Re: [Add] questions about the Examples section of svcb-dns-02

On Fri, Apr 9, 2021 at 12:37 AM Peter van Dijk <peter.van.dijk@powerdns.com>
wrote:

> Hi Ben,
>
> thank you for adding all those examples, this should unconfuse many
> readers.
>
> (I picked this email to reply to, instead of end of thread, because I'm
> typing something more inline below).
>
> On Thu, 2021-04-08 at 11:05 -0400, Ben Schwartz wrote:
> > OK, I've clarified (and corrected, oops) the explanation of the
> examples, and added another one to highlight the default-DoT behavior:
> https://github.com/bemasc/svcb-dns/commit/e59c995fa976a19b5baf1770afb231d3dcb729e1
> >
> > We can certainly remove the default ALPN, but personally I like having
> empty SvcParams correspond to a common default.  The size savings (~8
> bytes) are probably not important, although MTU could become relevant in
> the context of SVCB delegation responses as envisioned by
> draft-rescorla-dprive-adox.
>
> I think this one hits the core of the problem for me. I'm not confused
> about what -empty- SvcParams mean. I am (well, I was) confused by
> alpn=h2,h3 meaning alpn=dot,h2,h3.
>

I agree. Merging default with provided is a surprising behavior. If there
is a provided ALPN it should replace the default.

-Ekr

> So I wonder if having a default, but alpn= always *replacing* that
> default instead of appending to it, might make more sense. It certainly
> feels clearer to me.
>
> In terms of packet size, some records may spend four more bytes on
> 'dot,' because they do combine it with DoH in one SVCB record. Other
> records will spend a few bytes less on not needing no-default-alpn. I
> don't know how this balances out in the end.
>
> Kind regards,
> --
> Peter van Dijk
> PowerDNS.COM BV - https://www.powerdns.com/
>
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