Chap12

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Chap12

  1. 1. Chapter Twelve Troubleshooting Network Problems
  2. 2. Objectives <ul><li>Describe the elements of an effective troubleshooting methodology </li></ul><ul><li>Follow a systematic troubleshooting process to solve networking problems </li></ul><ul><li>Use a variety software and hardware tools to diagnose problems </li></ul><ul><li>Discuss practical issues related to troubleshooting </li></ul>
  3. 3. Troubleshooting Methodology <ul><li>Identify the symptoms </li></ul><ul><li>Identify the scope of the problem </li></ul><ul><li>Establish what has changed on the network </li></ul><ul><li>Determine the most probable cause of the problem </li></ul>
  4. 4. Troubleshooting Methodology <ul><li>Determine the most probable cause of the problem (cont.) </li></ul><ul><ul><li>Verify user competency </li></ul></ul><ul><ul><li>Re-create the problem </li></ul></ul><ul><ul><li>Verify the physical integrity of the network connection </li></ul></ul><ul><ul><li>Verify the logical integrity of the network connection </li></ul></ul>
  5. 5. Troubleshooting Methodology <ul><li>Implement a solution </li></ul><ul><li>Test the solution </li></ul><ul><li>Recognize the potential effects of the solution </li></ul><ul><li>Document the solution </li></ul>
  6. 6. Troubleshooting Methodology Figure 12-1: Simple flow chart of trouble-shooting steps
  7. 7. Identify the Symptoms <ul><li>Questions to help you identify symptoms of a network problem </li></ul><ul><ul><li>Is access to the network affected? </li></ul></ul><ul><ul><li>Is network performance affected? </li></ul></ul><ul><ul><li>Are data or programs (or both) affected? </li></ul></ul><ul><ul><li>Are only certain network services affected? </li></ul></ul>
  8. 8. Identify the Symptoms <ul><li>Questions to help you identify symptoms of a network problem (cont.) </li></ul><ul><ul><li>If programs are affected, does the problem include one local application, one networked application, or multiple networked applications? </li></ul></ul><ul><ul><li>What specific error messages do users report? </li></ul></ul><ul><ul><li>Is one or multiple users affected? </li></ul></ul><ul><ul><li>Do the symptoms manifest themselves consistently? </li></ul></ul>
  9. 9. Identify the Scope of the Problem <ul><li>Identify the scope of the problem </li></ul><ul><ul><li>How many users or network segments are affected? </li></ul></ul><ul><ul><li>When did the problem begin? </li></ul></ul><ul><li>If a problem is universal—if it affects the entire LAN or WAN—you will naturally want to answer these questions very quickly </li></ul>
  10. 10. Identify the Scope of the Problem Figure 12-2: Troubleshooting while identifying the demographic scope of a problem
  11. 11. Identify the Scope of the Problem FIGURE 12-3: Troubleshooting while identifying the chronological scope of a problem
  12. 12. Establish What Has Changed <ul><li>Did the operating system or configuration on a server, workstation, or connectivity device change? </li></ul><ul><li>Were new components added to a server, workstation, or connectivity device? </li></ul><ul><li>Were old components removed from a server, workstation, or connectivity device? </li></ul>
  13. 13. Establish What Has Changed <ul><li>Was a server, workstation, or connectivity device moved from its previous location to a new location? </li></ul><ul><li>Was a server, workstation, or connectivity device replaced? </li></ul><ul><li>Was new software installed on a server, workstations, or connectivity device? </li></ul><ul><li>Was old software removed from a server, workstation, or connectivity device? </li></ul>
  14. 14. Select the Most Probable Cause <ul><li>Verify user competency </li></ul><ul><li>Re-create the problem </li></ul><ul><ul><li>Can you make the symptoms recur every time? </li></ul></ul><ul><ul><li>Can you make the symptoms recur some of the time? </li></ul></ul><ul><ul><li>Do the symptoms happen only under certain circumstances? </li></ul></ul><ul><ul><li>Do the symptoms ever happen when you try to repeat them? </li></ul></ul>
  15. 15. Select the Most Probable Cause <ul><li>Verify physical connectivity </li></ul><ul><ul><li>Is the device turned on? </li></ul></ul><ul><ul><li>Is the NIC properly inserted? </li></ul></ul><ul><ul><li>Is a device’s network cable properly connected to both its NIC and the wall jack? </li></ul></ul><ul><ul><li>Do patch cables properly connect punch-down blocks to patch panels and patch panels to hubs or switches? </li></ul></ul>
