OSI Model (& TCP Model Ports/Protocol)
Objective 1.1: Explain concepts related to the Open Systems Interconnection (OSI) reference
model
● Introduction
○ Open Systems Interconnect Model (OSI)
■ Developed in 1977 by the International Organization for Standardization
■ OSI is a reference model
● Used to categorize the functions of a network
● Useful for troubleshooting
○ Networks today operate under the TCP/IP mode
○ Layers
■ Physical - Layer 1
■ Data Link - Layer 2
■ Network - Layer 3
■ Transport - Layer 4
■ Session - Layer 5
■ Presentation - Layer 6
■ Application - Layer 7
○ Networks are designed to make data flow across networks
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CompTIA Network+
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○ Names of data as it flows through the OSI model
■ Bits - Layer 1
■ Frames - Layer 2
■ Packets - Layer 3
■ Segments - Layer 4
■ Data - Layer 5
■ Data - Layer 6
■ Data - Layer 7
● Layer 1 (Physical)
○ Physical Layer Overview (Layer 1)
■ First layer of the OSI model where transmission of bits across the network
occurs and includes physical and electrical network characteristics
■ Data type occurs as bits
● Binary bits represented as a series of 1s and 0s
○ Transition Modulation
■ Switching between levels to represent 1 or 0
● Copper Wire (Cat5/Cat6) – Uses voltage (0V for 0, +5V/-5V for 1)
● Fiber Optic Cable – Uses light (on for 1, off for 0)
○ Connector Standards
■ RJ-45 Connector – Used in CAT5/CAT6 cables
■ Wiring Standards
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CompTIA Network+
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● TIA/EIA-568A
● TIA/EIA-568B
■ Crossover cables – TIA/EIA-568A on one end, and TIA/EIA-568B on the
other end
■ Straight-through cables – TIA/EIA-568B on both ends
○ Physical Topology
■ Different physical network layouts
● Bus
● Ring
● Star
● Hub-and-Spoke
● Full Mesh
● Partial Mesh
■ Based on how cables are physically connected
○ Synchronization
■ Asynchronous Communication
● Start and stop bits for out-of-sync data transmission
■ Synchronous Communication
● Real-time communication using a common time source
○ Bandwidth Utilization
■ Broadband
● Divides bandwidth into separate channels (e.g., cable TV)
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CompTIA Network+
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■ Baseband
● Uses all frequency of the cable all the time (e.g., telephone)
○ Multiplexing
■ Involves taking some limited amount of resource and using it more
efficiently
● Allows multiple people to use a baseband connection at the same
time
■ Time Division Multiplexing (TDM)
● Allocates dedicated time slots
■ Statistical Time Division Multiplexing (StatTDM)
● Dynamically allocates time slots based on when people need it
■ Frequency Division Multiplexing (FDM)
● Divides the medium into channels
○ Layer 1 Devices
■ Cables – media
● Fiber optic
● Ethernet
● Coaxial
■ Wireless Media
● Bluetooth
● Wi-Fi
● Near field communication
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■ Infrastructure Devices
● Hubs
● Access points
● Media converters
○ Layer 1 Device Characteristics
■ Simply repeat whatever they receive
■ No logic or decision-making at Layer 1
● Layer 2 (Data Link Layer)
○ Data Link Layer (Layer 2)
■ Responsible for packaging bits from Layer 1 into frames and transmitting
them across the network
■ Performs error detection and correction, identifies devices using MAC
addresses, and provides flow control
○ MAC Address (Media Access Control Address)
■ A means for identifying a device physically and allowing it to operate on a
logical topology
■ A unique 48-bit physical addressing system is assigned to every network
interface card (NIC) produced
● Written in hexadecimal numbers
● First 24 bits – identify the manufacturer
● Remaining 24 bits – identify the specific device
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■ Crucial for logical topology – identifying devices on the network
○ Logical Link Control (LLC)
■ Provides connection services and acknowledges message receipt,
ensuring controlled data flow
■ Most basic form of flow control
● Limits data sent by a sender and prevents receiver overwhelm
■ Uses a checksum to detect corrupted data frames
○ Synchronization Methods at Layer 2
■ Isochronous Mode
● Common reference clock
● Time slots for transmissions
● Less overhead
■ Synchronous Method
● Devices use the same clock, with beginning and ending frames,
and control characters for synchronization
■ Asynchronous
● Devices reference own clock cycles
● No strict control over communication timing
○ Layer 2 Devices
■ Network Interface Cards (NICs)
■ Bridges
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CompTIA Network+
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■ Switches
● Intelligent use of logic to learn and send data to specific devices
based on MAC addresses
○ Switch Operation
■ Switches use CAM tables with MAC addresses to identify physical ports
connected to devices
■ Enables selective data transmission to specific areas in the network.
