IPv6 address introduction

An IPv6 address consists of 128 bits. The normal format of an IPv6 address is eight fields, each separated by a colon (:). Each field contains four hexadecimal digits representing 16 bits:

hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh

In the example, h is a hexadecimal digit 1 through 0, A through F. This is sometimes called colon hexadecimal format.

Depending on the application, you can enter or display an IPv6 address using a shortened version when successive fields contain all zeros (0). You can use two colons (::) and omit leading zeros in a field. (The use of two colons to represent successive zero fields can be used only once in an address.) The following is an example IPv6 address:

2001:0DB8:0000:0000:0000:0000:0200:bb02

Using the shortened version, the example address is:

2001:DB8::200:bb02

However, the use of two colons to represent successive zero fields can be used only once in an address.

IPv6 addresses are often specified by a prefix that identifies a fixed value associated with the first part of the address, followed by a prefix length that specifies the number of bits in the prefix. In IPv6 addressing, a prefix length of 64 typically specifies a network or subnet. A prefix with a prefix length less than 64 typically identifies a portion of the IPv6 address space or a route.

The following is a list of those reserved portions of the IPv6 address space:

IPv6 addresses do not use subnet masks as in IPv4 formats. Instead, the prefix length can specify an entire network/subnet, or the network portion of a complete host address, as in the following example:

2001:DB8:1234:5678:abcd::ef01/64

In the example, /64 is the prefix length and indicates that 2001:DB8:1234:5678 is the network/subnet for the specific host uniquely identified by abcd::ef01.

For a more thorough discussion of IPv6 address formats and types, see the Internet Engineering Task Force (IETF) IPv6 RFCs, or see the documentation supplied with your IPv6-supported system or router.