计算机网络自顶向下方法答案(英文第六版)

Chapter 4 Network Layer1.Packetizing at the network layer involvesA) Encapsulating the payload at the sourceB) Adds a header that contains the source and destination informationC) Decapsulating the payload at the destinationD) All of the choices are correct2.Routers in the path are not allowed to ___________________________.A) fragment the packet they receiveB) decapsulate the packetC) change source or destination addressD) All of the choices are correct3.The network layer in the Internet provides _________________.A) comprehensive error and flow control.B) limited error control, but no flow control.C) comprehensive error control but limited flow control.D) All of the choices are correct4.In a virtual-circuit approach, the forwarding decision is based on the value of the _____________ field in the packet header.A) source addressB) destination addressC) labelD) None of the choices are correct5.In a datagram approach, the forwarding decision is based on the value of the _____________ field in the packet header.A) source addressB) destination addressC) labelD) None of the choices are correct6.The performance of a network can be measured in terms of ________.A) delayB) throughputC) packet lossD) all of the choices are correct7.Transmission delay (time) is the ratio of ______________________.A) transmission rate to packet lengthB) transmission rate to distanceC) packet length to transmission rateD) processing time to transmission rate8.Propagation delay (time) is the ratio of ______________________.A) transmission rate to propagation speedB) propagation speed to distanceC) packet length to propagation speedD) distance to propagation speed9.When the load in the network reaches the network capacity, the packet delay ___________ and the network throughput reaches ______________.A) increases sharply; its minimumB) increases sharply; its maximumC) decreases sharply; its minimumD) decreases sharply; its maximum10.In open-loop congestion control, policies are applied ____________________.A) to prevent congestion before it happensB) to alleviate congestion after it happensC) to either prevent congestion before it happens or to alleviate congestion after it happensD) None of the choices are correct11.The __________________ technique is one of the open-loop congestion policyA) backpressureB) choke packetC) implicit signalingD) None of the choices are correct12.The __________________ technique is one of the close-loop congestion policyA) acknowledgment policyB) choke packetC) discarding policyD) None of the choices are correct13.IP is a _________ protocol.A) connection-oriented unreliableB) connection-oriented reliableC) connectionless unreliableD) connectionless reliable14.An HLEN value of decimal 10 means _______.A) there are 10 bytes of optionsB) there are 10 bytes in the headerC) there are 40 bytes of optionsD) there are 40 bytes in the header15.If the fragment offset has a value of 100, it means that _______.A) the datagram has not been fragmentedB) the datagram is 100 bytes in sizeC) the first byte of the datagram is byte 800D) None of the choices are correct16.What is needed to determine the number of the last byte of a fragment?A) offset numberB) total lengthC) both offset number and the total lengthD) None of the choices are correct17.The IP header size is _______ bytes long.A) 20 to 60B) 20C) 60D) None of the choices are correct18.Packets in the IP layer are called _________.A) segmentsB) datagramsC) framesD) None of the choices are correct19.The total length field defines the total length of the datagram _________.A) including the headerB) excluding the headerC) excluding the option lengthD) None of the choices are correct20.When a datagram is encapsulated in a frame, the total size of the datagram must be lessthan the _______.A) MUTB) MATC) MTUD) None of the choices are correct21.An IPv4 address is normally represented in base ____ in dotted-decimal notation.A) 16B) 256C) 10D) None of the choices are correct22.In classful addressing, the IPv4 address space is divided into _______ classes.A) 3B) 4C) 5D) None of the choices are correct23.The number of addresses assigned to an organization in classless addressing _______.A) can be any numberB) must be a multiple of 256C) must be a power of 2D) None of the choices are correct24.The first address assigned to an organization in classless addressing _______.A) must be evenly divisible by the number of addresses in the organizationB) must be divisible by 128C) must belong to one of the A, B, or C classesD) None of the choices are correct25.In subnetting, the number of addresses in each subnet must _______.A) be a power of 2B) be a multiple of 128C) be divisible by 128D) None of the choices are correct26.What is the default prefix length for class A in CIDR notation?A) 9B) 8C) 16D) None of the choices are correct27.What is the default prefix length for class B in CIDR notation?A) 9B) 8C) 16D) None of the choices are correct28.What is the default prefix length for class C in CIDR notation?A) 24B) 8C) 16D) None of the choices are correct29.DHCP is a (an) ___________ layer protocol.A) applicationB) transportC) networkD) data-link30.In DHCP, the client uses ________ port and the server uses _________ port.A) an ephemeral; a well-knownB) a well-known; a well-knownC) a well-known; an ephemeralD) None of the choices are correct31.DHCP uses the services of _______.A) UDPB) TCPC) IPD) None of the choices are correct32._________ allows a site to use a set of private addresses for internal communication and a set of global Internet addresses for communication with the rest of the world.A) DHCPB) NATC) IMCPD) None of the choices are correct33.The idea of address aggregation was designed to alleviate the increase in routing table entries when using ________ addressing.A) classfulB) classlessC) classful or classlessD) None of the choices are correct34.The use of hierarchy in routing tables can ________ the size of the routing tables.A) reduceB) increaseC) neither reduce nor increaseD) None of the choices are correct35.ICMP is a (an) _________ layer protocol.A) application-layer protocol that helps TCP/IP at the network layerB) transport-layer protocol that helps TCP/IP at the network layerC) network-layer protocol.D) data-link layer protocol that helps TCP/IP at the network layer36.Which of the following is true about ICMP messages?A) An ICMP error message may be generated for an ICMP error message.B) An ICMP error message may be generated for a fragmented datagram.C) An ICMP error message may be generated for a multicast datagram.D) None of the choices are correct37.Routing inside an autonomous system is referred to as ________ routing.A) interdomainB) intradomainC) out-of-domainD) None of the choices are correct38.Routing between autonomous systems is referred to as ______ routing.A) interdomain routingB) intradomain routingC) out-of-domainD) None of the choices are correct39.In _______ routing, the least cost route between any two nodes is the route with the minimum distance.A) path vectorB) distance vectorC) link stateD) None of the choices are correct40.In ________, each node maintains a vector (table) of minimum distances