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

Tony Finch <dot@dotat.at> Mon, 25 June 2018 14:55 UTC

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Date: Mon, 25 Jun 2018 15:55:02 +0100
From: Tony Finch <dot@dotat.at>
To: Colm MacCárthaigh <colm@allcosts.net>
cc: IETF DNSOP WG <dnsop@ietf.org>, Ray Bellis <ray@bellis.me.uk>
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Subject: Re: [DNSOP] abandoning ANAME and standardizing CNAME at apex
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Colm MacCárthaigh <colm@allcosts.net> wrote:
> On Mon, Jun 25, 2018 at 7:02 AM, Tony Finch <dot@dotat.at> wrote:
> >
> > That isn't required if the ANAME target records are fetched/updated by an
> > out-of-band provisioning process. A server will want to do it this way if
> > its query rate is bigger than the number of ANAME targetss divided by
> > their TTLs.
>
> A challenge with that is that many people now use geographic or latency
> based DNS routing based on the resolver IP address or EDNS-client-subnet.
> That's one of the reasons why Route53's ALIAS works only for targets that
> Route53 is authoritative for.

I think there are two issues here:

If your server has special knowledge of the target then there's nothing
stopping it from taking short cuts to serve tricksy answers more
efficiently.

If you are worried about a third-party auth server handing out ANAME
targets that are suboptimal, then that is what recursive ANAME support
will fix.

At the moment a third-party auth server can't do any cunning tricks with
apex names, so it has to serve a suboptimal static answer; with ANAME, the
tricksy target service gains the option of moving traffic around with TTL
granularity, if not (in the short term before recursive support) more
fine-grained tricks.

Tony.
-- 
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