CCNA 6.0第一学期第2章答案

1. Which statements correctly identify the role of intermediary devices in the network? (Choose three.)determine pathways for data 确定数据通路initiate data communicationsretime and retransmit data signals 重分发originate the flow of datamanage data flows 管理数据final termination point for data flow2. Select the statements that are correct concerning network protocols. (Choose three.)define the structure of layer specific PDU'sdictate how to accomplish layer functionsoutline the functions necessary for communications between layers limit the need for hardware compatibilityrequire layer dependent encapsulationseliminate standardization among vendors3. What are two functions of encapsulation? (Choose two.)tracks delay between end devicesenables consistent network paths for communicationallows modification of the original data before transmissionidentifies pieces of data as part of the same communicationensures that data pieces can be directed to the correct receiving end device4. What is a primary function of the trailer information added by the data link layer encapsulation?supports error detection 支持错误检测‘ensures ordered arrival of dataprovides delivery to correct destinationidentifies the devices on the local networkassists intermediary devices with processing and path selection5. Which statements correctly identify the role of intermediary devices in the network? (Choose three.)determine pathways for datainitiate data communicationsretime and retransmit data signalsoriginate the flow of datamanage data flowsfinal termination point for data flow6. What is a PDU?corruption of a frame during transmissiondata reassembled at the destinationretransmitted packets due to lost communicationa layer specific encapsulation 一个具体的封装层7. Which characteristic correctly refers to end devices in a network?manage data flowsoriginate data flow 原数据流retime and retransmit data signalsdetermine pathways for data8.Refer to the exhibit. "Cell A" at IP address 10.0.0.34 has established an IP session with "IP Phone 1" at IP address 172.16.1.103. Based upon the graphic, which device type best describes the function of wireless device "Cell A?"the destination devicean end devicean intermediate devicea media device9.Refer to the exhibit. Which three labels correctly identify the network types for the network segments that are shown?(Choose three.)Network A -- WANNetwork B -- WANNetwork C -- LANNetwork B -- MANNetwork C -- WANNetwork A -- LAN10. Which three statements best describe a Local Area Network (LAN)? (Choose three.)A LAN is usually in a single geographical area.The network is administered by a single organization.The connection between segments in the LAN is usually through a leased connection.The security and access control of the network are controlled by a service provider.A LAN provides network services and access to applications for users within a common organization.Each end of the network is generally connected to a Telecommunication Service Provider (TSP).11.Refer to the exhibit. Which networking term describes the data interleaving process represented in the graphic?pipingPDUstreamingmultiplexingencapsulation12. What is the primary purpose of Layer 4 port assignment?to identify devices on the local mediato identify the hops between source and destinationto identify to the intermediary devices the best path through the network to identify the source and destination end devices that are communicating to identify the processes or services that are communicating within the end devices13. What device is considered an intermediary device?1．file serve2.IP phone ptop 4.printer 5.switch14.Refer to the exhibit. Which term correctly identifies the device type that is included in the area B? sourceendtransferintermediary 中间设备15.Refer to the exhibit. What type of network is shown?WANMANLANWLAN16. Which layer encapsulates the segment into packets?physicaldata linknetwork 网络层封装的是数据包transport17. What can be identified by examining the network layer header?the destination device on the local mediathe destination host address 网络层头部封装目的主机的地址the bits that will be transferred over the mediathe source application or process creating the data18. What is the purpose of the TCP/IP Network Access layer?path determination and packet switchingdata presentationreliability, flow control, and error detectionnetwork media control 接入层控制网络媒体the division of segments into packets19. During the encapsulation process, what occurs at the data link layer? No address is added.The logical address is added.The physical address is added. 数据链路层添加一个物理地址The process port number is added.20.Refer to the exhibit. Which set of devices contains only end devices? A, C, DB, E, G, HC, D, G, H, I, JD, E, F, H, I, JE, F, H, I, J21. What is the proper order of the layers of the OSI model from the highest layer to the lowest layer?4physical, network, application, data link, presentation, session, transportapplication, physical, session, transport, network, data link, presentationapplication, presentation, physical, session, data link, transport, networkapplication, presentation, session, transport, network, data link, physicalpresentation, data link, session, transport, network, physical, application22. Which two layers of the OSI model have the same functions as the TCP/IP model Network Access Layer? (Choose two.)34NetworkTransportPhysicalData Link TCP/IP 工作在第一层和第二层Session。

yy1 ・ Refer to the exhibit・ Identify the devices labeled A, B, C, and D in the network physical documentation. 匚A=bridge, B=switch, C=router, D=hubK A=bridge, B=hub, C=router, D=switchC A=bridge, B=router, C=hub, D=switchc A=hub, B=bridge, C=router, D=switch2 The central hub has malfunctioned in the network. As a result, the entire network is down. Which type of physical network topology is implemented?匚busE starC ring匚mesh3. A switch has failed in the network. As a result, only one segment of the network is down. Which type of physical network topology is implemented?C busC ring匚starE extended star4. Which three features apply to LAN connections? (Choose three.)厂operate using serial in terfacesV make network connection using a hubV limited to operation over small geographic areas厂 provide part-time connectivity to remote servicesV typically operate under local administrative control厂provide lower bandwidth services compared to WANs5. What is one advantage of defining network communication by the seven layers of the OSI model? 【:It in creases the ban dwidth of a n etwork.E It makes networking easier to learn and understand・It eliminates many protocol restrictions.匚It increases the throughput of a network.c It reduces the need for testing network connectivity.6. What makes it easier for different networking vendors to design software and hardware that willin teroperate?E OSI modelc proprietary desig ns匚IP addressing schemec standard logical topologies匚standard physical topologies7. Which term describes the process of adding headers to data as it moves down OSI layers?匚division匚encoding匚separation匚segmentationE encapsulation8. What is the term used to describe the transport layer protocol data unit?匚bits c packetsE segments匚framesc data streams9. Which of the following are layers of the TCP/IP model? (Choose three.)▽ Applicati onr PhysicalV Internet0 Network Access厂Prese ntation10. Which of the following are data link layer encapsulation details? (Choose two.)0 A header and trailer are added・厂Data is con verted into packets ・V Packets are packaged into frames・厂Frames are divided into segments.厂Packets are changed into bits for Internet travel.11. Which layer of the OSI model provides network services to processes in electronic mail and file transfer programs?匚data link匚transport匚n etworkE application12. Which two features apply to WAN connections? (Choose two.)V operate using serial interfacesP make network connection using a hub厂limited to operation over small geographic areasI- typically operate under local administrative control▽provide lower bandwidth services compared to LANs13. Which of the following are ways that bandwidth is commonly measured? (Choose three.)厂GHzps▽kbpsV Mbps厂Nbps厂MHzpsV Gbps14. Refer to the following list. Choose the correct order of data encapsulation when a device sends information. segments bits packetsdata frames匚1 -3-5-4-2C 2- 1-3-5-4C 2-4-3-5-1匚4-3-1-2-5E 4-1 -3-5-2C 3-5-1-2-415. Which of the following are factors that determine throughput? (Choose two.)厂types of passwords used on servers厂type of Layer 3 protocol usedV n etwork topologywidth of the network cable0 number of users on the network16. Refer to the exhibit・ Which column shows the correct sequenee of OSI model layers?E D17. Which layer of the OSI model provides connectivity and path selection between two end systems where routing occurs?c physical layer匚data link layerE network layer匚transport layer18. Which best describes the function of the physical layer?E Defines the electrical and functional specifications for the link between end systems・匚Provides reliable transit of data across a physical link.匚Provides connectivity and path selection between two end systems・匚Concerned with physical addressing, network topology and media access.。

CCNA学习指南第2章复习题中英文翻译版1. What are the decimal and hexadecimal equivalents of the binary number 10011101?(Choose two.)1. 二进制数10011101等效的十进制和十六进制数分别是多少？（选择两项。

）A. 159B. 157C. 185D. 0x9DE. 0xD9F. 0x1592. Which of the following allows a router to respond to an ARP request that is intended for a remote host？2. 下列哪一项允许路由器对远端主机的ARP请求做出响应？A. Gateway DP网关DPB. Reverse ARP (RARP)反向ARPC. Proxy ARP代理ARPD. Inverse ARP逆向ARPE. Address Resolution Protocol (ARP)地址解析协议3. You want to implement a mechanism that automates the IP configuration, including IP address, subnet mask, default gateway, and DNS information. Which protocol will you use to accomplish this?3. 你想实现自动IP配置，包括IP地址,子网掩码，默认网关和DNS信息。

你应该使用什么协议来完成这？A. SMTP简单邮件传输协议B. SNMP简单网络管理协议C. DHCP动态主机控制协议D. ARP地址解析协议4. What protocol is used to find the hardware address of a local device?4. 什么协议用来找本地设备的硬件地址？A. RARPB. ARPC. IPD. ICMPE. BootP5. Which of the following are layers in the TCP/IP model? (Choose three.)5. 下列哪些层属于TCP/IP模型？（选择三项。

