[DNSOP] Clarification: Complete or not-complete RRSets in AUTHORITY section? (non-DNSSEC)

Ondřej Surý <ondrej.sury@nic.cz> Mon, 10 April 2017 12:29 UTC

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Date: Mon, 10 Apr 2017 14:29:42 +0200
From: Ondřej Surý <ondrej.sury@nic.cz>
To: dnsop <dnsop@ietf.org>
Cc: knot-dns@labs.nic.cz
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Thread-Topic: Clarification: Complete or not-complete RRSets in AUTHORITY section? (non-DNSSEC)
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Subject: [DNSOP] Clarification: Complete or not-complete RRSets in AUTHORITY section? (non-DNSSEC)
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Hi there,

I am seeking clarification on NS RRSet completeness
in AUTHORITY section as we are tackling one particular
RPL test from Unbound (iter_pcname.rpl).

Imagine a situation where parent (.net/.com NS) gives this glue:

QUESTION
<anything>.example.com. IN A
ANSWER
AUTHORITY
example.com. IN NS ns.example.net.
example.com. IN NS ns.example.com.
ADDITIONAL
ns.example.net. IN A 10.0.0.1
ns.example.com. IN A 10.0.0.2

~~~

ns.example.net. gives

QUESTION
www.example.com. IN A
ANSWER
www.example.com. IN A 10.10.10.1
AUTHORITY
example.com. IN NS ns.example.com.
ADDITIONAL
ns.example.com. IN A 10.0.0.2

~~~

ns.example.com. just returns SERVFAIL

~~~

And resolver is asked to resolve:

Step 1:
www.example.com. -> OK, returns 10.10.10.1

Step 2:
mail.example.com. -> SERVFAIL, because the NS RRset has been
overwritten by www.example.com ANSWER data from AUTHORITY
due RFC 2181 5.4.1 Ranking:

> Data from the authority section of an authoritative answer,

Thus only ns.example.com. is asked and it SERVFAILs.

~~~

In my understanding it should be ok to return SERVFAIL,
because there's no way to honor the 5.4.1 Ranking and
not fail.  Or am I missing something really obvious?

Ondrej
--
 Ondřej Surý -- Technical Fellow
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 CZ.NIC, z.s.p.o.    --     Laboratoře CZ.NIC
 Milesovska 5, 130 00 Praha 3, Czech Republic
 mailto:ondrej.sury@nic.cz    https://nic.cz/
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