course|notes™
quick reference guide
Network+ Guide to Networks, 8th Edition
Welcome to Network+ Guide to Networks
The CompTIA Network+ (N10-007) exam tests a student’s knowledge and skills needed to
manage, troubleshoot, and configure a wired and wireless network. Successful candidates
must understand basic network design and technologies, including network limitations and
weaknesses. Network professionals must be able to maintain documentation, configure
network devices and protocols, and manage security. In addition, the candidate should
be familiar with enterprise technologies including virtualization, cloud computing, and
mobile devices.
Networking
Concepts
Network
Infrastructure
Network
Operations
VLAN
1
Trunk lines with traffic
for VLAN 1, VLAN 2,
and VLAN 3
Access
ports
Trunk
ports
VLAN 2
NETWORK
­Troubleshooting
and Tools
VLAN
1
Switch A
Router
Network
­Security
Switch C
Trunk line with traffic
for VLAN 1, VLAN 2,
and VLAN 3
Trunk
ports
Switch B
VLAN 3
Access
ports
What’s new in the CompTIA Network+ (N10-007) certification exam?
•
•
•
•
More emphasis on virtualization, cloud computing, remote access, and security
Focus on practical skills, as well as Data link layer and Network layer technologies
More coverage of emerging technologies such as IoT, NFC, and Ant+
Removal of legacy technologies
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Networking
Concepts
IP Addressing
IPv4 and IPv6 addresses are used to identify computers and networks. IPv4 addresses are 32-bit dotted decimal numbers and are
categorized by classes based on the value of the first octet as in
the following table:
Networks are composed of many pieces that must all work together
for proper operation. A network administrator must understand
the components of a network including network protocols and
­addresses, network topologies and technologies, wired and wireless
networks, and a variety of network services, including cloud services.
An essential tool for bringing these many pieces together is the OSI
model, which breaks network operations down into seven layers,
explaining the role of each component and its interaction with other
network components.
The OSI model describes a seven-layer approach to networking
from how applications should access network services to how bits
are transmitted and received on the physical media. The seven layers and the job each layer performs are described in the following
table:
Application
(7)
Presentation
(6)
Session
(5)
Transport
(4)
Network
(3)
Data Link
(2)
Physical
(1)
Description
Devices and Protocols
Provides network services
to applications
Translates data formats,
encryption, and
compression
Maintains connections
between systems
Transfers data between
applications; reliability, and
flow control
Provides logical addressing
and routing
Provides physical
addressing, frame
formatting, and error
detection
Transmits and receives bits
across the media
DNS, DHCP, HTTP, FTP,
and File sharing
ASCII, EBCDIC, JPEG, TIF,
and RDP
First Octet
Default Subnet
Mask
Hosts per
Network
A
B
C
0-127
128-191
192-223
255.0.0.0
255.255.0.0
255.255.255.0
16,277,214
65,534
254
Class D addresses are used for multicast applications and have a
first-octet value of 224-239. Class E addresses are reserved for
experimental use and have a first-octet value of 240-255. IPv4
addresses can be public or private. Private IP addresses can be
used on any network but public IP addresses are issued by IANA
and are used for Internet access. Users of private addresses must
use NAT/PAT to gain access to the public Internet.
IPv6 addresses are 128 bit numbers divided into 8 groups of 16
bits expressed as hexadecimal digits, for example:
FE80:1234:5678:9ABC:DEF0:F00D:BEEF
OSI Model
Layer Name
(Number)
Class
TCP and UDP Well-Known Ports
TCP/IP network applications communicate using Transport layer
protocol port numbers. TCP is a connection-oriented Transport layer
protocol and uses a three-way handshake to establish a connection
between two applications before data is transferred. UDP is a connectionless transport layer protocol that means that data is transferred
between the applications without the requirement for a connection to
be established. To configure and troubleshoot network communication,
you should know the most commonly used port numbers.