CCNA认证基础-习题分析讲义第一部分第一章1. Convert the binary number 10111010 into its hexadecimal equivalent. Select thecorrect answer from the list below. （3）1) 852) 903) BA4) A15) B36) 1C2. Convert the Hexadecimal number A2 into its Base 10 equivalent. Select thecorrect answer from the list below. （4）1) 1562) 1583) 1604) 1625) 1646) 1663. Which binary number is a representation of the decimal number 248? （3）1) 111010002) 111101003) 111110004) 111110104. Which of the following will test the internal loopback of a node? （3）1) ping 10.10.10.12) ping 192.168.1.13) ping 127.0.0.14) ping 223.223.223.2235) ping 255.255.255.2555. What can be verified by successfully pinging the reserved loopback address ona host? （2）1) Connectivity exists between two hosts on the LAN.2) The TCP/IP stack of the local host is configured correctly.3) A connection exists between a host and the default gateway.4) The route a packet takes from the local host to a remote host is valid.6. Which of the following commands could be used on a Windows-basedcomputer to view the current IP configuration of the system? (Choose two.) （3，4）1) configip2) ifconfig3) ipconfig4) winipcfg5) Winipconfig7.Refer to the exhibit. What must be configured on Host B to allow it to communicate withthe Host C? (Choose three.) （2，4，6）1)the MAC address of RTA router interface connected to Switch 12) a unique host IP address3)the IP address of Switch 14)the default gateway address5)the MAC address of Host C6)the subnet mask for the LAN8. What are important characteristics to consider when purchasing a networkinterface card? (Choose two.) （2，3）1) security used on the network2) media used on the network3) system bus used on the computer4) software installed on the network5) diagnostic tools installed on the network第二章1. Select the necessary information that is required to compute the estimated timeit would take to transfer data from one location to another. (Choose two.) （1，5）1) file size2) data format3) network in use4) type of medium5) bandwidth of the link2. Using the data transfer calculation T=S/BW, how long would it take a 4MB file tobe sent over a 1.5Mbps connection? （2）1) 52.2 seconds2) 21.3 seconds3) 6.4 seconds4) 2 seconds5) 0.075 seconds6) 0.0375 seconds3. What are features of the TCP/IP Transport layer? (Choose two.) （3，5）1) path determination2) handles representation, encoding and dialog control3) uses TCP and UDP protocols4) packet switching5) reliability, flow control and error correction4. Which of the following is the Layer 4 PDU? （4）1) bit2) frame3) packet4) Segment5. What is important to remember about the data link layer of the OSI model whenconsidering Peer to Peer communication? (Choose three.) （3，4，5）1) It links data to the transport layer.2) It encapsulates frames into packets.3) It provides a service to the network layer.4) It encapsulates the network layer information into a frame.5) Its header contains a physical address which is required to complete the datalink functions.6) It encodes the data link frame into a pattern of 1s and 0s (bits) for transmissionon the medium.6. Which statement describes a star topology? （2）1) Each host in the network is connected to a backbone cable that is terminated atboth ends.2) Each host is connected to a hub or switch, either of which acts as a central pointfor all network connections.3) Each host is directly connected to two other hosts to form a long chain of hosts.4) Each host has a connection to all other hosts in the network.7. Which statements describe the logical token-passing topology? (Choose two.)（2）1) Network usage is on a first come, first serve basis.2) Computers are allowed to transmit data only when they possess a token.3) Data from a host is received by all other hosts. Electronic tokens are passedsequentially to each other.4) Token passing networks have problems with high collision rates.8. Which technologies are considered to be LAN technologies? (Choose two.) （2，5）1) DSL2) Token Ring3) Frame Relay4) ISDN5) Ethernet9.Refer to the exhibit. Host A wants to send a message to host B. Place the following stepsin the correct order so that the message can be sent. （4）A - add network layer addressesB - transmit bitsC - create application dataD - add data link layer addresses1) B, A, D, C2) D, A, C, B3) A, D, A, B4) C, A, D, B5) C, D, A, B6) C, B, A, D10.After an uns u ccessful ping to the local router, the technician decides to investigate therouter. The technician observes that the lights and fan on the router are not operational.In which layer of the OSI model is the problem most likely occurring? （4）1) transport2) network3) data link4) physical11. Refer t o the exhibit. What is the order of the TCP/IP Protocol Data Units as datais moved as indicated through the OSI model? （3）1) data, segments, frames, packets, bits2) data, packets, segments, frames, bits3) data, segments, packets, frames, bits4) data, packets, frames, segments, bits第三章1. Which combinations of charges will be repelled by electric force? (Choose two.)（4，6）1) neutral and neutral2) neutral and positive3) neutral and negative4) positive and positive5) positive and negative6) negative and negative2. Which of the following are considered the best media for use in data networkcommunications? (Choose three.) （2，3，6）1) glass2) fibers3) copper4) gold5) plastic6) silicon7) Silver3. Which of the following wireless standards increased transmission capabilitiesto 11 Mbps? （2）1) 802.11a2) 802.11b3) 802.11c4) 802.11d4. What is attenuation? （3）1) opposition to the flow of current2) measurement of electrical signals relative to time3) degradation of a signal as it travels along the medium4) amount or volume of traffic that is flowing on the medium5. Which cable specifications are indicated by 10BASE-T? （3）1) 10 Mbps transmission speed, baseband signal, 500 meter cable length, coaxialcable2) 10 Mbps transmission speed, broadband signal, 100 meter cable length, coaxialcable3) 10 Mbps transmission speed, baseband signal, 100 meter cable length,twisted-pair cable4) 10 Gbps transmission speed, broadband signal, 500 meter cable length,twisted-pair cable6. For which Ethernet installations would fiber optic rather than Cat5 UTP be abetter media choice? (Choose two.) （2，4）1) a 3 meter connection between two 10BASE-T hubs2) an environment with many potential sources of EMI and RFI3) a peer to peer connection between two NICs with RJ45 connectors4) an installation between two buildings that are located 500 meters apart5) a single building installation where installation costs are the major concern7. Refer to the exhibit. Which type of UTP cable should be used to connect Host Ato Switch1? （4）1) rollover2) console3) crossover4) straight-through8. Refer to the exhibit. Which type of Category 5 cable is used to make an Ethernetconnection between Host A and Host B? （3）1) coax cable2) rollover cable3) crossover cable4) straight-through cable第四章1. During cable testing, which of the following are used to calculate theinformation carrying capacity of a data cable? (Choose two.) （2，5）1) bit speed2) attenuation3) wire map4) saturation limit5) analog bandwidth2. What type of wiring problem is depicted in this sample of a cable tester? （3）1) a fault2) a short3) an open4) a split a good map3. In a new network installation, the network administrator has decided to use amedium that is not affected by electrical noise. Which cable type will best meet this standard? （5）1) coaxial2) screened twisted pair3) shielded twisted pair4) unshielded twisted pair5) fiber optic4. How does network cable length affect attenuation? （3）1) Category 5 cable that is run in metal conduit has the highest attenuation in theshortest distance.2) Shorter cable lengths have greater signal attenuation.3) Longer cable lengths have greater signal attenuation.4) The length of the cable has no effect on signal attenuation.第五章1. The highest capacity Ethernet technologies should be implemented in whichareas of a network? (Choose three.) （3，4，5）1) between workstation and backbone switch2) between individual workstations3) between backbone switches4) between enterprise server and switch5) on aggregate access links2. What device must be used between an AUI port of a networking device and themedia to which it is being connected? （3）1) a transducer2) a transmitter3) a transceiver4) a transponder5) a port replicator3. An ISDN Basic Rate Interface (BRI) is composed of how many signalingchannels? （1）1) 12) 23) 34) 44. Which layer of the OSI model covers physical media? （1）1) Layer 12) Layer 23) Layer 34) Layer 45) Layer 56) Layer 65. What type of network cable is used between a terminal and a console port? （3）1) cross-over2) straight-through3) rollover4) patch cable6. What is the recommended maximum number of workstations configured on apeer-to-peer network? （3）1) 252) 153) 104) 55) 27. Which of the following increases the potential for a collision to occur? （4）1) the use of an active hub instead of an intelligent hub2) the use of an intelligent hub instead of an active hub3) a reduction in the number of devices attached to the hub4) an increase in the number of devices attached to the hub8. What is the maximum length of a media segment used for 100BASE-TX? （1）1) 100 meters2) 185 meters3) 400 meters4) 500 meters9. Which cable diagram displays the end to end pinout for a crossover cable usedwith Cisco devices? （3）1) Cable A2) Cable B3) Cable C4) Cable D第六章1. What does the "10" in 10Base2 indicate about this version of Ethernet? （2）1) The version uses Base10 numbering within the frames.2) The version operates at a transmission rate of 10 Mbps.3) Frames can travel 10 meters unrepeated.4) The maximum frame length is 10 octets.2. How is a MAC address represented? （4）1) four groups of eight binary digits separated by a decimal point2) four Base10 digits separated by a decimal point3) six hexadecimal digits4) twelve hexadecimal digits5) twenty-four Base10 digits3. Which of the following statements are correct about CSMA/CD? (Choose three.)（1，3，6）1) It is a media access method used in LANs.2) It is a media access method used in FDDI WANs.3) When a device needs to transmit, it checks to see if the media is available.4) A device sends data without checking media availability because all deviceshave equal access.5) Multiple devices can successfully transmit simultaneously.6) Only one device can successfully transmit at a time.4. Which devices shown in the graphic must have a MAC address? （5）1) only PC2) only router3) PC and router4) PC, hub, and router5) PC, printer, and router第七章1. Which of the following items are common to all 100BASE technologies?(Choose three.) （1，4，5）1) frame format2) media3) connectors4) timing5) multi-part encoding2. Which of the following does 1000BASE-T use to accomplish gigabit speeds onCat 5e cable? （4）1) the use of four conductors in full-duplex mode2) the use of two multiplexed pairs of wires, simultaneously3) the use of three pairs of wires for data and the fourth for stabilization andforward error correction4) the use of all four pairs of wires in full-duplex mode, simultaneously3. For which of the following is Ethernet considered the standard? (Choose three.)