Chapter12 -- troubleshooting networking problems
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Transcript of Chapter12 -- troubleshooting networking problems
Chapter 12: Troubleshooting Networking Problems
Network+ Guide to Networks
2
Objectives:
Describe the elements of an effective troubleshooting methodology
Follow a systematic troubleshooting process to solve networking problems
Use a variety of software and hardware tools to diagnose problems
Discuss practical issues related to troubleshooting
3
Troubleshooting Methodology
• Identify the Symptoms
• Identify the Scope of the Problem
• Establish What Has Changed
• Determine the Most Probable Cause• Verify user competency
• Re-create the problem
• Verify physical connectivity
• Verify logical connectivity
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Troubleshooting Methodology (continued)
• Recognize the potential effects of a solution
• Implement a solution
• Test the solution
• Document the solution
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Troubleshooting Methodology (continued)
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Troubleshooting Methodology (continued)
• Identify the Symptoms
• Access to the network affected
• Network performance affected
• Data or programs affected
• Only certain network services affected
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Troubleshooting Methodology (continued)
• Identify the Symptoms (continued)
• If programs are affected, does the problem include one local application, one networked application, or multiple networked applications
• What specific error messages do users report
• One user or are multiple users affected
• Do symptoms manifest themselves consistently
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Troubleshooting Methodology (continued)
• Identify the Scope of the Problem• How many users or network segments are
affected?
• One user or workstation?
• A workgroup?
• A department?
• One location within an organization?
• An entire organization?
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Troubleshooting Methodology (continued)
• Identify the Scope of the Problem (continued)• When did the problem begin?
• Has the network, server, or workstation ever worked properly?
• Did the symptoms appear in the last hour or day?
• Have the symptoms appeared intermittently for a long time?
• Do the symptoms appear only at certain times?
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Troubleshooting Methodology (continued)
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Troubleshooting Methodology (continued)
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Troubleshooting Methodology (continued)
• Establish What Has Changed• Did the operating system or configuration on a
server, workstation, or connectivity device change?
• Were new components added to a server, workstation, or connectivity device?
• Were old components removed from a server, workstation, or connectivity device?
• Were new users or segments added to the network?
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Troubleshooting Methodology (continued)
• Establish What Has Changed (continued)• Was a server, workstation, or connectivity device
moved from its previous location to a new location?
• Was a server, workstation, or connectivity device replaced?
• Was new software installed on a server, workstation, or connectivity device?
• Was old software removed from a server, workstation, or connectivity device?
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Troubleshooting Methodology (continued)
• Select the Most Probable Cause• Verify User Competency
• Re-create the Problem
• Can you make the symptoms recur every time?
• If symptoms recur, are they consistent?
• Can you make the symptoms recur some of the time?
• Do the symptoms happen only under certain circumstances?
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Troubleshooting Methodology (continued)
• Select the Most Probable Cause• Re-create the Problem (continued)
• In the case of software malfunctions, are the symptoms consistent no matter how many and which programs or files the user has open?
• Do the symptoms ever happen when you try to repeat them?
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Troubleshooting Methodology (continued)
• Select the Most Probable Cause• Verify Physical Connectivity
• Symptoms of Physical Layer Problems
• Lengths exceed standards
• Noise affecting a signal
• Improper connections
• Damaged cables
• Faulty NICs
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Troubleshooting Methodology (continued)
• Select the Most Probable Cause• Verify Physical Connectivity
• Diagnosing Physical Layer Problems
• Device turned on
• NIC properly inserted
• Device’s network cable properly connected
• Patch cables properly connect
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Troubleshooting Methodology (continued)
• Select the Most Probable Cause• Verify Physical Connectivity
• Diagnosing Physical Layer Problems (continued)
• Hub, router, or switch properly connected to the backbone
• Cables in good condition
• Connectors in good condition and properly seated
• Network lengths conform to specifications?
• Devices configured properly
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Troubleshooting Methodology (continued)
• Select the Most Probable Cause• Verify Physical Connectivity
• Swapping Equipment
• If you suspect a problem lies with a network component
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Troubleshooting Methodology (continued)
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Troubleshooting Methodology (continued)
• Select the Most Probable Cause• Verify Logical Connectivity
• Do error messages reference damaged or missing files or device drivers?
• Do error messages reference malfunctioning or insufficient resources (such as memory)?
• Has an operating system, configuration, or application been recently changed, introduced, or deleted?
• Does the problem occur with only one application or a few, similar applications?
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Troubleshooting Methodology (continued)
• Select the Most Probable Cause• Verify Logical Connectivity
• Does the problem happen consistently?
• Does the problem affect a single user or one group of users?
