个人技能树搭建V1.0

本课程到目前为止，已经介绍了数据网络为以人为本的网络提供的服务，阐明了 OSI 模型各层的功能和 TCP/IP 协议的工作原理，并深入研究了常用 LAN 技术 — 以太网。接下来，我们要介绍如何将这些要素组合成能够正常运行的网络。

• Each application or network service uses protocols, which define the standards and data formats to be used. Without protocols, the data network would not have a common way to format and direct data.
• To scale a network, several elements are required:
  • Network documentation - physical and logical topology
  • Device Inventory - list of devices that use or make up the network
  • Budget - Itemized IT budget, including fiscal year equipment purchasing budget
  • Traffic analysis - protocols, applications, and services and their respective traffic requirements should be documented
• Executive timeouts allow the Cisco device to automatically disconnect users after they have been idle for the specified time. Console, vty, and aux ports can be configured with executive timeouts.
• ipconfig /displaydns show any cached DNS entries for this web page
• Traceroute uses the ICMP (Internet Control Message Protocol) to send and receive echo-request and echo-reply messages.
• A firewall is one of the most effective security tools for protecting internal network users from external threats. A firewall resides between two or more networks, controls the traffic between them, and helps prevent unauthorized access. A host intrusion prevention system can help prevent outside intruders and should be used on all systems.
• The show file systems command displays all of the available file systems on the device. If usbflash0: appears then the router recognizes the USB drive as a valid storage device. The pwd command shows the current directory being navigated, and the cd command is used to change the current directory. The dir flash0: command will show the contents of flash memory, not the USB drive.
• When a Windows computer cannot communicate with an IPv4 DHCP server, the computer automatically assigns itself an IP address in the169.254.0.0/16 range. Linux and Apple computers do not automatically assign an IP address.​
• Capturing traffic during low utilization time will not give a good representation of the different traffic types. Because some traffic could be local to a particular segment, the capture must be done on different network segments.
• Not all traffic should receive the same treatment or priority through a network. Some types of traffic, such as voice and video, require the highest priority because they are very sensitive to network latency and delay. Other types of traffic, such as FTP, which is not sensitive to latency and delay, should be given the lowest level of priority so that the higher priority traffic can get through.
• The tracert command is used to initiate a trace from the command prompt on a Windows PC. The traceroutecommand is used to initiate a trace from a Cisco router or switch. Some other PC operating systems, such as Linux and Mac OS also use the traceroute command. The ping command does not display the network path to the remote host.
• The most common indicators of a ping issued from the Cisco IOS are “!”, “.”, and “U”. The “!” indicates that the ping completed successfully, verifying connectivity at Layer 3. The “.” may indicate that a connectivity problem, routing problem, or device security issue exists along the path and that an ICMP destination unreachable message was not provided. The “U” indicates that a router along the path may not have had a route to the destination address, and that it responded with an ICMP unreachable message.
• The correct syntax is RouterA(config)# login block-for (number of seconds) attempts (number of attempts) within (number of seconds)command will block login attempts on RouterA for a period .
• Small networks generally have only one link to an ISP to establish a connection to the Internet. Problems can occur in the network, which can cause the disruption of this service. In order to keep connectivity, redundancy has to be provided. If the problem is in the router interface that is connected to the ISP, another interface can be activated on the router, so if one interface fails, traffic may be redirected toward the other interface. However, if the router itself fails, a second router that is connected to another ISP can be used as a backup.
• Because worms take advantage of vulnerabilities in the system itself, the most effective way to mitigate worm attacks is to download security updates from the operating system vendor and patch all vulnerable systems.
• Whenever an administrator connects to the console port, the configuration applied under the line con 0 interface determines how the user is authenticated. The console port configuration has the login command with local as the keyword. That means the username and password are required before the administrator is even allowed to see the enable mode prompt. Because the correct username and password was typed, the administrator will be presented with the enable mode prompt.
• Physical threats can be classified into four categories:
  • Environmental threats -Temperature extremes (too hot or too cold) or humidity extremes (too wet or too dry)
  • Hardware threats - Physical damage to servers, routers, switches, cabling plant, and workstations
  • Electrical threats - Voltage spikes, insufficient supply voltage (brownouts), unconditioned power (noise), and total power loss
  • Maintenance threats - Poor handling of key electrical components (electrostatic discharge), lack of critical spare parts, poor cabling, and poor labeling

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