IPv6

IPv6 is version 6 of the Internet Protocol. IPv6 is intended to replace the previous standard, IPv4, which only supports up to about 4 billion (4 × 10⁹) addresses, whereas IPv6 supports up to about 3.4 × 10³⁸ addresses. This is the equivalent of 4.3 × 10²⁰ (430,000,000,000,000,000,000) unique addresses per square inch of the Earth's surface. On 20 July 2004 ICANN announced that the root DNS servers for the internet had been modified to support both IPv6 and IPv4. It is expected that IPv4 will be supported until about 2025, to allow time for bugs and system errors to be corrected.

The compelling reason behind the formation of IPv6 was lack of address space, especially in the heavily populated countries of Asia such as India and China. See the article IPv4 address exhaustion for more on this topic.

IPv6 is the second version of the Internet Protocol to be formally adopted for general use, and is forming the basis for future expansion of the Internet.

IPv6 addressing

The most dramatic change from IPv4 to IPv6 is the length of network addresses. IPv6 addresses, as defined by RFC 2373 and RFC 2374, are 128 bits long; this corresponds to 32 hexadecimal digits, which are normally used when writing IPv6 addresses, as described in the following section.

The number of possible addresses in IPv6 is 2¹²⁸ ≈ 3.4 x 10³⁸. The number of IPv6 addresses can also be thought of as 16³² as each of the 32 hexadecimal digits can take 16 values (see combinatorics).

In some situations, IPv6 addresses are composed of two logical parts: a 64-bit network prefix, and a 64-bit host-addressing part, which is often automatically generated from the interface MAC address.

Notation for IPv6 addresses

IPv6 addresses are 128 bits long but are normally written as eight groups of 4 hexadecimal digits each. For example,

is a valid IPv6 address.

If a 4 digit group is 0000, it may be omitted. For example,

is the same IPv6 address as

Following this rule, if more than two consecutive colons result from this omission, they may be reduced to two colons, as long as there is only one group of two or more consecutive colons. Thus

are all valid and mean the same thing, but

is invalid. (As it is ambiguous how many 0000 groups should be on each side.)

Also leading zeros in all groups can be omitted, thus

is the same thing as

If the address is an IPv4 address in disguise, the last 32 bits may be written in decimal; thus

The ::ffff:1.2.3.4 format is called an IPv4-compatible address.

IPv4 addresses are easily convertible to IPv6 format. For instance, if the decimal IPv4 address was 135.75.43.52 (in hexadecimal, 0x874B2B34), it could be converted to 0000:0000:0000:0000:0000:0000:874B:2B34 or ::874B:2B34. Then again, one could use the hybrid notation (

The header is composed of the first 40 bytes of the packet and contains both source and destination addresses (128 bits each), as well as the version (4 bit IP version), traffic class (8 bit, Packet Priority), flow label (20 bits, QoS management), payload length (16 bit), next header (for backwards compatibility), and hop limit (8 bits, time to live). Next comes the payload, which must be at least 1280 bytes long, or 1500 bytes long in an environment with a flexible MTU size. The payload can go up to 65,535 in standard mode, or can be set to a "jumbo payload" option.

IPv6 deployment

Disadvantages:

• the need for roll-out of pervasive support for IPv6 throughout the Internet and its connected devices
• to be reachable from the IPv4 universe during the transition phase, you still need an IPv4-address or some kind of NAT (=shared IP-address) in the gateway routers (IPv6<-->IPv4) which adds complexity there and means the large address space promised by the specification can't be immediately used effectively.
• remaining architectural problems, such as the lack of agreement for proper support for IPv6 multihoming.

To do:

• 6to4
• 6bone
• ICMPv6
• IPv6 multihoming

Major IPv6 announcements

• In 2003, Nihon Keizai Shimbun (as cited in CNET Asia Staff, 2003) reported that Japan, China, and South Korea claimed to have made themselves determined to become the leading nations in internet technology, which would partially take the form of jointly developing IPv6, and completely adopting IPv6 starting in 2005.
• ICANN announced on 20 July 2004 that the IPv6 AAAA records for the Japan (.jp) and Korea (.kr) country code Top Level Domain (ccTLD) nameservers became visible in the