Apex domains cannot have CNAME records.
Question and response
Question
dig 246.65.83.in-addr.arpa. NS
Answer
246.65.83.in-addr.arpa. 5 NS rns2.nameservice.at.
246.65.83.in-addr.arpa. 5 NS rns1.nameservice.at.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0