Private IPv6 addresses

The concept of private networks and special address reservation for such networks has been carried over to the next generation of the Internet Protocol, IPv6.
The address block fc00::/7 has been reserved by IANA as described in RFC 4193. These addresses are called Unique Local Addresses (ULA). They are defined as being unicast in character and contain a 40-bit random number in the routing prefix to prevent collisions when two private networks are interconnected. Despite being inherently local in usage, the IPv6 address scope of unique local addresses is global(cf. IPv6 addresses, section "IPv6 Address Scopes").
A former standard proposed the use of so-called "site-local" addresses in the fec0::/10 range, but due to major concerns about scalability and the poor definition of what constitutes a site, its use has been deprecated since September 2004 by RFC 3879.

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