Re: [DNSOP] Fundamental ANAME problems

Tim Wicinski <tjw.ietf@gmail.com> Fri, 09 November 2018 11:09 UTC

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To: Matthijs Mekking <matthijs@pletterpet.nl>, dnsop@ietf.org
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From: Tim Wicinski <tjw.ietf@gmail.com>
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Date: Fri, 9 Nov 2018 06:09:18 -0500
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Subject: Re: [DNSOP] Fundamental ANAME problems
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On 11/9/18 05:03, Matthijs Mekking wrote:
>
> It seems that everyone thinks that the latest ANAME draft requires DNS 
> UPDATE. This is just a use case that Tony provides and would help him 
> in his daily operations. However, it is not required to do so: ANAME 
> resolution can also happen by updating the zone file before loading it 
> into the primary server. Or it may happen in the authority server if 
> people desire to implement it there.
>
> I think the draft should be updated to make that absolutely clear. The 
> draft should standardize how ANAME resolution is done, and what it 
> means to have ANAME and sibling address records in the zone for 
> address rtype (A, AAAA, ...) and ANAME query lookup.
>

Agreed.



>> Second, and relatedly, I think the TTLs of replacement records 
>> established for non-transfer responses are too high. Respecting the 
>> TTL of every record in a chain that starts with the ANAME requires 
>> the TTL of final replacement records to be no higher than the minimum 
>> TTL encountered over the chain, potentially /reduced/ 
>> nondeterministically to mitigate query bunching. I would therefore 
>> add language encouraging resolvers synthesizing those records to 
>> engage in best-effort determination of original TTLs by (e.g., by 
>> directly querying authoritative servers and refreshing at 50% 
>> remaining), but *requiring* them to decrement TTLs of records for 
>> which they are not authoritative.
>
> I agree, the TTL language in this document is not ready and needs more 
> discussion.

If folks have some suggested text, please should send it along.


>
>> And finally, back on the question of what ANAME sibling address 
>> records actually represent, I think that NXDOMAIN and NODATA results 
>> should be treated as errors for the purposes of ANAME sibling 
>> replacement. This position can be justified on both practical and 
>> principled grounds—replacing functional records with an empty RRSet 
>> is undesirable for DNS users (or at least the sample of them that are 
>> Oracle+Dyn customers), and could inappropriately stretch the maximum 
>> specified ANAME sibling TTL (on the ANAME record itself) to the SOA 
>> MINIMUM value (which is doubly bad, because it results in extended 
>> caching of the /least/ valuable state). And adding insult to injury, 
>> resolvers in general will not even have the SOA, and will need to 
>> perform more lookups in order to issue a proper negative response of 
>> their own. Let's please just eliminate all of that by specifying that 
>> ANAME processing can never replace something with nothing.
>
> +1

"ANAME processing can never replace something with nothing"  should also 
be mentioned in the document.

Mr Gibson also mentioned this:
>> P.P.S. I think it has been discussed before, but this document should 
>> also introduce and use a new "Address RTYPE" registry or subregistry, 
>> rather than forever constraining ANAME exclusively to A and AAAA.
>>

I think that should be discussed.

thanks Matthijs,

tim