Troubleshooting Physical Network and Cabling Issues

Troubleshooting Physical Networks
Objective 5.2: Given a scenario, troubleshoot common cabling and physical interface issues
● Network Cable Limitations
○ Twisted Pair Copper Cables
■ Cat5
● Also known as Fast Ethernet or 100BASE-TX
● Operates at 100 Mbps up to 100 meters
■ Cat5e
● Also known as Gigabit Ethernet or 1000BASE-T
● Operates at 1000 Mbps/1 Gbps up to 100 meters
■ Cat6
● Also known as 1000BASE-T/10GBASE-T
● Operates at 1 Gbps up to 100 meters, or 10 Gbps up to 55 meters
■ Cat6a/Cat7
● Also known as 10GBASE-T
● Operates at 10 Gbps up to 100 meters
■ Cat8
● Also known as 40GBASE-T
● Operates at 40 Gbps up to 30 meters
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CompTIA Network+
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○ Coaxial and Twin Axial Copper Cables
■ Coaxial Cables
● Supports speeds up to 100 Mbps up to 500 meters
■ Twin Axial Cables
● Supports speeds up to 10 Gbps, but limited to 5 meters
● Newer versions can reach 100 Gbps up to 7 meters
○ Fiber Cables
■ Multimode Fiber
● 100BASE-FX – 100 Mbps up to 2 kilometers
● 100BASE-SX – 100 Mbps up to 300 meters
● 1000BASE-SX – 1 Gbps up to 220-500 meters
● 1000BASE-LX – 1 Gbps up to 550 meters
● 10GBASE-SR – 10 Gbps up to 400 meters
■ Single Mode Fiber
● 1000BASE-LX – 1 Gbps up to 5 kilometers
● 10GBASE-LR – 10 Gbps up to 10 kilometers
○ Cable Considerations
■ Shielded vs. Unshielded Twisted Pair
● Shielded offers more protection from EMI but is more expensive
○ Note: Fiber cables are truly immune to EMI
● Unshielded
○ Inexpensive
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CompTIA Network+
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○ Easy to install
○ lightweight
○ Flexible
● 100 meters – maximum recommended length for twisted pair
cables
■ Plenum vs. Riser Rated
● Plenum cables
○ Have higher fire ratings for spaces between ceilings and
floors
○ Used horizontally
● Riser cables
○ Used vertically between floors
○ Used in non-plenum areas only
○ Cable Applications
■ Rollover/Console Cables
● A type of null-modem cable that connects a computer terminal to
a router's console port for out-of-band communication
■ Crossover Cables
● Special type of network cable that connects two Ethernet devices
directly without a switch or router in between
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CompTIA Network+
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■ Power over Ethernet (PoE)
● Technology that passes electrical power over Ethernet cables to
power devices like wireless access points or IP cameras
● Requires at least Category 5e cables
● Can provide 15.4 to 100 watts of power using twisted pair
● Cable Signal Issues
○ Attenuation
■ Loss of signal strength on a network cable or connection over the length
of the cable
■ Common in both wired and wireless connections
■ Mainly affects copper cables like twisted pair or coaxial cables
■ Longer cables have higher resistance, causing the signal to weaken
● Maximum distance for twisted pair cables is about 100 meters due
to attenuation
● Coaxial cables can reach distances of up to about 500 meters
before attenuation becomes too much
■ Factors Affecting Attenuation
● Distance is the main factor
● Other factors
○ Frequencies used
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CompTIA Network+
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■ All networking and electrical cables operate at
specific frequencies
■ Higher frequencies allow for higher bandwidth but
can lead to interference if neighboring cables use
similar frequencies
○ Noise in the environment
■ Additional electrical or radio frequency noise in the
area where the cables are operating
● Noise from machinery or power generators
can increase attenuation
○ Physical surroundings
■ Things like temperature, the construction of the
walls or other barriers, and the type of wire
insulation, etc.