● Layer 3 (Network Layer)
○ Network Layer (Layer 3)
■ Concerned with routing and forwarding traffic using logical addresses
○ Logical Addressing
■ IP variants – common logical addressing schemes
● IPv4 – written in dotted octet notation which are four sets of
numbers separated by dots (e.g., 172.16.254.1)
● IPv6
■ Other protocols – these were replaced by IP (Internet Protocol)
● AppleTalk
● IPX (Internetwork Packet Exchange)
○ Switching/Routing Methods
■ Packet Switching (Routing)
● Data is divided into packets and then forwarded
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● Most commonly used method
■ Circuit Switching
● A dedicated communication link is established between two
devices
■ Message Switching
● Data is divided into messages which may be stored and then
forwarded
○ Route Discovery and Selection
■ Routers maintain routing tables for determining the best path
● Dynamic protocols (e.g., RIP, OSPF) enable routers to share and
update route information
■ Routing protocols help decide how data is going to flow across the
network and how the routers are going to communicate that information
○ Connection Services at Layer 3
■ Augments Layer 2 services
■ Involves flow control
● Prevents sender from overwhelming the receiver
■ Packet reordering
● Ensures data packets arrive and are reassembled in the correct
order
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○ Internet Control Message Protocol (ICMP)
■ Used for sending error messages and operational information to an IP
destination
■ PING
● Most commonly used ICMP
● Helps troubleshoot network issues by testing connectivity and
response times
■ Traceroute
● Traces the route of a packet through the network
○ Devices and Protocols
■ Routers
■ Multi-layer switches
● Combines Layer 2 switch and Layer 3 router features
● A switch is always a Layer 2 device, unless specifically mentioned
that it is a multi-layer switch, then it is considered as a Layer 3
device
■ Layer 3 protocols
● IPv4
● IPv6
● ICMP
○ IP and routers are commonly encountered Layer 3 devices in exams
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● Layer 4 (Transport Layer)
○ Transport Layer (Layer 4)
■ Dividing line between the upper layers and the lower layers of the OSI
model
■ Upper Layers
● Transport
● Session
● Presentation
● Application
○ Segments
■ Data Type in Transport Layer
○ Protocols in Layer 4
■ TCP (Transmission Control Protocol)
● Connection-oriented protocol that is a reliable way to transport
segments across the network
● With acknowledgement
● Uses Three-Way Handshake
○ SYN – synchronization
○ SYN-ACK – synchronization - acknowledgement
○ ACK – acknowledgement
● Windowing for flow control
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● Used for all network data that needs to be assured to get to its
final destination
■ UDP (User Datagram Protocol)
● A connectionless protocol that is an unreliable way to transport
segments (datagram)
● Used for audio and visual streaming
● No three-way handshake and less overhead
● No acknowledgment or retransmission
○ Remember the data types in Layer 4 for the exam
■ Segment – data type for TCP
■ Datagram – data type for UDP
○ TCP vs. UDP
■ TCP
● Reliable
○ Uses Three-way Handshake
● Connection-oriented
● Segment retransmission and flow control through windowing
● Sequencing
● Acknowledgment of segments
■ UDP
● Unreliable
○ No Three-way Handshake
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● Connectionless
● No retransmission and no windowing
● No sequencing
● No acknowledgment of datagrams
○ Windowing
■ Allows clients to adjust the amount of data in each segments during
transmission
■ Optimize throughput and bandwidth
■ Open or close window based on retransmissions
○ Buffering
■ Occurs when devices allocate memory to store segments if bandwidth is
not readily available
■ Buffer
● Temporary storage for segments
■ Prevents overflow by clearing segments
○ Layer 4 Devices
■ Protocols
● TCP and UDP
■ Devices
● WAN accelerators
● Load balancers and firewalls
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● Layer 5 (Session Layer)
○ Session Layer (Layer 5)
■ Manages sessions, ensuring separate conversations to prevent data
intermingling
○ Setting Up Session
■ Checking of user credentials and assigning numbers to sessions to help
identify
○ Maintaining Session
