User:Stefan00/IPV6 Addresses Introduction

DRAFT

Overview
The purpose of this article is to provide a short and simple introduction on IPv6 addresses and mechanisms. It is not intended to be a detailed technical documentation.

It is often claimed that IPv6 is not much different compared to IPv4 - just better and future proof. That's almost true. Yes, it is better and once fully understood it's great. But it is different compared to IPv4.

1. General Format
Every IPv6 Address is
 * 128 Bit long
 * noted in groups of 8x4 hex groups
 * hex groups divided by colons

Example IPv6 address: 2a02:810a:8240:0a2c:0202:c8ff:feeb:66d0

2. Prefix and Suffix
IPv6 addresses are always constructed out of 2 parts:
 * The Prefix - left part
 * The Suffix - right part

The Example from above divided into Prefix and Suffix: 2a02:810a:8240:0a2c :  0202:c8ff:feeb:66d0 PREFIX                 SUFFIX

Although combined in a single address, the two parts have completely different meanings. In a very simple way, think of it as:
 * Prefix is the network part of an address. If defines which network segment this address belongs to, where it can be routed, where it is valid.
 * Suffix is the interface part of an address. It's the "address" of the actual network interface within a network. It can be thought of as the "local" part of an IPv6. Every network interface (physical or virtual) has its own suffix which must be unique within a network. That's why, the official name of the suffix is "Interface Identifier (IID)".

3. Common Prefixes / Scopes
As written above, the Prefix part is the "network part" of an address. It defines what network it belongs to and where packages can be routed to - the Scope.

For setting up and administering IPv6 networks, it is necessary to clearly understand the meaning of prefixes. For example, the smallest routable "network" is a computer itself. That's why the smallest routable scope is loopback - packages send on this interface can only reach the local machine.

Just like in IPv4, some IPv6 address blocks are reserved for special purposes. To get started with the table below, think of a block as "Prefix begins with..."

4. Multiple IPv6 addresses on each interface
IPv6 uses multiple addresses on a single network interface. That's one of the most important aspects of IPv6. Period. Always keep this in mind!

By nature, IPv6 is divided in Scopes as seen above. Already be seeing the prefix of an address, it's clear where the address is valid and so where packages can be routed to. For example:
 * an address starting with fe80: (link local) can not reach the internet.
 * a network package from ::1 (loopback) can not even reach another machine.

IPv6 routing is smart. It always chooses the right IPv6 address to reach the right network segment.

A basic working IPv6 configuration could be: