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Internet Protocol version 6 (IPv6) is a network layer protocol 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 improvement brought by IPv6 is the increase in the number of addresses available for networked devices, allowing, for example, each mobile phone and mobile electronic device to have its own address. IPv4 supports 232 (about 4.3 billion) addresses, which is inadequate for giving even one address to every living person, let alone supporting embedded and portable devices. IPv6, however, supports 2128 (about 340 billion billion billion billion) addresses, or approximately 5×1028 addresses for each of the roughly 6.5 billion people alive today. With such a large address space available, IPv6 nodes can have as many universally scoped addresses as they need, and network address translation is not required.
By the early 1990s, it was clear that the change to a classless network introduced a decade earlier was not enough to prevent the IPv4 address exhaustion and that further changes to IPv4 were needed. By the winter of 1992, several proposed systems were being circulated and by the fall of 1993, the IETF announced a call for white papers (RFC 1550) and the creation of the "IPng Area" of working groups.
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. However, IPv4-only clients/servers will not be able to communicate directly with IPv6 clients/servers, and will require service-specific intermediate servers or NAT-PT protocol-translation servers. Free Ipv4 adresseses will exhaust around 2010, which is within the depreciation time of equipment currently being acquired.
Features of IPv6
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.
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 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). The address size also lacks the immediate memorability of the more familiar, shorter IPv4 address.
Stateless autoconfiguration of hosts
IPv6 hosts can be configured automatically when connected to a routed IPv6 network. When first connected to a network, a host sends a link-local multicast (broadcast) 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.
If IPv6 autoconfiguration is not suitable, a host can use stateful autoconfiguration (DHCPv6) or be configured manually.
Stateless autoconfiguration is only suitable for hosts: routers must be configured manually or by other means.
Multicast is part of the base protocol suite in IPv6. This is in opposition to IPv4, where multicast is optional.
Most environments do not currently have their network infrastructures configured to route multicast; that is — the link-scoped aspect of multicast will work but the site-scope, organization-scope and global-scope multicast will not be routed.
IPv6 does not have a link-local broadcast facility; the same effect can be achieved by multicasting to the all-hosts group (FF02::1).
The m6bone is catering for deployment of a global IPv6 Multicast network.
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 larger than 65,576 octets, 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 deployed except for securing traffic between IPv6 BGP 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 MIP nor MIPv6 are widely deployed today.
As of December 2005, IPv6 accounts for a tiny percentage of the live addresses in the publicly-accessible Internet, which is still dominated by IPv4. The adoption of IPv6 has been slowed by the introduction of classless inter-domain routing (CIDR) and network address translation (NAT), each of which has partially alleviated the impact of address space exhaustion. Estimates as to when the pool of available IPv4 addresses will be exhausted vary — in 2003, Paul Wilson (director of APNIC) stated that, based on then-current rates of deployment, the available space would last until 2023, while in September 2005 a report by Cisco Systems that the pool of available addresses would be exhausted in as little as 4–5 years. As of November 2006, a regularly updated report projected that the IANA pool of unallocated addresses would be exhausted in May 2011, with the various Regional Internet Registries using up their allocations from IANA in August 2012. 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 2024. The U.S. Government has specified that the network backbones of all federal agencies must deploy IPv6 by 2008. But there are two specific challenges to this requirement. 1) There is no special federal funding available for IPv6 transitions. Thus agencies are expected to make the migration via their ongoing equipment purchases and network updates. Most agencies now have their transition plan in place, but surveys have noted that many are lagging when it comes to making that transition a reality. . 2) Agency IT budgets are tight at the moment, especially since the current 2007 IT Budget has been stalled, thanks to the Continuing Resolution.
Meanwhile China is planning to get a head start implementing IPv6 with their 5 year plan for the China Next Generation Internet.
With the notable exceptions of stateless autoconfiguration, 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 address space exhaustion.
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