Transcript Chapter 19

Chapter 19: Network Troubleshooting
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Chapter 19 Objectives
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The Following CompTIA Network+ Exam Objectives Are
Covered in This Chapter:
4.1 Given a scenario, implement the following network
troubleshooting methodology
• Identify the problem
o Gather information
o Duplicate the problem, if possible
o Question users
o Identify symptoms
o Determine if anything has changed
o Approach multiple problems individually
• Establish a theory of probable cause
o Question the obvious
o Consider multiple approaches
- Top-to-bottom/bottom-to-top OSI model
- Divide and conquer
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Chapter 19 Objectives (cont)
• • Test the theory to determine cause
• o Once theory is confirmed, determine next steps to
resolve problem
• o If theory is not confirmed, re-establish new theory
or escalate
• • 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
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Chapter 19 Objectives (cont)
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4.3 Given a scenario, troubleshoot and resolve common wireless issues
• Signal loss
• Interference
• Overlapping channels
o Mismatched channels
• Signal-to-noise ratio
• Device saturation
• Bandwidth saturation
• Untested updates
• Wrong SSID
• Power levels
• Wrong antenna type
• Incompatibilities
• Wrong encryption
• Bounce
• Environmental factors
o Concrete walls
o Window film
o Metal studs
• Wireless standard related issues
o Throughput
o Frequency
o Distance
o Channels
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Chapter 19 Objectives (cont)
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4.4 Given a scenario, troubleshoot and resolve
common copper cable issues
• Shorts
• Opens
• Incorrect termination (mismatched standards)
o Straight-through
o Crossover
• Cross-talk
o Near end
o Far end
• EMI/RFI
• Distance limitations
• Attenuation/Db loss
• Bad connector
• Bad wiring
• Split pairs
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Chapter 19 Objectives (cont)
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• Tx/Rx reverse
• Cable placement
• Bad SFP/GBIC - cable or transceiver
4.5 Given a scenario, troubleshoot and resolve
common fiber cable issues
• Attenuation/Db loss
• SFP/GBIC - cable mismatch
• Bad SFP/GBIC - cable or transceiver
• Wavelength mismatch
• Fiber type mismatch
• Dirty connectors
• Connector mismatch
• Bend radius limitations
• Distance limitations
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Chapter 19 Objectives (cont)
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4.6 Given a scenario, troubleshoot and resolve common network
issues
• Incorrect IP configuration/default gateway
• Broadcast storms/switching loop
• Duplicate IP
• Speed and duplex mismatch
• End-to-end connectivity
• Incorrect VLAN assignment
• Hardware failure
• Misconfigured DHCP
• Misconfigured DNS
• Incorrect interface/interface misconfiguration
• Cable placement
• Interface errors
• Simultaneous wired/wireless connections
• Discovering neighboring devices/nodes
• Power failure/power anomalies
• MTU/MTU black hole
• Missing IP routes
• NIC teaming misconfiguration
o Active-active vs active-passive
o Multicast vs broadcast
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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.
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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.
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Narrowing Down the Problem
• Did You Check the Super Simple Stuff?
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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?
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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.
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Can the Problem Be Reproduced?
The Link and Collision Lights
The Power Switch
Operator Error
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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
– Near-End or Far-end crosstalk
– Attenuation
– Collisions
– Shorts
– Open impedance mismatch (echo)
– Interference
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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
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Troubleshooting Steps
Step 1: Identify the Problem
• Question Users
• Determine If Anything Has Changed
• Identify Symptoms
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Troubleshooting Steps
• 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
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Troubleshooting Steps
• Step 3: Test the Theory to Determine Cause
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Troubleshooting Steps
• Step 4: Establish a Plan of Action to Resolve
the Problem and Identify Potential Effects
Troubleshooting Steps
Step 5: Implement the Solution or Escalate as
Necessary
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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
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Troubleshooting Steps
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
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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
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Troubleshooting Steps Review
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Identify the problem.
Establish a theory of probable cause.
Test the theory to determine cause.
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.
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Summary
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Summary
Exam Essentials Section
Written Labs
Review Questions
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