Troubleshooting and Analysis of packet loss in Internet cafes or abnormal network logon failures

One day, an internet cafe user called our telecom operator to report a fault and asked us to solve the problem. The reason was that the technical staff of the Internet cafe Network Administrator analyzed that the fault was definitely caused by the telecom terminal. After receiving an obstacle message, I checked the information of this Internet cafe and found that the Internet cafe had just been opened for less than a month.

So I asked him first: What is the fault? He replied to me: frequent disconnection or even network access failures.

I asked him; you have pinged the gateway or the IP address, he said yes, all the packets were dropped and, in severe cases, He pinged the IP address 192.168.1.1 from the Intranet gateway and the IP address 62.62.62.62 from the telecom isp and the telecom DNS 100.100.100.100 continuously within three minutes. I originally wanted to ping the layer-3 Switch of China Telecom to check whether the packet is dropped. However, because the user's route cannot be pinged and the IP address cannot be found, I personally went to the Internet cafe, because I went to the client to perform network debugging two months ago. Its Internet cafe covers an area of more than seven hundred square meters and has 120 machines. It is equipped with a dedicated data center and is equipped with switches and servers.

I took my laptop to its dedicated data center. The first step was to test the telecom terminal, connect the portable device to the photoelectric converter, configure the portable device with an IP address, ping the telecom DNS, and then call the data center, ask the IDC room personnel to ping the portable ip address from the switch in the IDC room, that is, the ip address used by the internet cafe. The test will take 10 minutes. There is no packet loss at all. It can be seen that this fault is definitely not caused by the telecom end.

So focus on the Intranet. There is no other way, so we have to perform a step-by-step test: to restore the user's route to the network when the original user can access the Internet), because I can see that there are four LAN ports on the route, connect the device to one of the unused LAN ports of the route, and configure 192.168.1.1 in the Intranet of the Internet cafe as the ip address 192.168.1.244 of the gateway. Then, ping the DNS, the same is true.

Then we can connect to the vswitch because there are 120 computers in the internet cafe and six 24-port switches, one of which serves as the total switch, and the other five switches are connected to the vswitch.) The ping is still normal, so I connected the portable devices to other sub-switches, and the test results were normal without any packet loss.

This is silly. There is no problem with the device... What is the problem between the network cable and the computer Nic ????

In addition to these two possibilities, there is little other possibility, so he took the network cable from the sub-host that he just tested and said would be dropped to my portable, test .. Day .. The package is actually dropped, and it is very serious. Almost one packet is dropped for every five packages. In order to fully identify the network cable failure, I connected the network cable that I brought to the test to the switch port where the network cable was located for testing. The result was normal and the package was not dropped. This is definitely a problem with the network line, so I looked at the west and accidentally found that the distance from the switch to work is too long. I carefully measured the distance, and it must be more than 100 meters. The transmission distance of twisted pair wires is generally no more than 100 meters, and the actual transmission distance is about 95 meters. Internet cafe owners only provide dedicated data centers to pursue high-end services, but ignore the limit of network cable transmission distance. In addition, because the user connects all the computers farthest from the data center to the total switch, serious broadcast occurs on the total switch, resulting in frequent packet loss in Internet cafes.

Suggested solution: relocate the switch location or buy another switch to connect these computers far away from the data center.

Summary: During Integrated Wiring, You must select the switch location. The center switch is best placed in the center of the Internet cafe. The following switches should also be placed in the center of the connected computer. The first is to save the network cable, and the second is to make the network reach the Optimal Transmission status.

Experience Summary: you must first understand the networking of obstacles during the investigation; otherwise, there will be a lot of mistakes. This experience has helped me a lot of work groups in the future.

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