IPv6

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The five-layer TCP/IP model
5. Application layer
DHCP · DNS · FTP · Gopher · HTTP · IMAP4 · IRC · NNTP · XMPP · POP3 · RTP · SIP · SMTP · SNMP · SSH · TELNET · RPC · RTCP · RTSP · TLS (and SSL) · SDP · SOAP · GTP · STUN · NTP · (more)
4. Transport layer
TCP · UDP · DCCP · SCTP · RSVP · ECN · (more)
3. Network/internet layer
IP (IPv4 · IPv6) · OSPF · IS-IS · BGP · IPsec · ARP · RARP · RIP · ICMP · ICMPv6 · IGMP · (more)
2. Data link layer
802.11 (WLAN) · 802.16 · Wi-Fi · WiMAX · ATM · DTM · Token ring · Ethernet · FDDI · Frame Relay · GPRS · EVDO · HSPA · HDLC · PPP · PPTP · L2TP · ISDN · ARCnet · LLTD · (more)
1. Physical layer
Ethernet physical layer · RS-232 · SONET/SDH · G.709 · Optical fiber · Coaxial cable · Twisted pair · (more)
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Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. It is designated as the successor of IPv4, the current version of the Internet Protocol, for general use on the Internet.

The main change brought by IPv6 is a much larger address space that allows greater flexibility in assigning addresses. The extended address length eliminates the need to use network address translation to avoid address exhaustion, and also simplifies aspects of address assignment and renumbering when changing providers. It was not the intention of IPv6 designers, however, to give permanent unique addresses to every individual and every computer.

It is common to see examples that attempt to show that the IPv6 address space is extremely large. For example, IPv6 supports 2¹²⁸ (about 3.4×10³⁸) addresses, or approximately 5×10²⁸ addresses for each of the roughly 6.5 billion (6.5×10⁹) people alive today.^[1] In a different perspective, this is 2⁵² addresses for every star in the known universe^[2] – more than ten billion billion billion times as many addresses as IPv4 supported.

The large number of addresses allows a hierarchical allocation of addresses that may make routing and renumbering simpler. With IPv4, complex CIDR techniques were developed to make the best possible use of a restricted address space. Renumbering, when changing providers, can be a major effort with IPv4, as discussed in RFC 2071 and RFC 2072. With IPv6, however, renumbering becomes largely automatic, because the host identifiers are decoupled from the network provider identifier. Separate address spaces exist for ISPs and for hosts, which are "inefficient" in address space bits but are extremely efficient for operational issues such as changing service providers.

Contents 1 Introduction 2 Features and differences from IPv4 2.1 Larger address space 2.2 Stateless address autoconfiguration 2.3 Multicast 2.4 Link-local addresses 2.5 Jumbograms 2.6 Network-layer security 2.7 Mobility 2.8 Simpler processing by routers 3 Deployment status 3.1 IPv4 exhaustion 3.2 IPv6 readiness 3.2.1 IPv6 only clients 3.3 Government incentives 3.4 Current deployment 3.5 Per country deployment 3.5.1 France 3.5.2 United Kingdom 3.5.3 Other Countries 4 Addressing 4.1 128-bit length 4.2 Notation 4.3 Literal IPv6 addresses in URLs 4.4 Network notation 4.5 Kinds of IPv6 addresses 4.6 Special addresses 4.7 Zone indices 5 IPv6 packet 6 IPv6 and the Domain Name System 6.1 IPv6 and DNS RFCs 7 Transition mechanisms 7.1 Dual stack 7.2 Tunneling 7.2.1 Automatic tunneling 7.2.2 Configured tunneling 7.3 Proxying and translation 8 Major IPv6 announcements and availability 9 Disabling 10 IPv6 Test and Evaluation 11 See also 12 References 13 Standards 13.1 Core specifications 13.2 Stateless autoconfiguration 13.3 Addressing 13.4 Programming 14 External links 14.1 Related IETF working groups

[edit] Introduction

By the early 1990s, it was clear that the change to a classless network introduced a decade earlier was not enough to prevent IPv4 address exhaustion and that further changes to IPv4 were needed.^[3] By the beginning of 1992, several proposed systems were being circulated and by the end of 1992, the IETF announced a call for white papers (RFC 1650) and the creation of the "IP, the Next Generation" (IPng) area of working groups.^[3][4]

IPng was adopted by the Internet Engineering Task Force on July 25, 1994 with the formation of several "IP Next Generation" (IPng) working groups.^[3] By 1996, a series of RFCs were released defining IPv6, starting with RFC 2460. (Incidentally, IPv5 was not a successor to IPv4, but an experimental flow-oriented streaming protocol intended to support video and audio.)

