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发表于 2009-7-29 16:40:52
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CCNA640-802 题库试题分析9(艾迪飞吴老师讲解)
1．What can a network administrator utilize by using PPP Layer 2 encapsulation? (Choose three.)
A. VLAN support
B. compression
C. authentication
D. sliding windows
E. multilink support
F. quality of service
Answer: BCE
解释一下：PPP协议是能支持认证的，包括PAP和CHAP；PPP还支持压缩功能和差错校验，还可实现多链路捆绑。而他们的这些功能都是HDLC所没有的。[hide]
2．Refer to the exhibit. What is the meaning of the term dynamic as displayed in the output of the show frame-relay map command shown?
2.jpg (12.18 KB)
2007-11-20 13:48
A. The Serial0/0 interface is passing traffic.
B. The DLCI 100 was dynamically allocated by the router.
C. The Serial0/0 interface acquired the IP address of 172.16.3.1 from a DHCP server.
D. The DLCI 100 will be dynamically changed as required to adapt to changes in the Frame Relay cloud.
E. The mapping between DLCI 100 and the end station IP address 172.16.3.1 was learned through Inverse ARP.
Answer: E
解释一下：这是个关于MAP的知识。在图中可以看到这个MAP是dynamic的，因此是通过inverse ARP学习到的。而ip 172.16.3.1 dlci 100表示的是DLCI 100映射的地址为172.16.3.1。就像是以太网中的MAC和IP的映射一样，通过DLCI100可以找到IP 172.16.3.1。
3．What is the function of the Cisco IOS command ip nat inside source static 10.1.1.5 172.35.16.5?
A. It creates a global address pool for all outside NAT transactions.
B. It establishes a dynamic address pool for an inside static address.
C. It creates dynamic source translations for all inside local PAT transactions.
D. It creates a one-to-one mapping between an inside local address and an inside global address.
E. It maps one inside source address to a range of outside global addresses.
Answer: D
解释一下：ip nat inside source static 10.1.1.5 172.35.16.5 这条命令是静态创建一个一对一的地址转换。他把内部本地地址10.1.1.5转换为全局地址172.35.16.5。
4．Refer to the exhibit. When PC1 sends an ARP request for the MAC address of PC2, network performance slows dramatically, and the switches detect an unusually high number of broadcast frames. What is the most likely cause of this?
4.jpg (10.4 KB)
2007-11-20 13:48
A. The portfast feature is not enabled on all switch ports.
B. The PCs are in two different VLANs.
C. Spanning Tree Protocol is not running on the switches.
D. PC2 is down and is not able to respond to the request.
E. The VTP versions running on the two switches do not match.
Answer: C
解释一下：PC1发出一个ARP request的数据报，并且是以广播的形式发送出去的。当ARP报文传到switch 2，交换机对广播的流量是以泛洪的形式处理的，报文就从除了连接PC1的接口外的所有接口都发出去了。Switch1收到广播后也泛洪，因此一个广播环路就产生了，所以在感觉网络性能很差，因为广播的流量占有了很大的带宽。而我们阻断二层环路是通过生成树来实现的，在图中有环路存在因此就说明没有运行生成树了。
5．An administrator issues the command ping 127.0.0.1 from the command line prompt on a PC. If a reply is received, what does this confirm?
A. The PC has connectivity with a local host.
B. The PC has connectivity with a Layer 3 device.
C. The PC has a default gateway correctly configured.
D. The PC has connectivity up to Layer 5 of the OSI model.
E. The PC has the TCP/IP protocol stack correctly installed.
Answer: E
解释一下：地址127.0.0.0是一个私有的保留地址段，他是一个回环的地址，一般用于测试，测试TCP/IP协议栈是否起来了。在一台PC上能ping 通127.0.0.1说明这个PC的TCP/IP协议栈是正确安装的。 |
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