to every node.A) path vectorB) distance vectorC) link stateD) None of the choices are correct41.In distance vector routing, each node periodically shares its routing table with _________ and whenever there is a change.A) every other nodeB) its immediate neighborsC) one neighborD) None of the choices are correct42.The Routing Information Protocol (RIP) is an intradomain routing based on _________ routing.A) distance vectorB) link stateC) path vectorD) None of the choices are correct43.The metric used by _______ is the hop count.A) OSPFB) RIPC) BGPD) None of the choices are correct44.In RIP, the ________ timer controls the advertising of regular update messages.A) garbage collectionB) expirationC) periodicD) None of the choices are correct45.In RIP, the ________ timer is used to purge invalid routes from the table.A) garbage collectionB) expirationC) periodicD) None of the choices are correct46.In RIP, the ________ timer controls the validity of the route.A) garbage collectionB) expirationC) periodicD) None of the choices are correct47.RIP uses the services of _______.A) TCPB) UDPC) IPD) None of the choices are correct48.The _________ routing uses the Dijkstra algorithm to build a routing table.A) distance vectorB) link stateC) path vectorD) None of the choices are correct49.The Open Shortest Path First (OSPF) protocol is an intradomain routing protocol based on _______ routing.A) distance vectorB) link stateC) path vectorD) None of the choices are correct50.The _______ protocol allows the administrator to assign a cost, called the metric, to each route.A) OSPFB) RIPC) BGPD) None of the choices are correct51.In OSPF, a ________ link connects two routers without any other host or router in between.A) point-to-pointB) transientC) stubD) None of the choices are correct52.In OSPF, a _______ link is a network with several routers attached to it.A) point-to-pointB) transientC) stubD) None of the choices are correct53.In OSPF, a ________ link is a network connected to only one router.A) point-to-pointB) transientC) stubD) None of the choices are correct54.In OSPF, a ________ defines the links of a network.A) network linkB) router linkC) summary link to networkD) None of the choices are correct55.___________ is an interdomain routing protocol using path vector routing.A) BGPB) RIPC) OSPFD) None of the choices are correct56.A one-to-all communication between one source and all hosts on a network is classified as a _______ communication.A) unicastB) multicastC) broadcastD) None of the choices are correct57.A one-to-many communication between one source and a specific group of hosts is classified as a _______ communication.A) unicastB) multicastC) broadcastD) None of the choices are correct58.A one-to-one communication between one source and one destination is classified as a _______ communication.A) unicastB) multicastC) broadcastD) None of the choices are correct59.In ______, the router forwards the received packet through only one of its interfaces.A) unicastingB) multicastingC) broadcastingD) None of the choices are correct60.In multicast routing, each involved router needs to construct a ________ path tree for each group.A) averageB) longestC) shortestD) None of the choices are correct61.In the _______ tree approach to multicasting, each router needs to create a separate tree for each source-group.A) group-sharedB) source-basedC) destination-basedD) None of the choices are correct62.The Multicast Open Shortest Path First (MOSPF) routing uses the _______ tree approach.A) source-basedB) group-sharedC) destination-basedD) None of the choices are correct63.The Multicast Open Shortest Path First (MOSPF) protocol is an extension of the OSPF protocol that uses multicast routing to create source-based trees. The protocol is based on _______ routing.A) distance vectorB) link stateC) path vectorD) None of the choices are correct64.In RPF, a router forwards only the copy that has traveled the _______ path from the source to the router.A) shortestB) longestC) averageD) None of the choices are correct65.RPF eliminates the ________ in the flooding process.A) forwardingB) backwardingC) floodingD) None of the choices are correct66.RPB creates a shortest path _______ tree from the source to each destination.A) unicastB) multicastC) broadcastD) None of the choices are correct67.RPB guarantees that each destination receives _________ of the packet.A) only one copyB) no copiesC) multiple copiesD) None of the choices are correct68.In ________, the multicast packet must reach only those networks that have active members for that particular group.A) RPFB) RPBC) RPMD) None of the choices are correct69._______ adds pruning and grafting to _______ to create a multicast shortest path tree that supports dynamic membership changes.A) RPM; RPBB) RPB; RPMC) RPF; RPMD) None of the choices are correct70.__________ is an implementation of multicast distance vector routing. It is a source-based routing protocol, based on RIP.A) MOSPFB) DVMRPC) CBTD) None of the choices are correct71.DVMRP is a ________ routing protocol, based on RIP.A) source-basedB) group-sharedC) destination-basedD) None of the choices are correct72.Pruning and grafting are strategies used in _______.A) RPFB) RPBC) RPMD) None of the choices are correct73.PIM-DM is used when the number of routers with attached members is ______ relative to the number of routers in the internet.A) largeB) smallC) moderateD) None of the choices are correct74.PIM-SM is used when the number of routers with attached members is ______ relative to the number of routers in the internet.A) largeB) smallC) moderateD) None of the choices are correct75.An IPv6 address is _________ bits long.A) 32B) 64C) 128D) 25676.An IPv6 address consists of ________ bytes (octets);A) 4B) 8C) 16D) None of the choices are correct77.In hexadecimal colon notation, a 128-bit address is divided into _______ sections, each _____ hexadecimal digits in length.A) 8; 2B) 8; 3C) 8; 4D) None of the choices are correct78.An IPv6 address can have up to __________ hexadecimal digits.A) 16B) 32C) 8D) None of the choices are correct79.In IPv6, the _______ field in the base header restricts the lifetime of a datagram.A) versionB) priorityC) hop limitD) None of the choices are correct80.The _________ in IPv6 is designed to provide special handling for a particular flow of data.A) flow labelB) next headerC) hop limitD) None of the choices are correct81.When two computers using IPv6 want to communicate but the packet must pass through an IPv4 region, which transition strategy should be used?A) tunnelingB) header translationC) either tunneling or header translationD) None of the choices are correct82.When the majority of the Internet has moved to the IPv6 but some still use IPv4, which transition strategy should be used?A) tunnelingB) header translationC) either tunneling or header translationD) None of the choices are correct83.The protocols __________________________ in version 4 are combined into one single protocol, ICMPv6.A) ARP and IGMPB) ICMP and IGMPC) ICMP, ARP, and IGMPD) None of the choices are correctDCBCB DCCBA DBCDC CABAC BCCAA BCAAB ABBAC DBABB BABCA BBBBA ABCAA CBAAC BABAD CACAB ACABC CCBCA ABC。