（1，4，5）1) inter-building connection2) mid-length voice3) video conferencing4) vertical wiring5) horizontal wiring6) diagonal wiring4. To make sure timing limitations are not violated when implementing a 10 MbpsEthernet network involving hubs or repeaters, a technician should adhere to which rule? （4）1) the 4-5-3 rule2) the 6-4-2 rule3) the 3-4-5 rule4) the 5-4-3 rule5. What is the maximum distance that 10BASE-T will transmit data before signalattenuation affects the data delivery? （1）1) 100 meters2) 185 meters3) 300 meters4) 500 meters6. When using Category 5 UTP cable, which RJ-45 pin pairs are used to exchangedata between hosts on an Ethernet network? （2）1) 1 and 2; 4 and 52) 1 and 2; 3 and 63) 3 and 6; 7 and 84) 4 and 5; 7 and 8第八章1. John has been hired as the network administrator of a local company and hasdecided to add more hubs to the company's existing network. Which of the following has been caused by John's inexperience? （1）1) collision domain extended2) an increased number of collision domains3) increased network performance4) increased bandwidth5) extended bandwidth2. "CompA" is trying to locate a new computer named "CompB" on the network.Which of the following does "CompA" broadcast to find the MAC address of "CompB"? （2）1) MAC request2) ARP request3) ping4) Telnet5) proxy ARP3. Which of the following is a term associated with replacing hubs with switchesto increase the number of collision domains? （3）1) encapsulation2) latency3) segmentation4) layered model5) broadcast domain6) Extended4. The accumulation of traffic from which of the following can cause a networkcondition called broadcast radiation? (Choose three.) （3，5，6）1) anonymous FTP servers2) telnet sessions3) video over IP applications4) NAS services5) ARP requests6) RIP updates5. Which of the following describes the use of Spanning Tree Protocol (STP)? （4）1) resolve routing loops2) eliminate Split Horizon errors3) limit collisions4) resolve switching loops6. Which term describes the delay in time that occurs when a frame leaves itssource device and reaches its destination? （4）1) collision2) backoff3) attenuation4) latency5) broadcast7. Based on the graphic above, which of the following occurs as each host systemcomes on line in the topology? （2）1) The switch sends its MAC address to each host.2) The switch adds MAC address to the bridge table as each host sends a frame.3) Each host exchanges MAC addresses with each other.4) The switch listens for data traffic to block since the switch lacks an IP address. 8. Which devices segment collision domains? (Choose two.) （2，3）1) transceiver2) router3) switch4) hub5) media9. Which protocol is used to eliminate switching loops? （3）1) Transmission Control Protocol2) Routing Information Protocol3) Spanning Tree Protocol4) Interior Gateway Routing Protocol5) Internetworking Protocol10. Refer to the exhibit. A network associate needs to establish an Ethernetconnection between Host A and Host B. However, the distance between the two hosts is further than the cabling standards allow. Which two devices that operate at the physical layer of the OSI can be used to allow Host A and Host B to communicate? （2，5）1) switch2) hub3) bridge4) router5) repeater第九章1. Which term describes an ARP response by a router on behalf of a requestinghost? （3）1) ARP2) RARP3) Proxy ARP4) Proxy RARP2. Which protocol functions at the internet layer of the TCP/IP protocol suite? （4）1) File Transfer Protocol (FTP)2) Trivial File Transfer Protocol (TFTP)3) Transmission Control Protocol (TCP)4) Internet Protocol (IP)5) User Datagram Protocol (UDP)6) Simple Mail Transport Protocol (SMTP)3. Which of these workstation installation and setup tasks are concerned withnetwork access layer functions? (Choose two.) （2，4）1) configuring the e-mail client2) installing NIC drivers3) configuring IP network settings4) connecting the network cable5) using FTP to download application software updates4. Which part of an IP address identifies a specific device on a network? （4）1) first two octets2) third and fourth octets3) network portion4) host portion5) only the fourth octet5. Which of the following are features of the Internet Protocol (IP)? (Choose two.)（1，3）1) It is the most widely implemented global addressing scheme.2) It allows two hosts to share a single address on a local area network.3) It is a hierarchical addressing scheme allowing addresses to be grouped.4) It is only locally significant, used primarily on local area networks.6. Which of the following are useable Class A IP addresses with a default subnetmask? (Choose three.) （2，3，5）1) 127.0.39.12) 111.9.28.303) 123.1.2.1324) 128.50.38.25) 105.1.34.16) 0.23.92.37. Which application layer protocols use UDP at the transport layer? (Choose two.)（2，4）1) FTP2) SNMP3) Telnet4) DHCP5) SMTP第十章1. Which OSI layer encapsulates data into packets? （3）1) session2) transport3) network4) data link2. Which OSI layer defines the functions of a router? （3）1) physical2) data link3) network4) transport5) session3. Which of the following are Cisco proprietary routing protocols? (Choose two.)（2，6）1) RIPv22) IGRP3) OSPF4) BGP5) RIPv16) EIGRP4. A company with a Class B license needs to have a minimum of 1,000 subnetswith each subnet capable of accommodating 50 hosts. Which mask below is the appropriate one? （4）1) 255.255.0.02) 255.255.240.03) 255.255.255.04) 255.255.255.1925) 255.255.255.2245. A small company has a class C network license and needs to create five usablesubnets, each subnet capable of accommodating at least 20 hosts. Which of the following is the appropriate subnet mask? （3）1) 255.255.255.02) 255.255.255.1923) 255.255.255.2244) 255.255.255.2406. When a network administrator applies the subnet mask 255.255.255.248 to aClass A address, for any given subnet, how many IP addresses are available to be assigned to devices? （6）1) 10222) 5103) 2544) 1265) 306) 67. Host A is assigned the IP address 10.18.97.55 /21. How many more networkdevices can be assigned to this subnetwork if Host A is the only one that has an IP address assigned so far? （4）1) 2542) 5093) 10214) 20455) 40946) 81908.Refe r to the exhibit. The network administrator wants to create a subnet for thepoint-to-point connection between the two routers. Which subnetwork mask would provide enough addresses for the point-to-point link with the least number of wasted addresses?1) 255.255.255.1922) 255.255.255.2243) 255.255.255.2404) 255.255.255.2485) 255.255.255.2529. What is the correct number of usable subnetworks and hosts for the IP networkaddress 192.168.35.0 subnetted with a /28 mask?1) 6 networks / 64 hosts2) 14 networks / 32 hosts3) 14 networks / 14 hosts4) 30 networks / 64 hosts10. Which subnet masks would be valid for a subnetted Class B address? (Choosetwo.) （5，6）1) 255.0.0.02) 255.254.0.03) 255.224.0.04) 255.255.0.05) 255.255.252.06) 255.255.255.19211. Refer to the exhibit. How will the Fohi router dynamically learn routes to the192.168.16.16/28, 192.168.16.32/28, and 192.168.16.48/28 subnetworks? （3）1) with a static route2) with a routed protocol3) with a routing protocol4) with a directly connected route12. How many broadcast domains are shown in the diagram? （1）1) three2) four3) five4) six5) seven6) eight13. How many collision domains are shown in the diagram? （5）1) three2) four3) five4) six5) seven6) eight14. A router interface has been assigned an IP address of 172.16.192.166 with amask of 255.255.255.248. To which subnet does the IP address belong?1) 172.16.0.02) 172.16.192.03) 172.16.192.1284) 172.16.192.1605) 172.16.192.1686) 172.16.192.17615. Refer to the exhibit. Host A is sending data to Host B. Once R2 determines thatdata from Host A must be forwarded to R1 to reach Host B, which layer of the OSI model will R2 use to address and build the frames destined for R1?1) physical2) data link3) network4) transport5) session6) presentation16. Which type of address is 192.168.170.112/28?1) host address2) subnetwork address3) broadcast address4) multicast address17. Which type of address is 223.168.17.167/29?1) host address2) multicast address3) broadcast address4) subnetwork address18. Which combination of network id and subnet mask correctly identifies all IPaddresses from 172.16.128.0 through 172.16.159.255?1) 172.16.128.0 255.255.255.2242) 172.16.128.0 255.255.0.03) 172.16.128.0 255.255.192.04) 172.16.128.0 255.255.224.05) 172.16.128.0 255.255.255.19219. Refer to the exhibit. The internetwork in the exhibit has been assigned the IPaddress 172.20.0.0. What would be the appropriate subnet mask to maximize the number of networks available for future growth?1) 255.255.224.02) 255.255.240.03) 255.255.248.04) 255.255.252.05) 255.255.254.06) 255.255.255.0第十一章1. If a network administrator needed to download files from a remote server, whichprotocols could the administrator use to remotely access those files? (Choose two.) （3，5）1) NFS2) ASCII3) TFTP4) IMAP5) FTP6) UDP2. What is established during a connection-oriented file transfer betweencomputers? (Choose two.) （2，5）1) a temporary connection to establish authentication of hosts2) a connection used for ASCII or binary mode data transfer3) a connection used to provide the tunnel through which file headers aretransported4) a command connection which allows the transfer of multiple commands directlyto the remote server system5) a control connection between the client and server3. Which of the following protocols are used for e-mail transfer between clientsand servers? (Choose three.) （3，4，5）1) TFTP2) SNMP3) POP34) SMTP5) IMAP46) postoffice4. Which type of institution does the domain suffix .org represent? （4）1) government2) education3) network4) non-profit5. Which of the following services is used to translate a web address into an IPaddress? （1）1) DNS2) WINS3) DHCP4) Telnet6. Which part of the URL http://www.awsb.ca/teacher gives the name of thedomain? （4）1) www2) http://3) /teacher4) awsb.ca7. Which protocols are TCP/IP application layer protocols? (Choose two.) （2，4）1) UDP2) FTP3) IP4) SMTP5) TCP8. What are three characteristics of the TCP protocol? (Choose three.) （3，4，6）1) has less overhead than UDP2) is used for IP error messages3) forces the retransmission undelivered packets4) creates a virtual session between end-user applications5) carries the IP address of destination host in the TCP header6) is responsible for breaking messages into segments and reassembling9. Two peer hosts are exchanging data using TFTP. During the current session, adatagram fails to arrive at the destination. Which statement is true regarding the retransmission of the datagram? （2）1) Datagram retransmission requires user authentication.2) Datagram retransmission is controlled by the application.3) Datagram retransmission relies on the acknowledgements at transport layer.4) Datagram retransmission occurs when the retransmission timer expires in thesource host.案例学习1. 子网计算练习：Answer2. 子网号及广播地址计算练习Answer3. 子网规划练习：已知：给定一个C类地址201.16.5.0/24。

