[Dnsmasq-discuss] CNAME trouble with no AAAA

Kurt H Maier khm at sciops.net
Sun Oct 20 23:47:01 BST 2019

On Sun, Oct 20, 2019 at 12:55:44PM -0400, Dominick C. Pastore wrote:
> 2. In fact, Dnsmasq never follows a CNAME for MX or TXT requests, even
> when the CNAME does point to a host Dnsmasq knows locally. (I assume
> this is the reason for #1.)
RFC2181 explicitly forbids MX records from being aliases.  It's a bad
idea -- best case, it doubles DNS traffic.  MX et al fall into
additional section processing, which does not contain CNAME records.   
This means a CNAME-only MX record will cause no-address responses.
Which means the client, if it's trying hard enough, will just request a
regular lookup, get the CNAME, resolve that, and hopefully get the MX
record in additional-section along the way.
Yes, all sorts of DNS server software allows this crap.  It's still bad
behavior.  MX records should not be CNAMEs.  RFC5321 has more
information, including the directive that MX records MUST contain a   
domain name with an A or AAAA record.

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