[Pdns-dev] Suggested fix for a problem with CNAME records when recursion is not available.

Posner, Sebastian s.posner at telekom.de
Fri Jan 6 11:26:56 CET 2012

Vytautas Krakauskas wrote:

> >> e.g. if an authoritative zone has several RRs with CNAME RR amongst
> >> them, but the pdns server has no recursor defined, none of the RR
> >> will
> >> be returned since recursion failed and processing stopped.
> >
> > The way I'm reading this, you're saying you have a zone containing
> > something like
> >
> > www.example.com A
> > www.example.com CNAME www.example.net
> >
> > and that would simply be a misconfiguration. Can you show an example
> > of the kind of zone you mean?
> A zone example could be:
> example.com. MX 10 mail.example.com.
> example.com. CNAME www.example.net.

Repeating Peter, that would simply be a misconfiguration.  

RFC 1034, Section 3.6.2: "If a CNAME RR is present at a node, no other data
should be present; this ensures that the data for a canonical name and its
aliases cannot be different. This rule also insures that a cached CNAME can
be used without checking with an authoritative server for other RR types."

Let's imagine an additioanl RR to you example:

www.example.net. MX 10 mail.somebodyelse.com

Which MX should the nameserver return? Which one would be right?

Mit freundlichen Grüßen,

Sebastian Posner
Deutsche Telekom AG, Products & Innovation
"Es hat einmal einer gesagt, das geht nicht. Dann kam einer, der wusste das nicht und hat es einfach gemacht"

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