东北大学计算机网络复试资料必看 - 图文

…学 院 … … 课程名称：计算机网络（Computer Networks） … … ┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄班 级 ○┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄ …总分 一 二 三 四 五 ( )10．With respect to protocol layer, the ARP protocol in TCP/IP corresponds to: … 学 号 …… …密 姓 名 ……… …… ○… …… …… 封… …… … …○ …… …… 线… …… …… …… …………… Ⅰ. Multiple Choice（20 points,1 point for each） Directions: Choose the correct answer for each question and fill it in the corresponding blank. There is ONLY ONE correct answer for each question. ( )1．There are two kinds of coaxial cables usually used. One is the baseband cable and the other is the broadband cable. The impedance of the baseband cable is: A. 50Ω B. 70Ω C. 75Ω D. 90Ω ( )1．There are two kinds of coaxial cables usually used. One is the baseband cable and the other is the broadband cable. The impedance of the baseband cable is: A. 50Ω B. 70Ω C. 75Ω D. 90Ω ( )2．According to the ISO/OSI reference model, the Ethernet switch works on: A. Data link layer B. Network layer C. Transport layer D. Presentation layer ( )3． Which device extends the LAN on network layer? A. Repeater B. Hub C. Switch D. Router ( )4．How many network segments can be there at most for network connected by hubs? A. 5 B. 4 C. 3 D. 2 ( )5．10BaseT network takes: A. thick coaxial cable, bus topology B. twisted pair, ring topology C. thin coaxial cable, star topology D. twisted pair, star topology ( )6．When two computers communicate via a telephone line, which of the following device is necessary? A. network adapter B. MODEM C. repeater D. coaxial cable ( )7．If a package is to be broadcasted to the local network, then the destination IP address of the package should be: A. 255.255.255.255 B. 0.0.0.0 C. the lowest address of the subnet D. the highest address of the subnet ( )8．What many bytes are there in the payload of an ATM cell? 本试卷 共 4 页第 1 页

A. physical layer B. data link layer C. network layer D. transport layer ( )11．The lower layer of OSPF protocol uses: A. UDP B. TCP C. ARP D. IP ( )12．Which port on sever does the POP3 protocol use? A. 20 B. 23 C. 25 D. 110 ( )13．What is the mask for a smallest subnet usable in practice? A. 255.255.255.0 B. 255.255.255.254 C. 255.255.255.252 D. 255.255.255.255 ( )14．Which of the following IP address CANNOT be assigned to a host? A. 141.107.255.80/16 B. 201.255.0.11/24 C. 116.1.0.255/16 D. 198.121.254.255/24 ( )15．When installing a MODEM to a PC, the interface standard we take is: A. X.25 B. RJ11 C. RS232 D. RJ45 ( )16．Which of the following is NOT an advantage of a layer model? A. Dividing the complex network operation into a more manageable layer approach. B. Allowing changes to occur in one layer without having to change all layers. C. Allowing changes to occur in all layers without having to change one layer. D. Defining a standard interface for the plug-and-play multivendor integration. ( )17．How many bits are there for an Ethernet MAC address? A. 32 B. 48 C. 64 D. 128 ( )18．The protocol for two computers to transport files is: A. FTP B. WWW C. Telnet D. SMTP ( )19．The Internet can be traced back to its origin: A. ARPANET B. ALOHA C. NEFNET D. Ethernet ( )20．Which of the following IPv6 address is correct? A. 2001:::8::417A B. 12.20.3.3:0:0:0:0:0:FFFF C. ::145.20.15.29 D. 145.20.15.29:: …Ⅱ. Fill in the Blanks （10 points, 1 point for each blank） 学 院 …Directions: Fill proper contents into the blanks according to the context. … … … 1．The length of an IPv6 header is ___60____ bytes. 班 级 ○2. The TCP/IP protocol consists of _____5____ (how many) layers. …3． ping 127.0.0.1 command will test the internal loopback of a computer. (Fill the complete command with parameters) …4. _254_ (how many) usable subnets are created by applying the subnet mask … 学 号 … 255.255.255.0 to a Class B network. Ⅳ. Fill in the Forms （20 points）

Directions: Fill proper contents into the forms.