1 操作系统内核的作用是什么？•它会提供允许用户请求特定任务的用户界面。

•内核将硬件驱动程序与计算机底层的电子元件链接。

•它是一种可实现思科设备的初始配置的应用程序。

•内核会调配硬件资源以满足软件要求。

Option 42 网络管理员与交换机建立远程 CLI 连接对其实施管理时，需要确保用户 ID、密码和会话内容的保密性。

应中选择哪种访问方法？•Telnet•控制台•AUX•SSH•Option 43 当在平安环境下执行初始配置时，以下哪个程序可用来访问 Cisco 2960 交换机？•使用 Telnet 通过网络远程访问交换机。

•使用控制台端口从 PC 的串行接口或 USB 接口本地访问交换机。

•使用平安外壳协议通过网络远程访问交换机。

•使用 AUX 端口从 PC 的串行接口或 USB 接口本地访问交换机。

•Option 24 哪个命令或组合键让用户返回命令层级中的上一级？•end•exit•Ctrl-Z•Ctrl-C•Option 25 某台具有有效操作系统的路由器包含在 NVRAM 中存储的配置文件。

配置文件中包含一个使能加密密码，但没有控制台密码。

当该路由器启动时，将显示哪种模式？•全局配置模式•设置模式•特权 EXEC 模式•用户 EXEC 模式Option 46 Cisco IOS CLI 的上下文相关帮助功能为用户提供了哪两项功能？〔请选择两项。

〕•当提交了错误命令时显示错误消息•显示当前模式中的所有可用命令列表•允许用户使用 Tab 键完成缩写命令的其余局部•确定已输入命令的可用选项、关键字或参数•选择用于完成任务的最正确命令Option 2 and Option 4 are correct.7 show startup-config命令将显示哪些信息？•复制到 RAM 中的 IOS 映像•ROM 中的引导程序•RAM 中当前运行的配置文件的内容•NVRAM 中保存的配置文件的内容Option 48 为什么必须配置设备的主机名？•设置了主机名之后，思科路由器或交换机才会开始运行•主机名必须在其他所有参数之前配置•用于在远程访问过程〔SSH 或 Telnet〕中识别设备•用于通过控制台端口对设备进行本地访问Option 39 以下哪两个主机名遵循了 Cisco IOS 设备的命名约定指南？〔选择两项。