计算机网络教程自顶向下方法选择题及答案Chapt1Introduction-QUIZZChapter 1 Introduction1.A local area network (LAN) is defined by _______________.A) the geometric size of the networkB) the maximum number of hosts in the networkC) the maximum number hosts in the network and/or the geometric size of the networkD) the topology of the network2.The largest geographic area a wide area network (WAN) can span isA) a townB) a stateC) a countryD) the world3.The TCP/IP protocol suite consists of _______ layers.A) twoB) threeC) fiveD) six4.A router is involved in ____________ layers of the TCP/IP protocol suite.A) twoB) threeC) fourD) five5.A link-layer switch is involved in ______________ layers of the TCP/IP protocol suite.A) twoB) threeC) fourD) five6.In the TCP/IP protocol suite, which of the following is an application layer protocol?A) The User Datagram Protocol (UDP)B) The Internet Protocol (IP)C) The File Transfer Protocol (FTP)D) the Transmission Control Protocol (TCP)7.In the TCP/IP protocol suite, which of the following is a transport layer protocol?A) The Internet Control Message protocol (ICMP)B) The Internet Protocol (IP)C) The Address Resolution Protocol (ARP)D) The Transmission Control Protocol (TCP)8.In the TCP/IP protocol suite, which of the following is a network layer protocol?A) The Stream Control Transmission Protocol (SCTP)B) The Secure Shell (SSH)C) The Internet Protocol (IP)D) User Datagram Protocol (UDP)9.The transport-layer packet in the TCP/IP protocol suite is calledA) a messageB) a datagramC) a segment or a user datagramD) a frame10.In the TCP/IP protocol suite, the ______ layer is responsible for moving frames from one hop (node) to the next.A) physicalB) data linkC) transportD) network11.In the TCP/IP protocol suite, the physical layer is concerned with the movement of _______ over the physical medium.A) programsB) dialogsC) protocolsD) bits12.In the TCP/IP protocol suite, a port number is the identifier at the ____________.A) application layerB) transport layerC) network layerD) physical layer13.In the TCP/IP protocol suite, a logical address is the identifier at the _______________.A) network layerB) transport layerC) data-link layerD) application layer14.The _________ layer is responsible for the delivery of a message from one process to another.A) physicalB) transportC) networkD) application15.The Internet Protocol (IP) is ________ protocol.A) a reliableB) a connection-orientedC) a reliable and connection-orientedD) an unreliable16.The application layer in the TCP/IP protocol suite is usually considered to be the combination of ________ layers in the OSI modelA) application, presentation, and sessionB) application, transport, and networkC) application, data-link, and physicalD) network, data-link, and physical17.A proposed standard is elevated to ________ standard status after at least two successful tries.A) informationalB) historicC) draftD) None of the choices are correct18.An RFC is labeled ________ if it must be implemented by all Internet systems.A) requiredB) electiveC) recommendedD) None of the choices are correct19.In the original ARPANET, _______ were directly connected to each other.A) interface message processors (IMPs).B) host computersC) networksD) routers20._______ was formed to connect universities with no defense ties.A) ARPANETB) CSNETC) NSFNETD) ANSNET21.Currently _______ is responsible for the management of Internet domain names and addressesA) NICB) ICANNC) ISOCD) IEFE22.In TCP/IP, a message at the application layer is encapsulated in a packet at the ________ layer.A) networkB) transportC) data linkD) physical23.In TCP/IP, a message at the transport layer is encapsulated in a packet at the ________ layer.A) networkB) transportC) data linkD) physical24.In TCP/IP, a message belonging to the network layer is decapsulated from a packet at the ________ layer.A) networkB) transportC) data linkD) physical25.In TCP/IP, a message belonging to the transport layer is decapsulated from a packet at the ________ layer.A) networkB) transportC) data linkD) physical26.In TCP/IP, a logical connection between an entity at thenetwork layer can be made with another entity at the ________ layer.A) networkB) transportC) data linkD) physical27.In TCP/IP, a logical connection between an entity at the data-link layer can be made with another entity at the ________ layer.A) networkB) transportC) data linkD) physical28.In TCP/IP, a packet at the third layer carries data belonging to the ________ layer and the headerbelonging to the _________ layer.A) third; thirdB) third; fourthC) fourth; thirdD) fourth; fourthADCBA CDCCB DBABD ACAAB BBACB ACC。

课后习题答案（4-6单元）：Chapter 4 Review Questionsreview questions:1,2,3,4,8,10,15,16,18,20,23,27,33,34,361.网络层的分组名称是数据报.路由器是根据包的IP地址转发包;而链路层是根据包的MAC地址来转发包.2.数据报网络中网络层两个最重要的功能是:转发,选路.虚电路网络层最重要的三个功能是:转发,选路,和呼叫建立.3.转发是当一个分组到达路由器的一条输入链路时,该路由器将该分组移动到适当的输出链路.选路是当分组从发送方流向接收方时,网络层必须决定这些分组所采用的路由或路径.4.是,都使用转发表,要描述转发表,请参考4.2节.在虚电路网络中，该网络的路由器必须为进行中的连接维持连接状态信息。