Login/logout, SQL,
and NFS
TCP and UDP
IP, ICMP, ARP, and routers
Ethernet, Frame Relay, ATM,
switches, and NICs
Cables, connectors,
and hubs
Network Topologies
A network’s topology describes how devices are physically connected (physical topology) and how data moves from one device
to another (logical topology).
• Star—All devices are connected to a central device such as a
switch. The most common topology used in LANs.
• Ring—Data is passed along from one device to another in
a ring formation. Token Ring and FDDI are common ring
­topologies.
• Bus—Devices are connected by a length of cable, usually in
daisy-chain fashion. A bus is sometimes used as a network
backbone, connecting multiple network segments together.
• Mesh—Most often used in WANs or WLANs, devices are
­connected to multiple other devices.
Port #
Application
Transport Layer
Protocol
20, 21
22
23
25
53
67, 68
69
80, 443
110
143
161
389
445
3389
FTP
SSH
Telnet
SMTP
DNS
DHCP
TFTP
HTTP, HTTPS
POP
IMAP
SNMP
LDAP
SMB
RDP
TCP
TCP
TCP
TCP
UDP
UDP
UDP
TCP
TCP
TCP
UDP
TCP
TCP
TCP
Configuring a WLAN
Wireless LANs (WLANs) are an integral part of most wired networks, allowing mobile users access to a network without being
tethered to a cable. There are five common 802.11 (Wi-Fi) standards as listed in the following table:
Routing
Routing moves packets from one network to another until the
­packet reaches the destination network. Routers work with IP
­addresses to determine the best path. Dynamic routing information is learned using routing protocols:
• RIPv2, EIGRP—Distance vector routing protocols for small
to medium-size private internetworks.
• OSPF—A link-state routing protocol used for larger private
internetworks.
• BGP—A hybrid protocol used for Internet routing.
Wi-Fi 802.11 Standards
Standard
Frequency Band
Maximum Speed
802.11a
802.11b
802.11g
802.11n
802.11ac
5 GHz
2.4 GHz
2.4 GHz
2.4 or 5 GHz
5 GHz
54 Mbps
11 Mbps
54 Mbps
600 Mbps
6.93 Gbps
Terms and components associated with Wi-Fi networks include:
• Antenna—Antennas transmit and receive data and can be
­omnidirectional or unidirectional.
• Channels—The range of frequencies on which a device transmits data. 2.4 GHz standards use 11 or 14 channels and
5 GHz standards use up to 25 channels.
• Service set identifier (SSID)—The name of a WLAN; used by
clients to connect to the network.
Switching
Switching moves data from one device to another. A switch
­receives incoming data from one of its ports and redirects it to
one or more outgoing ports based on the destination MAC
address. Switches can be configured to work with routers
by using VLANs and trunking protocols such as 802.1q.
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Network
Infrastructure
Virtualization
Virtualization is a process that creates a software environment
to emulate a computer’s hardware, BIOS, and networking components, allowing multiple virtual machines (VMs) to run on
one physical computer and communicate across a virtual network.
Some of the components of virtualization include:
• Hypervisor—Creates and monitors the virtual hardware environment, allowing multiple VMs to share physical resources. A
hypervisor can be type 1 or type 2. Type 1 hypervisors are used
on production servers and run directly on the server hardware
whereas type 2 hypervisors run on top of the host operating
system and are most often used in testing and development
environments.
• Virtual switch—A network switch implemented within the hypervisor host.
• Virtual NIC—A software implementation of a network interface
card attached to a virtual machine. A virtual NIC connects to a
virtual switch.
• Virtual router/firewall—Software implementations of the hardware devices that allow secure communication between virtual
networks and the virtual network and physical network.
The infrastructure of a network is built upon the network devices
used to connect computers; the media types used to make network
connections; and the underlying network technologies, protocols,
and topologies that make everything work together. Network+
candidates must know how network devices work and how data
is moved from one device to another and from one network to
another. They must be familiar with network cabling, Ethernet standards, virtualization, network storage, and how and where to use
the network devices that communicate within and between LANs.
