Apex domains cannot have CNAME records.
Question and response
Question
dig 212.231.66.in-addr.arpa. NS
Answer
212.231.66.in-addr.arpa. 3 NS dns2.firstlight.net.
212.231.66.in-addr.arpa. 3 NS dns1.firstlight.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0