* In IPv6, < tt > 2001: db8 ::/ 32 </ tt > designates the address < tt > 2001: db8 ::</ tt > and its network prefix consisting of the most significant 32 bits.

IPv4 allows for only 4, 294, 967, 296 unique addresses worldwide ( or less than one address per person alive in 2012 ), but IPv6 allows for around addresses per person — a number unlikely ever to run out.

Options are implemented as additional extension headers after the IPv6 header, which limits their size only by the size of an entire packet.

Although adoption of IPv6 has been slow, as of June 2008, all United States government systems have demonstrated basic infrastructure support for IPv6 ( if only at the backbone level ).

In IPv6 this is the only acceptable form to denote network or routing prefixes.

For example, Cisco IOS releases meant for use on Catalyst switches are available as " standard " versions ( providing only basic IP routing ), " enhanced " versions, which provide full IPv4 routing support, and " advanced IP services " versions, which provide the enhanced features as well as IPv6 support.

RFC 2373 also restricted anycast IPv6 addresses to routers only.

The only remaining technical role of < tt > int </ tt > was for reverse translation of IPv6 addresses under the < tt > ip6. int </ tt > zone.

In IPv6, on the other hand, the loopback routing prefix < tt >:: 1 / 128 </ tt > consists of only one address < tt >:: 1 </ tt > (< tt > 0: 0: 0: 0: 0: 0: 0: 1 </ tt > in full notation, the address with a one at its least significant bit and zero otherwise ) is explicitly defined as the loopback address, though additional addresses may be assigned as needed to the loopback interface by the host administrator.

The host has multiple IP addresses ( e. g. < tt > 2001: db8 :: 1 </ tt > and < tt > 2001: db8 :: 2 </ tt > in IPv6 ), but only one physical upstream link.

However, from a pragmatic perspective, allocating a / 32 is equivalent in global address space cost to allocating a single IPv4 address, and this may be acceptable if, as seems to be likely for the foreseeable future, the number of multihomed sites can be numbered only in the millions, as opposed to the many billions of non-multihomed endpoints which are anticipated to comprise the vast majority of IPv6 endpoints.

The specification states that such relay routers must only advertise < tt > 2002 ::/ 16 </ tt > and not subdivisions of it to prevent IPv4 routes polluting the routing tables of IPv6 routers.

threedegrees is now discontinued and the certain features provided by the software have been partially integrated into MSN Messenger 7. threedegrees used to only run under Windows XP Service Packs 1 and 2, with a custom IPv6 stack installed.

* Universal adoption of IPv6 cannot help either, as it only allows all users to have fixed IP addresses.

Windows Meeting Space works only over peer-to-peer IPv6 local networks, not the internet, only has collaboration features and lacks NetMeeting's conferencing features, however Windows Live Messenger allows 1-to-1 audio-video conferencing.

The original specification used only IPv4 transports, but this has been extended to IPv6.

Whereas standard BGP supports only IPv4 unicast addresses, Multiprotocol BGP supports IPv4 and IPv6 addresses and it supports unicast and multicast variants of each.

The successor to Internet Protocol Version 4 ( IPv4 ), IPv6 also does not implement the broadcast method, so as to prevent disturbing all nodes in a network when only a few may be interested in a particular service.

Multicasting, the transmission of a packet to multiple destinations in a single send operation, is part of the base specification in IPv6.

Like IPv4, IPv6 supports globally unique static IP addresses, which can be used to track a single device's Internet activity.

The use of ephemeral addresses makes it difficult to accurately track a user's Internet activity by scanning activity streams for a single IPv6 address.

DOCSIS 2. 0 added support for S-CDMA PHY, while DOCSIS 3. 0 added IPv6 support and channel bonding to allow a single cable modem to use concurrently more than one upstream channel and more than one downstream channel in parallel.

The four modules of iptables ( IPv4, IPv6, ARP, and Ethernet bridging ) are replaced with a single unified implementation, implemented on the top of a virtual machine.

A Teredo server never forwards any traffic for the client ( apart from IPv6 pings ), and has therefore very modest bandwidth requirements ( a few hundred bits per second per client at most ), which allows a single server to support large numbers of clients.

Each Teredo relay serves a range of IPv6 hosts ( e. g. a single campus / company, an ISP or a whole operator network, or even the whole IPv6 Internet ); it forwards traffic between any Teredo clients and any host within said range.

ARIN manages the distribution of Internet number resources, including IPv4 and IPv6 address space and AS numbers.

* IPv6 address allocation and assignment

The IP address is represented as a name in reverse-ordered octet representation for IPv4, and reverse-ordered nibble representation for IPv6.

Alternatively, IPv6 hosts may use stateless address autoconfiguration.

However, due to the enormous growth of the Internet and the predicted depletion of available addresses, a new version of IP ( IPv6 ), using 128 bits for the address, was developed in 1995.

This work includes coordination of the Internet Protocol address spaces ( IPv4 and IPv6 ) and assignment of address blocks to regional Internet registries, for maintaining registries of Internet protocol identifiers, and for the management of the top-level domain name space ( DNS root zone ), which includes the operation of root nameservers.

IPv6 implements a new IP address system that allows for far more addresses to be assigned than is possible with IPv4, but as a result the two protocols are not compatible, complicating the transition to IPv6.

Decomposition of an IPv6 address into its binary form

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 ).

APNIC was the first RIR to exhaust its regional pool on 15 April 2011, except for a small amount of address space reserved for the transition to IPv6, which will be allocated in a much more restricted way.

Most transport and application-layer protocols need little or no change to operate over IPv6 ; exceptions are application protocols that embed internet-layer addresses, such as FTP and NTPv3, where the new address format may cause conflicts with existing protocol syntax.

The main advantage of IPv6 over IPv4 is its larger address space.

The length of an IPv6 address is 128 bits, compared to 32 bits in IPv4.

While these numbers are large, it wasn't the intent of the designers of the IPv6 address space to assure geographical saturation with usable addresses.

The standard size of a subnet in IPv6 is 2 < sup > 64 </ sup > addresses, the square of the size of the entire IPv4 address space.

Thus, actual address space utilization rates will be small in IPv6, but network management and routing efficiency is improved by the large subnet space and hierarchical route aggregation.

With IPv6, however, changing the prefix announced by a few routers can in principle renumber an entire network, since the host identifiers ( the least-significant 64 bits of an address ) can be independently self-configured by a host.

IPv6 does not implement traditional IP broadcast, i. e. the transmission of a packet to all hosts on the attached link using a special broadcast address, and therefore does not define broadcast addresses.

In IPv6, the same result can be achieved by sending a packet to the link-local all nodes multicast group at address, which is analogous to IPv4 multicast to address.

IPv6 also provides for new multicast implementations, including embedding rendezvous point addresses in an IPv6 multicast group address, which simplifies the deployment of inter-domain solutions.