Network Guide to Networks, Fourth Edition

1
Network Guide to Networks, Fourth Edition

• Chapter 12
• Troubleshooting Network Problems

2
Objectives

• Describe the steps involved in an effective
  troubleshooting methodology
• Follow a systematic troubleshooting process to
  identify and resolve networking problems
• Document symptoms, solutions, and results when
  troubleshooting network problems
• Use a variety of software and hardware tools to
  diagnose problems

3
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

4
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

5
Identify the Symptoms and Potential Causes

• Questions that may help identify non-obvious
  symptoms
• Access to network affected?
• Network performance affected?
• Data and/or programs affected?
• Only certain network services affected?
• Problems include local application, networked
  application, or multiple networked applications?
• Specific error messages reported?
• One user or multiple users affected?
• Symptoms manifested consistently?

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Identify the Affected Area
Figure 12-1 Identifying the area affected by a
problem
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Identify the Affected Area (continued)
Figure 12-1 (continued) Identifying the area
affected by a problem
8
Identify the Affected Area (continued)
Figure 12-2 Identifying the chronological scope
of a problem
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Identify the Affected Area (continued)
Figure 12-2 (continued) Identifying the
chronological scope of a problem
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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?

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Establish What Has Changed (continued)

• Questions to help pinpoint problems resulting
  from a network change (continued)
• 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?

12
Establish What Has Changed (continued)

• Two ways to react to problems caused by network
  changes
• Attempt to correct problem
• Attempt to reverse change and restore hardware or
  software to previous state
• Complete network change records should be kept
• Make available to staff members

13
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

14
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?

15
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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Verify Physical Connectivity (continued)

• Diagnosing Physical Layer problems
• Device turned on?
• NIC properly inserted?
• For wireless NICs, antenna turned on?
• Devices network cable properly connected to both
  NIC and wall jack?
• Patch cables properly connect punch-down blocks
  to patch panels and patch panels to hubs or
  switches?

17
Verify Physical Connectivity (continued)

• Diagnosing Physical Layer problems (continued)
• Hub, router, or switch properly connected to
  backbone?
• Cables in good condition?
• Connectors in good condition and properly seated?
• Network lengths conform to IEEE 802
  specifications?
• Devices configured properly to work with network
  type or speed?

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Verify Physical Connectivity (continued)

• Swapping equipment
• If you suspect problem lies with a network
  component, easy to test theory by exchanging for
  a functional component
• Cables, ports, data jacks, network adapters
• Difficult to swap routers and switches

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Verify Physical Connectivity (continued)
Figure 12-3 Verifying physical connectivity
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Verify Physical Connectivity (continued)
Figure 12-3 (continued) Verifying physical
connectivity
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Verify Logical Connectivity

• Questions to help identify logical connectivity
  problems
• Error messages reference damaged or missing files
  or device drivers?
• Error messages reference malfunctioning or
  insufficient resources?
• OS, configuration, or application been recently
  changed, introduced, or deleted?
• Problem occurs with only one application or a
  few, similar applications?
• Problem happens consistently?
• Problem affects single user or one group of users?

22
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

23
Implement an Action Plan and Solution Including
Potential Effects (continued)

• Use vendor information nothing to lose by
  referring to manual, except a little time
• Manuals, online information, technical support
• Implement the solution
• Collect all documentation about problems
  symptoms
• Make backups, keep old parts, print
  configurations
• Perform change, replacement, move, or addition
• Test solution
• Clean up
• Document solution and results
• Revisit problem later

24
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

25
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

26
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

27
Staff Involved in Troubleshooting

• Many staff members may contribute to
  troubleshooting network problems
• Help desk analysts often first-level support
• Creates record for incident and attempts to
  diagnose problem
• Second-level support analyst has specialized
  knowledge in one or more aspects of a network
• Most help desks include a help desk coordinator
• Ensures analysts divided into correct teams,
  schedules shifts, maintains infrastructure to
  enable analysts to better perform their jobs

28
Record Problems and Resolutions

• Call tracking system software used for
  documenting problems
• If no call tracking system, should keep records
  in electronic form
• Name, department, phone number of problem
  originator
• Software- or hardware-related problem?
• Software package or device/component to which it
  pertains
• Symptoms of problem
• Name/telephone number of network support contact
• Time spent troubleshooting
• Resolution