1．Make a comparison among the three network interconnection devices: hubs, routers and switches. Fill in “Yes” or “No” in the blanks of the following form to say whether the device can perform the corresponding function. (6 points) Hubs Routers Switches 姓 名 … 5. FF-FF-FF-FF-FF-FF is a Layer-2 broadcast address. 密6. The switching method that traditional telephone takes is circuit switching , …while the method that IP telephone takes is__packet switching__. …7. The common used guided transmission media are_coaxial cable_, _twisted pair_, …and _optical fiber_. ……○Ⅲ. True or False （10 points, 1 point for each） … Directions: Answer the following using T (True)/F (False). You do not …need to explain your answers. … …( T )1． Carrier Sense Multiple Access with Collision Detection uses first-come, …first-served approach. 封…( T ) 2．Ethernet provides unreliable, connectionless service. …( T ) 3．The feature of a Token Ring network is collisionless environment. ……( F ) 4．8 broadcast domains are created when you segment a network with an 8-port …switch. ○( T ) 5．Packet-switching networks place a tight upper limit on block size. ……( T ) 6．Network Address Translation technology is a solution to expand the number …of IP addresses available for public use. …( T ) 7．Latency through the store-and-forward switch varies with frame length. 线( F ) 8．Security is one of the advantages of using static routes over dynamic routes. ……( F ) 9．OSPF is an inter-AS routing protocol, while BGP is an intra-AS routing …protocol. …( F ) 10．In Time-Division Multiplexing, each user cannot get all of the bandwidth …periodically during its slot. ………………本试卷 共 4 页第 2 页… Traffic Isolation No Yes Yes Plug & Play Yes No Yes Optimal Routing No Yes No Cut Through Yes No Yes 2. Consider the TCP/IP protocol suite: (1) Fill the names of protocol data units corresponding to each layer in the PDU colunm. (4 points) (2) Match the following functions to one of the five layers in the Function colunm. (10 points) ①Reliable process-to-process message delivery ②Packet switching ③Defines frames ④Provides user services such as email and file transfer ⑤Transmission of bit stream across physical medium ⑥Mechanical, electronical, and functional interface ⑦Reassembly of data packets ⑧Ensure reliable transmission of data ⑨Network selection ⑩Route determination Layer PDU Functions Application Layer Message ④ Transport Layer Segment ① Network Layer Packet ②⑦⑨⑩ Data Link Layer Frame ③⑧ Physical Layer Bits on the wire ⑤⑥ …… 学 院 …Ⅴ. Comprehensive Calculation （40 points） … … 班 级 ○ … 1．(5 points) How long does it take to send a file of 640K bits from host A to host B over a … …circuit-switched network? ? All links are 1.536 Mbps 学 号 … ? Each link uses TDM with 24 slots/sec …? 500 milliseconds to establish end-to-end circuit 密 3．(6 points) Use Dijkstra Algorithm to find out the shortest paths from origin E to every other node in the following graph, and calculate corresponding costs. 1 A C 1 2 2 4 B 2 姓 名 . Solution: Transmission Speed: 1.536Mbps÷Transmission Time: 640K÷ 24=64Kbps 64Kbps=10s Connection Establishment Time: 0.5s File sending time: 10.5s 2. (5 points) The distance between host A and host B is L＝10000Km. The bandwidth of the link is R＝1Mbps (220 bps). Suppose the propagation speed over this link is V＝2.5×108m/s. (1) What is the propagation time Tp? (2) During this time, how many bits have been sent to the link by host A? (3) What is the distance d between two adjacent bits? Solution: Tp＝L÷V＝0.04s Numb＝Tp×R=41943 d＝L÷ Numb＝238m 本试卷 共 4 页第 3 页 E D 2 Solution: E→A: E→A, cost(E,A)=4 E→B: E→D→B, cost(E,B)=4 E→C: E→D→C, cost(E,C)=4 E→D: E→D, cost(E,D)=2 ……………○……………封……………○…………线……………………………… … 学 院 …4．(9 points) An organization is granted an IP address 211.17.185.0. The network

…administrator wants to create 32 subnets.

… (1) Find out the subnet mask.

…(2) Find out the number of host addresses in each subnet.

班 级 ○(3) Find out the network address of the first subnet.

…(4) Find out the first and last host addresses in the first subnet.

… (5) Find out the subnet directed broadcast address and limited broadcast address in the

…

学 号 … first subnet.

… 密

5．(15 points) Consider a router with the following routing table: Destination Address Subnet Mask Next Hop 128.96.57.0 255.255.255.128 Interface 0 128.96.39.128 Interface 1 128.96.90.0 255.255.255.128 R2 192.4.131.0 255.255.255.192 R3 Default R4 This router can forward packets directly through Interface 0 and Interface 1, and it can also forward packets through neighboring routers R2, R3, or R4. Suppose the router received 5 姓 名 …Solution:

…

…(1) 255.255.255.252

…(2) 2

…(3) 217.17.185.4 ○(4) 217.17.185.5

…217.17.185.6 (5) 211.17.185.7 … 255.255.255.255 … … … 封 … … …… …○…………线……………………………… 本试卷 共 4 页第 4 页packets with the following IP addresses respectively: (1) 128.96.57.10 (2) 128.96.90.12 (3) 128.96.39.128 (4) 192.4.131.17 (5) 192.4.131.90 Try to calculate the next hop of each packet. Solution: (1) The result of 128.96.57.0 AND 255.255.255.128 is 128.96.57.0, so Packet 1 is forwarded to Interface 0. (3 points) (2) The result of 128.96.90.12 AND 255.255.255.128 is 128.96.90.0, so Packet 2 is forwarded to R2. (3 points) (3) 128.96.39.128 has the single IP entry, so Packet 3 is forwarded to Interface 1. (3 points) (4) The result of 192.4.131.17 AND 255.255.255.192 is 192.4.131.0, so Packet 4 is forwarded to R3. (3 points) (5) The result of 192.4.131.90 AND MASK cannot match any entry, so Packet 5 is forwarded to R4. (3 points)

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