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

Petr Špaček <petr.spacek@nic.cz> Mon, 17 September 2018 10:29 UTC

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Date: Mon, 17 Sep 2018 12:29:13 +0200
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Subject: Re: [DNSOP] abandoning ANAME and standardizing CNAME at apex
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On 17/09/2018 11:30, Mukund Sivaraman wrote:
> Hi Ray
> 
> On Mon, Sep 17, 2018 at 09:47:50AM +0100, Ray Bellis wrote:
>> On 17/09/2018 08:43, Mukund Sivaraman wrote:
>>
>>> The suggestion is only to require support in resolvers going forward for
>>> CNAME co-existing with other types for now. That should not break any
>>> detail of how DNS is used today.
>>
>> ....
>>
>>> Although it changes current DNS protocol, AFAICT there does not seem to
>>> be anything badly wrong with allowing CNAME + other types at a node,
>>> where the CNAME is considered a fallback when the required type doesn't
>>> exist.
>>
>> This is not true.
>>
>> Ondrej demonstrated at the last hackathon that permitting a CNAME
>> alongside the apex can cause MX-related failures in resolvers that are
>> not upgraded.
> 
> "The suggestion is only to require support in resolvers going forward
> for CNAME co-existing with other types for now."
> 
> It is obvious if authoritatives did that today and a RFC 1035 resolver
> cached a CNAME, it would match the cached CNAME when doing a type lookup
> in cache.
Originally I thought that current workarounds for CNAME at apex (which
are almost everywhere) deal with it in a more deterministic way.
Unfortunatelly it is not the case so I think this is a dead end.

Petr Špacek  @  CZ.NIC