CEG 210 FALL 2011 Chapter 13 Troubleshooting Network Problems by 7Tu3e5

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									    CEG 210 FALL 2011
       Chapter 13
Troubleshooting Network
       Problems
        Troubleshooting Methodology

•   Proceed logically and methodically
•   Follow recommended steps
•   Use experience when necessary
•   Benefits of proceeding logically and methodically
    – Prevents wasteful, time-consuming efforts
       • Unnecessary software, hardware replacements




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         Troubleshooting Methodology

•   Troubleshooting steps
    1.   Identify symptoms
    2.   Identify affected area
    3.   Determine what has changed
    4.   Establish most probable cause
    5.   Determine if escalation necessary
    6.   Create a plan
    7.   Implement solution, test first
    8.   Effects of results
    9.   Document solution
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1. Identify the Symptoms and Problems

• Ask questions
• Avoid jumping to conclusions about symptoms
• Pay attention
  – Users, system, network, and error messages
  – Treat each symptom uniquely




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         2. Identify the Affected Area

• Determine affected area and group
  –   One user or workstation?
  –   A small area?
  –   A large area?
  –   One location within an organization?
  –   An entire organization?




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         2. Identify the Affected Area
• Time frame
   – When did the problem begin?
   – Has it ever worked properly?
   – Did the symptoms appear in the last hour or day?
   – Have the symptoms appeared intermittently, for a
     long time or a short time?
   – Do the symptoms appear only at certain times of the
     day, week, month, or year?
• Take time to troubleshoot correctly
   – Ask specific questions
       • Identify problem scope
   – Filter unrelated user information

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    3. Determine What Has Changed
• Become aware of recent network changes
• Possible actions if change generated problem
  – Correct problem
  – Reverse change
     • Less risky, less time consuming
• Network change records (Change Management)
  – Track what has changed
• Make records available to staff members



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 4. Establish the Most Probable Cause
• Verify user competency
  – Ensure human error is not problem source
  – Verify user is performing network tasks correctly
     • Watch
     • Connect using remote desktop software
     • Talk over phone
• Results
  – Catch user-generated mistakes
  – Gain clues for further troubleshooting



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 4. Establish the Most Probable Cause

• Try to re-create the problem
   – Learn more about problem causes
   – Reproduce symptoms
      • Log on as user; log on under privileged account
      • Follow same steps
   – Ask questions
      • Determine whether problem symptoms reproducible, to
        what extent
      • Ask user precisely what was done before error



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 4. Establish the Most Probable Cause
• Verify Physical layer connectivity
   – Half of all network problems occur at Physical layer
   – Symptoms of Physical layer problems
      • Cable lengths exceed standards
      • User added equipement
      • Improper terminations, faulty connectors, loose
        connectors, poorly crimped connections
      • Damaged cables
      • Faulty NICs
   – Software errors may point to physical connectivity
     problem

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4. Establish the Most Probable Cause

 – Diagnosing Physical layer Problems
    • Ask questions
    • Verify connections between devices
    • Verify soundness of connection hardware
 – Swapping equipment: tests theories
    • Exchange faulty component for functional one
    • Change patch cable




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 4. Establish the Most Probable Cause

• Verify logical connectivity
   – Logical connectivity problems more difficult to isolate,
     resolve than physical connectivity problems
   – Software-based causes
      • Improperly configured NIC
      • Improperly installed, configured client software
      • Improperly installed, configured network protocols,
        services




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  5. Determine Whether Escalation is
              Necessary
• Help desks
  – Help desk analysts
     • Proficient in basic workstation, network troubleshooting
     • First-level support
  – Network specialist
     • Second-level support
  – Help desk coordinator
     • Third-level support personnel
• Know when and how and who to escalate
  – Follow given procedure


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           6. Create an Action Plan

• Consider how solution affects users, network
  functionality
• Scope
   – Assess solution’s scope
      • Area of network effected
   – Wait if not an emergency
   – Best to do off hours
• Trade-offs
   – Restore functionality for one user group
      • May remove functionality for others

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             6. Create an Action Plan

• Security
  – Be aware of inadvertent security implications
     • Network access, resource privileges addition or
       removal consequences
     • Understand access changes for authorized,
       unauthorized users
     • Will the network be more, less, or same security




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           6. Create an Action Plan

• Solution type
      • fix organization will not outgrow
      • Temporary fix organization will outgrow
• Cost
   – Weigh options carefully
• Use vendor information
   – Manufacturer documentation
   – Free online troubleshooting information
• Consult with others, within, outside your
  organization
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   7. Implement and Test the Solution
• Implement only after proposed solution’s effects are
  known
• Implementation
   – Brief or long time frame
   – Use methodical and logical approach
      • Leads to efficient correction process
      • Unless major problem – fix as quickly as possible
   – Follow series of steps




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   7. Implement and Test the Solution

• Roll out solution in stages if necessary
   – Especially in large-scale fixes
• After solution implementation
   – Verify problem solved properly
• After testing solution implementation
   –   Determine how and why solution was successful
   –   Determine solution’s effect on users and functionality
   –   Avoid creating unintended, negative consequences
   –   Communicate solution to colleagues

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          8. Document the Solution

• Always record:
   – Problem symptoms and cause (or causes)
   – Solution
• Justification for recording
   – Impossible to remember each incident’s
     circumstances
   – Job changes
• Use centrally located database
   – Accessible to all networking personnel
• Call tracking system
• Follow-up with user                         19
    Troubleshooting Methodology Review

•    Troubleshooting steps
     1.   Identify symptoms
     2.   Identify affected area
     3.   Determine what has changed
     4.   Establish most probable cause
     5.   Determine if escalation necessary
     6.   Create a plan
     7.   Implement solution, test first
     8.   Effects of results
     9.   Document solution
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          Prevent Future Problems

• Avert network problems by
  –   Network maintenance
  –   Documentation
  –   Security
  –   Upgrades




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            Troubleshooting Tools

• Utilities help troubleshoot network problems
   – Ping as an example
   – Specialized tools (hardware, software)
      • Specifically designed to analyze, isolate network
        problems
   – Tool selection dependencies
      • Problem being investigated
      • Network characteristics




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                Crossover Cable

• Crossover cable
  – Directly interconnect two nodes without intervening
    connectivity device
     • Verify NIC transmitting, receiving signals properly




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                         Tools

• Tone Generator/Tone Locator
   – Telecommunications closet ports, wire terminations
     Usage - Determine where wire pair terminates
• Multimeter - Tests cables for faults
   – Isolates problems with network cables
• Cable Continuity Testers - Cable checkers
   – Tests whether cable carrying signal to destination
   – Tests cable continuity



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                         Tools

• Cable Performance Testers
  – Determines if cable carrying current
  – Continuity testers versus cable performance testers
     • Sophistication and price (performance tester more)
     • Performance tester accomplishes same as continuity
       test but does more
        – Measures distance
        – Some can print or send data to a computer
     • Isolates problems with network cables



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Tone Generator and Tone Locator




Figure 13-4 Use of a tone generator and tone locator


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             Multimeter




Figure 13-5 A multimeter


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Cable Continuity Testers




 Figure 13-6 Cable continuity testers


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Cable Performance Testers




   Figure 13-7 A cable performance tester

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               Network Monitors
• Software-based tool
  – Continually monitors network traffic from server and
    workstation attached to network
  – Determine protocols passed by each frame
  – Cannot interpret frame data
• Purchase or free download tools developed by other
  software companies
  – All use similar graphical interfaces




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                 Protocol Analyzers

• Protocol analyzer (network analyzer)
   – Captures traffic, analyzes frames
• Variety of protocol analyzer software available
   – Wireshark
• Same features as network monitor
   – Few extras
   – Generates traffic
• Before using network monitor or protocol analyzer
   – Learn what network traffic normally looks like
      • Capture data for time period on regular basis
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      Protocol Analyzers




Figure 13-10 Traffic captured by a protocol analyzer

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          Wireless Network Testers

• Tools containing wireless NICs, running wireless
  protocols
• Programs scan for wireless signals
   – Discover access points, wireless stations transmitting
   – Shows a little about wireless environment
      • Connection duration, signal speed and strength,
        number of packets exchanged




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Wireless Network Testers




 Figure 13-11 Wireless network testing tool

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                       Summary
• Methodical, logical troubleshooting methodology
   – Key to solving network problems
• Troubleshooting tools
   –   Tone generator and tone locator
   –   Multimeters
   –   Basic cable continuity testers
   –   Cable performance tester
   –   Network monitors and protocol analyzers
   –   Wireless network testing tools


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     End of Chapter 13




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