Eliminate "connectionless" faults

If the local network connection is normal, by default, we can see the specific connection speed from the local connection icon in the system tray area, on the contrary, we often observe the local connection icon status at the system tray area to determine whether the current network connection is normal.

During the actual network access process, we often encounter a yellow exclamation mark on the local connection icon, and a prompt indicating that the local connection is not connected or the local connection is restricted, so why does this fault prompt appear on the local connection icon at the system tray area?

How can we take measures to cope with this problem so as to receive the non-connection prompt displayed on the local connection icon? Now, this article will make contributions to the specific fault phenomena and troubleshooting process from a practical perspective for your reference by IT168 readers!

Fault symptom

Yesterday afternoon, the author received an emergency request from the staff in the room next to him when he arrived at the office and his ass was not hot. They said they were preparing to download a workbook from the LAN server for urgent use, however, they couldn't access the content on the LAN server even though they had no choice but to seek help from the author. After receiving a request for help, I quickly arrived at the scene of the accident in three steps and carefully checked the workstation that could not access the LAN server, the result shows a yellow exclamation mark on the local connection icon in the system tray area of the workstation. When you move the mouse over the local connection icon, an error message is displayed, such as local connection failure or local connection restriction.

Fault Exploration

Considering that the workstations in the LAN are obtained through the address automatically assigned by the DHCP server, when I see an error message, such as local no connection or local connection restrictions, the fault must be caused by a failure of applying IP addresses from the DHCP server. To check whether the workstation has obtained an IP address, I clicked the start button on the system desktop of the workstation and executed the run command from the Start Menu, open the run dialog box for the system, enter the cmd string command in it, click OK, switch the system interface to the MS-DOS work window; In the doscommand line of the window, enter the string command "ipconfig/all" and click the Enter key. The result information that appears later shows that the IP address used by the workstation is "169.254.0.8" 1 ), the result shows that the local workstation does not obtain the correct IP address from the lan dhcp server, because when the workstation fails to apply for an IP address from the DHCP server several times in a row, the system automatically goes from 169.254.0.1 ~ Assign an IP address to the local workstation within the range of 169.254.255.254. What causes the local workstation to fail to obtain a valid IP address from the DHCP server?

Is there a problem with the network cable connecting to this workstation? To verify my conjecture, I pulled out the network cables connected to the workstation and inserted them to my laptop, the result shows that a laptop with a static IP Address can normally access resources on the LAN server, which indicates that the network cable connecting to the workstation is normal. Next, I suspect that the DHCP server in the LAN is faulty. Therefore, based on this idea, I log on to the LAN server system as a super administrator, the DHCP server settings are carefully checked, but no suspicious information is found.

Will it be because the address lease term in the DHCP server has expired, and the workstation cannot apply for an IP address from the DHCP server? According to this analysis, the author opens the console window of the DHCP server, enters the scope attribute setting interface of the DHCP server, and finds the "address lease" setting option, delete the target workstation records that cannot be applied for an IP address, and refresh the records again. Next, return to the target workstation system that cannot apply for an IP address, and click "start"/"run". In the displayed system running dialog box, enter the string command "ipconfig/release" and click "OK" to release the IP address occupied by the workstation. Then, in the system running dialog box, run the "ipconfig/renew" string command, so that the local workstation can apply for an IP address from the lan dhcp server again, the faulty workstation system still prompts errors such as local no connection or local connection restrictions.

However, the author found that when the "ipconfig/renew" string command is executed in the faulty workstation, the system of the workstation actually displays a message similar to "RPC System Service unavailable, is it caused by RPC System Service errors such as local no connection or local connection restrictions? At this time, I also believed it was trustworthy and did not believe it was lost, so I quickly right-clicked the "my computer" icon on the desktop of the local workstation system, run the "manage" command from the shortcut menu to open the computer management window of the corresponding workstation. In the left-side area of the Management window, I expanded the "service and application"/"service" projects with the mouse, and in the List area on the right of the corresponding "service" project, the author finds "Remote Procedure Call (RPC)", right-click the service option, and click the "attribute" command from the shortcut menu that appears, open the System Service property setting interface. On the "General" tab page of the interface, I can see that the service is in the stopped status at the current time; so I click the "Start" button here, set the service to "automatic" in the "Start type" setting item, and click "OK. I thought this time it would be able to solve failures such as no local connection or local connection restrictions. However, when I try to reconnect to the LAN server, the system still cannot obtain the IP address from the DHCP server.

At this point, I really don't know how to troubleshoot, will it be a problem with the NIC device of the faulty workstation? When I was about to exit the System Service List window and disable the system Nic device, I accidentally saw that the "DHCP Client" service in the System Service List window was also in the stopped status, from the service name, I think it is very likely that the unexpected stop of this service causes the workstation to be unable to obtain the IP address from the DHCP server. According to this inference, I quickly double-click the "DHCP Client" service in the System Service List window with the mouse, as shown in service attribute setting page 2.) Click the "Start" button, restart the "DHCP Client" service and set the Service Startup type to "automatic" to ensure that the service can be started along with the system in the future. After the "DHCP Client" service is re-enabled, the system running dialog box of the faulty workstation is opened again, and the "ipconfig/renew" string command is re-executed. Hey, this time, the workstation was able to obtain the IP address from the DHCP server. When I tried to access the resources on the LAN server again, the workstation system no longer prompts that the connection was unavailable, in addition, in the tray area of the workstation system, I found that the yellow exclamation point on the local connection icon also disappears. When I move the mouse over the local connection icon, the error message, such as local connection failure or local connection restriction, is also absent, indicating that the fault mentioned above has been successfully removed.

Fault Summary

Although the above fault has been successfully solved, I am still wondering the cause of the above fault. By default, the workstation system will automatically enable "Remote Procedure Call (RPC) "Service and" DHCP Client "service, why are these system services of the faulty workstation stopped? At first, I thought it was a network virus. Later, my colleague next door told me that he recently downloaded and installed Super Rabbit from the Internet to improve the running speed of the workstation, this application is used to automatically optimize the workstation system. After the optimization operation, the running speed of the workstation is significantly improved, however, when trying to access resources on the LAN server, the above fault occurs. Obviously, the above fault is caused by the unexpected suspension of system-related services by the optimization software. Therefore, when we optimize the workstation system in the future, we should use as few automatic optimization functions as possible, to prevent the failure of the workstation system.

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