Handle lan network faults

Half a year ago, a group of original IBM brand-name machines were purchased in the LAN of the Organization, which were configured as P4 2.4 GB, 256 mb ddr memory, 80 GB hard disk, and a set of original Windows XP systems, overall, it seems quite upscale. I was lucky enough to have one, and I had to run it for more than half a year in the LAN, so I had nothing to worry about. I don't want to see a "trivial" network fault during the recent operation, but I 've been tossing around for the whole morning, and I 've also learned the taste of "Seeking farther and farther.

Fault symptom

One morning, the Windows XP system started normally. After the Windows XP system started normally, we opened the Internet Explorer browser and entered the Sina website to view the news reports of the day, but we found that the Windows in IE were empty. Check carefully and find that the IE prompt is "DNS error", and refresh several times is like this-it seems that there is a problem with the network.

Troubleshooting

First of all, I suspect that the DNS server is used, so I quickly started the system's "Control Panel> network connection> Network Properties" menu and clicked the TCP/IP protocol, check the DNS list and find that the configuration is correct. call the hotline of the local ISP data center. The answer is surprisingly positive: DNS No Problem! Is my network or system faulty?

Probably because of the recent flood of viruses, I thought about whether my computer had been infected with viruses or Trojans. So I immediately took out the latest anti-virus software and firewall software, and I was chasing them for a while, the result is no virus, and the website still cannot be accessed.

At this time, I began to suspect that there was a problem with the machine's sub-network configuration, so I clicked the "run" item in the "Start" menu, entered cmd and press enter to enter the doscommand line window, enter "Ipconfig/all" and press Enter. At this time, the NIC status of the local machine, including the MAC address, IP address, address mask, gateway address, DNS server, and other key parameters are listed. I did not find any errors. It seems that the problem is not software, but hardware is in trouble.

I accidentally checked the network status of the icon in the lower right corner of the desktop and found that the number of sent/received packets on the network was actually 0! How is this possible? Is the network card not working? However, the connectivity status prompt in the lower-right corner of the network clearly shows the "10 m speed connection" prompt, And I typed "Ping 127.0.0.1" in the "run" window for loop testing, it also reports that everything is normal. So I naturally excluded the possibility of NIC failure.

I turned my finger at the low-cost and out-of-service switch in the LAN. Let's see it. Hey! As expected, the switch port light connecting to my desktop computer is not on! Is this the root cause of the problem? However, I would like to ask my colleagues if they say that the Internet is normal, which means that this elderly switch is still healthy and has a long life. Then, I will switch the switch ports used by my colleagues so that they can still access the Internet normally, this indicates that there is no problem with the interface connected to the sub-host on the switch, and the only hope is to connect the network cable between the NIC and the switch.

Because the network cable has been normally connected to the Internet at ordinary times, there is no doubt about its wiring pairing. The only possibility is that the device may be aging and frequent plugging, resulting in poor contact. I borrowed a network cable connectivity Tester for a test, close to m of good connectivity almost made me angry! Looking at the almost Solidified "0" packet sending and receiving in the network status, I opened the chassis with the idea of trying it out, and looked at the NIC solidified on the motherboard, in a mess, I knocked it twice with my hands-I didn't expect a miracle to happen! The number of packets sent and received in the network status changes from "0" to "10", "90", "200 "...... With the IE browser opened, familiar websites suddenly caught eye! It turns out that the source of the fault is the least important network card! It is strongly bonded with the motherboard, causing the software to report everything normal during testing, and its slight loose at the network interface makes the network physically completely isolated, this led to the switch display of the connectivity indicator light off, and the packet sending and receiving of course cannot be talked about!

Fault experience

Although the problem was finally solved, a precious morning has passed. I have some experiences. Testing of network faults is often complicated. Compared with some system software and hardware faults, it still has a space span to overcome. When parsing, we should adopt the principle of being soft and hard, from near to far, and use one-by-one exclusion and Replacement Methods for troubleshooting. The method of looking for the source of the fault is obviously far-fetched, even if the problem is solved. In a word, it is: do not ignore the small faults that are close at hand, because they may be the source of the fault!