IP address conflict caused by Dial-Up Adapter

There are three types of Internet access methods available for both laptop and common desktop computers. One is to use a common Modem for dialing the Internet (although this method is rare, however, in some computers installed with Windows 98 operating systems, the dial-up adapter is often automatically installed by the system), one is to use the broadband "cat" telephone line for broadband dial-up access, another method is to directly access the Internet through LAN access. However, if multiple network access methods are used for the same computer, it is easy for Internet users to confuse the dial-up adapter and nic adapter when setting TCP/IP parameters in the future, once the IP addresses of these adapters are set to the same, the computer may suffer an IP address conflict and thus cannot access the Internet normally. This type of network failure is relatively concealed, so it will often cause trouble for our network troubleshooting; no, the IP address conflict fault below this article, the reason is that the Internet users cannot tell how they access the Internet, and thus modify the IP address of the adapter randomly.

The financial department of the organization has an old computer that requires an old version of financial software. Therefore, the computer is installed on Windows 98, it has not been updated and upgraded to the Windows XP operating system until now. The computer is currently directly connected to the LAN of the Organization through the network card, and a fixed static IP address is set, the internal network speed of the access unit is quite good at ordinary times! However, my colleague from the Finance Department recently found out that their old computer had no access to the internal network of the Organization these two days, so I could help them solve the problem. For the author and other network administrators, faults are tasks. Without a few words, the author quickly brought together the wire measuring instrument, network cable, crystal head and clamp, and went straight to the network fault site with his colleagues. When I arrived at the finance department's office, I opened the old computer that could not access the Internet and tried to access the internal network of the organization. In fact, I did not have access to the LAN. There were many factors that caused the inability to access the network, I plan to start with external network connection to investigate the possible causes of the inability to access the Internet one by one.

First, I first tested the connectivity of the Network cables connected to the old computer with the wire tester at hand. The test results show that the network connection cable and the crystal head interface of the cable are all correct; secondly, I have observed the NIC device installed on the old computer. Through careful observation, it is found that the signal lamp of the NIC device is working normally, in addition, to prevent the NIC device from being faulty or not installed properly, I opened the system running dialog box and executed the "ping 127.0.0.1" string command, the result shows that the local address can also be successfully pinged, which at least proves that the network card has no hardware problems and that the driver installation of the network card device is normal.

Secondly, in order to check whether the network parameters of the computer system are improperly set, the author finds a laptop that can access the Internet normally, connect the computer to the network cable interface of the old computer in the Finance Department, and perform the internal network access test. The result shows that the Internet access speed is very fast, this indicates that the connection line from the finance department to the LAN data center switch must communicate normally (although the connectivity test was conducted on the network cable with a wire tester, the test results indicate that the line is in the connected state, however, line connectivity does not prove that the line communication is normal, because if the intermediate core line of the network connection cable is in the transient connection status, the results tested by the wire measuring instrument are also connected, but in fact, the transient network connection cable cannot transmit information normally ). Obviously, most of the "hosts" that make the old computer unable to access the Internet are due to problems with the old computer hardware or system, or incorrect network parameter settings of the computer system.

Considering that the system responds normally when other applications are running in the old computer system, the author estimates that the computer has no hardware problems, in most cases, the network parameters are not correctly set or the network components of the system are damaged. Therefore, the author then checks the network parameters with confidence. when checking the network parameters, the author clicks the "Start"/"set"/"network connection" command in sequence, in the network connection List window that opens, right-click the "local connection" icon and run the "properties" command from the shortcut menu that appears, go to the local connection property settings page, click the "General" tab page on the page, and select the "Internet Protocol (TCP/IP)" project on the page, click properties to open the TCP/IP property Setting dialog box. In this dialog box, I carefully checked the IP address and gateway address of the computer and found that everything is normal. Since there is no problem with the network parameter configuration of the computer, is it true that there is a problem with the computer system?

The old computer of the finance department installed Windows 98. The author carefully checked some program files automatically loaded during the system startup, as well as some currently running applications, no suspicious information is found, and the author also used the system detection program to conduct a comprehensive inspection of the entire computer system file, no flaws were found in the results. Now I am really worried, because the old computer in the finance department has installed special software and cannot re-install the system at will, which forces the author to find the specific reason why he cannot access the Internet. In desperation, I intend to re-allocate a new IP address for the computer. In this way, I quickly opened the interface for setting local connection properties, select "Internet Protocol (TCP/IP)" for the corresponding Nic adapter, and then replace a new IP address in the TCP/IP attribute Settings dialog box, click the "OK" button in the Setting Dialog Box. Then, the system running dialog box is opened and the ping command is used to test the new IP address, the results showed that the new IP address did not conflict with other addresses. Finally, the author conducted an Intranet access test in the old computer system. This time, the Internet access speed was very fast. At this point, I have found the reason why the old computer cannot access the Internet, that is, the IP address of the computer conflicts with other addresses, but how can the IP address of the computer conflict, I am still puzzled, because when I checked the IP addresses of other workstation in the same subnet as the old computer in the Finance Department one by one, I found that no IP address is the same as the IP address of the old computer in the finance department, how is this special IP address conflict? I once again went to the local connection property settings page and checked each component item on the "General" tab page. The results showed that the dial-up network adapter is installed by default on this computer, when I enter the TCP/IP attribute Setting dialog box of the dial-up network adapter, I find that the IP address of the adapter is exactly the same as the IP address of the NIC. Originally, the old computer of the finance department was installed with the Windows 98 operating system. However, whether the computer is connected to a modem or not, the dial-up network adapter is usually installed by default; however, the dial-up network adapter generally does not need to be assigned a fixed IP address. You only need to use the default parameter configuration. We do not need to configure it. When a colleague from the finance department of the computer finds that the network speed is not fast, he tries to modify the network parameters by himself. But he does not know what the dial-up network adapter and network adapter are, therefore, the parameters of the dial-up network adapter were modified, resulting in a conflict between the NIC address and the address of the dial-up network adapter, which eventually caused the failure of the old computer in the finance department to access the Internet. When I change a new IP address for the NIC, the IP address conflict will automatically disappear, and the Internet access speed of the old computer will return to normal.

Summing up the troubleshooting process above, I think that I am not aware of the existence of the dial-up adapter in advance, and will also "Induce" ip address conflict faults, this leads to more detours in the process of eliminating network faults! Considering that there are few ways to access the Internet by dialing through a common Modem, I suggest that you use Windows 98 to access the Internet in the future, it is best to delete useless dial-up network adapter devices, because they will not only "Induce" ip address conflicts, but also affect normal internet access speed!