Re: [v6ops] draft-buraglio-v6ops-ula discussion

[David Farmer <[e-mail]>]

On Fri, Aug 5, 2022 at 4:04 PM Brian E Carpenter <
[e-mail]> wrote:

> Eric,
>
> On 06-Aug-22 08:13, Eric Vyncke (evyncke) wrote:
> > David,
> >
> > You are correct. I think that the priority order should be (from most
> suitable to least suitable):
> >
> >   * Global IPv6
> >   * Global IPv4
> >   * ULA
> >   * RFC 1918
>
> That may be your opinion, but many people disagree and that is why the
> consensus is otherwise.
>
> My own order of default preference for *destination* address selection
> would be:
>
> ULA
> Global IPv6
> RFC 1918
> Global IPv4
>
> The rationale is: Prefer IPv6 always. Prefer local addressing when
> available.
>
> Obviously this requires similar rules in discovery (whether by DNS or some
> other method). If you can't discover a ULA, you will never use a ULA.
>
> Source address selection is simple: longest match with the destination.
>
>      Brian
>

However, neither of those is what RFC6724 specifies. Currently, the order
is;

ULA Local /48 (if RFC6724, section 10.6, is implemented automatically or
manually, which is generally not the case in the wild)
Global IPv6
Global IPv4/ RFC1918
ULA /7

Further, the table from RFC 3484 was;

Global IPv6/ ULA
Global IPv4/ RFC1918

Personally, I think RFC6724 almost has it right; what it got wrong is that
section 10.6 should be mandatory and automatic, implemented by the IP
stack, and not effectively optional and left to manual implementation.

As I see it, the problem with distinguishing global IPv4 addresses from
local RFC1918 IPv4 addresses is that RFC1918 IPv4 addresses are most often
used as global IPv4 source addresses through the use of NAT.
Therefore, distinguishing global IPv4 addresses from local RFC1918 IPv4
addresses isn't practical with today's highly NATed IPv4 Internet.
Furthermore, adding RFC1918 IPv4 addresses to the table requires at least
three entries, one for 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16, and
maybe 100.64.0.0/10 from RFC6598 should be included as well.
So, distinguishing global IPv4 addresses from local RFC1918 IPv4 addresses
will add a lot of cruft to the table.

Thanks

===============================================
David Farmer               Email:[e-mail]
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
2218 University Ave SE        Phone: [phone]
Minneapolis, MN 55414-3029   Cell: 612-812-9952
===============================================