问题 单项选择题

ARP攻击造成网络无法跨网段通信的原因是(1)。可以使用(2)命令清除攻击影响的ARP缓存。空白(2)处应选择()

A.arp-s

B.arp-d

C.arp-all

D.arp-a

答案

参考答案:B

解析:

入侵者接收到主机发送的ARPRequest广播包,能够偷到其他节点的(IP,MAC)地址,然后便把自己主机的IP地址改为合法的目的主机的IP地址,伪装成目的主机,然后发送一个ping给源主机,要求更新主机的ARP转换表,主机便在ARP表中加入新的IP-MAC对应关系,合法主机就失效了,入侵主机的MAC地址变成了合法的MAC地址。

题目中ARP攻击造成网络无法跨网段通信的原因是入侵者把自己的IP地址改为了网关的IP地址,并使得主机更新了IP-MAC地址的对应关系,主机发送的报文则被入侵者截获,无法到达网关。ARP缓存表是可以查看的,也可以添加和修改。在命令提示符下,输入arp-a就可以查看ARP缓存表的内容了。用arp-d可以删除arp缓存表里的所有内容。用arp-s可以手动在ARP表中制定IP地址与MAC地址的对应关系。

阅读理解

Around twenty years ago I was going through hard times. I could not find a satisfying job. To my shame, I had to drive a school bus to make ends meet and lived in a friend’s house.

One afternoon, while driving through a quiet suburban (郊外的) neighborhood I was so sad that I kept asking myself “Why has my life become so hard?” “What’s wrong with the world?” Then I pulled over the bus to drop off a little girl and as she passed she handed me a pretty earring, saying she found it on the floor of the bus and I should keep it in case the owner came to look for it.

In the evening, the owner did come to look for her earring. When I handed it to her, she got very excited and continued saying “Thanks, you’re a real gentleman.” I told her that she should thank the little girl who had found it. She said, “Yes, and you are a good driver, too. What a lovely world it is!” Then she left with satisfaction. I was touched by her last words. I had thought something was wrong with the world just because of my poor condition. In fact, nothing was wrong with the world. I should change my attitude towards life. I should be positive about life.   

At first it was hard, and then it got easier. Every day I could find things to make me happy. Then one night there was a phone call for me at my friend’s house from a lady who was a manager in a large hospital. She said she had read my application form and asked me if I would like to work in the hospital. I said yes and got the job. Looking back at the experience I know the most important is to have a positive attitude towards life.

小题1:We know from the second paragraph that ________.

A.the author cried while driving that afternoon

B.a girl picked up an earring before getting off

C.there was only one passenger on the bus

D.the girl gave the author an earning as a gift小题2:The author decided to have a change in life because ________.

A.what the earring owner said moved him

B.he didn’t want to be a driver any more

C.his friends helped him become positive

D.he was offered a better job in a hospital小题3:When the author got a call from the manager of the hospital, he felt ________.

A.annoyed

B.delighted

C.shocked

D.disappointed小题4:Who was the owner of the earring lost on the bus according go the passage?

A.One of the author’s friends.

B.A real gentleman

C.A manager in a hospital

D.Not mentioned小题5:What does the author want to show in this passage?

A.Lost things should be returned to the owner.

B.Life is usually hard for the young at the beginning.

C.One should hold a positive attitude towards life.

D.It is not easy to find a good job nowadays.

单项选择题