Apex domains cannot have CNAME records.
Question and response
Question
dig diffusion.finances.gouv.fr. NS
Answer
diffusion.finances.gouv.fr. 5 NS ns2.diffusion.finances.gouv.fr.
diffusion.finances.gouv.fr. 5 NS ns1.diffusion.finances.gouv.fr.
Authority
The response has no authority records.
Additional
ns1.diffusion.finances.gouv.fr. 5 A 91.204.117.14
ns2.diffusion.finances.gouv.fr. 5 A 91.204.117.15
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0