IPv6

Internet Protocol version 6 (IPv6) is a version of the Internet Protocol that is designed to succeed IPv4, the first publicly used implementation, which is still in dominant use currently^[update]. It is an Internet Layer protocol for packet-switched internetworks. The main driving force for the redesign of Internet Protocol is the foreseeable IPv4 address exhaustion. IPv6 is specified by the Internet Engineering Task Force (IETF) and described in Internet standard document RFC 2460, which was published in December 1998.^[1]

IPv6 has a vastly larger address space than IPv4. This results from the use of a 128-bit address, whereas IPv4 uses only 32 bits. The new address space thus supports 2¹²⁸ (about 3.4×10³⁸) addresses. This expansion provides flexibility in allocating addresses and routing traffic and eliminates the primary need for network address translation (NAT), which gained widespread deployment as an effort to alleviate IPv4 address exhaustion.

IPv6 also implements new features that simplify aspects of address assignment (stateless address autoconfiguration) and network renumbering (prefix and router announcements) when changing Internet connectivity providers. The IPv6 subnet size has been standardized by fixing the size of the host identifier portion of an address to 64 bits to facilitate an automatic mechanism for forming the host identifier from Link Layer media addressing information (MAC address).

Network security is integrated into the design of the IPv6 architecture. Internet Protocol Security (IPsec) was originally developed for IPv6, but found widespread optional deployment first in IPv4 (into which it was back-engineered). The IPv6 specifications mandate IPsec implementation as a fundamental interoperability requirement.

In December 2008, despite marking its 10th anniversary as a Standards Track protocol, IPv6 was only in its infancy in terms of general worldwide deployment. A 2008 study^[2] by Google Inc. indicated that penetration was still less than one percent of Internet-enabled hosts in any country. IPv6 has been implemented on all major operating systems in use in commercial, business, and home consumer environments.^[3]

Motivation and origins

The first publicly used version of the Internet Protocol, Version 4 (IPv4), provides an addressing capability of about 4 billion addresses (2³²). This was deemed sufficient in the early design stages of the Internet when the explosive growth and worldwide proliferation of networks was not anticipated.

During the first decade of operation of the TCP/IP-based Internet, by the late 1980s, it became apparent that methods had to be developed to conserve address space. In the early 1990s, even after the introduction of classless network redesign, it became clear that this would not suffice to prevent IPv4 address exhaustion and that further changes to the Internet infrastructure were needed.^[4] 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 1550) and the creation of the "IP Next Generation" (IPng) area of working groups.^[4][5]

The Internet Engineering Task Force adopted IPng on July 25, 1994, with the formation of several IPng working groups.^[4] By 1996, a series of RFCs were released defining Internet Protocol Version 6 (IPv6), starting with RFC 1883.

Incidentally, the IPng architects could not use version number 5 as a successor to IPv4, because it had been assigned to an experimental flow-oriented streaming protocol (Internet Stream Protocol), similar to IPv4, intended to support video and audio.

It is widely expected that IPv4 will be supported alongside IPv6 for the foreseeable future. IPv4-only nodes are not able to communicate directly with IPv6 nodes, and will need assistance from an intermediary; see Transition mechanisms below.

IPv4 exhaustion

IPv4 address exhaustion from 1995 to 2010. The ordinate measures available /8 allocation units (16 millions addresses each)

While varying widely in the early 2000s, estimates of the time until complete exhaustion of the IPv4 address space converge on the time frame from 2011 to 2012.

In 2003, Paul Wilson (director of APNIC) stated that, based on then-current rates of deployment, the available space would last for one or two decades.^[6] In September 2005, a report by Cisco Systems suggested that the pool of available addresses would dry up in as little as 4 to 5 years.^[7] As of May 2009^[update], a daily updated report projected that the IANA pool would be exhausted in June 2011, with the various regional Internet registries using up their allocations from IANA in March 2012.^[8] As of 2008, a policy process has started for the end-game and post-exhaustion era.^[9]

Features and differences from IPv4

In most regards, IPv6 is a conservative extension of IPv4. Most transport- and application-layer protocols need little or no change to operate over IPv6; exceptions are application protocols that embed internet-layer addresses, such as FTP or NTPv3.

