Apex domains cannot have CNAME records.
Question and response
Question
dig 192.234.127.42.in-addr.arpa. NS
Answer
192.234.127.42.in-addr.arpa. 5 NS ns013-at83g3066ue9mf19.a.d-53.info.
192.234.127.42.in-addr.arpa. 5 NS ns013-at83g3066ue9mf19.a.d-53.net.
192.234.127.42.in-addr.arpa. 5 NS ns013-at83g3066ue9mf19.a.d-53.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0