IPv6
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Internet Protocol version 6 (IPv6) is the next-generation Internet Layer protocol for packet-switched internetworks and the Internet. IPv4 is currently[update] the dominant Internet Protocol version, and was the first to receive widespread use. In December 1998, the Internet Engineering Task Force (IETF) designated IPv6 as the successor to version 4 by the publication of a Standards Track specification, RFC 2460.
In December 2008, despite celebrating its 10-year anniversary as a Standards Track protocol, IPv6 was only in its infancy in terms of general world-wide deployment. A recent study[1] by Google indicates that penetration is still less than one percent of Internet traffic in any country. The leaders are Russia (0.76%), France (0.65%), Ukraine (0.64%), Norway (0.49%), and the United States (0.45%). Although Asia leads in terms of absolute deployment numbers, the relative penetration is smaller (e.g., China: 0.24%). IPv6 is implemented on all major operating systems in use in commercial, business, and home consumer environments. According to the study, Mac OS leads in IPv6 penetration of 2.44%, followed by Linux (0.93%) and Windows Vista (0.32%).[2]
IPv6 has a much larger address space than IPv4. This is based on the definition of a 128-bit address, whereas IPv4 used 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 need for network address translation (NAT). NAT gained wide-spread 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 wide-spread optional deployment first in IPv4 (into which it was back-engineered). The IPv6 specifications mandate IPsec implementation as a fundamental interoperability requirement.
The general requirements for implementing IPv6 on a network host are specified in RFC 4294.
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BGP · DHCP · DNS · FTP · Gopher · GTP · d in brackets, e.g.,
http://[2001:0db8:85a3:08d3:1319:8a2e:0370:7348]/. If the URL also contains a port number the notation is: 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." In Microsoft Windows operating systems, IP addresses were also allowed in Uniform Naming Convention (UNC) path names. Since the colon is an illegal character in a UNC path name, the use of IPv6 addresses is also illegal in UNC names. For this reason, Microsoft has registered a second-level Internet domain, ipv6-literal.net, as a means to facilitate symbolic substitution. IPv6 addresses may be transcribed in the following fashion: 2001:0db8:85a3:08d3:1319:8a2e:0370:7348 is written as 2001-db8-85a3-8d3-1319-8a2e-370-7348.ipv6-literal.net This notation is automatically resolved by Microsoft software without DNS queries to any nameservers. If the IPv6 address contains a zone index, it is appended to the address portion after an 's' character: fe80--1s4.ipv6-literal.net. [edit] IPv6 and the Domain Name SystemIPv6 addresses are represented in the Domain Name System by AAAA resource records (so-called quad-A records) for forward lookups. Reverse lookup takes place under ip6.arpa (previously ip6.int), where name space is allocated by the ascii representation of nibble units (digits) of the hexadecimal IP address. This scheme, which is an adaptation of the IPv4 method under in-addr.arpa, is defined in RFC 3596.
