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IP address conflict caused by 2SOHO routers 2

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СообщениеДобавлено: Чт Дек 07, 2017 7:11 am    Заголовок сообщения: IP address conflict caused by 2SOHO routers 2 Ответить с цитатой

{<p>The result of the command on the is only part of the content of the CAM table in 3750. By displaying the results, we found that the device with the IP address is is connected to the network through 3750 Gi1/0/13 ports. Then we find the office room number corresponding to the port on the distribution rack connected to Huawei Ar550 Series 8 Port Agile Gateways Ar550 8Fe D H Cisco 3750 Gi1/0/13 by connecting the 3750 Gi1/0/13 port and the network jumper in the distribution frame of the computer room. As a result, we found a D-Link router in that office. The connection diagram of the router in the network is shown in Figure 2. Figure 2 </p>
<p> address conflict caused by router connection graph </p>
<p> 4, then in connection with D-Link router in PC �� command line �� &ldquo ipconfig /all�� implementation; command, to find the gateway address of D-Link router is, then the PC in the browser address bar enter, Web configuration management interface enter the D- Link. The general management configuration of SOHO routers is entered in this way. Finally, an error configuration that causes the network IP address conflict is found in the Web page of D-Link, as shown in Figure 3. </p>
<p> Diagram 3 D-Link router's error set </p>
<p> 5, that is, the static address is also configured on this device, resulting in network failure. To eliminate conflicts, as long as &ldquo is in Web management interface, Internet connection �� �� > �� Internet connection type �� &ldquo is selected; dynamic �� then click save, as shown in Figure 4. </p>
<p> Figure 4 excludes the correct setting of IP address conflicts. </p>
<p> case summary: </p>
<p> 1 and SOHO routers generally use two important technologies: PAT and DHCP server functions. </p>
<p> (1) PAT (port address conversion). One of the three major rules in NAT and the other two are static NAT (Static NAT) and dynamic NAT (Dynamic NAT). PAT is sometimes called dynamic multiplexed NAT, Cisco Original Catalyst 3560 Ethernet Network Switch Ws C3560 24Ps Swhich changes the source port of outgoing packets, and performs port conversion and uses port multiplexing. All hosts in the internal network can share a legitimate external IP address to achieve access to Internet, which can maximize the saving of IP address resources. At the same time, you can also hide all the hosts within the network and effectively avoid attacks from Internet. Therefore, PAT rules are the most used in the network at present. </p>
<p> (2) DHCP server functionality. When a computer first connects to a DHCP server network, there is no IP data set on the client, that is, there is no IP address, DNS and default gateway address. At that time, it will send a DHCP Discover packet to the network. Because the client doesn't know which network it belongs to, the source address of the packet is, and the destination address is, which is broadcast to the network. When the client sends the first DHCP Discover packet, if there is no response in a second, there will be second DHCP Discover packets broadcast. If there is no response, the client will have four DHCP Discover packet broadcasts. </p>
<p> will make a response in the DHCP server receives a DHCP Discover message found after it from nonrental IP address to select one assigned to the DHCP client, and according to the original carrying customer DHCP Discover packets for MAC address, provides a message to the client sends a IP address, DNS contains rental and default gateway the address of the DHCP Offer. </p>
<p> 2, in-depth analysis of the failure. Through the analysis of the working principle of DHCP, found that when the network router SOHO configuration of the static address, if have PC access to the network, DHCP is assigned to the PC IP address, because it does not know that has been in the network configuration, so it is in accordance with the IP address of the distribution of the order, in front of the address has been allocated, naturally assigns the to the new PC in the network, resulting in a conflict fault. </p>
<p> 3, CAM table and ARP table. An address table for two layer switching is maintained on the two and three layer switches, that is, the CAM table. This table is the corresponding relationship between the MAC address and the switch outgoing interface. So when receiving an Ethernet frame, switches determine if the data frame is sent to their own, according to the data frame to the destination MAC address query CAM table, if you can find the MAC address corresponding to the entries in the CAM table, according to the results of the query, is usually a list of interfaces. The data frame is forwarded on the corresponding interface. If it cannot be found, the data frame is broadcast to all ports. </p>
<p> maintains a ARP table on the three tier devices in the network, which is used to find the IP address and MAC address of the client or server connected to the three tier device. As long as you know one of the MAC addresses and IP addresses, you can know the other one. Usually using these two 1900 Series 2 Port Gigabyte Integrated Security Van Router Cisco1921 Sec K9 tables in the network can quickly determine the specific location of a device. </p>
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