_管理网络环境

管理网络环境 一、CDP CDP：cisco发现协议。支持发现直连的设备，是cisco自有的协议。工作在数据链路层，ios在10.3版本以后支持。 Physical media must support the Subnetwork Access Protocol (SNAP) encapsulation. SNAP:子网访问协议 CDP会传输这些信息。 · Device identifiers · Address list · Port identifier · Capabilities list · Platform CDP缺省是打开的。CDP每60秒钟交换一次。 关闭CDP，可以关某个端口的，也可以关全部的。如你在广域网上，通过cdp可以看到你的ip，所以有安全问题。低速网络也考虑带宽，关闭cdp。 端口关闭时是 no cdp enable 全局时关是 no cdp run Holdtime从180开始递减，＝0时该项将被删除。 Show cdp entry * 显示cdp完整xinx Showcdp traffic Show cdp interface 二、在路由器中远程访问 # telnet 10.10.2.23 对方vty要设置密码才行 Show sessions:看我们连接到谁了。 * 表 关于同志近三年现实表现材料材料类招标技术评分表图表与交易pdf视力表打印pdf用图表说话 pdf 示正在挂起。 Show users：表示谁连到我们了。 挂起和恢复： 断掉连接。 1、断掉我们连的 #disconnet；；一般我们用exit; Disconnects a connection to a remote router from the originating router 2、断掉连我们的 #clear line 11;; Clears a connection connected via Telnet to your router Ping ip_address Traceroute ip_address ！！！！！：表示包都通了 ！！…：其中的点表示这个包丢了。 show history History size line(默认为10行，全局参数) Terminal history size lines :给telnet登陆的用户配置历史空间，只给当前会话起临时作用，会话结束，设置失效。 一般路由器出厂时有2个操作系统。一个是flash里的，一个是在ROM中的mini ios。 三、IOS引导 3、flash中有多个ios时一般去引导第一个，如果bootsystem里面有规定，则装载制定的。 4、网络上寻找tftp 5、引导最小版本IOS就是那个Mini IOS, Cisco叫它RXBOOT或bootloader, 6、Mini IOS也没有，进入ROMMON模式 Reg bit 13=1，则从网络上查5次，有一次成功，就从网络上装载；5次过后，进入rxboot模式。 wg_ro_a#show version IOS (tm) 2500 Software (C2500-JS-L), Version 12.0(3), RELEASE SOFTWARE (fc1) Configuration register is 0x2102 0x后面的数字是16进制的数字。 16位寄存器后4位控制路由器的启动。 后4位＝0，启动监控模式。0x2100。提示符为>，或者romon1>,romon2…. 2100 最后一位＝1，启动mini ios模式。提示符为Router(boot)> 2101 最后4位为2到F，在到NVRAM查语句是否存在boot system TFTP，如果没有，在启动顺序为flash－TFTP－ROM. 第六位＝1，即0x2142，忽略NVRAM（startup-config）。也就是忽略密码。用于恢复密码。进入setup状态 Config register ox2102，在全局模式 2100：ROM MONITOR模式 2101：Mini IOS模式，也叫rxboot模式 2142：忽略NVRAM模式，即越过startup模式 2102：正常模式 最后4位为2到F，在到NVRAM查语句是否存在boot system TFTP，如果没有，在启动顺序为flash－TFTP－ROM. Show flash Copy flash tftp copy tftp flash 在mini模式下升级ios： Interface e0 Ip address 192.168.10.10 No shutdown Copy tftp flash 有个别时候，在正常模式下，copy tftp flash 不能成功，或者找不到文件，就可以到mini ios模式下。 merge：合并。有冲突的以源为准，其它不变。 Configure terminal (merge): 往RAM中拷贝的都是merge方式。 Router(config)#service timestamps debug datetime msec Router#show processes ;;show memory CPU utilization for five seconds: 0%/0%; one minute: 0%; five minutes: 0% PID Q Ty PC Runtime(ms) Invoked uSecs Stacks TTY Process 1 C sp 602F3AF0 0 1627 0 2600/3000 0 Load Meter 2 L we 60C5BE00 4 136 29 5572/6000 0 CEF Scanner 3 L st 602D90F8 1676 837 2002 5740/6000 0 Check heaps 4 C we 602D08F8 0 1 0 5568/6000 0 Chunk Manager 5 C we 602DF0E8 0 1 0 5592/6000 0 Pool Manager 6 M st 60251E38 0 2 0 5560/6000 0 Timers Router#no debug all 第一行黄字是为debug显示的信息在行开始加时间标签。 第二行是看cpu忙不忙，不忙，可以用debug命令。当cpu利用率超过50％时，使用debug要当心。坚持在排错时再用debug，否则用show命令。 How can an administrator determine if a router has been configured when it is first powered up? A. A configured router prompts for a password. B. A configured router goes to the privileged mode prompt. C. An unconfigured router goes into the setup dialog. D. An unconfigured router goes to the enable mode prompt. [C. 原来if是是否的意思，而不是如果的意思呀] What is the function of the CSMA/CD algorithm in Ethernet technologies? a. defines how the media is accessed. b. Supplies a token to determine which host has access to the media c. Dddefines the encoding of electrical signals on the wire d. Determines the preamble bits Which three commands are needed to configure a router to run this image(IOS image in tftp server) as soon as possible? a. router#reload b. router(config)#service config c. router#copy tftp startup-config d. router (config) #boot system tftp e. router(config-line)#logging synchronous f. router#copy running0config startup-config answer: a d f Answer: A 要借4位做网络段，可得到16个网络，主机数位为2的4次方－2＝14 ，14个主机 service (config) Use the service config global configuration command to enable automatic download of the switch configuration file(startup file) from a Trivial File Transfer Protocol (TFTP) host during power up. Use the no service config command to disable automatic download of the configuration file. service config no service config Answer: B,D 尽量避免在网络中使用集线器，因为使用集线器的网络用户是共享带宽，而且存在一个控制冲突的环回电路，不断地检测回路并发出干扰信号以告知网络中的其他计算机网络发生冲突，而且会不断的进行，这样会产生很多的垃圾数据，从而形成网络广播风暴。