[DNSOP] SVCB proposals

[Ben Schwartz <[e-mail]>]

The SVCB/HTTPS RR draft is nearing completion, but there are a few
remaining topics on which the authors would appreciate feedback from the
working group.  Personally, I've written up three proposed changes that
would benefit from broader input.  Please share your thoughts.

1. Change IANA policy to Specification Required
(https://github.com/MikeBishop/dns-alt-svc/pull/262/files)

The current proposed IANA policy for SvcParamKeys has allocatable ranges
under three different policies ("Standards Action", "Expert Review",
and "First Come First Served").  This is very flexible and enables
experimentation, but creates compatibility risk: a FCFS SvcParamKey could
be allocated without a clear specification of its zone file syntax, leading
to zone file portability issues.

This proposal would replace all these ranges with a uniform Specification
Required policy.  The required documentation is minimal: it is only
required to describe the zone file format.

2. Skip the default port prefix
(https://github.com/MikeBishop/dns-alt-svc/pull/230/files)

Using SVCB with a new protocol requires the initial QNAME to end with
_(scheme).$HOSTNAME.  The current text suggests (non-normatively) to add
_$PORT for endpoints that are identified by a port number.  This turns out
to be inelegant for protocols that almost always use the default port.  For
example, in the DNS mapping (draft-schwartz-svcb-dns), this would
correspond to names like "_53._dns.resolver.example".

This proposal would change the guidance to skip the port prefix when
starting with the default port (like "_dns.resolver.example").

3. Add a SHOULD-level chain length limit for zone owners
https://github.com/MikeBishop/dns-alt-svc/pull/294/files

Constructing huge chains of CNAME and AliasMode records is clearly a bad
idea, but how huge is too huge?  This change suggests not to use more than
8.  This doesn't change the requirements for resolvers (which are free to
impose any limit greater than zero) but it might help us to converge on
common behavior.

--Ben Schwartz