In IPv6, subnets are designed to be /64. Many things assume this. By giving subscribers shorter prefixes (like /48), you enable them do cool things like run a

In IPv6, subnets are designed to be /64. Many things assume this. By giving subscribers shorter prefixes (like /48), you enable them do cool things like run a VPN server where each client has a publicly-routable address (otherwise you have to use NAT like in IPv4). If you give them a longer prefix, like /96, you can't do this sort of thing without a lot of pain. Also, many blacklists assume (for better or worse) that /64s belong to a single customer, so if you're sharing a /64 with other customers, you risk getting blocked for their bad behavior. In IPv6, we need to stop thinking in terms of number of addresses, and start thinking in terms of number of /64 subnets. A /96 may be 4 billion addresses, but it's a fraction of a subnet. There is enough address space in IPv6 to think this way, and in fact the RFCs recommend it.