2021年ccna考试题库.doc

QUESTION 37
What are two characteristics of RIPv2?(Choose two.)
A. classful routing protocol
B. variable-length subnet masks
C. broadcast addressing
D. manual route summarization
E. uses SPF algorithm to compute path
Answer：BD
Explanation/Reference:
A：有类路由合同，错误
B：可变长度子网掩码，对的
C：采用广播地址更新，错误
D：手动路由汇总，对的
E:使用spf算法计算途径，错误。
QUESTION 38
Which two Ethernet fiber-optic modes support distances of greater than 550 meters?
A. 1000BASE-CX
B. 100BASE-FX
C. 1000BASE-LX
D. 1000BASE-SX
E. 1000BASE-ZX
Answer：CE
Explanation/Reference:
A：最长距离25米
B：最长距离100米
C：最长距离3000米
D：最长距离550米
E：最长距离70千米
QUESTION 39
What two things will a router do when running a distance vector routing protocol?(Choose two.)
A. Send periodic updates regardless of topology changes.
B. Send entire routing table to all routers in the routing domain.
C. Use the shortest-path algorithm to the determine best path.
D. Update the routing table based on updates from their neighbors.
E. Maintain the topology of the entire network in its database.
Answer：AD
Explanation/Reference:
考点：考查距离矢量路由合同特性
A：周期性更新，对的
B：发送整个路由表到整个路由域，错误，只发送给邻居
C：使用SPF算法，错误
D：依托邻居发送更新来更新路由表，对的
E：在数据库中维护整个网络拓扑。错误
Which command shows if an access list is assigned to an interface?
A. show ip interface [interface] access-lists
B. show ip access-lists interface [interface]
C. show ip interface [interface]
D. show ip access-lists [interface]
Answer：C
Explanation/Reference:
QUESTION 42
Refer to the exhibit. Which rule does the DHCP server use when there is an IP address conflict?

A. The address is removed from the pool until the conflict is resolved.
B. The address remains in the pool until the conflict is resolved.
C. Only the IP detected by Gratuitous ARP is removed from the pool.
D. Only the IP detected by Ping is removed from the pool.
E. The IP will be shown，even after the conflict is resolved.
Answer：A
Explanation/Reference:
show ip dhcp conflict命令可以查看哪些ip地址在使用上有冲突。
有冲突地址不再分派出去。
A：地址被删除直到冲突解决，对的
B:地址保存直到冲突解决，错误
C/D：答案片面。
E：当冲突解决后，地址会被显示。错误。
QUESTION 44
Refer to the exhibit. If number 2 is selected from the setup script，what happens when the user runs setup
from a privileged prompt?

A. Setup is additive and any changes will be added to the config script.
B. Setup effectively starts the configuration over as if the router was booted for the first time.
C. Setup will not run if an enable secret password exists on the router.
D. Setup will not run，because it is only viable when no configuration exists on the router.
Answer：A
Explanation/Reference:
[0]不保存进入IOS命令配备模式
[1]不保存返回设立模式
[2]保存退出
A：设立和改动被保存到配备脚本
B：为有效地重新开始配备，如果路由器是第一次启动配备。
C：如果配备了密码，设立不会运营
D：设立不可用，由于它只能在没有配备存在时才有效
QUESTION 49
Which two statements describe the Cisco implementation of VLANs?(Choose two.)
A. VLAN 1 is the default Ethernet VLAN.
B. CDP advertisements are only sent on VLAN 1002.
C. By default，the management VLAN is VLAN 1005.
D. By default，the switch IP address is in VLAN 1005.
E. VLAN 1002 through 1005 are automatically created and cannot be deleted.
Answer：AE
Explanation/Reference:
考点：考查vlan知识点。
A：缺省都存在vlan1，端口都属于vlan1，对的
B：CDP信息只发送到vlan1002，错误，vlan1002是fddi网络vlan号。
C：缺省状况互换机IP配备在vlan1005，错误，vlan1005trnet网络vlan号。缺省在vlan1里面。
D：vlan1002-1005自动生成并不能被删除，对的，她们都是被保存特殊vlan。
QUESTION 56 没有理解什么意思
Refer to the exhibit. What does the (*) represent in the output?

A. Packet is destined for a local interface to the router.
B. Packet was translated，but no response was received from the distant device.
C. Packet was not translated，because no additional ports are available.
D. Packet was translated and fast switched to the destination.
Answer：D
Explanation/Reference:
由图中提示信息可以看出，源为10.10.0.2已有个一种转换，所后来续数据包迅速转发。
What are three advantages of VLANs?(Choose three.)
A. VLANs establish broadcast domains in switched networks.
B. VLANs utilize packet filtering to enhance network security.
C. VLANs provide a method of conserving IP addresses in large networks.
D. VLANs provide a low-latency internetworking alternative to routed networks.
E. VLANs allow access to network services based on department，not physical location.
F. VLANs can greatly simplify adding，moving，or changing hosts on the network.
Answer：AEF
Explanation/Reference:
A：VLAN在互换网络中建立广播域，对的
B：运用VLAN数据包过滤，增强网络安全性。错误，没有这个特性。
C：提供了在大型网络中保护IP地址办法。错误
D：提供低延迟互联网络代替路由网络。错误
E：vlan容许基于逻辑划分网络访问，不是物理位置。对的。
F：VLAN可以大大简化添加，移动或更改网络上主机。对的。
QUESTION 61
An administrator would like to configure a switch over a virtual terminal connection from locations outside
of the local LAN. Which of the following are required in order for the switch to be configured from a remote
location?(Choose two.)
A. The switch must be configured with an IP address，subnet mask，and default gateway.
B. The switch must be connected to a router over a VLAN trunk.
C. The switch must be reachable through a port connected to its management VLAN.
D. The switch console port must be connected to the Ethernet LAN.
E. The switch management VLAN must be created and have a membership of at least one switch port.
F. The switch must be fully configured as an SNMP agent.
Answer：AC
Explanation/Reference:
要想远程管理VLAN，1、互换机配备IP，2、路由可达
QUESTION 65
Which router IOS commands can be used to troubleshoot LAN connectivity problems?(Choose three.)
A. ping
B. tracert
C. ipconfig
D. show ip route
E. winipcfg
F. show interfaces
Answer：ADF
Explanation/Reference:
A：测试连通性
D：查看与否有路由
F：查看接口与否可用

QUESTION 64
Which of the following are benefits of VLANs?(Choose three.)
A. They increase the size of collision domains.
B. They allow logical grouping of users by function.容许顾客从逻辑上进行分组
C. They can enhance network security.
D. They increase the size of broadcast domains while decreasing the number of collision domains.
E. They increase the number of broadcast domains while decreasing the size of the broadcast domains.
F. They simplify switch administration.
Answer：BCE
Explanation/Reference:
考查VLAN特点
A：增长冲突域大小，错误
B：容许逻辑划分网段，对的
C：增强网络安全，对的。不同vlan不能直接通信。
D：当减少冲突域时增长广播域大小。错误
E：减少广播域大小时增长了广播域个数。对的。
F:简化互换机管理。答非所问。
QUESTION 71
Which characteristics are representative of a link-state routing protocol?(Choose three.)
A. provides common view of entire topology
B. exchanges routing tables with neighbors
C. calculates shortest path
D. utilizes event-triggered updates
E. utilizes frequent periodic updates
Answer：ACD
Explanation/Reference:
链路状态路由合同有合同特点？
A:提供查看拓扑命令，对的。show ip ospf database
B：邻居之间互换路由信息，错误。互换LSA
C：计算最短途径，对的。
D：运用触发更新，对的
E：运用周期更新，错误。
QUESTION 73
Use the output from the router shown in the graphic above to determine which of the following are correct.
(Choose two.)

