IPv6 (Unique Local Unicast Address)
Site-local unicast addresses have the same problems as IPv4 private addresses, such as IP address collisions during network integration and extranet construction.
Therefore, RFC3879, which came into force in September 2004, decided to abolish it, and RFC4193 defined a unique local unicast address as a new local address.
A site-local unicast address starts with the bit pattern "1111 110", or "FC00::/7" in hexadecimal notation.
*L=0 (FC00::/8): future definition
*L=1 (FD00::/8): independently allocated area
The 8th bit "L" from the beginning has the following meaning with "0" and "1".
0: centrally managed
1: locally managed address
It has now been decided that "locally administered addresses" will be standardized.
Local administration has the problem of randomly generated addresses colliding. Therefore, a method of assigning by centralized management (FC00::/8) is also being considered.