It is inevitable that a fault occurs during the operation of the switch, but after the fault occurs, it should be dealt with quickly to find the fault point as soon as possible and eliminate the fault. This is the responsibility of the network management personnel. But to do this, you must understand the type of switch failure and have the ability to analyze and deal with the failure. To this end, this article briefly introduces the types of failures that frequently occur in switches and the methods of analysis and troubleshooting.
electricity failure
The power supply is damaged or the fan stops due to unstable external power supply, aging of the power supply line or lightning strikes, so that it cannot work normally. Or damage to other components in the machine due to power supply will cause problems to the switch.
If the POWER indicator on the switch panel is green, it is normal; if the indicator is off, it means that the switch is not normally powered. Such problems are easy to find and easy to solve, and they are also the easiest to prevent.
In response to such failures, the external power supply should be done first. Generally, an independent power line is introduced to provide an independent power supply, and a voltage regulator is added to avoid instantaneous high-voltage or low-voltage phenomena. If conditions permit, you can add a UPS (uninterruptible power supply) to ensure the normal power supply of the switch, some UPS provide voltage stabilization function, and some do not, you should pay attention when choosing. Set up professional lightning protection measures in the equipment room to avoid lightning damage to the switch. Now there are many professional companies doing lightning protection projects, which can be considered when implementing network cabling.
Port failure
It is the most common hardware failure. Whether it is an optical fiber port or a twisted pair RJ-45 port, you must be careful when plugging or unplugging the connector. If you accidentally dirty the optical fiber plug, it may cause the optical fiber port to be contaminated and cannot communicate normally. We often see that many people like live plug-in connectors, which is theoretically possible, but this also inadvertently increases the incidence of port failures. Careless handling may also cause physical damage to the port. If the purchased crystal head is too large, it is easy to damage the port when it is inserted into the switch. In addition, if a section of the twisted pair connected to the port is exposed outdoors, in case this cable is struck by lightning, it will cause the connected switch port to be damaged or cause more unpredictable damage.
In general, a port failure is one or several ports damaged. Therefore, after troubleshooting the computer connected to the port, you can determine whether it is damaged by replacing the connected port. In case of such failures, you can clean the port with an alcohol cotton ball after the power is turned off. If the port is indeed damaged, it can only be replaced.
Module failure
The switch is composed of many modules, such as: stacking module, management module (also called control module), expansion module, etc. The chances of these modules failing are very small, but once problems occur, they will suffer huge economic losses. If you are careless when inserting or removing the module, or when the switch is transported, or if the power supply is unstable, it may cause such failures.
Of course, the three modules mentioned above all have external interfaces, which are easier to identify, and some can also identify faults through the indicator lights on the module. For example, there is a flat trapezoidal port on the stacking module, or some switches have a USB-like interface. There is a CONSOLE port on the management module, which is used to establish a connection with the network management computer for easy management. If the expansion module is connected by fiber, there will be a pair of fiber interfaces.
When troubleshooting such faults, first make sure that the power supply of the switch and modules is properly supplied, then check whether each module is inserted in the correct position, and finally check whether the cables connecting the modules are normal. When connecting the management module, it is also necessary to consider whether it uses the specified connection rate, whether there is a parity check, whether there is data flow control and other factors. When connecting the expansion module, you need to check whether it matches the communication mode, for example: whether to use full-duplex mode or half-duplex mode. Of course, if it is confirmed that the module is faulty, there is only one solution, that is, you should immediately contact the supplier for replacement.
Backplane failure
Each module of the switch is plugged into the backplane. If the environment is humid, the circuit board is wet and short-circuited, or the components are damaged due to high temperature, lightning strikes and other factors, the circuit board will not work properly. For example: poor heat dissipation performance or too high ambient temperature leads to an increase in the internal temperature of the unit, causing the components to burn out.
Under the condition that the external power supply is normal, if the internal modules of the switch are not working properly, it may be that the backplane is broken. In this case, even an electrical maintenance engineer may be unable to do anything. The only way is to replace the backplane. Board.
Cable fault
In fact, this kind of fault is theoretically not a fault of the switch itself, but in actual use, cable faults often cause the switch system or port to not work properly, so this type of fault is also classified as a switch hardware fault. For example, the connectors are not tightly connected, the order of the cables is incorrect or not standardized, and the cables should be connected with crossover cables but with straight cables. The two optical fibers in the optical cable are interleaved. The wrong circuit connection leads to network loops. Wait.
Judging from the above kinds of hardware failures, the poor environment of the equipment room can easily lead to various hardware failures, so when we build the equipment room, we must first do lightning protection and grounding and power supply, indoor temperature, indoor humidity, anti-electromagnetic interference, The construction of anti-static and other environments provides a good environment for the normal operation of network equipment.
system error
The switch system is a combination of hardware and software. There is a refreshable read-only memory inside the switch, which stores the software system necessary for this switch. This type of error is also the same as our common Windows and Linux. Due to the design at the time, there are some loopholes. When the conditions are suitable, it will cause the switch to be fully loaded, lost, and wrong. Therefore, the switch system provides methods such as Web and FTP to download and update the system. Of course, errors may occur when upgrading the system.
For such problems, we need to develop the habit of frequently browsing the website of the device manufacturer. If there is a new system launch or a new patch, please update it in time.
Improper configuration
Beginners are not familiar with switches, or due to different switch configurations, administrators often have configuration errors when configuring switches. For example, incorrect VLAN division leads to network disconnection, ports are closed by mistake, and the mode configuration of the switch and network card does not match. Such failures are sometimes difficult to find and require some experience accumulation. If you cannot ensure that the user's configuration is faulty, please restore the factory default configuration first, and then configure it step by step. It is best to read the manual before configuration, which is also one of the habits that the network management should develop. Each switch has a detailed installation manual, user manual, and a detailed explanation of each type of module. Since many manuals for switches are written in English, users with poor English can consult with the supplier's engineers for specific configuration.
external factors
Due to the presence of viruses or hacking attacks, it is possible that a host sends a large number of data packets that do not meet the encapsulation rules to the connected port, causing the switch processor to be too busy, causing the data packets to be too late to forward, which in turn causes buffer overflow Package phenomenon. Another situation is the broadcast storm, which not only takes up a lot of network bandwidth, but also takes up a lot of CPU processing time. If the network is occupied by a large number of broadcast data packets for a long time, normal point-to-point communication cannot be performed normally, and the network speed will become slow or paralyzed.
A failure of a network card or a port may cause a broadcast storm. Since the switch can only divide the conflict domain, but not the broadcast domain (in the case of no VLAN division), when the number of broadcast packets accounts for 30% of the total communication, the transmission efficiency of the network will decrease significantly.
to sum up:
Due to the variety of switch failures, there are no fixed troubleshooting steps, and some failures often have a clear direction and can be identified at a glance. So it can only be analyzed according to the specific situation, of course, no matter what kind of failure is a difficult thing for a new network administrator, so if you want to be a master of troubleshooting the switch, you must do your daily work Accumulate experience in China, and carefully review the root cause and solution of each problem. Only in this way can we better complete the work of network management.
Packet loss
1. Is the voltage on the motherboard normal?
2. Whether the reset voltage is normal, the crystal oscillator is normal, and whether the reset chip body is bad
3. RJ-45 poor contact
4. The parts connected to the signal line and whether the chip is open
5. Is the chip body bad?
Port is disconnected
1. The above five steps must be checked
2. Defective filter body
Crash
1. The above five steps must be checked
2. Check if the main chip is bad
No power
1. Whether the power supply voltage is normal; Note: 5V
2. The above five steps must be checked
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