每当跨越一台路由器则创建一个新连接，一个新的连接项必须加到该路由器转发表中；每当释放一个连接，必须从该表中删除该项。

注意到即使没有VC号转换，仍有必要维持连接状态信息，该信息将VC号与输出接口号联系起来。

每当一个端系统要发送分组时，它就为该分组加上目的地端系统的地址，然后将该分组推进网络中。

完成这些无需建立任何虚电路。

在数据报网络中的路由器不维护任何有关虚电路的状态信息。

每个路由器有一个将目的地址影射到链路接口的转发表；当分组到达路由器时，该路由器使用该分组的目的地址在该转发表中查找适当的输出链路接口。

然后路由其将该分组项该输出链路接口转发。

虽然在数据报网络中不维持连接状态信息，它们无论如何在其转发表中维持了转发状态信息。

在数据报网络中的转发表是由选录算法修改的，通常每1到5分钟左右更新转发表。

在虚电路网络中，无论何时通过路由器拆除一条现有的连接，路由器中的转发表就更新。

8.(1)经内存交换:在输入和输出端口之间的交换是在CPU控制下完成的.输入与输出端口的作用就像在传统操作系统中的I/O设备一样.一个分组到达一个输入端口,该端口会先通过中断方式向选路处理器发出信号.于是,该分组就被拷贝到处理器内存中.选路处理器从分组首部中取出目的地址,在转发表中找出适当的输出端口,并将该分组拷贝到输出端口的缓存中.(2)经一根总线交换:输入端口经一根总线将分组直接传送到输出端口,不需要选路处理器的干预.由于总线是共享的,故一次只能有一个分组通过总线传送.(3)经一个互联网络交换:使用一个纵横的网络,是一个由2n条总线组成的互联网络,它将n个输出端口和n个输入端口连接,一个到达某个端口的分组沿着连到输出端口的水平总线穿行,直至该水平总线与连到所希望的输出端口的垂直总线之交点.10.因为输出线速率慢而导致输出端队列长度加大，最终将耗尽输出端口的存储空间，在这样的情况下，分组就被丢弃了。

