Troubleshooting

1
Troubleshooting

• Dean (3rd), Chapter 12

2
Overview

• Need method
• Finding source of problem step-by-step
• Effects of solution
• Implement solution
• Test solution
• Document problems and solutions
• Troubleshooting tools

3
Troubleshooting Method

• Prevention (Chp 13) better than fixing problems
• Networks are complex
• Eliminating all problems not possible
• Need a method for finding source of problem and
  fixing problem

4
Steps to Find Source of Problem

• Identify symptoms
• Determine scope of problem
• Establish what has changed
• Ascertain most probable cause
• Verify user competency
• Re-create problem
• Verify physical connection
• Verify logical connection

5
Symptoms

• Is access to network affected?
• Is network performance affected?
• Are data, programs, or both affected?
• If programs
• One or more local programs affected?
• One network application affected?
• More than one network affected?
• What exactly is error message?
• Is more than one user affected?
• Are symptoms consistent or transient?

6
Scope of Problem

• How many user or segments?
• One user or workstation?
• One workgroup, department, or OU?
• One physical location within organization?
• Entire organization or network?
• When did problem begin?
• Has network, server, workstation ever worked
  properly?
• Did symptoms appear in last hour, day, week?
• Have symptoms been intermittent for long time?
• Are symptoms periodic? At certain times of day,
  week, month, or year?

7
Whats Changed

• Did operating system or configuration change?
• Were new components added?
• Were old components removed?
• Were components moved?
• Were components replaced?
• Were new user or segment added?
• Was new software installed?
• Was old software removed?

8
Probable Cause

• Some frequent causes of network problems
• Verify user competency
• Even competent users have bad days
• Watch user perform task
• Re-create problem
• Replication of a problem makes it easier to solve
• Use common sensesome problems are too sever to
  repeat
• Verify physical connection
• Verify logical connection

9
Physical Layer Troubleshooting

• Is the device turned on?
• Is the NIC properly installed? Has it worked
  loose?
• Is cable properly connected from NIC through wall
  jack, punch-down block, patch panel, to hub,
  switch, or router?
• Is hub, switch, or router properly connected to
  backbone?
• Are ALL cables in good condition?
• Are ALL connectors in good condition and properly
  seated?
• Do network (maximum and segment) lengths conform
  to IEEE 802 specifications?
• Are all devices properly configured by type and
  speed to work with network? (p. 615)

10
Logical Connectivity Troubleshooting

• Do error messages reference damaged or missing
  files or device drivers?
• Do error messages malfunctioning or insufficient
  resources?
• Has an application, configuration, or operating
  system recently changed, added, or deleted?
• Does problem occur with only one application or
  similar applications?
• Can the problem be replicated?
• Does problem effect single user or group of users?

11
Effects of Solution

• After analyzing problem, solution can be
  developed
• Before implementing solution, consider affect of
  solution on users and network functionality
• Potential effects
• Scopehow many users affected
• Tradeoffsdoes solution solve one problem and
  cause another
• Securitydoes solution create security
  vulnerability
• Scalabilitytemporary fix or long term
  improvement
• Costdon't use a sledge hammer on a tack size job

12
Implement Solution

• Collect, document, and use data from
  investigation of problem during implementation
• Backup data, record configurations, and save old
  parts in case solution doesn't work
• Make and record one change at a time
• Test solution at each step or change
• Clean up area before you leave
• Record actions in troubleshooting database for
  future reference
• Follow-upmake sure solution still works tomorrow

13
Troubleshooting Tools

• Crossover cabledirectly connect devices to
  reduce complexity
• Fox and houndtone generator and locator find
  the other end of the cable
• Multimetervoltmeter and ohmmeter test
  electrical properties of cables
• Continuity testeris cable carrying signal
• Cable performance testermeasures cable
  properties
• Distance to connectivity device, termination
  point, or fault
• Attenuation along cable
• Near end crosstalk
• Pass/fail CAT standards
• Network monitorssoftware monitors network
  traffic
• Protocol analyzerssoftware/hardware identify
  and assess network problems
• Wireless network testerassess wireless
  connection properties

14
Summary

• Analyze problem
• Identify symptoms
• Identify scope
• Determine what's changed
• Select most probable cause to form solution
• User error or unstable application environment
• Physical connectivity
• Logical connectivity
• Assess potential effects of solution
• Implement solution
• Test solution and follow-up
• Documenting problems and solutions
• Tools