Internet Protocol version 6

Internet Protocol version 6 (or as it is more commonly known "IPv6") is a method of addressing hosts or nodes on a computer network, using 128 bit addresses. IPv6 was conceived as a "next generation" upgrade from the older Internet addressing scheme IPv4, which relied on a 32-bit address space and is quickly being exhausted by the continued growth of the Internet. For more information on the "IPv4 address exhaustion" issue, please reference Geoff Huston's IPv4 Address Report.

Example of IPv6 addresses

# special IPv6 unicast addresses / ranges / address formats
::                   Unspecified_Address
::1                  Loopback  localhost  ipv6-localhost  ipv6-loopback

::<v4 address>       IPv4-Compatible Addresses (DEPRECATED)
::ffff:<v4 address>  IPv4-Mapped Addresses

2000::/3             (Currently active) Global Unicast Addresses
2001:0000::/32       Teredo service prefix
2002::/16            6to4 service prefix

fc00::/7             Unique-Local Addresses
fe80::/10            Link-Local Unicast
fec0::/10            Site-Local Unicast (DEPRECATED)

# special IPv6 multicast addresses / address formats
ff00::/8             ipv6-mcastprefix
ff02::1              ipv6-allnodes
ff02::2              ipv6-allrouters

ff02::1:ffXX:XXXX    Solicited-Node-Multicast 

Authoritative References

[http://tools.ietf.org/html/rfc2460 Why are these not showing up as links?]
[http://tools.ietf.org/html/rfc2460 IPv6, the RFC]
[http://tools.ietf.org/html/rfc5156 Special Use IPv6 Addresses]
[http://tools.ietf.org/html/rfc4443 ICMPv6]
[http://tools.ietf.org/html/rfc4861 Neighbor Discovery]
[http://tools.ietf.org/html/rfc4862 StateLess Address AutoConfiguration] (SLAAC)
[http://tools.ietf.org/html/rfc4760 MP-BGP]
[http://tools.ietf.org/html/rfc5340 OSPFv3]
[http://tools.ietf.org/html/rfc4213 Basic Transition] (including Protocol41 definition)
[http://tools.ietf.org/html/rfc3056 6to4]
[http://tools.ietf.org/html/rfc5214 ISATAP]
[http://tools.ietf.org/html/rfc4380 Teredo]
[http://tools.ietf.org/html/rfc4798 6PE]
[http://rfc-editor.org/rfcsearch.html RFC Search tool] (use this to make sure you are reading the latest and greatest RFC)