1、思科认证 640-802模拟试卷 3及答案与解析 1 After logging into a router and typing in a few show commands, you press the up arrow key. What will this do? （ A） It will recall the previous command line （ B） It will move the cursor one line up （ C） It will redisplay the current command line （ D） It will capitalize the
2、command line （ E） None of the above 2 Which line from the output of the show ip interface command indicates that there is a Layer 1 problem? （ A） Serial0/1 is up, line protocol is down （ B） Serial0/1 is down, line protocol is down （ C） Serial0/1 is up, line protocol is up （ D） Serial0/1 is administr
3、atively down, line protocol is down （ E） None of the above 3 Given that you have a class B IP address network range, which of the subnet masks below will allow for 100 subnets with 500 usable host addresses per subnet? （ A） 255.255.0.0 （ B） 255.255.224.0 （ C） 255.255.254.0 （ D） 255.255.255.0 （ E） 25
4、5.255.255.224 4 How can a Ezonexam administrator determine if a router has been configured when it is first powered up? （ A） A configured router prompts for a password （ B） A configured router goes to the privileged mode prompt （ C） An un configured router goes into the setup dialog （ D） An un confi
5、gured router goes to the enable mode prompt 5 A receiving host has failed to receive all of the segments that it should acknowledge. What can the host do to improve the reliability of this communication session? （ A） Start a new session using UDP （ B） Obtain a new IP address from the DHCP server （ C
6、） Use a different source port for the session （ D） Decrease the sequence number （ E） Decrease the window size 6 You are bringing up a new Ezonexam switch, and wish to connect it via a trunk to another switch from a different vendor, which uses the IEEE standard for the trunking method. When setting
7、the encapsulation type on the trunk, what should you configure on the Cisco switch? （ A） Switch(config)# switchport trunk encapsulation isl （ B） Switch(config)# switchport trunk encapsulation ietf （ C） Switch(config-if)# switchport trunk encapsulation isl （ D） Switch(config-if)# switchport trunk enc
8、apsulation ietf （ E） Switch(config-if)# switchport trunk encapsulation dot1q 7 At which layer of the OSI model does the protocol that provides the information displayed by the “show cdp neighbors“ command operate? （ A） Transport （ B） Physical （ C） Application （ D） Data link （ E） Network 8 In which c
9、ircumstance are multiple copies of the same unicast frame likely to be transmitted in the Ezonexam Switched LAN? A. During high traffic periods B. In an improperly implemented redundant topology C. After broken links are re-established D. When upper-layer protocols require high reliability E. When a
10、 dual ring topology is in use F. None of the above 9 Which of the protocols below, operates at Layer 2 of the OSI model, and is used to maintain a loop-free network? A. RIP B. STP C. IGRP D. CDP E. VTP F. None of the above 10 During startup, router VE1 displays the following error message: boot: can
11、not open “flash:“ What will VE1 do next? A. It will attempt to locate the configuration file from a TFTP server. If this fails, it will initiate the setup dialog. B. It will attempt to locate the IOS from a TFTP server. If this fails, it will load a limited IOS from ROM. C. It will attempt to locate
12、 the configuration file from a TFTP server. If this fails, it will load a limited configuration from ROM. D. Because of damaged flash memory, the router will fail the POST. E. It will attempt to locate the IOS from a TFTP server. If this fails, it will initiate the setup dialog. F. None of the above
13、 11 While working in setup mode, a configuration line is typed incorrectly. What should you do to exit setup mode, without executing or saving any of the mistakes you made? (Select two answer choices) A. Type exit at the setup dialog. B. Type close at the setup dialog. C. Press the Ctrl-C key combin
14、ation. D. Press the Ctrl-X key combination. E. Issue the copy startup-config command. F. Issue the write e“ command. G. Issue the “write mem“ command 12 A Ezonexam router boots up in ROMMON mode. What is ROM Monitor (ROMMON)? A. A memory component for storing the saved configuration file B. A memory
15、 management tool C. An operating system used for hardware troubleshooting and for password recovery D. Temporary storage space for the router operating files E. The source of the primary Cisco IOS software image F. None of the above 13 You have a single Class C IP address and a point-to-point serial
16、 link that you want to implement VLSM on. Which subnet mask is the most efficient for this point to point link? A. 255.255.255.0 B. 255.255.255.240 C. 255.255.255.248 D. 255.255.255.252 E. 255.255.255.254 F. None of the above 14 In which Spanning-Tree states does a switch port learn MAC addresses? (
17、Select two) （ A） Blocking （ B） Listening （ C） Forwarding （ D） Learning （ E） Relaying 15 Which router console commands shown below are used to manage telnet sessions to other routers? (Select three) A. EzonexamD# disconnect 3 B. EzonexamD# exit session 2 C. EzonexamD# kill connection 1 D. EzonexamD#
18、show sessions E. EzonexamD# show connection all F. EzonexamD# resume 4 16 The Ezonexam network administrator wants to use a router named VE1 to segment the local network. What are some of the advantages of using VE1 to segment the network? (Choose two) A. Routers generally cost less than switches B.