填空1计算机间的通信合作层次接口服务2语法语义同步3结构格式4OSI参考模型国际标准化5物理层数据链路层网络层传输层会话层表示层应用层表示层数据链路层6为数据端设备提供传送数据的通路传输数据完成物理层的一些管理工作7数据终端设备数据通信设备8链路管理、帧同步、流量控制、差错控制、透明传输、寻址9帧10面向字符面向比特11通信子网层、路径选择、流量控制、数据传输与中继、清除子网的质量差异12虚电路服务、数据报服务13数据传输层、表示层14网络接口层、网络互联层、传输层、应用层15简单文件传输协议、超文本传输协议、远程登录协议、文件传输协议16服务17会话层18ARP协议19远程登录20网络互连层判断：1对2错3错4错5错6对7错8对9对10错1.网络体系结构采用层次化的优点是什么？(1)各层之间相互独立，高层不必关心低层的实现细节，只要知道低层所提供的服务，经及本层向上层所提供的服务即可，能真正做到各司其职。

(2)有利于实现和维护，某个层次实现细节的变化不会对其他层次产生影响。

(3)易于实现标准化。

2.0SI模型和TCP/IP模型的共同点和不同点是什么？共同点：都采用了层次结构的思想、在传输层中定义了相似的功能。

不同点：二者在层次划分上、使用协议上有很大的区别；TCP/IP为工业标准模型，而OSI 是理论标准模型。

3.简述OS1网络层的主要功能？物理层具体解决了以下问题：使用什么类型的传输介质，使用什么样的连接器件和连接设备。

使用什么拓扑结构。

使用什么样的物理信号表示二进制的。

和1以及该物理信号与传输相关的特性如何。

数据链路层具体解决了以下问题：将bit信息加以组织封装成帧。

确定了数据帧的结构。

通过使用硬件地址及物理地址来寻址。

实现差错校验信息的组织。

对共享的介质实现访问控制。

网络层具体解决了以下问题：提供了网络层的地址(IP地址)，并进行不同网络系统间的路径选择。

数据包的分割和重新组合。

差错校险和恢复。

CCNA思科考试答案（全）第 1 章考试1一家拥有10 名员工的小型公司使用单个LAN 在计算机之间共享信息。

哪种类型连接适合此公司？由当地电话服务提供商提供的拨号连接能够使公司方便且安全地连接员工的虚拟专用网络通过当地服务提供商建立的私有专用线路通过当地服务提供商提供的宽带服务（如DSL）答案：4解析：对于这种小型办公室，比较适合通过被称为数字用户线路(DSL) 的常见宽带服务实现Internet 连接，这种服务由当地的电话服务提供商提供。

