Re: Link-local IPv6 addresses in the DNS

[Kerry Lynn <[e-mail]>]

On Tue, Nov 22, 2011 at 3:52 PM, Brian E Carpenter <
[e-mail]> wrote:

> On 2011-11-23 05:34, Philip Homburg wrote:
> > In your letter dated Tue, 22 Nov 2011 14:30:03 +1100 you wrote:
> >> On a related issue to link locals in URI's, we don't currently have
> >> a good method of supporting link locals in the DNS.  Sure we can
> >> add them as AAAA records but they are essentially useless as the
> >> scope information is lost.  People keep saying use LL for disconnected
> >> but it just doesn't work without more support.
>
> Other people keep saying "use ULA for disconnected". The fact
> that you can put ULA into (er, local) DNS without any fancy
> stuff is a distinct advantage.
>
> IMHO link-local should be used only for bootstrapping a host and
> for diagnostic purposes. I guess I could statically configure a
> printer on fe00::a%1 if I really had no choice.
>
> This is a distinctly different problem than the one that kicked off the
link-
local discussion.  In the web browser case, you know the link-local
destination address of the server a priori but it only has validity with
respect to a particular link, and there's no way to indicate the zone
index to the browser (assuming multi-homed client here).  The once-
existing capability was removed because there is no RFC support for it.

The DNS case seems like a server-side issue.  In the case of link-
local adresses stored in AAAA records, the zone index would seem to
indicate the corresponding interface with respect to the *server* (assuming
a multi-homed server here).  What's more, the DNS server would need to
keep track of the interface on which the query arrived and only respond
with a link-local address if the client and server are on the same
interface.

Some additional observations:
- If you want to stay with link-local addresses then perhaps multicast
  DNS is the best solution for you.
- If you want to stay with unicast DNS, then ULAs have the advantage
  of being routable and the problem goes away.
- If you want to stay with link-local addresses *and* DNS, then perhaps
  you need to engage dnsext WG to discuss the server-side issues.

-K-


  Brian
>
> >
> > For disconnected operation, why not have getaddrinfo fill in the scope?
> > Just set it to the interface over which the DNS reply arrived.
> >
> > I have to admit that this may become a bit tricky if the DNS resolver is
> local
> > or if interface information is lost in some other way.
> >
> >
>