Re: [DNSOP] SVCB without A/AAAA records at the service name

Ben Schwartz <bemasc@google.com> Tue, 19 January 2021 22:18 UTC

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From: Ben Schwartz <bemasc@google.com>
Date: Tue, 19 Jan 2021 17:17:47 -0500
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To: Martin Thomson <mt@lowentropy.net>
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Subject: Re: [DNSOP] SVCB without A/AAAA records at the service name
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On Tue, Jan 19, 2021 at 4:12 PM Martin Thomson <mt@lowentropy.net> wrote:

> On Wed, Jan 20, 2021, at 02:09, Ben Schwartz wrote:
> > I think #288 is quite "specific" about what happens in that case.
> > (Whether it's "sensible" is a separate question.)
>
> Sorry, I was talking mostly about #299, which has the problem I identified.
>
> The problem with #288 is that it doesn't say that the A/AAAA queries
> aren't made if they aren't needed.
>

As I noted in that discussion, the client generally doesn't know in advance
that they aren't needed.  In principle, we could describe two different
kinds of future protocols (one in which clients know they aren't needed,
and one in which they do not), but I think that would just add confusion.
I do expect these A/AAAA records to be useful in the common case for future
protocols.

Another thing I like about the arrangement in #288 is that it simplifies a
protocol-independent app/library boundary.  The app can say
"SVCBQuery(hostname, prefixes)" and get back a fully resolved object like
{svcbEntries: [{...}, ...], hostIPs: [...]}.  If the hostIPs aren't useful
for this protocol, the app can ignore them, while still getting the latency
benefit if any of the svcbEntries rely on them.