A. Router John uses a link-state routing protocol.
B. Router John will receive routing updates on the Serial0/0 interface.
C. Router John will receive routing updates on the Serial0/1 interface.
D. Router John will send routing updates out the Serial0/0 interface.
E. Router John will send routing updates out the FastEthernet0/0 interface.
F. Router John will send routing updates out the Serial0/1 interface.
Answer：BD
Explanation/Reference:
由图中几处画红线地方可知只有s0/0发送和接受路由信息。
QUESTION 74 2次方问题
A national retail chain needs to design an IP addressing scheme to support a nationwide network. The
company needs a minimum of 300 sub-networks and a maximum of 50 host addresses per subnet.
Working with only one Class B address，which of the following subnet masks will support an appropriate
addressing scheme?(Choose two.)
A. 255.255.255.0
B. 255.255.255.128
C. 255.255.252.0
D. 255.255.255.224
E. 255.255.255.192
F. 255.255.248.0
Answer：BE
Explanation/Reference:
需要至少300个子网，每个子网至少50台主机。使用一种B类地址来划分。
A：最多有256个子网，错误
C：只有64个子网
D：每个子网只有30个可用IP
F：只有32个子网
QUESTION 79
What information does a router running a link-state protocol use to build and maintain its topological
database?(Choose two.)
A. hello packets
B. SAP messages sent by other routers
C. LSAs from other routers
D. beacons 信息received on point-to-point links
E. routing tables received from other link-state routers
F. TTL packets from designated routers
Answer：AC
Explanation/Reference:
链路状态路由合同如何维护拓扑数据库？
A：hello包用于维护邻居关系，对的。
B：错误，没有这个概念。
C：通过其她路由器LSA，对的。
D：从点到点链路接受，错误。答案片面
E：从其她路由器接受路由表，错误。互相间不直接发送路由表。
F：从DR接受TTL包，错误，答非所问。
QUESTION 80
Which statements describe the routing protocol OSPF?(Choose three.)
A. It supports VLSM.
B. It is used to route between autonomous systems.
C. It confines network instability to one area of the network.
D. It increases routing overhead on the network.
E. It allows extensive control of routing updates.
F. It is simpler to configure than RIP v2.
Answer：ACE
Explanation/Reference:
A：支持VLSM，对的
B：在AS之间使用，错误。在AS内部使用
C：限制了不稳定网络范畴，对的。通过划分区域实现。
D：增长了网络开销，错误。
E：容许路由更新控制，对的。
F：比RIPv2更容易配备，错误，答非所问。
Which of the following are types of flow control?(Choose three.)
A. buffering
B. cut-through
C. windowing
D. congestion avoidance
E. load balancing
Answer：ACD
Explanation/Reference:
流控制有哪些？
A：缓存
B：直通
C：窗口机制
D：拥塞避免
E：负载均衡。
What can be determined from the line of show ip route output shown in the exhibit?(Choose two.)
注意R =rip 管理距离修改
Rout rip
Distance 10

A. The next routing update can be expected in 35 seconds.
B. The IP address 10.10.10.6 is configured on S0/1.
C. The IP address 10.10.10.8 is configured on S0/1.
D. This route is using the default administrative distance.
E. The 10.10.10.8 network is two hops away from this router.
Answer：DE
Explanation/Reference:
考点：考查RIP路由条目。通过RIP学习到一条到达10.10.10.8路由，下一跳是10.10.10.6，出接口是
s/1。
A：错误。rip更新周期为30s，正常计时器不会超过30
B：错误，这个ip是对端接口ip
C：错误。s0/1ip无法得知
D：对的，rip缺省管理距离是120
E：对的。
QUESTION 93
Refer to the exhibit. From RouterA，a network administrator is able to ping the serial interface of RouterB
but unable to ping any of the subnets attached to RouterB. Based on the partial outputs in the exhibit，what
could be the problem?

