Subject: Re: draft-ietf-ipngwg-dns-lookups-04.txt

From: "Matt Crawford" <[email-masked]>
Date: Thu, 14 Oct 1999 11:32:57 -0500

(Wow, the time zones invloved in this discussion!)

Matt:
>   | Which more closely matches the behavior of existing implementations?
>   | If in a v4-only world I type "telnet H" and H.D1 exists but has
>   | no A record, but H.D2 has an A record, what happens?

kre:
> Assuming that H.D1 also does not have a CNAME which then gets to an
> A record, H.D2 is found.

Francis:
> => I think the first choice is used by most of them, try first IPv6,
> if there is no result and no fatal error then fall back to IPv4.
> (ie. it is convenient to use the res_search() function)

Sure enough.  I dug through the most common genus of nameserver and
resolver for which I have source code and this is what will happen.
In capsule form, if an application prefers addresses coming from RR
type T1 over those coming from RR type T2, and T2 over T3, and if the
resolver has a domain search list D1, ..., Dn, then the conceptual
operation "get me a connection to H" will choose an H.Dx with the
most-preferred address type rather than the one with most-preferred
domain.

If a resolver's search list includes domains which have little or no
administrative relation to one another, then this could cause
surprises.  If, for example, one had been accustomed to reaching H.D1
with the less-preferred address type one might suddenly reach H.Dn
instead because it has added a more-preferred address type.

Pretty much the same thing can happen in a pure-IPv4 setting if one
is in the habit of specifying "H" to reach "H.D2" and then domain D1
adds a host "H".  Therefore, proposed that we not concern ourselves
about this except perhaps to mention it.  When and if multi-question
queries become available, other approaches will become possible.

				Matt