IPv6 - Overview

Internet Protocol version 6 (IPv6) is the successor to IPv4, designed to address the limitations of IPv4 and provide a foundation for the internet’s continued growth. Like IPv4, it operates at the Network Layer (Layer 3) of the OSI model. IPv6 offers a vastly expanded address space and incorporates several features that improve efficiency, security, and autoconfiguration.

Why a New IP Version?

IPv4, developed in the early 1980s, has been remarkably successful. However, its 32-bit address space (approximately 4.3 billion addresses) has proven insufficient for the internet’s exponential growth. Key motivations for developing IPv6 include:

Address Space Exhaustion: The primary driver. The proliferation of internet-connected devices (computers, smartphones, IoT devices) has depleted the available IPv4 addresses.
Simplified Header: IPv6 features a streamlined header to improve packet processing efficiency in routers.
Enhanced Autoconfiguration: IPv6 supports Stateless Address Autoconfiguration (SLAAC), allowing devices to configure their own IP addresses without needing a DHCP server, simplifying network setup.
Integrated Security: IPsec (IP Security) support was a mandatory part of the original IPv6 specification (though now optional for general use, it’s well-integrated), providing a framework for end-to-end security.
Improved Quality of Service (QoS): The ‘Flow Label’ and ‘Traffic Class’ fields in the IPv6 header provide better mechanisms for identifying and prioritizing traffic flows, crucial for real-time applications like VoIP and streaming.

What Happened to IPv5?

While IPv4 is version 4, the next widely adopted version is IPv6. IP version numbers 0 through 3 were experimental. IP version 5 was assigned to an experimental real-time streaming protocol called Internet Stream Protocol (ST2). ST2 was designed for voice and video but was never widely deployed for public internet use. Thus, the next available version number for a general-purpose IP successor was 6.

A simplified history of IP versions:

IP versions 0-3: Experimental, developmental stages.
IPv4 (version 4): The dominant internet protocol for decades.
IPv5 (version 5): Assigned to the Internet Stream Protocol (ST2), not a successor to IPv4.
IPv6 (version 6): The designated successor to IPv4.

Brief History & Key RFCs

The Internet Engineering Task Force (IETF) began work on a successor to IPv4 in the mid-1990s as concerns about address exhaustion grew. Key Request for Comments (RFCs) documents define IPv6:

RFC 8200: Internet Protocol, Version 6 (IPv6) Specification (obsoletes RFC 2460). Defines the basic IPv6 protocol.
RFC 4291: IP Version 6 Addressing Architecture. Defines the address types, formats, and text representation.
RFC 4861: Neighbor Discovery for IP version 6 (IPv6) (obsoletes RFC 2461). Defines how devices on the same link discover each other.
RFC 4862: IPv6 Stateless Address Autoconfiguration (SLAAC) (obsoletes RFC 2462). Defines how hosts can automatically configure their addresses.
RFC 8415: Dynamic Host Configuration Protocol for IPv6 (DHCPv6) (obsoletes RFC 3315). Defines stateful and stateless configuration via DHCPv6.
RFC 5952: A Recommendation for IPv6 Address Text Representation. Provides guidelines for writing IPv6 addresses consistently.

Major internet service providers and content companies started significant IPv6 deployments in the 2010s, often using a dual-stack approach (running IPv4 and IPv6 simultaneously) to ensure a smooth transition.