[计算机类试卷]思科认证640-802模拟试卷9及答案与解析.doc

1、思科认证 640-802模拟试卷 9及答案与解析 1 On the topic of VLSM, which one of the following statements best describes the concept of the route aggregation? （ A） Deleting unusable addresses through the creation of many subnets. （ B） Combining routes to multiple networks into one supernet. （ C） Reclaiming unused spac

2、e by means of changing the subnet size. （ D） Calculating the available host addresses in the AS. （ E） None of the above 2 The 201.145.32.0 network is subnetted using a /26 mask. How many networks and IP hosts per network exists using this subnet mask? （ A） 4 networks and 64 hosts （ B） 64 networks an

3、d 4 hosts （ C） 4 networks and 62 hosts （ D） 62 networks and 2 hosts （ E） 6 network and 30 hosts 3 How many usable IP addresses can you get from a conventional Class C address? （ A） 128 （ B） 192 （ C） 254 （ D） 256 （ E） 510 4 A Ezonexam switch is configured with all ports assigned to VLAN 2. In additio

4、n, all ports are configured as full-duplex FastEthernet. What is the effect of adding switch ports to a new VLAN on this switch? （ A） The additions will create more collisions domains. （ B） IP address utilization will be more efficient. （ C） More bandwidth will be required than was needed previously

5、. （ D） An additional broadcast domain will be created. （ E） The possibility that switching loops will occur will increase dramatically. 5 What is the purpose of the Spanning Tree Protocol (STP)? （ A） To prevent routing loops （ B） To create a default route （ C） To provide multiple gateways for hosts

6、（ D） To maintain a loop-free Layer 2 network topology （ E） To enhance the functions of SNMP 6 A network administrator needs to force a high-performance switch that is located in the MDF to become the root bridge for a redundant path switched network. What can be done to ensure that this switch assum

7、es the role of the Root Bridge? A. Configure the switch so that it has a lower priority than other switches in the network. B. Assign the switch a higher MAC address than the other switches in the network have. C. Configure the switch for full-duplex operation and configure the other switches for ha

8、lf-duplex operation. D. Connect the switch directly to the MDF router, which will force the switch to assume the role of root bridge. E. Establish a direct link from the switch to all other switches in the network. F. None of the above 7 A new trunk has been configured on a switch in the Ezonexam LA

9、N. By default, which VLANs are allowed over this trunk link? A. No VLANs B. Only the VLANs that are specified when creating the trunk C. Only VLANs 1-64 D. All VLANs E. All VLANs except VLAN 1 F. None of the above 8 When you compare the differences between half-duplex and full-duplex Ethernet, which

10、 of the following characteristics are exclusive to half-duplex? (Select two answer choices) （ A） Half-duplex Ethernet operates in a shared collision domain. （ B） Half-duplex Ethernet operates in an exclusive broadcast domain. （ C） Half-duplex Ethernet has efficient throughput. （ D） Half-duplex Ether

11、net has lower effective throughput. （ E） Half-duplex Ethernet operates in an exclusive collision domain. 9 Which two of the addresses below are available for host addresses on the Ezonexam subnet 192.168.15.19/28? (Select two answer choices) A. 192.168.15.17 B. 192.168.15.14 C. 192.168.15.29 D. 192.

12、168.15.16 E. 192.168.15.31 F. None of the above 10 Cisco is the leader in the router market space. What basic functions do their routers perform in a network? (Choose two) A. The microsegmentation of broadcast domains B. Path selection C. Packet switching D. Bridging between LAN segments E. Access l

13、ayer security F. VLAN membership assignment G. Application optimization 11 Which three of the protocols below belong to the application layer? (Select three answer choices) A. ARP B. HTTPS C. SMTP D. CDP E. TFTP F. ICMP 12 Ezonexam needs to ensure their IP network can be reached from the Internet. W

14、hich of the following host addresses are members of networks that can be routed across the public Internet? (Choose three.) A. 10.172.13.65 B. 172.16.223.125 C. 172.64.12.29 D. 192.168.23.252 E. 198.234.12.95 F. 212.193.48.254 13 Youve been assigned the CIDR (classless inter domain routing) block of

15、 115.64.4.0/22 from your ISP. Which of the IP addresses below can you use for a host? (Select all valid answers) A. 115.64.8.32 B. 115.64.7.64 C. 115.64.6.255 D. 115.64.3.255 E. 115.64.5.128 F. 115.64.12.128 思科认证 640-802模拟试卷 9答案与解析 1 【正确答案】 B 【试题解析】 Explanation: In the networking world route aggrega

16、te means combining routes to multiple networks into one. This is also known as route summarization or supernetting. It is normally used to reduce the number of route entries in the routing table by advertising numerous routes into one larger route. 2 【正确答案】 C 【试题解析】 Explanation: A class C network wi

17、th a 26 bit mask requires 2 bits for the network address, leaving 6 bits for host addresses. Using the 2n-2 formula (22 for the network and 26-2for hosts) we have 4 network addresses and 62 host addresses. Incorrect Answers: A, B: This is not a possible combination. No network mask will provide for

18、64 usable hosts, because we must always subtract 2 for the network and broadcast address. D. This would be the result of a /30 mask. E. This would be the result of a /27 network mask. 3 【正确答案】 C 【试题解析】 Explanation: Class Caddresses range from 192.0.0.0 through 223.225.225.225 and default subnet mask

19、of 255.255.255.0. In Class C addresses, the first 24 bits are used as for the network IDwhile only the last 8 bits is used for the host ID. Using the 2n-2 formula, we can calculate that Class C addresses can support a maximum of 254 (28-2) hosts. Incorrect Answers: D. Note that the question asked fo

20、r the number of usable addresses, and not the total number of all addresses. We must subtract 2 for the network and broadcast addresses to calculate the number of usable addresses in any subnet. 4 【正确答案】 D 【试题解析】 Explanation: A VLAN is a group of hosts with a common set of requirements that communic

21、ate as if they were attached to the same wire, regardless of their physical location. A VLAN has the same attributes as a physical LAN, but it allows for end stations to be grouped together even if they are not located on the same LAN segment. Networks that use the campus-wide or end-to-end VLANs lo

22、gically segment a switched network based on the functions of an organization, project teams, or applications rather than on a physical or geographical basis. For example, all workstations and servers used by a particular workgroup can be connected to the same VLAN, regardless of their physical netwo

23、rk connections or interaction with other workgroups. Network reconfiguration can be done through software instead of physically relocating devices. Cisco recommends the use of local or geographic VLANs that segment the network based on IP subnets. Each wiring closet switch is on its own VLAN or subn

24、et and traffic between each switch is routed by the router. The reasons for the Distribution Layer 3 switch and examples of a larger network using both the campus-wide and local VLAN models will be discussed later. A VLAN can be thought of as a broadcast domain that exists within a defined set of sw

25、itches. Ports on a switch can be grouped into VLANs in order to limit unicast, multicast, and broadcast traffic flooding. Flooded traffic originating from a particular VLAN is only flooded out ports belonging to that VLAN, including trunk ports, so a switch that connects to another switch will norma

26、lly introduce an additional broadcast domain. 5 【正确答案】 D 【试题解析】 Explanation: STPs main task is to stop network loops from occurring on your Layer 2 network (bridges or switches). It vigilantly monitors the network to find all links, making sure that no loops occur by shutting down any redundant ones

27、. STP uses the spanning-tree algorithm (STA) to first create a topology database, then search out and destroy redundant links. With STP running, frames will only be forwarded on the premium, STP-picked links. 6 【正确答案】 A 【试题解析】 Explanation: For all switches in a network to agree on a loop-free topolo

28、gy, a common frame of reference must exist. This reference point is called the Root Bridge. The Root Bridge is chosen by an election process among all connected switches. Each switch has a unique Bridge ID (also known as the bridge priority) that it uses to identify itself to other switches. The Bri

29、dge ID is an 8-byte value. 2 bytes of the Bridge ID is used for a Bridge Priority field, which is the priority or weight of a switch in relation to all other switches. The other 6 bytes of the Bridge ID is used for the MAC Address field, which can come from the Supervisor module, the backplane, or a

30、 pool of 1024 addresses that are assigned to every Supervisor or backplane depending on the switch model. This address is hardcoded, unique, and cannot be changed. The election process begins with every switch sending out BPDUs with a Root Bridge ID equal to its own Bridge ID as well as a Sender Bri

31、dge ID. The latter is used to identify the source of the BPDU message. Received BPDU messages are analyzed for a lower Root Bridge ID value. If the BPDU message has a Root Bridge ID (priority) of the lower value than the switchs own Root Bridge ID, it replaces its own Root Bridge ID with the Root Br

32、idge ID announced in the BPDU. If two Bridge Priority values are equal, then the lower MAC address takes preference. 7 【正确答案】 D 8 【正确答案】 A,D 【试题解析】 Explanation: A single device could not be sending a frame and receiving a frame at the same time because it would mean that a collision was occurring. S

33、o, devices simply chose not to send a frame while receiving a frame. That logic is called half-duplex logic. Ethernet switches allow multiple frames to be sent over different ports at the same time. Additionally, if only one device is connected to a switch port, there is never a possibility that a c

34、ollision could occur. So, LAN switches with only one device cabled to each port of the switch allow the use of full-duplex operation. Full duplex means that an Ethernet card can send and receive concurrently. Incorrect Answers: B. Full duplex effectively doubles the throughput of half-duplex operati

35、on, because data can be both sent and received at the full 10/100 speed. C, E. In half duplex operation, the network is shared between all devices in the collision domain. 9 【正确答案】 A,C 【试题解析】 Explanation: The network uses a 28bit subnet (255.255.255.240). This means that 4 bits are used for the netw

36、orks and 4 bits for the hosts. This allows for 14 networks and 14 hosts (2n-2). The last bit used to make 240 is the 4th bit (16) therefore the first network will be 192.168.15.16. The network will have 16 addresses (but remember that the first address is the network address and the last address is

37、the broadcast address). In other words, the networks will be in increments of 16 beginning at 192.168.15.16/28. The IP address we are given is 192.168.15.19. Therefore the other host addresses must also be on this network. Valid IP addresses for hosts on this network are: 192.168.15.17-192.168.15.30

38、. Incorrect Answers: B. This is not a valid address for this particular 28 bit subnet mask. The first network address should be 192.168.15.16. D. This is the network address. E. This is the broadcast address for this particular subnet. 10 【正确答案】 B,C 【试题解析】 Explanation: The primary functions of a rou

39、ter are: Packet Switching and Path Selection. It is the routers job to determine the best method for delivering the data, and switching that data as quickly as possible. 11 【正确答案】 B,C,E 【试题解析】 Explanation: The application layer is the highest OSI layer, and protocols at this layer are end-user orien

40、ted. HTTPS so people can get information on the internet, SMTP so people can manage networks, and TFTP so people can download files. Incorrect Answers: A, D, F. ARP, CDP, ICMP are protocols that equipment like routers and switches use to communicate with themselves, and belong to lower levels on the

41、 model. 12 【正确答案】 C,E,F 【试题解析】 Explanation: In Internet terminology, a private network is a network that uses RFC 1918 IP address space. Computers may be allocated addresses from this address space when its necessary for them to communicate with other computing devices on an internal (non-Internet)

42、network but not directly with the Internet. Three blocks of IP addresses are reserved for private use and are not routed over the Internet. Companies can assign these addresses to nodes on their private LANs at any time without conflict. 13 【正确答案】 B,C,E 【试题解析】 Explanation: 115.64.4.0 = 01110011.01000000.00000100.00000000 Subnet mask = 11111111.11111111.11111100.00000000= 255.255.252.0 Subnet number = 01110011.01000000.00000100.00000000= 115.64.4.0 Broadcast = 01110011.01000000.00000111.11111111= 115.64.7.255 Valid address range = 115.64.4.1 - 115.64.7.254