Troubleshooting of switches

In daily network fault maintenance, the most commonly used equipment is the switch, especially the access layer switch, which serves as a bridge connecting users and switching routing devices. The switch acts as an intermediate, it plays a very important role in troubleshooting network faults. If we have an understanding of its own faults, we may be able to help us quickly and more accurately identify and solve problems, we will share with you the troubleshooting of underlying switches.

Vswitch faults include physical layer faults, port negotiation, self-ring issues, Vlan issues, device compatibility issues, and other issues. We will explain these issues one by one.

I. Physical Layer faults

In a broad sense, physical layer faults mainly refer to the hardware faults of the vswitch and the physical line faults connecting the vswitch.

1. hardware faults

Hardware faults of the device generally include: interface or device hardware is damaged. The Bootrom or VRP software version is incorrect or not supported, and the optical Module Interface Type is incorrect, the user's PC Nic is faulty or the configuration is incorrect. After a vswitch or some interfaces break down, other interfaces gradually break down.

2. Physical line faults

The physical line faults of the connection switch generally include: network cable or optical fiber line itself physical damage, network cable type error (supporting MDI/MDI-X adaptive except) or optical fiber transceiver connection is incorrect, the intermediate transmission equipment (photoelectric converter, protocol converter, etc.) is faulty or is not working properly. The maximum transmission length and maximum rate supported by the interface cable are out of the scope of use.

The working rate, working mode, frame format negotiation, and matching problems between device interfaces can also cause physical layer faults.

For the above problems, we can find the problem in some ways, such:

1. Identify the status of the device interface indicator. If the Line light is off, the Line is not connected. If the light is on, the Line is connected. If the Active light is off, no data is sent and received. If the light is flashing, data is sent and received.

2. Check the output by using the port display command. For example, display interface ethernet0/1.

3. Use replacement method for determination. Including lines, cables and optical fiber cables, boards, slots, and devices.

4. Configure the interface loopback on the vswitch for judgment. Set the port to perform a loop test: loopback {external | internal }.

Ii. Port negotiation and self-Ring Failure

The problem of port negotiation on a vswitch is mainly caused by improper parameter matching such as the working rate and working mode, because the interface parameters of different manufacturers are different, or the negotiation capability between devices is not strong due to different hardware chips used by different devices in the same manufacturer or the default parameter configurations of the two devices are different, resulting in the failure of automatic port negotiation and abnormal port operation, unable to communicate normally. In this case, you need to manually adjust and set the port parameters to ensure that the parameters of both parties are consistent.

If a vswitch has a self-loop caused by connection or other reasons, you can enable the loop detection function and run the display loopback-detection command to check whether the output has a loop, currently, most vswitches support the Loopback-Detection function.

Iii. Vlan troubleshooting

Vlan technology is mainly used to isolate network storms and increase network security. It distinguishes data frames sent by different users. It is precisely because VLANs divide ports into ACCESS ports, TRUNK ports, and HYBRID ports. Vlan faults are mainly caused by improper configuration, including Spanning Tree, VTP, port type, and allowed Vlan.

Here, we will share a detailed troubleshooting method for Vlan troubleshooting for your reference.

Iv. device compatibility faults

Currently, the interconnection between network devices is common, and device compatibility problems are inevitable. Device compatibility faults can be roughly divided:

1. devices that use different protocols to implement the same function negotiate with each other during communication. For such faults, a unified international standard (defined by the IETF standards organization) is enough.

2. devices that use the same protocol specification but use different implementation methods negotiate with each other during communication. For such a fault, you can first confirm that the Protocol has a standard interface, and then configure the parameters of the Protocol Interface accurately to ensure the negotiation is successful.

3. devices that use the same protocol specification and the same implementation method but use different default parameters negotiate with each other during communication. For such problems, you only need to accurately configure the parameters on the protocol interface to ensure successful negotiation.

V. troubleshooting of other faults

The causes of network faults are complex and changeable. In addition to the faults caused by the above problems, there are also some other faults, such as network viruses and network topology defects. These faults have no special rules to find, you can only test your experience and use network tools for analysis and solution.

The network faults, analysis and troubleshooting methods described above are very helpful for us to clear and solve network faults. In addition to relevant theoretical knowledge, we also need accumulated experience to help us find the root cause of the problem as soon as possible.

In addition, there is also a "Troubleshooting of router networking faults" to explain the problem of inability to access the Internet during the use of router networking.