Chapter12 -- troubleshooting networking problems

Chapter 12: Troubleshooting Networking Problems

Network+ Guide to Networks

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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

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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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• Identify the Symptoms

• Access to the network affected

• Network performance affected

• Data or programs affected

• Only certain network services affected

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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• Diagnosing Physical Layer Problems

• Device turned on

• NIC properly inserted

• Device’s network cable properly connected

• Patch cables properly connect

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• 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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• Swapping Equipment

• If you suspect a problem lies with a network component

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• 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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• 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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• Recognize the Potential Effects of a Solution• Scope

• Tradeoffs

• Security

• Scalability

• Cost

• Using Vendor Information

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• 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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• 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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• Test the Solution

• Document Problems and Solutions• Staff Involved in Troubleshooting

• Recording Problems and Resolutions

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• 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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• 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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• 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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• 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

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• Preventing Future Problems• Review the troubleshooting questions and

examples

• Predict network problems by network maintenance, documentation, security, or upgrades

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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

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Troubleshooting Tools (continued)

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• Multimeter• Can measure many characteristics of an electric

circuit, including its resistance and voltage

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• 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

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• 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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• 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

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• 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

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• 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

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• 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

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• Abnormal data patterns and packets• Local collisions

• Late collisions

• Runts

• Giants

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• 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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• Wireless Network Testers• Learn about a wireless environment by viewing the

wireless network connection properties on your workstation

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• 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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• 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

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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

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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

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• Test your solution

• Operate a help desk

• Use a software program for documenting

• Record details about a problem

• Follow up

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• Change management system

• Tone generator and tone locator

• Multimeter

• Cable continuity testers

• Cable performance tester

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• Network monitor

• Protocol analyzers

• Wireless network testing tools

Chapter12 -- troubleshooting networking problems

Technology

logical connectivity

probable cause

connectivity device

symptoms consistent

symptoms access

physical layer problems

networking problems

network segments