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Network+ Guide to Networks, Fourth Edition

This chapter provides a step-by-step troubleshooting methodology for identifying and solving network problems. It covers how to identify symptoms and potential causes, establish what has changed, verify user competency, re-create the problem, and verify physical and logical integrity of network connections. It also discusses implementing action plans, testing results, identifying solution effects, documenting solutions, and preventing future problems.

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Network+ Guide to Networks, Fourth Edition

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  1. Network+ Guide to Networks, Fourth Edition Chapter 12 Troubleshooting Network Problems

  2. Troubleshooting Methodology • Steps for troubleshooting network problems: • Identify symptoms and potential causes • Identify affected area • Establish what has changed • Select most probable cause • Verify user competency • Re-create problem • Verify physical integrity of network connection • Verify logical integrity of network connection Network+ Guide to Networks, 4E

  3. Troubleshooting Methodology (continued) • Steps for troubleshooting network problems (continued): • Implement an action plan and solution and be prepared for all potential effects • Test the result • Identify results and effects of solution • Document solution and process Network+ Guide to Networks, 4E

  4. Establish What Has Changed • Questions to help pinpoint problems resulting from a network change: • OS or configuration on a server, workstation, or connectivity device changed? • New components added to server, workstation, or connectivity device? • Old components removed from server, workstation, or connectivity device? • New users or segments added to the network? • Server, workstation, or connectivity device moved from previous location to new location? Network+ Guide to Networks, 4E

  5. Select the Most Probable Cause: Verify User Competency • Ensure that human error is not source of problem • Problems caused by human error usually simple to solve • Best way to verify that a user is performing network tasks correctly is to watch them Network+ Guide to Networks, 4E

  6. Re-create the Problem • Try to reproduce symptoms both while logged on as the user who reported the problem and while logged on under a privileged account • Questions to help determine whether a problem’s symptoms are truly reproducible: • Make symptoms recur every time? • Make symptoms recur some of the time? • Symptoms happen only under certain circumstances? • Symptoms consistent no matter how many and which programs or files user has open? Network+ Guide to Networks, 4E

  7. Verify Physical Connectivity • Many network problems occur at Physical layer • Symptoms of Physical Layer problems: continuous or intermittent inability to connect to network and perform network related functions • Possible causes of Physical Layer problems: • Segment or network lengths exceeding IEEE maximum standards • Noise affecting wireless or wire-bound signal • Improper terminations, faulty connectors, loose connectors, or poorly crimped connections • Damaged cables • Faulty NICs Network+ Guide to Networks, 4E

  8. Implement an Action Plan and Solution Including Potential Effects • Scope: assess scope of solution before implementing • Tradeoffs: solution may restore functionality for one group of users, but remove it for others • Security: solution may inadvertently result in addition or removal of network access or resource privileges for a user or group of users • Scalability: does solution position network for additions and enhancements later on • Cost: if solution requires significant software or hardware cost, weigh options carefully Network+ Guide to Networks, 4E

  9. Test the Results • Must verify that problem solved properly • Type of testing depends on solution • Depends on area affected by problem • May not be able to test solution immediately after implementing it Network+ Guide to Networks, 4E

  10. Identify the Results and Effects of the Solution • Should be able to determine how and why solution was successful and effects on users and functionality • Want to avoid creating unintended, negative consequences as result of solution Network+ Guide to Networks, 4E

  11. Document the Solution and Process • Always record symptoms and cause(s) of a problem and solution • Impossible to remember circumstances of each incident • Networking personnel frequently change jobs Network+ Guide to Networks, 4E

  12. Help to Prevent Future Problems • Not all problems are preventable, but many can be avoided • Perform regular network health checks • Even continual network monitoring • When planning or upgrading a network, think about how good network designs and policies can prevent later problems Network+ Guide to Networks, 4E

  13. Troubleshooting Tools: Crossover Cable • Transmit and receive wire pairs in one connector are reversed • Directly interconnect two nodes without using an intervening connectivity device • Useful for quickly and easily verifying that node’s NIC is transmitting and receiving signals properly Network+ Guide to Networks, 4E

  14. Tone Generator and Tone Locator • Telecommunications closets often disorganized and poorly documented • Tone generator: Issues signal on wire pair • Tone locator: Emits tone when it detects electrical activity on wire pair • Cannot be used to determine cable characteristics • Such as whether it has defects or whether its length exceeds IEEE standards for a certain type of network Network+ Guide to Networks, 4E

  15. Tone Generator and Tone Locator (continued) Figure 12-4: Use of a tone generator and tone locator Network+ Guide to Networks, 4E

  16. Multimeter • Can measure many characteristics of an electric circuit, including its resistance and voltage • Voltmeter: measures voltage of electric current • Ohmmeter: measures resistance • Every type of wire has different resistance characteristics • Impedance: resistance that contributes to controlling signal • Telltale factor for ascertaining location of faults in a cable Network+ Guide to Networks, 4E

  17. Cable Continuity Testers • Test whether cable carrying signal to destination • When used on copper-based cables, applies small voltage to each conductor at one end of a cable • Checks whether voltage detectable at other end • Two parts: • Base unit: generates voltage • Remote unit: detects voltage • Some verify that wires in UTP or STP cables paired correctly and are not shorted, exposed, or crossed Network+ Guide to Networks, 4E

  18. Cable Continuity Testers (continued) Figure 12-6: Cable continuity testers Network+ Guide to Networks, 4E

  19. Cable Performance Testers • Accomplishes same continuity and fault tests as a continuity tester, and more • Performance testers perform following tasks: • Measure distance to connectivity device, termination point, or cable fault • Measure attenuation along cable • Measure near-end crosstalk between wires • Measure termination resistance and impedance • Pass/fail ratings for CAT 3, 5, 5e, 6, or 7 standards Network+ Guide to Networks, 4E

  20. Cable Performance Testers (continued) • Performance testers perform following tasks (continued): • Store and print cable testing results or directly save data • Graphically depict cable’s attenuation and crosstalk characteristics over length of cable • Time domain reflectometer (TDR): issues signal on cable and measures way signal reflects • Optical time domain reflectometer (OTDR): used for fiber optic cables Network+ Guide to Networks, 4E

  21. Cable Performance Testers (continued) Figure 12-7: A performance tester Network+ Guide to Networks, 4E

  22. Network Monitors • Software tool that continually monitors network traffic from a server or workstation • Typically can interpret up to Layer 3 • Determines protocols passed by each frame • Can’t interpret data inside frames • Many available programs: • Microsoft Network Monitor ships with Windows Server 2003 • Novell NETMON comes with NetWare 5.x and 6.x • Many others available Network+ Guide to Networks, 4E

  23. Protocol Analyzers • Capture traffic and analyze frames • Typically up to Layer 7 • Can interpret payload portion of frames • Can generate traffic in attempt to reproduce network problem and monitor multiple network segments simultaneously • Hardware-based protocol analyzers exist • Sole job is to identify and assess network problems • Tailored to particular type of network • May collect more information than can be processed Network+ Guide to Networks, 4E

  24. Protocol Analyzers (continued) Figure 12-8: Traffic displayed by protocol type Network+ Guide to Networks, 4E

  25. Wireless Network Testers • To test wireless connections, stations, or APs, need tools that contain wireless NICs and run wireless protocols • Programs exist that can scan for wireless signals over a geographical range and discover all APs and wireless stations transmitting in area • Determine whether AP functioning properly • Determine whether AP positioned correctly • Determine whether stations and APs are communicating over proper channels within a frequency band Network+ Guide to Networks, 4E

  26. Wireless Network Testers (continued) Figure 12-10: Wireless network testing tool Network+ Guide to Networks, 4E

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