--Aredridel <aredridel(_at_)nbtsc(_dot_)org> wrote:
> In section 4.8, you mention "A" lookup. Is AAAA explicitly not done
> in that case?
Sorry, I didn't check that reference.
Yes, the exists: mechanism explicitly checks *only* A records, even if
the MTA connection is via IPv6. This is to maintain compatibility
with already existing DNS blacklists and whitelists.
Any reason not to query for ANY?
I can come up with one, though I don't have a strong preference on this.
DNSBLs are often set up to return an A record if you are on the list (like
127.0.0.2) and a TXT record for "more info" (which not all users will care
about). Using a A query allows you to get the shortest response, and if
you want more info, you can query for txt, or some users might want to
query for ANY at the start, if they are always going to record the TXT if
present.
It is remotely possible that a directory structure might have TXT records
for a label but not A records. In that case, the TXT might contain
descriptive info about the IP (or whatever you are requesting) but not be
an "active listing". I would say if there is no A record it should be
considered not to exist for purposes of exists: even if there is other data
there. So, if someone does an ANY query, they should explicitly check for
an A in the reply.
Ari
--
Greg Connor <gconnor(_at_)nekodojo(_dot_)org>