IPv6 specifies a new packet format, designed to minimize packet-header processing.^[1][10] Since the headers of IPv4 packets and IPv6 packets are significantly different, the two protocols are not interoperable.

Larger address space

The most important feature of IPv6 is a much larger address space than that of IPv4: addresses in IPv6 are 128 bits long, compared to 32-bit addresses in IPv4.^[1]

Decomposition of an IPv6 address into its binary form

The very large IPv6 address space supports a total of 2¹²⁸ (about 3.4×10³⁸) addresses—or approximately 5×10²⁸ (roughly 2⁹⁵) addresses for each of the roughly 6.8 billion (6.8×10⁹) people alive in 2010.^[11] In another perspective, this is the same number of IP addresses per person as the number of atoms in a metric ton of carbon.

While these numbers are impressive, it was not the intent of the designers of the IPv6 address space to assure geographical saturation with usable addresses. Rather, the longer addresses allow a better, systematic, hierarchical allocation of addresses and efficient route aggregation. With IPv4, complex Classless Inter-Domain Routing (CIDR) techniques were developed to make the best use of the small address space. Renumbering an existing network for a new connectivity provider with different routing prefixes is a major effort with IPv4, as discussed in RFC 2071 and RFC 2072. With IPv6, however, changing the prefix announced by a few routers can in principle renumber an entire network since the host identifiers (the least-significant 64 bits of an address) can be independently self-configured by a host.

The size of a subnet in IPv6 is 2⁶⁴ addresses (64-bit subnet mask), the square of the size of the entire IPv4 Internet. Thus, actual address space utilization rates will likely be small in IPv6, but network management and routing will be more efficient because of the inherent design decisions of large subnet space and hierarchical route aggregation.

Stateless address autoconfiguration

IPv6 hosts can configure themselves 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.^[12]

If IPv6 stateless address autoconfiguration is unsuitable for an application, a network may use stateful configuration with the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) or hosts may be configured statically.

Routers present a special case of requirements for address configuration, as they often are sources for autoconfiguration information, such as router and prefix advertisements. Stateless configuration for routers can be achieved with a special router renumbering protocol.^[13]

Multicast

Multicast, the transmission of a packet to multiple destinations in a single send operation, is part of the base specification in IPv6. In IPv4 this is an optional feature, although usually implemented.

IPv6 does not implement traditional IP broadcast, i.e. the transmission of a packet to all hosts on the attached link using a special broadcast address, and therefore does not define broadcast addresses. In IPv6, the same result can be achieved by sending a packet to the link-local all nodes multicast group at address ff02::1, which is analogous to IPv4 multicast when sending to address 224.0.0.1.

IPv6 multicast addressing shares common features and protocols with IPv4 multicast, but also provides changes and improvements by eliminating the need for certain protocols.

Every unicast address assignment by a local Internet registry for IPv6 has at least a 64-bit routing prefix, the smallest subnet size available in IPv6. With such an assignment it is possible to embed this unicast address prefix into the IPv6 multicast address format, while still providing a 32-bit block, the least significant bits of the address, or approximately 4.2 billion multicast group identifiers. Thus each user of an IPv6 subnet automatically has available a set of globally routable source-specific multicast groups for multicast applications (RFC 3306).

In IPv4 it was very difficult for an organization to get even one globally routable multicast group assignment and implementation of inter-domain solutions was very arcane (RFC 2908).

IPv6 also supports new multicast solutions, including embedding Rendezvous Point addresses (RFC 3956) in an IPv6 multicast group address which simplifies the deployment of inter-domain solutions.^[14]

Mandatory network layer security

Internet Protocol Security (IPsec), the protocol for IP encryption and authentication, forms an integral part of the base protocol suite in IPv6.^[1] IPsec support is mandatory in IPv6; this is unlike IPv4, where it is optional (but usually implemented).

Simplified processing by routers

A number of simplifications have been made to the packet header, and the process of packet forwarding has been simplified, in order to make packet processing by routers simpler and hence more efficient.^[1][10] Specifically:

• The packet header in IPv6 is simpler than that used in IPv4, with many rarely used fields moved to separate options; as a result, although the addresses in IPv6 are four times larger, the option-less IPv6 header is only twice the size of the option-less IPv4 header.
• IPv6 routers do not perform fragmentation. IPv6 hosts are required to either perform PMTU discovery, perform end-to-end fragmentation, or to send packets no larger than the IPv6 default minimum MTU size of 1280 octets.
• The IPv6 header is not protected by a checksum; integrity protection is assumed to be assured by both a link layer checksum and a higher layer (TCP, UDP, etc.) checksum. (UDP/IPv4 may actually have a checksum of 0, indicating no checksum; IPv6 requires UDP must have its own checksum.) Therefore, IPv6 routers do not need to recompute a checksum when header fields (such as the TTL or Hop Count) change. This improvement may have been made less necessary by the development of routers that perform checksum computation at link speed using dedicated hardware, but it is still relevant for software based routers.
• The Time-to-Live field of IPv4 has been renamed to Hop Limit, reflecting the fact that routers are no longer expected to compute the time a packet has spent in a queue.

Mobility

Unlike mobile IPv4, mobile IPv6 avoids triangular routing and is therefore as efficient as native IPv6. IPv6 routers may also support network mobility (NEMO, RFC 3963) which allows entire subnets to move to a new router connection point without renumbering.

Options extensibility

The IPv4 protocol header has a fixed size (40 octets) for option parameters. In IPv6, options are implemented as additional extension headers after the IPv6 header, which limits their size only by the size of an entire packet. The extension header mechanism provides extensibility to support future services for quality of service, security, mobility, and others, without redesign of the basic protocol.^[1]

Jumbograms

IPv4 limits packets to 65535 (2¹⁶ - 1) octets of payload. IPv6 has optional support for packets over this limit, referred to as jumbograms, which can be as large as 4294967295 (2³² - 1) octets. The use of jumbograms may improve performance over high-MTU links. The use of jumbograms is indicated by the Jumbo Payload Option header.^[15]

Packet format

The IPv6 packet is composed of three main parts: the fixed header, optional extension headers and the payload.

The fixed header makes up the first 40 octets (320 bits) of an IPv6 data packet. The header contains the source and destination address, traffic classification options, a hop counter, and an indication of the next header. The Next Header field points to a chain of zero or more extension headers (chained by Next Header fields); the last Next Header field points to the upper-layer protocol that is carried in the packet's payload.

Extension headers carry options that are used for special treatment of a packet along the way or at its destination, routing, fragmenting, and for security using the IPsec framework.

The payload can have a size of up to 64 KB in standard mode, or larger with a "jumbo payload" option in a Hop-By-Hop Options extension header.

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

Addressing

The increased length of network addresses emphasizes a most important change when moving from IPv4 to IPv6. IPv6 addresses are 128 bits long,^[16] whereas IPv4 addresses are 32 bits; where the IPv4 address space contains roughly 4.3×10⁹ (4.3 billion) addresses, IPv6 has enough room for 3.4×10³⁸ (340 trillion trillion trillion) unique addresses.

IPv6 addresses are normally written with hexadecimal digits and colon separators like 2001:db8:85a3::8a2e:370:7334, as opposed to the dot-decimal notation of the 32 bit IPv4 addresses. IPv6 addresses are typically composed of two logical parts: a 64-bit (sub-)network prefix, and a 64-bit host part.

IPv6 addresses are classified into three types: unicast addresses which uniquely identify network interfaces, anycast addresses which identify a group of interfaces—mostly at different locations—for which traffic flows to the nearest one, and multicast addresses which are used to deliver one packet to many interfaces. Broadcast addresses are not used in IPv6. Each IPv6 address also has a 'scope', which specifies in which part of the network it is valid and unique. Some addresses have node scope or link scope; most addresses have global scope (i.e. they are unique globally).

Some IPv6 addresses are used for special purposes, like the loopback address. Also, some address ranges are considered special, like link-local addresses (for use in the local network only) and solicited-node multicast addresses (used in the Neighbor Discovery Protocol).

IPv6 in the Domain Name System

In the Domain Name System hostnames are mapped to IPv6 addresses by AAAA resource records, so-called quad-A records. For reverse resolution, the IETF reserved the domain ip6.arpa, where the name space is hierarchically divided by the 1-digit hexadecimal representation of nibble units (4 bits) of the IPv6 address. This scheme is defined in RFC 3596.

Transition mechanisms

Until IPv6 completely supplants IPv4, a number of transition mechanisms^[17] 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.

For the period while IPv6 hosts and routers co-exist with IPv4 systems various proposals have been made:

• RFC 2893 (Transition Mechanisms for IPv6 Hosts and Routers), obsoleted by RFC 4213 (Basic Transition Mechanisms for IPv6 Hosts and Routers)
• RFC 2766 (Network Address Translation - Protocol Translation NAT-PT), obsoleted as explained in RFC 4966 (Reasons to Move the Network Address Translator - Protocol Translator NAT-PT to Historic Status)
• RFC 2185 (Routing Aspects of IPv6 Transition)
• RFC 3493 (Basic Socket Interface Extensions for IPv6)
• RFC 3056 (Connection of IPv6 Domains via IPv4 Clouds)
• RFC 4380 (Teredo: Tunneling IPv6 over UDP through Network Address Translations NATs)
• RFC 4214 (Intra-Site Automatic Tunnel Addressing Protocol ISATAP)
• RFC 3053 (IPv6 Tunnel Broker)
• RFC 3142 (An IPv6-to-IPv4 Transport Relay Translator)
• RFC 5569 (IPv6 Rapid Deployment on IPv4 Infrastructures (6rd))
• RFC 5572 (IPv6 Tunnel Broker with the Tunnel Setup Protocol (TSP))

Dual IP stack implementation

The dual-stack protocol implementation in an operating system is a fundamental IPv4-to-IPv6 transition technology. It implements IPv4 and IPv6 protocol stacks either independently or in a hybrid form. The hybrid form is commonly implemented in modern operating systems supporting IPv6. Dual-stack hosts are described in RFC 4213.

Modern hybrid dual-stack implementations of IPv4 and IPv6 allow programmers to write networking code that works transparently on IPv4 or IPv6. The software may use hybrid sockets designed to accept both IPv4 and IPv6 packets. When used in IPv4 communications, hybrid stacks use an IPv6 application programming interface and represent IPv4 addresses in a special address format, the IPv4-mapped IPv6 address.

IPv4-mapped IPv6 addresses

Hybrid dual-stack IPv6/IPv4 implementations support a special class of addresses, the IPv4-mapped IPv6 addresses. This address type has its first 80 bits set to zero and the next 16 set to one, while its last 32 bits are filled with the IPv4 address. These addresses are commonly represented in the standard IPv6 format, but having the last 32 bits written in the customary dot-decimal notation of IPv4; for example, ::ffff:192.0.2.128 represents the IPv4 address 192.0.2.128.

Because of the significant internal differences between IPv4 and IPv6, some of the lower level functionality available to programmers in the IPv6 stack do not work identically with IPv4 mapped addresses. Some common IPv6 stacks do not support the IPv4-mapped address feature, either because the IPv6 and IPv4 stacks are separate implementations (e.g., Microsoft Windows 2000, XP, and Server 2003), or because of security concerns (OpenBSD). On these operating systems, it is necessary to open a separate socket for each IP protocol that is to be supported. On some systems, e.g., the Linux kernel, NetBSD, and FreeBSD, this feature is controlled by the socket option IPV6_V6ONLY as specified in RFC 3493.

Tunneling

In order to reach the IPv6 Internet, an isolated host or network must 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.

The direct encapsulation of IPv6 datagrams within IPv4 packets is indicated by IP protocol number 41. IPv6 can also be encapsulated within UDP packets e.g. in order to cross a router or NAT device that blocks protocol 41 traffic. Other encapsulation schemes, such as used in AYIYA or GRE, are also popular.

