Apex domains cannot have CNAME records.
Question and response
Question
dig hosting.ovh.net. NS
Answer
hosting.ovh.net. 5 NS dns111.ovh.net.
hosting.ovh.net. 5 NS ns111.ovh.net.
hosting.ovh.net. 5 NS dns18.ovh.net.
hosting.ovh.net. 5 NS ns18.ovh.net.
hosting.ovh.net. 5 NS ns103.ovh.net.
hosting.ovh.net. 5 NS dns103.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0