[dns-operations] CNAMEs pointing off into the weeds - inconsistent behavior from different recursive codebases

Dave Lawrence tale at dd.org
Wed Oct 9 19:49:28 UTC 2019


Viktor Dukhovni writes:
> Yes, the expected behaviour when you explicitly request a CNAME
> record is that (modulo DNAMEs in some parent zone) the qname is
> resolved without further indirection, returning a CNAME if present
> there, NXDOMAIN if the qname does not exist, or else NODATA.

Spot on.  I'd briefly considered the possibility that this was an
amusing underspecified edge-case involving language about restarting
the query when a CNAME is encountered, but even in 1980s RFC-speak,
RFC 1034 section 3.6.2 was pretty clear on this:

    "When a name server fails to find a desired RR in the resource set
    associated with the domain name, it checks to see if the resource
    set consists of a CNAME record with a matching class."

So, looking up qtype CNAME finds the desired RR and the subordinate
clause is not triggered.  But just to make it crystal clear, it goes
on to say, regarding an example of a USC-ISIC.ARPA alias pointing to
C.ISI.EDU with an address record:

    "Both of these RRs would be returned in the response to the 
    type A query, while a type CNAME or * [ANY] query should return
    just the CNAME."


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