Network Cabling
Network cabling makes physical connections between network
devices. Media types include copper and fiber-optic.
• Copper cables—Includes coaxial and twisted-pair cabling.
Coax cable types: RG-59 and RG-6. Twisted pair types: Cat3
through Cat7, can be shielded or unshielded, and can be PVC
or plenum-rated. Connectors include RJ-11 and RJ-45 for UTP
and BNC and F-type for coaxial. 110 blocks and 66 blocks are
termination panels. Copper cables are terminated using the
568A or 568B wiring standard.
• Fiber cables—Made of thin strands of glass, varieties include
single-mode fiber (SMF) for longer distances using lasers
and multimode fiber (MMF) for shorter distances using
LEDs. Connectors include ST, LC, SC, and MTRJ.
VM1
vNIC 1
VM2
vNIC 2
VM3
VM4
vNIC 3
vNIC 4
Host
machine
Ethernet Standards
The base standard for Ethernet is IEEE 802.3 but there are
many sections of the IEEE 802.3 standard that define operating
details such as bandwidth and type of cabling. These standards
are specified using the XBaseY naming convention, where X is
the bandwidth rating, Base means baseband communication,
and Y is the type of cabling used. Ethernet over twisted-pair
cabling has a maximum segment length of 100 meters. Some
fiber optic implementations can have segments up to 25 miles
in length. Some of the most common XBaseY standards are
described below:
• 100BaseT—100 Mbps Ethernet over twisted-pair cabling.
• 1000BaseT—1 Gbps Ethernet over twisted-pair cabling.
• 10GBaseT—10 Gbps Ethernet over twisted-pair cabling.
• 1000BaseLX—1 Gbps Ethernet over single-mode or multimode fiber. Up to 5000 meters.
• 1000BaseSX—1 Gbps Ethernet over multimode fiber. Up to
500 meters.
Virtual switch
Hypervisor
Physical NIC 1
Physical NIC 2
To physical
network
Network Storage
There are two primary types of network storage used by both physical and virtual devices:
• Storage Area Network (SAN)—Storage that uses a dedicated
network connection, typically Fibre Channel, FCoE, iSCSI, or
InfiniBand to connect computers directly to storage devices.
• Network Attached Storage (NAS)—Shared storage accessible
via the same network as the storage client. Uses standard file
sharing protocols such as SMB and NFS.
Network Devices
WAN Technologies
Network devices pass data from one device to another or from one
network to another to get the data to its final destination; sometimes performing complex filtering and processing of data packets
before they are forwarded. Some of the most common devices and
their functions include:
• Router—Manages traffic between two or more networks;
­forwards packets based on the network ID of the destination
IP address.
• Switch—Forwards data frames between devices based on
MAC address.
• Hub—Receives bit-level signals on one port and repeats the
signals out all other ports.
• Firewall—Performs routing functions and specialized filtering to
block certain types of traffic based on IP addresses, ports, and
packet contents.
• Wireless access point—Accepts wireless signals from wireless
clients and retransmits to the rest of the network. Used in an
infrastructure mode wireless network.
Advanced networking devices include multilayer switch, IDS/IPS,
content filter, load balancer, proxy server, VoIP gateway and
PBX, VPN concentrator, and RADIUS server.
WAN technologies connect LANs together over long distances,
primarily work at the Data Link layer, and include:
• Frame relay—Uses packet-switching over SVCs or PVCs.
• Leased line—Includes T1, T3, and OC-3 through OC-192
signaling rates.
• MPLS—Carries multiple Layer 3 protocols over packetswitched networks using labels for routing and prioritization.
• ATM—Uses fixed 53-byte packets called cells over virtual circuits.
Other wired WAN technologies include ISDN, DSL, and Metro Ethernet; wireless WANs include WiMax, GSM/CDMA,
LTE/4G, and satellite.
