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- Troubleshooting Network Problems
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- Describe the elements of an effective troubleshooting methodology
- Follow a systematic troubleshooting process to solve networking problems
- Use a variety software and hardware tools to diagnose problems
- Discuss practical issues related to troubleshooting
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- Identify the symptoms
- Identify the scope of the problem
- Establish what has changed on the network
- Determine the most probable cause of the problem
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- Determine the most probable cause of the problem (cont.)
- Verify user competency
- Re-create the problem
- Verify the physical integrity of the network connection
- Verify the logical integrity of the network connection
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- Implement a solution
- Test the solution
- Recognize the potential effects of the solution
- Document the solution
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- Questions to help you identify symptoms of a network problem
- Is access to the network affected?
- Is network performance affected?
- Are data or programs (or both) affected?
- Are only certain network services affected?
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- Questions to help you identify symptoms of a network problem (cont.)
- If programs are affected, does the problem include one local
application, one networked application, or multiple networked
applications?
- What specific error messages do users report?
- Is one or multiple users affected?
- Do the symptoms manifest themselves consistently?
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- Identify the scope of the problem
- How many users or network segments are affected?
- When did the problem begin?
- If a problem is universal—if it affects the entire LAN or WAN—you will
naturally want to answer these questions very quickly
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- Did the operating system or configuration on a server, workstation, or
connectivity device change?
- Were new components added to a server, workstation, or connectivity
device?
- Were old components removed from a server, workstation, or connectivity
device?
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- Was a server, workstation, or connectivity device moved from its
previous location to a new location?
- Was a server, workstation, or connectivity device replaced?
- Was new software installed on a server, workstations, or connectivity
device?
- Was old software removed from a server, workstation, or connectivity
device?
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- Verify user competency
- Re-create the problem
- Can you make the symptoms recur every time?
- Can you make the symptoms recur some of the time?
- Do the symptoms happen only under certain circumstances?
- Do the symptoms ever happen when you try to repeat them?
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- Verify physical connectivity
- Is the device turned on?
- Is the NIC properly inserted?
- Is a device’s network cable properly connected to both its NIC and the
wall jack?
- Do patch cables properly connect punch-down blocks to patch panels and
patch panels to hubs or switches?
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- Verify physical connectivity (cont.)
- Is the hub, router, or switch properly connected to the backbone?
- Are all cables in good condition?
- Are all connectors in good condition and properly seated?
- Do network segment lengths conform to the IEEE 802 specifications?
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- Questions to help you identify a problem with logical connectivity
- Do error messages reference damaged or missing files or device drivers?
- Do error messages reference malfunctioning or insufficient resources?
- Has an operating system, configuration, or application been recently
changed, introduced, or deleted?
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- Questions to help you identify a problem with logical connectivity
(cont.)
- Does the problem occur with only one application or a few, similar
applications?
- Does the problem happen consistently?
- Does the problem affect a single user or one group of users?
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- Steps to help you implement a safe and reliable solution
- Collect all the documentation you have about a problem’s symptoms
- If you are reinstalling software on a device, make a backup of the
device’s existing software installation
- Perform the change, replacement, move or add that you believe will
solve the problem
- Test your solution
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- Steps to help you implement a safe and reliable solution (cont.)
- Before leaving the area in which you were working, clean it up
- If the solution fixes the problem, record the details collected about
the symptoms, the problem, and the solution in your organization’s call
tracking database
- If your solution solved a significant change or addressed a significant
problem, revisit the solution a day or two later to verify the problem
is fixed and hasn’t caused other problems
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- After implementing the solution, it must be tested to verify that it
works properly
- Type of testing performed depends on the solution
- Often good to enlist the user who reported the problem in testing your
solution, too
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- When implementing a solutions, consider the:
- Scope
- Tradeoffs
- Security
- Scalability
- Cost
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- Name, department, and phone number of the problem originator
- Information regarding whether the problem is software- or
hardware-related
- If software-related, the package to which it pertains
- If hardware related, the device or components to which it pertains
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- Symptom of the problem, including when it was first noticed
- Name and telephone number of the network support contact
- Amount of time spent troubleshooting the problem
- Resolution of the problem
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- Crossover cable
- Cable in which the transmit and receive wire pairs in one of the
connectors are reversed
- Tone generator and tone locator
- A tone generator is a small electronic device that issues a signal on a
wire pair
- A tone locator is a device that emits a tone when it detects electrical
activity on a wire pair
- Combination of these devices is known as a fox and hound
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- Multimeter
- Simple instrument that can measure multiple characteristics of an
electric circuit
- Voltmeter
- Device used to measure voltage of an electric current
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- Resistance
- Opposition to electric current
- Resistance is measured in ohms
- The device used to measure resistance is an ohmmeter
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- Verify that a cable is properly conducting electricity
- Check for the presence of noise on a wire
- Verify that amount of resistance generated by terminators on coaxial
cable networks is appropriate or whether terminators are actually
present and functional
- Test for short or open circuits
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- Cable checkers
- Determine whether your cabling can provide connectivity
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- A cable tester performs the same continuity and fault tests as a cable
checker, but also provides the following functions:
- Ensures that cable is not too long
- Measure the distance to a cable fault
- Measures attenuation along a cable
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- Additional functions provided by a cable tester (cont.)
- Measures near-end crosstalk between wires
- Measures termination resistance and impedance for Thinnet cabling
- Issues pass/fail ratings for CAT3, CAT5, CAT6, or even CAT7 standards
- Stores and prints cable testing results
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- High-end instrument for testing qualities of a cable
- Optical time domain reflectors (OTDRs)
- TDRs made of fiber-optic cable
- Baseline
- Record of how well a network operates under normal conditions
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- Network monitors
- Software-based tools that continually monitor traffic on the network
from a server or workstation attached to the network
- To take advantage of software-based monitoring and analyzing tools, the
network adapter installed in your machine must support promiscuous mode
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- Local collisions occur when two or more stations are transmitting
simultaneously
- Late collisions take place outside the window of time in which they
would normally be detected by the network and redressed
- Runts are smaller than the medium’s minimum packet size
- Giants exceed the medium’s maximum packet size
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- Jabber is a device that handles electrical signals improperly
- Negative frame sequence checks are the result of the cyclic redundancy
checksum (CRC) generated by the originating node not matching the
checksum calculated from the data received
- Ghosts are frames that are not actually data frames, but aberrations
caused by a repeater misinterpreting stray voltage on the wire
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- Capturing network data traveling from one or many segments
- Capturing frames sent by or to a specified node
- Reproducing network conditions by transmitting a selected amount and
type of data
- Detecting any other running copies of NetMon on the network
- Generating statistics about network activity
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- LANalyzer performs the following functions:
- Initially discovering all network nodes on a segment
- Continuously monitoring network traffic
- Tripping alarms when traffic conditions meet preconfigured thresholds
- Capturing traffic to and from all or selected nodes
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- Tool that can capture traffic and analyze packets
- Also known as protocol analyzers
- Sniffer Portable
- Network analyzer from Network Associates
- Sniffer
- Laptop equipped with special network adapter and software that performs
network analysis
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- Segment problems
- Signal noise
- Cable damage
- Connector flaws
- Adapter flaws
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- Help desk staffed with help analysts
- Organizations may group their help desk analysts into teams based on
their expertise
- Most help desks have a help desk coordinator
- Most organizations have an operations manager, who supervises the help
desk coordinator
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- If a suspected problems lies with a network component, an easy way to
test the theory is to exchange that component for a functional one
- A better alternative to swapping parts is to have redundancy built into
your network
- Before swapping any network component, make sure the replacement has
exactly the same specifications as the original part
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- Change management system
- Process or program that provides support personnel with a centralized
means of documenting changes to the network
- Type of changes that should be recorded in a change management system
- Adding or upgrading software on network servers or other devices
- Adding or upgrading hardware components on network servers or other
devices
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- Type of changes that should be recorded in a change management system
(cont.)
- Adding new hardware on the network
- Changing the network properties of a network device
- Increasing or decreasing rights for a group of users
- Physically moving networked devices
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- Type of changes that should be recorded in a change management system
(cont.)
- Moving user IDs and their files/directories from one server to another
- Making changes in processes
- Making changes in vendor policies or relationships
- Preventing future problems
- Though not all network problems are preventable, many are avoidable
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- Before you can resolve a network problem, you must determine its cause
- The key to solving network problems is to approach them methodically and
logically
- When assessing a network problem, act like a doctor diagnosing a patient
- After implementing your solution, test it to ensure that it works
correctly
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- Be familiar with the different hardware-based troubleshooting tools
- Be familiar with the different software-based troubleshooting tools
- Most organizations operate a help desk
- If you suspect a problem lies with a network component, one of the
easiest ways to test your theory is to exchange that component for a
functional one
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- Keep a list of hardware and software vendors for your networking
equipment
- Some organizations use a call tracking system
- In addition to communicating problems and solutions to your peers
whenever you work on a network problem, you should follow up with the
person who reported the problem
- Organizations often implement change management systems to methodically
track changes on the network
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