Title: Network Guide to Networks, Fourth Edition
1Network Guide to Networks, Fourth Edition
- Chapter 12
- Troubleshooting Network Problems
2Objectives
- 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
3Troubleshooting 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
4Troubleshooting 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
5Identify 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?
6Identify the Affected Area
Figure 12-1 Identifying the area affected by a
problem
7Identify the Affected Area (continued)
Figure 12-1 (continued) Identifying the area
affected by a problem
8Identify the Affected Area (continued)
Figure 12-2 Identifying the chronological scope
of a problem
9Identify the Affected Area (continued)
Figure 12-2 (continued) Identifying the
chronological scope of a problem
10Establish 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?
11Establish 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?
12Establish 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
13Select 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
14Re-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?
15Verify 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
16Verify 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?
17Verify 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?
18Verify 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
19Verify Physical Connectivity (continued)
Figure 12-3 Verifying physical connectivity
20Verify Physical Connectivity (continued)
Figure 12-3 (continued) Verifying physical
connectivity
21Verify 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?
22Implement 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
23Implement 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
24Test 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
25Identify 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
26Document 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
27Staff 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
28Record 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
29Notify 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
30Notify 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
31Help 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
32Troubleshooting 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
33Tone 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
34Tone Generator and Tone Locator (continued)
Figure 12-4 Use of a tone generator and tone
locator
35Multimeter
- 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
36Cable 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
37Cable Continuity Testers (continued)
Figure 12-6 Cable continuity testers
38Cable 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
39Cable 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
40Cable Performance Testers (continued)
Figure 12-7 A performance tester
41Network 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
42Network 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
43Network 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
44Network Monitors (continued)
- Data errors that can be distinguished
- Local collisions
- Late collisions
- Runts
- Giants
- Jabber
- Negative frame sequence checks
- Ghosts
45Protocol 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
46Protocol Analyzers (continued)
Figure 12-8 Traffic displayed by protocol type
47Wireless 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
48Wireless 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
49Wireless 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
50Wireless 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
51Wireless Network Testers (continued)
Figure 12-10 Wireless network testing tool
52Summary
- 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
53Summary (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
54Summary (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
55Summary (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)