When you set up IPv6, you may need to set up your own local, non-routable IP addresses on your network - RFC4193.
Your IP address block assigned should be generated randomly from the fc00::/7 block. As IETF hasn't formalized fc00::/8, addresses should be assigned out of fd00::/8.
This means that your resulting IPv6 network will look like:
and you'll have
fdxx:xxxx:xxxx:0:/64 through fdxx:xxxx:xxxx:ffff:/64 as routable blocks within your private /48.
The 40 bytes of the /48 (xx:xxxx:xxxx) is supposed to be generated randomly. This page uses the first method suggested by IETF using the current timestamp plus the MAC address, SHA1 hashed, and the lower 40 bits to generate your random ULA.
Your Private IPv6 network is:
giving you access to the to the following /64s: