7 Layers of the OSI Model

OSI Model Overview

• Framework consisting of 7 layers for networking and telecommunications.
• Layers include Application, Presentation, Session, Transport, Network, Data Link, and Physical.

Layer 7: Application

• User-facing layer that displays data to users.
• Interacts directly with end-user applications.

Layer 6: Presentation

• Responsible for converting data formats between network and application.
• Handles encryption/decryption for secure data transmission.
• Compresses data for efficient transfer.

Layer 5: Session

• Manages communication sessions between hosts.
• Sets up, coordinates, and terminates connections between devices.

Layer 4: Transport

• Ensures end-to-end communication for data transfer.
• Controls the amount and rate of data sent.
• Assigns port numbers for services.
• Key protocols include:
  • TCP (Transmission Control Protocol) for reliable communication.
  • UDP (User Datagram Protocol) for faster, connectionless communication.

Layer 3: Network

• Facilitates packet forwarding and routing between routers.
• Segments data into packets for efficient transmission.
• Uses IP addresses for locating devices on the network.

Layer 2: Data Link

• Enables data transfer between directly connected network devices.
• Responsible for node-to-node communication and error correction.
• Contains two sub layers:
  • MAC (Media Access Control).
  • LLC (Logical Link Control).

Layer 1: Physical

• Covers the physical mediums for data transmission, such as cables and connectors.
• Responsible for the transmission of raw bits across media.

Traffic Flow in OSI Model

• Traffic from sender descends the OSI layers, while receiver traffic ascends.

Ports

• Networking constructs that manage multiple network requests.
• Total of 65,535 ports available.
• Categories of ports:
  • Well-known ports
  • Registered ports
  • Dynamic ports used by applications
• Notable ports include:
  • Port 22: SSH (Secure Shell) for remote connections.
  • Port 53: DNS (Domain Name System) for resolving domain names.
  • Port 25: SMTP (Simple Mail Transfer Protocol) for email.
  • Port 20/21: FTP (File Transfer Protocol) for file transfer.
  • Port 80: HTTP (Hyper Text Transfer Protocol) for web communication.
  • Port 443: HTTPS (Secured HTTP).

Protocols

• Established rules for data transmission across networks.
• Examples include:
  • ICMP (Internet Control Message Protocol) for diagnostic messages.
  • TCP for reliable data transfer via three-way handshake.
  • UDP for low-latency communications.

Cybersecurity

• CIA Triad:

  • Confidentiality: Access limited to authorized personnel.
  • Integrity: Data integrity and authorized modifications.
  • Availability: Authorized access to information.
  • Non-repudiation: Ability to deny actions by subjects.

• Cybersecurity Framework consists of five functions:

  • Identify: Develop security policies and capabilities.
  • Protect: Implementation of security measures.
  • Detect: Ongoing monitoring for security risks.
  • Respond: Contain and eradicate identified threats.
  • Recover: Restore systems and data post-incident.

Vulnerability, Threat, and Risk

• Vulnerability: Weakness that can be exploited.
• Threat: Potential to exploit a vulnerability.
• Risk: Likelihood and impact of threats exploiting vulnerabilities.

Malware Types

• Viruses and worms: Spread without authorization.
• Trojan: Malware disguised as legitimate software.
• Potentially Unwanted Programs (PUPs): Installed alongside other software.

Ransomware

• Software that threatens users to extort money.

Social Engineering Attacks

• Phishing: Deceives users into accessing malicious sites.
• Spear phishing: Targeted phishing attempts toward specific individuals.
• Whaling: Phishing aimed at high-profile targets like executives.

Cryptography Concepts

• Plaintext: Original unencrypted message.
• Ciphertext: Encrypted message.
• Cipher: Method used to encrypt/decrypt messages.
• Hashing: Generates fixed-length strings from input data.

Distributed Denial of Service (DDoS) Attacks

• Aim to make network resources unavailable by overwhelming them.

Linux Overview

• Created in 1991 by Linus Torvalds, widely used in smart devices and systems.
• Highly customizable open-source OS with distributions like Red Hat and Fedora.

Basic Linux Commands

• whoami: Displays the current user.
• pwd: Prints the working directory path.