[DNSOP] Minimum viable ANAME

[Tony Finch <[e-mail]>]

I think there's still a need to standardize ANAME, to provide at least
some level of zone file portability between the various existing
proprietary versions of this feature. And to provide something usable
by zone publisters on a much shorter timescale than a nsa SRV-alike.

So here's a sketch of a reduced ANAME:


Primary servers / zone provisioning
-----------------------------------

For each ANAME record, poll the target address records periodically
(according to the relevant TTLs). When the target addresses don't
match the owner's addresses, UPDATE the zone so they match.


Authoritative servers / zone transfers
--------------------------------------

No special new behaviour.


Additional section processing
-----------------------------

This applies to auth and rec servers. In response to an A / AAAA /
ANAME query, include any sibling A / AAAA / ANAME records, and any
ANAME target A / AAAA records. When DO=1, include DNSSEC proofs of
nonexistence for missing RRsets.

As usual for additional section processing, you don't have to include
records that aren't available, so (for instance) auth servers don't
have to include out-of-zone data in the response.


Recursive servers
-----------------

When responding to a query with DO=0 or when the ANAME owner's zone is
unsigned, a recursive server can substitute the target addresses in
place of the owner's addresses.


Rationale
---------

The primary server behaviour is an "as if" description: that's what
it looks like for the purpose of interop with secondary servers and
zone files.

There doesn't seem to be any point in making secondary servers do
anything: their view of the target address records will be just as
wrong or right as the primary server's. Zone publishers that want
clever auth servers will use some kind of multi-headed CDN distributed
stunt DNS server, and we aren't going to standardize that.

Putting cleverness in resolvers compensates for the lack of cleverness
in secondary servers.


Tony.
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