Apex domains cannot have CNAME records.
Question and response
Question
dig ip-51-81-30.us. NS
Answer
ip-51-81-30.us. 4 NS dns100.ovh.us.
ip-51-81-30.us. 4 NS ns100.ovh.us.
Authority
The response has no authority records.
Additional
ns100.ovh.us. 4 A 51.81.219.53
dns100.ovh.us. 4 A 135.148.3.205
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0