Re: [Autoconf] Working Group Last Call for draft-ietf-autoconf-addr-model-01

[Thomas Narten <[e-mail]>]

Mark,


> > I don't see a lot of difference between an IPv6 "on-link" prefix and
> > an IPv4 subnet prefix. It doesn't make sense to me that IPv6 and IPv4
> > are treated differently.

> I think I was the one who actively supported treating IPv6 and IPv4 
> differently in the document. IPv6 has a ULA range, IPv4 doesn't. IPv4 
> has a Private range, IPv6 doesn't.

This isn't a real difference. Net 10 is "private" in IPv4 and spans
multiple links/subnets. That is no different than a ULA in IPv6.

Yes, there are some important differences between ULAs and net 10
addresses (namely global uniqueness), but that doesn't change how
prefixes out of those networks are assigned to individual links, and
whether they are to be treated as being on-link (or not), which is
what is at issue.

> IPv4 global space is constrained, IPv6 isn't. IPv4 stacks remove
> IPv4 link-local addresses from an interface when a global or private
> is assigned, IPv6 stacks do not...  etc... etc... So, while there
> certainly are commonalities in the models, there are enough
> differences that describing each model separately seems to reduce
> the chance of misunderstanding the differences that do exist between
> one version vs. the other.

This doesn't really answer my core question. There is no real
difference between a /32 in IPv4 and a /128 in IPv6. What is the
justification for saying /32 should be used in IPv4 but no on-link
prefix is used in IPv6?

BTW, I'd be fine with having the IPv6 section say on-link with a
/128. That is what I would have expected for consistency.

I don't think doing this is a big deal, unless you have IPv4 and IPv6
be different, with no good technical justification, which is how I see
things at the moment.

Thomas