DNAME, which is what the SixXS nameservers return to you when asking for anything under ip6.int: ;; ANSWER SECTION: ip6.int. 604800 IN DNAME ip6.arpa. a CNAME automatically gets supplied by bind as part of the synthesis: jeroen@noc:~$ host -t any f.9.1.c.4.2.e.f.f.f.7.2.0.9.2.0.0.0.0.0.d.0.2.0.8.b.7.0.1.0.0.2.ip6.int f.9.1.c.4.2.e.f.f.f.7.2.0.9.2.0.0.0.0.0.d.0.2.0.8.b.7.0.1.0.0.2.ip6.int CNAME f.9.1.c.4.2.e.f.f.f.7.2.0.9.2.0.0.0.0.0.d.0.2.0.8.b.7.0.1.0.0.2.ip6.arpa !!! f.9.1.c.4.2.e.f.f.f.7.2.0.9.2.0.0.0.0.0.d.0.2.0.8.b.7.0.1.0.0.2.ip6.int CNAME record has zero ttl f.9.1.c.4.2.e.f.f.f.7.2.0.9.2.0.0.0.0.0.d.0.2.0.8.b.7.0.1.0.0.2.ip6.arpa PTR purgatory.unfix.org Because of this there are also no delegations to endusers for ip6.int, you only have to have the reverses in ip6.arpa. You could even stick ip6.int DNAME ip6.arpa and run the ip6.int this way on your own resolver to take care of this situation. Folks who still only have ip6.int and no ip6.arpa yet will never hop over anyway, thus why spend time on their problems?