推荐使用交换机（最好不好使用自适应的），因为交换机中采用了缓存技术，为每个用户提供专用的信道，而且支持全双工通讯方式，一般不会发生发生冲突，自然就不会产生大量的冲突检测数据了。 确保网络中没有网络回路，建议采用星型网络拓扑结构。 Which of the following statements correctly describe the differences between halfduplex and full-duplex Ethernet? (Select two answer choices.) A. Full-duplex Ethernet uses CSMA/CD to prevent collisions. B. Half-duplex Ethernet uses a loopback circuit to detect collisions. C. A full-duplex Ethernet card allows 20Mbps for data transmission. D. Full-duplex Ethernet makes use of two pairs of wires for data. E. An Ethernet hub can operate both half and full duplex simultaneously. Answer: B, D You have an Ethernet network. Which of the conditions below can lead to increased congestion on your network? (Select two answer choices) A. The use of Full-Duplex Mode. B. The Creation on New Collision Domains. C. The Creation on New Broadcast Domains. D. The Addition of Hubs to the Network. E. The use of switches in the Network. F. The Amount of ARP or IPX SAP Traffic. Answer: D, F Two stations on a LAN transmit at the same time, resulting in a collision. Whathappens when a collision occurs on the network? (Choose all that apply) A. Each device on the Ethernet segment stops transmitting for a short time. B. A jam signal informs all devices that a collision occurred. C. When data transmission resumes, the devices that were involved in the collisionhave priority to transmit. D. The devices that are involved in the collision stops transmitting for a short time. E. The collision invokes a random back-off algorithm. Answer: B, D, E How does using the service password-encryption command on a router provide additional security? a. by encrypting all passwords passing through the router b. by encrypting passwords in the plain text configuration file c. by requiring entry of encrypted passwords for access to the device d. by configuring an MD5 encrypted key to be used by routing protocols to validate routing exchanges e. by automatically suggesting encrypted passwords for use in configuring the router Answer: a.                 Service password-encryption 对所有的口令进行加密，保护口令，避免其通过idsplay命令 将口令显示出来 A legacy network that is prone to errors may have issues with services that use UDP. Which of the following services could have problems in this case, due to the fact that UDP is used? (Select three answer choices.) A. DNS B. Telnet C. SMTP D. SNMP E. HTTP F. TFTP Answer: A, D, F late collision的解释： 在以太网中，冲突被分为两大类：early和late。early collision 由发送方在帧的前64个字节进入线路之前检测到的冲突。early collision是以太网CSMA/CD访问方法中的组成部分。early collision通常导致小的被中断的帧或称为runt。Late collision发生在帧的多个字节（大于64）被发送到线路中时产生的冲突。在理论上，以太网不会产生此类冲突。产生late collision的原因包括： 电缆违反了距离规则。 发生故障的NIC卡不正确地监听线路。 也就是说late collision传输数据包序文报头后发生的碰撞叫late collisions。通常发生late collision都是因为以太网的线缆过长，超出了它所能传输的距离限制造成的。 Answer: C. fa0/0和s0/1网段重叠。 Answer: B, UDP has no sequencing field and has no idea in which order a segment arrives. It will just pass any segment to the upper layers as they arrive. ICMP= Internet Control Message Protocol , at the Network layer. CIDR: Classless Inter-Domain Routing (CIDR) RFC 1918 Private Address Space: Range of IP Addresses Class of Networks Number of Network 10.0.0.0 to 10.255.255.255.255 A 1 172.16.0.0 to 172.31.255.255 B 16 192.168.0.0 to 192.168.255.255 C 256 F. Issue the 'write e" command. G. Issue the "write mem" command F. This will have the effect of erasing the running configuration, and setting the router configuration back to the factory default settings. G. This is an old command that is still supported on the latest Cisco IOS. It is short for "write memory" and has the same effect as the "copy