■ Mitigating Attenuation
● Use proper cables for the environment
● Shorten cable distances
● Use amplifiers or repeaters to boost signals for longer distances
■ Fiber Cables
● Attenuation occurs at much longer distances compared to copper
cables
● Cheaply constructed or dirty connectors can cause attenuation
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CompTIA Network+
(N10-009) (Study Notes)
● Use higher quality cables or clean connectors to mitigate
attenuation
○ Interference
■ Occurs when multiple cables operate in the same frequency band and are
in close proximity
■ Mitigation
● Use high-quality twisted pair cables or higher category rated
cables
● Plan cable runs to avoid running cables directly next to
high-power cables
○ Decibel (dB) Loss
■ Measures the amount of signal deterioration on a connection
■ Higher dB loss indicates more signal deterioration
● For copper cables
○ Decrease in voltage
● For fiber cables
○ Amount of light lost
■ Use higher quality cables or clean connectors to mitigate dB loss
○ Testing Tools
■ Cable Certifier
● Measures attenuation and dB loss on network cables
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CompTIA Network+
(N10-009) (Study Notes)
■ Fiber Light Meter
● Tests for attenuation on and dB loss fiber connections
■ Spectrum Analyzer
● Detects interference by analyzing frequencies and signals on a
cable (copper and fiber)
■ Cable Analyzer
● Measures dB loss in copper cables
○ Exam Tip
■ Understand the tools used to troubleshoot cable signaling issues
● Copper Cable Issues
○ Incorrect Pinouts
■ Testing a twisted pair network connection that is not working may
indicate an incorrect pinout
■ Can occur at the patch panel, wall jack, or RJ45 connector
● Patch Panels
○ Typically use a TIA568B pinout
○ Visually inspect the back of the patch panel and its punch
down block to verify correct colors in proper pins
● Wall Jacks
○ Also know as keystone
○ Have 4 pins on each end
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CompTIA Network+
(N10-009) (Study Notes)
○ Labeled as pins 1 through 8 or using color-coded
stickers/markers
● RJ45 Connectors
○ Connect copper pins to inner twisted pair wires
○ Pins can be counted from left to right when the small
plastic clip is facing downward (1 to 8 pins)
○ Ensure inner twisted pair wires are color coded correctly
■ Testing and Verification
● Use a cable tester or wire mapping tool to test and verify pinouts
● If incorrectly pinned out
○ Re-strip and re-punch wires
○ Replace the RJ45 connector
○ Bad Ports
■ Network interface cards (NICs) and Ethernet ports on switches/routers
can have issues
■ Use a loopback plug and specialized software to test Ethernet ports on
NICs
● For switches/routers
○ Connect a loopback plug to the port and run a test using
specialized software
● Replace the NIC or switch/router port if found to be faulty
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CompTIA Network+
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○ Opens and Shorts
■ Open
● Occurs when there is a break in the wires between the source and
destination
■ Short
● Indicates two wires are connected together somewhere in the
connection
● To fix a short
○ Rewire the RJ45 connection
○ Examine the cable for damage
○ Tools
■ For incorrect pinouts, opens, and shorts
● Cable tester
● Cable certifier
● Wire mapping tool
■ For bad ports
● Loopback adapter
● Loopback plug
○ Exam Tip
■ Understand the tools used to troubleshoot copper cable connectivity
issues
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CompTIA Network+
(N10-009) (Study Notes)
● Fiber Cable Issues
○ Incorrect Transceivers
■ Transceivers
● Both transmitters and receivers in one device
● Convert network connections from one type to another
● Work at Layer 1 in the OSI model
● Commonly used in routers and switches for fiber connections
■ If the wrong transceiver is used, the connection won't work
■ Many transceivers are hot-pluggable, allowing easy replacement without
shutting down devices
■ Use the correct transceiver to avoid data loss and connectivity issues
○ Reversed Transmit and Receive
■ Most fiber connections consist of separate cables for transmission and
reception
■ Connecting the transmit cable to the receive port, and vice versa, will
prevent a valid connection
■ Easily identified and fixed by swapping the cables
○ Dirty Optical Cables
■ Dirt or dust on fiber optic cables and connectors can cause performance
issues or connection problems
■ Even small particles can severely block light transmission
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CompTIA Network+
(N10-009) (Study Notes)
■ Cleaning methods
● Dry cleaning
○ Involves simply using light pressure while rubbing the end
face of a fiber cable or connector using a dry cleaning cloth
in one direction
● Wet cleaning
○ Lightly moistening a piece of lint-free cloth with a fiber
optic cleaning solution ( 91% or higher isopropanol
alcohol), and then wiping the end face of the cable in one
direction as well
○ More invasive but necessary for removing fingerprints
■ Use a fiber light meter to quantify the need for cleaning based on decibel
readings
● Ethernet Issues
○ LED Status Indicators
■ Used to diagnose issues in fiber optic and copper connections
