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IPv4 (Internet Protocol version 4) Basics

IPv4 is the fourth version of the Internet Protocol used to identify devices (computers, smartphones, servers, etc.) and route data packets across the internet. It is the fundamental addressing system of the current global network.

1. Structure of an IPv4 Address

An IPv4 address has three primary characteristics:

  1. 32-bit Address: IPv4 consists of 32 bits. This allows for approximately 4.3 billion ($2^{32}$) unique addresses for devices.

  2. Dot-Decimal Notation: The 32 bits are divided into four 8-bit sections (Octets) to make them human-readable. Each octet is converted to a decimal number and separated by a dot (.).

    • Notation Example: 192.168.1.1
    • Each octet has a value ranging from $0$ to $255$.

  3. Network ID and Host ID: An IPv4 address is logically divided into two parts: the Network ID (where to send the data) and the Host ID (which specific device in that network). This division is defined by the Subnet Mask.

2. Address Classes (Classful Networking)

Initially, addresses were categorized into classes (A, B, and C) based on the size of the network.

Class Purpose Network ID Size Host ID Size
A Very Large Networks (Governments, large corporations) 8 bits 24 bits (Vast host capacity)
B Medium-to-Large Networks (Mid-sized companies, universities) 16 bits 16 bits
C Small Networks (Homes, small offices) 24 bits 8 bits (Max 254 hosts)

Note: Modern networks primarily use CIDR (Classless Inter-Domain Routing), which allows for flexible subnetting, making the old class system obsolete.

3. The Limitation of IPv4: Address Exhaustion

IPv4 provides only 4.3 billion addresses. Due to the explosion of smartphones and IoT devices, these addresses have been nearly exhausted.