IPv6 doesn't work like IPv4. In IPv4 Parlance, you would be given a CIDR block which you could then subnet as you saw fit. I.E. The ISP might give you a /19,

IPv6 doesn't work like IPv4. In IPv4 Parlance, you would be given a CIDR block which you could then subnet as you saw fit. I.E. The ISP might give you a /19, which you could then turn into 32 /24s (or 64 /25s, etc...) With IPv6, /64s are the basic unit, and you don't further subnet the network. So, instead of thinking of "addressable space", you should now think of "deployable networks." . An ISP that hands out a /64 is basically just giving the customer a single network. The smallest network any ISP should hand out to a customer is a /48, which lets the customer deploy up to 2^16, or 65K networks as they see fit.