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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) Network+ Guide to Networks, 4E Figure 12-4: Use of a tone generator and tone locator
  • 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) Network+ Guide to Networks, 4E Figure 12-6: Cable continuity testers
  • 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) Network+ Guide to Networks, 4E Figure 12-7: A performance tester
  • 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) Network+ Guide to Networks, 4E Figure 12-8: Traffic displayed by protocol type
  • 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) Network+ Guide to Networks, 4E Figure 12-10: Wireless network testing tool