Lesson 2 – Computer Network Models
Network Model: A set of rules (protocols) for transmitting data over a
network. Examples include the OSI model and the TCP/IP model.
4. Promotes interoperability among different network devices and
systems.
Disadvantages:
Data Packet: A packet is a unit of data sent across a network.
1. Complex and not practical for real-world use.
OSI Model (7 Layers):
2. Slow adoption, as it's mostly a reference model.
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Physical (Layer 1): Transfers bits across a physical medium.
3. Redundancy in certain functions across layers.
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Data-Link (Layer 2): Ensures error-free data transfer and formats data
into frames.
4. Less efficient compared to simpler models like TCP/IP.
TCP/IP Model: Advantages:
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Network (Layer 3): Routes data between devices using IP addresses.
1. Widely used and forms the backbone of the internet.
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Transport (Layer 4): Ensures complete data transfer without errors
(TCP/UDP).
2. Simpler and more efficient than the OSI model.
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Session (Layer 5): Manages sessions (dialog) between computers.
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Presentation (Layer 6): Translates data formats and manages
encryption/compression.
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Application (Layer 7): Provides network services to applications like
HTTP, FTP.
TCP/IP Model (4 Layers):
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Application: Network services (HTTP, FTP).
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Transport: Process-to-process data transfer (TCP/UDP).
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Internet: Routing and addressing (IP).
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Network Access: Physical and data-link layer functionalities.
OSI Model: Advantages:
1. Layered approach makes it easier to understand and troubleshoot.
2. Supports modular design, allowing technology updates in individual
layers.
3. Provides clear standards for different network protocols.
3. Highly scalable, suitable for both small and large networks.
4. Open standard, ensuring cross-platform compatibility.
Disadvantages:
1. Not very modular; hard to replace/update specific layers.
2. Lacks strict layering, making it less structured than OSI.
3. Limited support for new technologies compared to the OSI model.
4. Focuses more on implementation, neglecting theoretical aspects.
differences between the OSI and TCP/IP models:
OSI model
has 7 layers
OSI is a theoretical model
TCP/IP model
has 4 layers.
practical implementation used on internet.
OSI is less commonly used
protocol-independent
standard for internet communication
defines specific protocols like TCP and IP
Lesson 3 - Network Media
1. Ethernet Media: Ethernet, Fast Ethernet, and Gigabit Ethernet are
widely used LAN technologies, with speeds ranging from 10 to 1000 Mbps.
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Parity Check: Ensures data has even or odd number of 1s based on
parity bit.
2. Wireless Media:
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Hamming Code: Detects and corrects single-bit errors, detects two-bit
errors.
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Consists of devices like Access Points and wireless NICs. WLANs use
radio frequencies for communication and can operate up to 300 feet in
open areas.
Flow Control: Prevents fast senders from overwhelming slower receivers
using feedback mechanisms.
3. Cabling Methods:
MAC Protocols:
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CSMA/CD (used in wired networks): Detects collisions, stops
transmission, and retries after random delay.
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CSMA/CA (used in wireless networks): Avoids collisions by sending
intent to transmit before sending data.
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Straight-through: For switch-to-router, switch-to-PC, or hub-to-PC
connections.
Crossover: For connecting similar devices (switch-to-switch, PC-toPC).
Rollover: For terminal to console port connections.
4. LAN and WAN:
Framing: Converts packets to frames and ensures frames start/end are
detected.
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Error Handling:
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LANs use devices like hubs, bridges, and switches to manage traffic and
reduce congestion.
WANs use routers for connecting to the WAN and routing data packets.
5. Network Types:
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Peer-to-peer: All computers act as equal peers.
Client/server: Services are provided by a dedicated server to the clients.
Lesson 04 – Data link control
Data Link Layer: Responsible for transporting packets, media access
control, framing, synchronization, error control, and flow control.
Error Detection Methods:
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Checksum: Divides data into blocks, calculates and transmits
checksum.