由于员工人数很少，带宽的问题并不突出。

如果公司较大，在远程站点有分支机构，则专用线路会更加适合。

如果公司员工需要通过Internet 与公司联系，则采用虚拟专用网。

2哪种网络情况需要使用WAN？员工工作站需要获取动态分配的IP 地址。

员工在出差时需要通过VPN 连接到公司电子邮件服务器。

分支机构的员工需要与同一园区网络上的另一座建筑物内的公司总部共享文件。

员工需要访问托管在其建筑物内DMZ 中的公司Web 服务器上的网页。

答案：2解析：当出差的员工需要通过WAN 连接到公司电子邮件服务器时，VPN 将通过WAN 连接在员工笔记本电脑与公司网络之间创建一个安全隧道。

通过DHCP 获取动态IP 地址是LAN 通信的功能。

在企业园区的不同建筑物之间共享文件可通过LAN 基础设施来实现。

DMZ 是企业LAN 基础设施内一个受保护的网络。

3以下哪项描述了WAN 的特征？WAN 和LAN 在同一地理范围内运行，但有串行链路。

WAN 网络归运营商所有。

所有串行链路均被视为WAN 连接。

WAN 可提供到园区主干网的终端用户网络连接。

答案：2解析：WAN 可用于将企业LAN 互连到远程分支机构站点LAN 和远程工作人员站点。

WAN 归运营商所有。

虽然WAN 连接一般通过串行接口实现，但并不是所有串行链路均连接至WAN。

LAN（而非WAN）可在组织中提供终端用户网络连接。

4电路交换WAN 技术的两个常见类型是什么？（请选择两项。

CCNA第一学期Finalexam考试英文版答案(R&S.)C 1A medium-sized business is researching available options for connecting to the Internet.Thecompany is looking for a high speed option with dedicated, symmetric access.Whichconnection type should the company choose?DSLdialupsatelliteleased linecable modem2What is the purpose of having a converged network?to provide high speed connectivity to all end devicesto make sure that all types of data packets will be treated equallyto achieve fault tolerance and high availability of data network infrastructure devicesto reduce the cost of deploying and maintaining thecommunication infrastructure3What characteristic of a network enables it to quickly grow to support new users andapplications without impacting the performance of the service being delivered to existing users?reliabilityscalabilityquality of serviceaccessibility4Which connection provides a secure CLI session with encryption to a Cisco switch?a console connectionan AUX connectiona Telnet connectionan SSH connection5A network technician is attempting to configure an interface by entering the followingcommand:SanJose(config)#ip address192.168.2.1255.255.255.0.The command isrejected by the device.What is the reason for this? The command is being entered from the wrong mode of operation.The command syntax is wrong.The subnet mask information is incorrect.The interface is shutdown and must be enabled before the switch will accept the IP address.6After several configuration changes are made to a router, the copy running-configurationstartup-configuration command is issued.Where will the changes be stored?flashROMNVRAMRAMthe configuration registera TFTP server7Refer to the exhibit.From global configuration mode,an administrator is attempting to create a message-of-the-day banner by using thecommand banner motd V Authorized access only!Violators will be prosecuted!V When users log in using Telnet,the banner does not appear correctly.What is the problem? The banner message is too long.The delimiting character appears in the banner message.The symbol“!”signals the end of a banner message.Message-of-the-day banners will only appear when a user logs in through the console port.8What are three characteristics of an SVI?(Choose three.) It is designed as a security protocol to protect switch ports.It is not associated with any physical interface on a switch.It is a special interface that allows connectivity by different types of media.It is required to allow connectivity by any device at any location.It provides a means to remotely manage a switch.It is associated with VLAN1by default.9A technician configures a switch with these commands: SwitchA(config)#interface vlan1SwitchA(config-if)#ip address192.168.1.1255.255.255.0 SwitchA(config-if)#no shutdownWhat is the technician configuring?Telnet accessSVIpassword encryptionphysical switchport access10In computer communication,what is the purpose of message encoding?to convert information to the appropriate form for transmissionto interpret informationto break large messages into smaller framesto negotiate correct timing for successful communication11What protocol is responsible for controlling the size of segments and the rate at whichsegments are exchanged between a web client and a web server?TCPIPHTTPEthernet12What are two benefits of using a layered network model? (Choose two.)It assists in protocol design.It speeds up packet delivery.It prevents designers from creating their own model.It prevents technology in one layer from affecting other layers.It ensures a device at one layer can function at the next higher layer.13What is the process of dividing a data stream into smaller pieces before transmission?segmentationencapsulationencodingflow control14When IPv4addressing is manually configured on a web server,which property of the IPv4configuration identifies the network and host portion for an IPv4address?DNS server addresssubnet maskdefault gatewayDHCP server address15A network administrator is troubleshootingconnectivity issues on a ing a tester,the administrator notices that the signals generated by the server NIC are distorted and not usable.In which layer of the OSI model is the error categorized?presentation layernetwork layerphysical layerdata link layer16A network engineer is measuring the transfer of bits across the company backbone for amission critical database application.The engineer notices that the network throughputappears lower than the bandwidth expected.Which three factors could influence thedifferences in throughput?(Choose three.)the amount of traffic that is currently crossing the networkthe sophistication of the encapsulation method applied to the datathe type of traffic that is crossing the networkthe latency that is created by the number of network devices that the data is crossingthe bandwidth of the WAN connection to the Internetthe reliability of the gigabit Ethernet infrastructure of the backbone17Which type of UTP cable is used to connect a PC to a switch port?consolerollovercrossoverstraight-through18What is a characteristic of the LLC sublayer?It provides the logical addressing required that identifies the device.It provides delimitation of data according to the physical signaling requirements of the medium.It places information in the frame allowing multiple Layer 3protocols to use the same network interface and media.It defines software processes that provide services to the physical layer.19What are the three primary functions provided by Layer 2data encapsulation?(Choosethree.)error correction through a collision detection methodsession control using port numbersdata link layer addressingplacement and removal of frames from the mediadetection of errors through CRC calculationsdelimiting groups of bits into framesconversion of bits into data signals20What will a host on an Ethernet network do if it receives a frame with a destination MACaddress that does not match its own MAC address?It will discard the frame.It will forward the frame to the next host.It will remove the frame from the media.It will strip off the data-link frame to check the destination IP address.21What are two actions performed by a Cisco switch? (Choose two.)building a routing table that is based on the first IP address in the frame headerusing the source MAC addresses of frames to build and maintain a MAC address tableforwarding frames with unknown destination IP addresses to the default gatewayutilizing the MAC address table to forward frames via the destination MAC addressexamining the destination MAC address to add new entries to the MAC address table22What are two examples of the cut-through switching method?(Choose two.)store-and-forward switchingfast-forward switchingCRC switchingfragment-free switchingQOS switching23Refer to the exhibit.If host A sends an IP packet to host B,what will the destination address be in the frame when it leaves host A?DD:DD:DD:DD:DD:DD172.168.10.99CC:CC:CC:CC:CC:CC172.168.10.65BB:BB:BB:BB:BB:BBAA:AA:AA:AA:AA:AA24What are two services provided by the OSI network layer?(Choose two.)performing error detectionrouting packets toward the destinationencapsulating PDUs from the transport layerplacement of frames on the mediacollision detection25What information is added during encapsulation at OSI Layer3?source and destination MACsource and destination application protocolsource and destination port numbersource and destination IP address26What are two functions of NVRAM?(Choose two.)to store the routing tableto retain contents when power is removedto store the startup configuration fileto contain the running configuration fileto store the ARP table27Refer to the exhibit.The network administrator for a small advertising company has chosen to use the192.168.5.96/27 network for internal LAN addressing.As shown in the exhibit,a static IP address is assigned to the company web server.However,the web server cannot access the Internet.The administrator verifies that local workstations with IP addresses that are assigned by a DHCP server can access the Internet,and the web server is able to ping local workstations.Which component is incorrectly configured?subnet maskDNS addresshost IP addressdefault gateway address28Why does a Layer3device perform the ANDing process on a destination IP address andsubnet mask?to identify the broadcast address of the destination networkto identify the host address of the destination hostto identify faulty framesto identify the network address of the destination network29What are the three ranges of IP addresses that are reserved for internal private use?(Choosethree.)10.0.0.0/864.100.0.0/14127.16.0.0/12172.16.0.0/12192.31.7.0/24192.168.0.0/1630Which three addresses are valid public addresses? (Choose three.)198.133.219.17192.168.1.24510.15.250.5128.107.12.117192.15.301.24064.104.78.22731What type of IPv6address is FE80::1?loopbacklink-localmulticastglobal unicast32Refer to the exhibit.On the basis of the output,which two statements about network connectivity are correct? (Choose two.)There is connectivity between this device and the device at192.168.100.1.The connectivity between these two hosts allows for videoconferencing calls.There are4hops between this device and the device at 192.168.100.1.The average transmission time between the two hosts is2 milliseconds.This host does not have a default gateway configured.33Which subnet would include the address192.168.1.96as a usable host address?192.168.1.64/26192.168.1.32/27192.168.1.32/28192.168.1.64/2934How many hosts are addressable on a network that has a mask of255.255.255.248?268141625435Which statement is true about variable-length subnet masking?Each subnet is the same size.The size of each subnet may be different,depending on requirements.Subnets may only be subnetted one additional time.Bits are returned,rather than borrowed,to create additional subnets.36Refer to the exhibit.Consider the IP address of 192.168.10.0/24that has been assigned to a high school building.The largest network in this building has100 devices.If192.168.10.0is the network number for the largest network,what would be the network number for thenext largest network,which has40devices?192.168.10.0192.168.10.128192.168.10.192192.168.10.224192.168.10.24037In what two situations would UDP be the preferred transport protocol over TCP?(Choosetwo.)when applications need to guarantee that a packet arrives intact,in sequence,and unduplicatedwhen a faster delivery mechanism is neededwhen delivery overhead is not an issuewhen applications do not need to guarantee delivery of the datawhen destination port numbers are dynamic38What important information is added to the TCP/IPtransport layer header to ensurecommunication and connectivity with a remote network device?timing and synchronizationdestination and source port numbersdestination and source physical addressesdestination and source logical network addresses39What is the TCP mechanism used in congestion avoidance? three-way handshakesocket pairtwo-way handshakesliding window40Which three statements characterize UDP?(Choose three.)UDP provides basic connectionless transport layer functions.UDP provides connection-oriented,fast transport of data at Layer 3.UDP relies on application layer protocols for error detection.UDP is a low overhead protocol that does not provide sequencing or flow control mechanisms.UDP relies on IP for error detection and recovery.UDP provides sophisticated flow control mechanisms.41Which two tasks are functions of the presentation layer? (Choose two.)compressionaddressingencryptionsession controlauthentication42Which two protocols operate at the highest layer of the TCP/IP protocol stack?(Choose two.)DNSEthernetIPPOPTCPUDP43Which two roles can a computer assume in a peer-to-peer network where a file is beingshared between two computers?(Choose two.)clientmasterserverslavetransient44What is the function of the HTTP GET message?to request an HTML page from a web serverto send error information from a web server to a web clientto upload content to a web server from a web clientto retrieve client email from an email server using TCP port11045A wireless host needs to request an IP address.What protocol would be used to process therequest?FTPHTTPDHCPICMPSNMP46When planning for network growth,where in the network should packet captures take place toassess network traffic?on as many different network segments as possibleonly at the edge of the networkbetween hosts and the default gatewayonly on the busiest network segment47When applied to a router,which command would help mitigate brute-force password attacksagainst the router?exec-timeout30service password-encryptionbanner motd$Max failed logins=5$login block-for60attempts5within6048Refer to the exhibit.An administrator is testing connectivity to a remote device with the IP address10.1.1.1.What does the output of this command indicate?Connectivity to the remote device was successful.A router along the path did not have a route to the destination.A ping packet is being blocked by a security device along the path.The connection timed out while waiting for a reply fromthe remote device.。

