CIDR地址块的二进制表示为1010 1100.0001 0000 0000 1111.1111 1111,最大地址为172.16.15.255。

阅读理解

阅读理解

     Here is a story told an American general ( * * ) who was a very important figure in the American army

during the First World War. Everybody in the Untied States knew him and many people wished to have a

picture or something of his in their homes.

     Soon after the war, the general returned to Washington. One day he went to a dentist (牙医) and had

six teeth pulled out. A week later the general heard that his teeth were being sold in curiosity shops at $5

each. On each of the teeth there was a label (标签) with the name of the general and words, "Buy these

teeth and show them to your friends at home." The general got angry. He rushed to his office and ordered

six officers to go around the city and buy all his teeth.

     The officers went out and visited every curiosity shop in the capital. They were away from the office all

day. In the evening they returned and put on the table in front of the general the teeth they had bought.

They had collected 175 teeth.

1. The general's teeth were sold in __________.

A. the museum

B. the special shops selling some rare and interesting things

C. the department store

D. the hospital

2. In the evening, the officers went back with all the teeth which cost __________.

A. $785

B. $1, 050

C. $157

D. $875

3. The general felt __________ when he heard his teeth were sold.

A. happy

B. excited

C. sad

D. angry

4. There was the general's name on the label of each tooth. This shows that __________.

A. the general's name was known by most of the people in Washington

B. the shop-keeper wanted to have more customers buy the teeth

C. the shop-keeper tried to make the general more popular

D. Both A and C

5. The general ordered his men to __________.

A. look for his teeth and buy all of them

B. arrest the dentist at once

C. make all the shops stop selling teeth

D. buy all the teeth in all the shops

单项选择题