Jeffrey, thanks for the email, I'm trying to be concise below.
Dunn, Jeffrey H. wrote: [...]
My basic question is: What basic engineering problem is solved by
proscribing non-64 bit prefixes?
I don't know. But I know what problems are solved by using
longer-than-64bit prefixes, especially when autoconfiguring addresses
with stateless method.
Stateless autoconfiguration with IPv6 over Ethernet requires the
Interface ID to be 64bit (hence the prefix to he /64, or less, like /56,
or /48), otherwise it won't work: neither standards nor widespread
implementations can do stateless autoconfiguration with Ethernet and
longer than 64 prefixes (e.g. /65 doesn't work).
In a typical IPv6 ADSL household landscape...
An ADSL IPv6 operational deployment offers a /64 prefix at home. With
that, I can't subnet _and_ use IPv6 stateless auto-configuration.
Moreover, if I already have IPv4 at home, which is subnetted, with
2-level NATting I'm forced to have a subnet topology for IPv4 different
than for IPv6 - incoherency.
The problem can even be aggresive: if the /64 limit is not overcome and
Ethernet 64bit IIDs are not allowed to be shorter some new IPv6 subnet
solutions may approach very much NAT for IPv6.
In a typical WiFi Access Point landscape...
Sellers of these devices don't have a solution to program the WiFi AP
IPv6 in the same way they'd do it for IPv4. For IPv4, the AP receives
an IPv4 address on the wired Ethernet and then does NAT and subnet
further on the wireless interface. For IPv6, although it receives a
huge /64 IPv6 prefix on the wire it can't offer Stateless Autoconfig on
the wireless interface. This begs again for IPv6 NAT.
Alex
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