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Several Faults and Solutions of Network Switches
Dec 16 , 2022 291

The most common equipment in network equipment maintenance is network switches, especially the access layer switch. Connecting users and switching routing devices, as an intermediate, network switches play a vital role in troubleshooting network failures. Here are some common faults and solutions for switches.


Switch failures generally include physical layer failures, port negotiation and self-loop problems, Vlan problems, device compatibility problems, and other problems. Let's explain these problems one by one as below.

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First, Physical layer failures


Physical layer failures mainly refer to the hardware failure of the switch itself and that of the physical line connecting the switches.


Physical line failures connected to switches generally include physical damage to the network cable or optical fiber line itself, wrong type of network cable (except for support MDI/MDI-X self-adaptive cable) or incorrect connection of optical fiber transceivers, failure or abnormal operation of intermediate transmission equipment, such as photoelectric converters, protocol converters, etc., the maximum transmission length and maximum rate supported by the interface cable exceed the scope of usage and so on.


What's more, the working rate, working mode, frame format negotiation and matching between device interfaces will also cause the phenomenon to appear as a physical layer failure.


For the problems mentioned above, we can try to figure them out by following methods:


Use the status of the device interface indicator light to make a preliminary judgment. When the Line light is off, it means that the line is not connected. When it is on, it means that the line is connected; if the Active light is off, it means that there is no data transmission or reception, and when the light flashes, it means that there is data transmission and reception.


Judging by checking the output of the port through the command, such as display interface ethernet0/1.


Judge by substitution method. Efforts can be made to replace all items, including lines, cables and optical fibers, boards, slots, complete machines, exchange of line transceivers, etc.


Judge by configuring interface loopback on the switch. Set up the port for loopback testing: loopback { external | internal }.

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Second, 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 different manufacturers are different, or different devices of the same manufacturer use different hardware chips, leading too weak negotiation capabilities between devices, or the default parameter configurations of the devices at both ends are different, which causes the port auto-negotiation to fail, and the port works abnormally and cannot communicate normally. In this case, it is necessary to manually adjust and set the port parameters to ensure that the parameters of both parties are consistent.


For the self-loop problem caused by the switch due to 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, and most switches now support loopback-detection function.


Third, VLAN Troubleshooting


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


Fourth, Device compatibility failure


At present, the interconnection of network devices is very common, and device compatibility issues are inevitable. Device compatibility failures can be classified into:


Negotiation failures between devices that use different protocols to implement the same function when communicating with each other. For this kind of fault, it is sufficient to adopt a unified international general standard (specified by the IETF standard organization).


Negotiation failures between devices that use the same protocol specification but different implementation methods when communicating with each other. As for this kind of failure, you can first confirm that the protocol implementation has a standard interface, and secondly configure the parameters of the protocol interface accurately to ensure successful negotiation.


Negotiation failures between devices using the same protocol specification and the same implementation method but using different default parameters when communicating with each other. Such problems can be solved by accurately configuring the parameters of the protocol interface to ensure the success of the negotiation.


Fifth, other troubleshooting


The causes of network faults are complex and changeable. In addition to the faults caused by the above problems, there are other faults, such as network viruses and network topology defects. These failures have no specific rules to be found, and can only be analyzed and resolved based on one's own experience and the usage of network tools.


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


Our company has a professional technical team to provide users with network equipment repair and maintenance services, which mainly includes the configuration and usage of common network devices such as switches, routers and firewalls, network fault diagnosis, detection and maintenance of hardware devices in LAN and WLAN, basic detection and maintenance of network security, etc.


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