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Networking Workflow

** OSI Model vs. TCP/IP Model**

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  • OSI Model:

    • A seven-layer reference model for system communication.
    • Defines clear separation of tasks per layer.
    • Standardized by ITU and ISO, often called the ISO/OSI model.

    • TCP/IP Model:

    • A protocol family essential for Internet communication.

    • Includes TCP, IP, ICMP, and UDP for data transport and switching.
    • More practical and widely used compared to the OSI model.

    ** Packet Transfers**

  • In a layered network system, data is transferred as Protocol Data Units (PDU) at each layer.

  • When requesting a website, data moves down the OSI layers, each performing specific functions, until it reaches the physical layer for transmission.
  • The destination device receives the data and processes it up the layers until the application uses it. Pasted image 20250315182256.png

Encapsulation and Decapsulation

Pasted image 20250315182405.png - Encapsulation: Each OSI layer adds a header to the data from the upper layer to control and identify packets. - The PDU (Protocol Data Unit) is passed down the layers until it reaches the Physical or Network Layer for transmission. - Decapsulation: The receiver removes headers at each layer, using the information to process and deliver the data to the application. - This cycle continues until all data is successfully sent and received.

** Importance of OSI and TCP/IP Models for Penetration Testers**

  • TCP/IP Model: Helps quickly understand how a connection is established.
  • OSI Model: Allows detailed analysis by breaking down network traffic layer by layer.
  • Use Case: Penetration testers often intercept and analyze network traffic, requiring deep knowledge of both models.
  • Recommendation: Master both models to effectively perform network traffic analysis.

OSI Model and Its Role in Communication

  • Purpose: The OSI model standardizes communication across different systems using seven hierarchical layers
Layer Function
7. Application Manages data input/output and provides application functions.
6. Presentation Converts system-dependent data formats into an application-independent format.
5. Session Controls logical connections and maintains sessions between systems.
4. Transport Ensures reliable end-to-end communication, error detection, and flow control.
3. Network Handles routing, forwarding, and addressing of data packets across networks.
2. Data Link Ensures reliable, error-free transmission and organizes data into frames.
1. Physical Transmits raw data via electrical, optical, or wireless signals.
- Communication Process: Data travels downward (sender) and upward (receiver) through the layers, ensuring security, reliability, and performance in communication.

** TCP/IP Model and Its Functions**

  • Purpose: The TCP/IP model, also called the Internet Protocol Suite, standardizes communication across networks. It consists of four layers, each responsible for different aspects of networking.

  • Layer Functions:

TCP/IP Model Function Corresponding OSI Layers
Application (Layer 4) Defines communication protocols for applications (e.g., HTTP, FTP, SMTP, DNS) Application (7), Presentation (6), Session (5)
Transport (Layer 3) Manages data flow with TCP (reliable) and UDP (fast but unreliable) Transport (4)
Internet (Layer 2) Handles IP addressing, routing, and packet forwarding Network (3)
Link (Layer 1) Manages physical data transmission over the network medium Data Link (2), Physical (1)

  • Comparison with OSI:

    • The TCP/IP model has fewer layers but serves the same purpose as the OSI model.
    • TCP (Layer 4 in OSI) and IP (Layer 3 in OSI) are central protocols in networking.

Here’s a structured table for TCP/IP tasks and their corresponding protocols

Task Protocol Description
Logical Addressing IP Assigns logical addresses to nodes in a network, using network classes, subnetting, and CIDR to structure topology.
Routing IP Determines the next hop for each data packet to reach its destination efficiently.
Error & Control Flow TCP Maintains a virtual connection between sender and receiver with control messages to ensure connection reliability.
Application Support TCP/UDP Uses port numbers to differentiate applications and manage their communication.
Name Resolution DNS Resolves human-readable domain names (FQDNs) into IP addresses for internet communication.