Chapter 2 Application Layer1.In a client-server paradigm, a _______ program provides services to a (another) _______ program.A) client; clientB) client; serverC) server; clientD) server; server2.In a client-server paradigmA) both the server and the client must be running all the time.B) both the server and the client need to be running only when they are needed.C) the server must be running all the time but the client needs to be running only when it is needed.D) the client must be running all the time but the server needs to be running only when it is needed3.The first section of a URL identifier is the __________.A) protocolB) pathC) hostD) port4.A _______ document is a fixed-content document that is created and stored in a server. The client can get a copy of the document only.A) staticB) dynamicC) activeD) None of the choices are correct5._____________ is a language for creating a static document.A) Extensible Style Language (XSL)B) Hypertext Markup Language (HTML)C) Extensible Markup Language (XML)D) All choices are correct6.A _______ document is created by a Web server whenever a browser requests the document.A) staticB) dynamicC) activeD) None of the choices are correct7.For many applications, we need a program or a script to be run at the client site. These are called_______________ documents.A) staticB) dynamicC) activeD) None of the choices are correct8.HTTP uses the services of _________.A) UDPB) IPC) TCPD) DNS9.In HTTP, the first line in a request message is called a _______ line; the first line in the response message is called the ________ line.A) request; responseB) status; responseC) status; statusD) None of the choices are correct10.In a ___________ connection, one TCP connection is made for each request/response.A) persistentB) nonpersistentC) persistent or a nonpersistentD) None of the choices are correct11.In a ___________ connection, the server leaves the connection open for more requests after sending a response.A) persistentB) nonpersistentC) persistent or nonpersistentD) None of the choices are correct12.In HTTP, _______ server is a computer that keeps copies of responses to recent requests.A) a regularB) a proxyC) an auxiliaryD) a remote13.An HTTP request message always contains _______.A) a header line and a bodyB) a request line and a header lineC) a request line, a header line, and a bodyD) a request line, a header line, a blank line, and a bodyWhich of the following is present in both an HTTP request line and a status line?A) version numberB) URLC) status codeD) method15.FTP uses the services of ________.A) UDPB) IPC) TCPD) none of the choices are correct16.In FTP, _________ well-known port(s) is (are) used.A) oneB) twoC) threeD) four17.During an FTP session the control connection is opened _______.A) onceB) twiceC) many timesD) none of the choices are correct18.During an FTP session the data connection may be opened _______.A) only onceB) only two timesC) as many times as neededD) none of the choices are correct19.In FTP, a file can be organized into records, pages, or a stream of bytes. These are types of an attribute called _______.A) file typesB) data structuresC) transmission modesD) none of the choices are correct20.In FTP, there are three types of _______: stream, block, and compressed.A) file typesB) data typesC) transmission modesD) none of the choices are correctIn FTP, ASCII, EBCDIC, and image define an attribute called _______.A) file typeB) data structureC) transmission modeD) none of the choices are correct22.In FTP, when we _______, it is copied from the client to the server.A) retrieve a fileB) store a fileC) open a fileD) none of the choices are correct23.In the common scenario, the electronic mail system needs _________________________.A) two UAs, two MTAs and one MAAB) two UAs, two MTAs and two MAAsC) two UAs, two pairs of MTAs and a pair of MAAsD) two UAs, two pairs of MTAs and a two pairs of MAAs24.________ provides service to the user to make the process of sending or receiving a message easier.A) An MTAB) An MAAC) A UAD) None of the choices are correct25.An e-mail message contains the ________ and the __________.A) header; envelopB) header; bodyC) envelop; bodyD) None of the choices are correct26.In the Internet, an e-mail address consists of two parts: a _______ and a _______.A) local part; domain nameB) global part; domain nameC) label; domain nameD) local part; label27._________ is a supplementary protocol that allows non-ASCII data to be sent through e-mail.A) SMPTB) MPEGC) MIMED) POP28.The formal protocol that defines the MTA client and server in the Internet is called ___________.A) SMTPB) SNMPC) TELNETD) SSH29.SMTP is a __________ protocol.A) pullB) pushC) push and pullD) None of the choices are correct30.The message access protocol is a ________ protocol.A) pullB) pushC) push and pullD) None of the choices are correct31.In the _______ encoding scheme, each 24 bits become four 6-bit chunks, and eventually are sent as32 bits.A) 8bitB) binaryC) base64D) quoted-printable32.In the _______ encoding scheme, a non-ASCII character is sent as 3 characters.A) 8bitB) base64C) quoted-printableD) binary33.TELNET is an abbreviation for ____________.A) terminal networkB) telephone networkC) telecommunication networkD) None of the choices are correct34.When a user logs into a local time-sharing system, it is called ________ login.A) localB) remoteC) local or remoteD) None of the choices are correct35.When a user wants to access an application program or utility located on a remote machine, he or she performs ___________ login.A) localB) remoteC) local or remoteD) None of the choices are correct36.Network Virtual Terminal (NVT) uses two sets of characters, one for _____ and one for __________.A) sending; receivingB) request; replyC) data; controlD) None of the choices are correct37.For data, NVT uses US ASCII characters with the highest order bit set to ______.A) 1B) 0C) 1 or 0D) None of the choices are correct38.For control, NVT uses US ASCII characters with the highest order bit set to ______.A) 1B) 0C) 1 or 0D) None of the choices are correct39.The _______ translates local characters into NVT characters.A) terminal driverB) TELNET clientC) TELNET serverD) pseudoterminal driver40.The _______ translates NVT characters into a form acceptable by the remote operating system.A) terminal driverB) TELNET clientC) TELNET serverD) pseudoterminal driver41.The _________ component in the SSH provides confidentiality, integrity, authentication and compression.A) SSH ApplicationB) SSH-AUTHC) SSH-CONND) SSH-TRANPort forwarding is ____________________________.A) a protocol used to forward messages from one port to another portB) a procedure for changing an ephemeral port to a well-known portC) a service, provided by SSH, that creates a secure channel for applications that do not have security services.D) None of the choices are correct43.In a _______ name space, a name is a sequence of characters without structure.A) linearB) flatC) hierarchicalD) organized44.In a _________ name space, each name is made of several parts.A) linearB) flatC) hierarchicalD) organized45.In the DNS, the names are defined in ___________ structure.A) a linear listB) an inverted-treeC) a three-dimensionalD) None of the choices are correct46.The root of the DNS tree is _______.A) a string of 127 charactersB) a string of 63 charactersC) a string of 15 charactersD) an empty string47.In the domain name space, a full domain name is a sequence of labels separated by ________.A) colonsB) semicolonsC) dotsD) commas48.In the domain name space, if a label is terminated by a null string, it is called a __________.A) PQDNB) CQDNC) SQDND) None of the choices are correctIn the domain name space, if a label is not terminated by a null string, it is called a __________.A) FQDNB) PQDNC) SQDND) None of the choices are correct50.In the domain name space, a _________ is a subtree of the domain name space.A) labelB) nameC) domainD) None of the choices are correct51.In the domain name space, what a server is responsible for or has authority over is called a _________.A) domainB) labelC) zoneD) None of the choices are correct52.A _______ server is a computer whose zone system consists of the whole tree.A) domainB) zoneC) rootD) primary53.A ________ server is a computer that stores a file about the zone for which it has an authority.A) primaryB) secondaryC) zoneD) root54.A ________ server is a computer that transfers the complete information about a zone from another server.A) primaryB) secondaryC) zoneD) root55.In the Internet, the country domain section uses ___________ country abbreviations.A) two-characterB) three-characterC) four-characterD) None of the choices are correct56.In __________ resolution, the resolver expects the server to supply the final answer.A) iterativeB) recursiveC) straightD) None of the choices are correct57.In __________ resolution, the server returns the IP address of the server that it thinks can resolve the query.A) iterativeB) recursiveC) straightD) None of the choices are correct58.DNS can use the services of ________.A) UDPB) TCPC) either UDP or TCPD) None of the choices are correct59.A registrar, a commercial entity accredited by ________ is responsible for adding new domains to DNS data baseA) NICB) ICANNC) ISOCD) IEFE60.In a centralized P2P network, the directory system uses the ________ paradigm; the storing and downloading of the files are done using __________ paradigm.A) client-server; client-serverB) peer-to-peer; client-serverC) client-server; peer-to-peerD) peer-to-peer; peer-to-peer61.Napster is an example of a ____________ peer-to-peer networkA) centralizedB) structured-decentralizedC) unstructured-decentralizedD) None of the choices are correct62.Gnutella is an example of a ____________ peer-to-peer networkA) centralizedB) structured-decentralizedC) unstructured-decentralizedD) None of the choices are correct63.BitTorrent is an example of a ____________ peer-to-peer networkA) centralizedB) structured-decentralizedC) unstructured-decentralizedD) None of the choices are correct64.In a structured-decentralized P2P network, ________________.A) the directory system is kept in a centerB) a query to find a file must be flooded through the networkC) a pre-defined set of rules is used to link nodes so that a query can be effectively and efficiently resolvedD) None of the choices are correct65.In a DHT-based network, each peerA) has a partial knowledge about the whole network.B) has a complete knowledge about the whole network.C) only has a knowledge about its successor.D) None of the choices are correct66.The finger table is the routing table used in ______________.A) GnutellaB) PastryC) KademliaD) None of the choices are correct67.Which of the following is not a Chord interface.A) LookupB) Fix nodeC) StabilizeD) Join68.In __________ a key is stored in a node whose identifier is numerically closest to the key.A) ChordB) PastryC) KademliaD) None of the choices are correct69.To resolve a query, _________ uses two entities: a routing table and a leaf set.A) ChordB) PastryC) KademliaD) None of the choices are correct70.In Kademlia, the distance between the two identifiers (nodes or keys) are measured as the bitwise-___________ between them.A) ANDB) NORC) ORD) None of the choices are correct71.In ________, nodes and data items are m-bit identifiers that create an identifier space of 2m points distributed at the leaves of a binary treeA) ChordB) PastryC) KademliaD) None of the choices are correct72.In Kademlia, each node in the network divides the binary tree into m subtrees that.A) include the node itselfB) do not include the node itselfC) include the node itself and the successor nodeD) None of the choices are correct73.Trackerless BitTorrent uses __________ DHT to do the job of tracking.A) ChordB) PastryC) KademliaD) None of the choices are correctCCAAD BCCDB ABBAC BACBC ABCCB ACABA CCAAB CBABC DCBCB CCDBC CCABA BACBC ACBCA DBBBD CBC。