■ Network interface cards (NICs) typically have two lights
● Activity light
○ Off – no link or connection established
○ Solid orange – link or connection established
○ Blinking orange – data activity occurring
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CompTIA Network+
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● Link speed light
○ Off – operating at 10 Mbps
○ Orange – operating at 100 Mbps
○ Green – operating at 1 Gbps
■ Network switches also have LEDs for each Ethernet port to indicate status
and activity
○ Duplexing Issues
■ Duplex Mismatch
● Occurs when one device thinks the connection is full duplex, while
the other thinks it is half duplex
● Most common issue
● Symptoms
○ High rate of packet loss without hight rate of jitter
○ High receive error rate
○ Runt packets
● Prevention
○ Configure both devices to use autonegotiate
○ Manually configure devices as full or half duplex if
autonegotiate fails
○ Use full duplex for switches, as each switch port is its own
collision domain
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CompTIA Network+
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● Interface Issues
○ Interface Issues
■ Refer to any problems in the network's interface operation that can
impact data transmissions and network performance
○ Types of Interface Issues
■ Increasing Interface Counters
● Cyclical Redundancy Check (CRC) Errors
○ Occur when the data block's integrity check upon
reception does not match the value attached during
transmission, indicating data corruption or alteration
○ Causes
■ Noise interference
■ Physical issues affecting network conductivity
● Runts
○ Frames smaller than the minimum frame size
○ Created by collisions or disruptions during packet
transmissions
○ Causes
■ Network card malfunction
■ Using a large collision domain
■ Cabling issues
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CompTIA Network+
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● Giants
○ Frames that exceed the maximum frame size of the
network
○ Often created due to misconfiguration or malfunctioning
of a network device
○ Effects
■ Network congestion
■ Poor performance
● Drops
○ Occur when a device's buffer is full and can't
accommodate incoming frames or packets anymore
○ Causes
■ High network traffic
■ Device operating beyond its capacity limits
■ Issues with Various Port Statuses
● Error Disabled Port Status
○ Indicates that a port on a switch has been automatically
shut down due to a network error or policy violation
● Administratively Down Port Status
○ Signifies that a network port has been intentionally
disabled by network administrators, not due to an error
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CompTIA Network+
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● Suspended Port Status
○ Indicates a violation of an established protocol or policy
within the network
○ Remediation
■ Monitor network traffic to identify and address the root cause of
interface issues
■ Address physical issues such as electrical interference, cable damage, or
hardware faults
■ Resolve configuration issues, network card malfunctions, or collision
domain size problems
○ Understanding and addressing these interface issues can significantly improve
network performance and reliability
● Power over Ethernet (PoE) Issues
○ Power over Ethernet (PoE)
■ A technology that allows network cables to carry both electrical power
and data over a single line
■ Useful for devices like IP cameras, VoIP phones, and WiFi access points,
enabling them to receive power and data through the same cable
■ Types
● Power over Ethernet (PoE)
○ Defined by IEEE 802.3af standard
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CompTIA Network+
(N10-009) (Study Notes)
○ Provides up to 15.4 Watts of DC power per device
● Power over Ethernet Plus (PoE+)
○ Defined by IEEE 802.3at standard
○ Provides up to 30 Watts of DC power per device
■ Power Loss
● Occurs as power moves from the switch to the end device,
resulting in a lower actual power available at the device
○ Issues
■ Power Budget Exceeded Error
● Occurs when the power demand from devices exceeds the
switch's power supply capacity
● Power Budget
○ Sum of all of the DC power available to the endpoint
devices, not just the amount of power available on a single
switchport
● Resolution
○ Check and compare power requirements of devices with
the total power budget available
○ Consider removing non-essential devices or upgrading the
PoE source
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CompTIA Network+
(N10-009) (Study Notes)
■ Incorrect Standard
● Occurs when there is a mismatch between the PoE standard
supported by the end device and the switch
● Resolution
○ Check and ensure compatibility between the end device
and the switch
● Resolution for Mismatch
○ Replace the switch with one that supports the required
standard
○ Use PoE injectors that match the required standard to
provide more power
■ PoE Injector
● Device that adds electrical power to a
standard Ethernet data cable so that both
power and data can be provided to
PoE-capable endpoint device
■ Symptoms of Issues
● Devices may randomly restart, behave erratically, or refuse to
power on
○ Understand issues to identify and resolve PoE issues within the network
effectively