Unicast and anycast addresses are typically composed of two logical parts: a 64-bit network prefix used for routing, and a 64-bit interface identifier used to identify a host's network interface.
Can you use more than those 64 bits to identify a network - or is this not in compliance with any RFC? Also: Can you use more than 64 bits to identify a host?
I know that those questions are probably not of any practical use, since 2 ^ 64 addresses will be enough for most networks. I am just curious.