Apex domains cannot have CNAME records.
Question and response
Question
dig hosting.cdn.ovh.net. NS
Answer
hosting.cdn.ovh.net. 5 NS ns14.ovh.net.
hosting.cdn.ovh.net. 5 NS dns14.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0