On Sun 13/Jan/2019 17:41:18 +0100 John Levine wrote:
In some cases, it is possible to guess what the initiator wants in
the answer (but not always). Some implementations have implemented
the spirit of this document by returning all RRsets of RRTYPE CNAME,
MX, A, and AAAA that are present at the owner name while suppressing
others. This heuristic seems to work well in practice; [...]
I think someone should remark that the best guess to intention for DNSxL is to
return A and TXT. However obvious that may seem, some implementors still get
it wrong. For example:
Since rfc5782 details A and TXT semantics and operations, perhaps a new
could also clarify this point.
Looking at a recent log file for one of my dnsbls, I see 113,617 A
queries, 7701 (useless) AAAA queries, 2311 TXT queries, and only 34
TXT and ANY are so small that could have been issued by hand.
The ANY queries look like they're from a few dusty forgotten servers,
no doubt run by people who will never understand that sending an ANY
query to a cache may or may not get you all the records.
What sort of TXT does that dnsbl serve? Zen.spamhaus.org returns just A
records whether I ask for A or for ANY. If I ask for TXT, they return http
URLs that I could have synthesized myself from their A's. So, yes, a server
who asks ANY or TXT to spamhaus is poorly coded/configured.
However, some lists return relevant information in TXT records. I'll try and
get more stats from dnswl.org.
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