第一章：正确答案：2.4.5•解析：由于不需要使用网络设备和专用服务器，对等网络易于创建，复杂性更低，且成本更少。

而且对等网络也没有集中管理。

这种网络安全性更低，不可扩展，而且那些同时充当客户端和服务器的设备可能性能更差正确答案：1解析：正确答案： 3.5解析：选择网络介质的条件包括：所选介质可以成功传送信号的距离、要安装所选介质的环境、必须传输的数据量和速度以及介质和安装的成本。

正确答案：3和4解析：终端设备上的应用程序可以生成数据，更改数据内容并且负责启动封装过程。

正确答案：1和4解析：终端设备会发出通过网络传输的数据。

中间设备会在链路发生故障时通过备用路径传输数据，并且会过滤数据传输以增强安全性。

网络介质提供网络消息的传输通道。

正确答案：4解析：外联网是公司外部的人或企业合作伙伴访问数据的网络区域。

内部网只描述通常仅供内部人员访问的网络区域。

当设备连接到有线网络时，有线LAN 会受BYOD（自带设备）影响。

使用大学无线LAN 的设备多为平板电脑和智能手机。

大学生主要使用无线WAN 来访问他们的手机运营商网络。

.正确答案：2解析：由于通过Internet 可以联系在线供应商，所以家庭用户通过Internet 进行网上购物。

内联网基本上是仅供内部使用的局域网。

外联网是外部合作伙伴访问组织内部特定资源的网络。

家庭用户并不一定使用LAN 来访问Internet。

例如，PC 可以通过调制解调器直接连接到ISP。

正确答案：1解析：内部网这个术语用于表示一个组织的私有局域网和广域网连接。

内部网的设计旨在仅允许该组织的成员、员工或其他获得授权的人员进行访问。

正确答案：2和4解析：电缆和DSL 均能实现高带宽、始终联网，并提供到主机计算机或LAN 的以太网连接。

10正确答案：2和3解析：移动电话连接需要使用移动电话网络。

卫星连接通常用于家庭或企业外部不便使用物理布线的位置。

11正确答案：2解析：当对网络资源的请求超出了可用容量时，网络就会变得拥堵。

CCNA第一学期各章习题和参考答案第二章网络通信1、TCP/IP网络接入层有何作用？A路径确定和数据包交换B数据表示、编码和控制C可靠性、流量控制和错误检测E将数据段划分为数据包2、下列哪些陈述正确指出了中间设备在网络中的作用？（选择三项）B发起数据通信D发送数据流F数据流最后的终止点3、下列哪三项陈述是对局域网(LAN) 最准确的描述？（选择三项）C LAN 中的不同网段之间一般通过租用连接的方式连接。

D此类网络的安全和访问控制由服务提供商控制。

F此类网络的每个终端通常都连接到电信服务提供商(TSP)。

004 什么是PDU？A传输期间的帧损坏B在目的设备上重组的数据C因通信丢失而重新传输的数据包005 OSI 模型哪两层的功能与TCP/IP 模型的网络接入层相同？（选择两项）018哪个应用层协议通常用于支持客户端与服务器之间的文件传输？A HTMLB HTTP D Telnet019哪个应用层协议中规定了Microsoft 网络中用于文件共享的服务？A DHCPB DNS D SMTP E Telnet020服务器上的应用层通常如何处理多客户端服务请求？A终止与服务的所有连接B拒绝与单一守护程序的多个连接C暂停当前连接，建立新连接第四章OSI传输层001下列哪两项是用户数据报协议(UDP) 的功能？（选择两项）A流量控制 D 面向连接E 序列和确认002请参见图示。

此Wireshark 捕获输出的第7 行中执行的是哪一项TCP 操作？A会话创建B 数据段重传C 数据传输D 会话断开003数据段的TCP 报头中为什么包含端口号？A指示转发数据段时应使用的正确路由器接口B 标识接收或转发数据段时应使用的交换机端口C确定封装数据时应使用的第3 层协议让接收主机转发数据到适当的应用程序E让接收主机以正确的顺序组装数据包004OSI 模型哪一层负责规范信息从源设备到目的设备准确可靠地流动？A应用层 B 表示层 C 会话层传输层 E 网络层005请参见图示。