Apex domains cannot have CNAME records.
Question and response
Question
dig dgfip.finances.gouv.fr. NS
Answer
dgfip.finances.gouv.fr. 5 NS dns1.dgfip.finances.gouv.fr.
dgfip.finances.gouv.fr. 5 NS dns2.dgfip.finances.gouv.fr.
Authority
The response has no authority records.
Additional
dns1.dgfip.finances.gouv.fr. 5 A 145.242.11.11
dns2.dgfip.finances.gouv.fr. 5 A 145.242.6.173
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0