[DNSOP] BCP on rrset ordering for round-robin? Also head's up on bind 9.12 bug (sorting rrsets by default)

[Erik Nygren <[e-mail]>]

A number of folks have been bitten by a bug in bind 9.12 where it silently
changes the default sorting of rrsets to always be sorted (even if the
authoritative response wasn't sorted).  This causes problems for services
assuming at least some degree of round-robin behavior by clients as now
many clients would sent all traffic to only the lowest IP.  Bug details:
https://gitlab.isc.org/isc-projects/bind9/issues/336   If you are upgrading
to or have upgraded to bind 9.12 you likely want to take a fix or override
in config.


This raises the question of whether there would be value in a more modern
BCP covering round-robin expectations for recursive resolvers?  I suspect
many (most?) service operators take at least some degree of DNS round-robin
behavior by recursive resolvers as a default.

I suspect starting assumptions are roughly in the range of:

* Recursive (and stub?) resolvers (SHOULD/MUST?) do some form of
round-robin in RRset responses.

* There are a variety of ways to implement round-robin (randomize, permute,
etc).

* Server operators need to be aware that round-robin may be a part of a
load balancing scheme (especially if capacity is far greater than average
demand) but should not be relied on exclusively.  (Perhaps with examples of
why...)

Am I missing something in-terms of an existing BCP to this effect?  There's
RFC 1794, but I couldn't find much else (but given the sheer number of DNS
RFCs it's very likely I missed one).

Best, Erik