WAN connections to the local network occur at the demarcation
point and typically involve a smart jack and a CSU/DSU.
Demarcation
point
Main office
Demarcation
point
CSU/DSU
CSU/DSU
CSU/DSU with
multiplexer
CSU/DSU with
multiplexer
Customer responsibility
Smart
jack
Smart
jack
Telco responsibility
Branch office
Customer responsibility
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Network
Operations
Disaster recovery is the ability of a network to maintain operations in the event of a major disaster such as fire, flood, or extended
power or network outage. Disaster recovery may involve these
components:
• Cold site—An alternate location where equipment and data can
be moved and service restored within several days.
• Warm site—An alternate location that is provisioned with some
equipment and data, usually only requiring minor setup and
data restoration before operations can be resumed; usually
within a day.
• Hot site—A fully operational alternate location with current data
where service can be resumed within minutes or hours.
• Backups—An integral component of a disaster recovery plan
where data is backed up to an external media such as tapes
or external drives. Types of backups include full, differential,
and incremental. A snapshot is a type of backup where a
copy of data or an entire system is made so the system can
be fully restored back to the moment in time the snapshot was
taken.
Network administrators have a variety of tools, processes, and
technologies available to help ensure a reliable and high-performance
network. Network documentation makes troubleshooting and scaling
a network easier through the use of diagrams, inventory management,
labeling, and device configuration documentation and performance
baselines. Network uptime is critical and high availability and disaster
recovery must be a part of every network plan. In addition, network
documentation must include the identification and execution of network
policies and best practices.
Network Documentation
Network documentation includes both physical and logical network
diagrams. Physical diagrams show the location of devices and
cabling whereas logical diagrams show the overall network topology and logical addressing scheme. Standard symbols are used to
indicate types of devices as in the following figure:
Wireless access point
Scanning and Monitoring
A network administrator must continually monitor the network
and its devices to ensure optimal operating conditions while also
scanning for security vulnerabilities to prevent attacks. Some
of the components and processes involved in this undertaking
include:
• Log reviewing—Most network devices and operating systems
generate notifications and alerts of events that have been detected. Network and security devices usually send notifications
to a Syslog server or a SIEM service, while Windows OSs
use the Event Viewer.
• SNMP monitoring—A TCP/IP based protocol used to collect
performance metrics from multiple devices and send the data
to a network management system for analysis and display.
SNMP runs over UDP ports 161 and 162. SNMPv3 adds
authentication and encryption for increased security. SNMP
uses a Management Information Base (MIB) to store data
gathered from network management agents.
• Patch management—Network devices and OSs must be
continually updated to fix bugs and vulnerabilities. A patch
management system provides automatic updates and reporting
to ensure all systems are up-to-date.
Laptop
Web server
Internet
Firewall
Router
Switch
File server
Printer
Switch
Workstation
Additional types of documentation should include:
• Rack diagrams—Show representations of physical devices
such as routers, switches, and servers and their placement and
connections in a standard equipment rack.
• MDF/IDF documentation—The MDF is where a WAN provider’s
connection is installed and serves as the interconnect between
the IDFs. An IDF is where devices connect to patch panels and
switches. Usually one or more IDFs per floor connect to the
MDF.
• Performance baselines—Include the percent utilization of the
network, error statistics, CPU utilization on key servers, network
service usage, and so forth. Baselines can be used to detect
bottlenecks and malfunctioning devices.
• Change management—Documents additions, removals,
and configuration changes made to network devices and
cabling.
• Network configuration—Contains device type, model, and
configuration details.
Analyzing Metrics
After data is collected from a network, many performance values
must be analyzed to determine the network’s health. Network administrators often create a baseline that includes the percent utilization of the network, error statistics, CPU utilization on key servers,
network service usage, and so forth. Baselines can be used to
detect bottlenecks and malfunctioning devices. Error statistics
might include the following:
• Discarded packets—Packets that are discarded, or dropped,
by the receiving device because the device was too busy, the
packet was no longer relevant or had an error.
