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Network Guide to Networks, Fourth Edition

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Network+ Guide to Networks, Fourth Edition Chapter 12 Troubleshooting Network Problems – PowerPoint PPT presentation

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Title: 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?

6
Identify the Affected Area
Figure 12-1 Identifying the area affected by a
problem
7
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
9
Identify the Affected Area (continued)
Figure 12-2 (continued) Identifying the
chronological scope of a problem
10
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?

11
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

16
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?

18
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

19
Verify Physical Connectivity (continued)
Figure 12-3 Verifying physical connectivity
20
Verify Physical Connectivity (continued)
Figure 12-3 (continued) Verifying physical
connectivity
21
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

31
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

32
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

34
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

51
Wireless Network Testers (continued)
Figure 12-10 Wireless network testing tool
52
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)
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