John C Klensin wrote:
--On Saturday, 25 August, 2007 12:28 -0400 Keith Moore <moore@cs.utk.edu> wrote:
/64 is too small for a home network. It might indeed turn out that it's possible to bridge several different kinds of media on a single subnet, but it's bad planning to assume that this will be the case and overly constrain home users. In addition, part of the popularity of NAT has resulted from its allowing a consumer to simply "plug in" a new network to an existing network. But the popularity of NAT in IPv4 has also greatly limited the ability of the IPv4 network to support new applications, and increased the expense required to support others. A lot of the value add in IPv6 results from its having enough address bits that NAT is no longer necessary. But if we constrain home users to the point that they see a benefit from NATting, we will have destroyed much of the additional value of IPv6.
Keith,
Will all due respect, even if you assume a "home" with ten occupants, a few hundred subnets based on functions, and enough sensor-type devices to estimate several thousand of them per occupant and a few thousand more per room, 2**64 is still a _lot_ of addresses. And 2**45 prefixes under 2000:/3 is a _lot_ of prefixes. But the sheer number of addresses in a subnet or prefixes available to be assigned doesn't seem to be the limiting factor in either address block assignment or subnetting of leaf networks. Every level of delegation seems to eat a couple of address bits.
What bothers me about a /64 is not the scarcity of addresses, but the inability to subnet it. (and that, IMHO, was a poor design choice in IPv6, but I think it's rather late to revisit that choice, just like I think it's late to revisit /48.)
Now that number goes down significantly --and I would agree with your assertion-- if we were still assuming the use of hardware-assigned MAC addresses to populate that space. But we largely are not. If we changed IPv6 so that users can have subnet prefixes longer than /64, I must have missed it.
The use of NAT to expand address space in residential use of IPv4 has been largely to expand one or two addresses into around 2**16. I guess I'm of the opinion that "residential" use is highly varied, and will become more varied in the future. I don't want Internet protocol design choices to constrain what people might reasonably do in a future home or home office. I also don't think it should be assumed that "residential" prefixes will exclusively be used in residences.
Keith