Automatic tunneling

Automatic tunneling refers to a technique where the routing infrastructure automatically determines the tunnel endpoints. RFC 3056 recommends 6to4 tunneling for automatic tunneling, which uses protocol 41 encapsulation.^[18] 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.

Teredo is an automatic tunneling technique that uses UDP encapsulation and can allegedly cross multiple NAT boxes.^[19] IPv6, including 6to4 and Teredo tunneling, are enabled by default in Windows Vista.^[20] Most Unix systems only implement native support for 6to4, but Teredo can be provided by third-party software such as Miredo.

ISATAP^[21] treats the IPv4 network as a virtual IPv6 local link, with mappings from each IPv4 address to a link-local IPv6 address. Unlike 6to4 and Teredo, which are inter-site tunnelling mechanisms, ISATAP is an intra-site mechanism, meaning that it is designed to provide IPv6 connectivity between nodes within a single organisation.

Configured and automated tunneling (6in4)

In configured tunneling, the tunnel endpoints are explicitly configured, either by an administrator manually or the operating system's configuration mechanisms, or by an automatic service known as a tunnel broker;^[22] this is also referred to as automated tunneling. Configured tunneling is usually more deterministic and easier to debug than automatic tunneling, and is therefore recommended for large, well-administered networks. Automated tunneling provides a compromise between the ease of use of automatic tunneling and the deterministic behaviour of configured tunneling.

Raw encapsulation of IPv6 packets using IPv4 protocol number 41 is recommended for configured tunneling; this is sometimes known as 6in4 tunneling. As with automatic tunneling, encapsulation within UDP may be used in order to cross NAT boxes and firewalls.

Proxying and translation for IPv6-only hosts

After the regional Internet registries have exhausted their pools of available IPv4 addresses, it is likely that hosts newly added to the Internet might only have IPv6 connectivity. For these clients to have backward-compatible connectivity to existing IPv4-only resources, suitable IPv6 transition mechanisms must be deployed.

One form of address translation is the use of a dual-stack application layer proxy server, for example a web proxy.

NAT-like techniques for application-agnostic translation at the lower layers have 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.

IPv6 readiness

Adoption issues

Barriers to IPv6 adoption include:

• Legacy Equipment
  • manufacturer no longer exists
  • manufacturer refuses to support IPv6 or makes updates prohibitively expensive
  • software upgrades are impossible (software in permanent ROM)
  • device has insufficient resources to implement the IPv6 stack
  • IPv6 is supported but performance is poor
• New Equipment
  • IPv6 hardware support increases cost to the consumer
  • IPv6 software development is expensive
• Consumer Apathy
  • Consumers aren't interested until they need to be
  • Applications work fine right now
  • Publicity and education are expensive; who will pay?

Even though consumers are most likely to suffer when their equipment has to be replaced they tend to look at networking devices like household appliances that only rarely need repairs and never have to be configured or updated. Commercial grade equipment is more likely to support IPv6, so it is the small consumer with his cost-effective disposable networking technology who will be most affected by the eventual change from IPv4 to IPv6.

Smart equipment that contains software needs explicit IPv6 support. Lower-level equipment like cables, network adapters, and switches may not be affected by the change. In general, layer-1 and layer-2 equipment won't require updates.

IPv6 compatibility is mainly a software/firmware issue like the year-2000. Unlike the year-2000 issue, there is little interest in ensuring compatibility of older equipment and software by manufacturers. The realization that IPv4 exhaustion is imminent is recent and manufacturers haven't shown much initiative in updating equipment. There is hope that a combined IPv4/IPv6 internet will streamline the transition. The internet community is divided on the issue of whether the transition should be a quick switch or a longer process. It has been suggested that all internet servers be prepared to serve 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 or firmware update if the device has sufficient storage and memory space for the new IPv6 stack. However, as with 64-bit Windows, UEFI and Wi-Fi Protected Access support, manufacturers are unlikely to spend on development costs for hardware they have already sold when they are poised to make more sales from "IPv6-ready" equipment.

