Apex domains cannot have CNAME records.
Question and response
Question
dig 42.112.212.in-addr.arpa. NS
Answer
42.112.212.in-addr.arpa. 5 NS dns4.lidnet.net.
42.112.212.in-addr.arpa. 5 NS dns2.lidnet.net.
42.112.212.in-addr.arpa. 5 NS dns1.lidnet.net.
42.112.212.in-addr.arpa. 5 NS dns3.lidnet.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0