19、 Filtering can occur based on Layer 3 information C. Broadcasts are not forwarded across the router D. Broadcasts are eliminated E. Adding a router to the network decreases latency F. Routers can generally support more LAN ports than switches 17 Both bridges are switches are being used throughout th
20、e Ezonexam LAN. Which of the following statements are true regarding bridges and switches in this network? (Choose 3) A. Switches are primarily software based while bridges are hardware based. B. Switches usually have a higher number of ports than most bridges. C. Bridges are frequently faster than
21、switches. D. Bridges define broadcast domains while switches define collision domains. E. Both bridges and switches forward Layer 2 broadcasts. F. Both bridges and switches make forwarding decisions based on Layer 2 addresses. 18 With regard to Ethernet media access methods, which of the following a
22、re true? (Choose all that apply.) （ A） A device waits for an electronic signal before transmitting. （ B） A device listens and waits until the media is not busy before transmitting. （ C） All devices on an Ethernet segment see data that passes on the network medium. （ D） Only the sender and the receiv
23、er devices see data that passes on the network medium. （ E） Ethernet networks allow you to configured devises with higher transmission priority. 19 You are experiencing intermittent issues relating to congestion within the Ezonexam network. What are the possible causes of congestion on this LAN? (Ch
24、oose all that apply) A. A broadcast domain with too many hosts. B. Full duplex operation. C. Broadcast storms. D. Multicasting. E. Network Segmentation. F. Low bandwidth. 20 When comparing and contrasting the similarities and differences between bridges and switches, which of the following are valid
25、 statements? Choose all the valid answer choices) A. Bridges are faster than switches because they have fewer ports. B. A switch is a multiport bridge, C. Bridges and switches learn MAC addresses by examining the source MAC address of each frame received. D. A bridge will forward a broadcast but a s
26、witch will not. E. Bridges and switches increase the size of a collision domain. F. None of the above statements are true. 思科认证 640-802模拟试卷 3答案与解析 1 【正确答案】 A 【试题解析】 Explanation: The up arrow key is used to recall the previous command line entry. The commands that were entered previously can be displ
27、ayed by repeatedly pressing the up arrow key, or by entering the “show history“ command. 2 【正确答案】 B 【试题解析】 Explanation:When the physical interface itself is down, then the problem is related to layer 1. When it is up, but the line protocol is down, then the problem is related to layer 2.3 【正确答案】 C 【
28、试题解析】 Explanation: Using the 2n-2 formula for host addresses, 29-2 = 510 host address, so a 9-bit subnet mask will provide the required number of host addresses. If these 9 bits are used for the hosts in a class B network, then the remaining 7 bits are used for the number of networks. Again using th
29、e 2n-2 formula, we have 2n-2 = 126 networks that are available. Incorrect Answers: A. This will provide for only 1 network with 216-2 = 65534 hosts B. This will provide for 6 networks with 8190 host addresses. D. This will provide 254 networks and 254 hosts. E. This will provide 2046 different netwo
30、rks, but each network will have only 30 hosts. 4 【正确答案】 C 【试题解析】 Explanation: If a non-configured router is started, then it goes into setup mode and ask for the minimum configuration parameters (hostname, IP address to interfaces, enable password, etc). If the router is already configured it boots
31、by implementing the saved startup-config. 5 【正确答案】 E 【试题解析】 Explanation: A TCP window the amount of outstanding (unacknowledged by the recipient) data a sender can send on a particular connection before it gets an acknowledgment back from the receiver that it has gotten some of it. For example if a
32、pair of hosts are talking over a TCP connection that has a TCP window size of 64 KB (kilobytes), the sender can only send 64 KB of data and then it must stop and wait for an acknowledgment from the receiver that some or all of the data has been received. If the receiver acknowledges that all the dat
33、a has been received then the sender is free to send another 64 KB. One way to improve the reliability of the TCP connection is to reduce the window size that the receiver needs to receive before sending an acknowledgement. However, this will reduce throughput as more segments and acknowledgements wi
34、ll need to be sent in order to transfer the same amount of data. 6 【正确答案】 E 【试题解析】 Explanation: The only real choices for setting up switching trunks are ISL and 802.1Q. ISL is Cisco proprietary, while 802.1Q uses the IEEE defined standard for trunking between switches. To configure the 802.1Q stand
