Apex domains cannot have CNAME records.
Question and response
Question
dig renater.fr. NS
Answer
renater.fr. 5 NS ns1.renater.fr.
renater.fr. 5 NS ns4.cnrs.fr.
renater.fr. 5 NS ns2.renater.fr.
renater.fr. 5 NS dns-3.dfn.de.
Authority
The response has no authority records.
Additional
ns1.renater.fr. 5 A 193.49.159.2
ns2.renater.fr. 5 A 193.49.159.9
ns1.renater.fr. 5 AAAA 2001:660:3001:4002:0:0:0:2
ns2.renater.fr. 5 AAAA 2001:660:3001:4002:0:0:0:9
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0