>The main (only?) advantage of doing it with EDNS is that you can work
>with existing name servers. It means adding more logic to our already
>fabulously complicated resolvers to get full benefit, but nobody ever
>said DNS was easy.
If you're adding logic to servers and clients, why couldn't some of
that logic listen on a different port?
But honestly, I don't see what problem is being solved here. The
original motivation was to ask for SPF and TXT records at the same
time, rather than sending two queries. You don't need a new version
of DNS to handle that, all you need is a kludge in your server that
knows that when it gets a query for one, it can return the other in
the additional section. MX queries already have their kludge,
returning A and AAAA records.
The meta-reason for doing two queries is that it's still so hard to
provision new RR types that people fake them with TXT. If we're going
to hack on our DNS software, I'd rather work on that.