13 Troubleshooting Network Problems 1 Approach to Troubleshooting Proceed slowly logically and methodically Use experience when necessary Benefits of a logical approach Prevents wasteful timeconsuming efforts ID: 637390
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CEG 2400 FALL 2012 Chapter 13Troubleshooting Network Problems
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Approach to TroubleshootingProceed slowly, logically and methodicallyUse experience when necessaryBenefits of a logical approach
Prevents wasteful, time-consuming effortsUnnecessary software purchasesUnnecessary hardware replacements
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Troubleshooting Steps Troubleshooting stepsIdentify problem
Gather informationIdentify symptomsQuestion usersDetermine if anything has changed
Establish
theory
Always q
uestion
the obvious
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Troubleshooting StepsTroubleshooting steps (cont’d.)Test theory to determine cause
If theory confirmed, determine next stepsIf not, establish new theory or escalateTest must not be destructive
Establish action plan
Implement solution or escalate
Verify full functionality
Implement preventative measures if applicable
Document findings, actions, outcomes
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1. Identify the Problem and Its SymptomsAsk questionsAvoid jumping to conclusionsPay attention to:
UsersSystem and network behaviorsError messagesTreat each symptom uniquely
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Identify the Problem and Its SymptomsDetermine the problem’s scopeIdentify affected problem areaFind
out how many users or network segments are affectedNarrow down the time frame during which problem occurredDiscover time and frequency of problem May reveal more subtle network
problems
Benefits
of narrowing scope
Eliminate causes,
may point
to
other
problems
Take your time to troubleshoot correctly
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Identify the Problem and Its SymptomsQuestion users
Ensure human error is not source of problemWatch the user if possibleUse remote desktop
software if you can’t be there to watch
Watch each step user takes
Determine if anything has changed
Be aware of recent network changes
Possible actions if network change created problem
Correct problem
Reverse change
Have/make network change records available to staff members
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2. Establish a TheoryRe-create the symptoms if can be done safely
Follow same steps as person reporting symptomVerify Physical layer connectivityCabling and network adapters a common source of
problems
Diagnosing Physical layer problems
Ask questions
Verify connections between devices
Verify soundness of connection
hardware
Check cable
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Establish a TheoryVerify logical connectivityConsider error messages
Note changes in operating system or applicationsDetermine if the problem is repeatable
Verify firmware and software configurations of devices in path
Try Ping utility
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3. Test the Theory to Determine CauseTest Physical layer theoriesExample approachesUse a cable testing toolCheck to make sure NIC is seated firmly in slot
Use wireless analyzerFollow cables to verify physical connectivityTry different port, data jackConnect/use
another
device
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Test the Theory to Determine CauseTest logical connectivity theoriesExample approachesView switch configuration to determine which nodes are included in VLANs
Investigate user permissionsExamine NIC configuration (dhcp, ip address,
etc
)
Ensure routing table includes valid entries
Use tools such as ping, netstat, route, traceroute
Check wireless client settings
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Test the Theory to Determine CauseEscalate if necessaryAsk colleague with more experience or knowledge
Help desk analysts/ first-level supportProficient in basic workstation, network troubleshooting
Network
specialist / Second-level support
Network coordinator/ Third-level support
Follow escalation procedures
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4. Establish a Plan of Action to Resolve the ProblemConsider how the solution affects users/network functionality
ScopeAssess solution’s scope before implementingTrade-offsSolution may restore functionality for one user
group but
may remove functionality for
others
Security
Be aware of security implications
Understand access changes for authorized, unauthorized users
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Establish a Plan of Action to Resolve the ProblemScalability of solutionPosition network for future additions, enhancementsTry not to use temporary
fix organization will outgrowCostWeigh options carefullyUse vendor information
Manufacturer documentation
Free online troubleshooting
information (phone support/web support)
Consult
with others within, outside your organization
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5. Implement the Solution or Escalate as NecessarySolution implementationTime required may be minimal or long
Use methodical and logical approachProblem causing catastrophic outages should be solved as quickly as possible
Follow series of steps
Implement a safe, reliable solution
Large-scale fixes
Roll out changes in stages
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6. Verify Full System FunctionalityVerify problem solution is completeType of testing depends on solutionType of testing depends on area
May not be able to test solution immediatelyDetermine how and why solution workedEvaluate effects on users (no negative consequences)
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7. Implement preventative measures if applicableConsider how similar problems may be prevented in the futureIncreased maintenance