running-config startup-config" command. You are logged into a router and with to view the layer 3 information about your neighboring Cisco routers. What IOS command gives layer 3 information for of the directly connected router interfaces? A. show ip links B. show cdp neighbor C. show cdp neighbor detail D. show ip clients E. show ip route F. None of the above Answer: C While troubleshooting a connectivity problem on the network, you issue the ping command from your PC command prompt, but the output shows "request times out." At which OSI layer is this problem associated with? A. The data link layer B. The application layer C. The access layer D. The session layer E. The network layer Answer: E Explanation: TCP/IP includes ICMP, a protocol designed to help manage and control the operation of a TCP/IP network. The ICMP protocol provides a wide variety of information about a network's health and operational status. Control message is the most descriptive part of a name. ICMP helps control and manage IP's work and therefore is considered part of TCP/IP's network layer. A host computer has been correctly configured with a static IP address, but the default gateway is incorrectly set. Which layer of the OSI model will be first affected by this configuration error? A. Layer 1 B. Layer 2 C. Layer 3 D. Layer 4 E. Layer 5 F. Layer 6 E. Layer 7 Answer: C Explanation: IP Addressing and IP routing resides on the OSI Network layer, which is layer 3. QUESTION NO: 5 Which layer of the OSI reference model is responsible for ensuring reliable end-to-end delivery of data? A. Application B. Presentation C. Session D. Transport E. Network F. Data-Link Answer: D Explanation: A new Catalyst switch is connected to an existing switch using a crossover cable. As a result of this, what would the switch port link lights display? A. The switch port link lights will be off on both switches indicating the ports are not connected. B. The switch port link light will be off on one switch indicating that STP has disabled the port. C. The switch port link lights will flash amber indicating an error. D. The switch port link lights will be green indicating normal operation. Answer: D Explanation: To connect one Cisco switch to another Cisco switch, the crossover cable is the proper cable to use. So if you were to use one, the lights would be green indicating that all is well. If you were to connect a switch to a router, a server, or a PC host then a straight through cable should be used. * Connect a Category 3, 4, or 5 crossover cable to any 10/100 port on the switch and to a 10BaseT port on the target hub or switch. * Connect a Category 5 crossover cable to any 10/100 port on the switch and to a 100BaseTX port on the target hub or switch. Refer to the router output shown in the graphic. What can be assumed about the network attached to this router interface? A. The network hosts are attached to a hub. B. The interface is being used at near maximum capacity. C. There should never be any collisions in this network. D. The network has an excessive number of errors. E. The network is using an unusual Ethernet encapsulation. Answer: C Explanation: Based on the output shown, this interface is configured to operate in full duplex mode. Full-duplex is a data communications term that refers to the ability to send and receive data at the same time. QUESTION NO: 11 (Select all valid answer choices) A. The extended ping command is supported from user EXEC mode. B. The extended ping command is available from privileged EXEC mode. C. With the extended ping command you can specify the TCP and UDP port to be pinged. D. With the extended ping command you can specify the timeout value. E. With the extended ping command you can specify the datagram size. Answer: B, D, E After executing the "show host" command, which of the information below would you see? (Select two answer choices.) A. The