I will hijack this post to point out CloudFlare really doesn't understand RFC1034, their DNS authoritative interface only blocks A and AAAA if there is a CNAME defined, e.g. see this:

  $ echo "A AAAA CAA CNAME DS HTTPS LOC MX NS TXT" | sed -r 's/ /\n/g' | sed -r 's/^/rfc1034.wlbd.nl /g' | xargs dig +norec +noall +question +answer +authority @coco.ns.cloudflare.com
  ;rfc1034.wlbd.nl.  IN A
  rfc1034.wlbd.nl. 300 IN CNAME www.example.org.
  ;rfc1034.wlbd.nl.  IN AAAA
  rfc1034.wlbd.nl. 300 IN CNAME www.example.org.
  ;rfc1034.wlbd.nl.  IN CAA
  rfc1034.wlbd.nl. 300 IN CAA 0 issue "really"
  ;rfc1034.wlbd.nl.  IN CNAME
  rfc1034.wlbd.nl. 300 IN CNAME www.example.org.
  ;rfc1034.wlbd.nl.  IN DS
  rfc1034.wlbd.nl. 300 IN DS 0 13 2 21A21D53B97D44AD49676B9476F312BA3CEDB11DDC3EC8D9C7AC6BAC A84271AE
  ;rfc1034.wlbd.nl.  IN HTTPS
  rfc1034.wlbd.nl. 300 IN HTTPS 1 . alpn="h3"
  ;rfc1034.wlbd.nl.  IN LOC
  rfc1034.wlbd.nl. 300 IN LOC 0 0 0.000 N 0 0 0.000 E 0.00m 0.00m 0.00m 0.00m
  ;rfc1034.wlbd.nl.  IN MX
  rfc1034.wlbd.nl. 300 IN MX 0 .
  ;rfc1034.wlbd.nl.  IN NS
  rfc1034.wlbd.nl. 300 IN NS rfc1034.wlbd.nl.
  ;rfc1034.wlbd.nl.  IN TXT
  rfc1034.wlbd.nl. 300 IN TXT "Check my cool label serving TXT and a CNAME, in violation with RFC1034"

The result is DNS resolvers (including CloudFlare Public DNS) will have a cache dependent result if you query e.g. a TXT record (depending if it has the CNAME cached). At internet.nl (https://github.com/internetstandards/) we found out because some people claimed to have some TXT DMARC record, while also CNAMEing this record (which results in cache dependent results, and since internet.nl uses RFC 9156 QName Minimisation, if first resolves A, and therefor caches the CNAME and will never see the TXT). People configure things similar to https://mxtoolbox.com/dmarc/dmarc-setup-cname instructions (which I find in conflict with RFC1034).

▲ ZoneZealot 8 hours ago | parent [-]

> People configure things similar to https://mxtoolbox.com/dmarc/dmarc-setup-cname instructions (which I find in conflict with RFC1034).

I don't think they're advising anyone create both a CNAME and TXT at the same label - but it certainly looks like that from the weird screenshot at step 5 (which doesn't match the text).

I think it's mistakenly a mish-mash of two different guides, one for 'how to use a CNAME to point to a third party DMARC service entirely' and one for 'how to host the DMARC record yourself' (irrespective of where the RUA goes).

▲

bwblabs 8 hours ago | parent [-]

I'm not sure, but we're seeing this specifically with _dmarc CNAMEing to '.hosted.dmarc-report.com' together with a TXT record type, also see this discussion users asking for this at deSEC: https://talk.desec.io/t/cannot-create-cname-and-txt-record-f...

My main point was however that it's really not okay that CloudFlare allows setting up other record types (e.g. TXT, but basically any) next to a CNAME.

	▲	ycombiredd an hour ago \| parent [-]
		Yes. This type of behavior was what I was referring to in an earlier comment mentioning flashbacks to seeing logs from named filled with "cannot have cname and other data", and slapping my forehead asking "who keeps doing this?", in the days when editing files by hand was the norm. And then, of course having repeats of this feeling as tools were built, automations became increasingly common, and large service providers "standardized" interfaces (ostensibly to ensure correctness) allowing or even encouraging creation of bad zone configurations. The more things change, the more things stay the same. :-)