Re: [DNSOP] RCODE and CNAME chain

"Peter van Dijk" <peter.van.dijk@powerdns.com> Wed, 05 April 2017 07:03 UTC

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From: "Peter van Dijk" <peter.van.dijk@powerdns.com>
To: dnsop@ietf.org
Date: Wed, 05 Apr 2017 09:03:43 +0200
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Subject: Re: [DNSOP] RCODE and CNAME chain
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Hello Mukund,

On 5 Apr 2017, at 7:43, Mukund Sivaraman wrote:

> Evan just pointed out a case due to a system test failure that is
> interesting.. it's not clear what the behavior should be in this case,
> so please discuss:
>
> There's a nameserver that's authoritative for 2 zones example.org. and
> example.com.
>
> In the example.org. zone, foo.example.org. is CNAME to bar.example.com.
>
> In the example.com. zone, the name bar.example.com. doesn't exist (NXDOMAIN).
>
> A query for "foo.example.org./A" is answered by the nameserver. It adds
> the foo.example.org. CNAME bar.example.com. in the answer section, and
> then, following RFC 1034 4.3.2. 3.(a.), sets the QNAME to
> "bar.example.com" and looks into the "example.com" zone for
> "bar.example.com.". It is not found.
>
> The question is: what is the expected reply RCODE for this?
>
> 1. Is it NOERROR (0) because there is an answer section with the CNAME?
>
> 2. Is it NXDOMAIN (3) because the CNAME target was not found?

NXDOMAIN is correct. The text on this on 103x is a bit weak but 2308 2.1 clarifies this.

> 3. Does it not matter if it is either?

2308 does say
“
Some name servers fail to set the RCODE to NXDOMAIN in the presence
of CNAMEs in the answer section.  If a definitive NXDOMAIN / NODATA
answer is required in this case the resolver must query again using
the QNAME as the query label.
“

but not all resolvers honour this. So I’d say it does matter.

Kind regards,
-- 
Peter van Dijk
PowerDNS.COM BV - https://www.powerdns.com/