IPv6 Addresses
IPv6 Addresses

The main reason for establishment IPv6 is its enormously large address space. During the development of IPv6, the authors followed the motto "IPv6 addresses must not be ever exhausted" and therefore they chose the length of IPv6 addresses of 128 bits. The fundamental document that defines the IPv6 addresses is RFC 4291. This document defines lengths, structures and types of addresses. It also defines other conceptual elements. There are several RFC documents that describe individual types of IPv6 addresses in more detail. We mention only the fundamental of IPv6 addresses in this module. RFC 4291 defines the following types of addresses:

In IPv6, the broadcast addresses are not used. Multicast addresses take over the function of broadcast addresses. For this purpose, the special groups were defined. For example, the group for all IPv6 nodes within link-local scope that replace original broadcast addresses.

IPv6 addresses are assigned to network interfaces as well as in IPv4. In IPv6, interfaces can have more addresses of different types. Even it is ordered that the interface has to have several mandatory IPv6 addresses for each node.

Structure and Notation of IPv6 Addresses

IPv6 address has a length of 128 bits and is composed of 8 groups of 16 bits. Each group is expressed in four digits of hexadecimal system and the individual groups are separated by a colon. Example of IPv6 address is

2001:0718:0000:0000:28F6:19FF:FE00:1984

The possibility to compressing the addresses is an important feature of IPv6. There are the rules:

After applying these rules, the mentioned IPv6 address can be written as

2001:718::28F6:19FF:FE00:1984

Prefixes

Prefixes express the membership of a particular network or subnet and use the fact that all interfaces have the same begin of address within a single network. This approach has been used in IPv4 and it is known as CIDR (Classless Inter-Domain Routing). Prefix notation is taken from CIDR:

IPv6_address/Prefix_length

Prefix_length determines how many bits from the beginning of the address are regarded as a prefix. Example of 64-bit prefix is

2001:718::/64