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IP address conflict caused by SOHO routers 1
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Сообщение IP address conflict caused by SOHO routers 1 
SOHO routers, a lot of units are in use, the common brands are Cisco, H3C, TP-Link, D-Link and so on. SOHO Huawei Optix Osn 500 Ethernet Board have routing, switching, and some wireless functions. With the increase in the number of SOHO routers used in the network, more and more related failures are brought. This article, through an example, gives you a better understanding of the function and use of SOHO routers.

Figure 1 network structure diagram

1, the company network structure

unit network structure diagram as shown in Figure 1. In order to ensure the stability and redundancy of important equipment, the core layer switch uses two Cisco 4506 and connects through the Trunk line. A number of Cisco 3750 switches are used in the access layer. For the sake of simplicity, only two sets are drawn. Some important servers are connected to the core switch, such as DHCP, E-MAIL server, WEB server and so on. The deployment of the unit IP address is the address of the private 172 network segment of the B class. The IP address of the DHCP server is 172.16.1.1. Cisco 4506 and Cisco 3750 are also Trunk connections. 4506 through fiber connections to the Internet.

two, during the failure process,

unit recruited an employee to connect its PC to the network, but it always prompted &ldquo when accessing. The IP address conflicts with other systems on the network &rdquo. Later, the network cable on the computer network card was pulled out and reinserted to get the computer to get the IP address from the DHCP server again, but the failure was still. Then, in the &ldquo of the computer, User Side Ont Modem Huawei Modem Hg8040 command line &rdquo, &ldquo, ipconfig /release&rdquo, command release the IP address on the network card, then execute the command &ldquo, ipconfig /renew&rdquo, let the computer retrieve the address again, but the system still prompts the address conflict.

then, we are in “ the command line ” execute “ ipconfig /all” find the IP address obtained by the computer is 172.16.11.34/24. Since the address conflicts are prompted, there is a certain device that is sure to use the 172.16.11.34 address in the network. In order to verify this judgement, we first turn off the computer that is newly connected to the network, then execute &ldquo, Ping 172.16.11.34&rdquo and command on the network, and the result is Ping as expected. This proves that one of the devices in the network is using 172.16.11.34. The next thing is to find out the device.

three, troubleshooting steps

1, according to the design of the original network, the client automatically obtains IP address from the DHCP server, that is, the IP address used by the client is not fixed. When the IP address rented from the DHCP server expires, the IP address will change if you re - get it again. But in the same VLAN network, the use of 172.16.11.34/24 address, there may be more than 100 PC, the total can not be checked by one by one, the efficiency is too low.

2, and finally we put the way of finding 172.16.11.34/24 on Cisco 4506 and Cisco 3750, because there are ARP tables in all three switches, but there are two layers CAM tables corresponding to host MAC address and switch interface in the two level and the three level switch. With these two tables, it is easy to find a device that corresponds to the IP address. First, we execute the following commands in Cisco 4506:

Cisco-4506#show ARP include 172.16.11.34Protocol | Address Age (min) Hardware Addr Type InterfaceInternet 172.16.11.34 8 00d1.8624.1a02 ARPA Vlan11

the above command displays the results in table 4506 is only part of ARP content. Through it, you can find the MAC address 00d1.8624.1a02 corresponding to the IP address 172.16.11.34.

3, because each computer's Cisco Router Cisco1921 Sec K9 1900 Series MAC address is the only global, so we go on Cisco 3750 performs the following command:

Cisco-3750#show mac-address-table dynamic include Address Table-------------------------------------------Vlan Mac | 00d1.8624.1a02Mac Address Type Ports----------------------------11 00d1.8624.1a02 DYNAMIC Gi1/0/13

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