《计算机网络自顶向下》课后习题答案（第二章中文版）2复习题1.The Web: HTTP; file transfer: FTP; remote login: Telnet; Network News: NNTP; email: SMTP.2.P51 网络体系结构是指以分层的方式来描述通信过程的组织体系。

（例如五层网络结构）另一方面，应用体系结构是由应用程序的研发者设计，并规定应用程序的主要结构（例如客户机/服务器或P2P）从应用程序研发者的角度看，网络体系结构是固定的，并为应用程序提供了特定的服务集合。

3.P52 在即时讯息中，发起人连接到中心服务器，查找接收方的IP地址是典型的客户机/服务器模式。

在这之后，即时信息可以在相互通信的双方进行直接的端到端通信。

不需要总是打开的中间服务器。

4.P53 发起通信的进程为客户机，等待联系的进程是服务器。

5.No. As stated in the text, all communication sessions havea client side and a server side. In a P2P file-sharingapplication, the peer that is receiving a file is typically the client and the peer that is sending the file is typically the server.6.P54 目的主机的IP地址和目的套接字的端口号。

7.在日常生活中你或许会使用Web浏览器和邮件阅读器。

你或许还会用到FTP用户代理，Telnet用户代理，音频/视频播放器用户代理（比如Real Networks player），即时信息代理，P2P文件共享代理。

8.There are no good examples of an application that requires no data loss and timing. If you know of one, send an e-mail to the authors.9.当两个通信实体在相互发送数据前第一次交换控制分组信息时使用握手协议。

《计算机网络自顶向下》课后习题答案答案(第一章中文版)(总5页)--本页仅作为文档封面，使用时请直接删除即可----内页可以根据需求调整合适字体及大小--1复习题1.没有不同。