It is expected that IPv4 will be supported alongside IPv6 for the foreseeable future. IPv4-only nodes (clients or servers) will not be able to communicate directly with IPv6 nodes, and will need to go through an intermediary; see Transition mechanisms below.

[edit] Features and differences from IPv4

To a great extent, IPv6 is a conservative extension of IPv4. Most transport- and application-layer protocols need little or no change to work over IPv6; exceptions are applications protocols that embed network-layer addresses (such as FTP or NTPv3).

Applications, however, usually need small changes in order to run over IPv6.

[edit] Larger address space

The main feature of IPv6 that is driving adoption today is the larger address space: addresses in IPv6 are 128 bits long versus 32 bits in IPv4.

The larger address space avoids the potential exhaustion of the IPv4 address space without the need for network address translation (NAT) and other devices that break the end-to-end nature of Internet traffic. It also makes administration of medium and large networks simpler, by avoiding the need for complex subnetting schemes. Subnetting will, ideally, revert to its purpose of logical segmentation of an IP network for optimal routing and access.

The drawback of the large address size is that IPv6 carries some bandwidth overhead over IPv4, which may hurt regions where bandwidth is limited (header compression can sometimes be used to alleviate this problem).

[edit] Stateless address autoconfiguration

IPv6 hosts can be configured automatically when connected to a routed IPv6 network using ICMPv6 router discovery messages. When first connected to a network, a host sends a link-local multicast router solicitation request for its configuration parameters; if configured suitably, routers respond to such a request with a router advertisement packet that contains network-layer configuration parameters.^[5]

If IPv6 autoconfiguration is not suitable, a host can use stateful configuration (DHCPv6) or be configured manually. Stateless autoconfiguration is only suitable for hosts: routers must be configured manually or by other means.^[6]

[edit] Multicast

Multicast is part of the base specifications in IPv6, unlike IPv4, where it was introduced later.

IPv6 does not have a link-local broadcast facility; the same effect can be achieved by multicasting to the all-hosts group (FF02::1).

Most environments, however, do not currently have their network infrastructures configured to route multicast: multicast on single subnet will work, but global multicast might not.

[edit] Link-local addresses

IPv6 interfaces have link-local addresses in addition to the global addresses that applications usually use. These link-local addresses are always present and never change, which simplifies the design of configuration and routing protocols.

[edit] Jumbograms

In IPv4, packets are limited to 64 KiB of payload. IPv6 has optional support for packets over this limit, referred to as jumbograms, which can be as large as 4 GiB. The use of jumbograms may improve performance over high-MTU networks.

[edit] Network-layer security

IPsec, the protocol for IP network-layer encryption and authentication, is an integral part of the base protocol suite in IPv6; this is unlike IPv4, where it is optional (but usually implemented). IPsec, however, is not widely used at present except for securing traffic between IPv6 Border Gateway Protocol routers.

[edit] Mobility

Unlike mobile IPv4, Mobile IPv6 (MIPv6) avoids triangular routing and is therefore as efficient as normal IPv6. This advantage is mostly hypothetical, as neither MIPv4 nor MIPv6 are widely deployed today.

[edit] Simpler processing by routers

IPv4 has a checksum field that covers the entire packet header. Since certain fields (such as the TTL field) change during forwarding, the checksum must be recomputed by every router. IPv6 has no error checking at the network layer but instead relies on link layer and transport protocols to perform error checking, which should make forwarding faster.

[edit] Deployment status

As of May 2008, IPv6 accounts for a minuscule fraction of the live addresses in the publicly-accessible Internet, which is still dominated by IPv4.^{[citation needed]}

With the notable exceptions of stateless auto-configuration, more flexible addressing and Secure Neighbor Discovery (SEND), many of the features of IPv6 have been ported to IPv4 in a more or less elegant manner. Thus IPv6 deployment is primarily driven by IPv4 address space exhaustion, which has been slowed by the introduction of classless inter-domain routing (CIDR) and the extensive use of network address translation (NAT).

