Re: [v6ops] AWS ipv6-only features

On Tue, Nov 30, 2021 at 1:57 PM Brian E Carpenter <
brian.e.carpenter@gmail.com> wrote:

> On 01-Dec-21 06:14, Owen DeLong wrote:
> >
> >
> >> On Nov 30, 2021, at 01:47 , Philip Homburg <pch-v6ops-11@u-1.phicoh.com>
> wrote:
> >>
> >>>    On Nov 29, 2021, at 10:33 , Nick Buraglio <[1]buraglio@es.net>
> >>>    wrote:
> >>>
> >>>    "ULAs are preferred over GUAs, so when a host is presented with
> >>>    both a ULA and GUA as possible ways to reach a destination, the
> >>>    host will select the ULA. Once the ULA destination address is
> >>>    chosen, the host will then choose its ULA as a source address
> >>>    to reach the ULA destination. This preference of ULA addressing
> >>>    over GUA addressing is the mechanism that provides internal
> >>>    network connectivity independence from concurrent external
> >>>    Internet connectivity."
> >>>
> >>>    Yep... The moral of the story is that GUA works as intended and
> >>>    ULA is a bit of a mess.
> >>
> >> I'm a bit confused about this scenario.
> >>
> >> Typically a hosts gets addresses from DNS. So this suggests that people
> >> create DNS RR sets that contains both GUAs and ULAs.
> >>
> >> Is this common practice somewhere? Do people expect that something
> sensible
> >> will happen if you try that? Is it documented what should happen?
> >
> > Probably more common in mDNS than DNS, but yes, something sensible SHOULD
> > happen as documented in the RFCs:
> >
> > AAAA record sorting in getaddrinfo() or getnameinfo() should return the
> ULA records
> > before the GUA records in the linked list.
>
> That should be an application programmer's choice, I think, because whether
> ULAs should be preferred is an application-specific choice. In some cases,
> a "happy eyeballs" heuristic might even be best. In any case, I don't see
> how the IETF can design a one-size-fits-all solution.
>
> Also, of course, there are choices like: does a printer need a GUA? Why
> wouldn't a ULA be sufficient? The same goes for any internal-use-only
> server.
>
> Also a site could decide not only to use split-horizon DNS, but also
> to use different DNS names for different addresses, e.g.
> internal-server@example.org for the ULA and server@example.org
> for the GUA.
>
> We abandoned draft-ietf-v6ops-ula-usage-recommendations and
> draft-ietf-v6ops-ula-usage-considerations. Maybe it's time to restart such
> an effort.
>

That, at least, would be something. Whether we like it or not, ULA is a
current, active technology. Making operational IPv6 easier to understand,
deploy, and support should be a direct result of the work produced.

>
>     Brian
>
> >
> > As a result, an application that sensibly iterates through the list in
> order (as is expected
> > behavior) should connect via GUA if possible (if not, it should rapidly
> receive an error
> > and move on to the next item in the list, so no extraordinary processing
> or coding
> > is required in the application).
>
>
> _______________________________________________
> v6ops mailing list
> v6ops@ietf.org
> https://www.ietf.org/mailman/listinfo/v6ops
>