How to solve the problem of IP conflict in LAN

As we all know, when using TCP/IP protocol on Internet and Intranet networks, each host must have an independent IP address, and the host with IP address can communicate with other hosts on the network, so I won't go into details about this. But I believe you have encountered IP address conflicts, at least I have. On that day, I found that my network client could not work normally. As long as the power is turned on, the prompt of address conflict will appear frequently. But it was fine the day before, and no new settings have been made! After careful consideration, the only difference is that the personnel in the computer room have been adjusted. Maybe the IP address set by the newcomer conflicts with mine, which is exactly what I asked. If he and I hadn't turned on the machine, I wouldn't have found the problem! It can be seen that even if there are conflicting machines on the network, sometimes problems cannot be found in time. Only when conflicting network clients are turned on at the same time can they be exposed. It seems to be still hidden. Let me reveal the secret to you. There are several main reasons for IP conflicts. Some people may not know TCP/IP, and don't know how to set the parameters \IP address \, \ subnet mask \ and \ default gateway \ (don't laugh at them, after all, we have come step by step). Sometimes the parameter information they get may not be told by the administrator, or it may be correct at first, and then it is accidentally modified. Even if the administrator gives the correct parameter data, we will always make mistakes, because the tiger still dozes off, and the parameter input error is inevitable. In addition, when someone repairs and debugs the machine, the maintenance personnel may use some temporary IP addresses, and if they forget to change them, there may be conflicts. Another situation we hate is that someone steals someone else's IP address. After receiving the conflict report, there are several things to do. First, determine the VLAN where the conflict occurs. Through the vlan definition of IP planning and the conflicting IP address, the network segment where the conflicting address is located can be found. This is very important to successfully find the MAC address of the network card, because some network commands cannot be accessed across network segments. Let's isolate the client from the network first and let the microcomputer with illegal IP address run, so that we have a chance to find it. Then do some simple tests on the network. The main commands are ping command and arp command. Use the ping command, assuming that the conflicting IP address is 146. 127.35.3. In the msdos window, the command format is as follows: C:\ \ Widow \ \ > ping146.127.35.3: bytes = 37.35.3. 127.35.3: bytes = 32time reply from146.127.35.3: bytes = 32time ARP-a Internet address/physical address/type Before searching, we must first find out the switch positions in VLAN, find out the IP addresses of these switches, and use the switch addresses to access the network management information of the switches. We have to do the following work: first, start the browser on the network management machine, enter the IP address of the switch, enter the user name and password after seeing the prompted login information, and then enter the \MAC address table \ option. In this way, you can get the following information: index /MAC address/learning on the port/learning method/filtering packets to this address 2 00: 00: 8 1: 65: C3: A0n/ A static no 3 00: 00: A2: F7: C3: E4 25 dynamic no Haha, you can see the fourth item in the index, which is what we are looking for. According to the comprehensive wiring data, the physical position of the corresponding information point can be accurately found, and then the position of the connected microcomputer can be located. Of course, it may not be so convenient for you to solve this problem. You often need to find many switches, and finally you may be relieved to find the MAC address. When VLAN has a large number of switches, we need to find them one by one. If the port of a switch has a downlink switch, in this case, because the switch supports multiple MAC addresses, the record of the lower MAC will be saved in the upper MAC table, so it is necessary to find the upper MAC table first, and then find the lower switch after determining the specific location, thus greatly narrowing the search scope. In the local area network, we often encounter this problem of IP address conflict, especially when the user scale is very large, which will make the search more and more difficult, so the network administrator must act cautiously and finally solve it. At present, there are two schemes, one is to use dynamic IP address allocation (DHCP) and the other is to use static address allocation, but the management of MAC addresses must be strengthened. The biggest advantage of using dynamic IP address assignment (DHCP) is that the configuration of the client network is very simple, so that we can even establish our own network connection without the help and intervention of the administrator. However, because the IP address is dynamically allocated, the network administrator cannot identify the identity of the customer from the IP address, and the corresponding IP layer management will not play a role. In addition, it also has a disadvantage, using dynamic IP address allocation also needs to set up additional DHCP servers. If static IP address allocation is adopted, reasonable IP address planning can be carried out for each department first, so as to facilitate tracking management at the third level. At the same time, if we strengthen the management of MAC addresses, this problem can be effectively solved. Let's talk about some topics other than technology In fact, it is essential for the normal operation and corresponding management of the network. Remember, when we are networking, it is best to establish an information file of IP address and MAC address, so that we can implement strict management and registration system for LAN customers from beginning to end, and save the information of each user's IP address, MAC address, uplink port, physical location and user identity in the database of network management. Think about it. Knowing the MAC address of illegal users, if we can search from the administrator database, we can find the culprit immediately, so how much valuable time can be saved!