Troubleshooting Physical Networks

Question 1

Network Troubleshooting Methodology

Answer 1

1. Identify the problem
2. Establish a theory to determine the cause
3. Test the theory to determine the cause
4. Establish a plan of action to resolve the problem and identify potential effects
5. Implement the solution or escalate as necessary
6. Verify the whole system functionality and if applicable, implement preventive
   measures
7. Document findings, actions, outcomes, and lesson learned
   ▪ Gather more details
   ▪ Identify symptoms
   ▪ Check for changes
   ▪ Duplicate problem

Question 2

How to implement the network troubleshooting methodology

Answer 2

Approach multiple problems individually
▪ Top-to-bottom
▪ Bottom-to-top
▪ Divide and conquer
o If confirmed, determine next steps
o If unconfirmed, reestablish new theory or escalate

Question 3

o Plenum Cable

Answer 3

Used when running cables horizontally in a building across a particular
level

Question 4

Riser Cable

Answer 4

Used to run network cables vertically between floors in a building in a
cable riser or elevator shaft
▪ Riser cables cannot be used in plenum spaces since they are not made
from PVC or FEP
● Rollover/Console Cable
o A type of null-modem cable that is used to connect a
computer terminal to a router’s console port
● Crossover Cable
o Connects two Ethernet network devices directly, such as
two computers without a switch or a router in between
● Power Over Ethernet (or PoE)
o Passes electric power over twisted pair Ethernet cable to
powered devices
o PoE provides 15.4 to 60 watts of power using two twisted
pairs, and between 60-100 watts of power using all four

Question 5

Snips or Cutter

Answer 5

Used to simply cut a piece of cable off a larger spool or run of cable
▪ Looks a lot like a pair of scissors, but uses stronger blades to cut twisted
copper cables, coaxial, cables, or even larger cable bundles

Question 6

Cable strippers

Answer 6

Strips the end of the cable to prepare it the attachment of a RJ-45 or
other type of connector

Question 7

Cable Crimper

Answer 7

▪ Used to attach the connector to the end of the cable
▪ support both RJ-45 and RJ-11 connectors
▪ If you are working with coaxial cables, then you will need a cable crimper
that supports an RG-6 or RG-59 connector

Question 8

Cable Tester

Answer 8

Verifies continuity for each wire in the cable to ensure there are no
breaks
▪ Verifies the pinouts of the connectors
▪ Different testers for different cable types

Question 9

Multi-tester

Answer 9

Supports not just ethernet cables using RJ-45, but also BNC connectors
for coaxial cables, as well as IDE, PATA, SATA, RJ-45, fiber, DB25, DB9s
and anything else that you might need to test

Question 10

Wire Map tool

Answer 10

Like a cable tester, but it works specifically for twisted pair ethernet
cables
▪ It can diagnose any issues with that cable
● Open Pair
o Occurs when one or more of the conductors in the pair are
not connected to a pin at one or the other end
● Short Pair
o Occurs when the conductors of a wire pair are connected
to each other at any location in the cable
● Short Between Pairs
o Occurs when the conductors of two wires in different pairs
are connected at any location in the cable
● Reversed Pair
o Occurs when the two wires in a single pair are connected
to the opposite pins of the pair at the other end of the
cable
● Crossed Pairs
o Occur when both wires of one color pair are connected to
the pins of a different color pair at the opposite end
● Split Pairs
o Occur when the wire from one pair is split away from the
other and crosses over a wire in an adjacent pair

Question 11

Cable Certifier

Answer 11

Used with an existing cable to determine its Category or data throughput

Question 12

Multimeter

Answer 12

▪ Checks the voltage or the amperage or the resistance of a copper cable
▪ Used to verify if a cable is broken or not

Question 13

Punch-Down Tool

Answer 13

Used to terminate wires on a punch-down block without stripping off the
insulation
▪ Used with 66 block or 110 block, network jacks, and patch panels

Question 14

Toner Generator/Probe

Answer 14

▪ Allows technicians to generate a tone at one end of a connection and use
the probe to audibly detect the wire pair connected to the tone
generator
▪ Often called a “Fox and Hound”
▪ Fox is a tone generator
▪ Hound is a toner probe

Question 15

Loopback Adapter

Answer 15

▪ Connects transmit pins (or fibers) to receive pins (or fiber) to test a
network interface
● Ethernet Pinout
o Pins 1 to 3 (Tx+ to Rx+)
o Pins 2 to 6 (Tx- to Rx-)
● Fiber
o Transmit fiber to Receive fiber
o Used with diagnostic software to test Ethernet
connectivity of a client

Question 16

Time-domain Reflectometer (TDR)

Answer 16

▪ Locate breaks in a copper cable and provide an estimate of the severity
and the distance to the break
● Optical Time-domain Reflectometer (OTDR)
o Used for fiber optic cables

Question 17

Fiber Light Meter

Answer 17

A device that provides a continuous wave of stable source of energy for
attenuation measurements

Question 18

Fusion Splicer

Answer 18

A machine that is used to permanently join two fibers together

Question 19

Cable Signal Issues

Answer 19

Attenuation
▪ Loss of signal strength on a network cable or connection over the length
of the cable
▪ Twisted pair cables can transmit data over a maximum distance of 100
meters
▪ Coaxial cables can transmit data over a maximum distance of 500 meters
● Frequency
● Noise
● Physical surroundings
▪ The higher the frequency, the higher the bandwidth

Question 20

Copper Cable Issues

Answer 20

There are many types of issues that could occur withing your copper cables
▪ Incorrect pinouts
● By default, the patch panel should use the TIA-568B pinout, with
pins 1 through 8 being connected as:
o White/Orange – Orange – White/Green – Blue –
White/Blue – Green – White/Brown – Brown
▪ Bad port
● If you suspect a bad port on a switch or router, you should
connect a loopback plug to the port on that device and run a test
using specialized software
▪ Open
● There is nothing on the other end of the connection or there’s a
break in the wires between the source and the destination
▪ Short
● Indicates there are two wires are connected together somewhere
in the connection

Question 21

Fiber Cable Issues

Answer 21

Transceiver
▪ A transmitter and a receiver combined into a single device that converts a
network connection from one type to another
▪ They are designed to support a certain type of connection and a certain
cable type
o Dry Cleaning
▪ Using light pressure while rubbing the end face of a fiber cable or
connector with a dry-cleaning cloth in one direction
o Wet Cleaning
▪ Moistening a piece of lint-free cloth with a fiber optic cleaning solution
and wiping the end face of the cable or connector

Question 22

Ethernet Issues

Answer 22

Duplex Mismatch
▪ When one device thinks the connection is full duplex and the other thinks
it is half duplex
▪ Ensure both devices are configured to auto negotiate the connection
properly