We may encounter network troubleshooting in actual projects. When encountering problems, we need to have a clear solution idea to stay calm and find the problem quickly. Let’s take a look.
1. Basic steps of network troubleshooting
For some experienced and sensitive engineers, it may be possible to find the problem quickly when troubleshooting network problems. But in fact, they also accumulate experience bit by bit and constantly summarize to do so quickly and efficiently. Therefore, for novices, you must not be too anxious and want to get it all done in one step. You should implement it step by step on the basics and accumulate slowly from the basics. Here you must first understand the five steps in network troubleshooting:
(1) Look at the symptoms first.
(2) List as many reasons as possible that cause the symptom.
(3) Then investigate each reason.
(4) Find the cause.
(5) Solve the problem.
The second step is very critical, because the more possible reasons found, the greater the success rate of troubleshooting.
II. Troubleshooting Cases
The sequential process is particularly important. It reflects a person’s logical thinking. Here, we use a simple example to familiarize ourselves with the specific steps:
As shown in the figure, the customer’s network topology diagram shows two APs connected to a POE switch, a gateway device connected to the POE switch, and a “cat” (modem) connected to the gateway. Now the customer can only receive network signals with his mobile phone, but cannot connect to the Internet.
First, we should follow a certain order when troubleshooting. Here, we use the order from bottom to top as an example.
When the mobile phone is connected to Wifi and there is no signal, we start from the AP and analyze it step by step:
AP:
(1) The POE switch does not supply power to the AP. After the AP is powered off, there is naturally no signal.
(2) In order to prevent freeloading, the SSID of the AP is hidden, which also leads to the inability to search for signals.
(3) AP performance. AP performance includes hardware and software. Hardware is divided into CPU, function, and antenna. If any of these parts has problems, AP performance may be poor and the signal cannot be found.
POE switch:
(1) Hardware failure leads to power supply problems. The AP has no power and therefore cannot find a signal.
(2) Network cable problems lead to connection problems.
(3) The speed or working mode of the switch port does not match. Sometimes when the traffic is too large, the speed is not enough, causing the AP to go offline and cannot find a signal. Gateway:
Gateway:
(1) Power failure. The POE switch does not supply power.
(2) Dial-up failure may be caused by incorrect username and password, or by the gateway’s own configuration, or by arrears of network fees.
After analyzing so many reasons, we can test them one by one and the problem can be easily solved. However, the customer’s current situation is that there is a signal but cannot access the Internet, so we have to go through it step by step from bottom to top. Connecting a mobile phone to the Internet can actually be roughly divided into two steps:
The first step is to scan the SSID for the mobile phone to access the Internet through wireless WiFi, that is, to find the signal name and encryption method, that is, to find the name of the WIFI and enter the password to join.
The second step is that the mobile phone tries to connect to the network:
(1) If the signal is unstable during the connection process, it may be a performance problem of the AP. The AP performance includes the software part + hardware part. It may also be caused by interference that causes the signal to be unstable.
(2) If the connection process shows that the IP is being obtained, it means that the mobile phone can access the AP, that is, the AP has power and is working properly, then the AP and POE switch are normal;
(3) If the IP can be successfully obtained, it means that the DHCP function of the gateway’s internal network part, that is, the dynamic allocation of IP addresses, is normal, and the gateway’s internal network part is also fine. However, the gateway’s external network part cannot be defined yet. Then only the gateway’s external network part to the “cat” is left. The signal can be received but the Internet cannot be accessed. Analysis of the cause may be that the network cable is plugged in incorrectly. It should be plugged into the gateway’s external network interface (Wan port). Otherwise, it cannot access the external network and naturally cannot access the Internet.
(4) Of course, there is another common fault, which is the problem with the network cable. If there is a problem in the production process of the network cable crystal head, it will also cause various network problems such as being unable to connect to the Internet.