Thoughtful planningPerform network health checksUpgrading networkGood planningGood design
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8. Document Findings, Actions, and OutcomesNecessary to record:Problem symptoms and causes and solutions
Justification for recordingImpossible to remember each incident’s circumstancesPeople leave/Job
changes
Use centrally located
database accessible
to all networking personnel
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Document Findings, Actions, and OutcomesHave a good call tracking system (help desk software)Supported
services list documentContact personnel list both local and software companiesLists all supported hardware, services, and software
Follow-up with user who reported problem
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Document Findings, Actions, and OutcomesNotify others in organization of changesRecord resolution in call tracking system
Alert others about problem, solution, and network changes madeHave a change
management system
Means
of documenting network
changes
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Troubleshooting ToolsUtilities help troubleshoot network problemsPingSpecialized tools Simple
continuity testersProtocol analyzersTool selection dependenciesProblem being investigated
Network characteristics
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Tone Generator and Tone LocatorProbe kitGenerator and locator combinationTone generator (toner)Small electronic device that issues signal on wire pair
Tone locator (probe)Emits tone when electrical activity detectedTesting requires trial and errorUsed to determine where wire pair terminates
Not used to determine cable characteristics
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23 Use of a tone generator and tone locatorSlide24
MultimeterSpecialized tool used to test cables for faultsIsolate problems with network cables
Measures electric circuit characteristicsMultimeterSingle instrument for measuring impedance, resistance, and voltage on a wire
Has several uses
Sophistication, features, and costs vary
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25A multimeterSlide26
Cable Continuity TestersCable checkers (continuity testers, cable testers)Tests whether cable carries signal to destination
Series of lights, audible toneUsed to signal pass/failSome continuity testers verify UTP, STP wires paired correctlyNot shorted, exposed, crossed
Fiber optic continuity tester
Issues light pulses on fiber
Determines whether pulses reach other
end
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27Cable continuity testerSlide28
Cable Performance TestersDetermines if cable carrying currentContinuity testers versus performance testersDiffer in
sophistication and pricePerformance tester accomplishes same testsCan also perform additional tasksIssue
signal, measures signal bounce back
Indicates distance between
nodes/ measure length
Indicates whether terminators properly installed,
functional, d
etermine
faulty splice locations, breaks, connectors, bends
Expensive
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29 A high-end cable performance testerSlide30
Butt SetLineman’s handset, telephone test setUsesDetermine if line functioning (detects dial tone)
Receives signalPicks up noise affecting signal
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31Butt setSlide32
Network MonitorsSoftware-based toolContinually monitors network traffic Interprets up to Layer 3
Determines protocols passed by each frameCannot interpret frame dataTools developed by other software companies
Purchase or free
download
Network adapter
Must support promiscuous mode
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Protocol AnalyzersProtocol analyzer (network analyzer)Captures traffic, analyzes framesTypically to Layer 7Same
features as network monitor but includes additional featuresGenerates traffic to reproduce network problem
Can collect more information than can be reasonably processed
Set filters on gathered
data
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Protocol AnalyzersBefore using network monitor or protocol analyzer:Learn what network traffic normally looks like
Capture data for time period on regular basisEstablish a baseline to compare with future analysesSniffer (packet sniffer)Older term referring to hardware device
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35Traffic captured by a protocol analyzerSlide36
Wireless Network TestersTools containing wireless NICs, running wireless protocolsA workstation wireless network connection
Shows little about wireless environmentOnly applies to one workstationPrograms that scan
for wireless signals
Both software and hardware based
Discover access points, wireless stations transmitting
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Wireless Network Testers (cont’d.)Hardware instruments for wireless network testingTypically more portable than workstation with software toolsPreinstalled with network analysis tools
Accessible from simple, graphical interfaceContain powerful antennasSpectrum analyzer tool
Tool to assess wireless signal quality
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38 Wireless network testing toolSlide39
Network Monitors/Protocol analyzerNetwork Monitor softwareMicrosoft’s Network MonitorNagios
GangliaPlus there are commercial software alsoVariety of protocol analyzer software availableWireshark
Ethereal
SmartSniff
Plus there are commercial software
also
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SummaryMethodical, logical troubleshooting methodology8 troubleshooting stepsTroubleshooting tools
Tone generator, tone locatorMultimetersCable continuity testersCable performance tester
Butt
set
Network monitors and protocol analyzers
Wireless network testing tools
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End of Chapter 13
Questions
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