We provide the mechanism (exclude) but don't populate exclude with a
default of ::ffff:0.0.0.0/96.

5.1.4.  Special Exclusion Set for AAAA Records

   Some IPv6 addresses are not actually usable by IPv6-only hosts.  If
   they are returned to IPv6-only querying agents as AAAA records,
   therefore, the goal of decreasing the number of failure modes will
   not be attained.  Examples include AAAA records with addresses in the
   ::ffff:0:0/96 network, and possibly (depending on the context) AAAA
   records with the site's Pref64::/n or the Well-Known Prefix (see
   below for more about the Well-Known Prefix).  A DNS64 implementation
   SHOULD provide a mechanism to specify IPv6 prefix ranges to be
   treated as though the AAAA containing them were an empty answer.  An
   implementation SHOULD include the ::ffff/96 network in that range by
   default.  Failure to provide this facility will mean that clients
   querying the DNS64 function may not be able to communicate with hosts
   that would be reachable from a dual-stack host.

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE:	+61 2 9871 4742		         INTERNET: marka@isc.org