  16. 16. Select the Most Probable Cause <ul><li>Verify physical connectivity (cont.) </li></ul><ul><ul><li>Is the hub, router, or switch properly connected to the backbone? </li></ul></ul><ul><ul><li>Are all cables in good condition? </li></ul></ul><ul><ul><li>Are all connectors in good condition and properly seated? </li></ul></ul><ul><ul><li>Do network segment lengths conform to the IEEE 802 specifications? </li></ul></ul>
  17. 17. Select the Most Probable Cause Figure 12-4: Troubleshooting while verifying physical connectivity
  18. 18. Verify Logical Connectivity <ul><li>Questions to help you identify a problem with logical connectivity </li></ul><ul><ul><li>Do error messages reference damaged or missing files or device drivers? </li></ul></ul><ul><ul><li>Do error messages reference malfunctioning or insufficient resources? </li></ul></ul><ul><ul><li>Has an operating system, configuration, or application been recently changed, introduced, or deleted? </li></ul></ul>
  19. 19. Verify Logical Connectivity <ul><li>Questions to help you identify a problem with logical connectivity (cont.) </li></ul><ul><ul><li>Does the problem occur with only one application or a few, similar applications? </li></ul></ul><ul><ul><li>Does the problem happen consistently? </li></ul></ul><ul><ul><li>Does the problem affect a single user or one group of users? </li></ul></ul>
  20. 20. Implement a Solution <ul><li>Steps to help you implement a safe and reliable solution </li></ul><ul><ul><li>Collect all the documentation you have about a problem’s symptoms </li></ul></ul><ul><ul><li>If you are reinstalling software on a device, make a backup of the device’s existing software installation </li></ul></ul><ul><ul><li>Perform the change, replacement, move or add that you believe will solve the problem </li></ul></ul><ul><ul><li>Test your solution </li></ul></ul>
  21. 21. Implement a Solution <ul><li>Steps to help you implement a safe and reliable solution (cont.) </li></ul><ul><ul><li>Before leaving the area in which you were working, clean it up </li></ul></ul><ul><ul><li>If the solution fixes the problem, record the details collected about the symptoms, the problem, and the solution in your organization’s call tracking database </li></ul></ul><ul><ul><li>If your solution solved a significant change or addressed a significant problem, revisit the solution a day or two later to verify the problem is fixed and hasn’t caused other problems </li></ul></ul>
  22. 22. Test the Solution <ul><li>After implementing the solution, it must be tested to verify that it works properly </li></ul><ul><li>Type of testing performed depends on the solution </li></ul><ul><li>Often good to enlist the user who reported the problem in testing your solution, too </li></ul>
  23. 23. Recognize the Potential Effects of the Solution <ul><li>When implementing a solutions, consider the: </li></ul><ul><ul><li>Scope </li></ul></ul><ul><ul><li>Tradeoffs </li></ul></ul><ul><ul><li>Security </li></ul></ul><ul><ul><li>Scalability </li></ul></ul><ul><ul><li>Cost </li></ul></ul>
  24. 24. Document the Problems and Solutions <ul><li>Name, department, and phone number of the problem originator </li></ul><ul><li>Information regarding whether the problem is software- or hardware-related </li></ul><ul><li>If software-related, the package to which it pertains </li></ul><ul><li>If hardware related, the device or components to which it pertains </li></ul>
  25. 25. Document the Problems and Solutions <ul><li>Symptom of the problem, including when it was first noticed </li></ul><ul><li>Name and telephone number of the network support contact </li></ul><ul><li>Amount of time spent troubleshooting the problem </li></ul><ul><li>Resolution of the problem </li></ul>
  26. 26. Hardware Troubleshooting Tools <ul><li>Crossover cable </li></ul><ul><ul><li>Cable in which the transmit and receive wire pairs in one of the connectors are reversed </li></ul></ul><ul><li>Tone generator and tone locator </li></ul><ul><ul><li>A tone generator is a small electronic device that issues a signal on a wire pair </li></ul></ul><ul><ul><li>A tone locator is a device that emits a tone when it detects electrical activity on a wire pair </li></ul></ul><ul><ul><li>Combination of these devices is known as a fox and hound </li></ul></ul>
  27. 27. Tone Generator and Tone Locator Figure 12-5: Use of a tone generator and tone locator
  28. 28. Multimeter <ul><li>Multimeter </li></ul><ul><ul><li>Simple instrument that can measure multiple characteristics of an electric circuit </li></ul></ul><ul><li>Voltmeter </li></ul><ul><ul><li>Device used to measure voltage of an electric current </li></ul></ul>
  29. 29. Multimeter <ul><li>Resistance </li></ul><ul><ul><li>Opposition to electric current </li></ul></ul><ul><ul><li>Resistance is measured in ohms </li></ul></ul><ul><ul><li>The device used to measure resistance is an ohmmeter </li></ul></ul>Figure 12-6: A multimeter
  30. 30. Uses for a Multimeter <ul><li>Verify that a cable is properly conducting electricity </li></ul><ul><li>Check for the presence of noise on a wire </li></ul><ul><li>Verify that amount of resistance generated by terminators on coaxial cable networks is appropriate or whether terminators are actually present and functional </li></ul><ul><li>Test for short or open circuits </li></ul>
  31. 31. Cable Checkers <ul><li>Cable checkers </li></ul><ul><ul><li>Determine whether your cabling can provide connectivity </li></ul></ul>Figure 12-7: Basic cable checker
  32. 32. Cable Testers <ul><li>A cable tester performs the same continuity and fault tests as a cable checker, but also provides the following functions: </li></ul><ul><ul><li>Ensures that cable is not too long </li></ul></ul><ul><ul><li>Measure the distance to a cable fault </li></ul></ul><ul><ul><li>Measures attenuation along a cable </li></ul></ul>
  33. 33. Cable Testers <ul><li>Additional functions provided by a cable tester (cont.) </li></ul><ul><ul><li>Measures near-end crosstalk between wires </li></ul></ul><ul><ul><li>Measures termination resistance and impedance for Thinnet cabling </li></ul></ul><ul><ul><li>Issues pass/fail ratings for CAT3, CAT5, CAT6, or even CAT7 standards </li></ul></ul><ul><ul><li>Stores and prints cable testing results </li></ul></ul>
  34. 34. Cable Testers Figure 12-8: A high-end cable tester
  35. 35. Time Domain Reflectors (TDRs) <ul><li>High-end instrument for testing qualities of a cable </li></ul><ul><li>Optical time domain reflectors (OTDRs) </li></ul><ul><ul><li>TDRs made of fiber-optic cable </li></ul></ul><ul><li>Baseline </li></ul><ul><ul><li>Record of how well a network operates under normal conditions </li></ul></ul>
  36. 36. Software Troubleshooting Tools <ul><li>Network monitors </li></ul><ul><ul><li>Software-based tools that continually monitor traffic on the network from a server or workstation attached to the network </li></ul></ul><ul><ul><li>To take advantage of software-based monitoring and analyzing tools, the network adapter installed in your machine must support promiscuous mode </li></ul></ul>
  37. 37. Abnormal Data Patterns and Packets <ul><li>Local collisions occur when two or more stations are transmitting simultaneously </li></ul><ul><li>Late collisions take place outside the window of time in which they would normally be detected by the network and redressed </li></ul><ul><li>Runts are smaller than the medium’s minimum packet size </li></ul><ul><li>Giants exceed the medium’s maximum packet size </li></ul>
  38. 38. Abnormal Data Patterns and Packets <ul><li>Jabber is a device that handles electrical signals improperly </li></ul><ul><li>Negative frame sequence checks are the result of the cyclic redundancy checksum (CRC) generated by the originating node not matching the checksum calculated from the data received </li></ul><ul><li>Ghosts are frames that are not actually data frames, but aberrations caused by a repeater misinterpreting stray voltage on the wire </li></ul>
  39. 39. Capabilities of Microsoft’s Network Monitor (NetMon) <ul><li>Capturing network data traveling from one or many segments </li></ul><ul><li>Capturing frames sent by or to a specified node </li></ul><ul><li>Reproducing network conditions by transmitting a selected amount and type of data </li></ul><ul><li>Detecting any other running copies of NetMon on the network </li></ul><ul><li>Generating statistics about network activity </li></ul>
  40. 40. Novell’s LANalyzer <ul><li>LANalyzer performs the following functions: </li></ul><ul><ul><li>Initially discovering all network nodes on a segment </li></ul></ul><ul><ul><li>Continuously monitoring network traffic </li></ul></ul><ul><ul><li>Tripping alarms when traffic conditions meet preconfigured thresholds </li></ul></ul><ul><ul><li>Capturing traffic to and from all or selected nodes </li></ul></ul>
