IPv4: Internet Protocol Version 4

Introduction

Internet Protocol (IP) addresses form the backbone of network communications. IPv4, the fourth iteration of the IP address system, remains the most widely-implemented version despite its limitations. This guide explains IPv4's structure, classification, and its position relative to the newer IPv6 protocol.

What is IPv4?

IPv4 serves as a unique identifier system for devices connected to networks. Each device on the Internet receives an IP address enabling communication across both internal and external networks.

IPv4 addresses are 32-bit integers displayed in dotted decimal notation (x.x.x.x), where each octet ranges from 0-255. For example, 192.168.100.1 represents a valid private IP address. These addresses are typically assigned by DHCP servers, routers, or ISPs.

IPv4 Classes

IPv4 addresses divide into five classes, with A, B, and C being the primary ones used for general networking:

Class A

  • Capacity: Over 16 million addresses
  • Network Values: 1-127
  • Public Range: 1.0.0.0 to 127.0.0.0
  • Private Range: 10.0.0.0 to 10.255.255.255
  • Subnet Mask: 255.0.0.0
  • Best for: Very large networks

Class B

  • Capacity: 65,535 addresses
  • Network Values: 128-191
  • Public Range: 128.0.0.0 to 191.255.0.0
  • Private Range: 172.16.0.0 to 172.31.255.255
  • Subnet Mask: 255.255.0.0
  • Best for: Medium to large networks

Class C

  • Capacity: 254 addresses
  • Network Values: 192-223
  • Public Range: 192.0.0.0 to 223.255.255.0
  • Private Range: 192.168.0.0 to 192.168.255.255
  • Localhost Range: 127.0.0.1 to 127.255.255.255
  • Subnet Mask: 255.255.255.0
  • Best for: Small local networks

Special Classes

  • Class D: Reserved for multicasting (224.0.0.0 to 239.255.255.255)
  • Class E: Used only for research (240.0.0.0 to 255.255.255.255)

Classful Addressing Problems

The rigid class-based system created inefficiency as networks grew. Organizations needing slightly more addresses than a class provided were forced into the next class up, wasting large blocks of IP addresses. For instance, a network requiring 255 addresses would receive a Class B allocation with 65,535 addresses, leaving most unused.

This inefficient allocation accelerated IPv4 address exhaustion as the Internet expanded rapidly.

Current Status of IPv4

Despite its limitations, IPv4 remains dominant due to its widespread integration. Solutions like Classless Inter-Domain Routing (CIDR) and dual-stack deployments with IPv6 have extended IPv4's viability.

IPv4 vs. IPv6 Comparison

The key differences between IPv4 and IPv6:

Address Space

IPv4 has 32-bit addressing (~4.3 billion addresses) vs. IPv6's 128-bit space (~340 trillion trillion trillion addresses)

Header Structure

IPv6 offers enhanced packet headers for improved routing

Mobile Support

IPv6 provides better support for mobile network devices

Broadcast

IPv4 supports broadcast addresses while IPv6 uses multicast addressing

While IPv6 offers significant improvements, most networks still primarily use IPv4 addresses, with some implementing dual-stack configurations to support both protocols simultaneously.