Re: "DNS-4to6 automatic mapping" - No more DNS-ALGs & 6then4 DNSqueries

[Remi Denis-Courmont <rdenis@simphalempin.com>]

On Wed, 28 Nov 2007 22:26:21 -0600, "Todd T. Fries" <todd@fries.net> wrote:

> I'm sorry, turning off IPv6 routing does not imply the userland should

not

> and cannot query for v6 addresses.  That's just bogus.  The operating

> system

> can inform the application that the v6 address has no route, and the

> application can try the next address, just as if it were a v4 host with

> multiple v4 addresses, and the first one is not reachable, only faster,

> because no default route means the application will get notified much

> sooner.



Like it or not, just about every major dual-stackable operating system

"fail" to query AAAA RRs if the host has no IPv6 address except for

loopback and link-local ones.

There are simply way too many broken DNS servers and somewhat-DNS-aware

middleboxes in the field that screw up on AAAA queries.



Besides, if an application really wants to resolve a name to an IPv6

address, it can probably request it explicitly (e.g.

hints.ai_family = PF_INET6 with getaddrinfo()). Still, from a

connectivity perspective, you would normally not be using DNS for

loopback (::1). And you simply cannot use DNS for link-local

addressing, since link-local addresses require a host-specific

scope, which DNS cannot provide.





Since this part of the problem is essentially fixed in the field,

I think the main remaining issue is what Nathan describes - lame

automatic 6to4 deployment.



-- 

Rémi