Internal and external network connection failure

Mr. Wang, who is responsible for the development and research of e-government systems, often communicates and shares files with colleagues in other brother organizations on the Internet. However, the Internet access speed on the LAN is too slow, communication with colleagues online and shared files are often interrupted. Therefore, Mr. Smith had to report to the Organization's leadership that he had applied to install the ADSL dial-up Internet line, it is intended to be used in case of shared files with large transmission capacity or slow local network access speed. Recently, when Mr. Wang connected his new laptop to the LAN to access the Internet, he found that the Internet access through the ADSL dial-up line could work normally, while accessing the Internet through the LAN, but cannot access the network content. In the face of the internal network failure of the external network, how can Mr. Wang perform both internal and external repairs to make the internal network accessible?

Fault Analysis: Is there a problem with the switch port?

Because the laptop can access external network content through the ADSL dial-up Internet line, Mr. Wang believes that the NIC equipment of the laptop should work normally and the network cables connected to the laptop should be in a smooth state, in addition, the system where the laptop is located is running normally. This requires you to start from the vswitch port used when the laptop is connected to the Intranet and the corresponding network connection settings, to find out why the Intranet cannot access the Internet.

To prevent problems with the switch ports used by the laptop to connect to the Intranet, Mr. Wang specially connected the laptop to another switch port that has been tested and is working properly, however, the laptop cannot access the Internet through the Intranet. Mr. Wang was uneasy and restarted the switch system to eliminate the potential hidden faults of the switch. However, such efforts did not take effect.

Obviously, this internal network failure has nothing to do with the switch equipment of the local area network. It seems that most of the problems are caused by the Intranet parameter settings of the laptop. Wang knows that the lan must verify the parameters of each online workstation. Only when the parameters are correctly set can the workstation access the content of the external network through the LAN, the newly purchased laptop may be unable to access the intranet due to improper Internet access parameter settings. With this in mind, Mr. Wang first opens the TCP/IP attribute setting interface on the workstation that can access the Internet, record the main internet parameters, such as IP addresses, Gateway Addresses, subnet masks, and DNS server addresses one by one. Then, re-enter the laptop system and record the parameters, mr. Wang also checked whether the laptop's Internet parameters were correctly set. The results showed that all the parameters were normal. This showed that the failure of the laptop's access to the Intranet had nothing to do with the network settings.

Without a clue, Mr. Wang's eyes accidentally fell onto the paper just used to record the Internet parameters. He found that there was a DHCP server in the local LAN, and each workstation in the LAN did not need to specify an IP address, if you enable the "automatically obtain IP addresses" function, you can obtain the appropriate IP address from the DHCP server to access the LAN. Because the "automatically obtain IP Address" function has been enabled for the laptop, will it be because the DHCP server has not automatically assigned a suitable IP address, which will make the laptop unable to access the lan? To verify that the laptop gets a proper IP address from the DHCP server, Mr. Smith switches the system to the MS-DOS window in his laptop and enters the "ipconfig/all" command in the command line of the window, after clicking the Enter key, he finds that the IP address of his laptop has changed to "169.254.56.66". In fact, the network address of the LAN is "10.176.6.0 ", obviously, the laptop does not get a proper IP address from the DHCP server, so the laptop naturally cannot access the LAN.

Troubleshooting: DHCP server configuration

Although he found the cause of the inability of his laptop to access the LAN, he was puzzled by the reason why the DHCP server could correctly assign IP addresses to other workstations in the LAN, but I cannot assign an IP address to my laptop. Is there a problem with the network connection between my laptop and the DHCP server? As a result, Mr. Wang used the Ping command to test the IP address of the DHCP server in the text box running on the laptop. The result showed that the DHCP server could be pinged normally. Obviously, the problem lies in the DHCP server's own settings.

Considering that only a few workstations in the LAN cannot obtain the correct IP address, Mr. Smith judges what restrictions are adopted by the DHCP server, for example, specifying the IP address range, or the policy of binding the IP address to the physical address of the network card is enabled. in order to check whether your judgment is correct, Mr. Wang immediately came to the DHCP server site and carefully checked the setting parameters of the server, the results show that the server limits the IP address range and the number of valid IP addresses in the range is smaller than the number of workstations in the LAN, obviously, the IP address pool of the DHCP server is not allocated enough, which leads to the failure of the laptop to obtain the appropriate IP address from the DHCP server. After appropriately expanding the IP address range, the DHCP server quickly assigned a valid IP address to the laptop so that the laptop can access the LAN immediately.