> Just writing a resolver based on reading the RFC-1035, the first idea
> was: hey! you can put both queries into same message, just have the
> QDCOUNT=2...
>
> ... but, we quickly found that apparently nobody supports such thing.
>
> Anyone care to comment the background of this: why the multiple query
> feature of RFC-1035 is not implemented?
I thought it was lazy implementors of BIND when I first noticed that
lack of support. But they instantly convinced me that the problem is
in the spec: what's the right RCODE when you can answer one query but
not the other? What do you do if you have the answer to one in the
cache? And so on.
draft-ietf-dnsind-edns1-NN.txt addresses this.
> The KAME resolver appears to first send an AAAA query, and if that
> results an error, it then sends A query.
>
> Another idea is to send both AAAA and A in parallel and then use the
> first good answer, if any arrives. And, when A6 is added, we have 3
> queries to send?
Other suggested reading:
RFC 1933
draft-ietf-ipngwg-dns-lookups-08.txt (recently passed by IESG):
On the client side, when looking up and IPv6 address, the order of
A6 and AAAA queries MAY be configurable to be one of: A6, then AAAA;
AAAA, then A6; A6 only; or both in parallel. The default order (or
only order, if not configurable) MUST be to try A6 first, then AAAA.
If and when the AAAA becomes deprecated a new document will change
the default.
The guidelines and options for precedence between IPv4 and IPv6
addresses are specified in [TRANS]. All mentions of AAAA records in
that document are henceforth to be interpreted as meaning A6 and/or
AAAA records in the order specified in the previous paragraph.
Where [TRANS] = 1933.
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