■ Continuous data transfer between parties
■ If connection breaks, it will require re-establishment
■ Includes acknowledgement of data
○ Tearing Down a Session
■ Ending a session once communication goals are achieved
■ Mutual agreement or one party disconnects
○ Layer 5 Devices and Protocols
■ H.323
● Used for setting up, maintaining, and tearing down voice and
video connections
● Operates over the real-time transport protocol (RTP)
■ NetBIOS
● Utilized by computers for file sharing over a network
● Commonly associated with Windows file sharing
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○ Layer 5 issues involve protocols and software rather than specific devices
● Layer 6 (Presentation Layer)
○ Presentation Layer (Layer 6)
■ Responsible for formatting data for exchange and securing it through
encryption
○ Data Formatting
■ Formatting data by a computer to have compatibility between different
devices
■ Formats
● American Standard Code for Information Interchange (ASCII)
○ Text-based language to use
○ Ensures data is readable by receiving system
○ Provides proper data structures
○ Negotiates data transfer syntax for the Application Layer
(Layer 7)
● GIFs – motion pictures
● JPEG – photographs
● PNG – Internet images
■ Formats enable compatibility between different devices
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○ Encryption
■ Used to scramble data in transit to keep it secure and provide data
confidentiality
■ Transport Layer Security (TLS)
● Ensures secure data transfer
● Creates an encrypted tunnel, protecting sensitive information
○ Scripting languages in Layer 6
■ Control how ASCII text is displayed on the screen
● HTML
● XML
● PHP
● JavaScript
○ Standard text formats
■ Different ways of displaying text using ones and zeros
● ASCII
● Unicode
● EBCDIC
○ Image formats
■ Different graphical representations of 1s and 0s
● GIFs
● JPEGs
● TIFFs
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● SVGs
● PNGs
○ Movie file formats
■ 1s and 0s formatted to create watchable videos
● MP4s
● MPEGs
● MOV
○ Encryption Algorithms
■ Scrambles data to provide confidentiality and security during transit and
storage
● TLS
● SSL (Secure Sockets Layer)
■ Focus on Security
● Layer 7 (Application Layer)
○ Application Layer (Layer 7)
■ Provides application-level services where users communicate with the
computer
■ Focus on lower-level applications
● File transfer
● Network transfer
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CompTIA Network+
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○ Application Services
■ Unites components for more than one network application
● File transfer
● File sharing
● Email
○ Low-level protocols
■ POP3 (Post Office Protocol 3)
■ IMAP (Internet Message Access Protocol)
■ SMTP ( Simple Mail Transfer Protocol)
● Remote access
● Network management
● Client-server processes
○ Service Advertisement
■ Applications send announcements to other devices on the network
■ Devices advertise the services they offer
● Printers and file servers managed by Active Directory
● Self-advertising devices like wireless printers
○ Layer 7 Protocols
■ Email Applications
● POP3
● IMAP
● SMTP
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CompTIA Network+
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■ Web Browsing
● HTTP
● HTTPS
■ Domain Name Service (DNS)
■ File Transfer Protocols
● FTP
● FTPS
● SFTP
■ Remote Access
● Telnet
● SSH
● SNMP
● Encapsulation and Decapsulation
○ Encapsulation
■ Process of putting headers and sometimes trailers around data
○ Decapsulation
■ Removing the applied encapsulation to access the original data
○ OSI Model Layers
■ Moving down from Layer 7 to 1 – encapsulation
■ Moving up from Layer 1 to 7 – decapsulation
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CompTIA Network+
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○ Protocol Data Units (PDUs) in OSI Model
■ A single unit of information transmitted in a computer network
● Terminology used for each layer is written as L(layer number) PDU
○ Example – L7 PDU for Layer 7
■ There are special names for the PDUs for layers 1, 2, 3, and 4
● Layer 1 – Bits
● Layer 2 – Frames
● Layer 3 – Packets
● Layer 4 – Segments (TCP) or Datagrams (UDP)
○ TCP Header (Layer 4)
■ 10 mandatory fields, totalling 20 bytes of information