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Cyclic Redundancy Check (CRC): Adds zeros and computes
remainder to detect errors.
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Error-Correcting Codes (ECC): Corrects errors, used in wireless
networks.
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Error-Detecting Codes (EDC): Detects errors but does not correct
them, common in wired networks.
Lesson 05 – Ethernet standard
Ethernet Overview:
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Networking technologies like Legacy Ethernet, Fast Ethernet, and
Gigabit Ethernet.
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Speeds: 10 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps.
Types of Ethernets:
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10BASE Ethernet: Uses coaxial or UTP cables, bus/star topology,
half/full-duplex.
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100BASE Ethernet (Fast Ethernet): UTP or fiber optic cables, star
topology, 100–200 Mbps.
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1000BASE Ethernet (Gigabit Ethernet): UTP/fiber optic cables, fullduplex, speeds up to 1 Gbps.
Ethernet Frame:
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Frame size: 64–1518 bytes.
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Components: Destination MAC address, Source MAC address, Type,
Data, and Frame Checksum.
Ethernet Operations:
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Half Duplex: Devices take turns sending data.
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Full Duplex: Simultaneous sending and receiving of data.
Collision Detection (CSMA/CD): Devices monitor the network to avoid
collisions and handle them using random backoff timers.
Types of Ethernet Errors: Collisions, frame errors, FCS (Frame Check
Sequence) errors, and alignment errors.
Lesson 06 – Network Layer
Network Layer:
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Transports packets from sender to receiver.
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Handles routing and forwarding to determine the best path for data.
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Routing algorithms such as RIP (Routing Information Protocol) and
BGP (Border Gateway Protocol) are used.
Lesson 07 - Logical Addressing Protocol
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Link State: Routers build a network map to calculate best paths.
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Path Vector: Similar to distance vector but includes paths.
Routing Protocols:
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RIP: Oldest, uses hop count.
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OSPF: Uses Shortest Path First (SPF) algorithm.
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BGP: Border Gateway Protocol for path vector routing.
ICMP (Internet Control Message Protocol):
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Handles error reporting and network management.
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Tools like Ping and Traceroute use ICMP messages.
Other Routing Protocols:
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ARP: Maps IP addresses to MAC addresses.
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DHCP: Dynamically assigns IP addresses to devices on a network.
Lesson 08 – Transport Layer and Quality of Service
Transport Layer:
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Ensures data transport between processes on hosts.
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Responsible for error handling, maintaining message order, and end-toend delivery.
Transport Layer Protocols:
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TCP (Connection-oriented, reliable): Sets up, maintains, and closes
connections.
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UDP (Connectionless, unreliable): Simple, no flow or error control,
used for short requests like DNS, TFTP, SNMP.
Routing Basics:
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Routing: Determines the path for packets from sender to receiver.
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Forwarding: Moves packets between router input and output ports.
Routing Algorithms:
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Distance Vector: Routers share distance to nodes.
TCP Characteristics:
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Point-to-point, full duplex.
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Reliable with acknowledgments (ACK), sequence numbers, and error
control.
UDP Characteristics:
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No connection setup.
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No error control or retransmission, useful for quick communication.
Quality of Service (QoS):
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Manages data speed, delay, jitter (delay variation), and packet loss in a
network.
Why QoS is Important:
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Ensures that different types of traffic (voice, video, data) get appropriate
bandwidth, reducing congestion.
QoS Implementation:
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Traffic shaping, queue management, congestion avoidance, bandwidth
reservation.
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Prioritize traffic types based on application needs.
Lesson 10 - Computer Security
Computer Security
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Definition: Protection of computer assets which include hardware,
software, data, networks, and people.
Cyber Security
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Definition: Protection of internet-connected assets like hardware,
software, servers, mobile devices, networks, and data.
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Categories: Network security, application security, information security,
and operational security.
Security Cube Principles
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Availability: Ensuring authorized users can access computer assets.
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Confidentiality: Ensuring only authorized parties can view assets.
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Integrity: Ensuring only authorized parties can modify assets.