[edit] IPv4 exhaustion

Main article: IPv4 address exhaustion

Estimates as to when the pool of available IPv4 addresses will be exhausted vary widely, and should be taken with caution. In 2003, Paul Wilson (director of APNIC) stated that, based on then-current rates of deployment, the available space would last until 2023.^[7] In September 2005 a report by Cisco Systems reported that the pool of available addresses would be exhausted in as little as 4 to 5 years.^[8] As of November 2007, a daily updated report projected that the IANA pool of unallocated addresses would be exhausted in May 2010, with the various Regional Internet Registries using up their allocations from IANA in April 2011. ^[9]

At the point at which the RIR and IANA pools are exhausted, while there would still be unused IPv4 addresses, the existing mechanisms for allocating those addresses would no longer be capable of being applied, and it is at the moment unclear as to what those mechanisms might be. Mechanisms that have been discussed for allocating IPv4 addresses beyond this point have included the reclamation of unused address space, re-engineering hosts and routers to allow the use of areas of the IPv4 address space which are currently unusable for technical reasons, and the creation of a market in IPv4 addresses.

[edit] IPv6 readiness

The issues of IPv6 adoption are:

• legacy equipment where
  • the manufacturer no longer exists to provide support
  • the manufacturer refuses to produce updates to support IPv6 or provides them but only at a cost that ensures most users won't purchase them.
  • the software is not upgradeable, being in permanent ROM
  • the device has insufficient resources to handle the IPv6 stack (usually a lack of ROM & RAM)
  • the device can handle IPv6 but only at a much lower performance than IPv4 (an issue with many older routers)
• manufacturers ensuring new equipment has sufficient resources to handle IPv6
• manufacturers investing in developing new software for IPv6 support
• publicity to persuade end-users to prepare to upgrade existing equipment
• publicity to inform end-users to create demand for IPv6-capable equipment
• ISPs not investing technical resources into preparing for IPv6

There are two distinct classes of users of networking equipment, informed (mainly commercial and professional), and uninformed (mainly consumer). The former understand that network devices are specialist computers which may need software upgrades for security and performance fixes. The latter generally treat their networking equipment as appliances, which are configured only when first unboxed, if at all, and only ever undergo firmware upgrades when absolutely necessary. Inevitably it is the latter group who have no knowledge of IPv4 or v6, but who are most likely to suffer when their equipment has to be replaced, since commercial grade equipment has generally handled IPv6 for quite a few years.

Most equipment such as hosts and routers require explicit IPv6 support. The main exception is equipment which only does low-level transport, such as cables, most ethernet adapters, and most layer 2 switches.

As of 2007, IPv6 readiness is currently not considered in most consumer purchasing decisions. If such equipment is not IPv6-capable, it might need to be upgraded or replaced prematurely if connectivity from or to new users and to servers using IPv6 addresses is required.

As with the year-2000 compatibility, IPv6 compatibility is mainly a software/firmware issue. However, unlike the year-2000 issue, there seems to be virtually no effort to ensure compatibility of older equipment and software by manufacturers. Furthermore, even compatibility of products now available is unlikely for many types of software and equipment. This is caused by only a recent realisation that IPv4 exhaustion is imminent, and the hope that we will be able to get by for a relatively long time with a combined IPv4/IPv6 situation. There is a tug-of-war going on in the internet community whether the transition will/should be rapid or long. Specifically, an important question is whether almost all internet servers should be ready to serve to new IPv6-only clients by 2012. Universal access to IPv6-only servers will be even more of a challenge.

Most equipment would be fully IPv6 capable with a software/firmware update - IF the device has sufficient code and data space to support the additional protocol stack. However, as with 64-bit Windows and Wi-Fi Protected Access support, manufacturers are likely try to save on development cost for hardware which they are no longer selling, and try to get more sales from new "IPv6-ready" equipment. Even when chipset makers develop new drivers for their chipsets, device manufacturers might not pass these on to the consumers. Moreover, as IPv6 gets implemented, optional features might become really important, such as IPv6 mobile. It is therefore important to check your supplier on its support record, and get guarantees if you can or need to. Examples of equipment which currently usually are not IPv6 ready, are home routers. As for the CableLabs consortium, the 160 Mbit/s DOCSIS 3.0 IPv6-ready specification for cable modems has only been issued in August 2006. IPv6 capable Docsis 2.0b was skipped while the widely used Docsis 2.0 does not support IPv6. The new 'DOCSIS 2.0 + IPv6' standard also supports IPv6, which may on the cable modem side only require a firmware upgrade [1] [2]. . It is expected that only 60% of cable modems' servers and 40% of cable modems will be Docsis 3.0 by 2011 ^[10]. Other equipment which is typically not IPv6-ready range from Skype and SIP phones to oscilloscopes and printers. Professional network routers in use should be IPv6-ready. Most personal computers should also be IPv6-ready, because the network stack resides in the operating system. Most applications with network capabilities are not ready, but could be upgraded with support from the developers. Since February 2002, with J2SE 1.4, all applications that are 100% Java have implicit support for IPv6 addresses^[11].

