Explanation/Reference:
Explanation/Reference:
A unique local address (ULA) is an IPv6 address in the block fc00::/7, defined in RFC 4193. It is the approximate IPv6 counterpart of the IPv4 private address.
The address block fc00::/7 is divided into two /8 groups:
The block fc00::/8 has not been defined yet.

The block fd00::/8 is defined for /48 prefixes, formed by setting the 40 least-significant bits of the prefix

to a randomly generated bit string.
Prefixes in the fd00::/8 range have similar properties as those of the IPv4 private address ranges:
They are not allocated by an address registry and may be used in networks by anyone without outside

involvement.
They are not guaranteed to be globally unique.

Reverse Domain Name System (DNS) entries (under ip6.arpa) for fd00::/8 ULAs cannot be delegated

in the global DNS.
Reference: RFC 4193