Analysis of the most probable causes of switch failure

The switch is out of order, do not know how to do it? How to repair, the following author for you to recommend a summary of the very detailed switch may be the cause of the failure, to help you to a one-way, I hope to help you.

In the day-to-day maintenance of network failures We are most exposed to the device is the switch, in particular, the access layer switch, which is a bridge connecting users and switching routing devices, as an intermediate, for us to troubleshoot network failures play a very important role, if we have an understanding of its own fault, may be able to help us faster, More accurate to find and solve problems, now on the bottom of the switch troubleshooting and share with you.

The trouble with the switch includes physical layer failures, port negotiation and self-loop issues, VLAN issues, device compatibility issues, and other issues, and so on, here are one by one explanations.

First, physical layer failure

In a broad sense, physical layer failure is mainly referred to the hardware failure of the switch itself and the physical circuit fault connecting the switch.

1, hardware failure

Hardware failures of the device itself generally include: interface or equipment hardware damage, interface bootrom or VRP software version is incorrect or not matched, Optical module interface type is incorrect, user PC network card failure or improper configuration, etc. Usually some of the switch or some of the interface is broken, the other interface will gradually broken down.

2, physical circuit failure

The physical wiring failure of the connecting switch generally includes: the network cable or the optical fiber line itself physical damage, cable type error (except support Mdi/mdi-x) or optical fiber transceiver connection is incorrect, intermediate transmission equipment (photoelectric Converter, protocol converter, etc.) failure or work is not normal, The maximum transmission length, maximum speed, etc. that the interface cable supports exceeds the usage range.

Also, the working rate, working mode, frame negotiation and matching problem between the device interfaces can also cause the phenomenon to be physical layer fault.

There are a number of ways we can find out about these problems, such as:

1, with the aid of the state of the device interface indicator to the initial sentence. Line Lights out means that the lines are not connected, the light indicates that the line is connected; Active Lights out indicates no data to send and receive, lights flashing indicates that there is data transceiver.

2, through the Port display command to view the output to determine. such as display interface ETHERNET0/1.

3, use the substitution method to judge. including lines, cables and optical fiber, board cards, slots, machine, replacement lines and send and receive.

4, on the switch to configure the interface loop back to judge. Set port for loopback test: loopback {external | internal}.

Ii. port negotiation and self-loop fault

The problem of switch port negotiation is mainly caused by improper matching of working rate and working mode, because different equipment interface parameters are different, or the same manufacturer of different equipment due to the use of different hardware chips, resulting in the negotiation ability between the equipment is not strong or both ends of the device default parameter configuration is not the same, resulting in automatic port negotiation does not pass, port work is abnormal, not normal communication, at this time, the parameters of the port need to be manually adjusted and set to ensure that both parameters are consistent.

For the switch due to wiring or other reasons caused by the problem of the loop, you can open the loop detection function, using display command displays loopback-detection to see if the output of the loop, Most switches now support the Loopback-detection feature.

Third, VLAN troubleshooting

The introduction of VLAN technology is mainly used to isolate network storms, increase network security, distinguish the data frames sent by different users and so on, it is the VLAN that divides the ports into Access ports, trunk ports and hybrid ports. For VLAN failure, it is mainly due to improper configuration, involving spanning tree, VTP, port type and allowed VLAN, etc.

Here, share a "VLAN troubleshooting detailed exclusion method" for your reference.

Four, equipment compatibility failure

At present, network equipment interconnection phenomenon is very common, equipment compatibility problem is unavoidable. Device compatibility failures can be broadly divided into:

1, the use of different protocols to achieve the same function of the equipment, in mutual communication negotiations. For this failure, the use of Uniform international standards (IETF standards Organization) can be.

2, the use of the same protocol specifications but the use of different methods of implementation of equipment, in the mutual communication between the negotiations. This fault can first confirm that the protocol implementation has a standard interface, followed by the exact configuration of protocol interface parameters to ensure successful negotiation.

3, using the same protocol specification also uses the same implementation method but uses the different default parameter the equipment, in the mutual communication consultation. This type of problem only requires the exact configuration of the Protocol interface parameters to ensure successful negotiation.

V. Other troubleshooting

Network fault causes complex, changeable, in addition to the above problems caused by the fault, there are some other failures, such as network viruses, network topology defects, these faults do not have a unique law can be found, can only test their own experience accumulation and the use of network tools to analyze and solve.

These network failures, analyses, and exclusions, as described above, are helpful for us to sort out and solve the problems that occur in the network. In addition to the relevant theoretical knowledge, we also need to accumulate experience to help us find out the root of the problem as soon as possible.