  41. 41. Network Analyzers <ul><li>Tool that can capture traffic and analyze packets </li></ul><ul><li>Also known as protocol analyzers </li></ul><ul><li>Sniffer Portable </li></ul><ul><ul><li>Network analyzer from Network Associates </li></ul></ul><ul><li>Sniffer </li></ul><ul><ul><li>Laptop equipped with special network adapter and software that performs network analysis </li></ul></ul>
  42. 42. Physical Layer Problems and Symptoms Figure 12-9: Services and devices in the OSI Model
  43. 43. Physical Layer Problems and Symptoms <ul><li>Segment problems </li></ul><ul><li>Signal noise </li></ul><ul><li>Cable damage </li></ul><ul><li>Connector flaws </li></ul><ul><li>Adapter flaws </li></ul>
  44. 44. Staff Involved in Troubleshooting <ul><li>Help desk staffed with help analysts </li></ul><ul><ul><li>Organizations may group their help desk analysts into teams based on their expertise </li></ul></ul><ul><li>Most help desks have a help desk coordinator </li></ul><ul><li>Most organizations have an operations manager, who supervises the help desk coordinator </li></ul>
  45. 45. Swapping Equipment <ul><li>If a suspected problems lies with a network component, an easy way to test the theory is to exchange that component for a functional one </li></ul><ul><li>A better alternative to swapping parts is to have redundancy built into your network </li></ul><ul><li>Before swapping any network component, make sure the replacement has exactly the same specifications as the original part </li></ul>
  46. 46. Using Vendor Information Table 12-1: Links for troubleshooting resources on the Web
  47. 47. Notify Others of Change <ul><li>Change management system </li></ul><ul><ul><li>Process or program that provides support personnel with a centralized means of documenting changes to the network </li></ul></ul><ul><li>Type of changes that should be recorded in a change management system </li></ul><ul><ul><li>Adding or upgrading software on network servers or other devices </li></ul></ul><ul><ul><li>Adding or upgrading hardware components on network servers or other devices </li></ul></ul>
  48. 48. Notify Others of Change <ul><li>Type of changes that should be recorded in a change management system (cont.) </li></ul><ul><ul><li>Adding new hardware on the network </li></ul></ul><ul><ul><li>Changing the network properties of a network device </li></ul></ul><ul><ul><li>Increasing or decreasing rights for a group of users </li></ul></ul><ul><ul><li>Physically moving networked devices </li></ul></ul>
  49. 49. Notify Others of Change <ul><li>Type of changes that should be recorded in a change management system (cont.) </li></ul><ul><ul><li>Moving user IDs and their files/directories from one server to another </li></ul></ul><ul><ul><li>Making changes in processes </li></ul></ul><ul><ul><li>Making changes in vendor policies or relationships </li></ul></ul><ul><li>Preventing future problems </li></ul><ul><ul><li>Though not all network problems are preventable, many are avoidable </li></ul></ul>
  50. 50. Chapter Summary <ul><li>Before you can resolve a network problem, you must determine its cause </li></ul><ul><li>The key to solving network problems is to approach them methodically and logically </li></ul><ul><li>When assessing a network problem, act like a doctor diagnosing a patient </li></ul><ul><li>After implementing your solution, test it to ensure that it works correctly </li></ul>
  51. 51. Chapter Summary <ul><li>Be familiar with the different hardware-based troubleshooting tools </li></ul><ul><li>Be familiar with the different software-based troubleshooting tools </li></ul><ul><li>Most organizations operate a help desk </li></ul><ul><li>If you suspect a problem lies with a network component, one of the easiest ways to test your theory is to exchange that component for a functional one </li></ul>
  52. 52. Chapter Summary <ul><li>Keep a list of hardware and software vendors for your networking equipment </li></ul><ul><li>Some organizations use a call tracking system </li></ul><ul><li>In addition to communicating problems and solutions to your peers whenever you work on a network problem, you should follow up with the person who reported the problem </li></ul><ul><li>Organizations often implement change management systems to methodically track changes on the network </li></ul>

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