● Source port
● Destination port
● Sequence number
● Acknowledgment numbers
● TCP data offset
● Reserved data – always set to zero
● Control flags
○ SYN – synchronize connection in three-way handshake
○ ACK – acknowledgment of the successful receipt of data
○ FIN (Finished) – tears down connections created by
three-way handshake
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CompTIA Network+
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○ RST (Reset) – used when an unexpected packet is received
○ PSH (Push) – ensures data is given priority
○ URG (Urgent) – identifies incoming data as urgent
● Window size
● TCP checksum
● Urgent pointer
● mTCP – optional
○ UDP Header (Layer 4)
■ 8-byte header
● Source port
● Destination port
● Length – indicates the total packet bytes
● Checksum – not mandatory
○ IP Header (Layer 3)
■ Contains various fields
● Version
● Length of IP header
● Type of service
● Total length of packet and header
● Identifier
● Flags
● Fragmented offset
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CompTIA Network+
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● Time to live
● Protocol
● Header checksum
● Source IP Address
● Destination IP Address
● Options and Padding
○ Ethernet Header (Layer 2)
■ Features a few things
● Destination MAC Address
● Source MAC address
○ MAC Address
■ Physical address that is used to identify a network
card on a local area network
■ Processed by switches
● EtherType field
○ Used to indicate which protocol is encapsulated in the
payload of a frame
■ IPv4 or IPv6
● VLAN Tag – optional
○ IEEE 802.1Q
○ IEEE 802.1AD
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CompTIA Network+
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■ A frame being sent at Layer 2 will also contain a payload
● Payload
○ Data that being sent across the network
○ 42 bytes – using VLANs
○ 46 bytes – no VLANs
○ Maximum Transmission Unit (MTU)
■ Maximum size for payload
● 1500 bytes for Ethernet
● Jumbo Frames
○ Frames larger than 1500 bytes
○ Require reconfiguring MTU
○ Data Transmission
■ Encapsulation of data and adding header at each layer
● Layer 4 – source/destination ports
● Layer 3 – source/destination IP addresses
● Layer 2 – soure/destination MAC addresses
● Layer 1 – data transmitted as 1s and 0s
■ Decapsulation at each intermediate device until the final host is reached
■ Final host decapsulates to Layer 7 for application understanding
● Understanding the OSI Model: Practical Example
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CompTIA Network+
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Ports and Protocols
Objective 1.4: Explain common networking ports, protocols, services, and traffic types
● Introduction
○ Port
■ Virtual entry/exit point for communications used by software applications
to exchange information
○ Protocol
■ Set of rules and conventions for data exchange between network devices
● Network Port Fundamentals
○ IP address
■ Used to direct data to the correct system in a network
○ Port
■ A logical opening in a computer
■ Identifies specific applications or services on a computer that represents
a service or application
■ Numbered from 0 to 65,535
○ Three Groups of Ports
■ Well-known ports
● Numbered from 0 to 1,023 Ephemeral ports (49,152-65,535)
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● Examples
○ FTP (20, 21)
○ SMTP (25)
○ HTTP (80)
○ HTTPS (443)
■ Registered ports
● Numbered from 1,024 to 49,151
■ Ephemeral Ports
● Temporary, short-lived ports for dynamic use
● Numbered from 49,152 to 65,535
● No registration is required and anyone can use them
○ Both Well-known and Registered Ports are registered with IANA for specific
applications or services
○ Data Transfer Example
■ Client communicates with a website using IP addresses and ports
■ Client's source IP and random ephemeral port connect to the website's
destination IP and default port (e.g., 80)
○ Two-Way Communication
■ Web server responds using its well-known port (e.g., 80) back to the
client's ephemeral port
■ Two-way communication is established between client (ephemeral port)
and web server (port 80)
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CompTIA Network+
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○ Ephemeral ports opened for specific tasks and closed after data transmission.
