Re: [DNSOP] abandoning ANAME and standardizing CNAME at apex

tjw ietf <tjw.ietf@gmail.com> Tue, 19 June 2018 14:44 UTC

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From: tjw ietf <tjw.ietf@gmail.com>
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Date: Tue, 19 Jun 2018 10:43:58 -0400
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To: Tony Finch <dot@dotat.at>
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Subject: Re: [DNSOP] abandoning ANAME and standardizing CNAME at apex
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With all of you here. 

As an Operator who gets these requests regularly (just 10 minutes ago!) when you tell users the  world of BIND/PowerDNS/NSD/Knot do not support such a mechanism they say “we’re off to use route 53. okthxbai “

I find it personally appalling we can spend so many cycles injecting dns into http but we can’t be bothered to fix what end users want. 

Tim
Just an infrastructure operations person. 
From my high tech gadget

> On Jun 19, 2018, at 10:20, Tony Finch <dot@dotat.at>; wrote:
> 
> Petr Špaček <petr.spacek@nic.cz>; wrote:
>> 
>> Given that resolver side somehow works already ...
>> could we standardize this obvious violation of RFC 1035?
> 
> The feature I would like is CNAME and other data (typically CNAME + MX +
> TXT), because I have a lot of deeply hierarchial subdomains in my main
> zone. CNAME at apex does not need to be (and I think should not be treated
> as) a special case.
> 
> As I understand it, in the RFC 883 era, CNAME was allowed to coexist with
> other records, but that led to consistency problems. eg, if you have a
> CNAME cached for a particular name, and you get a query for MX at the same
> name, do you go and ask the CNAME's owner or its target for the MX? And do
> you get a different answer to the MX query when you don't have a CNAME
> cached?
> 
> My guess is that it was hard to fix this at the time because the semantics
> of negative cache entries was not well developed (e.g. RFC 1034 section
> 4.3.4 says it was still a new and experimental feature). For
> CNAME-with-siblings to work, a resolver needs to remember whether it
> already asked for the other data, for each RR type. 1980s caches couldn't
> do this, so CNAMEs were made exclusive instead.
> 
> I think the resolver's algorithm for handling CNAMEs can be updated to
> allow CNAME-with-siblings and preserve compatibility. There will be some
> latency cost for later queries that can no longer immediately follow the
> CNAME shortcut. NSEC/NSEC3 records could be used to eliminate this cost.
> 
> I'm much less sure about whether it's possible to publish
> CNAME-with-siblings in a reliably compatible way. I would feel a lot more
> comfortable with an ANAME implementation that copies the sibling records
> from the target to the owner when the zone is published or signed.
> 
> Tony.
> -- 
> f.anthony.n.finch  <dot@dotat.at>;  http://dotat.at/
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