For ADSL services, a problem can be that the access networks of the incumbent telephone connection are not IPv6 compatible, such that independent ADSL providers cannot provide native IPv6 connectivity.

[edit] IPv6 only clients

Once address exhaustion occurs at the RIR level, there will be IPv6 only devices. For these clients to experience full connectivity, all internet exposed servers need to be IPv6 capable. For the short term, IPv4-NAT for people with private IPv4 addresses. Also NAT-PT exists, but is regarded as deprecated and historic.

[edit] Government incentives

A number of governments, however, are starting to require support for IPv6 in new equipment. The U.S. Government, for example, has specified that the network backbones of all federal agencies must be capable of deploying IPv6 by 2008,^[12] and spent the money to acquire a /16 block (281 trillion subnet addresses) to start the deployment.^[13][14][15]

The Peoples Republic of China has a 5 year plan for deployment of IPv6 called the China Next Generation Internet.

[edit] Current deployment

Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion.

In February 1999, The IPv6 Forum,^[16] a world-wide consortium of worldwide leading Internet vendors, industry subject matter experts, research and education networks was founded to promote the IPv6 technology and raise the market and industry awareness.

To drive the deployment of IPv6, regional and local IPv6 Task Forces were created.^[17] On 20 July 2004 ICANN announced that the root DNS servers for the Internet had been modified to support both IPv6 and IPv4. The current integration of IPv6 on existing network infrastructures could be monitored from different sources, for example:

• Regional Internet Registries (RIR) IPv6 Prefix Allocation^[18]
• IPv6 Transit services^[19]
• Japan ISP IPv6 services^[20]

In addition modern operating systems have IPv6 turned on by default. Despite this core design, development, deployment, promotion and encouragement work, practically no modern network aware applications have been adapted to use IPV6.

[edit] Per country deployment

[edit] France

• AFNIC, the NIC for (among others) the .fr Top Level Domain, has implemented IPv6 operations.^[21]

• Renater, the french national academical network, is offering IPv6 connectivity including multicast support to their members.

• Free, a major French ISP rolled-out IPv6 at end of year 2007^[22].

• Orange has done IPv6 experimentation, official support is still unclear.

[edit] United Kingdom

• JANET, the UK's education and research network, is introducing IPv6 unicast support into its service level agreement by August 2008^[23]. Several major UK universities (e.g., Cambridge) are upgrading their campus routing infrastructure during summer 2008 to provide IPv6 unicast support to their users.

[edit] Other Countries

Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion.

[edit] Addressing

[edit] 128-bit length

The primary change from IPv4 to IPv6 is the length of network addresses. IPv6 addresses are 128 bits long (as defined by RFC 4291), whereas IPv4 addresses are 32 bits; where the IPv4 address space contains roughly 4 billion addresses, IPv6 has enough room for 3.4×10³⁸ unique addresses.

IPv6 addresses are typically composed of two logical parts: a 64-bit (sub-)network prefix, and a 64-bit host part, which is either automatically generated from the interface's MAC address or assigned sequentially. Because the globally unique MAC addresses offer an opportunity to track user equipment, and so users, across time and IPv6 address changes, RFC 3041 was developed to reduce the prospect of user identity being permanently tied to an IPv6 address, thus restoring some of the possibilities of anonymity existing at IPv4. RFC 3041 specifies a mechanism by which time-varying random bit strings can be used as interface circuit identifiers, replacing unchanging and traceable MAC addresses.

[edit] Notation

IPv6 addresses are normally written as eight groups of four hexadecimal digits, where each group is separated by a colon (:). For example, 2001:0db8:85a3:08d3:1319:8a2e:0370:7334 is a valid IPv6 address.

If one or more four-digit group(s) is 0000, the zeros may be omitted and replaced with two colons(::). For example, 2001:0db8:0000:0000:0000:0000:1428:57ab can be shortened to 2001:0db8::1428:57ab. Following this rule, any number of consecutive 0000 groups may be reduced to two colons, as long as there is only one double colon used in an address. Leading zeros in a group can also be omitted (as in ::1 for localhost). Thus, the addresses below are all valid and equivalent:

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
2001:db8::1428:57ab

Having more than one double-colon abbreviation in an address is invalid, as it would make the notation ambiguous. i.e., Given 2001:0000:0000:FFD3:0000:0000:0000:57ab, 2001::FFD3::57ab could imply 2001:0000:0000:0000:0000:FFD3:0000:57ab, 2001:0000:FFD3:0000:0000:0000:0000:57ab, or any other similar permutation.

