OSI reference model and troubleshooting experience

OSI reference model and troubleshooting

The bottom layer of the OSI reference model provides services for its upper layer. Therefore, troubleshooting should also be performed from the bottom layer to the upper layer.

If you are an IT support staff member of a company and an employee calls to say that the webpage cannot be opened, what should you do?

1) physical layer check. First, check whether the network connection is normal. Open the network connection of the client. If there is a Red Cross, as shown in 1-16, it indicates that the network cable is not properly connected and is a physical layer fault. If there is no Red Cross, and the connection is not always normal, double-click to open the "local connection status" dialog box, View "sent" and "received" packets, none of them can communicate normally. As shown in figure 1-17, you can check whether there is a problem with the contact between the network cable and the network card, and press the crystal head again with the network clamp.

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▲Figure 1-16 red forks ▲ Figure 1-17 receives a packet of 0

If the crystal head of the network cable is re-configured and the "sent" or "received" data packet is still 0, you can try to uninstall the NIC Driver first and then re-load the driver, the network failure caused by the NIC driver can be solved.

Right-click my computer and choose manage from the shortcut menu. On the Device Manager page, right-click the NIC, in the shortcut menu that appears, run the "Uninstall" command.

In the displayed confirm device deletion dialog box, click OK, as shown in figure 1-18.

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▲Figure 1-18 detach an Eni

You can see that the NIC Driver is deleted, and the local connection will no longer exist.

Then scan and detect the hardware changes again to reload the NIC driver. The local connection will appear again, as shown in figure 1-19.

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▲Figure 1-19 re-scan the hardware

2) data link layer troubleshooting. Ping the gateway. If it is timed out, it may be caused by network congestion or MAC address conflict. I have encountered a MAC address conflict and used VMWare to clone an operating system, the cloned operating system conflicts with the MAC address of the existing operating system.) ping the gateway fails, and check whether the port of the Computer-connected switch is in the correct VLAN.

3) network layer troubleshooting. First, check whether the IP address is correctly configured and conflict with other IP addresses. If the IP address and gateway configuration are incorrect, the Internet cannot be accessed, as shown in figure 1-20.

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▲Figure 1-20 IP address Error

4) Presentation Layer failure. For example, the webpage we open is garbled, that is, the presentation layer is faulty. As shown in figure 1-21, when you open the Baidu webpage, the page content is displayed normally. From 1 to 22, select "View"> "encoding"> "Others"> "Spanish ". As shown in figure 1-23, garbled characters appear when ie explains the web page in Spanish.

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▲Figure 1-21 the presentation layer is normal ▲ Figure 1-22 changes the IE Encoding

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▲Figure 1-23 presentation layer error

5) Application Layer faults. Check IE configurations. If the security level of IE is set to high, some web pages cannot run normally. If an incorrect proxy server is set or the Internet Explorer plug-in is installed, the web page cannot be opened.

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