IP addresses of workstations allowed gain access to the router via an access list B. Permanent name-to-address mappings created using the ip host command. C. Temporary and permanent DNS entries. D. The names of the routers created using the hostname command. E. The length of time of users logged into the router, as well as the duration Answer: B, D While troubleshooting a connectivity issue from a PC you obtain the following information: Local PC IP address: 190.0.3.35/24 Default Gateway: 190.0.3.1 Remote Server: 190.0.5.250/24 You then conduct the following tests from the local PC: Ping 127.0.0.1 - Unsuccessful Ping 190.0.3.35 - Successful Ping 190.0.3.1 - Unsuccessful Ping 190.0.5.250 - Unsuccessful What is the underlying cause of this problem? A. TCP/IP not correctly installed B. Local physical layer problem C. NIC not functioning D. Remote physical layer problem Answer: A Explanation: Every Windows based PC uses the 127.0.0.1 as the local loopback IP address. Every PC will respond to this local IP address if the TCP/IP stack is correctly installed and running on the machine. If you cannot ping the loopback address of 127.0.0.1, then something is wrong with the TCP/IP protocol stack. A Cisco router TestKing2 and a Catalyst Switch TestKing switch are connected as shown in the exhibit. The TestKing.com technician is working on a computer that is connected to the management console of the switch. In order to configure the default gateway for the switch, the technician needs to learn the IP address of the attached router interface. Which IOS command will provide this information in the absence of Layer 3 connectivity? A. ping router_ip_address B. ping switchr_ip_address C. show ip rarp D. show cdp neighbors detail E. show ip neighbors F. show dhcp-config Answer: D Explanation: The "show cdp neighbor detail" command can be issued on a Cisco router or the switch. This command shows the information about all attached devices, assuming that they are also Cisco attached network devices, with CDP enabled. The "show interface Ethernet 0" command was issued on a TestKing router as shown below: The router output shown in the graphic indicates that 534 runts have been detected by the router interface. What are possible causes of this condition? A. A large number of collisions B. A faulty network interface card C. A decrease in the size of the collision domain D. Fragment-free switching E. Incorrect network addressing F. TTL failures Runts are packets that are discarded because they are smaller than the medium's minimum packet size. Any Ethernet packet that is less than 64 bytes is considered a runt. In half-duplex environments, it is possible for both the switch and the connected device to sense the wire and transmit at exactly the same time and result in a collision. Collisions can cause runts, FCS, and alignment errors, caused when the frame is not completely copied to the wire, which results in fragmented frames. Runts are the result of collisions, faulty NIC's, duplex mismatch, IEEE 802.1Q (dot1q), or an Inter-Switch Link Protocol (ISL) configuration issue. Runts 是指大小小于最小值的报文。在示例的以太网中，该值为64。以太网中指定最小报文大小大小是由于在这种传输模式下的工作站需要检测碰撞。如果以太网段中包 含以太网中继器并且其距离符合规定的标准，最小报文大小大小可以使处在这种传输模式下的工作站检测线路中的任何碰撞。 Giants 指大小超过线路可以承受的最大报文大小的报文。以太网的MTU通常为1500字节，或者最大的封装数据为1500字节。 Input errors 指到达报文中检测到的错误，也可能表明网段本身发生了错误。 Output errors 指输出报文中的错误，它可能表明路由器接口本身发生了故障。 CRCs 由于报文不正确的以太网校验和而检测到的循环冗余校验错。它可能由于网段的噪声引起，或者由于网卡故障、报文冲突引发。CRC的频率应是每100000个输入报文中发生一次。 Frame errors 指接收到的帧的类型与路由器以太网帧类型（IP协议帧类型为ARPA）不匹配。 Aborts 在碰撞检测中过度的重传而导致的问题。在以太网中，重传的最大次数不超过15次。 Dribble condition 指接收到的帧比MTU大，但不属于Giants。 Babble 是指持续接收到可疑的帧。 Deferred 如果线路繁忙，报文在传输时将被延缓发送。 Interface resets 在检测到过多的错误时，路由器将重置接口。这些错误可能存在于局域网段中，也可能是接口本身的错误。在此不能够判断具体是那儿发生故障，但是，如果伴随着大量的输出错误，则表明路由器接口本身发生故障。 Collisions 在以太网中，冲突被分为两大类：early和late。early collision 由发送方在帧的前64个字节进入线路之前检测到的冲突。early collision是以太网CSMA/CD访问方法中的组成部分。