Re: draft-bourbaki-6man-classless-ipv6-00

[Lorenzo Colitti <[e-mail]>]

On Sun, Jun 4, 2017 at 8:05 PM, Philip Homburg <
[e-mail]> wrote:

> Moving on to a network architecture point of view, when using pseudo random
> IIDs there will be a longest prefix that can be supported. Lets say for the
> sake of argument we can support of /96.
>
> Then the effect will be that if in the future hosts support SLAAC upto /96
> then we are back at the same hard limit. We have just moved be boundary by
> 32 bits.
>

That's *exactly* right.


> There is no reason to expect this to change if we make longer prefixes
> possible.
> It is just that end users will then end up with a /96 and find that they
> can't subdivide it any further.
>

Right. So then someone will say, "we need to extend the network at the
edges!". And we move the boundary again, to /112. And then to 120, and then
to /124, until we get to one /128 per device. But long before that, a)
SLAAC is dead because there's not enough space in the prefix to form a
random IID, b) the hosts start doing NAT because they don't want to waste
their time. We now have 128-bit IPv4. Except that at least in IPv4, address
shortage was real. In IPv6 it isn't.

Or, if we remove the boundaries altogether, we end up with /128 straight
away, because operational consistency. We now have 128-but IPv4 again.