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  1. 1. Network+ Guide to Networks, Fourth Edition Chapter 12 Troubleshooting Network Problems
  2. 2. Troubleshooting Methodology <ul><li>Steps for troubleshooting network problems: </li></ul><ul><ul><li>Identify symptoms and potential causes </li></ul></ul><ul><ul><li>Identify affected area </li></ul></ul><ul><ul><li>Establish what has changed </li></ul></ul><ul><ul><li>Select most probable cause </li></ul></ul><ul><ul><ul><li>Verify user competency </li></ul></ul></ul><ul><ul><ul><li>Re-create problem </li></ul></ul></ul><ul><ul><ul><li>Verify physical integrity of network connection </li></ul></ul></ul><ul><ul><ul><li>Verify logical integrity of network connection </li></ul></ul></ul>Network+ Guide to Networks, 4E
  3. 3. Troubleshooting Methodology (continued) <ul><li>Steps for troubleshooting network problems (continued): </li></ul><ul><ul><li>Implement an action plan and solution and be prepared for all potential effects </li></ul></ul><ul><ul><li>Test the result </li></ul></ul><ul><ul><li>Identify results and effects of solution </li></ul></ul><ul><ul><li>Document solution and process </li></ul></ul>Network+ Guide to Networks, 4E
  4. 4. Establish What Has Changed <ul><li>Questions to help pinpoint problems resulting from a network change: </li></ul><ul><ul><li>OS or configuration on a server, workstation, or connectivity device changed? </li></ul></ul><ul><ul><li>New components added to server, workstation, or connectivity device? </li></ul></ul><ul><ul><li>Old components removed from server, workstation, or connectivity device? </li></ul></ul><ul><ul><li>New users or segments added to the network? </li></ul></ul><ul><ul><li>Server, workstation, or connectivity device moved from previous location to new location? </li></ul></ul>Network+ Guide to Networks, 4E
  5. 5. Select the Most Probable Cause: Verify User Competency <ul><li>Ensure that human error is not source of problem </li></ul><ul><li>Problems caused by human error usually simple to solve </li></ul><ul><li>Best way to verify that a user is performing network tasks correctly is to watch them </li></ul>Network+ Guide to Networks, 4E
  6. 6. Re-create the Problem <ul><li>Try to reproduce symptoms both while logged on as the user who reported the problem and while logged on under a privileged account </li></ul><ul><li>Questions to help determine whether a problem’s symptoms are truly reproducible: </li></ul><ul><ul><li>Make symptoms recur every time? </li></ul></ul><ul><ul><li>Make symptoms recur some of the time? </li></ul></ul><ul><ul><li>Symptoms happen only under certain circumstances? </li></ul></ul><ul><ul><li>Symptoms consistent no matter how many and which programs or files user has open? </li></ul></ul>Network+ Guide to Networks, 4E
  7. 7. Verify Physical Connectivity <ul><li>Many network problems occur at Physical layer </li></ul><ul><ul><li>Symptoms of Physical Layer problems: continuous or intermittent inability to connect to network and perform network related functions </li></ul></ul><ul><ul><li>Possible causes of Physical Layer problems: </li></ul></ul><ul><ul><ul><li>Segment or network lengths exceeding IEEE maximum standards </li></ul></ul></ul><ul><ul><ul><li>Noise affecting wireless or wire-bound signal </li></ul></ul></ul><ul><ul><ul><li>Improper terminations, faulty connectors, loose connectors, or poorly crimped connections </li></ul></ul></ul><ul><ul><ul><li>Damaged cables </li></ul></ul></ul><ul><ul><ul><li>Faulty NICs </li></ul></ul></ul>Network+ Guide to Networks, 4E
  8. 8. Implement an Action Plan and Solution Including Potential Effects <ul><li>Scope: assess scope of solution before implementing </li></ul><ul><li>Tradeoffs: solution may restore functionality for one group of users, but remove it for others </li></ul><ul><li>Security: solution may inadvertently result in addition or removal of network access or resource privileges for a user or group of users </li></ul><ul><li>Scalability: does solution position network for additions and enhancements later on </li></ul><ul><li>Cost: if solution requires significant software or hardware cost, weigh options carefully </li></ul>Network+ Guide to Networks, 4E
  9. 9. Test the Results <ul><li>Must verify that problem solved properly </li></ul><ul><ul><li>Type of testing depends on solution </li></ul></ul><ul><ul><li>Depends on area affected by problem </li></ul></ul><ul><li>May not be able to test solution immediately after implementing it </li></ul>Network+ Guide to Networks, 4E
  10. 10. Identify the Results and Effects of the Solution <ul><li>Should be able to determine how and why solution was successful and effects on users and functionality </li></ul><ul><li>Want to avoid creating unintended, negative consequences as result of solution </li></ul>Network+ Guide to Networks, 4E
  11. 11. Document the Solution and Process <ul><li>Always record symptoms and cause(s) of a problem and solution </li></ul><ul><ul><li>Impossible to remember circumstances of each incident </li></ul></ul><ul><ul><li>Networking personnel frequently change jobs </li></ul></ul>Network+ Guide to Networks, 4E
  12. 12. Help to Prevent Future Problems <ul><li>Not all problems are preventable, but many can be avoided </li></ul><ul><ul><li>Perform regular network health checks </li></ul></ul><ul><ul><ul><li>Even continual network monitoring </li></ul></ul></ul><ul><li>When planning or upgrading a network, think about how good network designs and policies can prevent later problems </li></ul>Network+ Guide to Networks, 4E
  13. 13. Troubleshooting Tools: Crossover Cable <ul><li>Transmit and receive wire pairs in one connector are reversed </li></ul><ul><ul><li>Directly interconnect two nodes without using an intervening connectivity device </li></ul></ul><ul><ul><li>Useful for quickly and easily verifying that node’s NIC is transmitting and receiving signals properly </li></ul></ul>Network+ Guide to Networks, 4E
  14. 14. Tone Generator and Tone Locator <ul><li>Telecommunications closets often disorganized and poorly documented </li></ul><ul><li>Tone generator: Issues signal on wire pair </li></ul><ul><li>Tone locator: Emits tone when it detects electrical activity on wire pair </li></ul><ul><li>Cannot be used to determine cable characteristics </li></ul><ul><ul><li>Such as whether it has defects or whether its length exceeds IEEE standards for a certain type of network </li></ul></ul>Network+ Guide to Networks, 4E
  15. 15. Tone Generator and Tone Locator (continued) Network+ Guide to Networks, 4E Figure 12-4: Use of a tone generator and tone locator
  16. 16. Multimeter <ul><li>Can measure many characteristics of an electric circuit, including its resistance and voltage </li></ul><ul><li>Voltmeter: measures voltage of electric current </li></ul><ul><li>Ohmmeter: measures resistance </li></ul><ul><ul><li>Every type of wire has different resistance characteristics </li></ul></ul><ul><li>Impedance: resistance that contributes to controlling signal </li></ul><ul><ul><li>Telltale factor for ascertaining location of faults in a cable </li></ul></ul>Network+ Guide to Networks, 4E
  17. 17. Cable Continuity Testers <ul><li>Test whether cable carrying signal to destination </li></ul><ul><ul><li>When used on copper-based cables, applies small voltage to each conductor at one end of a cable </li></ul></ul><ul><ul><ul><li>Checks whether voltage detectable at other end </li></ul></ul></ul><ul><li>Two parts: </li></ul><ul><ul><li>Base unit: generates voltage </li></ul></ul><ul><ul><li>Remote unit: detects voltage </li></ul></ul><ul><li>Some verify that wires in UTP or STP cables paired correctly and are not shorted, exposed, or crossed </li></ul>Network+ Guide to Networks, 4E
  18. 18. Cable Continuity Testers (continued) Network+ Guide to Networks, 4E Figure 12-6: Cable continuity testers
  19. 19. Cable Performance Testers <ul><li>Accomplishes same continuity and fault tests as a continuity tester, and more </li></ul><ul><li>Performance testers perform following tasks: </li></ul><ul><ul><li>Measure distance to connectivity device, termination point, or cable fault </li></ul></ul><ul><ul><li>Measure attenuation along cable </li></ul></ul><ul><ul><li>Measure near-end crosstalk between wires </li></ul></ul><ul><ul><li>Measure termination resistance and impedance </li></ul></ul><ul><ul><li>Pass/fail ratings for CAT 3, 5, 5e, 6, or 7 standards </li></ul></ul>Network+ Guide to Networks, 4E
  20. 20. Cable Performance Testers (continued) <ul><li>Performance testers perform following tasks (continued): </li></ul><ul><ul><li>Store and print cable testing results or directly save data </li></ul></ul><ul><ul><li>Graphically depict cable’s attenuation and crosstalk characteristics over length of cable </li></ul></ul><ul><li>Time domain reflectometer (TDR): issues signal on cable and measures way signal reflects </li></ul><ul><li>Optical time domain reflectometer (OTDR): used for fiber optic cables </li></ul>Network+ Guide to Networks, 4E
  21. 21. Cable Performance Testers (continued) Network+ Guide to Networks, 4E Figure 12-7: A performance tester
  22. 22. Network Monitors <ul><li>Software tool that continually monitors network traffic from a server or workstation </li></ul><ul><ul><li>Typically can interpret up to Layer 3 </li></ul></ul><ul><ul><li>Determines protocols passed by each frame </li></ul></ul><ul><ul><li>Can’t interpret data inside frames </li></ul></ul><ul><li>Many available programs: </li></ul><ul><ul><li>Microsoft Network Monitor ships with Windows Server 2003 </li></ul></ul><ul><ul><li>Novell NETMON comes with NetWare 5.x and 6.x </li></ul></ul><ul><ul><li>Many others available </li></ul></ul>Network+ Guide to Networks, 4E
  23. 23. Protocol Analyzers <ul><li>Capture traffic and analyze frames </li></ul><ul><ul><li>Typically up to Layer 7 </li></ul></ul><ul><ul><li>Can interpret payload portion of frames </li></ul></ul><ul><li>Can generate traffic in attempt to reproduce network problem and monitor multiple network segments simultaneously </li></ul><ul><li>Hardware-based protocol analyzers exist </li></ul><ul><ul><li>Sole job is to identify and assess network problems </li></ul></ul><ul><ul><li>Tailored to particular type of network </li></ul></ul><ul><li>May collect more information than can be processed </li></ul>Network+ Guide to Networks, 4E
  24. 24. Protocol Analyzers (continued) Network+ Guide to Networks, 4E Figure 12-8: Traffic displayed by protocol type
  25. 25. Wireless Network Testers <ul><li>To test wireless connections, stations, or APs, need tools that contain wireless NICs and run wireless protocols </li></ul><ul><li>Programs exist that can scan for wireless signals over a geographical range and discover all APs and wireless stations transmitting in area </li></ul><ul><ul><li>Determine whether AP functioning properly </li></ul></ul><ul><ul><li>Determine whether AP positioned correctly </li></ul></ul><ul><ul><li>Determine whether stations and APs are communicating over proper channels within a frequency band </li></ul></ul>Network+ Guide to Networks, 4E
  26. 26. Wireless Network Testers (continued) Network+ Guide to Networks, 4E Figure 12-10: Wireless network testing tool