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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. Objectives • Describe the steps involved in an effective troubleshooting methodology • Follow a systematic troubleshooting process to identify and resolve networking problems • Document symptoms, solutions, and results when troubleshooting network problems • Use a variety of software and hardware tools to diagnose problems Network+ Guide to Networks, 4E

  3. 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

  4. 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

  5. Identify the Symptoms and Potential Causes • Questions that may help identify non-obvious symptoms: • Access to network affected? • Network performance affected? • Data and/or programs affected? • Only certain network services affected? • Problems include local application, networked application, or multiple networked applications? • Specific error messages reported? • One user or multiple users affected? • Symptoms manifested consistently? Network+ Guide to Networks, 4E

  6. Identify the Affected Area Figure 12-1: Identifying the area affected by a problem Network+ Guide to Networks, 4E

  7. Identify the Affected Area (continued) Figure 12-1 (continued): Identifying the area affected by a problem Network+ Guide to Networks, 4E

  8. Identify the Affected Area (continued) Figure 12-2: Identifying the chronological scope of a problem Network+ Guide to Networks, 4E

  9. Identify the Affected Area (continued) Figure 12-2 (continued): Identifying the chronological scope of a problem Network+ Guide to Networks, 4E

  10. 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

  11. Establish What Has Changed (continued) • Questions to help pinpoint problems resulting from a network change (continued): • Was a server, workstation, or connectivity device replaced? • Was new software installed on a server, workstation, or connectivity device? • Was old software removed from a server, workstation, or connectivity device? Network+ Guide to Networks, 4E

  12. Establish What Has Changed (continued) • Two ways to react to problems caused by network changes: • Attempt to correct problem • Attempt to reverse change and restore hardware or software to previous state • Complete network change records should be kept • Make available to staff members Network+ Guide to Networks, 4E

  13. 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

  14. 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

  15. 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

  16. Verify Physical Connectivity (continued) • Diagnosing Physical Layer problems: • Device turned on? • NIC properly inserted? • For wireless NICs, antenna turned on? • Device’s network cable properly connected to both NIC and wall jack? • Patch cables properly connect punch-down blocks to patch panels and patch panels to hubs or switches? Network+ Guide to Networks, 4E

  17. Verify Physical Connectivity (continued) • Diagnosing Physical Layer problems (continued): • Hub, router, or switch properly connected to backbone? • Cables in good condition? • Connectors in good condition and properly seated? • Network lengths conform to IEEE 802 specifications? • Devices configured properly to work with network type or speed? Network+ Guide to Networks, 4E

  18. Verify Physical Connectivity (continued) • Swapping equipment: • If you suspect problem lies with a network component, easy to test theory by exchanging for a functional component • Cables, ports, data jacks, network adapters • Difficult to swap routers and switches Network+ Guide to Networks, 4E

  19. Verify Physical Connectivity (continued) Figure 12-3: Verifying physical connectivity Network+ Guide to Networks, 4E

  20. Verify Physical Connectivity (continued) Figure 12-3 (continued): Verifying physical connectivity Network+ Guide to Networks, 4E

  21. Verify Logical Connectivity • Questions to help identify logical connectivity problems: • Error messages reference damaged or missing files or device drivers? • Error messages reference malfunctioning or insufficient resources? • OS, configuration, or application been recently changed, introduced, or deleted? • Problem occurs with only one application or a few, similar applications? • Problem happens consistently? • Problem affects single user or one group of users? Network+ Guide to Networks, 4E

  22. 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

  23. Implement an Action Plan and Solution Including Potential Effects (continued) • Use vendor information: nothing to lose by referring to manual, except a little time • Manuals, online information, technical support • Implement the solution: • Collect all documentation about problem’s symptoms • Make backups, keep old parts, print configurations • Perform change, replacement, move, or addition • Test solution • Clean up • Document solution and results • Revisit problem later Network+ Guide to Networks, 4E

  24. 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

  25. 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

  26. 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

  27. Staff Involved in Troubleshooting • Many staff members may contribute to troubleshooting network problems • Help desk analysts often first-level support • Creates record for incident and attempts to diagnose problem • Second-level support analyst has specialized knowledge in one or more aspects of a network • Most help desks include a help desk coordinator • Ensures analysts divided into correct teams, schedules shifts, maintains infrastructure to enable analysts to better perform their jobs Network+ Guide to Networks, 4E

  28. Record Problems and Resolutions • Call tracking system: software used for documenting problems • If no call tracking system, should keep records in electronic form • Name, department, phone number of problem originator • Software- or hardware-related problem? • Software package or device/component to which it pertains • Symptoms of problem • Name/telephone number of network support contact • Time spent troubleshooting • Resolution Network+ Guide to Networks, 4E

  29. Notify Others of Change • Record resolution in call tracking system • Notify others of solution and what, if anything, needed to change to fix problem • Alerts others about problem and solution • Notifies others of network changes made, in case they affect other services • Change management system: process or program that provides support personnel with centralized means of documenting network changes Network+ Guide to Networks, 4E

  30. Notify Others of Change (continued) • Types of changes that network personnel should record in change management system: • Adding or upgrading software or hardware • Changing network properties of network device • Increasing or decreasing rights for group of users • Physically moving networked devices • Moving user accounts, files, and directories • Making changes in processes • Making changes in vendor policies or relationships Network+ Guide to Networks, 4E

  31. 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

  32. 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

  33. 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

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

  35. 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

  36. 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

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

  38. 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

  39. 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

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

  41. 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

  42. Network Monitors (continued) • Network monitoring tools perform following functions: • Continuously monitor network traffic on segment • Capture network data transmitted on segment • Capture frames sent to or from specific node • Reproduce network conditions by transmitting selected amount and type of data • Generate statistics about network activity Network+ Guide to Networks, 4E

  43. Network Monitors (continued) • Some network monitoring tools can also: • Discover all network nodes on a segment • Establish a baseline • Record of how network operates under normal conditions, including performance, collision rate, utilization rate, and so on • Store traffic data and generate reports • Trigger alarms when traffic conditions meet preconfigured conditions Network+ Guide to Networks, 4E

  44. Network Monitors (continued) • Data errors that can be distinguished: • Local collisions • Late collisions • Runts • Giants • Jabber • Negative frame sequence checks • Ghosts Network+ Guide to Networks, 4E

  45. 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

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

  47. 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

  48. Wireless Network Testers (continued) • Some programs can capture data transmitted between stations and APs • Useful for troubleshooting wireless connection problems • Some programs contain a spectrum analyzer • Assess quality of wireless signal • Ascertain where noise (or interference) is greatest Network+ Guide to Networks, 4E

  49. Wireless Network Testers (continued) • Capabilities common to wireless network testers: • Identify transmitting APs and stations and channels over which they are communicating • Measure signal strength from and determine range of AP • Indicate effects of attenuation, signal loss, and noise • Interpret signal strength information Network+ Guide to Networks, 4E

  50. Wireless Network Testers (continued) • Capabilities common to wireless network testers (continued): • Ensure proper association and reassociation when moving between APs • Capture/interpret traffic exchanged between wireless APs and stations • Measure throughput and assess data transmission errors • Analyze the characteristics of each channel within a frequency band to indicate the clearest channels Network+ Guide to Networks, 4E