Apex domains cannot have CNAME records.
Question and response
Question
dig ip-51-178-201.eu. NS
Answer
ip-51-178-201.eu. 5 NS dns105.ovh.net.
ip-51-178-201.eu. 5 NS ns105.ovh.net.
Authority
The response has no authority records.
Additional
ns105.ovh.net. 2 A 5.135.60.37
dns105.ovh.net. 2 A 5.196.40.17
ns105.ovh.net. 2 AAAA 2001:41d0:b00:f900:0:0:0:2
dns105.ovh.net. 2 AAAA 2001:41d0:d00:ff00:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0