Layered diagnosis Technology of network fault

Network fault diagnosis is based on network principle, network configuration and network operation knowledge. From the phenomenon of fault, it is the technical means used by network management technicians to get the diagnosis information, to determine the network fault point, to find the root of the problem, to troubleshoot and to restore the normal operation of network.

1. Physical layer and its diagnosis

The physical layer is the most basic layer in the OSI layered structure system. Based on the communication media, it realizes the physical interface between the system and the communication media, transparently transmits between the data link entities, and provides services for establishing, maintaining and dismantling the physical connection between the computer and the network.

The failure of the physical layer is mainly manifested in the physical connection of the equipment is appropriate, the connection cable is correct; MODEM, CSU/DSU and other equipment configuration and operation is correct.

The best way to determine whether a physical connection to a router port is intact is to use the show interface command to check the status of each port, interpret screen output information, view port status, protocol build status, and EIA status.

2. Data link layer and its diagnosis

The main task of the data link layer is to make the network layer obtain reliable transmission without knowing the characteristics of the physical layer. The data link layer is used to package, package, error detection and correction of data through the link layer, and coordinate the shared media. Before the data link layer exchanges data, the protocol is concerned with forming frames and synchronizing devices.

To find and troubleshoot the data link layer, you need to look at the configuration of the router and check the encapsulation of the same data link layer that the connection port is sharing. Each pair of interfaces has the same encapsulation as the other devices it communicates with. Check its encapsulation by looking at the configuration of the router, or use the show command to view the encapsulation of the corresponding interface.

3. Network layer and its diagnosis

The network layer provides the means to establish, maintain and release network layer connections, including routing, flow control, transmission acknowledgement, interruption, error and failback.

The basic way to troubleshoot a network layer is to follow the path from source to destination, view the Router routing table, and check the IP address of the router interface. If the route does not appear in the routing table, you should check to determine whether the appropriate static route, default route, or dynamic route has been entered. Then manually configure some of the missing routes, or troubleshoot some of the dynamic routing processes, including RIP or IGRP routing protocol failures. For example, for IGRP routing information to exchange data only between systems of the same autonomous system number (AS), view the matching of autonomous system numbers for router configuration.