early collision通常导致小的被中断的帧或称为runt。Late collision发生在帧的多个字节（大于64）被发送到线路中时产生的冲突。在理论上，以太网不会产生此类冲突。产生late collision的原因包括： ?;; 电缆违反了距离规则。 ?;; 发生故障的NIC卡不正确地监听线路。 Lost carrier 表明在计数器最后一次清0后，载波和线路协议发生的故障。此类故障通常与路由器无关。例如，载波丢失可能是因为路由器与集线器之间的电缆连接中断。 Buffer parameters show interface命令还提供与缓冲区分配有关的故障信息，它包括no buffer、overruns、ignored、underruns、buffer failures和swapped out buffers等。 上面，我们详细讨论了show interface命令的用法。这些命令的输出提供了与路由器接口相关以及与传输介质相关的参数等有价值的信息。 show controller命令提供连接到路由器接口物理线路以及传输介质的详细信息。并且提供状态的历史信息。其中一些详细信息很少被使用，它们一般仅被TAC技术人员用于解决十分复杂的问题。 与协议相关的命令 本节将讨论如何使用与不同协议相关的显示命令。 show protocol命令给出了路由器运行的协议信息以及路由这些协议的每一个接口的地址信息. A TestKing.com network technician is testing an ISDN circuit that uses PPP between two IP hosts. Match the success indicator with the layer of OSI functionality on the right that the success indicator verifies. answer: In the communications industry, what are the features and benefits of using the layered OSI model? (Select the two best answers) A. It encourages industry standardization by defining what functions occur at each layer of the model. B. It necessitates changes in functionality in one layer to other layers. C. It enables equipment efficiency from different vendors to use the same electronic components. D. It divides the network communication process into smaller and simpler components, thus aiding component development, design, and troubleshooting. E. It supports the evolution of multiple competing standards, and thus enhances business equipment manufacturing opportunities. Answer: A, D Explanation: The OSI (Open System Interconnection) reference model was created as a reference point for communications devices. A layered approach is used to segment the entire telecommunications process into a series of smaller steps. A is correct because it encourages a level of standardization by encouraging that functions be compared to known layers. D is also correct because it allows engineers to focus on the development, refining, and perfection of simpler components. In the OSI model, at which layers do WANs operate at? (Select two answer choices) A. Application layer B. Presentation layer C. Session layer D. Transport layer E. Network layer F. Data link layer G. Physical layer Answer: F, G Explanation: WAN (Wide Area Network) operates at OSI Layer 1(Physical) and Layer 2 (Data link) layers. The WAN provides for the exchanging of data packets between Routers and the LAN's that the routers support 数据段――数据包――数据帧――数据位 segment----packet----frame------bits Which three of the following OSI model layers also belong to the TCP/IP model? (Select three answer choices) A. The application layer B. The session layer C. The data link layer D. The transport layer E. The network interface layer F. The physical layer Answer: A, D, E The TCP/IP network model differs from the more popular OSI model. Which of the layers below belong to the TCP/IP model? (Select all that apply) A. application layer B. session layer C. transport layer D. internet layer E. network layer F. data link layer G. physical layer Answer: A, C, D What is the IEEE standard associated with Gigabit Ethernet? (Select two answer choices) A. 802.11 B. 802.5 C. 802.3ab D. 802.3ae E. 802.3z F. 802.3u Answer: C, E Part of the job as a network administrator is being able to make a distinction between routed protocols and routing protocols. Which of the following statements is true regarding them? (Choose all that apply) A. A routing protocol is assigned to an interface and determines the method of packet delivery. B. A routed protocol is assigned to an interface and determines the method of packet delivery. C. A routing protocol determines the path of a packet through a network. D. A routed protocol determines the path of a packet through a network. E. A routing protocol operates at the transport layer of the OSI model. F. A routed protocol updates the routing table of a router. Answer: B,