35、ard, the keyword “dot1q“ is used in Cisco switches. Incorrect Answers: A, B, D. These are not valid options in a Cisco switch. C. ISL is a Cisco proprietary method for setting up trunks, and will only work between Cisco switches. 7 【正确答案】 D 【试题解析】 Explanation: CDP is a device discovery protocol that
36、 runs over Layer 2 (the data link layer) on all Cisco-manufactured devices (routers, bridges, access servers, and switches) and allows network management applications to discover Cisco devices that are neighbors of already known devices. With CDP, network management applications can learn the device
37、 type and the Simple Network Management Protocol (SNMP) agent address of neighboring devices running lower-layer, transparent protocols. 8 【正确答案】 B 【试题解析】 Explanation: A redundant topology eliminates single points of failure, but it also causes broadcast storms, multiple frame copies, and MAC addres
38、s table instability problems. Multiple Frame Copies-when a new switch is added, the other switches may not have learned its correct MAC address. The host may send a unicast frame to the new switch. The frame is sent through several paths at the same time. The new switch will receive several copies o
39、f the frame. This causes MAC database instability. MAC database instability results when multiple copies of a frame arrive on different ports of a switch. Layer 2 has no mechanism to stop the loop. This is the main reason for the Spanning Tree Protocol(STP) IEEE 802.1d which was developed to prevent
40、 routing loops. If multiple connections between switches are created for redundancy purposes, network loops can occur iin an imprperly designed topology. Spanning Tree Protocol (STP) is used to stop network loops while still permitting redundancy. 9 【正确答案】 B 【试题解析】 Explanation: STP (spanning tree pr
41、otocol) operates on layer 2 to prevent loops in switches and bridges. Incorrect Answers: A, C. RIP and IGRP are routing protocols, which are used at layer 3 to maintain a loop free routed environment. D. CDP does indeed operate at layer 2, but it doest not provide for a loop free topology. CDP is us
42、ed by Cisco devices to discover information about their neighbors. E. VTP is the VLAN Trunking Protocol, used to pass VLAN information through switches. It relies on the STP mechanism to provide a loop free network. 10 【正确答案】 B 【试题解析】 Explanation: The boot sequence of a Cisco router is shown below:
43、Booting up the router and locating the Cisco IOS 1. POST (power on self test) 2. Bootstrap code executed 3. Check Configuration Register value (NVRAM) which can be modified using the config-register command 0 = ROM Monitor mode 1 = ROM IOS 2 - 15 = startup-config in NVRAM 4. Startup-config file: Che
44、ck for boot system commands (NVRAM) If boot system commands in startup-config a. Run boot system commands in order they appear in startup-config to locate the IOS b. If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM)? If no boot system commands in startu
45、p-config use the default fallback sequence in locating the IOS: a. Flash (sequential) b. TFTP server (netboot) c. ROM (partial IOS) or keep retrying TFTP depending upon router model 5. If IOS is loaded, but there is no startup-config file, the router will use the default fallback sequence for locati
46、ng the IOS and then it will enter setup mode or the setup dialogue. 6. If no IOS can be loaded, the router will get the partial IOS version from ROM 11 【正确答案】 C 【试题解析】 Explanation: Here is the partial output from new router while it boots up: At any point you may enter a question mark ? for help. Re
47、fer to the Getting Started Guide for additional help. Use ctrl-c to abort configuration dialog at any prompt. Incorrect Answers: A. The Exit command can not be used during setup mode. B. This is an invalid command E. This command is used to save the configuration stored on NVRAM to a location. F. Th
48、is will have the effect of erasing the running configuration, and setting the router configuration back to the factory default settings. G. This is an old command that is still supported on the latest Cisco IOS. It is short for “write memory“ and has the same effect as the “copy running-config start
49、up-config“ command. 12 【正确答案】 C 【试题解析】 Explanation: The ROM Monitor is a very limited code set that enables you to perform elementary functions to manually get the router or switch back to a functioning state. You can perform low-level diagnostics and even copy a new IOS file to the Cisco device over the console port. It is also used after the break sequence is issued during bootup for password recovery use. 13 【正确答案】 D 【试题解析】 Explanation: For a single point to point link, only 2 IP addresses are required, one for the serial interface of the router at each end. Therefore, the 255.255.2