Threats to Security
1. Availability
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Hardware: Devices disabled or removed.
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Software: Programs deleted.
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Data: Files deleted.
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Communication: Messages destroyed or deleted.
2. Confidentiality
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Unauthorized access to hardware, software, data, and communication.
3. Integrity
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Hardware replaced or removed.
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Software modified by unauthorized users.
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Data/information altered.
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Communication messages modified, delayed, or duplicated.
Ensuring Security
1. Availability:
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Regular maintenance, system updates, backups, disaster planning, new
technologies, and monitoring.
2. Confidentiality:
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Use authentication, authorization, and accounting (AAA).
3. Integrity:
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Validation, verification, reliability checks, backups, access controls,
encryption, and monitoring.
Types of Harm
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Methods: Firewalls, access control, Advanced Malware Protection
(AMP), Email Security Application (ESA), Web Security Application
(WSA).
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Disclosure: Unauthorized access to assets.
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Deception: Unauthorized changes leading to false data being accepted
as true.
Objectives of Secure Communications
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Disruption: Interruptions to system operations.
1. Authentication: Verifying the message's authenticity (e.g., Hash
Message Authentication Code - HMAC).
Access Control
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Definition: Determines how resources or services are allowed or denied
on a system.
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Models:
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Discretionary Access Control (DAC): Resource owners set access
permissions.
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Mandatory Access Control (MAC): System-enforced policy
determines access.
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Role-Based Access Control (RBAC): Access based on user roles.
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Attribute-Based Access Control (ABAC): Access based on attributes
and contextual factors.
2. Integrity: Ensuring the message is not altered during transmission (e.g.,
Hash Algorithms).
3. Confidentiality: Protecting the message from being read by
unauthorized parties (e.g., Symmetric Encryption Algorithms).
Authentication Methods
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Services: Ensure the message is from a real source and verify personal
identification (e.g., ATM PIN).
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Non-repudiation: Sender cannot deny sending the message; receiver
can verify the source.
Encryption
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Definition: Converting information into a secret code (plaintext to
ciphertext).
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Key: Required for encrypting and decrypting messages.
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Algorithms:
Physical Security Implementation
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Elements: Restricted areas, CCTV, locks, access control, barriers,
security services, and intrusion detection systems.
Lesson 11 – Cryptography-Concepts
Symmetric Encryption: Same key for encryption and decryption.
Cryptography Basics
Common Algorithms: Data Encryption Standard (DES), Three timesData Encryption Standard (3DES), Software Encryption Algorithm
(SEA).
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Definition: Secure communication techniques that allow only the
sender and receiver to view the message contents.
Cryptography Services
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Network Security: Protect network infrastructure (routers, switches,
servers).
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Data Security: Ensure the safety of data/information.
Types of Encryptions
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Data Encryption Standard (DES): Operates in block mode,
encrypting data in 64-bit blocks.
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3DES: Applies DES three times to a plaintext block.
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Hash Function: Transforms a string into a shorter, fixed-length value
(e.g., password hashing).
Cryptography Techniques
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Transposition Ciphers: Rearranging letters without replacement.
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Example: Message "FLANK EAST ATTACK AT DAWN"
transposed to "NWAD TA KCATTA TSAE KNALF".
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Substitution Cipher: Shifting each letter in the plaintext a certain
number of places.
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One-time Password (OTP): Unique password used once for logging in
to a network/service.
Firewalls
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Definition: Network security device that monitors and controls
incoming and outgoing traffic.
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Types:
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Packet Filtering Firewall: Operates at junction points like routers
and switches; compares packets against criteria.
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Stateful Firewall: Monitors the state of connections and analyzes
traffic at OSI Layers 4 and 5.
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Application Gateway Firewall: Filters information at multiple OSI
layers, often works with a proxy server.
Firewall Design
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DMZ (De Militarized Zone): Firewall design with one interface
connected to a private network and another to a public network.
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Key Considerations: Device interfaces, traffic type, source, and
destination.