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

Lanlan Pan <> Tue, 19 June 2018 14:47 UTC

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From: Lanlan Pan <>
Date: Tue, 19 Jun 2018 09:47:09 -0500
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Subject: Re: [DNSOP] abandoning ANAME and standardizing CNAME at apex
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Petr Špaček <>于2018年6月19日周二 下午9:19写道:

> Hello dnsop,
> beware, material in this e-mail might cause your head to explode :-)
> This proposal is based on following observations:
> - It seems that DNS protocol police lost battle about CNAME at apex,
>    is is deployed on the Internet.
> - Major DNS resolvers like BIND, Unbound, PowerDNS Recursor, dnsmasq
>    already have code to cope with the "impossible" case of CNAME at the
>    apex and deal with it in ways which do not break stuff on resolver
>    side.
> - Authoritative servers of vendors named above refuse to serve CNAME at
>    apex.
> - There are CDNs etc. which allow users to create CNAME at apex
>    no matter what the standards and "normal" servers say and do.
> (We have found out this because Knot Resolver is missing hacks for CNAME
> at apex and users complain that "it works with every other resolver".)
> Take a deep breath!
> Given that resolver side somehow works already ...
> could we standardize this obvious violation of RFC 1035?
> It is very clear violation of the standard, but almost everyone found
> his way around it using different hacks. These hacks are not going away
> because all the CDNs just don't care about standards so we will have
> to maintain this code no matter what a great solution we will invent for
> future. I.e. adding ANAME will just increase complexity because CNAME at
> apex will be there for a long time (if not forever).
> I personally do not like this but it seems better to think though
> corner cases in code we already have in production (i.e. think through
> current hacks for CNAME at apex) instead of inventing new things like
> ANAME (or whatever else).
I think ANAME RR is hard to compatible with many old version resolvers.
If there are mutiple ANAME RR at compatible resolvers, authoritatives may
not know that resolvers will choose which A RR for client response.

ANAME can ease apex CNAME configuration, maybe a work round is that
authoritatives directly return A RR to resolvers (but not ANAME RR).

> Opinions? Tomatoes? Can it work? If not, why not?
> --
> Petr Špacek  @  CZ.NIC
> _______________________________________________
> DNSOP mailing list
致礼  Best Regards

潘蓝兰  Pan Lanlan