○ In subsequent communications, the client uses the well-known port (e.g., 80) but
selects a new random ephemeral port
○ Communication Flow
■ Source IP and port initiate communication
■ Data is transmitted
■ Ports closed when the task is completed
● Transmission Control Protocol (TCP)
○ Transmission Control Protocol (TCP)
■ Fundamental protocol in the Internet Protocol Suite that governs data
exchange over the internet
■ Ensures reliable delivery of packets
● Error checking
● Data sequencing
● Acknowledgment
■ Operates at the transport layer of the OSI model
■ Breaks down larger messages into smaller packets for efficient data
transfer and reassembles at the destination
○ Three-Way Handshake
■ Initiated to establish a connection between two systems
● SYN (Synchronize)
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CompTIA Network+
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● SYN-ACK (Synchronize-Acknowledgement)
● ACK (Acknowledgement)
■ Ensures readiness for secure data transmission
○ Error Checking and Flow Control
■ Error checking
● Uses sequence numbers and acknowledgment messages
● Detects and retransmits lost or corrupted packets
■ Flow control
● Prevents overwhelming the receiver
● Windowing
○ Controls the amount of data sent at a time
○ Allows dynamic adjustment based on network conditions
○ Ports
■ Numerical identifiers for services or applications in TCP/IP suite
■ Distinguish between different services on the same server
■ Each connection identified by source and destination IP addresses and
ports
● e.g., secure websites use port 443 (HTTPS)
■ Enable multiple network applications on the same server
○ TCP's Role in Internet Communication
■ Ensures reliability and ordered delivery between client and server
■ Operates at the transport layer of the OSI model
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CompTIA Network+
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■ Utilizes packetization, acknowledgment, and error checking
■ Three-way handshake establishes a secure connection
■ Ports facilitate the logical differentiation of services on a single machine
● User Datagram Protocol (UDP)
○ User Datagram Protocol (UDP)
■ Communication protocol used for time-sensitive transmissions on the
internet
● Ideal for applications prioritizing speed over error checking
● Low latency and reduced processing overhead.
● Lacks error checking and recovery services like TCP
■ Operates at the transport layer, similar to TCP
■ Connectionless communication model
○ Packet Structure
■ Datagrams
● Term for data packets in UDP
● Sent without prior setup of transmission channels
● Contains source/destination port numbers, length field, and
checksum
● Smaller and simpler headers (8 bytes) compared to TCP (20-60
bytes)
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CompTIA Network+
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○ UDP’s Stateless Nature
■ UDP does not maintain connection state or track packets
■ Often referred to as a "fire and forget" protocol
■ No waiting for acknowledgments, leading to faster transfer rates
○ Reliability Trade-off
■ UDP is less reliable due to lack of packet tracking
■ Suitable for scenarios where speed is crucial, and packet loss is
acceptable
○ Use Cases
■ Used in applications like live broadcasts, online gaming, and VoIP calls
■ Effective for simple request-response communications (e.g., DNS lookup)
○ UDP utilizes ports to differentiate between multiple services on the same
client/server
○ UDP relies on application-level error handling due to lack of built-in error
recovery
○ UDP contains a checksum in the header for minimal protection against data
corruption
○ UDP is not as robust as TCP in ensuring data integrity and delivery
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● Internet Control Message Protocol (ICMP)
○ Internet Control Message Protocol (ICMP)
■ An integral part of the Internet Protocol Suite which is considered to be a
network layer protocol for diagnosing network communication issues
■ Not used for data transmission between systems unlike TCP and UDP
■ Operates at the network layer of the OSI model
○ ICMP Messages
■ Used for indicating host or service unreachability, expired time to live,
and router buffer issues
○ Ping Utility
■ Utilizes ICMP to test host reachability on an IP network
■ Measures roundtrip time (latency) for network connection
○ ICMP Message Structure
■ Header
● Type – indicates the type of ICMP message (1 byte)
● Code – provides additional context about the message type (1
byte)
● Checksum – used for error checking the message header and data
(2 bytes)
○ ICMP Reliability and Design
■ Lacks reliability mechanisms like TCP
● No guaranteed delivery, ordering, or error correction
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■ Designed for speed and simplicity, not data integrity or security
○ Security Concerns
■ ICMP can be used in attacks
● ICMP Flood Attack
○ Overwhelms target with echo request packets, leading to
Denial of Service (DoS) Attack
○ Amplified up to Distributed Denial of Service (DDoS) Attack
to be effective
● Ping of Death
○ Exploits vulnerabilities in older systems, causing system
crashes
○ Modern Security Measures
■ Many modern systems are not vulnerable to Ping of Death due to
improved security measures
■ Network administrators may choose to block ICMP traffic for security but
face challenges in troubleshooting network issues
● Web Ports and Protocols
○ Web Ports and Protocols
■ Standardized rules and numerical gateways that govern data
transmission and communication on the internet for websites
