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Chapter 19: Network TroubleshootingInstructor:

Chapter 19 Objectives• The Following CompTIA Network+ Exam Objectives Are

Covered in This Chapter:

1.8 Given a scenario, implement the following network

troubleshooting methodology:

• Identify the problem:

– Information gathering

– Identify symptoms

– Question users

– Determine if anything has changed

• Establish a theory of probable cause:

– Question the obvious

• Test the theory to determine cause:

– Once theory is confirmed determine next steps to resolve problem.

– If theory is not confirmed, re-establish new theory or escalate.

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• Establish a plan of action to resolve the problem and identify• potential effects• Implement the solution or escalate as necessary• Verify full system functionality and if applicable implement preventative measures• Document findings, actions, and outcomes

2.4 Given a scenario, troubleshoot common wireless

problems.• Interference• Signal strength• Configurations• Incompatibilities

Chapter 19 Objectives (cont)

Chapter 19 Objectives (cont)

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• Incorrect channel

• Latency

• Encryption type

• Bounce

• SSID mismatch

• Incorrect switch placement

2.5 Given a scenario, troubleshoot common router and

switch problems.

• Switching loop

• Bad cables/improper cable types

• Port configuration

• VLAN assignment

• Mismatched MTU/MUT black hole

• Power failure

• Bad/missing routes

Chapter 19 Objectives (cont)

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• Bad modules (SFPs, GBICs)

• Wrong subnet mask

• Wrong gateway

• Duplicate IP address

• Wrong DNS

3.6 Given a scenario, troubleshoot common physical

connectivity problems.

• Cable problems:

• Bad connectors

• Bad wiring

• Open, short

• Split cables

• DB loss

• TXRX reversed

Chapter 19 Objectives (cont)

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• Cable placement

• NN EMI/Interference

• NN Distance

• NN Cross-talk

Network Troubleshooting

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• Troubleshooting computers and networks is a combination of art and science, and the only way to get really good at it is by doing it.

• Check quickly for problems in the “super-simple stuff” category.

• Move to common troubleshooting models that you can use like a checklist to go through to solve a surprising number of network problems.

Narrowing Down the Problem

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• Did You Check the Super Simple Stuff?– Check to ensure login procedures and rights.

– Look for link lights and collision lights.

– Check all power switches, cords, and adapters.

– Look for user errors.

• Are There Any Cabling Issues?

Narrowing Down the Problem

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• Correct Login Procedure and Rights

– Username and password is being entered correctly?

– Check that Caps Lock key.

• Can the Problem Be Reproduced?

• The Link and Collision Lights

• The Power Switch

• Operator Error

Narrowing Down the Problem

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• Is Hardware or Software Causing the Problem?

• Is It a Workstation or a Server Problem?

• Which Segments of the Network Are Affected?

• Is It Bad Cabling or Cabling issues?

– Crosstalk

– Nearing or near-end crosstalk

– Attenuation

– Collisions

– Shorts

– Open impedance mismatch (echo)

– Interference

Narrowing Down the Problem

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• Unbounded Media Issues (Wireless)

– Interference

– Incorrect encryption

– Incorrect channel

– Incorrect frequency

– ESSID mismatch

– Standard mismatch

– Distance

– Bounce

– Incorrect antenna placement

Troubleshooting Steps

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Step 1: Identify the Problem

• Question Users• Determine If Anything Has Changed• Identify Symptoms

Troubleshooting Steps

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• Step 2: Establish a Theory of Probable Cause

Question the Obvious

• Port speed

• Port duplex mismatch

• Mismatched MTU

• Incorrect VLAN

• Incorrect IP address

• Wrong gateway

• Wrong DNS

• Wrong subnet mask

Troubleshooting Steps

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• Step 3: Test the Theory to Determine Cause

Troubleshooting Steps

• Step 4: Establish a Plan of Action to Resolve

the Problem and Identify Potential Effects

Troubleshooting Steps

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Step 5: Implement the Solution or Escalate as Necessary

Some of the calamities that you should escalate are as follows:

• Switching loops• Missing routes• Routing loops• Routing problems• MTU black hole• Bad modules• Proxy Address Resolution Protocol (ARP)• Broadcast storms

Troubleshooting Steps

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Step 6: Verify Full System Functionality and If

Applicable Implement Preventative Measures

Step 7: Document Findings, Actions, and Outcomes• A description of the conditions surrounding the

problem• The OS version, the software version, the type

of computer, and the type of NIC• Whether you were able to reproduce the

problem• The solutions you tried• The ultimate solution

Troubleshooting Tips

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• Don’t Overlook the Small Stuff• Prioritize Your Problems• Check the Software Configuration• Don’t Overlook Physical Conditions• Don’t Overlook Cable Problems• Check for Viruses

Troubleshooting Steps Review

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1. Identify the problem.

2. Establish a theory of probable cause.

3. Test the theory to determine cause.

4. Establish a plan of action to resolve the problem and identify potential effects.

5. Implement the solution or escalate as necessary.

6. Verify full system functionality and if applicable implement preventative measures.

7. Document findings, actions, and outcomes.

Summary

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• Summary

• Exam Essentials Section

• Written Labs

• Review Questions