RFC 3484 specifies how applications should select an IPv6 or IPv4 address for use, including addresses retrieved from DNS. The DNS protocol is independent from its transport layer. Queries and replies may be transmitted over IPv6 or IPv4 transports regardles of the address family of the data requested. At the design-stage of the IPv6 DNS architecture, the AAAA scheme faced a rival proposal. This alternate approach, designed to facilitate network renumbering, uses A6 records for the forward lookup and a number of other innovations such as bit-string labels and DNAME records. It is defined in RFC 2874 and its references (with further discussion of the pros and cons of both schemes in RFC 3364), but has been deprecated to experimental status. [edit] Disabling IPv6 because of incompatibilitiesVarious Internet forums carry reports of people disabling IPv6 because of perceived slowdowns when connecting to hosts on the Internet. In most cases, this "slow-down" results from DNS resolution failures due to faulty NAT 'routers' and other DNS resolvers which improperly handle the AAAA DNS query. These DNS resolvers just drop the DNS request for AAAA records, instead of properly returning the appropriate negative DNS response. Because the request is dropped, the host sending the request has to wait for a timeout to trigger, thus causing a perceived slow down when connecting to new hosts. Since there is no result of the request that could be cached locally, even if a DNS cache is running, the problem will persist for identical lookups in the future. If the domain name system is working properly, another likely delay is caused by misrouting of IPv6 packets. [edit] Transition mechanismsUntil IPv6 completely supplants IPv4, a number of transition mechanisms[16] 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, RFC 2893 (Transition Mechanisms for IPv6 Hosts and Routers) and RFC2185 (Routing Aspects of IPv6 Transition) define compatibility and transition mechanisms. These techniques, sometimes collectively called Simple Internet Transition (SIT),[17] include:
[edit] Dual stackSince IPv6 represents 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. [edit] IPv4 mapped addressesDual stack IPv6/IPv4 implementations typically support a special class of addresses, the IPv4 mapped addresses. This address type has its first 80 bits set to zero, the next 16 set to one, while its last 32 bits represent an IPv4 address. For example, As an exception to standard IPv6 addresses notation, IPv4 mapped addresses are commonly represented with their last 32 bits written in the customary dot-decimal notation of IPv4, appended to the standard IPv6 notation of the leading bits, e.g., This address type allows the transparent use of the Transport Layer protocols over IPv4 through the IPv6 networking API. A beneficial feature of this mechanism is that server applications only need to open a single listening socket to handle connections from clients using IPv6 or IPv4 protocols. IPv6 clients will be handled natively by default, and IPv4 clients appear as IPv6 clients with an appropriately mapped address. It can also be used to establish IPv4 connections specifically with an IPv6 socket. While the network protocol on the transmission medium is IPv4, the connection is presented as an IPv6 interface to the application. Because of the significant internal differences between IPv4 and IPv6 at all levels of the IP stack, some of the lower level functionality that may be exposed by the IPv6 stack might not work with IPv4 mapped addresses, if there is no direct translation to IPv4. Some common IPv6 stacks do not support the IPv4 mapped address feature, either because the IPv6 and IPv4 stacks are separate implementations (Microsoft Windows prior to Vista/Longhorn: e.g. XP/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., Linux, NetBSD, FreeBSD) this feature is controlled by the socket option IPV6_V6ONLY as specified in RFC 3493. [edit] TunnelingIn 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. [edit] Automatic tunnelingAutomatic 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, an automatic tunneling technique that uses UDP encapsulation, can allegedly cross multiple NAT boxes.[19] Teredo is not widely deployed today, but an experimental version of Teredo is installed with the Windows XP SP2 IPv6 stack. 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. [edit] Configured tunneling (6in4)In configured tunneling, better known as 6in4 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] 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 IP protocol number 41 over the IPv4 tunnel. [edit] Proxying and translation for IPv6-only hostsAfter 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 translation mechanisms must be deployed. 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] IPv6 readiness[edit] Adoption issuesIssues of IPv6 adoption include:
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. Fewer problems arise with 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 to try to save on development costs for hardware which they no longer sell, and to 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 important, such as IPv6 mobile. Home routers are usually not IPv6 ready.[citation needed] 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.[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 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.[26] ADSL services offer a problem if the access networks of the incumbent telephone connection cannot support IPv6, such that independent ADSL providers cannot provide native IPv6 connectivity. [edit] IPv6 conformance testing and evaluationA 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. Fault injection and mutation test equipment is available from companies such as Mu Dynamics, whereby tests can be customized. Other classes of test equipment, including load and performance and conformance are available from companies like Spirent, Ixia and Agilent Technologies. [edit] IPv6 deploymentAlthough IPv4 address exhaustion has been slowed by the introduction of classless inter-domain routing (CIDR) and the extensive use of network address translation (NAT), address uptake has accelerated again in recent years.[citation needed] Some forecasts expect complete depletion by the year 2011.[27] 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.[28] The 2008 Summer Olympic Games were a notable event in terms of IPv6 deployment. For 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.[29]It is believed that the Olympics provided the largest showcase of IPv6 technology since the inception of IPv6.[30] [edit] Major IPv6 announcements and availability
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