Post on 03-Jun-2018
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Chapter 2
Describe troubleshooting methods.
Describe the troubleshooting process.
Select appropriate troubleshooting method for agiven situation.
Explain the factors involved in incorporating
troubleshooting into routine maintenance.
Chapter 2 Troubleshooting Processesfor Complex Enterprise Networks
Objectives
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Chapter 2
Troubleshooting Methodologies
Troubleshooting is not an exact science, and a particularproblem can be diagnosed and sometimes even solved in manydifferent ways.
However, when you perform structuredtroubleshooting, youmake continuous progress, and usually solve the problemsfaster than it would take using an ad hoc approach.
Note that the solution to a network problem cannot alwaysbe readily implemented and an interim workaroundmight
have to be proposed.The difference between a solution and a workaround is that asolution resolvesthe root cause of the problem, whereas aworkaround only alleviates the symptomsof the problem.
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Structured TroubleshootingApproach
DefineProblem Analyse
Eliminate
Propose
Hypothesis
Test
Hypothesis
Solve
Problem
All troubleshooting methods include the elements of gathering and analysinginformation, eliminating possible causes, and formulating and testing hypotheses.Each of these steps has its merits and requires some time and effort; how andwhen one moves from one step to the next is a key factor in the success level of atroubleshooting exercise.
GatherInformation
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Troubleshooting Approaches
The key to all structured troubleshooting methods is
systematicelimination of hypothetical causes and narrowingdown on the possible causes.
If at some point you decide to seek help or hand the taskover to someone else, your findings can be of help to thatperson and your efforts are not wasted.
Commonly used troubleshooting approaches include thefollowing:
1. Top down
2. Bottom up3. Divide and conquer4. Follow the path5. Spot the difference6. Move the problem
7. Shoot from the hip
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Define the Problem
Unless an organization
has a strict policy on howproblems are reported,the reported problem canunfortunately be vagueoreven misleading.
A good problemdescription consists ofaccurate descriptions ofsymptoms and not ofinterpretations orconclusions.
Determine whether thisproblem is yourresponsibility or if itneeds to be escalated to
another department orperson.
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Gather & Analyse Information
Decide which devices, clients,or servers you want to collectinformation from, and what tools
you intend to use to gather thatinformation .
Acquire acces
s to theidentified targets.
Escalate the issue to adifferent department orperson to obtain access ifrequired.
If the escalationprocess will slow theprocedure down and theproblem is urgent,reconsider thetroubleshootingmethod.
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Eliminating Possible Causes
Consult network documentation to
interpret the information in thecontext of the actual network'simplementation.
Determine twothings: What ishappening on thenetwork and whatshould be happening.
Differences provideclues for what iswrong or at least adirection to take forfurther informationgathering.
A good baselineof the
behaviour of thenetwork can assist atthe analysis stage helps to spot anomaliesin the behavior of thenetwork and derive
clues from thosedeviations
The benefit ofrelevant pastexperience is important- experienced networkengineers will spendsignificantly less timeon researching than an
inexperienced engineer
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Hypothesis TestingAlthough the elimination processseems to be a rational, scientific
procedure, be aware thatassumptions play a role in thisprocess, too, and you have to bewilling to go back and re-examineand verifyyour assumptions.
Failure to do so may mistakenlyeliminate the actual root cause of a
problem as a non-probable cause,thus delaying the troubleshootingprocess.
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Solving The Problem - 1
Before starting to test the
proposal, reassess whether theproposed problem cause is withinyour area of responsibilities.
If the problem needs to be escalated,
does this end your involvement in theprocess?
Is there a need for a workaround? This temporary fix alleviates thesymptoms experienced by the user, even if it does not address theroot cause of the problem.
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Solving The Problem - 2Implementing a possible solutioninvolves making changes to the
network - follow your organisation'sregular changeprocedures.
Assess the impact of the change onthe network and balance that
against the urgency of the problem can you revert back if it all goeshorribly wrong?
Verifythat theproblem is solved andthat the changesmade did what youexpected it to do.
Check that thesolution has notintroduced any newproblems.
Create backups of anychanged configurationsor
upgraded software.
Document all changes tomake sure that thenetwork documentationstill accurately describesthe current state of thenetwork.
T bl h i & N k
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Troubleshooting & NetworkMaintenance
Tasks that do not revolve around fault management, such as adding or
replacing equipment, moving servers and users, and performing softwareupgrades, will regularly include troubleshooting processes.
Hence, troubleshooting should not be seen as a standaloneprocess, butas an essentialskill that plays an important role in many different typesof network maintenance tasks.
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Network Documentation
Having accurate and current
network documentation cantremendously increase the speedand effectivenessoftroubleshooting processes.
On the other hand,
documentation that is wrong oroutdated is often worse thanhaving no documentation at all.
After a problem has been solved or a workaround has beenimplemented always go through any of the standard administrativeprocesses for updatingthe documentation.
To assist this process, maintain a logof the changes made whiletroubleshooting.
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Creating a BaselineThe following list describes some useful data to gather and create a
baseline:1. Basic performance statistics such as the interface load for critical
network links and the CPU load and memory usage of routers andswitches: These values can be polled and collected on a regular basisusing SNMP and graphed for visual inspection.
2. Accounting of network traffic: Remote Monitoring (RMON),Network Based Application Recognition (NBAR), or NetFlowstatistics can be used to profile different types of traffic on thenetwork.
3. Measurements of network performance characteristics: The IP SLA
feature in Cisco IOS can be used to measure critical performanceindicators such as delay and jitter across the networkinfrastructure.
These baseline measurements are useful for troubleshooting, but theyare also useful inputs for capacity planning, network usage accounting,and SLA monitoring.
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Communication
DefineProblem Analyse
Eliminate
Propose
Hypothesis
Test
Hypothesis
Solve
Problem
GatherInformation
"What do you mean exactlywhen you say thatsomething is failing? Didyou make any changesbefore the problemstarted?
Might need to obtaininformation containedin server or applicationlogs, configurations ofdevices that you do notmanage
May have trouble interpretingcertain results, so askspecialists on your team tohelp you out
Even if changes will not have a major impact onthe users or the business, you should stillcoordinate and communicate any changes that youare making.
Report back to the person who originallyreported the problem that the problemhas been solved.
Go through any communication that isinvolved in the normal change processes,
to ensure that any changes made areproperly integrated into requireddocumentation.
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Change Control
Change control is one of the most fundamental processes
in network maintenance. By strictly controlling when changes are made, defining
what type of authorization is required and what actionsneed to be taken as part of that process, the frequency
and durationof unplanned outages can be reduced,increasing uptime.
The biggest difference between regular changes andemergency changes is the authorisationrequired to make a
change and the schedulingof the change. Within change-control procedures, there is always an
aspect of balancing urgency, necessity, impact, and risk change now or schedule for later?
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Describe troubleshooting methods.
Describe the troubleshooting process.
Select appropriate troubleshooting method for agiven situation.
Explain the factors involved in incorporating
troubleshooting into routine maintenance.
Chapter 2 Troubleshooting Processesfor Complex Enterprise Networks
Objectives
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Any
Questions?