Detailed description of Network Fault Diagnosis concepts and application steps (1)

As a comprehensive technology, network fault diagnosis involves many aspects of network technology. Before learning the concept of network fault diagnosis, let's take a look at the basic concepts of networks and routers that are closely related to it?

A prelude to Network Fault Diagnosis: What is a network or router?

A computer network is a system composed of computers and communication facilities. It connects geographically dispersed computers by various communication means, systems that communicate with each other and share software, hardware, data, and other resources. Computer Networks are generally divided into LAN and WAN according to their computer distribution. Lan covers a small geographical range, generally ranging from several meters to dozens of kilometers. The wide area network covers a large geographical range, such as campuses, cities, and even the world. The development of computer networks leads to various forms of connections between networks. Unified protocols are used to interconnect different networks, making the interconnected networks easy to expand. The Internet is the network connecting networks in this way. The Internet uses the TCP/IP protocol as a communication agreement to connect computer networks around the world and become the world's largest and most popular international network. In order to complete the communication between computers, the interconnection functions of each computer are divided into clearly defined layers, and the protocols for the same layer of communication and interfaces and services between adjacent layers are defined, the protocols for communication between these layers and processes at the same layer and interfaces between adjacent layers are collectively referred to as the network architecture. The Open System Interconnection Reference Model OSI proposed by ISO is the core of the modern computer network technology system. This model divides network functions into seven layers: physical layer, data link layer, network layer, transmission layer, Session Layer, presentation layer, and application layer.

TCP/IP is a set of network protocols. TCP/IP originated from ARPANET, which has become a standard communication protocol used by the Internet. TCP/IP enables computers using different operating systems to exchange data in an orderly manner. A vro is a network device used for network connection and route selection tasks. The router works at the network layer, forwards packets, and has the filtering function. A vro can connect two networks using different technologies and establish a network connection between multiple types of networks, such as the LAN or WAN. It transmits the information of the network layer in the layer-7 model from the network layer to the network layer of the other network based on the fastest and most direct routing principle to achieve the best route selection. At the same time, high-speed internal BUS is used internally to connect interfaces suitable for various network protocols. It also provides multiple network management functions to monitor some network devices connected to routers and their configuration and running status.

CISCO routers are the most commonly used routers in network construction. They come in a variety of grades and series. Currently, they are commonly used in the 2500 series. This article takes the 2500 series as an example. Vrouters of the 2500 series are fixed-interface multi-protocol routers that support all cisco ios functions. According to the specific Protocol environment, there are four types: Fixed-configuration vro2501 2507), router 2514 with hub port), router 2511 with touch block) and access server ). They are simple in structure, easy to operate, easy to configure and manage. They are a routing device used for small-scale LAN and WAN network layer relay. Cisco ios is a CISCO-specific Internet Operating System. All CISCO products run IOS, and IOS seamlessly connects them to work together. A Scalable open network that supports any hardware interface, any link layer, and network layer protocols. IOS supports many protocols, including various network communication protocols and routing protocols. Cisco ios has become a de facto standard for Internet interconnection in the industry. Cisco ios provides several different operation modes, each of which provides a set of related command sets, different operation permissions, and operation functions. For security purposes, the CISCO user interface has two levels of access permissions: user level and privilege level. The first-level access allows you to view the Route status, which is called the user EXEC mode and the view mode. The second-level access allows you to view router configurations, modify configurations, and run Debugging commands, which are called the Privileged EXEC mode, it is also called the configuration mode. In the privileged level, you can enter different configuration patterns based on different configurations, such as global configuration mode, interface configuration mode, and line configuration mode.

Concept and principle of network fault diagnosis:

Network Fault Diagnosis should achieve the following three objectives: to determine the network fault point and restore the normal operation of the network; To improve and optimize network performance when network planning and configuration are poor; observe the running status of the network and timely predict the network communication quality. Network Fault Diagnosis is based on network principles, network configurations, and network operation knowledge. Starting from the fault phenomenon, the Network diagnosis tool is used as a means to obtain the diagnosis information, determine the network fault point, find the root cause of the problem, eliminate the fault, and restore the normal operation of the network. There are several possible network faults: physical device connection failures in the physical layer, hardware and line problems, and interface configuration problems of network devices on the data link layer; network layer network protocol configuration or operation error; transmission layer device performance or communication congestion problem; Layer 3 cisco ios or network application error. The process of diagnosing network faults should start from the physical layer up along the OSI Layer-7 model. First, check the physical layer, then the data link layer, and so on, and try to identify the failure point of the communication until the system communication is normal. Network diagnosis can use a variety of tools including LAN or WAN Analyzer: Router diagnostic commands, network management tools and other fault diagnosis tools. The tools provided by CISCO are sufficient to handle most network faults. Viewing the route table is a good place to start solving network faults.

ICMP ping, trace, Cisco show, and debug commands are network tools used to obtain useful information for fault diagnosis. We usually use one or more commands to collect the relevant information and, under a given situation, determine which commands are used to obtain the required information. For example, you can use the ping command to determine whether a device can be reached through the IP protocol. Ping sends an ICMP packet from the source point to the target. If the packet is successfully sent, the returned ping packet confirms that all the physical layer, data link layer, and network layer functions from the source point to the target are running normally.

After the Internet is running, how does one know its information, whether the network is running properly, how does one monitor and understand the running details of the network under normal conditions, and how the network is faulty. What about monitoring? The show interface command can be used to easily obtain information about each interface to be checked. In addition, the show buffer command regularly displays the buffer size, usage, and usage. The Show proc command and show proc mem command can be used to track CPU and memory usage, and collect the data on a regular basis for diagnostic reference when a fault occurs. Network faults are manifested by some symptoms, including general symptoms such as users cannot access a server) and special ones such as vrouters not in the routing table ). You can use specific fault diagnostic tools and methods to find one or more Fault Causes for each symptom. The Troubleshooting mode is as follows: