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IPV 6




IPv6

Internet Protocol version 6 (IPv6) is an Internet Layer protocol for packet-switched internetworks. IPv4 is currently the dominant Internet Protocol version, and was the first to receive widespread use. The Internet Engineering Task Force (IETF) has designated IPv6 as the successor to version 4 for general use on the Internet.
IPv6 has a much larger address space than IPv4, which provides flexibility in allocating addresses and routing traffic. The extended address length (128 bits) is intended to eliminate the need for network address translation to avoid address exhaustion, and also simplifies aspects of address assignment and renumbering, when changing Internet connectivity providers.
The very large IPv6 address space supports 2128 (about 3.4×1038) addresses, or approximately 5×1028 (roughly 295) addresses for each of the roughly 6.5 billion (6.5×109) people alive today. In a different perspective, this is 252 addresses for every observable star in the known universe more than ten billion billion billion times as many addresses as IPv4 (232) supported.
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 large number allows 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 in a few routers can renumber an entire network ad hoc, because the host identifiers (the least-significant 64 bits of an address) are decoupled from the subnet identifiers and the network provider's routing prefix. The size of each subnet in IPv6 is 264 addresses (64 bits); 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.

Motivation for IPv6

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 design stages of the early Internet when the explosive growth and worldwide distribution of networks were 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 was clear that this was not enough to prevent IPv4 address exhaustion and that further changes to the Internet infrastructure were needed.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.
The Internet Engineering Task Force adopted IPng on July 25, 1994, with the formation of several IPng working groups. By 1996, a series of RFCs were released defining Internet Protocol Version 6 (IPv6), starting with RFC 2460.
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.

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).
IPv6 specifies a new packet format, designed to minimize packet-header processing. Since the headers of IPv4 and IPv6 are significantly different, the two protocols are not interoperable.

Larger address space:IPv6 features a larger address space than that of IPv4: addresses in IPv6 are 128 bits long versus 32 bits in IPv4.

Address scopes: IPv6 introduces the concept of address scopes. An address scope defines the "region" or "span" where an address can be defined as a unique identifier of an interface. These spans are the local link, the site network, and the global network, corresponding to link-local, site-local or unique local unicast, and global addresses, as defined in RFC 3513 and RFC 4193.Interfaces configured for IPv6 almost always have more than one address, usually one for the local link (the link-local address), and additional ones for site-local or global addressing. Link-local addresses are often used in network address autoconfiguration where no external source of network addressing information is available. In addition to address scopes, IPv6 introduces the concept of "scope zones". Each address can only belong to one zone corresponding to its scope. A "link zone" (link-local zone) consists of all network interfaces connected on one link. Addresses maintain their uniqueness only inside a given scope zone. Zones are indicated by a suffix (zone index) to an address. For example, fe80::211:d800:97:c915%eth0 (link-local address) and fec0:0:0:ffff::1%4 (site-local address) show the additional suffix indicated by the percent (%) character.

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. If IPv6 stateless address autoconfiguration (SLAAC) proves unsuitable, a host can use stateful configuration (DHCPv6) or be configured manually. In particular, stateless autoconfiguration is not used by routers, these must be configured manually or by other means.

Multicast: Multicast, the ability to send a single packet to multiple destinations, is part of the base specification in IPv6. This is unlike IPv4, where it is optional (but usually implemented). IPv6 does not implement broadcast, the ability to send a packet to all hosts on the attached link. The same effect can be achieved by sending a packet to the link-local all hosts multicast group. Most environments, however, do not currently have their network infrastructures configured to route multicast packets; multicasting on single subnet will work, but global multicasting might not.


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. IP packet header support is mandatory 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.

Simplified processing by routers:The format of the IPv6 packet header aims to minimize header processing at intermediate routers. Although the addresses in IPv6 are four times larger, the default headers are only twice the size of the default IPv4 header.

source : Wikipedia
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