The superior performance of the switch and the substantial drop in price have promoted the rapid popularity of the switch. Network engineers often encounter various switch failures in their work.The problem of switch failure generally includes physical layer failure, port negotiation and self-loop issues , VLAN issues , device compatibility issues , and other problems.

1. Physical layer failure

The physical layer failure mainly refers to the hardware failure of the switch itself and the failure of the physical line connecting the switch.

Hardware failure

Physical circuit failure

The faults of physical lines connected to switches include: physical damage to the network cable or optical fiber line, the wrong network cable type (except for supporting MDI/MDI-X adaptation) or incorrect optical fiber transceiver connection, intermediate transmission equipment (photoelectric converter, protocol converter, etc.) ) failure or abnormal operation, the maximum transmission length and maximum rate supported by the interface cable are beyond the usage range, etc.

In addition, the working speed, working mode, frame format negotiation and matching problems between the device interfaces can also cause the phenomenon to appear as a physical layer failure.

For the above problems, we can find the problem through the following methods:

(1) Make a preliminary judgment with the aid of the status of the device interface indicator. The Line light is off to indicate that the line is not connected. The light is on to indicate that the line is connected; the Active light is off to indicate that no data is being sent or received, and the light is flashing to indicate that there is data to be sent or received.

(2) Judge by viewing the output through the port display command. For example, display interface ethernet0/1.

(3) Use the substitution method to make judgments. Including lines, cables and optical fibers, boards, slots, complete machines, exchange line transceivers, etc.

(4) Configure interface loopback on the switch for judgment. Set up the port for loopback test.{external|internal}

2. Port negotiation and self-loop failure

The problem of switch port negotiation is mainly caused by improper matching of parameters such as working speed and working mode, because the interface parameters of equipment of different manufacturers are different, or different equipment of the same manufacturer adopts different hardware chips, resulting in poor negotiation ability between equipment or The default parameter configuration of the devices at both ends is different, which causes the port to fail to automatically coordinate, and the port works abnormally and cannot communicate normally. At this time, you need to manually adjust and set the port parameters to ensure that the parameters of both parties are consistent.

For the problem of self-loop caused by the switch connection or other reasons, you can enable the loop detection function and use the display command display loopback-detection to check whether there is a loop in its output.

3. VLAN troubleshooting

The introduction of VLAN technology is mainly used to isolate network storms and increase network security; to distinguish data frames sent by different users, etc. It is precisely because of VLAN that ports are divided into ACCESS ports, TRUNK ports and HYBRID ports. VLAN faults are mainly caused by improper configuration, including spanning tree, VTP, port type, and allowed vlans, etc.

4. Equipment compatibility failure

At present, the phenomenon of network equipment interconnection is very common, and equipment compatibility problems are inevitable. Equipment compatibility failures can be roughly divided into:

(1) Negotiations between devices that use different protocols to achieve the same function when communicating with each other. For this kind of failure, a unified international standard (the IETF standards organization) can be used.

(2) Negotiation between devices that use the same protocol specification but use different implementation methods when communicating with each other. This kind of failure can firstly confirm that the protocol implementation has a standard interface, and secondly, accurately configure the parameters of the protocol interface to ensure the success of the negotiation.

(3)_Negotiations for devices that use the same protocol specification and the same implementation method but fail to dial the default parameters when communicating with each other. For this type of problem, you only need to prepare the parameters of the configuration protocol interface to ensure the success of the negotiation.

5. Other troubleshooting

The causes of network failures are complex and changeable. In addition to the faults mentioned above, there are other faults, there are other failures, such as network viruses, network topology defects, etc. These failures have no unique rules to be found, and can only rely on their own experience and the use of the network tools to analyze and solve.

The network faults, analysis and troubleshooting methods introduced above are very helpful for us to sort out and solve the faults in the network. In addition to the relevant theoretical knowledge, the judgment and resolution of network failures also need the experience accumulated in peacetime to help us find the root cause of the problem as soon as possible.