The CableLabs consortium published the 160 Mbit/s DOCSIS 3.0 IPv6-ready specification for cable modems in August 2006. 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.^[23][24] It is expected that only 60% of cable modems' servers and 40% of cable modems will be DOCSIS 3.0 by 2011.^[25]

Other equipment which is typically not IPv6-ready ranges 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 Java 1.4 (February 2002) all applications that are 100% Java compatible have support for IPv6 addresses.^[26]

IPv6 testing and evaluation

A few organizations are involved, locally and internationally, with IPv6 testing and evaluation ranging from the United States Department of Defense to the University of New Hampshire. Fuzzing, Fault injection and mutation test equipment and software is available from companies such as Mu Dynamics, Ixia, Candela Technologies:^[27] and Codenomicon;^[28] which all also provide capability for creating and customizing your own IPv6 tests. Other classes of test equipment, including load and performance and conformance are available from companies like Spirent, Ixia, Candela Technologies and Agilent Technologies.

• On 13 July 2010, native IPv6 over UMTS has been successfully tested in the Netherlands. The test was performed both in gsm and in tethering mode using a Nokia smart-phone. This test was performed by Logica Nederland within the SPITS project, in cooperation with Mobistar Belgium.

Deployment

The introduction of Classless Inter-Domain Routing (CIDR) in the Internet routing and IP address allocation methods in the mid-1990s and the extensive use of network address translation (NAT) has delayed the inevitable IPv4 address exhaustion. However, final exhaustion is predicted for the 2011 to 2012 time frame at the major allocation levels.^[8]

As of 2008, IPv6 accounts for a minuscule fraction of the used addresses and the traffic in the publicly-accessible Internet which is still dominated by IPv4.^[29]

The 2008 Summer Olympic Games were a notable event in terms of IPv6 deployment, being the first time a major world event has had a presence on the IPv6 Internet at http://ipv6.beijing2008.cn/en (IP addresses 2001:252:0:1::2008:6 and 2001:252:0:1::2008:8) and all network operations of the Games were conducted using IPv6.^[30] It is believed that the Olympics provided the largest showcase of IPv6 technology since the inception of IPv6.^[31]

Cellular telephone systems present a large deployment field for Internet Protocol devices as mobile telephone service is being transitioned from 3G systems to next generation (4G) technologies in which voice is provisioned as a Voice over Internet Protocol (VoIP) service. This mandates the use of IPv6 for such networks. In the U.S., cellular operator Verizon has released technical specifications for devices operating on its future networks.^[32] The specification mandates IPv6 operation according to the 3GPP Release 8 Specifications (March 2009) and deprecates IPv4 as an optional capability.

Some implementations of the BitTorrent peer-to-peer file transfer protocol make extensive use of IPv6 to avoid NAT issues common for IPv4 private networks.^[33]

All major operating systems in use as of 2010 on personal computers and server systems have production quality IPv6 implementations. Microsoft Windows has supported IPv6 since Windows 2000, and in production ready state beginning with Windows XP. Windows Vista and later have improved IPv6 support ^[34] (DHCPv6, PPPv6/IPv6CP and broadband/PPP connection auto configuration) which Windows XP does not support. Mac OS X Panther (10.3) and Linux 2.6 also have production quality implementations.

Major milestones

See also

• China Next Generation Internet
• Comparison of IPv6 application support
• ICMPv6
• IPv4 address exhaustion
• IPv6 address
• IPv6 deployment
• List of IPv6 tunnel brokers
• Miredo
• SATSIX
• University of New Hampshire InterOperability Laboratory involvement in the IPv6 Ready Logo Program
• The US DoD Joint Interoperability Test Command DoD IPv6 Product Certification Program

References

External links

• IPv6 at the Open Directory Project
• Introduction to the IPv6 Standard
• IPv6 Backbone Network Topology
• RFC 4942 IPv6 Transition/Coexistence Security Considerations, E. Davies, S. Krishnan, P. Savola, September 2007.
• draft-itojun-v6ops-v4mapped-harmful
• IPv6ActNow.org The IPv6 information website from the RIPE NCC
• List of product, services and applications with IPv6 support
• Security Implications of IPv6
• Getipv6.info Technical information on IPv6 deployment from ARIN
• Microsoft Internet Protocol Version 6 (IPv6)