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CompTIA Network+
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○ Two Fundamental Ports
■ Port 80 (HTTP)
● HTTP (Hypertext Transfer Protocol)
○ An application layer protocol. This designed to enable
communications between clients and servers
○ Uses port 80 by default
○ Foundation of data communication on the worldwide web
○ Requests and receives web content in plain text
● HTTP over Port 80 lacks security makes data vulnerable to
eavesdropping and attacks
■ Port 443 (HTTPS)
● HTTPS (Hypertext Transfer Protocol Secure)
○ Similar to HTTP but adds encryption via SSL/TLS
○ Uses port 443
○ Encrypts data, securing it from interception or tampering
○ Importance of HTTPS (Port 443)
■ Vital for websites handling sensitive data like banking, e-commerce, or
login pages
■ Automatic redirection from insecure HTTP (port 80) to secure HTTPS
■ Encryption ensures secure transmission of sensitive information
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CompTIA Network+
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○ Key Differences between HTTP (Port 80) and HTTPS (Port 443)
■ Security and Encryption
● HTTP (port 80) – unencrypted, plain text
● HTTPS (port 443) – encrypted using SSL/TLS, more secure against
data breaches
■ Default Usage
● HTTP (port 80) – traditional, default for unsecured browsing
● HTTPS (port 443) – introduced later, became default for secure
browsing in recent years
■ Search Engine Optimization (SEO) and Trust
● HTTPS (port 443) – favored for increased security and ranked
higher by search engines due to user trust and encryption
● Email Ports and Protocols
○ Email Ports and Protocols
■ Govern the transmission of emails across the Internet
■ Ensure efficient sending, receiving, and management of messages
○ Main Email Protocols
■ SMTP (Simple Mail Transfer Protocol)
● The standard protocol used for sending emails over the internet
● Operates over port 25
○ Default port used by email servers
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○ Insecure because data is sent in plain text
● Only used for sending emails
● SMTPS (SMTP Secure)
○ A secure variant of SMTP
○ Not really a protocol itself, but a way to secure the SMTP
protocol by transporting it via the secure socket layer or
transport layer security protocols
○ Operates over ports 465 or port 587
■ POP3 (Post Office Protocol version 3)
● Used to retrieve emails from a remote server to a local client
● Operates over port 110
● Designed to download and delete messages from the server
● Transmits emails in plain text (insecure)
● POP3S (POP3 Secure)
○ A secure variant of POP3 that overcomes the limitations of
POP3
○ Operates over port 995 via SSL/TLS
■ IMAP (Internet Message Access Protocol)
● Offers more flexibility than POP3
● Operates over port 143
● Allows managing emails directly on the server, synchronizing
across multiple devices
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CompTIA Network+
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● Transmits emails in plain text (insecure)
● IMAPS (IMAP Secure)
○ A variant of IMAP that can provide a secure and encrypted
connection by transmitting data inside of an encrypted
SSL/TLS using the standard IMAP protocol
○ Operates over port 993
○ SMTP and SMTPS are used for sending emails
○ POP3 and IMAP are both used for receiving emails
■ IMAP offers more sophisticated email management
○ Understanding protocols ensures secure and efficient email communication
○ Configure systems with secure variants to protect against security threats
● File Transfer Ports and Protocols
○ File Transfer Ports and Protocols
■ Specialized rules and procedures that are utilized for the transmission of
files across networks
○ FTP (File Transfer Protocol)
■ Oldest protocol for file transfer
■ Ports:
● Port 20 – actual data transfer
● Port 21 – sending control commands
■ Lack of encryption poses security risks
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CompTIA Network+
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■ Transmissions are sent in plain text
■ Widely used for its simplicity across platforms
○ SFTP (Secure File Transfer Protocol)
■ Addresses FTP security concerns
■ Also stands for SSH File Transfer Protocol
■ Operates on port 22 – standard port for SSH connections
■ Encrypts data for secure file transmissions
○ TFTP (Trivial File Transfer Protocol)
■ Basic version of FTP that lacks authentication and directory browsing
■ Operates on port 69
■ Designed for sending files when minimal security is sufficient
○ SMB (Server Message Block)
■ A network file sharing protocol that allows applications to read and write
to files and request services from the server programs
■ Operates on port 445
■ Predominantly used for Windows file sharing
■ Samba
● A cross-platform version of SMB that exists on Linux systems
■ Almost exclusively used inside of LANs and it is not a protocol to send
data across the Internet
○ Key Considerations for Protocol Selection
■ Align security requirements, network environment, and functionality
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CompTIA Network+
(N10-009) (Study Notes)
● FTP – basic transfers (ports 20, 21)
● SFTP – secure transfers (port 22)
● TFTP – simple, unsecured transfers (port 69)
● SMB – Windows file sharing in LANs (port 445)
● Remote Access Ports and Protocols
○ Remote Access Ports and Protocols
■ Build and manage systems and networks remotely from anywhere in the
world
■ Crucial for interconnected environments, allowing control over systems,
commands, and files.
○ Remote Access Protocols
■ SSH (Secure Shell)
● Protocol for secure remote login and network services over an
unsecure network
● Operates on port 22
● Provides a secure channel, strong authentication, and encrypted
data communication
● Used by network administrators for remote control of web and
server applications
■ Telnet
● Early remote log-in protocol
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CompTIA Network+
(N10-009) (Study Notes)
● Operates on port 23
● Allows remote login to another computer on the same network
● Transfers data in plain text, making it susceptible to eavesdropping
and on-path attacks
● Replaced by SSH due to lack of encryption
■ RDP (Remote Desktop Protocol)
● Proprietary protocol by Microsoft for graphical user interface
remote connection
● Operates on port 3389
● Allows remote access to a window system, supporting different
network topologies
● Supports data encryption, smart card authentication, and
bandwidth reduction
○ Considerations
■ Choose the appropriate protocol based on security requirements and
specific tasks
■ SSH is recommended for secure command-line management.
■ Telnet should be avoided due to its lack of encryption
■ RDP is essential for secure graphical access to Windows-based systems
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CompTIA Network+
(N10-009) (Study Notes)
● Network Service Ports and Protocols
○ Network Services, Ports, and Protocols
■ Fundamental services for smooth digital communication and network
management
■ Different services that ensure that the network devices can discover each
other, communicate efficiently, and relay important system information to
each other
○ DNS (Domain Name System)
■ Used for translating human-friendly domain names to IP addresses
■ Operates on ports 53 (UDP by default) for queries and responses
■ Uses TCP for larger messages
○ DHCP (Dynamic Host Configuration Protocol)
■ Automates the assignment of IP addresses and networking parameters to
client devices
■ Listens on port 67 (UDP) for client requests
■ Responds on port 68 (UDP)
○ SQL Services
■ Refers to protocols used by database servers for managing queries
■ Microsoft SQL Server operates on port 1433
■ MySQL Server on port 3306
○ SNMP (Simple Network Management Protocol)
■ Used for collecting information and configuring network devices
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CompTIA Network+
(N10-009) (Study Notes)
■ Operates on port 161 (UDP) for polling
■ Operates on port 162 (UDP) for unsolicited trap messages
■ Crucial for network diagnostics and performance monitoring
○ Syslog (System Logging)
■ Standard for message logging allowing devices to send event messages
across IP networks
● Syslog Server
○ Event message collector where syslog messages are sent to
■ Operates on port 514
● Uses UDP by default
● Can use TCP for reliability
● Other Network Service Ports and Protocols
○ Other Network Service Ports and Protocols
■ Refers to different network, service, ports, and protocols that play a
pivotal role in the network, time synchronization, and the establishment
of communication sessions, as well as directory services
■ Crucial for organizing and providing access to distributed information
located all across the network
○ Network Time Protocol (NTP)
■ Used to synchronize clocks of computers over a network
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CompTIA Network+
(N10-009) (Study Notes)
■ Vital for time-dependent processes, timestamping events, transaction
logging, and security protocols
■ Operates over port 123 using the User Datagram Protocol (UDP)
■ Example
● Ensures consistency between server and client times, affecting
encryption and decryption functions
○ Session Initiation Protocol (SIP)
■ Initiates, maintains, and terminates real-time sessions for voice, video,
and messaging
● Common usage includes Voiceover IP applications for internet
phone calls
■ Operates over port 5060 (traditionally) on both UDP and TCP for
unencrypted signaling
■ Uses port 5061 using TCP with TLS (Transport Layer Security) for
encrypted signaling
○ Lightweight Diectory Access Protocol (LDAP)
■ Protocol for accessing and maintaining distributed directory information
services over an IP network
■ Used to look up personal information in email programs
■ Ports
● LDAP (Insecure): Communicates over port 389 using both TCP and
UDP
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CompTIA Network+
(N10-009) (Study Notes)
● LDAPS (Secure): Encrypted with SSL or TLS, runs over port 636
using TCP