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Troubleshooting Methodology (continued)
• Recognize the Potential Effects of a Solution• Scope
• Tradeoffs
• Security
• Scalability
• Cost
• Using Vendor Information
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Troubleshooting Methodology (continued)
• Implement a Solution• Implement a safe and reliable solution:
1. Collect documentation about a problem’s symptoms
2. Backup existing software and keep the old parts handy
3. Perform the change and record your actions
4. Test your solution
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Troubleshooting Methodology (continued)
• Implement a Solution• Implement a safe and reliable solution:
5. Before leaving the area clean it up
6. Record the details you have collected about the symptoms, the problem, and the solution
7. If solution involved a significant change or problem, revisit the solution a day or two later to verify that the problem has been solved
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Troubleshooting Methodology (continued)
• Test the Solution
• Document Problems and Solutions• Staff Involved in Troubleshooting
• Recording Problems and Resolutions
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Troubleshooting Methodology (continued)
• A typical problem record form should include
• The name, department, and phone number of the problem originator
• Information regarding whether the problem is software- or hardware-related
• If the problem is software-related, the package to which it pertains; if the problem is hardware-related, the device or component to which it pertains
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Troubleshooting Methodology (continued)
• A typical problem record form should include (continued)
• Symptoms of the problem, including when it was first noticed
• The name and telephone number of the network support contact
• The amount of time spent troubleshooting the problem
• The resolution of the problem
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Troubleshooting Methodology (continued)
• Notifying Others of Changes
• A change management system
• Adding or upgrading software
• Adding or upgrading hardware or other devices
• Adding new hardware
• Changing the properties of a network device
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Troubleshooting Methodology (continued)
• A change management system (continued)
• Increasing or decreasing rights
• Physically moving networked devices
• Moving user accounts and their files/directories
• Making changes in processes
• Making changes in vendor policies or relationships
31
Troubleshooting Methodology (continued)
• Preventing Future Problems• Review the troubleshooting questions and
examples
• Predict network problems by network maintenance, documentation, security, or upgrades
32
Troubleshooting Tools
• Crossover Cable• Use to directly interconnect two nodes
• Tone Generator and Tone Locator• Tone generator is a small electronic device that
issues a signal on a wire pair
• Tone locator is a device that emits a tone when it detects electrical activity on a wire pair
33
Troubleshooting Tools (continued)
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Troubleshooting Tools (continued)
• Multimeter• Can measure many characteristics of an electric
circuit, including its resistance and voltage
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Troubleshooting Tools (continued)
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Troubleshooting Tools (continued)
• Use a multimeter to:• Verify that a cable is properly conducting electricity
• Check for the presence of noise on a wire
• Verify that the amount of resistance on coaxial cable
• Test for short or open circuits in the wire
37
Troubleshooting Tools (continued)
• Cable Continuity Testers• In troubleshooting a Physical layer problem, you
may find the cause of a problem by simply testing whether your cable is carrying a signal to its destination
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Troubleshooting Tools (continued)
39
Troubleshooting Tools (continued)
• Cable Performance Testers• Measure the distance to a connectivity device,
termination point, or cable fault
• Measure attenuation along a cable
• Measure near-end crosstalk between wires
• Measure termination resistance and impedance
40
Troubleshooting Tools (continued)
• Cable Performance Testers (continued)• Issue pass/fail ratings for CAT 3, CAT 5, CAT 5e,
CAT 6, or CAT 7 standards
• Store and print cable testing results or directly save data to a computer database
• Graphically depict a cable’s attenuation and crosstalk characteristics over the length of the cable
41
Troubleshooting Tools (continued)
42
Troubleshooting Tools (continued)
• Network Monitors• Continuously monitor network traffic on a segment
• Capture network data transmitted on a segment
• Capture frames sent to or from a specific node
• Reproduce network conditions
• Generate statistics about network activity
43
Troubleshooting Tools (continued)
• Network Monitors (continued)• Discover all network nodes on a segment
• Establish a baseline that reflects network traffic
• Store traffic data and generate reports
• Trigger alarms when traffic conditions meet preconfigured conditions
44
Troubleshooting Tools (continued)
• Abnormal data patterns and packets• Local collisions
• Late collisions
• Runts
• Giants
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Troubleshooting Tools (continued)
• Abnormal data patterns and packets (continued)• Jabber
• Negative frame sequence checks
• Ghosts
• Protocol Analyzers• Can capture traffic
• Can also analyze frames
• To Layer 7 of the OSI Model
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Troubleshooting Tools (continued)
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Troubleshooting Tools (continued)
• Wireless Network Testers• Learn about a wireless environment by viewing the
wireless network connection properties on your workstation
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Troubleshooting Tools (continued)
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Troubleshooting Tools (continued)
• Wireless network testing tools• Identify transmitting APs, stations and channels
• Measure signal strength and range
• Indicate the effects of attenuation, signal loss, and noise
• Interpret signal strength information
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Troubleshooting Tools (continued)
• Wireless network testing tools (continued)• Ensure proper association and reassociation
• Capture and interpret traffic
• Measure throughput and assess data
• Analyze the characteristics of each channel
51
Troubleshooting Tools (continued)
52
Chapter Summary
• Before you can resolve a network problem, you need to determine its cause
• Act like a doctor diagnosing a patient
• Identify the scope of the problem
• At each point, stop to consider
• Ensure that the user is performing all functions correctly
53
Chapter Summary (continued)
• Attempt to reproduce the problem’s symptoms
• Check for sound connections
• Exchange component for a functional one
• Determine properly configured software
• Consult vendor information
54
Chapter Summary (continued)
• Test your solution
• Operate a help desk
• Use a software program for documenting
• Record details about a problem
• Follow up
55
Chapter Summary (continued)
• Change management system
• Tone generator and tone locator
• Multimeter
• Cable continuity testers
• Cable performance tester
56
Chapter Summary (continued)
• Network monitor
• Protocol analyzers
• Wireless network testing tools