• Error packets—Packets that are too small (runts), too large
­(giants), continually retransmit (jabber), or anomalous
(ghosts).
• Utilization and throughput—Measures what percentage of
the network and computing bandwidth is being used and the
amount of data that passes through the network in a given time
period.
Business Continuity and Disaster Recovery
Business continuity depends on a business’s ability to ensure its
network’s high availability. High availability typically involves:
• Fault tolerance—The ability for a device to continue to operate
after a component failure.
• Load balancing—The ability to use two or more of the same
devices or media pathways to share the processing or network
traffic load.
• NIC teaming—The use of two or more NICs in a single computer, with the NICs working together to provide increased
bandwidth and fault tolerance.
• Port aggregation—Two or more ports on a switch that are
bonded together to provide higher bandwidth.
• Clustering—Two or more servers working together to provide
load balancing and fault tolerance.
• Battery backup/UPS—The use of a battery backup and uninterruptible power supply (UPS) to provide power to a network
device in the event of a power failure.
Remote Access
Most networks have provisions for users to access the network
while working from home or while traveling. A number of remote
access methods exist, with the most common being virtual private
network (VPN). A VPN provides secure client-to-site or site-tosite communication using authentication and encryption. Common
VPN protocols include IPSec, PPTP, and SSL. Other remote
­access protocols include remote desktop protocol (RDP),
virtual network computing (VNC), SSH, and Telnet.
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Network Security
Access controls may include one or more of the following:
• 802.1X—Also known as EAPoL, a port-based mechanism used
to control access to wired or wireless clients by restricting
­access to the AP or switch port to only authenticated devices.
• NAC—A policy-driven system used to determine the level and
type of access granted to a device such as firewalls, routers,
and switches.
• Access control lists—A list of rules configured on a device
that permits or denies traffic based on source and destination
­address, and network protocol.
A lot of time is spent configuring a network to ensure that
authorized users have access to network resources; perhaps
more important is ensuring that unauthorized persons do
not have access to the network. Network security is of
paramount importance because so much important data is
kept on networks, from social security numbers, to credit card
information, to private health data. Network security involves
concepts such as disaster recovery, encryption protocols, attacks
and threats, malware, access controls, and physical security.
A network technician’s understanding of security risks and
countermeasures is of utmost importance on both wired and
wireless networks.
Wireless Security
Wireless security requires special considerations because, unlike
wired media, the network signals are unbounded and can therefore
be captured by anybody with the appropriate radio receiver. To
mitigate the problem, wireless networks should always be encrypted and may also require user or device authentication. Wireless
encryption and authentication methods include:
• WPA2—The strongest encryption standard; uses the AES or
AES-CCMP encryption algorithm. WPA2-Enterprise or WPA2802.1X requires an authentication server.
• WPA—Less secure than WPA2; uses TKIP-RC4 for ­encryption.
• EAP (Extensible Authentication Protocol)— A framework for
authentication protocols that use authentication and encryption.
Common EAP variants include EAP-TLS, EAPoL, EAP-FAST,
and PEAP. EAP can be used with smart cards, biometrics, and
traditional username/password authentication methods.
• MAC Filtering—A method that restricts access to the wireless
network to devices with specific MAC addresses. Since MAC
addresses can be spoofed, it should not be used as the sole
security method.
Physical Security
If someone has physical access to a device, it is not secure.
­Network devices and servers must be installed in a secure location
with strict rules governing who has access to the location, and with
well-defined procedures for enforcing those rules and detecting if
a breach has occurred. To summarize: the two tenets of physical
security are prevention and detection. Common prevention methods
include:
• Badges and Smart cards—A security badge may simply contain information a security guard can use to verify a person’s
identify, such as a photo, name, and title. Most, however,
are smart cards that have digital data encoded on them that
specifies which doors a person can open by swiping the card
through a reader or by using a proximity sensor.
