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

"Peter van Dijk" <peter.van.dijk@powerdns.com> Mon, 10 April 2017 10:04 UTC

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From: "Peter van Dijk" <peter.van.dijk@powerdns.com>
To: dnsop@ietf.org
Date: Mon, 10 Apr 2017 12:04:52 +0200
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Subject: Re: [DNSOP] new ANAME draft: draft-hunt-dnsop-aname-00.txt
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On 10 Apr 2017, at 11:29, Florian Weimer wrote:

> On 04/07/2017 08:11 PM, Evan Hunt wrote:
>> Title:		Address-specific DNS Name Redirection (ANAME)
>
> I think the introduction should discuss why it is not possible to push 
> the CNAME to the parent zone, replacing the entire zone with an alias.

Why this is not possible seems obvious to me, but we’ll see what we 
can write.

> 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?

> 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.

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