Syngress - Eleventh Hour Network+ Exam N10-004 Study Guide (11 ...

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164 CHAPTER 10 Network Troubleshooting Sending Computer Application Receiving Computer Application Presentation Presentation Session Session Transport Transport Network Network Data Link Data Link Physical Physical Network Media FIGURE 10.1 Each layer of the OSI model communicates with the corresponding layer DID YOU KNOW In general, you can break down the items necessary to troubleshoot a network issue into the following seven steps: 1. Identify the symptoms and potential causes Determine exactly what’s wrong, and ensure that there is actually a problem. Ask questions and get very specific details on the issue. Having as much information as possible at hand will help you determine the potential causes of an issue. 2. Identify the affected area Is only one user having trouble, or is there an issue that’s affecting an entire subnet or your entire network 3. Establish what has changed Attempt to discover if anything has changed that may have caused the issue to surface. Knowing what has changed on a network will usually give you a good starting point from which you can begin the troubleshooting process. 4. Select the most probable cause Based on the information you gathered in the first three steps, try to determine the most likely reason why you are experiencing the particular problem. Keep in mind that your first guess might be incorrect and that there may be more than one cause for the problem. 5. Implement an action plan and solution, including potential impact Define the impact of any steps that you are going to take to fix the problem. Follow any change management guidance that your organization may have in place and be thoughtful of any changes you make to production systems.
Troubleshooting the Data Link Layer 165 6. Test the result Determine if your solution fixed the problem, and also examine the overall connectivity on your network to make sure that you didn’t inadvertently create another issue by implementing the fix. 7. Document the solution and process Document the information that you gathered in each of these steps: how the problem manifested itself, the systems that were affected, the details about the solution and how you implemented it, and any side effects that came about as a result of implementing the fix. TROUBLESHOOTING THE PHYSICAL LAYER When troubleshooting the physical layer, you’ll be most concerned with NICs, network cables, and hubs. ■ ■ ■ ■ Troubleshooting the NIC ■ Verify that the NIC does match the media access type ■ Verify that the NIC does have the correct connector for the cable your network uses ■ Verify that the NIC driver is properly installed and updated Troubleshooting cables ■ Verify that the cable meets the appropriate specifications for the network ■ Verify that the cable is not broken or damaged ■ Verify that the maximum allowable segment length for the cable type in use has not been exceeded to prevent attenuation ■ For coax networks, ensure the network is following the restrictions imposed by the 5-4-3 rule Troubleshooting the installation of the TCP/IP stack ■ Ensure the protocol is loaded properly by pinging the loopback address of 127.0.0.1 ■ Verify that the proper addressing is configured on the NIC Troubleshooting repeaters and hubs ■ For active hubs, ensure that the device has power ■ Ensure that the computers’ NICs are communicating with the device by checking status lights on active hubs ■ Ensure that devices are installed in accordance with the Institute of Electrical and Electronic Engineers (IEEE) specifications for the particular network architecture ■ Ensure that all ports on the device are functional by checking for a green LED lights when you attach a computer to the port through a network cable TROUBLESHOOTING THE DATA LINK LAYER When troubleshooting the data link layer, you’ll be most concerned with bridges and switches.
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