29
Notify Others of Change

• Record resolution in call tracking system
• Notify others of solution and what, if anything,
  needed to change to fix problem
• Alerts others about problem and solution
• Notifies others of network changes made, in case
  they affect other services
• Change management system process or program that
  provides support personnel with centralized means
  of documenting network changes

30
Notify Others of Change (continued)

• Types of changes that network personnel should
  record in change management system
• Adding or upgrading software or hardware
• Changing network properties of network device
• Increasing or decreasing rights for group of
  users
• Physically moving networked devices
• Moving user accounts, files, and directories
• Making changes in processes
• Making changes in vendor policies or relationships

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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

33
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
35
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

36
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

37
Cable Continuity Testers (continued)
Figure 12-6 Cable continuity testers
38
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

39
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

40
Cable Performance Testers (continued)
Figure 12-7 A performance tester
41
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

42
Network Monitors (continued)

• Network monitoring tools perform following
  functions
• Continuously monitor network traffic on segment
• Capture network data transmitted on segment
• Capture frames sent to or from specific node
• Reproduce network conditions by transmitting
  selected amount and type of data
• Generate statistics about network activity

43
Network Monitors (continued)

• Some network monitoring tools can also
• Discover all network nodes on a segment
• Establish a baseline
• Record of how network operates under normal
  conditions, including performance, collision
  rate, utilization rate, and so on
• Store traffic data and generate reports
• Trigger alarms when traffic conditions meet
  preconfigured conditions

44
Network Monitors (continued)

• Data errors that can be distinguished
• Local collisions
• Late collisions
• Runts
• Giants
• Jabber
• Negative frame sequence checks
• Ghosts

45
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

46
Protocol Analyzers (continued)
Figure 12-8 Traffic displayed by protocol type
47
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

48
Wireless Network Testers (continued)

• Some programs can capture data transmitted
  between stations and APs
• Useful for troubleshooting wireless connection
  problems
• Some programs contain a spectrum analyzer
• Assess quality of wireless signal
• Ascertain where noise (or interference) is
  greatest

49
Wireless Network Testers (continued)

• Capabilities common to wireless network testers
• Identify transmitting APs and stations and
  channels over which they are communicating
• Measure signal strength from and determine range
  of AP
• Indicate effects of attenuation, signal loss, and
  noise
• Interpret signal strength information

50
Wireless Network Testers (continued)

• Capabilities common to wireless network testers
  (continued)
• Ensure proper association and reassociation when
  moving between APs
• Capture/interpret traffic exchanged between
  wireless APs and stations
• Measure throughput and assess data transmission
  errors
• Analyze the characteristics of each channel
  within a frequency band to indicate the clearest
  channels

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

• Key to solving network problems is to approach
  them methodically and logically, using your
  experience to inform your decisions, and knowing
  when to ask for someone elses help
• First step in troubleshooting is identifying the
  symptoms and potential causes for a problem
• Second step in troubleshooting is to identify the
  affected area
• At each point in the troubleshooting process,
  stop to consider what kind of changes have
  occurred on the network that might have created a
  problem

53
Summary (continued)

• Based on an analysis of the symptoms and how
  changes might have affected the network, select a
  probable cause for the problem
• After you have identified the probable cause,
  implement an action plan and your solution, while
  considering the potential effects of the solution
• After implementing your solution, test your
  result to ensure that you solved the problem and
  havent created new problems
• Next identify the effects and results of your
  solution

54
Summary (continued)

• Last step in troubleshooting is to document the
  solution and the process of solving the problem
• A tone generator and tone locator are used to
  identify the terminating location of a wire pair
• A multimeter is a simple device that can measure
  the voltage, resistance, impedance, and other
  characteristics of an electrical circuit
• Basic cable continuity testers determine whether
  your cabling can provide connectivity

55
Summary (continued)

• A network monitor is a software-based tool that
  monitors network traffic from a server or
  workstation attached to the network
• Protocol analyzers can typically interpret data
  up to Layer 7 of the OSI Model
• Wireless network testing tools can be dedicated
  instruments or software that run on a workstation
  (usually a laptop)