Network Net-surfing caused by broken cable

The author has built a company's network center, which is responsible for the exchange of information between the branches of the city, to achieve the sharing of resources among the branches. All branches through the DDN line through the router with TCP/IP protocol and host connection.

Network Center Ethernet is divided into two network segments: 192. 168. 1. X and 192. 168 2. X, hereinafter referred to as network Segment 1 and network Segment 2. One of the production machines and development machines used for processing the information of the subsidiary company, and the other two routers which communicate with each branch in remote communication. There are other computers for development and monitoring. Network Segment 2 has more than one computer, the development and commissioning of the customer end. The development machine and a computer are connected to two network segments at the same time.

One day, the network found that each branch of the data transmission is not normal, and Dan is the use of TCP/IP protocol and the center of the branch to connect the information is not normal. After a period of time to find that these branches of the data communication room can not be carried out, after a few days efforts or can not be resolved, but the normal operation of the company must use the network, so to the author for help.

　　 Diagnostics Process

The author rushed to the scene, carefully observe the phenomenon of failure, basically can be judged to be caused by communication problems because whether in the network Segment 1 or in the network Segment 2 on the connection between the computer and the production machine has been intermittent phenomenon. The connection between the console and the host, which is directly connected to the production machine (not over Ethernet), is fine. From the main console, no exceptions were found in either memory footprint or CPU utilization. Also, no exceptions were found on all processes on the production machine. It appears that the problem is on Ethernet.

Since two network segments and host connections have problems, is not two network segments have problems? Ping the command test with the most basic test method in the TCP/IP protocol, it turns out that there is no problem with the connections between the computers in segment 2, and network Segment 1, which is not just a break-through ping between the computers and the production machines, but also a ping between the other computers. The problem must be in net segment 1. The network Segment 2 to the production machine communication has the problem, is because from the network segment 2 to the production machine must pass through the network segment 1.

What is wrong with the place? Network Segment 1 Since all the computers are connected through a hub, then the probability of the hub problem is very large, so first of all to check the hub. After checking, H U B is working in a normal state, but the LED state of the twisted pair in a port is abnormal; is a flashing red light (the LEDs on each port should be green when connected to a functioning computer). Unplug the twisted-pair cable in this port, and the communication between the computers in segment 1 is restored to normal.

This is better to do, the author of "Follow Up" along this line to troubleshoot, the problem of this line connected to the computer is the network Segment 1. It was verified that the user who used the computer would just turn on the computer when the problem occurred.

Could it be the problem of this computer? The computer has not been changed since it was set up, and the problem should not be on the software. Is the NIC out of the question? The author uses another good network card to replace the original network card in the computer, the problem still exists, indicating that the problem is not out of the network card. The author brought another computer connected to this network cable, or not properly connected to the Internet, it seems that the problem is mostly in network cable. According to past experience, the problem of network cable more appear in the Crystal Head, Crystal Head if the pressure is not good, the number of pull plug is easy to go wrong. I simply cut the original crystal head on both sides of the line to do it again. Unexpectedly, the problem still exists. So the problem can only be in the middle of the line. The author from a side along the twisted-pair line check, finally found the root of the problem, the original line was a cabinet pressure. Because the cabinet is very heavy, the pressure of the time is relatively long, so that the twisted pair of the outer skin, resulting in twisted-pair line mix. After replacing the new twisted pair, troubleshoot the problem.

　　 excluding Experience

As the hub connected to the LAN using CSMA/CD (that is, with the collision detection of carrier interception multi-channel access) technology for information transmission, so when the network cable mixed line, the signal can not be normal transmission and generate error signals, even the network section is full of error signals, so that normal signals can not be smoothly transmitted, Causes network traffic to be intermittent. From this example we can get some experience: in the Ethernet, especially in the hub-connected shared Ethernet, any point in the network problems, can cause the entire network is not normal to paralysis. Although the network cable is connected between the hub and a single computer, it may affect the entire web if there is a problem.