A. EIGRP does not support VLSM.
B. The EIGRP network statements are incorrectly configured.
C. The IP addressing on the serial interface of RouterA is incorrect.
D. The routing protocol has summarized on the classful boundary.
E. EIGRP has been configured with an invalid autonomous system number.
Answer：D
QUESTION 97
For what two purposes does the Ethernet protocol use physical addresses?(Choose two.)
A. to uniquely identify devices at Layer 2
B. to allow communication with devices on a different network
C. to differentiate a Layer 2 frame from a Layer 3 packet
D. to establish a priority system to determine which device gets to transmit first
E. to allow communication between different devices on the same network
F. to allow detection of a remote device when its physical address is unknown
Answer：AE
Explanation/Reference:
考点：考查mac地址作用。
A：在二层唯一拟定一台设备，对的
B：是设备在不同网络中通信，错误，不同网络通信需要通过IP地址拟定。
C：区别二层和三层帧，错误。
D：拟定设备优先级，错误。没有这个功能。
E：是同一网络不同设备可以通信，对的
F：当不懂得远程设备物理地址时可以查询，错误。不能跨网段。
QUESTION 98
As a frame leaves a Layer 3 device，the Layer 2 encapsulation information is changed from what it was
when it entered the device. For what two reasons can this happen?(Choose two.)
A. The data is moving from 10BASE-TX to 100BASE-TX.
B. The WAN encapsulation type has changed.
C. The data format has changed from analog to digital.
D. The source and destination hosts are in the same subnet.
E. The source and destination MAC addresses have changed.
Answer：BE
Explanation/Reference:
考点：数据包转发过程。当数据包离开三层设备时，二层封装哪些信息变化了。
A：从10M网络到100M网络，错误。带宽变化不会变化数据包封装。
B：广域网封装变化，对的。如从HDCL变成PPP
C：数据格式从模仿型号变成数据信号，错误，物理层信号方式变化不会影响二层数据格式。
D：错误。
E：原蜜MAC变化，对的。
QUESTION 99
Which two statements are true regarding EIGRP?(Choose two.)
A. Passive routes简朴说就是：能被路由器路由合同。例如：IP、IPX、APPLE TALK等are in the process of being calculated by DUAL.
B. EIGRP supports VLSM，route summarization，and routing update authentication.
C. EIGRP exchanges full routing table information with neighboring routers with every update.
D. If the feasible successor has a higher advertised distance than the successor route，it becomes the
primary route.
E. A query process is used to discover a replacement for a failed route if a feasible successor is not
identified from the current routing information.
Answer：BE
Explanation/Reference:
A：被动路由在路由进程中由dual计算，错误。
B：至此VLSM，路由汇总，认证，对的
C：每次更新都发送所有路由信息，错误，增量更新。
D：如果可行后继路由器有一种比后继路由器高告示距离，它会成为主路由条目，错误。
E：如果不存在FS，使用查询进程去发当代替失效路由信息，对的。
What is an appropriate use of a default route?
A. to provide routing to a local web server
B. to provide routing from an ISP to a stub network
C. to provide routing that will override the configured dynamic routing protocol
D. to provide routing to a destination that is not specified in the routing table and which is outside the local
network
Answer：D
Explanation/Reference:
考点：考查缺省路由特点
A：提供路由到本地web服务器，错误
B：提供从ISP到末节网络路由，错误
C：提供优先于动态路由合同路由，错误。依照最长匹配原则，缺省路由最后才匹配。
D：对的
QUESTION 103
Refer to the exhibit. A junior network engineer has prepared the exhibited configuration file. What two
statements are true of the planned configuration for interface fa0/1?(Choose two.)

A. The two FastEthernet interfaces will require NAT configured on two outside serial interfaces.
B. Address translation on fa0/1 is not required for DMZ Devices to access the Internet.
C. The fa0/1 IP address overlaps with the space used by s0/0.
D. The fa0/1 IP address is invalid for the IP subnet on which it resides.
E. Internet hosts may not initiate connections to DMZ Devices through the configuration that is shown.
Answer：BE
Explanation/Reference:
DMZ使用公网地址，不需要做NAT，图中ACL第二条错将DMZ做了NAT，因而导致不能访问
QUESTION 111
Refer to the exhibit. Some 2950 series switches are connected to the conference area of the corporate
headquarters network. The switches provide two to three jacks per conference room to host laptop
connections for employees who visit the headquarters office. When large groups of employees come from
other locations，the network administrator often finds that hubs have been connected to wall jacks in the
conference area although the ports on the access layer switches were not intended to support multiple
workstations.
What action could the network administrator take to prevent access by multiple laptops through a single
switch port and still leave the switch functional for its intended use?

A. Configure static entries in the switch MAC address table to include the range of addresses used by
visiting employees.
B. Configure an ACL to allow only a single MAC address to connect to the switch at one time.
C. Use the mac-address-table 1 global configuration command to limit each port to one source MAC
address.
D. Implement Port Security on all interfaces and use the port-security maximum 1 command to limit port
access to a single MAC address.
E. Implement Port Security on all interfaces and use the port-security mac-address sticky command to
limit access to a single MAC address.
F. Implement Port Security at global