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Worth knowing

Why do we need IPv6?

The whole IPv4 address space provides

28 x 28 x 28 x 28 = 4 294 967 296 possibilities.


What looks like a lot of addresses on first sight has proven to be not sufficient in practice.


That's why IPv6 has been published as official successor in December 1998 already (RFC 2460). It does not only extend the address space significantly, it will also provide improved and newly introduced features.


Thus, approximately 340 sextillions (3.4 x 1038) addresses will be available with the new version of the Internet protocol. This is by far sufficient for providing every home computer, every server and even every mobile phone with a unique IP address.

Info box

  • Why IPv6?
  • IPv4 / IPv6
  • Privacy extensions
  • IPv6 and operating systems

Comparison:  IPv4 and IPv6 addresses

In case of a IPv4 address that is composed of four blocks with numbers from 0 to 255, you don't know which of the digits identify the network and which the participant at first.

You need the subnet mask to find this out.

Only now, you know that the 192.168.100 identifies the network – and the 10 the participant in the network.

An IPv6 address consists of 8 blocks, each consisting of four hexadecimal numbers. The distribution is more clear here.



The first half identifies
the network affiliation

... the second half
the participant.

The first 4 blocks or 16 digits are called Prefix,

the last 4 blocks or 16 digits Interface Identifier.


The Prefix  identifies the first four blocks (64 bit) of an IPv6 address.

The first part of the prefix identifies the provider. According to the IPv6 standard, providers do not have to assign a complete 64 bit prefix, 48 bits are sufficient for example. The remaining part of the prefix can then be freely selected by the user with the intention to get different prefixes for own sub-networks.

An IPv6 address does not show how large the prefix part assigned by the provider (the Global Routing Prefix) actually is and how much bits are selected by the user himself (Subnet Identifier).




The last four blocks (64 bit) of an IPv6 address are called Interface Identifier.


The Interface Identifier identifies a device that connects to the Internet via the router.

Abridging an address:

It is possible to abridge the longest series of zeros within IPv6 addresses; only two colons are remaining. The address

2001:0DB8:0000:0001:0000:0000:0010:01FF  can be abridged to



Leading zeros in the 16 bit blocks can be omitted without substitution, so that the address

2001:0DB8:0000:0001::0010:01FF shrinks to 2001:DB8:0:1::10:1FF .

Privacy Extensions

The standard RFC 4941 describes the Privacy Extensions.

If IPv6 is enabled and the command ipconfig is entered under Windows or ifconfig under Linux, ones IPv6 addresses will be shown.

One has several IP addresses with IPv6 enabled as can be seen in the screenshot on the right.

The last part of an IPv6 address, the Interface Identifier, is something like a world-wide unique license plate for Internet devices.

The respective interface gets additional Interface Identifiers (license plates) that serve for de-personalisation to be identifiable from the Internet.


This technology generates a random Interface Identifier for a network device, checks whether this is still available in your network, and assigns it to the device then.

Moreover, the Interface Identifier gets a date of expiry.

The average expiry is one day.

Then, the operating system responsible for the de-personalisation generates a new random Interface Identifier and assigns it to the device again. Thus, inferences from manufacturer or device identifier are not possible any more.

IPv6 and Operating Systems

All current Windows operating systems support IPv6.

IPv6 must be installed manually for Windows XP.


Windows Phone supports IPv6 from version 8.


Android supports IPv6 since version 2.3.4, but the Privacy Extensions must be enabled manually.


IOS from version 4.3 supports IPv6 inclusive Privacy Extensions.

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