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RE: v6ops-v6onbydefault: link-locals and AI_ADDRCONFIG



Pekka Savola wrote:
> > It is not a problem if you follow addr selection rules and prefer
> > matching scopes. This will cause IPv4 to be used if there is only a LL,
> > trying to talk to a AAAA global.
>
> Uhh, I don't think Default Address Selection helps at all here.  The
> question is NOT how you prefer the addresses after you've queried them,
> it's whether you query them *at all*.
>
> I.e., the point of the AI_ADDRCONFIG as it seems to me is to avoid an
> unnecessary query of IPv6 addresses in the first place.
>
> For example, the app wants to look up www.example.com.  Prior to making
> that lookup, it must know which addresses are configured on the node if
> AI_ADDRCONFIG is used.  It doesn't know about scopes of www.example.com at
> this point.
>
> If there are no IPv6 addresses (including link-locals) configured, it'll
> query only A records and then perform default address selection as you
> say, naturally ending up with IPv4 as there are no alternatives.
>
> If there are IPv6 addresses (including link-locals), it'll query both A
> and AAAA records and perform default address selection, probably also
> resulting in IPv4 if no global IPv6 addresses were configured.

So you want to standardize an implementation & optimization issue ... This
is an optimization that you may want to use in any implementation you do,
but it is not an issue we need to standardize. In particular, it precludes
use of IPv6 if a local network has a name service intelligent enough to
provide LL information to the right place. Please stop assuming that the
world will not evolve beyond where we are, and trying to prevent it from
doing so. Yes we do not want LL addresses to show up in the global name
space, and the current DNS is too lame to prevent that, but that is no
reason to specify that nobody can ever use it.

Tony



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