5 Layers of the TCP/IP Model :

   -  Layer 1: Physical  (Bit Level Transmission)

   -  Layer 2: Data Link  (Frames)

   -  Layer 3: Network  (Packets/Datagrams)

   -  Layer 4: Transport  (Segments/Datagrams)

   -  Layer 5: Application  (Data)

Unit of Communication :

   -  Layer 1 : Bits

   -  Layer 2 : Frames

   -  Layer 3 : Packets (IPv4/IPv6)

   -  Layer 4 : Segments (TCP), Datagrams (UDP)

   -  Layer 5 : Data (Message, Request, Response)

Addressing Used :

   -  Layer 2 (Data Link) : MAC addresses (physical)

   -  Layer 3 (Network) : IP addresses (logical)

   -  Layer 4 (Transport) : Port numbers

Delivery Types :

   -  Layer 2 : Local (direct delivery)

   -  Layer 3 : Indirect (routing across networks)

   -  Layer 4 : End-to-end (process-to-process delivery)

Encapsulation/Decapsulation :

   -  Encapsulation: Adding headers as data moves down the layers.

   -  Decapsulation: Removing headers as data moves up the layers.

Command to Set Yourself as Root User : sudo -i or su -

Command to Edit Files : nano <filename> or vi <filename>

Command to Check Network Interfaces : - ip a (replaces ifconfig)

Pinging Between 3 Machines :

    - LN (Private VM) ,  RN (Public VM) ,  GW (Router VM) :

    - Use ping <IP Address> to test connectivity.

 - Make sure routing is correctly set up in the Router VM (GW) to enable communication between the Private and Public VMs.

Layer 2 (Data Link Layer) :

    Main Protocol : Ethernet

Frame Fields :

     -  Preamble : Synchronization

     -  Destination MAC : Identifies recipient

     -  Source MAC : Identifies sender

     -  Type/Length : Protocol type or data size

     -  Payload : Data being transferred

     -  FCS (Frame Check Sequence) : Error checking

Frame Size :

     -  Min Length : 64 bytes (including header)

     -  Max Length : 1518 bytes

     -  Data Length : Varies but the standard payload can be up to 1500 bytes.

MAC Addresses :

     -  Unicast : Single device communication

     -  Multicast : Group communication

     -  Broadcast : All devices on the network

  Padding : Ensures the frame meets minimum size requirements.

Layer 3 (Network Layer) :

  Main Protocol : IP (Internet Protocol)

  Services :

     - Routing

     - Logical addressing

     - Packet forwarding

 Datagram Header Fields :

     -  Version: IPv4 or IPv6

     -  Header Length : Size of the header

     -  Source Address : Sender's IP address

     -  Destination Address : Recipient's IP address

     -  Time to Live (TTL) : Limits packet's lifetime to avoid loops

   Header Length :

     -  Min : 20 bytes (IPv4)

     -  Max : 60 bytes (IPv4)

Purpose of Fragmentation: Breaks large packets into smaller pieces for transmission across networks with different maximum transmission units (MTU).

TTL (Time to Live) : Limits the lifetime of a packet to prevent it from circulating indefinitely.