Troubleshooting PDF

Troubleshooting Problem Solving Process Trial and Error Solve by Example The Replacement Method Step by Step with the OSI Model Approaches to Troubleshooting Trial and Error This method requires a repeated process of: • an assessment of the problem • a guess of the solution • an implementa...

Troubleshooting Problem Solving Process Trial and Error Solve by Example The Replacement Method Step by Step with the OSI Model Approaches to Troubleshooting Trial and Error This method requires a repeated process of: • an assessment of the problem • a guess of the solution • an implementation of the solution • a test of the results Has a time and a place • Not always the best approach • Not to be relied on exclusively Solve by Example • This is the process comparing something that doesn’t work with something that does and then making modifications to the non-functioning item until it performs like the functioning one. • A copy of configuration can be used as a model to base on or to modify from • Only use when the working sample has a similar environment as the machine with the problem • Don’t make changes that could cause conflicts • Be careful to not destroy data The Replacement Method • It is effective only if the problem source can be determined and source is a defective part • The rules of the replacement method • Narrow the list of potentially defective parts down to a few possibilities • Make sure you have the correct replacement parts on hand • Replace only on part at a time • If your first replacement does not fix the problem, reinstall the original part before replacement another part Step by Step with the OSI Model • Top-down • Test a problem starting from the Application layer and keep testing at each layer until the problem is resolved • Bottom-up • Test a problem starting from the physical layer and keep testing at each layer until the problem is resolved • Networks can be complex, multilayered systems, using the layered approach to troubleshoot can be helpful Step by Step with the OSI Model Scenario • A user at PC A complains that an error occurs when she tries to access files on the File Server, but users at PCs B and C are not having similar problems. Using the File Explorer to browse the network, no devices are shown. A B • A bottom-up approach: • Check the cabling, is it damaged? Is it plugged in? Are the link lights on on the NIC? • Check the NIC driver is functional and installed correctly • Check the addressing settings • Use ping and tracert File server C Some Common Problems Default gateway not set, or is incorrect? • The default gateway is the address of the router that the PC will use to access the outside world. It must be physically and logically connected Subnetting error • Is the device in the same subnet as other devices on the local link? • Is the subnet mask correct? Cabling • Not connected • Damaged • Incorrect cable used Routing • Wrong entries • Missing entries • Summarisation error Router interfaces • Interfaces are disabled by default • Clock rate on DCE interfaces must be set Network Troubleshooting Tools • ICMP-based utilities • Using ping for connectivity troubleshooting • Run ipconfig /all • • • • • • • • tracert/traceroute Network monitors Protocol analyser Cable testers The Internet Vendor support services Experience Network Documentation Using ping for connectivity troubleshooting • Run ipconfig /all to display all related addressing information • Ping the loopback address to verify that TCP/IP stack is functioning correctly • Ping the local IP address to verify the computer’s capability to receive ICMP packets • Ping the default gateway to identify the scope of the network problem • Ping the target host • Ping DNS servers • Query the name service for information about the specified IP address or domain name, e.g. nslookup Prototyping in Packet Tracer Reference • Chapter 13 Troubleshooting and Support, G. Tomsho, Guide to Networking Essentials, 7th Edition, Cengage Learning