主机和端系统可以互换。

端系统包括PC，工作站，WEB服务器，邮件服务器，网络连接的PDA，网络电视等等。

2.假设爱丽丝是国家A的大使，想邀请国家B的大使鲍勃吃晚餐。

爱丽丝没有简单的打个电话说“现在我没一起吃晚餐吧”。

而是她先打电话给鲍勃建议吃饭的日期与时间。

鲍勃可能会回复说那天不行，另外一天可以。

爱丽丝与鲍勃不停的互发讯息直到他们确定一致的日期与时间。

鲍勃会在约定时间（提前或迟到不超过15分钟）出现再大使馆。

外交协议也允许爱丽丝或者鲍勃以合理的理由礼貌的退出约会。

3.联网（通过网络互联）的程序通常包括2个，每一个运行在不同的主机上，互相通信。

发起通信的程序是客户机程序。

一般是客户机请求和接收来自服务器程序的服务。

4.互联网向其应用提供面向连接服务（TCP）和无连接服务（UDP）2种服务。

每一个互联网应用采取其中的一种。

面相连接服务的原理特征是：①在都没有发送应用数据之前2个端系统先进行“握手”。

②提供可靠的数据传送。

也就是说，连接的一方将所有应用数据有序且无差错的传送到连接的另一方。

③提供流控制。

也就是，确保连接的任何一方都不会过快的发送过量的分组而淹没另一方。

④提供拥塞控制。

即管理应用发送进网络的数据总量，帮助防止互联网进入迟滞状态。

无连接服务的原理特征：①没有握手②没有可靠数据传送的保证③没有流控制或者拥塞控制5.流控制和拥塞控制的两个面向不同的对象的不同的控制机理。

流控制保证连接的任何一方不会因为过快的发送过多分组而淹没另一方。

拥塞控制是管理应用发送进网络的数据总量，帮助防止互联网核心（即网络路由器的缓冲区里面）发生拥塞。

6.互联网面向连接服务通过使用确认，重传提供可靠的数据传送。

当连接的一方没有收到它发送的分组的确认（从连接的另一方）时，它会重发这个分组。

Chapter 4 Network Layer1.Packetizing at the network layer involvesA) Encapsulating the payload at the sourceB) Adds a header that contains the source and destination informationC) Decapsulating the payload at the destinationD) All of the choices are correct2.{Routers in the path are not allowed to ___________________________.A) fragment the packet they receiveB) decapsulate the packetC) change source or destination addressD) All of the choices are correct3.The network layer in the Internet provides _________________.A) comprehensive error and flow control.B) limited error control, but no flow control.;C) comprehensive error control but limited flow control.D) All of the choices are correct4.In a virtual-circuit approach, the forwarding decision is based on the value of the _____________field in the packet header.A) source addressB) destination addressC) labelD) None of the choices are correct·5.In a datagram approach, the forwarding decision is based on the value of the _____________ field in the packet header.A) source addressB) destination addressC) labelD) None of the choices are correct6.The performance of a network can be measured in terms of ________.A) delay/B) throughputC) packet lossD) all of the choices are correct7.Transmission delay (time) is the ratio of ______________________.A) transmission rate to packet lengthB) transmission rate to distanceC) packet length to transmission rateD) processing time to transmission rate…8.Propagation delay (time) is the ratio of ______________________.A) transmission rate to propagation speedB) propagation speed to distanceC) packet length to propagation speedD) distance to propagation speed9.When the load in the network reaches the network capacity, the packet delay ___________ and the network throughput reaches ______________.&A) increases sharply; its minimumB) increases sharply; its maximumC) decreases sharply; its minimumD) decreases sharply; its maximum10.In open-loop congestion control, policies are applied ____________________.A) to prevent congestion before it happensB) to alleviate congestion after it happensC) to either prevent congestion before it happens or to alleviate congestion after it happens{D) None of the choices are correct11.The __________________ technique is one of the open-loop congestion policyA) backpressureB) choke packetC) implicit signalingD) None of the choices are correct12.—The __________________ technique is one of the close-loop congestion policyA) acknowledgment policyB) choke packetC) discarding policyD) None of the choices are correct13.IP is a _________ protocol.A) connection-oriented unreliableB) connection-oriented reliable）C) connectionless unreliableD) connectionless reliable14.An HLEN value of decimal 10 means _______.A) there are 10 bytes of optionsB) there are 10 bytes in the headerC) there are 40 bytes of optionsD) there are 40 bytes in the header:15.If the fragment offset has a value of 100, it means that _______.A) the datagram has not been fragmentedB) the datagram is 100 bytes in sizeC) the first byte of the datagram is byte 800D) None of the choices are correct16.What is needed to determine the number of the last byte of a fragment A) offset number$B) total lengthC) both offset number and the total lengthD) None of the choices are correct17.The IP header size is _______ bytes long.A) 20 to 60B) 20C) 60D) None of the choices are correct!18.Packets in the IP layer are called _________.A) segmentsB) datagramsC) framesD) None of the choices are correct19.The total length field defines the total length of the datagram _________.|A) including the headerB) excluding the headerC) excluding the option lengthD) None of the choices are correct20.When a datagram is encapsulated in a frame, the total size of the datagram must be less than the _______.A) MUTB) MATC) MTU[D) None of the choices are correct21.An IPv4 address is normally represented in base ____ in dotted-decimal notation.A) 16B) 256C) 10D) None of the choices are correct22.#In classful addressing, the IPv4 address space is divided into _______ classes.A) 3B) 4C) 5D) None of the choices are correct23.The number of addresses assigned to an organization in classless addressing _______.A) can be any numberB) must be a multiple of 256~C) must be a power of 2D) None of the choices are correct24.The first address assigned to an organization in classless addressing _______.A) must be evenly divisible by the number of addresses in the organizationB) must be divisible by 128C) must belong to one of the A, B, or C classesD) None of the choices are correct（25.In subnetting, the number of addresses in each subnet must _______.A) be a power of 2B) be a multiple of 128C) be divisible by 128D) None of the choices are correct26.What is the default prefix length for class A in CIDR notationA) 9【B) 8C) 16D) None of the choices are correct27.What is the default prefix length for class B in CIDR notationA) 9B) 8C) 16D) None of the choices are correct|28.What is the default prefix length for class C in CIDR notationA) 24C) 16D) None of the choices are correct29.DHCP is a (an) ___________ layer protocol.】A) applicationB) transportC) networkD) data-link30.In DHCP, the client uses ________ port and the server uses _________ port.A) an ephemeral; a well-knownB) a well-known; a well-knownC) a well-known; an ephemeral—D) None of the choices are correct31.DHCP uses the services of _______.A) UDPB) TCPC) IPD) None of the choices are correct)_________ allows a site to use a set of private addresses for internal communication and a set of global Internet addresses for communication with the rest of the world.A) DHCPB) NATC) IMCPD) None of the choices are correct33.The idea of address aggregation was designed to alleviate the increase in routing table entries when using ________ addressing.A) classfulB) classless~C) classful or classlessD) None of the choices are correct34.The use of hierarchy in routing tables can ________ the size of the routing tables.A) reduceB) increaseC) neither reduce nor increaseD) None of the choices are correct~35.ICMP is a (an) _________ layer protocol.A) application-layer protocol that helps TCP/IP at the network layerB) transport-layer protocol that helps TCP/IP at the network layerC) network-layer protocol.D) data-link layer protocol that helps TCP/IP at the network layer36.Which of the following is true about ICMP messagesA) An ICMP error message may be generated for an ICMP error message. ：B) An ICMP error message may be generated for a fragmented datagram.C) An ICMP error message may be generated for a multicast datagram.D) None of the choices are correct37.Routing inside an autonomous system is referred to as ________ routing.A) interdomainB) intradomainC) out-of-domainD) None of the choices are correct@38.Routing between autonomous systems is referred to as ______ routing.A) interdomain routingB) intradomain routingC) out-of-domainD) None of the choices are correct39.In _______ routing, the least cost route between any two nodes is the route with the minimum distance.