Apex domains cannot have CNAME records.
Question and response
Question
dig monext.fr. NS
Answer
monext.fr. 5 NS dnsext-1.monext.fr.
monext.fr. 5 NS dnsext-2.monext.fr.
Authority
The response has no authority records.
Additional
dnsext-1.monext.fr. 5 A 31.210.2.20
dnsext-2.monext.fr. 5 A 31.210.6.20
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0