A sequence of 4 bytes at the end of an IPv6 address can also be written in decimal, using dots as separators. This notation is often used with compatibility addresses (see below). This addressing scheme is convenient when dealing with the mixed environment of IPv4 and IPv6 addresses. The general notation is of the form x:x:x:x:x:x:d.d.d.d where the x's are the 6 higher order groups of hexadecimal digits whereas the d's correspond to the decimal digits of lower order octets of the address, as it is in the IPv4 format. For example, ::ffff:12.34.56.78 is the same address as ::ffff:0c22:384e and 0:0:0:0:0:ffff:0c22:384e. Usage of this notation is deprecated and unsupported by numerous applications.

Additional information can be found in RFC 4291 - IP Version 6 Addressing Architecture.

[edit] Literal IPv6 addresses in URLs

In a URL the IPv6-Address is enclosed in brackets. Example:

http://[2001:0db8:85a3:08d3:1319:8a2e:0370:7348]/

This notation allows parsing a URL without confusing the IPv6 address and port number:

https://[2001:0db8:85a3:08d3:1319:8a2e:0370:7344]:443/

This is not only useful but mandated when using shortform:

https://[2001:db8::1428:57ab]:443/

Additional information can be found in "RFC 2732 - Format for Literal IPv6 Addresses in URL's" and "RFC 3986 - Uniform Resource Identifier (URI): Generic Syntax."

[edit] Network notation

IPv6 networks are written using CIDR notation.

An IPv6 network (or subnet) is a contiguous group of IPv6 addresses the size of which must be a power of two; the initial bits of addresses, which are identical for all hosts in the network, are called the network's prefix.

A network is denoted by the first address in the network and the size in bits of the prefix (in decimal), separated with a slash. For example, 2001:0db8:1234::/48 stands for the network with addresses 2001:0db8:1234:0000:0000:0000:0000:0000 through 2001:0db8:1234:ffff:ffff:ffff:ffff:ffff

Because a single host can be seen as a network with a 128-bit prefix, you will sometimes see host addresses written followed with /128.

[edit] Kinds of IPv6 addresses

IPv6 addresses are divided into 3 types:^[24]

• Unicast Addresses
• Multicast Addresses
• Anycast Addresses

A Unicast address identifies a single network interface. A packet sent to a unicast address is delivered to that specific computer. The following types of addresses are unicast IPv6 addresses:

• Global unicast addresses
• Link-local addresses
• Site-local addresses
• Unique local IPv6 unicast addresses
• Special addresses

Multicast addresses are assigned to a set of interfaces that typically belong to different nodes. A packet that is sent to a multicast address is delivered to all the interfaces identified by that address. Multicast addresses begin with the prefix FF00::/8, and their second octet identifies the addresses' scope, i.e. the range over which the multicast address is propagated. Commonly used scopes include link-local (0x2), site-local (0x5) and global (0xE).

Anycast addresses are also assigned to more than one interface, belonging to different nodes. However, a packet sent to an anycast address is delivered to just one of the member interfaces, typically the “nearest” according to the routing protocol’s idea of distance. Anycast addresses cannot be identified easily: they have the structure of normal unicast addresses, and differ only by being injected into the routing protocol at multiple points in the network.

[edit] Special addresses

There are a number of addresses with special meaning in IPv6:

Link local

• ::/128 — the address with all zeros is an unspecified address, and is to be used only in software.
• ::1/128 — the loopback address is a localhost address. If an application in a host sends packets to this address, the IPv6 stack will loop these packets back to the same host (corresponding to 127.0.0.1 in IPv4).
• fe80::/10 — The link-local prefix specifies that the address only is valid in the local physical link. This is analogous to the Autoconfiguration IP address 169.254.0.0/16 in IPv4.

Site local

• fc00::/7 — unique local addresses (ULA) are routable only within a set of cooperating sites. They were defined in RFC 4193 as a replacement for site-local addresses (see below). The addresses include a 40-bit pseudorandom number that minimizes the risk of conflicts if sites merge or packets somehow leak out.

IPv4

• ::ffff:0:0/96 — this prefix is used for IPv4 mapped addresses (see Transition mechanisms below).
• 2002::/16 — this prefix is used for 6to4 addressing.

Multicast

• ff00::/8 — The multicast prefix is used for multicast addresses^[25] as defined in "IP Version 6 Addressing Architecture" (RFC 4291).

