Re: [IPv6] I-D Action: draft-ietf-6man-rfc6724-update-00.txt

[David Farmer <[e-mail]>]

On Wed, Oct 18, 2023 at 2:03 PM Ole Troan <otroan=
[e-mail]> wrote:

> > An IPv6 ULA address will only be preferred over an IPv4 address; IFF,
> both IPv6 ULA source and destination addresses are available. As discussed
> in this thread and section 7 of this update, with rule 5 of section 6 of
> RFC6724 and the ULA label added in RFC6724, an IPv4 source and destination
> will be preferred over an IPv6 ULA source and an IPv6 GUA destination
> address, even though generally IPv6 ULA addresses are preferred over IPv4
> in the policy table as proposed in this update.
> >
> > Furthermore, in order for the scenario you describe, ULA used with
> NPTv6, NAT66, or NAPT66 and to be preferred over IPv4, the separate ULA
> label actually MUST be removed from the policy table.
> >
> > Therefore, the policy table, as proposed, discourages the use of ULA
> with NPTv6, NAT66, or NAPT66, which, if I'm understanding you correctly, is
> what you would like.
>
> The behaviour _I_ would like is for RFC1918 and ULA sources to be treated
> equally for global DA.
> Expecting HE / host heuristics would deprioritize one or the other as the
> host learns the SAs actual reachability.
>
> I don’t think the answer to that problem is a separate block of IPv6 space
> for ULA with global reachability (how many address classes are we going to
> have) or to per-network modify the host SAS policy.
> Operators are then instead solving it by using an address space that does
> behave that way. E.g. 2001:db8::/32.
>

Using ULA for global communications and reachability conflicts with the
very definition of ULA in RFC4193. From the Intro of RFC 4193, "This
document defines an IPv6 unicast address format that is globally unique and
is intended for local communications [IPV6]... They are not expected to be
routable on the global Internet."

As currently defined, if the host only has a ULA source address, the host
can expect only to have local connectivity. If the host also has a GUA
source address, the host can expect global connectivity. Just because we
blurred this distinction in IPv4 doesn't mean we should also blur the
distinction in IPv6. We have plenty of IPv6 addresses to have separate
local and global address formats, and that is why ULA was defined as a
separate address format.

There is no good way to maintain the distinction between local names and
global names in the DNS. If we can't maintain a clear distinction between
local and global IPv6 addresses, then we are doomed to confuse the local
and global domains forever. Let's not do that!

Thanks.



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