Re: [DNSOP] new ANAME draft: draft-hunt-dnsop-aname-00.txt

Florian Weimer <fweimer@redhat.com> Tue, 11 April 2017 19:22 UTC

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To: Peter van Dijk <peter.van.dijk@powerdns.com>, dnsop@ietf.org
References: <20170407181139.GB66383@isc.org> <cc3bbc7a-3f48-2f7f-a3d9-3f752874fc00@redhat.com> <86FE867E-E1BE-4427-9FB2-D148B3F9C8C2@powerdns.com>
From: Florian Weimer <fweimer@redhat.com>
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Date: Tue, 11 Apr 2017 21:11:54 +0200
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Subject: Re: [DNSOP] new ANAME draft: draft-hunt-dnsop-aname-00.txt
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On 04/10/2017 12:04 PM, Peter van Dijk wrote:

>> Section 3 is currently written in such a way that a recursive DNS
>> lookup must be performed at the authoritative server side.  I don't
>> think it is necessary to require that.  A recursive DNS lookup of the
>> target is just one way to implement this.
>
> What other ways did you have in mind?

Private arrangement with the target zone operator (that is, direct, out 
of-band access to the zone).

>> In particular, the suggested recursive DNS lookup needs some form of
>> distributed loop detection.  Otherwise, a malicious customer could
>> publish two zones with ANAME records and achieve significant traffic
>> amplification, potentially taking down the DNS hoster.  A hop count in
>> an EDNS option or an “ANAME lookup in progress” indicator would be one
>> way to implement this.  Another approach would impose restrictions on
>> the owner name of an ANAME record and its target, and restrict where
>> CNAMEs can appear, so that a valid ANAME can never point to another
>> valid ANAME.
>
> I’m not sure it’s feasible to forbid chaining ANAMEs. I do agree there
> is a vector for DoS here. Section 6 currently cowardly says “Both
> authoritative servers and resolvers that implement ANAME should
> carefully check for loops and treat them as an error condition.” but I
> am aware that more words are needed.

I don't see how you can detect loops without DNS protocol changes.  The 
query that comes back will look like a completely fresh query.

Thanks,
Florian