Apex domains cannot have CNAME records.
Question and response
Question
dig 0-26.94.55.185.in-addr.arpa. NS
Answer
0-26.94.55.185.in-addr.arpa. 5 NS gateway2.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0