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IPv4

IPv4_Header_Structure_061120A
(IPv4 Header Structure)

 

- Overview

IPv4 is the first widely used version of the Internet Protocol, introduced in 1983, and is still the most common way to identify network devices. 

It utilizes 32-bit addresses, resulting in approximately 4.3 billion unique addresses, although some are reserved. 

Key characteristics : 

  • Historical Context: IPv4 was the first version of IP to be standardized and deployed on a large scale.
  • Address Format: IPv4 uses 32-bit addresses, which are typically represented as four sets of numbers separated by periods (e.g., 192.168.1.1).
  • Address Space: The 32-bit address space allows for roughly 4.3 billion unique addresses.
  • Special Uses: Some address blocks within the 4.3 billion are reserved for specific purposes like private networks or multicast addresses.
  • Prevalence: Despite the introduction of IPv6 with its larger address space, IPv4 remains widely used due to its simplicity and widespread deployment.
  • Limitations: The limited address space of IPv4 has become a concern as the number of internet-connected devices has grown, leading to the development and adoption of IPv6.

 

Please refer to the following for more information:

 

- IPv4 Addressing

IPv4, defined in RFC 791, is a connectionless protocol using a best-effort delivery model, meaning it doesn't guarantee packet delivery, sequencing, or duplicate avoidance. It utilizes 32-bit addresses represented in dot-decimal notation (e.g., 192.168.1.1) and is divided into five classes (A, B, C, D, and E) for addressing. 

Key Aspects of IPv4:

  • Connectionless: Data is transmitted in packets without a prior connection setup.
  • Best-Effort Delivery: IPv4 doesn't guarantee packet delivery or proper sequencing.
  • 32-bit Addressing: Each device is identified by a 32-bit address, allowing for approximately 4.3 billion unique addresses.
  • Dot-Decimal Notation: Addresses are written as four decimal numbers separated by periods.
  • Classful Addressing: Originally divided into classes A, B, C, D, and E, with different bit allocations for network and host portions.
  • RFC 791: The official specification document for IPv4.
  • Upper Layer Protocols: Protocols like TCP handle aspects like data integrity and error control, often alongside IPv4.

 

- IPv4 Datagram Header

The IPv4 datagram header is a crucial part of an IPv4 packet, containing metadata about the data being transmitted. It essentially acts as an address label and routing guide for the packet as it travels across a network. The header includes 13 mandatory fields, and an optional "Options" field, and varies in size from 20 to 60 bytes. 

Here's a breakdown of the key fields: 

1. Mandatory Fields:

  • Version: Specifies the IP version (4 for IPv4).
  • Internet Header Length (IHL): Indicates the length of the header in 32-bit words.
  • Type of Service (TOS): (Now more commonly known as Differentiated Services Code Point (DSCP)) used for traffic prioritization.
  • Total Length: Specifies the total length of the datagram (header + data) in bytes.
  • Identification: Used to identify fragments of an original IP datagram.
  • Flags: Used for fragmentation control.
  • Fragment Offset: Indicates the position of a fragment within the original datagram.
  • Time to Live (TTL): Limits the lifetime of a datagram to prevent it from endlessly circulating.
  • Protocol: Identifies the protocol of the data carried in the payload (e.g., TCP, UDP).
  • Header Checksum: Used for error detection in the header.
  • Source Address: The IP address of the sending device.
  • Destination Address: The IP address of the receiving device.

2. Optional Field:
  • Options: Provides additional, less frequently used functionalities and can vary in length.

 

[More to come ...]

 

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