Used in examples, deprecated, or obsolete

• ::/96 — the zero prefix was used for IPv4-compatible addresses; it is now obsolete.
• 2001:db8::/32 — this prefix is used in documentation (RFC 3849). Anywhere where an example IPv6 address is given, addresses from this prefix should be used.
• fec0::/10 — The site-local prefix specifies that the address is valid only inside the local organisation. Its use has been deprecated in September 2004 by RFC 3879 and systems must not support this special type of address.

Teredo

• 2001::/32 — typically used for Teredo tunneling addresses

There are no address ranges reserved for broadcast in IPv6 — applications use multicast to the all-hosts group instead. IANA maintains the official list of the IPv6 address space. Global unicast assignments can be found at the various RIR's or at the GRH DFP pages.

[edit] Zone indices

Link-local addresses present a particular problem for systems with multiple interfaces. Because each interface may be connected to different networks and the addresses all appear to be on the same subnet, an ambiguity arises that cannot be solved by routing tables.

For example, host A has two interfaces which automatically receive link-local addresses when activated (per RFC 4862): fe80::1/64 and fe80::2/64, only one of which is connected to the same physical network as host B which has address fe80::3/64; if host A attempts to contact fe80::3 how does it know which interface (fe80::1 or fe80::2) to use?

The solution defined by RFC 4007 is the addition of a unique zone index for the local interface, represented textually in the form <address>%<zone_id>, for example: http://[fe80::1122:33ff:fe11:2233%eth0]:80/ - this however may cause its own problems because of clashing with the percent-encoding used with URIs.^[26]

• Microsoft Windows IPv6 stack uses numeric zone IDs: fe80::3%1
• BSD applications typically use the interface name as a zone ID: fe80::3%pcn0
• Linux applications also typically use the interface name as a zone ID: fe80::3%eth0, although GNU/Linux network interface configuration utilities, such as ifconfig and iproute2, do not display zone IDs.

Relatively few IPv6-capable applications understand zone ID syntax, thus rendering link-local addresses unusable within them if multiple interfaces use link-local addresses.

[edit] IPv6 packet

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

The header is in the first 40 octets (320 bits) of the packet and contains:

• Version - version 6 (4-bit IP version).
• Traffic class - packet priority (8-bits). Priority values are divided into ranges: traffic where the source provides congestion control and non-congestion control traffic.
• Flow label - QoS management (20 bits). Originally created for giving real-time applications special service, but currently unused.
• Payload length - payload length in bytes (16 bits). When cleared to zero, the option is a "Jumbo payload" (hop-by-hop).
• Next header - Specifies the next encapsulated protocol. The values are compatible with those specified for the IPv4 protocol field (8 bits).
• Hop limit - replaces the time to live field of IPv4 (8 bits).
• Source and destination addresses - 128 bits each.

The payload can be up to 64KiB in size in standard mode, or larger with a "jumbo payload" option.

Fragmentation is handled only in the sending host in IPv6: routers never fragment a packet, and hosts are expected to use PMTU discovery.

The protocol field of IPv4 is replaced with a Next Header field. This field usually specifies the transport layer protocol used by a packet's payload.

In the presence of options, however, the Next Header field specifies the presence of an extra options header, which then follows the IPv6 header; the payload's protocol itself is specified in a field of the options header. This insertion of an extra header to carry options is analogous to the handling of AH and ESP in IPsec for both IPv4 and IPv6.

[edit] 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; reverse lookups take place under ip6.arpa (previously ip6.int), where address space is delegated on nibble boundaries. This scheme, which is a straightforward adaptation of the familiar A record and in-addr.arpa schemes, 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, designed to facilitate network renumbering, 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 (with further discussion of the pros and cons of both schemes in RFC 3364).

AAAA record fields

NAME	Domain name
TYPE	AAAA (28)
CLASS	Internet (1)
TTL	Time to live in seconds
RDLENGTH	Length of RDATA field
RDATA	String form of the IPV6 address as described in RFC 3513

RFC 3484 specifies how applications should select an IPv6 or IPv4 address for use, including addresses retrieved from DNS.

[edit] IPv6 and DNS RFCs

• RFC 2874 - DNS Extensions to Support IPv6 Address Aggregation and Renumbering - Defines the A6 record
• RFC 3364 - Tradeoffs in Domain Name System (DNS) Support for Internet Protocol version 6 (IPv6)
• RFC 3484 - Default Address Selection for Internet Protocol version 6 (IPv6)
• RFC 3513 - Internet Protocol Version 6 (IPv6) Addressing Architecture
• RFC 3596 - DNS Extensions to Support IP Version 6 - Defines the AAAA record and obsoletes RFC 1886 and RFC 3152

[edit] Transition mechanisms

Until IPv6 completely supplants IPv4, which is not likely to happen in the foreseeable future, a number of so-called transition mechanisms are needed to enable IPv6-only hosts to reach IPv4 services and to allow isolated IPv6 hosts and networks to reach the IPv6 Internet over the IPv4 infrastructure.^[27] contains an overview of the transition mechanisms mentioned below.

[edit] Dual stack

Since IPv6 is a conservative extension of IPv4, it is relatively easy to write a network stack that supports both IPv4 and IPv6 while sharing most of the code. Such an implementation is called a dual stack, and a host implementing a dual stack is called a dual-stack host. This approach is described in RFC 4213.

Most current implementations of IPv6 use a dual stack. Some early experimental implementations used independent IPv4 and IPv6 stacks. There are no known implementations that implement IPv6 only.

[edit] Tunneling

In order to reach the IPv6 Internet, an isolated host or network must be able to use the existing IPv4 infrastructure to carry IPv6 packets. This is done using a technique known as tunneling which consists of encapsulating IPv6 packets within IPv4, in effect using IPv4 as a link layer for IPv6.

IPv6 packets can be directly encapsulated within IPv4 packets using protocol number 41. They can also be encapsulated within UDP packets e.g. in order to cross a router or NAT device that blocks protocol 41 traffic. They can of course also use generic encapsulation schemes, such as AYIYA or GRE.

[edit] Automatic tunneling

Automatic tunneling refers to a technique where the tunnel endpoints are automatically determined by the routing infrastructure. The recommended technique for automatic tunneling is 6to4 tunneling, which uses protocol 41 encapsulation.^[28] Tunnel endpoints are determined by using a well-known IPv4 anycast address on the remote side, and embedding IPv4 address information within IPv6 addresses on the local side. 6to4 is widely deployed today.

Another automatic tunneling mechanism is ISATAP.^[29] This protocol treats the IPv4 network as a virtual IPv6 local link, with mappings from each IPv4 address to a link-local IPv6 address.

Teredo is an automatic tunneling technique that uses UDP encapsulation and is claimed to be able to cross multiple NAT boxes.^[30] Teredo is not widely deployed today, but an experimental version of Teredo is installed with the Windows XP SP2 IPv6 stack. IPv6, 6to4 and Teredo are enabled by default in Windows Vista and Mac OS X Leopard and Apple's AirPort Extreme.^[31]

[edit] Configured tunneling

Configured tunneling is a technique where the tunnel endpoints are configured explicitly, either by a human operator or by an automatic service known as a tunnel broker.^[32] Configured tunneling is usually more deterministic and easier to debug than automatic tunneling, and is therefore recommended for large, well-administered networks.

Configured tunneling uses protocol 41 in the Protocol field of the IPv4 packet. This method is also known as 6in4.

[edit] Proxying and translation

Main article: IPv6 translation mechanisms

When an IPv6-only host needs to access an IPv4-only service (for example a web server), some form of translation is necessary. One form of translation is the use of a dual-stack application-layer proxy, for example a web proxy.

NAT-like techniques for application-agnostic translation at the lower layers have also been proposed. Most have been found to be too unreliable in practice because of the wide range of functionality required by common application-layer protocols, and are considered by many to be obsolete.

[edit] Major IPv6 announcements and availability

Year	Announcements and availability
1996	Linux gains alpha quality IPv6 support in kernel development version 2.1.8.[33]
1997	In the end of 1997, a large number of implementations existed and were interoperable. [34][35]
	In the end of 1997 IBM's AIX 4.3 was the first commercial platform that supported IPv6.[36][37]
1998	Microsoft Research[38] first released an experimental IPv6 stack in 1998. This support was not intended for use in a production environment.
2000	Production-quality BSD support for IPv6 has been generally available since early to mid-2000 in FreeBSD, OpenBSD, and NetBSD via the KAME project.[39]
	Microsoft releases an IPv6 technology preview version for Windows 2000 in March 2000.[38]
	Sun Solaris has IPv6 support since Solaris 8 in February 2000.[40]
2001	Cisco Systems introduced IPv6 support on Cisco IOS routers and L3 switches in 2001.[41]
2002	Microsoft Windows NT 4.0 and Windows 2000 SP1 had limited IPv6 support for research and testing since at least 2002.
	Microsoft Windows XP (2001) had IPv6 support for developmental purposes. In Windows XP SP1 (2002) and Windows Server 2003, IPv6 is included as a core networking technology, suitable for commercial deployment.[42]
	IBM z/OS has supported IPv6 since version 1.4 that has been generally available since September 2002.[43]
2003	Apple Mac OS X v10.3 "Panther" (2003) has IPv6 supported and enabled by default.[44]
	In July, ICANN announced 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. The IPv6 records for France (.fr) were added a little later. This made IPv6 operational in a public fashion.
2005	Linux 2.6.12 removes IPv6's "experimental" status.[45]
2007	Microsoft Windows Vista (2007) has IPv6 supported and enabled by default.[42]
	Apple's AirPort Extreme 802.11n base station is an IPv6 gateway in its default configuration. It uses 6to4 tunneling and can optionally route through a manually configured IPv4 tunnel.[46]
2008	On February 4th 2008, IANA added AAAA records for the IPv6 addresses of six of the thirteen root name servers.[47][48] With this transition, it is now possible for two internet hosts to communicate via DNS without using IPv4 at all.
	On March 12th, 2008, Google launched an IPv6 version of www.google.com, the most visited page on the Internet, under an alternative host name (ipv6.google.com).[49]

[edit] Disabling

Some networks have good IPv4 connectivity, but poor IPv6 connectivity. Some users on such networks choose to disable IPv6 functionality in their operating system in order to avoid the performance penalty associated to using the poor IPv6 routing.

As network managers become increasingly aware of IPv6, such issues should disappear in the near future.

[edit] IPv6 Test and Evaluation

A few international organizations are involved with IPv6 test and evaluation ranging from the United States Department of Defense to the University of New Hampshire.

• The US DoD Joint Interoperability Test Command DoD IPv6 Product Certification Program
• University of New Hampshire InterOperability Laboratory involvement in the IPv6 Ready Logo Program[3]
• SATSIX

[edit] See also

• ICMP for IPv6
• Comparison of IPv6 application support
• Miredo - Teredo implementation, allowing IPv6 access from behind NAT.
• China Next Generation Internet
• IPv9: purported Chinese IPv6-variant from 2004.
• List of IPv6 tunnel brokers

[edit] References

[edit] Standards

[edit] Core specifications

• RFC 2460: Internet Protocol, Version 6 (IPv6) Specification (obsoletes RFC 1883)
• RFC 4861: Neighbor Discovery for IP Version 6 (IPv6), obsoletes RFC 2461
• RFC 4862: IPv6 Stateless Address Autoconfiguration, obsoletes RFC 2462
• RFC 4311: IPv6 Host-to-Router Load Sharing, updates RFC 2461
• RFC 4443: Internet Control Message Protocol (ICMPv6) for the IPv6 Specification (obsoletes RFC 2463)
• RFC 2464: Transmission of IPv6 Packets over Ethernet Networks
• RFC 4291: Internet Protocol Version 6 (IPv6) Addressing Architecture (obsoletes RFC 3513)
• RFC 3587: An IPv6 Aggregatable Global Unicast Address Format

[edit] Stateless autoconfiguration

• RFC 4861: Neighbor Discovery for IP Version 6 (IPv6), obsoletes RFC 2461
• RFC 4862: IPv6 Stateless Address Autoconfiguration, obsoletes RFC 2462
• RFC 4941: Privacy Extensions for Stateless Address Autoconfiguration in IPv6, obsoletes RFC 3041

[edit] Addressing

• RFC 4291: IP Version 6 Addressing Architecture (obsoletes RFC 3513)
• RFC 3587: IPv6 Global Unicast Address Format (obsoletes RFC 2374)
• RFC 4193: Unique Local IPv6 Unicast Addresses
• RFC 3879: Deprecating Site Local Addresses
• RFC 4007: IPv6 Scoped Address Architecture

[edit] Programming

• RFC 3493: Basic Socket Interface Extensions for IPv6 (obsoletes RFC 2553)
• RFC 3542: Advanced Sockets Application Program Interface (API) for IPv6 (obsoletes RFC 2292)
• RFC 4038: Application Aspects of IPv6 Transition
• RFC 3484: Default Address Selection for Internet Protocol version 6 (IPv6)

[edit] External links

• IPv6 at the Open Directory Project
• Everything you need to know about IPv6 from Ars Technica

[edit] Related IETF working groups

• 6man IPv6 Maintenance
• 6lowpan IPv6 over Low power WPAN
• multi6 Site Multihoming in IPv6
• shim6 Site Multihoming by IPv6 Intermediation
• v6ops IPv6 Operations