• Biometrics—Biometric sensors authenticate a person
using unique traits such as fingerprint, iris pattern, or facial
recognition.
• Key fob—A small handheld device, often placed on a key ring
that contains identifying and access information for a user.
In the event of a security breach or attempted breach, detection
methods must be in place:
• Motion detection—Detects movement in a room or ­
outdoor space that can generate an alarm, notification,
or ­countermeasures.
• Video surveillance—Creates a video log of all activity for
­real-time monitoring or archival purposes.
• Asset tracking tags—Small tags placed on items that generate
a signal that can be picked up by a reader when an item enters
or exits a room or building.
• Tamper detection—Detects whether a device has been physically opened or otherwise tampered with.
Common Network Attacks
Networks face varied and numerous threats from hackers and
malware. Network administrators must know what threats they face
to properly secure a network. Some of the more common network
attacks include the following:
• Denial of service (DoS)—A network attack that attempts to
prevent legitimate users from accessing a network or service; usually works by consuming excessive network or server
resources. A distributed DoS (DDoS) is a coordinated attack
that comes from multiple sources. Distributed reflective DoS
(DRDoS) attacks use spoofing to hide the source identity.
• Brute force—An attempt to guess a password or encryption key
using numerous character combinations.
• Social engineering—An attack that uses a person’s trust or
naiveté to gain access to a system.
• Man-in-the-middle—An attack that captures secure transmissions between two parties without either party’s knowledge.
• Ransomware—A program that locks a user’s data or computer
system until a ransom is paid.
• DNS poisoning—An attack in which the hacker redirects traffic
to the attacker’s web server by altering DNS records.
Authentication and Access Controls
System and data security is founded on two components:
­Authentication verifies someone’s identity and access controls
allow or deny an authenticated user access to a system or data.
There are a variety of authentication methods including:
• Kerberos—Used with Windows Active Directory and supported
on other systems, it uses the concept of keys to validate identity and tickets to grant access.
• RADIUS—A centralized authentication, authorization, and
accounting (AAA) service commonly used for remote access,
wireless networks, and network device access.
• TACACS+—Another AAA service, developed by Cisco, typically used for network device access control.
• Certificates—A digital document that contains identifying information and usually an encryption key for identity verification and
secure communication. Commonly used by HTTPS and SSL in
a public key infrastructure (PKI).
• Multifactor authentication (MFA)—Combines two or more authentication methods, such as a user name plus password and
biometrics.
Network Device Hardening
Network hardening attempts to reduce network and system vulnerabilities, thereby stopping or detecting attacks before they are
exploited. Some technologies and techniques for network hardening include:
• Anti-malware software—Install software that detects and
sometimes removes malware such as viruses, worms, rootkits,
spyware, and adware.
• Credentials—Change default administrator credentials on OSs
and network devices. Use strong passwords.
• Software updates—Keep software and device firmware up-todate and apply patches in a timely manner.
• Services and ports—Disable unnecessary network services
and TCP/UDP ports. Disable unused physical switch and
router ports.
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Network
Troubleshooting
and Tools
•
•
Troubleshooting a network is as much an art as it is a science.
There is no substitute for practice and experience, but there is a
methodology you should follow that will help with troubleshooting
not only networks, but most problems you encounter in life. In
addition, you need to be familiar with the various tools, both
software and hardware, that are commonly used to troubleshoot
networks. The successful network troubleshooter will draw
upon a variety of skills, technologies, and techniques to solve
the problems encountered on increasingly complex LANs and
internetworks.
Troubleshoot Wireless Connections
Wireless networks pose unique problems compared to wired networks since there is no tangible media to inspect and test. Some of
the more common problems and wireless signal characteristics that
can affect signal quality include:
• Interference—Signal quality can be adversely affected by other
radio signals using the same frequencies as a WLAN.
• Overlapping channels—Nearby WLANs using the same or
adjacent channels degrade signal quality.
