Network Troubleshooting. Overview A network administrator’s job has many aspects, all of which must be mastered through experience and education. Troubleshooting

Network Troubleshooting

Overview

• A network administrator’s job has many aspects, all of which must be mastered through experience and education. Troubleshooting network problems is no exception. Some administrators can easily hone in on a problem; others take a while to get the hang of it. There simply is no magic wand for troubleshooting—each administrator needs to become very familiar with their network and how it should act.

Topics

Troubleshooting Models

TCP/IP Troubleshooting Utilities

Hardware Troubleshooting Tools

System Monitoring Tools

Network Baselining

First Things First

Check the obviousCorrect syntax

User error

Correct components

Correct configuration

Check the trouble indicatorsWarning lights

Error messages and log files

Is the problem hardware or software?

Is the problem a single or multiple workstation?

Check the cables

Troubleshooting

RecognitionRecognition DiagnosisDiagnosis ResolutionResolution

Troubleshooting Models

Step-by-step approachStep-by-step approach

Administrator

The CompTIA Network+ Troubleshooting Model

1. Establishing the symptoms and potential causes

2. Identifying the affected area

3. Establishing what has changed

4. Selecting the most probable cause

5. Implementing an action plan and solution

6. Testing the result

7. Identifying the results and effects of the solution

8. Documenting the solution and process

The Network+ Troubleshooting Model – Step 1

1. Establishing the symptoms and potential causes Gather information Re-create the problem List potential causes

2. Identifying the affected area3. Establishing what has changed4. Selecting the most probable cause5. Implementing an action plan and solution6. Testing the result7. Identifying the results and effects of the

solution8. Documenting the solution and process



2. Identifying the affected area One user Several users One server One segment The network

3. Establishing what has changed4. Selecting the most probable cause5. Implementing an action plan and solution6. Testing the result7. Identifying the results and effects of the solution8. Documenting the solution and process



2. Identifying the affected area3. Establishing what has changed

Could you ever do this? When did things change? What has changed?

4. Selecting the most probable cause5. Implementing an action plan and solution6. Testing the result7. Identifying the results and effects of the




2. Identifying the affected area3. Establishing what has changed4. Selecting the most probable cause

Start with most obvious cause Work backward Try simple solutions

5. Implementing an action plan and solution6. Testing the result7. Identifying the results and effects of the




2. Identifying the affected area3. Establishing what has changed4. Selecting the most probable cause5. Implementing an action plan and solution

Create a plan Determine potential effects of the plan Implement step by step

6. Testing the result7. Identifying the results and effects of the




2. Identifying the affected area3. Establishing what has changed4. Selecting the most probable cause5. Implementing an action plan and solution6. Testing the result

Verify that it solved the problem Verify that no new problems introduced Test various conditions

7. Identifying the results and effects of the solution





solution Re-examine your list of potential effects Test for potential effects Adjust if needed






Use a troubleshooting template Document all information Maintain records for reference

Troubleshooting IP Configuration

Incorrect IP configurationIncorrect IP

configuration

Troubleshooting with Ping

Ping to default gateway failsPing to default gateway fails

Ping to local system succeeds

Ping to local system succeeds

Troubleshooting with Tracert

Start troubleshootingat last valid connectionStart troubleshooting

at last valid connection

Troubleshooting with Arp

Incorrect mappingIncorrect mapping

Troubleshooting with Telnet

C:\> telnet 10.1.1.3Password:

11 Upper-level service failsUpper-level service fails 22 Use Telnet to connectUse Telnet to connect

Troubleshooting with Nbtstat

Server service running as desired

Server service running as desired

Troubleshooting with Netstat

No adapter errorsNo adapter errors

Connection validConnection valid

Queue shows activityQueue shows activity

Listening ports validListening

ports valid

Troubleshooting with FTP

Patches and utilitiesPatches and utilities

Vendor FTP site FTP client

Troubleshooting with Nslookup

Verify default serverVerify default server

Verify that server is responding to

queries

Verify that server is responding to

queriesVerify that server can

resolve namesVerify that server can

resolve names

Network Technician’s Hand Tools

Various small hand toolsVarious small hand tools

Electrical Safety Rules

• Professionals should service high-power equipment

• Always disconnect before servicing

• Work with a partner

• Never bypass safety devices

• Use anti-static devices

Wire Crimpers

Specific to media typeSpecific to media type

A Punch Down Tool

Strips insulation and embeds wire

Strips insulation and embeds wire

A Circuit Tester

Displays circuit statusDisplays circuit status

Plugs into socketPlugs into socket

Voltmeters

Digital Analog

A Cable Tester

Adapters for different network types

Adapters for different network types

Ports for network cablePorts for network cable

Displays media statusDisplays media status

Crossover Cables

Wires crossed over internally

Wires crossed over internally

A Hardware Loopback Plug

Crosses over transmit/receive lines

Crosses over transmit/receive lines

LED Indicator Lights

Link lightLink light

Activity lightActivity light

Tone Generators and Tone Locators

Port for network cable

Port for network cable

Probe detects signal

Probe detects signal

Tone generator Tone locator

Network Analyzers

Network AnalyzersWindows 2000 = Network monitorNovell = LANalyzerOther third party

Protocol analyzersEvaluate the data at all layers of the OSI modelOperate in promiscuous mode

A Performance Monitor

Displays results

Displays results

Monitors countersMonitors counters

A Protocol Analyzer

Captures framesCaptures frames

Displays frame contentsDisplays frame contents

The Protocol Analysis Process

Capture frames

Decode contents

Analyze contents

Using the Baseline

1. Predict the impact of changes to network

2. Use to find the reason for degradation in performance

3. Show best locations to invest money in the network

A Baseline

• Record of current performance

• Basis for identifying abnormal conditions

• Starting point for improving performance

Baseline

Various testsVarious tests

Record of normal performance

Record of normal performance

3. Schedule tests

1. Evaluate network

The Baseline Process

4. Run tests

5. Document results

8. Upgrade or reconfigure as needed

6. Analyze data

7. Repeat tests when performance low

2. Design tests

Renewing the Baseline

When do you redo your baseline?When role of network changesWhen services are added to networkWhen services are removed from network

Reflective Questions

1. Describe a troubleshooting situation you were involved in, or that you read or heard about. Was it resolved through a structured methodology?

2. Which of the troubleshooting tools and processes presented in this lesson do you think you will find most useful or use most frequently? Why?

Collect, Isolate, and Correct Model

Collect information Isolate the problemCorrect the problem

Network Support Tools

Tools help you troubleshoot only if you have mastered their useSoftware-based tools

Diagnostic utilitiesPerformance monitorsTCP/IP Utilities

Documents

Network Troubleshooting. Overview A network administrator’s job has many aspects, all of which must be mastered through experience and education. Troubleshooting