Apex domains cannot have CNAME records.
Question and response
Question
dig 160-27.36.212.213.in-addr.arpa. NS
Answer
160-27.36.212.213.in-addr.arpa. 5 NS ns.dataphone.se.
160-27.36.212.213.in-addr.arpa. 5 NS ns.itiden.se.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0