• Power level—The transmitter power can be increased or
­decreased to provide the best wireless signal coverage.
• Rogue access point—An unauthorized access point (AP) can
degrade signal quality or pose as a valid AP to steal data or
gain unauthorized access to another network.
• Antenna type—Using the proper antenna type (unidirectional or
omnidirectional) for a given scenario is critical for a strong signal.
• AP placement—A site survey must be done to determine the
best placement for access points. Environmental factors such
as concrete walls, reflective materials on windows, and metals
studs can all affect signal quality. Keep in mind signal phenomena: reflection (bounce), diffraction, and scattering.
• Mismatches—The wireless client must use the same ­encryption
protocol and passphrase as the AP and the correct SSID
(SSIDs are case sensitive).
Troubleshooting Methodology
CompTIA defines a seven-step approach to network troubleshooting as follows:
1. Identify the problem
2. Establish a theory of probable cause
3. Test the theory to determine cause
4. Establish a plan of action
5. Implement the solution or escalate as necessary
6. Verify system functionality
7. Document findings, actions, and outcomes
Using Troubleshooting Tools
Some of the tools needed to troubleshoot a network are built right
into the operating system in the form of command-line tools as
described in the following table:
Command
Description
ipconfig
ping
tracert
nslookup
arp
pathping
netstat
nmap
View IP address configuration
Verify host connectivity
View path to a device
Perform DNS lookups
View arp cache
Verifies path and connectivity
Displays TCP/IP connection information
Scans a network for open ports and provides application and
OS information about hosts
Troubleshoot Network Issues
Numerous things that can go wrong with a network, ranging from
misconfigured devices to hardware failures. Network technicians
must be able to recognize the signs and symptoms of some of the
most common reasons for network failure so they can quickly identify and resolve them. The following list describes some common
reasons for network errors or failures:
• Incorrect IP configuration—Occurs when the IP address,
subnet mask or default gateway of a device doesn’t match the
network configuration. Most often occurs with static addresses.
Use ipconfig to verify.
• Blocked ports—Misconfigured firewalls can result in ports
­being blocked that applications require. Ports can also be
blocked by incorrect ACL settings on routers.
• Duplicate IP—Most often occurs when addresses are assigned
statically or if the DHCP server is malfunctioning. Use ipconfig
to verify or examine the DHCP server lease data.
• Misconfigured DHCP—If the DHCP server has incorrect scope
data or options, all devices on the network that use dynamic
addresses will be affected. Check for exhausted DHCP
scope. In addition, protect against rogue DHCP servers using DHCP snooping on switches.
You may also need to use a variety of other tools and equipment to
install, troubleshoot, and test a network:
Tool
Description
Protocol analyzer
Multimeter
Cable tester
Spectrum analyzer
Tone generator
Light meter
TDR/OTDR
Capture and view packets; also called a sniffer
Test electrical properties
Check patch cables and cable terminations
Assesses the quality of a wireless signal
Verifies cable location and continuity
Measures light power for fiber optic cabling
Measures copper/fiber cable length
EMI/RFI—Electromagnetic or radio frequency interference
generated by motors, fluorescent lights, power lines, and large
machinery and electronic equipment.
Attenuation—The weakening of the signal as it travels across
the length of the media. Attenuation can be a problem if the
media exceeds the maximum length.
Troubleshoot Wired Connections
Copper cables must be properly terminated by installing an RJ-45
plug or by punching down the ends into an RJ-45 jack or a 110
block patch panel. Improper termination or incorrect installation
can cause a variety of problems including the following:
• Open—A problem that occurs when a circuit does not exist
such as when a wire breaks or is not making contact with a
conductor.
• Short—A problem that occurs when two wires that should not
touch, come into contact with each other.
• Crosstalk—Interference caused by the electromagnetic field
of one wire traveling to an adjacent wire. Near end crosstalk
(NEXT) occurs near the transmitter and far end crosstalk
(FEXT) occurs near the receiver.
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