IPv6 unique local address
Unique local IPv6 addresses have the same function as private addresses in IPv4 – to allow communication throughout a site while being routable to multiple local networks. They are not registered with any numbering authority and cannot be routed to the Internet. Unique local IPv6 addresses begin with FD00::/8.
A unique local IPv6 address is constructed by appending a randomly generated 40-bit hexadecimal string to the FD00::/8 prefix. The subnet field and interface ID are created in the same way as with global unicast IPv6 addresses.
Here is a graphical representation of an unique local IPv6 address: