Chap 2 -Troubleshooting Processes

8/12/2019 Chap 2 -Troubleshooting Processes

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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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Chapter 2

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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Chapter 2

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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Chapter 2

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?


16/17Chapter 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


17/17Chapter 2

Any

Questions?

Chap 2 -Troubleshooting Processes

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