1 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 combinatoricsCombinatorics Discrete mathematics Combinatorics is a branch of mathematics that studies finite collections of objects that satisfy specified criteria, and is in particular concerned with "counting" the objects in those collections enumerative combinatori).

In many 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 addressIn computer networking a media access control address (MAC address is a code on most forms of networking equipment that allows for that device to be uniquely identified. Address details A MAC address is an identifier physically stored inside a network car. The host part is called a EUI-64 (or 64-bit Extended Unique Identifier).

2 Notation for IPv6 addresses

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

2001:0db8:85a3:08d3:1319:8a2e:0370:7344

is a valid IPv6 address.

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

2001:0db8:85a3:0000:1319:8a2e:0370:7344

is the same IPv6 address as

2001:0db8:85a3::1319:8a2e:0370:7344

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

2001:0DB8:0000:0000:0000:0000:1428:57ab 2001:0DB8:0000:0000:0000::1428:57ab 2001:0DB8:0:0:0:0:1428:57ab 2001:0DB8:0::0:1428:57ab 2001:0DB8::1428:57ab

are all valid and mean the same thing, but

2001::25de::cade

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

2001:0DB8:02de::0e13

is the same thing as

2001:DB8:2de::e13

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

::ffff:192.168.89.9 is the same as ::ffff:c0a8:5909, but not the same as ::192.168.89.9 or ::c0a8:5909.

The ::ffff:1.2.3.4 format is called an IPv4-mapped address , and is deprecated. The ::1.2.3.4 format is 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 ( IPv4-compatible address ), in which case the address would be ::135.75.43.52 .

3 IPv6 packet

The IPv6 packet is composed of two main parts; the header, and the payload.

The header is in 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 MTUThe Maximum Transmission Unit MTU is a term for the size (in bytes) of the largest datagram that can be passed by a layer of a communications protocol. In the Internet Protocol the 'path MTU' of an Internet transmission path is defined to be the smallest size. The payload can go up to 65,535 in standard mode, or can be set to a "jumbo payload" option.

There have been two very slightly different versions of IPv6; the (now-obsolete) initial version, described in RFC 1883, differs from the current proposed standard version, described in RFC 2460, in one field. This is the traffic class, which has its size increased from 4 to 8 bits. All other differences are minor.

Fragmentation is handled in the host only in IPv6. In IPv6, options also move out of the standard header and are specified by a Next Protocol field, similar in function to IPv4's Protocol field.

4 IPv6 and the Domain Name System

IPv6 addresses are represented in the Domain Name System by AAAA records (so-called quad-A records) for forward lookups (by analogy with A records for IPv4); reverse lookups take place under ip6 .arpa (previously ip6 .int), where address space is delegated on nibble boundaries. This scheme is defined in RFC 3596.

The AAAA scheme was one of two proposals at the time the IPv6 architecture was being designed. The other proposal would have had A6 records for the forward lookup and a number of other innovations such as bit-string labels and DNAME records. It is defined in the experimental RFC 2874 and its references.

While the AAAA scheme is a simple generalisation of the IPv4 DNS, the A6 scheme was an overhaul of the DNS to be more general, and hence more complex:

• A6 records allowed a single IPv6 address to be broken across several records, perhaps held in different zones; this allowed in principle for rapid renumbering of networks, for example.
• Address delegation by use of NS records was largely replaced with DNAME records (analogous to the existing CNAME but renaming an entire tree). This permitted related forward and reverse components to be managed together.
• A new data type called the bit label was introduced to domain names, primarily for reverse lookups.

The AAAA scheme was effectively standardised on in August 2002 by RFC 3363 (with further discussion of the pros and cons of both schemes in RFC 3364).

5 IPv6 deployment

On 20 July 2004 ICANN announced[3] that the root DNS servers for the Internet had been modified to support both IPv6 and IPv4.

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

6 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 DNS root server zone files with serial number 2004072000. It was expected that the IPv6 records for France (.fr) would be added soon. This made IPv6 operational in a public fashion.

7 Related IETF working groups

• 6bone IPv6 Backbone
• ipng IP Next Generation (concluded)
• ipv6 IP Version 6
• ipv6mib IPv6 MIB (concluded)
• multi6 Site Multihoming in IPv6
• v6ops IPv6 Operations

8 Further reading

• RFC 2460 - Internet Protocol, Version 6 - current version
• RFC 1883 - Internet Protocol, Version 6 - old version

9 External links

• IPv6 News & Links - HS247
• Why you want IPv6 (linuxreviews.org)
• http://www.iana.org/assignments/ipv6-address-space
• http://www.kame.net/
• http://www.freeswan.org/
• CNET Asia Staff. (2003). Report: Japan, China, S. Korea developing next Net. Retrieved January 14, 2003.
• http://www.moonv6.org/

Internet protocols Internet standards Internet architecture

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