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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 · (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 · (more) |
| 1. Physical layer |
| Ethernet physical layer · Modems · PLC · SONET/SDH · G.709 · Optical fiber · Coaxial cable · Twisted pair · (more) |
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 people alive today.U.S. Census Bureau In a different perspective, this is 252 addresses for every star in the known universeabc.net.au – a million times as many addresses per star than IPv4 supported for our single planet.
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 |
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.RFC 1750 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.History of the IPng Effort
IPng was adopted by the Internet Engineering Task Force on July 25, 1994 with the formation of several "IP Next Generation" (IPng) working groups. 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.
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 and a recompile in order to run over IPv6.
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). IPv6 addresses are also very difficult to remember; use of the Domain Name System (DNS) is necessary.
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.IPv6 Stateless Address Autoconfiguration, RFC 2462, December 1998
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.Router Renumbering for IPv6, RFC 2894, M. Crawford, August 2000
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.
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.
In IPv4, packets are limited to 64 KiB of payload. When used between capable communication partners and on communication links with a maximum transmission unit (MTU) larger than 65,576 octets (65536 + 40 for the header), 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.
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.
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.
IPv4 has a checksum field that covers all of the 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.
As of November 2007, IPv6 accounts for a minuscule percentage of the live addresses in the publicly-accessible Internet, which is still dominated by IPv4.
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).
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.Exec: No shortage of Net addresses By John Lui, CNETAsia 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.A Pragmatic Report on IPv4 Address Space Consumption by Tony Hain, Cisco Systems 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.IPv4 Address Report This report also argues that, if assigned but unused addresses were reclaimed and used to meet continuing demand, allocation of IPv4 addresses could continue until 2017.
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,August 2005 directive from the Office of Management Budget and spent the money to acquire a /16 block (281 trillion network addresses) to start the deployment.DOD to allocate its IPv6 addressesBitten by IPv6 (correction to the first report)Providing the Tools for Information Sharing: Net-Centric Enterprise Services (Department of Defense Chief Information Officer Information Policy Directorate)
The Peoples Republic of China has a 5 year plan for deployment of IPv6 called the China Next Generation Internet.
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Please help improve this article by expanding this section. See talk page for details. Please remove this message once the section has been expanded. |
In February 1999, The IPv6 Forum,The IPv6 Forum a world-wide consortium of worldwide leading Internet vendors, Industry Subject Matter Experts, Research & 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.IPv6 Task Forces 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:
In addition modern operating systems have IPv6 turned on by default.
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.
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 x\'s are the 6 higher order hexadecimal digits whereas d\'s correspond to the decimal digits of lower order 8 bit pieces of address, as it is 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.
In a URL the IPv6-Address is enclosed in brackets. Example:
http://[2001:0db8:85a3:08d3:1319:8a2e:0370:7344]/
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."
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.
IPv6 addresses are divided into 3 categories:RFC 2373 - IP Version 6 Addressing Architecture
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:
Multicast addresses are used to define a set of interfaces that typically belong to different nodes instead of just one. When a packet is sent to a multicast address, the protocol delivers the packet to all 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.
There are a number of addresses with special meaning in IPv6:
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.
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 2462): 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 %
Relatively few IPv6-capable applications understand zone ID syntax, thus rendering link-local addresses unusable within them if multiple interfaces use link-local addresses.
The structure of an IPv6 packet header.
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:
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.
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).
| 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.
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.IPv6 Transition Mechanism / Tunneling Comparison contains an overview of the transition mechanisms mentioned below.
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.
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.
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.RFC 3056 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.RFC 4214 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.RFC 4380 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.The Windows Vista Developer Story: Application Compatibility Cookbook
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.RFC 3053 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 better known as 6in4.
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.
| Year | Announcements and availability |
|---|---|
| 1996 | Linux gains alpha quality IPv6 support in kernel development version 2.1.8.Linux IPv6 Development Project |
| 1997 | In the end of 1997 IBM\'s AIX 4.3 was the first commercial platform that supported IPv6.IPv6 support shipping in AIX 3.3Its AIX 4.3. |
| 1998 | Microsoft ResearchInternet Protocol Version 6 (old Microsoft Research IPv6 release) 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.KAME project |
| Sun Solaris has IPv6 support since Solaris 8 in February 2000.Sun Solaris 8 changes from Solaris 7 | |
| 2001 | Cisco Systems introduced IPv6 support on Cisco IOS routers and L3 switches in 2001.Cisco main IPv6 site |
| 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.Microsofts main IPv6 site | |
| IBM z/OS has supported IPv6 since version 1.4 that has been generally available since September 2002.IBM: z/OS operating system | |
| 2003 | Apple Mac OS X v10.3 "Panther" (2003) has IPv6 supported and enabled by default.Mac OS X 10.3 Using IPv6 |
| 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. | |
| 2007 | Microsoft Windows Vista (2007) has IPv6 supported and enabled by default. |
| 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.Apple AirPort Extreme technical specifications. | |
| 2008 | On February 4th 2008, IANA added AAAA records for the IPv6 addresses of six of the thirteen root name servers.IPv6: coming to a root server near youIANA - IPv6 Addresses for the Root Servers 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). |
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The neutrality of this article is disputed. Please see the discussion on the talk page.(March 2008) Please do not remove this message until the dispute is resolved. |
Some users disable IPv6 functionality in their operating system to increase their connection speed behind faulty routers or ISP connections. This should not be an issue for most users.[dubious]
There are a number of IPv6 books:
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia
