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Don't think in terms of addresses. In a hierarchically-allocated and aggregated space like IP addresses, there's a massive difference between 64 bits of address

Don't think in terms of addresses. In a hierarchically-allocated and aggregated space like IP addresses, there's a massive difference between 64 bits of address space and 2^64 usable addresses. By the time you've gone through six levels of allocations (IANA -> RIR -> ISP -> Customer -> Network -> Device) the vast majority of the total address space will be unused -- or rather: used for the purpose of aggregation, but not used for end machines. A 64-bit address space might only reasonably be able to handle something like 2^40-2^48 devices in total, which isn't that much more than we already have today. > Unless you're expecting consumers to start having ~2^64 devices You'd definitely need something longer than 64 bits long, long before this point.

tsimionescu 5y ago
If ISPs are allocating /64s or more to end consumers, how is this different from a 64 bit address space where they handed out a single address to each consumer?
- Dagger2 5y ago
  In terms of rate of consumption of the overall address space, it's not. But consumers have started to have more than one device at home -- in fact almost everybody has an entire network with multiple machines these days, so a single address isn't sufficient. v6 has enough space to give everybody multiple networks, not just multiple addresses (and those networks are always big enough for however many devices you end up attaching to them).