Must watch OSI Video : https://www.youtube.com/watch?v=ZF9j3w95swU&list=PLRjPlu6MAom7Kj0efDQJDtdpcazYJOAwf&index=6
Must watch networking linux command : https://www.youtube.com/watch?v=EjiX1cjm_H8&t=66s
Introduction:
The OSI (Open Systems Interconnection) model is a popular framework for understanding the journey of data across the internet.
It explains the different layers involved in the data transmission process and what happens to the data in each of these layers.
The OSI model consists of 7 layers: Layer 7 to Layer 1, or Layer 1 to Layer 7 if viewed from the end of the data transmission.
DNS (Domain Name System) Resolution:
This is the process of mapping a domain name (e.g., www.google.com) to an IP address.
The router or browser first checks the local cache for the IP address mapping, and if not found, it queries the internet service provider's DNS server.
TCP (Transmission Control Protocol) Handshake:
The TCP handshake is a three-way process that establishes a connection between the client (e.g., your laptop) and the server (e.g., the Google server).
The client sends a SYN (synchronize) packet, the server responds with a SYN-ACK (synchronize-acknowledge) packet, and the client completes the handshake by sending an ACK (acknowledge) packet.
Layer 7 - Application Layer:
The Application layer is responsible for defining the format and structure of the data being transmitted.
example - The browser initiates an HTTP or HTTPS or FTP request to the server.
Layer 6 - Presentation Layer:
The data is encrypted, and the format and encoding are handled.
The Presentation layer is responsible for translating data between different formats and encodings.
It ensures that the data sent by the Application layer can be understood and processed by the receiving system.
This layer handles tasks such as encryption, decryption, and data compression.
Layer 5 - Session Layer:
A session is created between the client and the server. (jisse baar baar login na manage example - transaction process bich mein na ruk jaye)
The Session layer is responsible for establishing, maintaining, and synchronizing communication sessions between applications.
layer 7,6,5 happening at the browser level
Layer 4 - Transport Layer: (@ Firewall level)
The data is segmented, and the protocol (TCP or UDP) is identified.
example- For http the protocol is TCP and for DNS etc the protocol is UDP.
the Transport layer is responsible for the TCP handshake. It handles tasks such as segmentation means carving up information into smaller pieces(10GB data ko samller piece s mein convert krna jisse bich mein process break na ho) .
The Transport layer is responsible for end-to-end data delivery, ensuring that the data is transmitted reliably and without errors.
Layer 3 - Network Layer: (@ Router level)
The source and destination IP addresses are added to the data segments, which are now called packets.
It determines the best path for the data to travel from the source to the destination.
The Network layer is responsible for logical addressing and routing of data across the network.
Layer 2 - Data Link Layer: (@Switch level) ... Router is connected to switches which are ethernet ports.
The packets are converted into frames, and MAC addresses/info are added.
MAc info tells switch what are the other components within your network
Layer 1 - Physical Layer: (@ Hub or Modem or fiber/optical Cables)
The data is converted into electronic signals and transmitted over the physical network. Fibre cables only understand electronic signals.
Data Journey through the OSI Model:
The data travels through the OSI model layers, from Layer 7 to Layer 1, when the client sends a request.
The reverse process happens when the server responds to the client's request, with the data traveling back through the OSI model layers.
