Network Guide to Networks, Fourth Edition

1
Network Guide to Networks, Fourth Edition

• Chapter 12
• Troubleshooting Network Problems

2
Troubleshooting Methodology

• Steps for troubleshooting network problems
• Identify symptoms and potential causes
• Identify affected area
• Establish what has changed
• Select most probable cause
• Verify user competency
• Re-create problem
• Verify physical integrity of network connection
• Verify logical integrity of network connection

3
Troubleshooting Methodology (continued)

• Steps for troubleshooting network problems
  (continued)
• Implement an action plan and solution and be
  prepared for all potential effects
• Test the result
• Identify results and effects of solution
• Document solution and process

4
Establish What Has Changed

• Questions to help pinpoint problems resulting
  from a network change
• OS or configuration on a server, workstation, or
  connectivity device changed?
• New components added to server, workstation, or
  connectivity device?
• Old components removed from server, workstation,
  or connectivity device?
• New users or segments added to the network?
• Server, workstation, or connectivity device moved
  from previous location to new location?

5
Select the Most Probable Cause Verify User
Competency

• Ensure that human error is not source of problem
• Problems caused by human error usually simple to
  solve
• Best way to verify that a user is performing
  network tasks correctly is to watch them

6
Re-create the Problem

• Try to reproduce symptoms both while logged on as
  the user who reported the problem and while
  logged on under a privileged account
• Questions to help determine whether a problems
  symptoms are truly reproducible
• Make symptoms recur every time?
• Make symptoms recur some of the time?
• Symptoms happen only under certain circumstances?
  
• Symptoms consistent no matter how many and which
  programs or files user has open?

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Verify Physical Connectivity

• Many network problems occur at Physical layer
• Symptoms of Physical Layer problems continuous
  or intermittent inability to connect to network
  and perform network related functions
• Possible causes of Physical Layer problems
• Segment or network lengths exceeding IEEE maximum
  standards
• Noise affecting wireless or wire-bound signal
• Improper terminations, faulty connectors, loose
  connectors, or poorly crimped connections
• Damaged cables
• Faulty NICs

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Implement an Action Plan and Solution Including
Potential Effects

• Scope assess scope of solution before
  implementing
• Tradeoffs solution may restore functionality for
  one group of users, but remove it for others
• Security solution may inadvertently result in
  addition or removal of network access or resource
  privileges for a user or group of users
• Scalability does solution position network for
  additions and enhancements later on
• Cost if solution requires significant software
  or hardware cost, weigh options carefully

9
Test the Results

• Must verify that problem solved properly
• Type of testing depends on solution
• Depends on area affected by problem
• May not be able to test solution immediately
  after implementing it

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Identify the Results and Effects of the Solution

• Should be able to determine how and why solution
  was successful and effects on users and
  functionality
• Want to avoid creating unintended, negative
  consequences as result of solution

11
Document the Solution and Process

• Always record symptoms and cause(s) of a problem
  and solution
• Impossible to remember circumstances of each
  incident
• Networking personnel frequently change jobs

12
Help to Prevent Future Problems

• Not all problems are preventable, but many can be
  avoided
• Perform regular network health checks
• Even continual network monitoring
• When planning or upgrading a network, think about
  how good network designs and policies can prevent
  later problems

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Troubleshooting Tools Crossover Cable

• Transmit and receive wire pairs in one connector
  are reversed
• Directly interconnect two nodes without using an
  intervening connectivity device
• Useful for quickly and easily verifying that
  nodes NIC is transmitting and receiving signals
  properly

14
Tone Generator and Tone Locator

• Telecommunications closets often disorganized and
  poorly documented
• Tone generator Issues signal on wire pair
• Tone locator Emits tone when it detects
  electrical activity on wire pair
• Cannot be used to determine cable characteristics
• Such as whether it has defects or whether its
  length exceeds IEEE standards for a certain type
  of network

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Tone Generator and Tone Locator (continued)
Figure 12-4 Use of a tone generator and tone
locator
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Multimeter

• Can measure many characteristics of an electric
  circuit, including its resistance and voltage
• Voltmeter measures voltage of electric current
• Ohmmeter measures resistance
• Every type of wire has different resistance
  characteristics
• Impedance resistance that contributes to
  controlling signal
• Telltale factor for ascertaining location of
  faults in a cable

17
Cable Continuity Testers

• Test whether cable carrying signal to destination
• When used on copper-based cables, applies small
  voltage to each conductor at one end of a cable
• Checks whether voltage detectable at other end
• Two parts
• Base unit generates voltage
• Remote unit detects voltage
• Some verify that wires in UTP or STP cables
  paired correctly and are not shorted, exposed, or
  crossed

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Cable Continuity Testers (continued)
Figure 12-6 Cable continuity testers
19
Cable Performance Testers

• Accomplishes same continuity and fault tests as a
  continuity tester, and more
• Performance testers perform following tasks
• Measure distance to connectivity device,
  termination point, or cable fault
• Measure attenuation along cable
• Measure near-end crosstalk between wires
• Measure termination resistance and impedance
• Pass/fail ratings for CAT 3, 5, 5e, 6, or 7
  standards

20
Cable Performance Testers (continued)

• Performance testers perform following tasks
  (continued)
• Store and print cable testing results or directly
  save data
• Graphically depict cables attenuation and
  crosstalk characteristics over length of cable
• Time domain reflectometer (TDR) issues signal on
  cable and measures way signal reflects
• Optical time domain reflectometer (OTDR) used
  for fiber optic cables

21
Cable Performance Testers (continued)
Figure 12-7 A performance tester
22
Network Monitors

• Software tool that continually monitors network
  traffic from a server or workstation
• Typically can interpret up to Layer 3
• Determines protocols passed by each frame
• Cant interpret data inside frames
• Many available programs
• Microsoft Network Monitor ships with Windows
  Server 2003
• Novell NETMON comes with NetWare 5.x and 6.x
• Many others available

23
Protocol Analyzers

• Capture traffic and analyze frames
• Typically up to Layer 7
• Can interpret payload portion of frames
• Can generate traffic in attempt to reproduce
  network problem and monitor multiple network
  segments simultaneously
• Hardware-based protocol analyzers exist
• Sole job is to identify and assess network
  problems
• Tailored to particular type of network
• May collect more information than can be processed

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Protocol Analyzers (continued)
Figure 12-8 Traffic displayed by protocol type
25
Wireless Network Testers

• To test wireless connections, stations, or APs,
  need tools that contain wireless NICs and run
  wireless protocols
• Programs exist that can scan for wireless signals
  over a geographical range and discover all APs
  and wireless stations transmitting in area
• Determine whether AP functioning properly
• Determine whether AP positioned correctly
• Determine whether stations and APs are
  communicating over proper channels within a
  frequency band

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Wireless Network Testers (continued)
Figure 12-10 Wireless network testing tool