{A) path vectorB) distance vectorC) link stateD) None of the choices are correct40.In ________, each node maintains a vector (table) of minimum distances to every node.A) path vectorB) distance vectorC) link state【D) None of the choices are correct41.In distance vector routing, each node periodically shares its routing table with _________ and whenever there is a change.A) every other nodeB) its immediate neighborsC) one neighborD) None of the choices are correct42.…The Routing Information Protocol (RIP) is an intradomain routing based on _________ routing.A) distance vectorB) link stateC) path vectorD) None of the choices are correct43.The metric used by _______ is the hop count.A) OSPFB) RIP￥C) BGPD) None of the choices are correct44.In RIP, the ________ timer controls the advertising of regular update messages.A) garbage collectionB) expirationC) periodicD) None of the choices are correct$45.In RIP, the ________ timer is used to purge invalid routes from the table.A) garbage collectionB) expirationC) periodicD) None of the choices are correct46.In RIP, the ________ timer controls the validity of the route.A) garbage collection《B) expirationC) periodicD) None of the choices are correct47.RIP uses the services of _______.A) TCPB) UDPC) IPD) None of the choices are correct[48.The _________ routing uses the Dijkstra algorithm to build a routing table.A) distance vectorB) link stateC) path vectorD) None of the choices are correct49.The Open Shortest Path First (OSPF) protocol is an intradomain routing protocol based on _______?A) distance vectorB) link stateC) path vectorD) None of the choices are correct50.The _______ protocol allows the administrator to assign a cost, called the metric, to each route.A) OSPFB) RIPC) BGP—D) None of the choices are correct51.In OSPF, a ________ link connects two routers without any other host or router in between.A) point-to-pointB) transientC) stubD) None of the choices are correct52.'In OSPF, a _______ link is a network with several routers attached to it.A) point-to-pointB) transientD) None of the choices are correct53.In OSPF, a ________ link is a network connected to only one router.A) point-to-pointB) transient*C) stubD) None of the choices are correct54.In OSPF, a ________ defines the links of a network.A) network linkB) router linkC) summary link to networkD) None of the choices are correct;55.___________ is an interdomain routing protocol using path vector routing.A) BGPB) RIPC) OSPFD) None of the choices are correct56.A one-to-all communication between one source and all hosts on a network is classified as a _______ communication.A) unicast|B) multicastC) broadcastD) None of the choices are correct57.A one-to-many communication between one source and a specific group of hosts is classified as a _______ communication.A) unicastB) multicastC) broadcastD) None of the choices are correct<58.A one-to-one communication between one source and one destination is classified as a _______ communication.A) unicastB) multicastC) broadcastD) None of the choices are correct59.In ______, the router forwards the received packet through only one of its interfaces.#A) unicastingB) multicastingC) broadcastingD) None of the choices are correct60.In multicast routing, each involved router needs to construct a ________ path tree for each group.A) averageB) longestC) shortest-D) None of the choices are correct61.In the _______ tree approach to multicasting, each router needs to create a separate tree for each source-group.A) group-sharedB) source-basedC) destination-basedD) None of the choices are correct62.'The Multicast Open Shortest Path First (MOSPF) routing uses the _______ tree approach.A) source-basedB) group-sharedC) destination-basedD) None of the choices are correct63.The Multicast Open Shortest Path First (MOSPF) protocol is an extension of the OSPF protocol that uses multicast routing to create source-based trees. The protocol is based on _______ routing.A) distance vectorB) link state!C) path vectorD) None of the choices are correct64.In RPF, a router forwards only the copy that has traveled the _______ path from the source to the router.A) shortestB) longestC) averageD) None of the choices are correct（65.RPF eliminates the ________ in the flooding process.A) forwardingB) backwardingC) floodingD) None of the choices are correct66.RPB creates a shortest path _______ tree from the source to each destination.A) unicast~B) multicastC) broadcastD) None of the choices are correct67.RPB guarantees that each destination receives _________ of the packet.A) only one copyB) no copiesC) multiple copiesD) None of the choices are correct（68.In ________, the multicast packet must reach only those networks that have active members for that particular group.A) RPFB) RPBC) RPMD) None of the choices are correct69._______ adds pruning and grafting to _______ to create a multicast shortest path tree that supports dynamic membership changes.)A) RPM; RPBB) RPB; RPMC) RPF; RPMD) None of the choices are correct70.__________ is an implementation of multicast distance vector routing. It is a source-based routing protocol, based on RIP.A) MOSPFB) DVMRPC) CBT<D) None of the choices are correct71.DVMRP is a ________ routing protocol, based on RIP.A) source-basedB) group-sharedC) destination-basedD) None of the choices are correct72.#Pruning and grafting are strategies used in _______.A) RPFB) RPBC) RPMD) None of the choices are correct73.PIM-DM is used when the number of routers with attached members is ______ relative to the number of routers in the internet.A) largeB) small.C) moderateD) None of the choices are correct74.PIM-SM is used when the number of routers with attached members is ______ relative to the number of routers in the internet.A) largeB) smallC) moderateD) None of the choices are correct·75.An IPv6 address is _________ bits long.A) 32B) 64C) 128D) 25676.An IPv6 address consists of ________ bytes (octets);A) 4^B) 8C) 16D) None of the choices are correct77.In hexadecimal colon notation, a 128-bit address is divided into _______ sections, each _____ hexadecimal digits in length.A) 8; 2B) 8; 3C) 8; 4D) None of the choices are correct78.An IPv6 address can have up to __________ hexadecimal digits.A) 16B) 32C) 8D) None of the choices are correct79.In IPv6, the _______ field in the base header restricts the lifetime of a datagram.A) versionB) priorityC) hop limitD) None of the choices are correct80.The _________ in IPv6 is designed to provide special handling for a particular flow of data.A) flow labelB) next headerC) hop limitD) None of the choices are correct81.When two computers using IPv6 want to communicate but the packet must pass through an IPv4 region, which transition strategy should be usedA) tunnelingB) header translationC) either tunneling or header translationD) None of the choices are correct82.When the majority of the Internet has moved to the IPv6 but some still use IPv4, which transition strategy should be usedA) tunnelingB) header translationC) either tunneling or header translationD) None of the choices are correct83.The protocols __________________________ in version 4 are combined into one single protocol, ICMPv6.A) ARP and IGMPB) ICMP and IGMPC) ICMP, ARP, and IGMPD) None of the choices are correctDCBCB DCCBA DBCDC CABAC BCCAA BCAAB ABBAC DBABB BABCA BBBBA ABCAA CBAAC BABAD CACAB ACABC CCBCA ABC%。