SYSTEM ADMINISTRATION
Chapter 18
Network Troubleshooting Tools
General Tools
• Every technician requires a set of tools to perform all
of the tasks he or she will encounter while
troubleshooting network problems.
• This set of tools can range from a screwdriver and
pair of pliers to a fully stocked toolkit containing
specialized diagnostic equipment.
• Technicians who perform the majority of their
troubleshooting tasks in the field, or away from an
office, should consider some additional tools.
• In addition, try to maintain a supply of spare parts.
Specialty Tools
• Specialty tools are those that are used in special or
peculiar circumstances.
Wire Crimper
• Wire crimpers are used to attach terminals or connectors
onto pieces of wire.
• The head of the crimper contains indentations known as
cavities. Once the terminator is slipped over the wire, the
jaws of the crimpers are opened and the terminator is
slipped into the appropriate cavity. When the handles are
squeezed shut, the terminator is mashed onto the wire.
• Correct cavity selection is critical and is based on wire
size.
• The cavities on most standard wire crimpers are color
coded to correspond with to wire size markings.
• Crimpers are commonly used to connect coaxial cable
with BNC connectors.
• The cavities on coaxial crimpers are shaped in such a
way that the actual crimp is made in a hex configuration.
This makes for a much more secure connection.
Media Tester
• Media testers are used to test cable media, or in
plain language, network and telephone cables.
• Most cable testers can be used to test both twisted
pair and coaxial cable. Media testers can test and
confirm the actual wiring configuration for twisted
pair cable to include whether or not the RJ-45
connectors are attached correctly.
• With coaxial cable, the physical cable and
termination can be tested.
• Media testers work by sending an electrical signal
down the length of the cable. Once the signal
reaches the other end, the quality and strength of
the signal is evaluated.
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Media Tester
(continued)
• Most common cable testers can be used to perform the
following tests:
– Continuity
• Continuity testing is used to determine if a cable
meets the electrical standards identified by the
manufacturer.
– Crosstalk
• Crosstalk is noise that comes from adjacent wire
pairs. Twisted pair cable uses the twisted wires to
help reduce the amount of crosstalk that occurs
between wires that are located near each other.
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Media Tester
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– Noise
• Electrical noise can be caused by a number of
sources. Some of the most common sources are
electrical cables and fluorescent lights. Since this
noise may occur sporadically, line noise tests may
need to be conducted over a period of time to
obtain accurate readings.
– Attenuation
• As a signal travels down a length of cable, is starts
to lose its strength. Attenuation checks can
determine the amount of signal loss on a piece of
cable.
(continued)
Media Tester
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– Capacitance
• Capacitance is measured in pF, or picofards per
foot. This measurement can tell you if the cable is
kinked or if it has been stretched.
– Cable Tracing
• Tracing is used to trace the path a cable takes
through a wall or ceiling. Cable tracing uses a tone
generator to send a signal through the cable. While
the tone is traveling through the cable, you can
listen through the wall or ceiling for the tone.
• When purchasing a cable tester, be sure you pick one
that meets the requirements of the cable type you are
testing.
Time Domain Reflectometer
(TDR)
• Time Domain Reflectometers (TDR) are a type of
cable tester.
• TDRs are used to determine if the cable is broken or
has a short.
• A TDR works by sending a signal to the end of a
cable and then measuring the length of time it takes
for the signal bounce back.
– If a cable is broken or has a short, the signal
bounces back at a different speed or amplitude,
depending on the location of the defect.
(continued)
Time Domain Reflectometer
(TDR) (continued)
• TDRs are made for testing both copper and fiber-optic
cables.
– Copper
• With copper cables, the TDR sends an electrical
signal down a length of cable and then records the
amount of time it takes for the signal to reflect
back.
– Fiber-optic
• Optical Time Domain Reflectometers (OTDRs) use
reflected light to identify items such as the length
of the fiber-optic cable, the location of cable
breaks, and the affects of attenuation.
Optical Tester
• Optical testers are used to test fiber-optic cabling
systems by detecting reflected light.
• By attaching probes to the optical fibers, items such
as the output power of signal fibers and attenuation
can be measured.
• Optical testers are commonly used to evaluate
splices in the cabling system and connector joints,
and to locate faults.
Punch-Down Tool
• Punch-down tools are used to attach telephone and
data wires to punch-down blocks and patch panels.
• The actual tool is a hand-held device containing a
plunger and cutter assembly.
Tone Generator
• Tone generators are used to trace problems in
phone lines.
• To use a tone generator, plug the RJ-11 connector
from the tone generator into a modular telephone
jack. If working at the punch-down block, use
alligator clamps to connect the generator directly to
the connectors or wires.
• Turn the tone generator on to begin transmitting a
signal down the length of the wire.
• At the next junction of the wire, a tone probe is used
to detect the tone.
Loopback Plug
• A loopback plug is used to ensure that electrical
signals are being sent out of a network interface
card.
• In order to make a loopback plug, a single piece of
twisted pair cable and an RJ-45 connector are
required.
• On the connector, connect pin 1 to pin 3 and pin 2 to
pin 6.
Visual Indicators
• Many devices have built-in lights that are designed
to show you when a connection has been made and
when data collisions occur.
• Some of the more common pieces of hardware that
contain these types of lights are network interface
cards, hubs, switches, bridges, and routers.
Link Lights
• Link lights are designed to demonstrate link connectivity
at the Physical layer. In simpler terms, that means that a
link exists between two network devices.
• Link light status will vary from device to device.
• In the event you are troubleshooting a network problem
and you believe that connectivity may be the problem,
always check to see if the link light is lit. If not, check
these items:
– Trying to reseat the connection by unplugging the
connection and plugging it back in.
– Unplug the cable from the other end that is, the wall
jack, hub, switch, etc., and reconnect it. Inspect the
cable and connector. If the cable or connectors look
questionable, replace the cable.
– Restart the computer. Restarting should initialize the
NIC, which may re-establish the connection.
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Link Lights
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– At the hub or switch, check the corresponding link
light. If it is not lit, plug the cable into another port. If
link connectivity is established, you’ll know the port on
the hub was defective.
– Check to make sure the hub or switch has power.
– If you are using a managed switch, check to see if
someone has made changes to the switch
configuration, or if a port has been disabled.
– While at the hub, check the cable and connector just
as you did at the workstation. Replace the cable if you
have any questions about its dependability.
– Use a cable tester to verify that all of the patch cables
and network cable runs are operating correctly.
– If a new patch cable has been installed, check to
make sure it is not a crossover cable.
Collision Lights
• Collision lights are used to detect
collisions on an Ethernet network.
• Whenever a device transmits data and a
collision occurs, this light will glow.