Editing IP address (section)

==IPv6 addresses==
{{Main|IPv6 address}}
[[Image:Ipv6 address.svg|right|300px|thumb|Decomposition of an IPv6 address from [[hexadecimal]] representation to its binary value]]

In IPv6, the address size was increased from 32 bits in IPv4 to 128 bits, thus providing up to 2<sup>128</sup> (approximately {{val|3.403|e=38}}) addresses. This is deemed sufficient for the foreseeable future.

The intent of the new design was not to provide just a sufficient quantity of addresses, but also redesign routing in the Internet by allowing more efficient aggregation of subnetwork routing prefixes. This resulted in slower growth of [[routing table]]s in routers. The smallest possible individual allocation is a subnet for 2<sup>64</sup> hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization ratios will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment, i.e. the local administration of the segment's available space, from the addressing prefix used to route traffic to and from external networks. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the [[routing policy]] change, without requiring internal redesign or manual renumbering.

The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With a large address space, there is no need to have complex address conservation methods as used in CIDR.

All modern desktop and enterprise server operating systems include native support for [[IPv6]], but it is not yet widely deployed in other devices, such as residential networking routers, [[voice over IP]] (VoIP) and multimedia equipment, and some [[networking hardware]].

===Private addresses===
Just as IPv4 reserves addresses for private networks, blocks of addresses are set aside in IPv6. In IPv6, these are referred to as [[unique local address]]es (ULAs). The routing prefix {{IPaddr|fc00::|7}} is reserved for this block,{{Ref RFC|4193}} which is divided into two {{IPaddr||8}} blocks with different implied policies. The addresses include a 40-bit [[pseudorandom number]] that minimizes the risk of address collisions if sites merge or packets are misrouted.

Early practices used a different block for this purpose ({{IPaddr|fec0::}}), dubbed site-local addresses.{{Ref RFC|3513}} However, the definition of what constituted a ''site'' remained unclear and the poorly defined addressing policy created ambiguities for routing. This address type was abandoned and must not be used in new systems.{{Ref RFC|3879}}

Addresses starting with {{IPaddr|fe80::}}, called [[link-local address]]es, are assigned to interfaces for communication on the attached link. The addresses are automatically generated by the operating system for each network interface. This provides instant and automatic communication between all IPv6 hosts on a link. This feature is used in the lower layers of IPv6 network administration, such as for the [[Neighbor Discovery Protocol]].

Private and link-local address prefixes may not be routed on the public Internet.